NON LINEAR MATERIALS AND BIOMATERIALS

NON LINEAR MATERIALS AND BIOMATERIALS

BIREFRINGENCE AND KERR EFFECT

The appearance of double refraction under the influence of an external agent is known as artificial double refraction or induced birefringence.

Optical Kerr Effect

Anisotropy induced in an isotropic medium under the influence of an electric field is known as Kerr effect.

A sealed glass cell known as Kerr cell filled with a liquid comprising of asymmetric molecules is used to study the Kerr effect.

Two plane electrodes are placed in parallel to each other.

When a voltage is applied to there electrodes, a uniform electric field is produced in the cell.

The Kerr cell is placed between a crossed polarizer system (Fig), When the electric field is applied, the molecules of the liquid tend to align along the field direction.

As the molecules are asymmetric, the alignment causes anisotropy and the liquid becomes double refracting.

The induced birefringence is proportional to the square of the applied electric field E and      to   the   wavelength   λ   of   incident   light.

Fig. Kerr effect –Birefringence is induced in a liquid subjected to an electric field

The change in refractive influx is given by

∆μ= K λE²

Where K is known as the Kerr constant

EXPLAIN NON LINEAR PROPERTIES AND SECOND HARMONIC GENERATION

Basic Principle of Non Linear Properties

We know that a light wave is electromagnetic in nature ie., it consists of electric and magnetic fields.

When the light propagates through a material, it changes the properties of the medium, such as the refractive index.

It depends on the electric and magnetic fields associated with the light.

For example, we could not observe nonlinear effects with the ordinary light beam of low intensity, since the electric and magnetic fields associated with the light beams is very weak.

With the invention of laser, it is now possible to have electric fields which are strong enough to observe interesting non linear effects.

Thus if electric and magnetic fields are strong enough, the properties of the medium will be affected which in turn will affect the propagation of the light beam.

NON LINEAR PROPERTIES

Few of the nonlinear phenomena observed are

1. Second harmonic generation
2. Optical mixing
3. Optical phase conjugation
4. Soliton

SECOND HARMONIC GENERATION

 In a linear medium, polarization P is directly proportional to the electric field E

P ∝E

P = ε_oχE

Where_o    ε-     Permittivity of free space

χ – electrical susceptibility

In nonlinear medium for higher fields

ie., higher intensities of light the non linear effects are observed.

In the above equation, 1^st term gives rise to dc field across the medium, the second term gives external polarization and is called first or fundamental harmonic polarisability.

The third term which oscillates at a frequency 2w is called second harmonic of polarization and other terms are referred as higher harmonic polarization.

Both first term (dc field) and third term (second harmonic of polarization) added together is called optical rectification.

The second harmonic generation is possible only the crystals lacking inversion symmetry. SHG crystals are quartz, potassium dihydrogen phosphate (KDP), Ammonium dihydrogen phosphate (ADP), Barium titante (BaTiO₃) and Lithium lodate (LiIO₃)

The observation of second harmonic generation by KDP is shown in figure.

Fig. Arrangement for observing second harmonic generation

When the fundamental radiation (1.064 m) from Nd: YAG laser is sent through SHG crystal like KDP, conversion takes place to double the frequency. i.e., half the wavelength (0.532 m) takes place.

BIOMATERIALS WITH THEIR PROPERTIES AND APPLICATIONS

The materials which are used for structural applications in the field of medicine are known as Biomaterials.

In the recent years, new biomaterials like nanobiomaterials are emerging up due to the requirements in the medical field for different applications.

CLASSIFICATION OF BIOMATERIALS

Based on the applications in the field of medicine, biomaterials are classified as

1. Metals and alloys biomaterials
2. Ceramics biomaterials.
3. Polymer biomaterials.
4. Composite biomaterials

Sometimes, a single material mentioned above cannot fulfill the complete requirements imposed for specific applications. In such case, combinations of more than one material are required.

Metals and Alloys

Metals and alloys are used as biomaterials due to their excellent electrical and thermal conductivity and mechanical properties.

TYPES OF BIOMATERIALS USING METALS AND ALLOYS

1. Cobalt based alloys
2. Titanium
3. Stainless steel
4. Protosal from cast alloy
5. Conducting metals such as Platinum

APPLICATIONS

The metals and alloys biomaterials are used in implant and orthopedic applications.

1. Stainless steel is the predominant implant alloy. This is mainly due to its ease of fabrication and desirable mechanical properties and corrosion resistant.
2. Proposal from cast alloy of Co –Cr –Mo is used to make stem and used for implant hip endoprosthesis.
3. The advanced version of protosal –10 from Co–Ni –Cr –Mo alloy is widely used in Hip joints, Ankle joints, Knee joints, leg lengthening spaceas.
4. ASTMF –136 (composition of Ti –6A1 –4V, EL1 alloy, forged) due to its high strength / weight ratio, high corrosion resistance and high bio compatibility, this alloy is used in dental applications for making screws, wires and artificial teeth.
5. Ni –Ti shape memory alloy is used in dental arch wires, micro surgical instruments, blood clot filters, guide wires etc.

CERAMICS

Ceramics are used as biomaterials due to their high mechanical strength and biocompatibility.

Types of Bio-Ceramic materials

1. Tricalcium phosphate
2. Metal oxides such as Al₂O₃and SiO₂
3. Apatite ceramics
4. Porous ceramics
5. Carbons and Alumina

Applications

1. Ceramic implants such as Al₂O₃and with some SiO₂ and alkali metals are used to make femoral head. This is made from powder metallurgical process.
2. Tricalcium phosphate is used in bone repairs.
3. Orthopedic uses of alumina consists of hip and knee joints, tibical plate, femur shaft, shoulders, radius, vectebra, leg lengthening spaces and ankle joint prosthesis. Porous alumina is also used in teeth roots.
4. Apatite ceramics are new bio active ceramics. They are regarded as synthetic bone, readily allows bone ingrowth, better than currently used alumina Al₂O_3.
5. Carbon has good biocompatibility with bone and other tissues. It has high strengths and an elastic molecules close to that of bone.
6. Carbon coatings find wide applications in heart valves, blood vessel grafts, percutaneous devices because of exceptional compatibility with soft tissues and blood.
7. Percutaneous carbon devices containing high density electrical connectors have been used for the chronic stimulation of the cochlea for artificial hearing and stimulation of the visual cortex to aid the blind.

Bio Polymers

Biopolymers are macromolecules (protein, nucleic acids and polysachacides) formed in nature during the growth cycles of all organisms.

Biopolymers find variety of applications as biomaterials.

The most prominent among them are collagens, muco-polysaccharides –chitin, collagens and its derivatives.

Collagnes which are major animal structural proteins are widely used in a variety of forms such as solution, gel, fibers, membranes, sponge and tubing for large number of biomedical applications including drug delivery system, vessels, valves corneal prosthesis, wound dressing, cartilage substitute and dental applications.

Biomaterials in Opthamology

Biomaterials find important applications in opthalmology.

They are used to improve and maintain vision.

Eye implants are used to restore functionality of cornea, lens, etc, when they are damaged or diseased.

The biomaterials include viscoelastic solutions intraocular lenses, contact lenses, eye shields, artificial tears, vitreous replacements, correction of corneal curvature.

Dental Materials

Polymers, composites, ceramic materials and metal alloys are four main groups of materials used for dental applications.

A large number of materials are tested for porous dental implants, which include stainless steel,Co –Cr –Mo alloy, PMMA,proplast and Daceon, velour coated metallic implants, porous calcium aluminate single crystal alumina, bioglass, vitreous and pyrolytic carbons.

