MICROMACHINED ULTRASONIC TRANSDUCERS - 11.4 MHZ TRANSMISSION IN AIR AND MORE

The fabrication and modeling of novel, capacitive, ultrasonic air tran sducers is reported. Transmission experiments in air at 11.4, 9.2, and 3.1 MHz are shown to correspond with theory. The transducers are made using surface micromachining techniques, which enable the realization of center frequencies ranging from 1.8 to 11.6 MHz. The bandwidth of the transducers ranges from 5% to 20%, depending on processing paramet ers. Custom circuitry is able to detect 10 MHz capacitance fluctuation s as small as 10(-18) F which correspond to displacements on the order of 10(-3) Angstrom, in a bandwidth of 2 MHz with a signal to noise ra tio of 20 dB. Such detection sensitivity is shown to yield air transdu cer systems capable of withstanding over 100 dB of signal attenuation a figure of merit that has significant implications for ultrasonic ima ging, nondestructive evaluation, gas flow and composition measurements , and range sensing. (C) 1996 American Institute of Physics.