Ultrasonic transducer advantageously usable for diagnostic purpose includes a piezoelectric element such as a PVDF film backed with a reflective layer of a reduced thickness specified in relation to the wavelength of sound waves within the reflective layer at one-half of the free resonant frequency of...http://www.google.fr/patents/US4296349?utm_source=gb-gplus-shareBrevet US4296349 - Ultrasonic transducer