The dental applications include impression materials, dentine base and ceorons, bridges, inlays and repair or cavities, artificial teeth, repair of alveolar bone, support for mandible .

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Characteristics of sound and Classification of Sound

Acoustics of buildings in Civil engg

Absorption coefficient in Acoustics

Properties of Ultrasonic waves and Production of Ultrasonic waves

Piezo Electric Crystals – Principle, Construction, working

Principle and working of SONAR – Sound Navigation and Ranging

Determination of Ultrasonic Velocity in Liquid(Acoustical Grating Method): Principle, Construction and working

Industrial Applications of Ultrasonic waves

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

Metallic Glasses

SHAPE MEMORY ALLOYS

Nanotechnology and Nanomaterials

 

NanoTechnology And Nanomaterials

NanoTechnology is deeply explained in this page with Nanomaterials and their properties uses and application.

NANOMATERIALS in Nanotechnology

 Nanoparticles are the particles that have three dimensional nanoscale, the particle is between 1 and 100 nm in each spatial dimension.

A nano meter is a unit of measure equal to one-billionth of a meter, or three to five atoms across.

Nanotechnology is the design, fabrication and use of nanostructured systems, and the growing, assembling of such systems either mechanically, chemically or biologically to form nanoscale architectures, systems and devices.

COMPARISON OF DIFFERENT OBJECTS

1. Diameter of sun    –        1,393,000 km
2. Diameter of earth –        1,28,000km
3. Height of Himalaya mountain –        8,848km
4. Height of man      –        1.65km
5. Virus –        20-250nm
6. Cadmium Sulphide nanoparticle       –        1-10 nm

CLASSIFICATION OF NANOMATERIALS in Nanotechnology

Clusters

A collection of atoms or reactive molecules up to about 50 units.

Colloid

A stable liquid phase containing particles in 1 to 1000 nm range.  A colloidal particle is one such 1 to

1000 nm sized particle.

Nanoparticle

A solid particle in the 1 to 100 nm range that could be non-crystalline, an aggregate of Crystalites, or a single Crystalite.

Nanocrystal

A solid particle that is a single crystal in the nanometer size.

Nanostructured or Nanoscale Material

Any solid materials has a nanometer dimension.

Three dimensions  — >   Particles

Two dimensions  — >   Thin films

One dimension  — >   Thin wire

Quantum Dots

A particle that exhibits a size quantization effect in at least one dimension.

TOP-DOWN AND BOTTOM-UP PROCESS

Top-down Process

In this processes, bulk materials are broken into nano sized particles as shown in

In to-down processes, the building of nanostructures starting with small components like atoms and molecules that are removed from a bulk material so as to obtain desired microstructure.

Bottom-up Processes

In this processes, nano phase materials are produced by building of atom by atom as shown in.

This processes building larger objects from smaller buildings blocks. Nanotechnology seeks to use atoms and molecules as those building blocks. This is the opposite of the top-down approach. Instead of taking material away to make structures, the bottom-up approach selectively adds atoms to create structures.

SYNTHESIS TECHNIQUES in Nanotechnology

Nanomaterials are newly developed materials with grain size at the nanometre range (10^-9m)

i.e., in the order of 1 –100 nm. The particle size in a nanomaterial is in the order of nm.

PULSED LASER DEPOSITION

Priniciple

The laser pulse of high intensity and energy is used to evaporate carbon from graphite.

These evaporated carbon atoms are condensed to from nano tubes.

Description

The experimental arrangement of pulsed laser4 deposition is shown in fig.

A quartz tube which contains a graphite target is kept inside a high temperature muffle furnace.

Fig. Pulsed Laser Deposition CNT

This quartz tube is filled with argon gas and it is heated to 1473 K.

A water cooled copper collector is fitted at the other end of the tube.

The target material graphite contains small amount of nickel and cobalt as a catalyst to nucleate the formation of nanotubes.

Working

When an intense pulse of laser beam is incident on the target, it evaporates the carbon from the graphite. The evaporated carbon atoms are swept from the higher temperature argon gas to the colder copper collector.

When the carbon atoms reach the colder copper collector, they condense into nanotubes.

CHEMICAL VAPOUR DEPOSITION

The deposition of nano films from gaseous phase by chemical reaction on high temperature is  known as chemical vapour deposition.

This method is used to prepare nano-powder.

Principle

In this technique, initially the material is heated to gaseous state and then it is deposited on a solid surface under vacuum condition to form nano powder by chemical reaction with the substrate.

Description and Working

The CVD reactor built to perform CVD processes is shown in fig.

Chemical vapour deposition (CVD) involves the flow of a gas with diffused reactants (substances to be deposited in the vapour) over a hot substrate surface.

The gas that carries the reactants is called the carrier gas.

While the gas flows over the hot solid surface, the heat energy increases chemical reactions of the reactants that form film during and after the reactions.

The byproduct of the chemical reactions are then removed.

The thin film of desired composition can thus be formed over the surface of the substrate.

PROPERTIES OF NANOPHASE MATERIALS.

Properties of Nanophase Particles

The mechanical, electrical, chemical, magnetic and structural properties of nanophase materials change with the reduction in the particle size of the material.

PHYSICAL PROPERTIES

Variation of physical properties with geometry

Starting from the bulk, the first effect of reducing the particle size is to create more surface sites. This in turn changes surface pressure and interparticle spacing.

(i) Inter particle spacing decreases with decrease in grain size for metal clusters.

For example in copper, it decrease from 2.52 (cluster size –50A) to 2.23A (Cu dimer) fig.

The change in inter particle spacing and large surface to the volume ratio in particles have a combined effect on material properties.

Therefore, the nanophase materials have very high strength and super hardness.

Because of the cluster of grains, the nanophase materials are mostly free from dislocations and stronger than conventional metals.

Fig. Inter atomic distance in Cu_n as a function of grain size.

(ii)             Melting point reduces with decrease in cluster size.

The melting point of gold in nanophase (Au_n) varies as a function of particle size (fig.)

Fig. Melting point of small Au_n particles as a function of size

The melting point decreases from 1200 K to 800 K when the particle size decreases from 300 A to 20 A.

(iii) Ionization potential changes with cluster size of the nanograins.

The electronic bands in metals become narrower when the size is reduced from bulk which changes the value of ionization potential.

Fig. shows the ionization potential and reactivity of Fe_n clusters as a function of size. Ionisation potentials are higher at small sizes than that for the bulk and show marked fluctuations as a function of size.

Fig. Ionisation potential and reactivity of Fen clusters as a function of size (iv) The large surface to volume ratio, the variations in geometry and the electronic structure have a strong effect on catalytic properties.

As an example, the reactivity of small clusters is found to vary by higher orders of magnitude when the cluster size is changed by only a few atoms.

MAGNETIC PROPERTIES

Nanoparticles of non-magnetic solids also exhibit totally new type of magnetic properties.

(i)                Bulk magnetic moment increases with decrease in co-ordination number

The change in magnetic moment on the nearest coordination number is shown in fig.-0

Fig. Change in magnetic moment on the nearest coordination number

As the coordination number decreases, the magnetic moment increases with the atomic value which means that small particles are more magnetic than the bulk material.

The magnetic moment of iron (Fe) of nanoparticles is 30% more than that of bulk.

At smaller sizes, the clusters become spontaneously magnetic.

(ii) The nano-materials shows variation in their magnetic property when they change from bulk state to cluster (nano-particle) state.

(iii) Non-magnetic materials become magnetic when the cluster size reduces to 80 atoms.

MECHANICAL PROPERTIES

 (i)    In nanophase materials, the elastic strength is low however, its plastic behavior is high.

