BTech_Unit_I.pptx Ultrasonic sound ppt for students
- 2. What is mean by sound to you? Sound is a pressure wave which is created by a vibrating object.
- 3. Intensity of sound- Sound intensity, also known as acoustic intensity, is defined as the power carried by sound waves per unit area in a direction perpendicular to that area. The SI unit of intensity, which includes sound intensity, is the watt per square meter (W/m2). Sound intensity is not the same physical quantity as sound pressure. Human hearing is sensitive to sound pressure which is related to sound intensity. The decibel (dB) is a relative unit of measurement. Frequency of Sound- The frequency f of a wave is measured as the number of complete back- and-forth vibrations of a particle of the medium per unit of time. 1 Hertz = 1; vibration/second; f = 1/Time
- 5. Why is sound a mechanical wave? Sound waves move through air by displacing air particles in a chain reaction. As one particle is displaced from its equilibrium position, it pushes or pulls on neighbouring molecules, causing them to be displaced from their equilibrium. As particles continue to displace one another with mechanical vibrations, the disturbance is transported throughout the medium. These particle-to-particle, mechanical vibrations of sound conductance qualify sound waves as mechanical waves. Sound energy, or energy associated with the vibrations created by a vibrating source, requires a medium to travel, which makes sound energy a mechanical wave.
- 6. Ultrasonic wave is defined as “inaudible sound with high frequency for human” the frequency of which generally exceeds 20 kHz. Since They have smaller wavelengths, penetrating power is high. P is directly proportional to frequency. They have high energy content. They can be transmitted over a large distance without much loss of energy. They produce intense heat when they are passed through objects. Ultrasonic
- 7. Ultrasonic produce by following methods Magneto-striction oscillator Piezoelectric oscillator Production of ultrasonic waves
- 8. Production of ultrasonic waves- Magneto-striction oscillator Magneto-striction oscillator Magnetostriction effect: When ferromagnetic rod like nickel/iron is placed in a magnetic field parallel to its length, the rod experiences a small change in its length. Continues change in length (increase and decrease) produce ultrasonic sound.
- 9. Production of ultrasonic waves- Magneto-striction oscillator
- 10. Construction: XY is a rod of ferromagnetic materials like iron/Nickel clamped in the middle The altering magnetic field is generated by electronic oscillator The coil L1 wound on the right hand portion of the rod along with a variable capacitor C. This forms the resonant circuit of the collector tuned oscillator. The frequency of oscillator is controlled by variable capacitor. The coil L2 wound on the left hand portion of the rod is connected to the base circuit. The coil L2 acts as feedback loop. Production of ultrasonic waves- Magneto-striction oscillator
- 11. When High Tension battery is switched on, The collector oscillate with a frequency f This AC current flowing through the coil L1 produces an alternating magnetic field along the length of the rod. The frequency of vibration of the rod is given by- l = length of the rod; Y= Young modulus of the rod; Rho= density of the rod Capacitance is adjusted to such that frequency of circuit is equal to natural frequency of the rod and thus resonance take place Production of ultrasonic waves- Magneto-striction oscillator
- 12. Advantage Design of this oscillator is easy and cheap At low frequency ultrasonic, the large power output can be produced without the risk of damage of circuit. Disadvantage High frequency circuit can damage, upper limit is around 3 MHz Frequency is depend on temperature Loss of energy due to eddy current. Production of ultrasonic waves- Magneto-striction oscillator
- 13. Production of ultrasonic waves- Piezoelectric oscillator If mechanical pressure is apply on the opposite faces of pair of certain crystals (like quartz etc), equal and opposite charges appear on another faces. This is called Piezo-Electric effect. Converse Piezo-electric effect is also true. Hence, If we apply equal and opposite charges on other sides of pair of crystals like quartz, it will produce mechanical pressure on other sides, hence crystals will change size/shape.
- 14. Production of ultrasonic waves- Piezoelectric oscillator When High Tension battery is switched on, The collector oscillate with a frequency f Due to transformer action, oscillatory emf is induced in the coil L3. High frequency AC voltages are fed on surfaces of crystal The frequency of vibration is given by- P= 1,2,3,…(fundamental first over tone, second over tone) ; l = length of the crystal; Y= Young modulus of the crystal; Rho= density of the crystal; Capacitance is adjusted to such that frequency of circuit is equal to natural frequency of the crystal and thus resonance take place
- 15. Advantage This can produce high frequency ultrasonic up to 500 MHz. Output of oscillator is very high. It is not affected by temperature and humidity. Disadvantage The cost of Piezo-electric quartz is very high. Cutting and shaping quartz is complex. Production of ultrasonic waves- Piezoelectric oscillator
- 16. Grating A diffraction grating is an optical element, which separates (disperses) white light into its constituent wavelengths (colours). The polychromatic light incident on the grating is dispersed so that each wavelength is reflected from the grating at a slightly different angle. The dispersion arises from the wavefront division and interference of the incident radiation from the periodic structure of the grating. If Monochromatic source use we will gate diffraction pattern Diffraction grating
- 17. Acoustic Grating Crystal oscillator Ultrasonic Liquid When ultrasonic pass through a liquid, the density of liquid varies layer by layer due to variation in pressure and liquid will act as a diffraction grating, so called acoustic grating. Under this condition, When a monochromatic source of the light passed through acoustic grating, the light get diffracted . Then, by using the condition for diffraction, the velocity of ultrasonic waves can be determine.
