what is a 'ultrasonic transducer'?

Question

This is made of using ferroelectric materials

Answer 1

An ultrasonic transducer is a device that converts energy into ultrasound, or sound waves above the normal range of hearing for humans. While technically a dog whistle is an ultrasonic transducer that converts mechanical energy in the form of air pressure into ultrasonic sound waves, the term is more apt to be used to refer to piezoelectric transducers that convert electrical energy into sound. Piezoelectric crystals have the property of changing size when an electric voltage is applied, thus applying an alternating voltage (AC) can cause them to oscillate at very high frequencies producing very high frequency sound waves. Since piezoelectric crystals generate a voltage when force is applied to them the same crystal can be used as an ultrasonic detector. Alternative methods for creating and detecting ultrasound include magnetostriction and capacitive actuation. Ultrasonic transducers are used in many applications including humidifiers, sonar, medical ultrasonography, burglar alarms, and non-destructive testing.

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Answer 2

Transducers are generally used for measurments (accurate measurements) .
for example you may use a "Ultrasonic Trancducer" to measure the speed of a liquid(e.g water) in a pipe.
it is using Doppler effect to measure.

Answer 3

It is basically either a device similar to a microphone or speaker that operates at ultrasonic frequencies (frequencies above those that we can hear.)

Used for ultrasound imaging, remote control and so on.