 (ii) In some nanophase materials, it is noted that there is decrease in hardness when the grain size is less than 10 nm.

However for many nanocrystalline, pure metals (10 nm), the hardness is about 2 to 7 times greater than that of large-grained (>1 μ m) metals.

(iii)Higher hardness and mechanical strength (2-7 times) when grain size reduces from 1 μ m to 10 nm.

(iv)It has very high ductility and superplastic behavior at low temperatures.

APPLICATIONS OF NANOPHASE MATERIALS

Materials Technology

We can synthesis harder metals having hardness 5 times higher than normal metals using nanoparticles.

Stronger, lighter, wear resistant, tougher and flame retardant polymers are synthesized with nanoparticles as fillers.

They are used in replacement of body parts and metals (bio-materials).

We can produce unusual colour paints using nanoparticles since nanoparticles exhibit entirely different optical properties.

Nanophase materials are used in nanoelectronic devices such as nanotransistore, ceramic capacitors for energy storage, noise filters and stabilizers.

The special features of these devices include smaller sizes and reduced power losses.

ZnO thermistors are used in thermal –protection and current-controlling devices.

Information Technology

Nanoparticles are used for data storage.

Quantum electronic devices have started replacing bulk conventional devices.

Nanomaterials are used to produce very tiny permanent magnets of high energy products.

Hence, they are used in high-density magnetic recording.

Magnetic devices made of Cu-Fe alloy are used in RAM, READ / WRITE heads and sensors.

Quantum dots, quantum wells and quantum wires are mainly produced from semiconductor nanomaterials.

Hence, they are used in computer storage (memory) devices.

Biomedicals

Biosensitive nanoparticles are used for tagging of DNA and DNA chips.

Controlled drug delivery is possible using nanotechnology.

Diffusion of medicine through nanoporous polymer reservoir as per the requirement is very useful in controlling the disease.

Nanostructured ceramics readily interact with bone cells and bence finds applications as an implant material.

Energy storage

Since the hydrogen absorbing capability increases with decrese of size of nanoparticles, nanoparticles of Ni, Pd and Pt are useful in hydrogen storage devices.

Metal nanoparticles are very useful in fabrication of ionic batteries.

Optical devices

Nanoparticulate zinc oxide is used to manufacture effective Sunscreens.

Nanoparticles are used in the coatings for eye glasses to protect from scratch or breakage.

Transmission lines

 Nanophase materials are used in the fabrication of signal processing elements such as filters,  delay lines, switches etc.

Nanomicro – Electro Mechanical Systems (Nano MEMS) have direct implications on integrated circuits, optical switches, pressure sensors and mass sensors.

Molecular Nano

Technology (MNT) is aimed to develop robotic machines, called assembler son a molecular scale, molecular-size power sources and batteries.

Underwater nanosensor networks are used to detect the movement of ships in an efficient manner with faster response. They can also detect chemical, biological or radio logical materials in cargo containers.

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Characteristics of sound and Classification of Sound

Acoustics of buildings in Civil engg

Absorption coefficient in Acoustics

Properties of Ultrasonic waves and Production of Ultrasonic waves

Piezo Electric Crystals – Principle, Construction, working

Principle and working of SONAR – Sound Navigation and Ranging

Determination of Ultrasonic Velocity in Liquid(Acoustical Grating Method): Principle, Construction and working

Industrial Applications of Ultrasonic waves

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

Metallic Glasses

SHAPE MEMORY ALLOYS

NON-LINEAR MATERIALS AND BIO-MATERIALS

SHAPE MEMORY ALLOYS

SHAPE MEMORY ALLOYS is explained in detail in this page.

SHAPE MEMORY ALLOYS

 A group of metallic alloys which shows the ability to return to their original shape or size

i.e.,  alloy appears to have memory

when they are subjected to heating or cooling are called shape memory alloys.

Phase of shape memory alloys

Martensite and austenite are two solid phases in SMA as shown in fig.

Fig. Phases of SMA

Martensite is relatively soft and it is easily deformable phase which exists at low temperature (monoclinic).

(i) Austenite is a phase that occurs at high temperature having a crystal structure and high degree of symmetry (cubic).

TYPES OF SHAPE MEMORY ALLOYS

 There are two types of shape memory alloys

 (i)One-way shape memory alloy

 (ii)Two-way shape memory alloy

A material which exhibits shape memory effect only upon heating is known as one-way shape memory.

A material which shows a shape memory effect during both heating and cooling is called two-way shape memory.

Examples of shape memory alloys

Generally, shape memory alloys are intermetallic compounds having super lattice structures and metallic-ionic-covalent characteristics.

Thus, they have the properties of both metals and ceramics.

Ni –Ti alloy (Nitinol)

Cu –Al –Ni alloy

Cu –Zn –Al alloy

Au –Cd alloy

Ni –Mn –Ga and Fe based alloys

CHARACTERISTICS OF SHAPE MEMORY ALLOYS – SMAS

• Shape memory effect

The change of shape of a material at low temperature by loading and regaining of original shape by heating it, is known as shape memory effect.

The shape memory effect occurs in alloys due to the change in their crystalline structure with the change in temperature and stress.

While loading, twinned martensite becomes deformed martensite at low temperature.

On heating, deformed martensite becomes austenite (shape recovery) and upon cooling it gets transformed to twinned martensite (fig.).

SMAs exhibit changes in electrical resistance, volume and length during the transformation with temperature.

The mechanism involved in SMA is reversible (austenite to martensite and vice versa.)

5. Stress and temperature have a great influence on martensite transformation.
6. Pseudo elasticity

Pseudo –elasticity occurs in shape memory alloys when it is completely in austenite phase (temperature is greater than A_faustenite finish temperature).

Unlike the shape memory effect, Pseudo-elasticity occurs due to stress induced phase transformation without a change in temperature.

The load on the shape memory alloy changes austenite phase into martensite (Fig.).

As soon as the loading decreases the martensite begins to transform to austenite.

This phenomenon of deformation of a SMA on application of large stress and regaining of shape on removal of the load is known as pseudo elasticity.

This pseudo elasticity is also known as super elasticity

• Hysteresis

The temperature range for the martensite to austenite transformation which takes place upon heating is somewhat higher than that for the reverse transformation upon cooling.

The difference between the transition temperature upon heating and cooling is called hysteresis. The hysteresis curve for SMAs is shown in fig.

The difiference of temperature is found to be 20-30^oC,

COMMERCIAL SHAPE MEMORY ALLOYS

 The only two alloy systems that have achieved any level of commercial exploitation are,

 (i)                Ni-Ti alloys, and

(ii)             Copper base alloys.

Properties of the two systems are quite different.

• Nickel-Titanium Alloys

The basis of the Nickel-Titanium alloy is the binary, equi-atomic inter-metallic compound of Ti-Ni. The inter-metallic compound is extraordinary because it has moderate solubility range for excess Nickel or Titanium, as well as most other metallic elements. This solubility allows alloying with many of the elements to modify both the mechanical properties and the transformation properties of the system. Excess Nickel strongly depresses the transformation temperature and increases the yield strength of the austenite. The contaminants such as Oxygen and Carbon shift the transformation temperature and degrade the mechanical properties. Therefore, it is also desirable to minimize the amount of such elements.

Properties:

(i)                The Ni-Ti alloys have greater shape memory strain upto 8.5% tend to be much more thermally stable.

(ii)             They have excellent corrosion resistance and susceptibility, and have much higher ductility.

(iii)           Machining by turning or milling is very difficult except with special tools.

(iv)           Welding, brazing or soldering the alloys is generally difficult.

(v)             The material do respond well to abrasive removal such as grinding, and shearing.