- 18. Acoustic Grating Construction/Working The liquid is taken in a glass cell. The Piezo-electric crystal is fixed at one side of the wall inside the cell and ultrasonic waves are generated The waves travelling from the crystal are reflected by reflector placed at the opposite wall. The reflected waves get superimposed with the incidentt waves producing longitudinal standing wave pattern called acoustic grating. If light from a laser source such as He-Ne or diode laser is allowed to pass through the liquid in a direction perpendicular to the grating, diffraction takes place and once can observe the higher order diffraction pattern on the screen.
- 19. Acoustic Grating Grating equation d sin θ = nλ for acaustic grating d= λu /2 λu = 2n λ/sin θ λu= wavelength of ultrasonic wave λ = wavelength of incident light n= order of maxima Velocity = f λ Vu = 2n λf/ sin θ where f is a frequency of ultrasonic wave
- 20. Acoustic Grating Gratings are generally better than prisms - they are more efficient, they provide a linear dispersion of wavelengths and do not suffer from the absorption effects that prisms have which limits their useful wavelength range.
- 21. Application of Ultrasonic wave
- 22. Ultrasonic drilling of brittle solid, precious stones, semiconductor, hard alloy etc Ultrasonic welding – Energy convert into heat Ultrasonic cleaning of electronic device manufacture Echo Sounder- wave can travel through water for larger distance, this property utilised in measurement of depth of the ocean. λ= v.t/2 SONAR Sonography To destroy bacteria in water, milk etc.
- 23. Acoustic Acoustics, the science concerned with the production, control, transmission, reception, and effects of sound. Architecture acoustic deals with the properties of sound in close space and their design. Reverberation- Sound produce in a hall undergoes multiple reflection from walls, floor, ceiling. Time taken by sound in a room to fall from its average intensity to inaudible level, is called reverberation time.
- 24. Basic requirement for acoustically good hall: Site selection- A site should be away from the highway, vehicular traffic, rail traffic, airport or any other noise. Volume- The hall should be big enough so that sound intensity spreads uniformly over entire area. Shape- The shape of hall should avoid reflection and focusing of sound wave, concave ceiling should be avoided. Proper reverberation time should be maintained. Too long reverberation time makes room noisy while too short reverberation time makes room dead. Seating arrangement- The seats should be arrange in conical area of the circles.
- 25. Reverberation time- Sabine formula Reverberation time (T) is proportional to (volume of hall/ absorption) More the absorption less reverberation time Bigger the hall more reverberation time T = K. (V/A) T= 0.161 (V/ Σ αiSi) Absorption depends on many factor A= Σ αiSi Where α is some energy absorb by the surface divided by total sound energy incident on the surface
- 26. 1. Find reverberation time for a hall of dimensions 20 m x 10 m and celling around 7 m having average absorption coefficient of 0.15 2. How much area of Curtain is needed to get reverberation time 0.8s, if absorption coefficient of curtain is 1.2?
- 27. T= 0.161 (V/ Σ αiSi) = 0.161 s.m-1 X (20 X10X7) m3 _______________________________ = 1.8 s (0.15). X ( 2 X (20X10 + 20X7 + 10X7) ) m2 = 0.161 X (20 X10X7) _______________________________ ___________________ = 0.8 {(0.15 ) X ( 2 X (20X10 + 20X7 + 10X7) ) } + { (1.2 ) X ( C ) 225.4 ___________ = 0.8. >>> 132 m2 123 +1.2 C
- 28. 1. What is a ultrasonic sound? 2. Write down properties of ultrasonic sound. 3. What are two methods of production of ultrasonic waves? 4. Explain working principle and construction of magneto-striction oscillator. 5. What are Advantage and Disadvantage of the magneto-striction oscillator? 6. Explain working principle and construction of Piezo-electric oscillator. 7. What are Advantage and Disadvantage of the Piezo-electric oscillator? 8. Explain construction and working of acoustic grating using ultrasonic waves. 9. What are application of ultrasonic sound. 10.What are best requirements of acoustically good hall? 11.Define the reverberation time and give Sabine formula for ultrasonic sound. 12.Find reverberation time for a hall of dimensions 40 ft x 50 ft and celling around 20 ft , having average absorption coefficient of 0.04 for walls, for 4kHz sound wave and constant K for 0.049 s.ft-1 13.How many curtain of 10 ft X 3 ft will be needed to get reverberation time reduced by 0.2 s, absorption coefficient of curtain 1.2? 14.Find the velocity of ultrasonic sound of wavelength 0.30 mm and frequency