An Endoscopic Tri-Frequency (1 MHz, 5 MHz, 30 MHz) Transducer for Combined Imaging and Therapy

A new endoscope design was built and tested that incorporates a 1 MHz pump transducer for increased peak pressure capability, and a 30 MHz imaging array in front designed to have minimal attenuation to the 5 MHz therapy transducer. Our novel design combines three different frequency transducers stacked together without affecting the device cross section. The thicknesses of the piezo and coupling layers were optimized using a COMSOL FEM model and maximize the peak pressure of the therapeutic pulse. This was tested in two designs. The first used an off-the-shelf piezo stack actuator for the pump transducer. In the second design, this is replaced by a PMN-PT Electrostrictor (PMN-38) transducer; E-Solder 3022 conductive epoxy was used for the coupling layer to provide an attenuating backing to the imaging array. The imaging transducer was a PZT5H laser cut 64- element array. A silicone Fresnel lens was cast on a PZT5A composite and characterized, and a concept for adapting it to this design was proposed. The therapy transducer with backing layers produced a pressure equivalent to an air-backed composite. Simultaneously pulsing the pump transducer increased the overall peak negative pressure. Adding the imaging transducer with coupling layer reduced the therapy signal by 3.7 dB in the first design, and 5.7 dB in the second design due to increased loss from the conductive epoxy coupling layer.