ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

3aEA7. Effect of electromagnetic interference on a continuous wave ultrasonic field.

David L. Cosnowski

Mardi C. Hastings

Ohio State Univ., Dept. of Mech. Eng., 206 W 18th Ave., Columbus, OH 43210

Continuous-wave ultrasound for imaging and other measurement applications requires the use of a separate source and receiver transducer. When this system is used in air or water, the receiver transducer often detects a signal at the ultrasonic frequency even in the absence of a target. At ultrasonic frequencies, significant electromagnetic coupling between the transducers can occur due to their own and extraneous electromagnetic fields. This study examines the effect of this interference on the 3-dB sample volume defined by the crossed beams. The sample volume is determined mathematically by modeling the source and receiver transducers as plane piston radiators [J. Zemanek, 181--191 (1971)]. The effect of interference is obtained by adding a constant term to the sample volume matrix, which, in general, is complex. Experimental measurements using an ultrasonic source and receiver in air at several frequencies from 40 to 100 kHz correlate well with model predictions. The electromagnetic interference was found to have a significant effect on the observed field. [Work supported by NSF Grant No. MSS 9058607.]