A comparison of coupling horns for waveguides used in medical ultrasonics

The performance of medical instruments utilising ultrasonic waveguides is largely dependent upon transmission efficiency between the tissue and the transducer. Loss occurring in the transducer-waveguide interface is appreciable enough to degrade the performance of such instruments under certain conditions. Transmission loss has been measured for a variety of differently shaped brass and stainless steel horns that have been used to try to reduce coupling lossed in a waveguide-transducer interface. Sound transmission measurements indicate that, for wavelengths of ultrasound much less than the diameter of the flared end of the horn, there appears to be little advantage of using a horn apart from practical considerations. However, the measurements were limited by significant repeatability errors which may have masked important horn-shape effects.