1. What is an ultrasonic transducer?

The ultrasonic transducer is a device that can transmit and receive ultrasonic waves. When transmitting, it converts electrical energy into mechanical energy, in the form of ultrasound. When receiving, it converts mechanical energy into electrical energy. Ultrasonic transducers are widely used in NDT, object detection, distance, and flow measurements. The figure below shows the basic structure of a typical ultrasonic transducer.

2. Piezoelectric element

Piezoelectric elements are made from piezoelectric materials, which generate an electric charge when subjected to mechanical stress and change dimensions when an electric field is applied across the material.

Piezoelectric materials can be classified into the following categories

(1) Single crystalline material (such as quartz)

(2) Piezoceramics (such as lead zirconate titanate, PZTs

(3)Piezoelectric semiconductors (such as ZnO2)

(4) Polymer (such as polyvinylidene fluoride, PVDF)

(5) piezoelectric composites

(6) glass ceramics (such as Li2Si2O5 and Ba2TiSiO6).

3. Matching

The matching layer, sometimes called the acoustic window or wear plate, is usually made of plastic or epoxy materials. It helps protect the piezoelectric element from the environment and also improves the acoustic energy penetration from the transducer to the media when its material and thickness are carefully chosen.

4. Backing

The backing is usually made of epoxy mixed with tiny solid particles, and it is very attenuative. Its acoustic impedance is preferred to match the acoustic impedance of the piezoelectric element so that it can absorb the backward emitted sound waves and achieve better range resolution. If the backing is not working efficiently, the transducer may have a lower resolution due to a longer waveform duration but can be higher in signal strength or greater in sensitivity.

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