A monolithic multi-sensor for small unmanned aerial vehicles is presented in the paper; it consists of a three-axis piezoresistive accelerometer, a piezoresistive absolute pressure sensor and a silicon thermistor temperature sensor. The accelerometer is designed with four silicon beams supporting the seismic mass and appropriate piezoresistors arrangement to detect three-axis acceleration and greatly reduce cross-axis sensitivities. For minimizing the effect of stress on the temperature sensor, the thermistor is designed along [100] and [010] crystal orientation. The multi-sensor is fabricated on SOI wafers by using MEMS bulk-micromachining technology. Some effective micromachining steps are applied in the fabrication. The two-step wet anisotropic etching process on the backside of the wafers can form the whole backside shape of the multi-sensor. The metal electrode sputtered on the Pyrex glass can avoid sticking between the Pyrex glass and the seismic mass in the process of anodic bonding. The die size of the multi-sensor is 4×6×0.9mm 3 . The measured results show that the multi-sensor is appropriate for its application field.
The general vibration control strategy of beam structures is a global vibration control method based on the principle of modal superposition. However, the vibration wave control of beams can achieve local control of the vibration energy. This paper presents a wave control method for the local vibration control of fractional viscoelastic composite beams based on the operating principle of a piezoelectric sheet. To obtain better control performance, a particle swarm optimization algorithm was adopted to optimize the parameters of the piezoelectric sheet. A linear quadratic regulator control algorithm was designed to verify the validity of the proposed method. In addition, the effects of the piezoelectric sheet number and fractional order on the amplitude response and optimization parameters were investigated. We observed that the proposed method has a good control effect on the local area vibration, and it can control the flow direction of the vibration power. The proposed method can be used to directly design the voltage and phase of a piezoelectric sheet without real-time feedback computation. This method is suitable for reducing local vibration under single repetitive operating conditions in engineering and can provide a theoretical basis for a follow-up study on the acoustic black hole phenomenon.
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