(vi)           Punching can be done if thicknesses are kept small.

ADVANTAGES OF SHAPE MEMORY ALLOYS

They are simple, compact and high safe.

They have good bio –compatibility.

They have diverse applications and offer clean, silent and spark-free working condition

They have good mechanical properties and are strong corrosion-resistant.

DISADVANTAGES OF SHAPE MEMORY ALLOYS

They have poor fatigue properties.

They are expensive.

They have low energy efficiency.

APPLICATIONS OF SHAPE MEMORY ALLOYS

• Microvalve (Actuators)

One of the most common applications of SMAs is mocrovalves. Fig. shows a microvalve made of Ni –Ti alloy actuator. Actuator is a microsensor that can trigger the operation of a device. The electrical signal initiates an action.

Fig. Schematic of microvalves that open and close according to temperature

When an electrical current of 50 to 150 mA flows in Ni-Ti actuator, it contracts and lifts the poppet from the orifice and opens the valve.

• Toys and novelties

Shape memory alloys are used to make toys and ornamental goods.

A butterfly using SMA. Moves its wings in response to pulses of electricity.

• Medical field Blood clot filters

(i)                Blood clot filters are SMAs, properly shaped and inserted in veins to stop the passing blood clots.

When the SMA is in contact with the clot at a lower temperature, it expands and stops the clot and blood passes through the veins.

(ii)             They are used in artificial hearts.

(iii)           Orthodontic applications

NiTi wire holds the teeth tight with a constant stress irrespective of the strain produced by the teeth movement. It resists permanent deformation even if it is bent. NiTi is non-toxic and non-corrosive with body fluid.

(iv)           SMAs (NiTi) are used to make eye glass frames and medical tools. Sun-glasses made from superelastic Ni-Ti frames provide good comfort and durability.

• Antenna wires

The flexibility of superelastic Ni –Ti wire makes it ideal for use as retractable antennas.

• Thermostats

SMAs are used as thermostat to open and close the valves at required temperature.

• Cryofit hydraulic couplings

SMAs materials are used as couplings for metal pipes

• Springs, shock absorbers, and valves

Due to the excellent elastic property of the SMAs, springs can be made which have varied industrial applications. Some of them are listed here.

Engine micro valves

Medical stents (Stents are internal inplant supports provided for body organs)

Firesafety valves and

Aerospace latching mechanisms

• Stepping motors

Digital SMA stepping motors are used for robotic control.

Titanium-aluminium shape memory alloys offer excellent strength with less weight and dominate inthe aircraft industry.

They are high temperature SMAs, for possible use in aircraft engines and other high temperature environments.

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Characteristics of sound and Classification of Sound

Acoustics of buildings in Civil engg

Absorption coefficient in Acoustics

Properties of Ultrasonic waves and Production of Ultrasonic waves

Piezo Electric Crystals – Principle, Construction, working

Principle and working of SONAR – Sound Navigation and Ranging

Determination of Ultrasonic Velocity in Liquid(Acoustical Grating Method): Principle, Construction and working

Industrial Applications of Ultrasonic waves

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

Metallic Glasses

Nanotechnology and Nanomaterials

NON-LINEAR MATERIALS AND BIO-MATERIALS

METALLIC GLASSES

 The Metallic glasses are materials which have the properties of both metals and glasses.

Metallic glass = Amorphous metal

In general, metallic glasses are strong, ductile, malleable, opaque and brittle.

They also have good magnetic properties and high corrosion resistance.

METHODS OF PREPARATION and Principle

 The principle used in making metallic glasses is extreme rapid cooling of the molten alloy. The technique is called as rapid quenching.

 The cooled molten alloys are fed into highly conducting massive rollers at high speeds to give ribbons of metallic glasses.

 PREPARATION OF METALLIC GLASSES

Principle

The principle used in making metallic glasses is extreme rapid cooling of the molten metal alloy.

This technique is called as rapid quenching.

Melt spinning system

A melt spinner consists of a copper roller over which a refractory tube with fine nozzle is placed.

The refractory tube is provided with induction heater as shown in fig.

The metal alloy is melted by induction heating under inert gas atmosphere (helium or argon).

The properly super heated molten alloy is ejected through the fine nozzle at the bottom of the refractory tube.

The molten alloy falls on the copper roller which is rotated at high speed.

Thus, the alloy is suddenly cooled to form metallic glass.

In this method a continuous ribbon of metallic glass can be obtained.

TYPES OF METALLIC GLASSES:

 Metallic glasses are classified into two types:

 (i)Metal –Metal metallic glasses

They are combination of metals

Metals                  Metals

Examples:   Nickel (Ni)  –        Niobium (Nb)

Magnesium (Mg)  –        Zinc (Zn)

Copper (Cu)         –        Zirconium (Zr)

(ii)Metal –Metalloid metallic glasses

These are combinations of metals and metalloids.

Examples:  Metals                            Metalloids

Fe, Co, Ni            –        B, Si, C, P

 PROPERTIES OF METALLIC GLASSES

Structural properties

2. They do not have any crystal defects such as grain boundaries, dislocation etc.
3. Metallic glasses have tetrahedral close packing (TCP).

Mechanical properties

4. Metallic glasses have extremely high strength, due to the absence of point defects and dislocation.
5. They have high elasticity.
6. They are highly ductile.
7. Metallic glasses are not work-harden but they are work –soften. (work harnening is a process of hardening a material by compressing it).

Electrical properties

3. Electrical resistivity of metallic glasses is high and it does not vary much with temperature.
4. Due to high resistivity, the eddy current loss is very small.
5. The temperature coefficient is zero or negative.

Magnetic properties

5. Metallic glasses have both soft and hard magnetic properties.
6. They are magnetically soft due to their maximum permeabilities and thus they can be magnetised and demagnetized very easily.
7. It exhibit high saturation magnetisation.
8. They have less core losses.
9. Most magnetically soft metallic glasses have very narrow hysteresis loop with same crystal composition. This is shown in fig.

Fig. Hysteresis loop of iron based alloy in crystalline and metallic glassy phase.

Chemical properties

3. They are highly resistant to corrosion due to random ordering.
4. It highly reactive and stable.
5. They can act as a catalyst. The amorphous state is more active than the crystalline state from the catalytic point of view.

APPLICATIONS OF METALLIC GLASSES

 Metallic – glasses also called as met glasses have found wide applications in different fields.

Structural application

3. They posses high physical and tensile strength. They are superior to common steels and thus they are very useful as reinforcing elements in concrete, plastic and rubber.
4. Strong ribbons of metallic glasses are used for simple filament winding to reinforce pressure vessels and to construct large fly wheels for energy storage.
5. Due to their good strength, high ductility, rollability and good corrosion resistance, they are used to make razor blades and different kinds of springs.

Electrical and Electronics application

4. Since metallic – glasses have soft magnetic properties, they are used in tape recorder heads, cores of high-power transformers and magnetic shields.
5. They use of metallic glasses in motors can reduce core loss very much when compared with conventional crystalline magnets.
6. Superconducting metallic glasses are used to produce high magnetic fields and magnetic levitation effect.
7. Since metallic glasses have high electrical resistance, they are used to make accurate standard resistance, computer memories and magneto resistance sensors.

Metallic glasses as transformer core material

5. Metallic – glasses have excellent magnetic properties. When they are used as transformer core, they give maximum magnetic flux linkage between primary and secondary coils and thus reduce flux leakage losses.
6. In view of their features like small thickness, smaller area, light weight, high resistivity, soft magnetic property and negligible hysteresis and eddy current loss, metallic glasses are considered as suitable core materials in different frequency transformers.

