Ferroelectret transducers for water immersion and medical imaging

This paper investigates the possibility of using ferroelectret films to produce wideband ultrasonic transducers for applications in water immersion and medical imaging. Ultrasonic transducers with different sizes (apertures) were fabricated using a polypropylene ferroelectret film (0.6 MHz thickness resonant frequency) as active component. Then, they were characterized in pulse-echo operation mode in water immersion. Fabricated transducers show a useful frequency bandwidth from 0.3 to 2.5 MHz with a 6 dB relative bandwidth of 175% and minimum two-way Insertion-loss of -65 dB that depends on transducer active area. The use of matching layers to improve the Insertion loss figure is also investigated. Finally, the application of these transducers to discern between different echoes coming from layered reflectors is tested, in particular, the simple case of a rubber plate attached to a steel reflector is studied. Pulse-echo mode and both time domain and resonant frequency domain techniques have been tested and discussed, in relationship with the possibility of using this technique to determine thicknesses of the different layers in a layered reflector, which is a problem commonly found in different medical applications.