The effect which is used for both production and detection of ultrasonic waves
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Piezoelectric Detector
Piezoelectric effect can also be used to detect ultrasonics. If ultrasonics comprising of compressions and rarefactions are allowed to fall upon a quartz crystal a certain potential difference is developed across the faces which after amplification by a value amplifier can be used to detect ultrasonics.
2. Kundt’s Tube Method
Kundt’s tube is a long glass tube supported horizontally with a air column in it when the ultrasonic waves are passed the Kundt’s tube, the lycopodium powder sprinkled in the tube collects in the form of heaps at the nodal points and is blown off at the antinodal points. This method is used provided that the wavelength is not very small.
3. Thermal Detector
Thermal detectors can also be used to detect ultrasonics. A thermal detector is nothing but a fine platinum wire fixed at two ends.
It is placed in the region to be tested for waves. The wire is set into rapid vibrations. At a node compressions and rarefactions occurs very quickly and cause adiabatic changes. The platinum wire is, therefore, alternately heated and cooled and its resistance changes accordingly. These changes in resistance can be detected by suitable means. No such changes occur at an antinode.
4. flame Method
A narrow sensitive flame is moved along the medium. At the position of the antinode, the flame is steady. At the position of the node the flame flickers because there is change in pressure. In this way the positions of nodes and antinodes can be found out in a medium. The average distance between two adjacent nodes is equal to half the wavelength. If the value of frequency of ultrasonic wave is known, the velocity of the ultrasonic wave through the medium can be calculated.
5. Acoustic Diffraction Method
This method is based on the fact that ultrasonic waves which consist of alternate compressions and rarefactions changes the density of the medium through which they pass.
This leads to a periodic variation of refractive index of the liquid, such a liquid column is subjected to ultrasonic waves constitutes an acoustical grating. If monochromatic light is passed through the waves the liquid causes the diffraction of light.
the experimental arrangement, standing ultrasonic waves are produced in a liquid contained in a glass tube. The density and so the refractive index of the liquid is maximum at the nodal point and minimum at antinodal points. Hence the nodal area acts as opaque region, while antinodal area acts as transparent region for light. The liquid column thus resembles the rules grating.
The grating period d equal to /λ/2 and is given by
d sine θ=mλ
λ= wavelength of monochromatic light beam
m = order of minima.
An acoustic diffraction grating produced by a liquid column subjected to ultrasonic waves.
1. Depth sounding
The depth of sea or depth of water below a ship can be found out by using the echo sounding
principle. Ultrasonic waves generated by a crystal transducer in the range of 40-50 kHz aredirected towards the bottom of the sea. The time lag between the sending of ultrasonic signals and return back as an echo to the ship is recorded. Knowing the velocity and with measurement of the time lag, the depth of sea water below the ship can be calculated.
depth of sea= velocity of sound in sea * time /2
The velocity v of sound in sea water at t°C is given by
v = v0 + 1.14 S + 4.21 t – 0.037 t2
where v0 = velocity of sound in sea water at 0°C = 1510 m/ sec
S = The salinity (gm/litre)
t = temperature of sea water in oc.
2. Signalling
Since the frequency of the ultrasonics can be made very high so that wavelength is reduced to a small value. Therefore ultrasonics can be transmitted in the form of a narrow beam of small amplitude and large energy. The ship captain uses ultrasonics to steer its path in mist when light fails within few metres.
3. Sonar Exploration
Sonar stands for sound navigation and ranging.
SO stands for sound
N stands for Navigation
A stands for And
R stands for Ranging
Sonar is similar to RADAR in working. In radar we use microwaves, which are electromagnetic in nature, whereas in SONAR, we make use of ultrasonics. Ultrasonic waves are sent by the ultrasonic transmitter towards the target through water and are received back by the receiver lowered into the sea water from a ship as shown in Figure 3.7. Knowing the time interval between sending and receiving of ultrasonics e can find the position of target or sub-marine. We can also find the direction and the velocity of the moving sub-marine with this apparatus. So this sonar technique is used for the detection of nergy sub-marine inside water during war time in a similar manner as RADAR is used to trace the enemy aeroplanes in the atmosphere. During piece time, sonar is used for detecting the glaciers, icebergs, searocks and other submerged objects.