Nuclear reactor engineering

• The magnetic properties of metallic glasses are not affected by irradiation and so they are useful in preparing containers for nuclear waste disposal and magnets for fusion reactors.
• Chromium and phosphorous based (iron chromium, phosphorous-carbon alloys) metallic glasses have high corrosion resistances and so they are used in iner surfaces of reactor vessels, etc.

Bio-medical Industries

1. Due to their high resistance to corrosion, metallic glasses are ideal materials for making surgical instruments.
2. They are used as prosthetic materials for implantation in human body.

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Characteristics of sound and Classification of Sound

Acoustics of buildings in Civil engg

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Properties of Ultrasonic waves and Production of Ultrasonic waves

Piezo Electric Crystals – Principle, Construction, working

Principle and working of SONAR – Sound Navigation and Ranging

Determination of Ultrasonic Velocity in Liquid(Acoustical Grating Method): Principle, Construction and working

Industrial Applications of Ultrasonic waves

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

SHAPE MEMORY ALLOYS

Nanotechnology and Nanomaterials

NON-LINEAR MATERIALS AND BIO-MATERIALS

Industrial Applications of Ultrasonic waves

The industrial Applications of Ultrasonic waves are explained in detail.

INDUSTRIAL APPLICATIONS

Ultrasonic waves find application in two major fields:

1. Engineering filed
2. Medical field

Application of ultrasonic waves in engineering and industry

Ultrasonic waves in the wide applications in engineering and industry as follows.

1. Non destructive testing (detection of flaws in metals)
2. Ultrasonic drilling
3. The ultrasonic welding
4. Ultrasonic drilling
5. A ultrasonic soldering
6. ultrasonic cutting and machinery
7. A ultrasonic cleaning
8. Sonar

Ultrasonic Non destructive Testing – Industrial Applications of Ultrasonic waves

Principle:

The basic principle behind the ultrasonic inspection is the transmission of the Ultrasound with the medium and the reflection or scattering at any surface or internal discontinuity in the medium due to the change in the acoustic impedance.

The Discontinuity means the existence of the flaw or detect or cracks or hole in the material.

The reflected or scattered sound waves are received and amplified and hence, the defects in the specimen are suitably characterized.

Block diagram of the Ultrasonic Flaw detector

Principle:

Whenever there is a change in the medium, then the Ultrasonic waves will be reflected.

This is the principle used in Ultrasonic flaw detector.

Thus, from the intensity of the reflected echoes, the flaws are detected without destroying the material and hence this method is known as a Non Destructive method.

Working:

1. The pulse generator generates high frequency waves and is applied to the Piezo-electric transducer and the same is recorded in the CRO.
2. The piezo electric crystals are resonated to produce Ultrasonic waves.
3. These Ultrasonic waves are transmitted through the given specimen.
4. These waves travel through the specimen and is reflected back by the other end.
5. The reflected Ultrasonic are received by the transducer and is converted into electric signals. These reflected signals are amplified and is recorded in the CRO.
6. If the reflected pulse is same as that o the transmitted pulse, then it indictes that there is no defect in the specimen.
7. On the other hand, if there is any defect on the specimen like a small hole or pores, then the Ultrasonic will be relected bby the holes(i.e.) defects due to change in the medium.
8. From the time delay between the transmitted and received pulses, the position of the hole can be found.
9. From the height o the pulse received the depth of the hole can also be determined.

ULTRASONIC SCANNING METHODS – A,B AND C SCAN DISPLAYS – Industrial Applications of Ultrasonic waves

In the Ultrasonic scanning methods, the principle, construction and working is the same as that of the Ultrasonic law detector.

Here, it is based on the position o the transducer and the output displayed in the CRO screen, we can classiy the scanning methods into three types

1. A-scan
2. B-scan
3. T-M scan or C-scan

All these three modes of scanning are obtained with respect to the pulses of Ultrasound transmitted into and received from the specimen.

The three modes are explained below.

A-Scan or Amplitude mode display

Amplitude mode display gives only one-dimensional information about the given specimen.

In this, a single transducer is used to transmit and receive the pulses from the specimen.

The received or the reflected echo signals from the specimen is given to the Y-Plate and time base is connected to the X-Plate of the CRO, so that they are displayed as vertical spikes along horizontal base line as shown in the figure 1.10.1.

The height of the vertical spikes corresponds to the strength of the echo from the specimen.

The position of the vertical spike from left to right along the X-axis corresponds to the depth of penetration.

i.e, it gives the total time taken by the Ultrasonic sound to travel from transmitter to the specimen and from the specimen to the receiver.

Thus by passing Ultrasonic waves o known velocity and by noting the time delay, we can find the distance at which the detect or flaws are present, by using the formula.

Distance = Velocity x time

In ultrasonic flaw detector, A-scan method is used to detect the position and size of the flaws.

B-Scan or Brightness Mode Scan

B-scan or Brightness mode display gives a two dimensional image.

The principle of the B-Scan is same as that of A-Scan except with a small difference.

Here in the B-Scan the transducer can be moved rather than keeping in a fixed position.

As a result each echo’s are displayed as dots on the screen as shown in the figure 1.10.2.

T.M Scan or Time –Motion Mode or C-Scan display

This method is used to obtain the information about the moving object.

This combines the features of both A-Scan as well as B-Scan. In this the transducer is held stationary as in A-scan and echoes appear as dots in the B-scan.

Here, the X-axis indicates the dots at the relevant location and Y-axis indicates the movement of the object.

Therefore when the object moves, the dot also moves at a low speed.

Thus an object with the oscillatory movement will appear as a trace as shown in the figure 1.10.3.

Sonogram Recording of movement of Heart

Fetal Heart Movement

Principle:

It works under the principle of Doppler Effect

i.e., there is an apparent change in the frequency between the incident sound waves on the fetus and the reflected sound waves from the fetus.

Description:

It consists of a Radio Frequency Oscillator(RFO), for producing 2 MHz of frequency and RFA (Radio Frequency Amplifier) to amplify the receiver signal as shown in the figure.

Working:

The transducer is fixed over the mother’s absominal wall, with the help of a gel or oil.

RFO is switched on to drive the pulses and hence the transducer produces Ultrasonic waves of 2 MHz.

These Ultrasonic waves are made to be incident on the fetus.

The reflected Ultrasonic waves from the etch are received by the transducer and are amplified by RFA.

Both the incident and the received signals are mixed by the mixer and is filtered to distinguish the various types of sound and finally the Doppler shift or change in frequency is measured.

The movement o the heart can be viewed visually by CRO or can be heard by the Loud Speaker, after necessary amplification by AF.

Ultrasonic Imaging System – Industrial Applications of Ultrasonic waves

Principle of working

During the scanning of the body surface by Ultrasonic transducer, the Ultrasonic waves are transmitted into the patient’s body.

The echoes from the body are collected by the receiver circuit.

Since some echoes come from the depth, they are weak; therefore, proper depth gain compensation is given by DGC circuit.

Then these signals are converted into digital signals by an analog to digital converter and are stored in the memory of the Control Processing Unit (CPU) o a computer.

Meanwhile, the control unit in the CPU receives the signals of transducer position and TV synchronous pulses.

These signals generates X plate and Y plate address information’s or the T.V monitor and is also stored in the memory of the CPU.

The stored signals are processed and colour coded and is given to the digital to analog(D/A converter), which converts the digital into analog signal.

Finally the mixing circuit mixes the analog signals and TV synchronous signals properly.

The mixed signals are finally fed to the video section of the television monitor as shown in the igure 1.12.

The TV monitor produces the coloured Ultrasonic image of the internal part o the Body.

