Multi-layer PZT transducer arrays for improved sensitivity [for medical US]

Two-dimensional arrays are used in medical ultrasound. Poor sensitivity is a serious problem with such 2-D arrays. 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 16-layer, 1-MHz prototype transducer is fabricated using thick-film hybrid technology. With a light epoxy backing, the element impedance is 50 Ω at series resonance and the minimum round-trip insertion loss is 41 dB. This is compared to a single-layer control array with an impedance of 3 kΩ per element and an insertion loss of 64 dB per element. These results are consistent with model simulations