Piezoelectric effect can also be used to detect ultrasonics. If ultrasonics comprising of compressions and rarefactions are allowed to fall upon a quartz crystal a certain potential difference is developed across the faces which after amplification by a value amplifier can be used to detect ultrasonics.
2. Kundt’s Tube Method
Kundt’s tube is a long glass tube supported horizontally with a air column in it when the ultrasonic waves are passed the Kundt’s tube, the lycopodium powder sprinkled in the tube collects in the form of heaps at the nodal points and is blown off at the antinodal points. This method is used provided that the wavelength is not very small.
3. Thermal Detector
Thermal detectors can also be used to detect ultrasonics. A thermal detector is nothing but a fine platinum wire fixed at two ends.
It is placed in the region to be tested for waves. The wire is set into rapid vibrations. At a node compressions and rarefactions occurs very quickly and cause adiabatic changes. The platinum wire is, therefore, alternately heated and cooled and its resistance changes accordingly. These changes in resistance can be detected by suitable means. No such changes occur at an antinode.
4. flame Method
A narrow sensitive flame is moved along the medium. At the position of the antinode, the flame is steady. At the position of the node the flame flickers because there is change in pressure. In this way the positions of nodes and antinodes can be found out in a medium. The average distance between two adjacent nodes is equal to half the wavelength. If the value of frequency of ultrasonic wave is known, the velocity of the ultrasonic wave through the medium can be calculated.
5. Acoustic Diffraction Method
This method is based on the fact that ultrasonic waves which consist of alternate compressions and rarefactions changes the density of the medium through which they pass.
This leads to a periodic variation of refractive index of the liquid, such a liquid column is subjected to ultrasonic waves constitutes an acoustical grating. If monochromatic light is passed through the waves the liquid causes the diffraction of light.
the experimental arrangement, standing ultrasonic waves are produced in a liquid contained in a glass tube. The density and so the refractive index of the liquid is maximum at the nodal point and minimum at antinodal points. Hence the nodal area acts as opaque region, while antinodal area acts as transparent region for light. The liquid column thus resembles the rules grating.
The grating period d equal to /λ/2 and is given by
d sine θ=mλ
λ= wavelength of monochromatic light beam
m = order of minima.
An acoustic diffraction grating produced by a liquid column subjected to ultrasonic waves.
1. Depth sounding
The depth of sea or depth of water below a ship can be found out by using the echo sounding
principle. Ultrasonic waves generated by a crystal transducer in the range of 40-50 kHz aredirected towards the bottom of the sea. The time lag between the sending of ultrasonic signals and return back as an echo to the ship is recorded. Knowing the velocity and with measurement of the time lag, the depth of sea water below the ship can be calculated.
depth of sea= velocity of sound in sea * time /2
The velocity v of sound in sea water at t°C is given by
v = v0 + 1.14 S + 4.21 t – 0.037 t2
where v0 = velocity of sound in sea water at 0°C = 1510 m/ sec
S = The salinity (gm/litre)
t = temperature of sea water in oc.
2. Signalling
Since the frequency of the ultrasonics can be made very high so that wavelength is reduced to a small value. Therefore ultrasonics can be transmitted in the form of a narrow beam of small amplitude and large energy. The ship captain uses ultrasonics to steer its path in mist when light fails within few metres.
3. Sonar Exploration
Sonar stands for sound navigation and ranging.
SO stands for sound
N stands for Navigation
A stands for And
R stands for Ranging
Sonar is similar to RADAR in working. In radar we use microwaves, which are electromagnetic in nature, whereas in SONAR, we make use of ultrasonics. Ultrasonic waves are sent by the ultrasonic transmitter towards the target through water and are received back by the receiver lowered into the sea water from a ship as shown in Figure 3.7. Knowing the time interval between sending and receiving of ultrasonics e can find the position of target or sub-marine. We can also find the direction and the velocity of the moving sub-marine with this apparatus. So this sonar technique is used for the detection of nergy sub-marine inside water during war time in a similar manner as RADAR is used to trace the enemy aeroplanes in the atmosphere. During piece time, sonar is used for detecting the glaciers, icebergs, searocks and other submerged objects.
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