introduction to usw

ULTRASONIC WAVE

Ass.Prof. A. TITUS SAMUELDepartment of Physics,Sairam Engineering college, Chennai

INTRODUCTIONDerived from 2 latin

words i.e. ultra--- “beyond” sonic---’hearing sound’

It is a mechanical wave of high frequency i.e. >20,000Hz.

In medical term it is called ‘ultrasound’

Ranges

• Audible range of human ear is 20-20,000Hz.

• Cat & dogs can hear up to 30KHz.• Bat can detect up to 100KHz.• Some insect can produce ultrasound up to

40KHz.

PRODUCTION OF US WAVE

CAN BE PRODUCED BY FOLLOWING METHOD

1.Mechanical method[Galton’s whistle]2.Magnetostriction oscillator3.Piezoelectric oscillator

GENERAL PRINCIPLE OF PRODUCTION OF ULTRASONIC WAVES

General principle involved in generating ultrasonic wave is to cause dense vibration in a dense material to vibrate very rapidly.

The vibration caused surrounding material to vibrate with same frequency. The

vibration then spread out in the form of ultrasonic wave.

GALTON’S WHISTLE

Galton's whistle can be used to produce sounds varying in pitch from audible to ultrasonic. It is useful in measuring the highest audible frequency of the human ear.

A graduated barrel with a micrometer measures the length of the column of air vibrating in the whistle. An oscilloscope can be used to display the silent sound waves and to measure their frequency.

Galton’s whistle

Magneto-striction Oscillator

In this case an iron or nickel element is magnetized to change its dimensions, thereby

producing ultrasonic waves.

Magneto-striction Oscillator

Magneto-striction Oscillator AnimationMerits and Demerits

Magnetostriction materials are easily available and inexpensive.Simple circuit to construct.Large output power-generated.

Single frequency is not possible –since varying elastic constant due to repeated magnetization.Only up to 300kHz is possible.Energy loss due to eddy current loss

What is Piezoelectricity?• Piezoelectricity means “pressure electricity”, which is

used to describe the coupling between a material’s mechanical and electrical behaviors. – Piezoelectric Effect • when a piezoelectric material is squeezed or stretched,

electric charge is generated on its surface.– Inverse Piezoelectric Effect • Conversely, when subjected to a electric voltage input, a

piezoelectric material mechanically deforms.

Quartz Crystals• Highly anisotropic• X-cut: vibration in the direction perpendicular to the cutting

direction• Y-cut: vibration in the transverse direction

Piezoelectric Materials

• Piezoelectric Ceramics (man-made materials)– Barium Titanate (BaTiO3)– Lead Titanate Zirconate (PbZrTiO3) = PZT, most widely used – The composition, shape, and dimensions of a piezoelectric ceramic

element can be tailored to meet the requirements of a specific purpose.

Photo courtesy of MSI, MA

Piezoelectric Materials

• Piezoelectric Polymers– PVDF (Polyvinylidene flouride) film

• Piezoelectric Composites– A combination of piezoelectric ceramics and polymers to

attain properties which can be not be achieved in a single phase

Image courtesy of MSI, MA

Piezoelectric Properties

• Anisotropic• Notation: direction X, Y, or Z is represented by the

subscript 1, 2, or 3, respectively, and shear about one of these axes is represented by the subscript 4, 5, or 6, respectively.

Piezoelectric Properties• The electromechanical coupling coefficient, k, is an

indicator of the effectiveness with which a piezoelectric material converts electrical energy into mechanical energy, or vice versa. – kxy, The first subscript (x) to k denotes the direction along which the

electrodes are applied; the second subscript (y) denotes the direction along which the mechanical energy is developed. This holds true for other piezoelectric constants discussed later.

– Typical k values varies from 0.3 to 0.75 for piezoelectric ceramics.

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StoredEnergy Mechanicalk

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Piezoelectric Properties

• The piezoelectric charge constant, d, relates the mechanical strain produced by an applied electric field, – Because the strain induced in a piezoelectric material by an

applied electric field is the product of the value for the electric field and the value for d, d is an important indicator of a material's suitability for strain-dependent (actuator) applications.

– The unit is Meters/Volt, or Coulombs/Newton

Field Electric Applied

tDevelopmenStrain d

j

iij V

xd

PIEZOELECTRIC OSCILLATOR 1. When a specially cut piezoelectric quartz crystal is

compressed, the crystal becomes electrically charged and an electric current is generated.

2. On reversing this process the direction of current will reverse itself. Alternatively compressing & stretching the crystal will produce an alternating current.

3.So by applying an alternating current of natural frequency of crystal, crystal can be made to expand & contract with the alternating current

4.Such current on crystal produce ultrasonic wave.

PIEZOELECTRIC OSCILLATOR

AnimationMerits and demeritsCan generate above 500 MHzStable frequency.Wide range of frequencies are possible.

Piezoelectric crystals are costly.Cutting and shaping is very hard.

Properties of ultrasonic waves• Highly energetic< can go for longer distance• Can go under reflection , refraction &

absorption process.• Produces stationary wave when passes

through liquid.• Exposure to an object for a longer time

cause heat effect.• Due to high freq. & short wavelength , can

be focused in a narrow beams.

Refrences

• www.wikepedia.org• www.sonochemistry.info/index.htm• http://science.jrank.org• www.scienceclarified.com• www.scholarsresuorce.com