A DUAL-FREQUENCY ULTRASONIC PROBE FOR MEDICAL APPLICATIONS

A dual frequency probe using a multilayer ceramic is proposed for simu ltaneously obtaining a high resolution B mode and a high sensitivity D oppler mode image. This ceramic consists of two layers in which the po ling directions are opposite and the individual thicknesses are differ ent. It is possible to control the values of relative electromechanica l coupling factors in the fundamental and the second harmonic by chang ing the thickness ratio. A thickness ratio of 1:0.7 was decided from c omputer simulation based on the Mason's model. A sufficient resolution has been shown from the fact that the intima of the carotid artery co uld be distinguished by an actually fabricated probe with dual frequen cies of 3.75 and 7.5 MHz. Also, the sensitivity of this probe in the D oppler mode at 5 cm depth from the surface has been improved as much a s 5 dB over that of a conventional one.