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Properties of Ultrasonic waves and Production of Ultrasonic waves

Piezo Electric Crystals – Principle, Construction, working

Principle and working of SONAR – Sound Navigation and Ranging

Determination of Ultrasonic Velocity in Liquid(Acoustical Grating Method): Principle, Construction and working

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

Metallic Glasses

SHAPE MEMORY ALLOYS

Nanotechnology and Nanomaterials

NON-LINEAR MATERIALS AND BIO-MATERIALS

Determination of Ultrasonic Velocity in Liquid (Acoustical Grating Method)

Determination of Ultrasonic Velocity in Liquid – Acoustical Grating Method.

Acoustical Grating Method Principle:

When ultrasonic waves travel through a transparent liquid, due to alternate compression and rare action, longitudinal stationery waves are produced.

If monochromatic light is passed through the liquid perpendicular to these waves, the liquid behaves as diffraction grating.

Such a grating is known as Acoustic Grating.

Here the lines of compression and rareaction act as transparent light waves.

It is used to find wavelength and velocity(v) of ultrasonic waves in the liquid.

Acoustical Grating Method – Construction;

It is consists of a glass tank, filled with the liquid.

A piezo-electric (Quartz) is fixed at the bottom of the glass tank and is connected with piezo-electric oscillatory circuit as shown in the figure 1.7.

An incandescent lamp is used as a monochromatic source (S) and a telescope arrangement is used to view the diffraction pattern.

A collimator consisting of two lenses L1 and L2 is used to ocus the light effectively in the glass tank.

Acoustical Grating Method – Working:

(i) When the piezo-electric crystal is kept at rest:

Initially the piezo-electric crystal is kept at rest and the monochromatic at light is switched ON.

When the light is focused in the glass tank filled with the liquid, a single image, a vertical peak is observed in telescope.

i.e., there is no diffraction.

(ii) When the piezo-electric crystal is set into vibrations:

Now the crystal is put into vibrations using piezo-electric oscillatory circuit.

At Resonance, Ultrasonic waves are produced and are passed through the liquid.

These Ultrasonic waves are reflected by the walls of the glass tank and form a stationery wave pattern with nodes and antinodes in the liquid.

At nodes the density of the liquid becomes more and at antinodes the density o the liquid becomes less.

Thus, the liquid behaves as a directing element called acoustical grating element.

Now when the monochromatic light is passed the light gets directed and a diffraction pattern consisting of central maxima and principle maxima on either side is viewed through the telescope as shown in figure 1.7.2 as well as in 1.7.3.

Calculation of Ultrasonic Velocity

The velocity of Ultrasonic waves can be determined using the condition.

Thus, this method is useul in measuring the wavelength and velocity of ultrasonic waves in liquids and gases at various temperatures.

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Properties of Ultrasonic waves and Production of Ultrasonic waves

Piezo Electric Crystals – Principle, Construction, working

Principle and working of SONAR – Sound Navigation and Ranging

Industrial Applications of Ultrasonic waves

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

Metallic Glasses

SHAPE MEMORY ALLOYS

Nanotechnology and Nanomaterials

NON-LINEAR MATERIALS AND BIO-MATERIALS

Sound Navigation and Ranging (SONAR):

Sound Navigation and Ranging (SONAR) are explained in this page.

SONAR – Sound Navigation and Ranging

Principle:

It is based on the principle of Echo – Sounding.

When the Ultrasonic waves are transmitted through water, it is reflected by the objects in the water and will produce an echo signal.

The change in frequency of the echo signal, due to Doppler Effect helps us in determining the velocity and direction of the object.

Description:

It consists of timimg section which triggers the electric pulse from the pulse generator.

This pulse generator is connected to the transducer so that ultra sonic can be produced.

The transducer is further connected with the CRO for display.

The timing section is also connected to the CRO display or reference of the timing at which the pulse is transmitted as shown in the block diagram.

Working:

The transducer is mounted on the ship’s hull without any air gap between them as shown.

The timing at which the pulse generated is recorded at the CRO or reference and this electrical pulse triggers the transducer which is kept in hull of the ship to produce ultrasonic waves due to the principle of inverse piezo electric effect.

These ultrasonic waves are transmitted through the water in sea.

On stricking the object the ultrasonic waves (echo pulses) are reflected in all directions as shown

Cavitation:

Definition:

The Ultrasonic sound waves that propagate into the liquid media result in alternating high pressure (compression) and low-pressure (rarefaction) cycles, with rates depending on the frequency.

During the low pressure cycle, high intensity ultrasonic waves create small vcuum bubbles or voids in the liquid.

When the bubbles attain a volume at which they can no longer absorb energy, they collapse violently during a high pressure cycle.

This phenomenon is termed cavitation.

During the low pressure cycle, high intensity ultrasonic waves create small vacuum bubbles or voids in the liquid.

When the bubbles attain a volume at which they can no longer absorb energy, they collapse violently during a high pressure cycle.

This phenomenon is termed cavitation.

During the implosion very high temperature(approx 5,000K) and pressures (approx 2,000atm) are reached locally,

The implosion of the cavitation bubble also results in liquid jets of up to 280m/s velocity.

Acoustic Grating

The ultrasonic waves generated with the help o a quartz crystal inside the liquid in a container sets up standing wave pattern consisting of nodes and anti-nodes.

The nodes are transparent and anti-nodes are opaque to the incident light.

In effect the nodes and anti-nodes acts like grating(a setup of large number of slits of equal distance) similar to that of ruling in diffraction grating. It is called as acoustic grating or aqua grating.

At nodes the density of the liquid is maximum and at antinodes density is minimum.

This arrangement is very much similar to the diffraction grating and is called acoustic grating.

Hence, by using the condition for direction, we can ind the wavelength of ultrasound and thereby the velocity of sound in the liquid medium.

When ultrasonic waves are generated in a liquid kept in rectangular vessel, the wave can be reflected from the walls of the vessel.

The direct and reflected waves get superimposed, which causes a standing wave to be formed.

The density o the liquid at the node will be more than the density at an antinode.

Under these conditions, if a beam of light is passed through the liquid at right angles to the wave the liquid acts as a diffraction grating. Such a grating is known as an acoustical grating.

Here, the antinode acts as the transmitting slit and the node acts as the opaque part. Thus resembling a normal ruled diffraction grating.

This is obvious because the nodes have points o minimum density and hence allow more amount o light to pass through them than those at antinodes.

Thus, the nodes act like slits.

Diffraction Grating

A Diffraction grating is an extremely useful device.

It consists of large number of narrow slits side by side.

The slits are separated by opaque surfaces.

When a wavefront is incident on the grating surface, light is transmitted through the slits and obstructed by the opaque spaces.

Such a grating is called transmission grating.

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Characteristics of sound and Classification of Sound

Acoustics of buildings in Civil engg

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Properties of Ultrasonic waves and Production of Ultrasonic waves

Piezo Electric Crystals – Principle, Construction, working

Determination of Ultrasonic Velocity in Liquid(Acoustical Grating Method): Principle, Construction and working

Industrial Applications of Ultrasonic waves

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

Metallic Glasses

SHAPE MEMORY ALLOYS

Nanotechnology and Nanomaterials

NON-LINEAR MATERIALS AND BIO-MATERIALS

Piezo Electric Crystals:

Piezo Electric Crystals Principle, Construction, working, Advantages and Disadvantages

The crystals which produce piezo-electric eect and converse Piezo electric effect are termed as Piezo electric crystal. Example: Quartz, Tourmaline, Rochelle Salts etc.

Piezo Electric Crystals

The crystals which produce piezo-electric effect and converse Piezo electric effect are termed as Piezo electric crystal.

