Micro-electromechanical system (MEMS) microphones (mics) with two ports are receiving considerable interest in both industry and academia, with the prospect of achieving higher directional sensitivity than their one port counterpart. However, two-port mics measures the pressure differences that exists inside the soundwave itself to record sound, which is fundamentally smaller than the absolute pressure measured in typical one-port mics. This typically commands the use of softer sensing element that are potentially more prone to interference from external vibrations. This work derives a universal expression for microphone sensitivity to vibration and validates it experimentally for two emerging two-port mics. We find that the acoustically-referred vibration sensitivity of two-port MEMS mics, in unit of measured acoustic pressure per external acceleration (i.e., Pascals per g), does not depend on the sensing element stiffness nor on its natural frequency. The vibration sensitivity of two-port MEMS mics is also shown to be inversely proportional to frequency as opposed to the frequency independent behavior observed in one-port MEMS mics.
Current issues on air pollution monitoring or greenhouse gases emissions rely on the sparse use of expensive gas sensors. We target to develop a portable miniaturized sensor with the capacity of being gas-specific, lightweight and autonomous. We present here results obtained with our newly packaged Photoacoustique Module. We also present the development of its dedicated electronic companion system.
Drift degrades stability of MEMS accelerometer a lot, in terms of temperature and long-term impacts. This study proposed an integrated resonant accelerometer with an all-quartz sensitive structure, which was designed to achieve resistance to temperature and long-term drift. Processes such as wet etching, quartz-on-quartz direct bonding, and femtosecond laser micro welding were utilized to fabricate and assemble the prototype. Experimental platforms were built up to characterize its stability, and results demonstrated that the stability at full-temperature range was 34.64 mu g/degrees C, and the long-term stability was less than 100 mu g. Combined with stability performances already measured, the accelerometer is comparable to, or even better than, state-of-the-art counterparts without compensation.
Novel, paper-based sensors with a sensitive layer of PEDOT:PSS, an organic semiconductor, are investigated for their suitability to monitor the curing process inside epoxy-based fiber composite materials. PEDOT:PSS shows a strong response toward temperature which appears to be increased by increasing humidity. At the same time, paper is expected to be an excellent substrate material for embedding in hybrid materials, as it is completely soaked by the resin that forms the matrix and thus adapts the material properties far better than conventional sensor substrates. Therefore, it is expected that the curing process can be monitored with these sensors directly inside the material layers offering improved process control, especially for thick composite parts.
Amorphous carbon film (a-C) has many outstanding characteristics, such as low friction, anti-wear properties and chemical stability. Its preparation is low cost, simple, and can well combined with microelectromechanical system (MEMS) process. Because it has remarkable piezoresistive effect, a-C piezoresistor was integrated in accelerometer to get a high-performance sensor. Using electron cyclotron resonance (ECR) plasma sputtering and ion evaporation deposition process, a-C was integrated on the quad-beam-mass structure as piezoresistor which had high gauge factor. By adjusting process parameters, the gauge factor could be controlled. In the ECR sputtering process, bias voltage +50 V and +100 V was applied to the substrate, respectively. And the gauge factor was within the range of 3.2-6.7 and 5.5-9.6; in the other process, a negative bias voltage 2 kV was applied to the substrate, then the hydrogenated amorphous carbon films (a-C: H) was deposited, which had a higher gauge factor 40.5-54.2. A MEMS piezoresistive accelerometer based on a-C piezoresistor was designed and fabricated. The piezoresistive accelerometer which used a-C: H had higher sensitivity 0.023 mV/V/g and natural frequency 18.1 kHz. This study provided a new method to further improvement of the comprehensive performance of MEMS piezoresistive accelerometer.
