We propose a design that decreases the acoustic energy reflected by ultrasonic transducers for medical use.
To achive good images without artifacts, it is necessary to decrease the multiple reflections that are generated between the transducer and tissue boundaries in the human body. This can be done by decreasing the transducer's reflection coefficient.
However, conventional transducers reflect much acoustic energy because they are designed to achieve high efficiency and a wide bandwidth. Reflection ordinarily receives little consideration.
We devised a new technique to decrease the reflection. Input acoustic impedance is assumed to be that seen from the transducer's surface to the backing material through the matching layers and the piezoelectoric ceramic. Input acoustic impedance at the center frequency is designed to equal the acoustic impedance of the load.
We analyzed the reflection coefficient of several transducers by computer simulation. We found a structure that provides a small reflection coefficient, good efficiency, and a wide bandwidth.
The reflection coefficient of the thin-disk transducer we fabricated is 10 dB lower than that ofco nventional transducers.