Piezoelectric ultrasound generators and detectors

The most commonly employed US transducers are thin platelets of piezoelectric (mainly ceramic) materials with metallic electrodes on both surfaces (see Section 1.4). Such transducers have resonance frequencies determined by the interference of the ultrasonic signals created at both surfaces and internal reflections. The interferences cause distortions (broadening) in the echo pattern in pulse-echo measurements. The resonances also introduce phase shifts in the signals and lead to restrictions in the bandwidth. The frequency range can be expanded by using concave, cylindrical or spherical piezotransducers. 

Piezoelectric transducers can be of the high contact, two- or one- point contact types. The contact force between the sample and the transducer has been found to affect resonance spectra. Thus, resonant peaks increase with decreasing contact force also, the resonant frequency is dependent on the contact force [8]. Electrical and mechanical cross-talk between 

In order to minimize the problem faced in separating the specimen response from the as-measured spectra of a resonator by minimizing sample-transducer contact, a one-point contaot design was developed by replacing the receiving transducer with an optical interferometer and measuring elastic wave speeds in a 1-mm diameter ceramic ball [15]. 

The new generation of silicon technology imaging transducers combined with ongoing electronic miniaturization and the availability of extremely fast and powerful portable laptop computers will lead to the development of portable or even wearable high-resolution scanners affording wireless data transfer. This technology will help to make communication with remote locations and advanced medical applications more affordable. 

---