Testing and Packaging for MEMS Acoustic Emission Sensors

The goal of this research is to improve the structure and dimension of the MEMS acoustic emission sensor. Acoustic emission sensor (AE sensor) based on the piezoelectric transducer is a well-developed technology in non-destructive testing that is widely used to determine permanent damage such as cracks and corrosions in buildings and structures. The AE sensor can be used to monitor cracks in structures and to check leakage in pressurized systems. The location of cracks in a structure or system leakage causes a high-frequency surface vibration while releasing ultrasonic energy. The frequency of this energy is typically between 30 kHz to 1MHz. The AE sensor can detect this high frequency transient acoustic wave. By using this AE sensor, the structure and pressurized system can be monitored to generate an evaluation report in order to facilitate maintenance and structure repair. Currently, the commercial AE sensor is bulky because it is made of a piezoelectric transducer. It also needs a lot of wires to connect with the pre-amplifier and signal conditioning systems. Because of the cost, brittleness and the volume of the commercial AE sensor, new affordable AE sensor technology is desired to replace the commercial AE sensor. The new AE sensor should be economical, small, and lightweight. The performance of the output signal should be comparable with the commercial AE sensor in terms of signal strength and signal to noise ratio. The MEMS AE sensors provide the potential solution to this problem. The MEMS AE sensors can overcome the problems of the commercial AE sensor. The MEMS AE sensor combines the pre- amplifier on the chip in a single package. Through the MEMS technology, the AE sensor can be manufactured in mass quantity and high quality. This study focuses on simulating and measuring the performance of the MEMS acoustic emission sensors. Through simulation, the capacitance value is influenced by the gap between the suspended membrane (top perforated metal plate), metal ground, and also influenced by the effective area of the perforated top layer. The perforation is introduced to reduce the squeeze film damping effect. Through measurement verification, the MEMS AE sensors have exhibited comparable performance before and after inclusion of the 3D printed package that serves as the housing for the completed sensor assembly. The C-V measurement is the key method to extract the capacitance value, which is the key parameter to determine the signal strength and signal to noise ratio for capacitive MEMS acoustic emission sensors. The damping coefficient is also the key factor to receive the time domain measurement data in a fashion that resemble the bulky commercial piezoelectric AE transducers