Example: Quartz, Tourmaline, Rochelle Salts etc.

At typical example or a piezo electric crystal (Quartz) is as shown

It has an hexagonal shape with pyramids attached at both ends. It consists of 3 axes. Viz.,

(i) Optic Z axis, which joins the edges of the pyramid

(ii) Electrical axis(X axis), which joins the corners of the hexagon and

(iii) Mechanical axis, which joins the center or sides of the hexagon as shown

X-cut and Y cut crystals

X-Cut crystal:

When the crystal is cut perpendicular to the X-axis, as shown in the figure 1.4.2, then it is called X-crystals.

Generally X-cut crystals are used to produce longitudinal ultrasonic waves.

Y-Cut Crystal:

When the crystal is cut perpendicular to the Y-axis, as shown in the figure 1.4.3, then it is called Y-cut crystal.

Generally, Y-Cut crystal produces transverse ultrasonic waves.

Piezoelectric Effect

Definition: When a mechanical stress is applied to the mechanical axis with respect to optical axis, a potential difference is developed across the electrical axis with respect to optic axis

Inverse Piezoelectric Effect:

Definition: When an alternating electric field is applied to electrical axis with respect to optical axis, expansion or contraction takes place in the mechanical axis with respect to optical axis.

Production of Ultra sonic waves – Piezo Electric Effect

Principle:

This is based on the Inverse piezoelectric effect.

When a quartz crystal is subjected to an alternating potential difference along the electric axis, the crystal is set into elastic vibrations along its mechanical axis.

If the frequency of electric oscillations coincides with the natural frequency of the crytal, the vibrations will be of large amplitude.

If the frequency of the electric field is in the ultrasonic frequency range, the crystal produces ultrasonic waves.

Construction:

The circuit diagram is shown in the figure 1.5

It is base turned oscillator circuit.

A slice of Quartz crystal is placed between the metal plates A and B so as to form a parallel plate capacitor with the crystal as the dielectric.

This is coupled to the electronic oscillator through the primary coil L₃ of the transformer.

Coils L₂ and L₁ of oscillator circuit are taken for the primary of the transformer. The collector coil L₂ is inductively coupled to base coil L₁.

The coil L₁ and variable capacitor C form the tank circuit of the oscillator.

Working:

When the battery is switched on, the oscillator produces high frequency oscillations.

An oscillatory e.m.f is induced in the coil L3 due to transformer action.

So the crystal is now under high frequency alternating voltage.

The capacitance of C1 is varied so that the frequency of oscillations produced is in resonance with the natural frequency of the crystal.

Now the crystal vibrates with larger amplitude due to resonance.

Thus high power ultrasonic waves are produced.

Condition for Resonance:

Frequency of the oscillator circuit = Frequency of the vibrating crystal

Where ‘l’ is the length o the rod

‘E’ is the Young’s modulus o the rod

‘ρ’ is the density of the material of the rod.

‘P’ = 1,2,3 …. Etc for fundamental, first overtone, second overtone etc respectively

Advantages:

1. Ultrasonic frequencies as high as 500MHz can be generated.
2. The output power is very high. It is not affected by temperature humidity.
3. It is more efficient than the Magnetostriction oscillator.
4. The breadth of the resonance curve is very small. So we can get a stable and constant frequency of ultrasonic waves.

Disadvantages:

1. The cost of the quartz crystal is very high.
2. Cutting and shaping the crystal is quite complex.

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Characteristics of sound and Classification of Sound

Acoustics of buildings in Civil engg

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Properties of Ultrasonic waves and Production of Ultrasonic waves

Principle and working of SONAR – Sound Navigation and Ranging

Determination of Ultrasonic Velocity in Liquid(Acoustical Grating Method): Principle, Construction and working

Industrial Applications of Ultrasonic waves

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

Metallic Glasses

SHAPE MEMORY ALLOYS

Nanotechnology and Nanomaterials

NON-LINEAR MATERIALS AND BIO-MATERIALS

Properties of Ultrasonic waves and Production of Ultrasonic waves

The properties of Ultrasonic waves and Production of Ultrasonic waves are explained here

Properties of Ultrasonic waves

 

The human ear is sensitive to sound waves in the frequency range from 20-20, 000 Hz.

This range is called Auduble range. Sound waves of frequency more than 20,000Hz are called Ultrasonics. These frequencies are beyond the audible limit.

These waves also travel with the speed of sound(330m/s)

Their wavelength are small.

Production of Ultrasonic waves

Production of Ultrasonic waves

Principle:

When a rod of ferromagnetic material like nickel is magnetized. Longitudinally, it undergoes a very small change in length.

This is called Magnetostriction effect.

Construction:

The circuit diagram of magnetostriction ultrasonic generator is as shown in the figure1.3.2.

A short permanently magnetized nickel rod is clamped in the middle between two knife edges.

A coil L₁ is wound on the right hand portion of the rod.

C is a variable capacitor. L₁ and C₁ form the resonant circuit of the collector-tuned oscillator.

Coil L₂ wound on the LHS of the rod is connected in the base circuit.

The coil L₂ is used as a feed back loop.

Working:

When the battery is switched on, the resonant circuit L₁C₁ sets up an alternating current o frequency.

This current lowing round the coil L1 produces an alternating magnetic iels of frequency f along the length of the nickel rod.

The rod starts vibrating due to magnetostrictive effect.

The vibrations of the rod create ultrasonic waves.

The longitudinal expansion and contraction of the rod produces an E.M. in the coil L₂.

This e.m.f is applied to the base of the transistor.

Hence the amplitude of high frequency of high oscillations in coil L1 is increased due to positive feedback.

The developed alternating current frequency can be turned with the natural frequency of the rod by adjusting the capacitor.

Condition for Resonance:

Frequency of the oscillator circuit = Frequency of the vibrating rod

Where ‘l’ is the length o the rod

‘E’ is the Young’s modulus o the rod

‘ρ’ is the density of the material of the rod.

The resonance condition is indicated by the rise in the collector current shown in the milliammeter.

Advantages:

Magnetostriction Oscillators are mechanically rugged.

The construction cost is low.

They are capable of producing large acoustical power with fairly good efficiency.

Limitations

It can produce frequencies up to 3MHz only.

They frequency o oscillation depends upon the temperature.

Breadth o the resonance curve is large. It is due to vibrations of elastic constants of ferromagnetic material with the degree of magnetization.

So we cannot get a constant single frequency.

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Characteristics of sound and Classification of Sound

Acoustics of buildings in Civil engg

Absorption coefficient in Acoustics

Piezo Electric Crystals – Principle, Construction, working

Principle and working of SONAR – Sound Navigation and Ranging

Determination of Ultrasonic Velocity in Liquid(Acoustical Grating Method): Principle, Construction and working

Industrial Applications of Ultrasonic waves

Ultrasonic Non destruction Testing

Ultrasonic Scanning Methods A, B and C Scan Displays

Sonogram Recording of movement of Heart: Principle and working

Metallic Glasses

SHAPE MEMORY ALLOYS

Nanotechnology and Nanomaterials

NON-LINEAR MATERIALS AND BIO-MATERIALS

ABSORPTION COEFFICIENT

The ABSORPTION COEFFICIENT we know that all the sound waves when pass through as open window passes through it.

ABSORPTION COEFFICIENT

Thus, we can say that the open window behaves as a perfect absorber of sound and hence the absorption coefficient can be defined as the rate of sound energy absorbed by a certain area of the surface to that o an open window of same area.

Definition:

The absorption coefficient of a surface is defined as the reciprocal of its area which absorbs the same amount of sound energy as absorbed by a unit o an open window.

