Performance of multi-layer PZT transducer arrays
Two-dimensional arrays are critical to the future of medical ultrasound for focusing and phase correction in the elevation dimension and for 3-D scanning. Poor sensitivity is a serious problem with such 2-D arrays because their small element size results in a small clamped capacitance and a high electrical impedance near resonance. Sensitivity can be improved by reducing the array element impedance using an N layer structure of PZT connected electrically in parallel and acoustically in series. The clamped capacitance is multiplied by a factor of N2 and the impedance by 1/N2 compared to a single layer transducer. A 3 layer, 3×43 array was fabricated using thick film hybrid technology. Each element had dimensions of 0.37×3.5×0.71 mm. With a light epoxy backing, the element impedance was 100 Ω at series resonance and the minimum round-trip insertion loss was 24 dB. This was compared to a single layer control array with an impedance of 550 Ω per element and an insertion loss of 34 dB per element. Images were made on the Duke ultrasound scanner which showed greater sensitivity for the multi-layer ceramic.
