Igal Ladabaum
B. T. Khuri-Yakub
E. L. Ginzton Lab., Stanford Univ., Stanford, CA 94305
Dimitri Spoliansky
Ecole Normale Superieure, 75005 Paris, France
The successful modeling and fabrication of capacitive ultrasonic air transducers is reported. Emission and reception in air at 11.4, 9.2, and 3.1 MHz is demonstrated. Furthermore, transmission experiments through air--glass--air (70 dB of signal loss) at 3.8 and 5.1 MHz are reported. The transducers are made using surface micromachining techniques, which enable the realization of center frequencies ranging from 1.8 to 11.6 MHz. A theory explaining both the static and dynamic operation of the devices is presented. In addition to agreeing well with the experiments, the theory predicts that displacements on the order of 10[sup -3] angstroms (with potential for 10[sup -5] angstroms) are detectable with a 20-dB signal-to-noise ratio. Such detection sensitivity is shown to yield air transducer systems capable of withstanding over 100 dB of signal attenuation, a figure of merit that has significant implications for ultrasonic imaging, nondestructive evaluation, gas flow and composition measurements, and range sensing. [This work has been supported by a grant from ONR.]