For example if 2m² of a carpet absorbs the same amount of sound energy as absorbed by 1 m² of an open window, then the absorption coefficient of the carpet is 1.2=0.5.

The absorption coefficient is measured in open window unit (O.W.U) or Sabines. 

Average absorption coefficient

The average absorption coefficient is defined as the ratio between the total absorption in the hall to the total surface area of the hall.

Measurement of sound absorption coefficient

Let us consider a smaple for which the absorption coefficient (a_m) is to be measured.

Initially without this material the reverberation time in a room and again the reverberation time is measured and let it be T₂.

Then rom Sabine’s ormula

For Case (1) i.e. without the sample

Here, by knowing the terms on the right hand side the absorption coefficient of the given sample can be determined.

FACTORS AFFECTING THE ACOUSTICS OF BUILDING

We know, when sound waves are produced in a hall, it reaches the observer directly as well as after reflections from walls, floors, ceilings, etc.

Thus there is a possibility for causing interference between these waves, which in turn affects the originality of the sound produced.

The actors affecting the acoustics (sound) of building are as follows.

1. Unoptimised reverberation time
2. Very low or very high loudness
3. Improper focusing of sound to a particular area, which may cause interference
4. Echoes or echelon effects produced inside the buildings
5. Resonance caused due to matching of sound waves.
6. Unwanted sound rom outside or inside the building, so called noise may also affect the acoustics o buildings.

OPTIMUM REVERBERATION TIME AND ITS REMEDY

We know Reverberation time is the taken for the sound to fall to one millionth o its original sound intensity, when the source of sound is switched off.

This reverberation time is high then it produces, echoes in the hall and if the reverberation time is very low, the sound will not be cleary heard by the audience.

Therefore, for clear audibility, we should maintain optimum reverberation.

The optimum reverberation time can be achieved by the following steps

1. By having the full capacity o audience in the auditorium.
2. By choosing absorbents like felt, fiber, board, glass etc inside the auditorium and even at the back of chairs.
3. Reverberation time can be optimized by providing windows and ventilators at the places wherever necessary and using curtains with folds or the windows.
4. The reverberation time can also be optimized by decorating the walls with beautiful pictures.

The optimum reverberation time will not be constant for all types of building; it varies from one building to another as follows.

• For concert halls, the speech should have the optimum reverberation time of 0.5 seconds and music should have the optimum values o 1 or 2 seconds
• For auditorium, or theatres, the optimum reverberation time should be between 1.1 to 1.5 seconds for smaller area and between 1.5 to 3 seconds for larger area.

Loudness and its remedy:

We know loudness is the degree of sensation produced on the ear; it varies from observer to observer.

But, it is found that for a single observer the loudness varies from one place to another in the same auditorium.

This defect is caused due to the bad acoustical construction of buildings.

The loaudness will be very low in some area and will be very high in some areas. It can be optimized by the following remedies.

Remedies

1. Loudspeakers should be placed at the places where we have low loudness.
2. The loudness can also be increased by making reflecting surfaces, wherever necessary
3. Loudness can be increased by constructing low ceilings
4. Absorbents are placed at the places where we have high loudness.

Thus, the loudness should be made even, all over the auditorium, so that the observer can hear the sound at a constant loudness at all the places.

FOCUSING AND INTERFERENCE EFFECTS

In some places of a hall, the sound will not be heard properly and that place is said to be a dead space, which is due to presence of convex or concave surfaces in the hall as shown in the figure.

Sometimes the sound waves will have interference pattern because of ceiling surfaces which will create maximum intensity of sound(due to constructive interference) in some places and minimum intensity of sound(due to destructive interference) at some places and hence causing uneven distribution of sound intensity in the hall and hence causing uneven distribution of sound intensity in the hall.

Remedies

1. By avoiding curved surfaces (or) covering the curved surfaces by suitable absorbents the focusing can be avoided.
2. By evenly polishing and decorating with absorbents the interference effects can be avoided.

ECHOES AND ECHELON EFFECT

In some halls, the walls o the halls will scatter the sound waves rather than reflecting it, thus way create nuisance effect due to echoes.

The echoes are formed when the time interval between the direct and reflected sound waves are about 1/15^th of a second.

This effect occurs due to the reason that the reflected sound waves reaches the observer later than the direct sound.

If there is a greater repetition of echoes of the original sound to the observer then the effect is called as Echelon effect.

Remedies

 The echo can be avoided by lining the surfaces with suitable sound absorbing materials and by providing enough number of doors and windows.

RESONANCE

Resonance occurs when a new sound note of frequency matches with standard audio frequency.

Sometimes, the window panel, sections of the wooden portion is thrown into vibrations to produce new sounds, which results in interference between original sound and created sound.

This will create disturbance to the audience.

Remedies

1. The resonance effect can be avoided by providing proper ventilation and by adjusting the reverberation time to the optimum level.
2. Nowadays the resonance is completely eliminated by air conditioning the halls.

NOISE

Noise is an unwanted sound produced due to heavy traffic outside the hall which leads to displeasing effect on the ear. There are three types of noises.

1. Air Borne noise
2. Structure Born Noise
3. Inside Noise

All these three noises pollute the area at which it has been produced and create harmful effects to the human beings.

Fortunately human beings have the capability to reject the sound within certain limits with conscious efforts and to carry on his normal work.

But sometimes the noises are strong which results in the following effects.

EFFECTS PRODUCED DUE TO NOISE POLLUTION

• It produces mental fatigue and irritation.
• Diverts the concentration on work and hence reduces the efficiency of the work.
• It sometimes affects the nervous system and lowers the restorative quality of sleep.
• Some strong noises leads to damage the eardrum and make the worker hearing impaired.
• The noises which are produced regularly will even retard the normal growth of infants and young children.

• AIR BORNE NOISE

The noise which reaches the hall through open windows, doors, and ventilations are called as air borne noise.

This type of noise is produced both in rural areas natural sound of wind and animals and in urban areas noise that arises from factories, aircrafts, automobile, trains, Flights etc.

REMEDIES

1. By making the hall air conditioned, this noise may be eliminated
2. By allotting proper places or doors and windows, this noise can be reduced.
3. It can be further by using double doors and windows with separate rames and by pacing the absorbents in-between them

• STRUCTURE BORNE NOISE

The noise that reaches the hall through the structure of the building is termed as Structure Borne noise.

Those types of noise produced inside the building, which may be due to the machinery operation, movement of furniture’s footsteps etc and these sounds will produce structural vibration giving rise to the Structure Borne Noise.

REMEDIES

1. By properly breaking the continuity of the interposing layers by some acoustical insulators this type of noise can be avoided.
2. By providing carpets, resilent, antivibration mounts etc., this type of noise can be reduced.

• INSIDE NOISE

The noises that are produced inside the halls is known as inside noise.

Or example in some offices the sound produced by machinery, type writers ect produces this type of noise.

REMEDIES

1. By placing the machineries and type writers over the absorbing materials or pads this type of noise can be reduced.
2. It can be reduced by covering the floors with carpet.
3. By fitting the engine on the floor with a layer of wood or elt between them this type of noise can be avoided.

FACTORS TO BE FOLLOWED FOR GOOD ACOUSTICS OF BUILDING

To have a clear audibility of sound have an optimum level

1. The reverberation time should have an optimum level
2. The sound must be evenly distributed to each and every part of the building.
3. There should not be any focusing of sound to any particular area.
4. Each and every syllable of sound must be herd clearly and distinctly, without any interference.
5. There should not be any echoes, echelon effects and resonance inside the buildings.
6. The building should be made as sound proof building, so that external noises may be avoided.
7. Generally to say the total quality o sound should be maintained all over the building to all the audience.

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