Piezo crystal barotrauma8/26/2023 ![]() Backing layer can be used to damp out the ringing by absorbing part of the energy from the vibration of the back face. For imaging applications, it is highly undesirable to have a pulse with long duration. This would cause long ring– down of the ultrasonic pulse, which is the so–called ringing effect. Due to the acoustic mismatch between the air and the piezoelectric material, the reflected wave reverberates inside the transducer element. In fact, 100 % transmission is impossible for only considering the front matching layer. Parylene is a common polymer which minimizes the acoustic impedance mismatch and acts as a protecting layer as well. Coating a polymer onto the piezoelectric layer is also an alternative method to fabricate the matching layer. ![]() The scattering effect can be minimized efficiently by choosing proper size of the powder especially for high–frequency transducers. The acoustic impedance of the matching layer can be adjusted by the content of the powder. Mixing micro or nano scale powder into a polymer is one of the common approaches to fabricate matching layers. The transducer is usually treated as a three–port network including two mechanical ports and one electrical port as shown in Fig. Since the piezoelectric material itself exhibits much higher acoustic impedance (~30 MRayl) than that of biological tissue or water (~1.5 MRayl), a substantial part of the acoustic energy would be lost at the rear interface and not directed into the forward direction, resulting in poor resolution and sensitivity, if not properly matched acoustically. The selection criteria of these mechanical layers are presented in next section.Ī transducer rings at its natural frequency once it is excited by an electrical source. For specific applications, proper piezoelectric materials are chosen according to a number of factors such as their piezoelectric performance, dielectric properties, elastic properties and stability. Consequently, piezoelectric elements play a very important role in transducer technology. Ultrasonic transducers operate based on both converse and direct effects of piezoelectric materials in which the vibration would be produced upon the application of a potential difference across the electrodes and then the signal would be generated when receiving an echo. 1.1 Basic principles of the ultrasonic transducer
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