ULTRASONIC WAVE

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ULTRASONIC WAVE: 

ULTRASONIC WAVE

INTRODUCTION: 

INTRODUCTION Derived 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 ’

PowerPoint Presentation: 

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: 

PRODUCTION OF US WAVE CAN BE PRODUCED BY FOLLOWING METHOD 1.Mechanical method[Galton whistle] 2.Magnetostriction oscillator 3.Piezoelectric oscillator

GENERAL PRINCIPLE OF PRODUCTION OF ULTRASONIC WAVES: 

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 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.

PowerPoint Presentation: 

Galton’s whistle

PIEZOELECTRIC OSCILLATOR: 

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.

Magneto-striction oscillator : 

Magneto- striction oscillator In this case an iron or nickel element is magnetized to change its dimensions, thereby producing ultrasonic waves.

Properties of ultrasonic waves: 

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.

Absorption & Dispersion : 

Absorption & Dispersion The freq. dependance of the wave velocity of ultrasonic wave within a medium is called dispersion. Normally dispersion occurs at high frequency. Dispersion by solid – depends on individual grains of solid. By liquid – scattering of molecule, viscosity , thermal conductivity.

Attenuation: 

Attenuation In a medium intensity gets decreased with distance It is due to scattering & absorption of sound wave. This combined effect of scattering & absorption is called Attenuation. It is the decay rate of the wave as it propagate A = A 0 .e -αz

Reflection & Transmission coefficient: 

Reflection & Transmission coefficient Ultrasonic waves are reflected at boundries where there is difference in acoustic impedance[z] of materials on each side of boundary. z = pv Reflection coefficients [R] R = [(Z 2 -Z 1 )/(Z 2 +Z 1 )] 2 Transmission coefficient = 1-R, Both are expressed in Decibel(dB).

Ultrasonication: 

Ultrasonication Passage of ultrasonic wave in liquid medium creates alternating areas of compression & rarefaction which changes rapidly with time. So this property of ultrasonic wave can be used to produce some mechanical effect in liquid so called ultrasonication . Eg . cavtation

USES OF ULTRASONIC WAVE: 

USES OF ULTRASONIC WAVE 1.To measure thickness of materials. 2.Fat layers on cattle before marketing. 3.Investigate phy . Properties of materials. 4.Determine mol. Wt. Of polymer. 5.Speed up chemical reaction 6.Estimate fuel in aircraft. 7.Increase germination of seed on exposure to ultrasound 8.Medical uses. 9.In Burglar alarm.

Refrences: 

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