A piezoelectric cantilever with a Helmholtz resonator as a sound pressure sensor

In this paper, a piezoelectric cantilever with a Helmholtz resonator (HR) is proposed as a sound pressure sensor that generates a sufficiently large output voltage at a specific frequency without a power supply to drive the sensing element. A Pb (Zr, Ti) O₃ (PZT) cantilever with dimensions of 1500 μm × 1000 μm × 2 μm is designed so that its mechanical resonance frequency agrees with the target frequency. When sound pressure is applied at the target frequency, a large piezoelectric voltage can be obtained due to a high amplification ratio. Additionally, the PZT cantilever is combined with a HR whose resonant frequency is designed to be equal to that of the cantilever. This multiplication of two resonant vibration systems can generate detectable signals by sound pressures of several Pascals. The fabricated sensor generated a piezoelectric voltage of 13.4 mV Pa^-1 at the resonant frequency of 2.6 kHz. Furthermore, the fabricated sensor performed as an electrical trigger switch when a sound pressure of 2 Pa was applied at the resonant frequency.