A High-Sensitivity Bowel Sound Electronic Monitor Based on Piezoelectric Micromachined Ultrasonic Transducers

High-Sensitivity Piezoelectric MEMS Accelerometer for Vector Hydrophones

In response to the growing demand for high-sensitivity accelerometers in vector hydrophones, a piezoelectric MEMS accelerometer (PMA) was proposed, which has a four-cantilever beam integrated inertial mass unit structure, with the advantages of being lightweight and highly sensitive. A theoretical energy harvesting model was established for the piezoelectric cantilever beam, and the geometric dimensions and structure of the microdevice were optimized to meet the vibration pickup conditions. The sol-gel and annealing technology was employed to prepare high-quality PZT thin films on silicon substrate, and accelerometer microdevices were manufactured by using MEMS technology. Furthermore, the MEMS accelerometer was packaged for testing on a vibration measuring platform. Test results show that the PMA has a resonant frequency of 2300 Hz. In addition, there is a good linear relationship between the input acceleration and the output voltage, with V = 8.412a - 0.212. The PMA not only has high sensitivity, but also has outstanding anti-interference ability. The accelerometer structure was integrated into a vector hydrophone for testing in a calibration system. The results show that the piezoelectric vector hydrophone (PVH) has a sensitivity of -178.99 dB@1000 Hz (0 dB = 1 V/μPa) and a bandwidth of 20~1100 Hz. Meanwhile, it exhibits a good "8" shape directivity and consistency of each channel. These results demonstrate that the piezoelectric MEMS accelerometer has excellent capabilities suitable for use in vector hydrophones.

A High-Sensitivity MEMS Accelerometer Using a Sc0.8Al0.2N-Based Four Beam Structure

In this paper, a high-sensitivity microelectromechanical system (MEMS) piezoelectric accelerometer based on a Scandium-doped Aluminum Nitride (ScAlN) thin film is proposed. The primary structure of this accelerometer is a silicon proof mass fixed by four piezoelectric cantilever beams. In order to enhance the sensitivity of the accelerometer, the Sc_0.2Al_0.8N piezoelectric film is used in the device. The transverse piezoelectric coefficient d₃₁ of the Sc_0.2Al_0.8N piezoelectric film is measured by the cantilever beam method and found to be -4.7661 pC/N, which is approximately two to three times greater than that of a pure AlN film. To further enhance the sensitivity of the accelerometer, the top electrodes are divided into inner and outer electrodes; then, the four piezoelectric cantilever beams can achieve a series connection by these inner and outer electrodes. Subsequently, theoretical and finite element models are established to analyze the effectiveness of the above structure. After fabricating the device, the measurement results demonstrate that the resonant frequency of the device is 7.24 kHz and the operating frequency is 56 Hz to 2360 Hz. At a frequency of 480 Hz, the sensitivity, minimum detectable acceleration, and resolution of the device are 2.448 mV/g, 1 mg, and 1 mg, respectively. The linearity of the accelerometer is good for accelerations less than 2 g. The proposed piezoelectric MEMS accelerometer has demonstrated high sensitivity and linearity, making it suitable for accurately detecting low-frequency vibrations.