High sensitivity and wideband design for impedance matching layer between protection metal and piezoelectric layer of ultrasonic transducers

The matching layer inserted between the front protection metal and piezoelectric layer has been designed when the protection metal is half-wavelength thick. This matching layer plays the role of a bonding layer. The optimum thickness ranges from λ/4 to 3λ/8 in the Mason model simulation, which has been confirmed by experiments. In the optimum range, the sensitivity was much higher and the bandwidth was broader than the non-appropriate thickness of the bonding layer. When the protection layer was replaced by a metal-polymer-metal resonance structure, the bandwidth was further improved.