In this work, a porous multilayer graphene film is designed as thermoacoustic speaker using laser scribing technology and a theoretical model based on thermally induced EDFs (Energy Density Fluctuations) is proposed to study its electrical-thermal-acoustic conversion behavior. According to this model, the relationship of the heat energy Qair with the input power is obtained, and the relationship of the sound pressure with the measuring distance, the frequency and the input power is obtained. The measurement of temperature distribution shows that the maximum temperature of graphene film increases linearly with the input power. The measurement of sound pressure shows that SPL (Sound Pressure Level) decreases with the measuring distance. SPL has a rapid growth in low frequency while slow growth in high frequency. SPL has a logarithmic relationship with the input power. The measured results have a good agreement with the theoretical results. The theoretical model based on EDFs has certain reference value for further research on thermoacoustic speakers. This porous multilayer graphene film has the characteristics of one-step fabrication, no mechanical vibration, simple structure and high performance. It could open broad applications in biology, medicine, wearable electronics and other fields.

In order to improve the sensitivity characteristic and the fabrication reliability, a novel capacitive power sensor based on double MEMS cantilever beams is proposed in this work. It is designed and fabricated using GaAs MMIC process and MEMS technology. A lumped circuit model is built to study the microwave characteristic of this capacitive microwave power sensor. The influence of impedance value and electric length of the coplanar waveguide on the microwave performance of the double MEMS beams are studied. The microwave characteristic of both ports are measured. The return loss of port A is from −11.5dB to −14.6dB, and the return loss of port B is from −12.1dB to −14.3dB at 8-12GHz. The insertion loss of port A is from −3.6 dB to −2.8dB, and the insertion loss of port B is from −3.7 dB to −2.9dB at 8-12GHz. The measured results show that this capacitive power sensor has a good microwave characteristic. The measured sensitivity of this capacitive microwave power sensor is about 51.6 fF/W @10 GHz, and the theoretical sensitivity is 55.97 fF/W. The relative error is 7.8%. Compared with the capacitive microwave power detection system based on single cantilever beam, the sensitivity characteristics have been greatly improved. It is valuable to realize the multiple beams detection technology and enable further interesting possibilities in the field of microwave power detection.

In order to optimize the sensitivity and overload power of microwave power sensor, a dual-channel MEMS microwave power sensor with cantilever beam is proposed in this paper. GaAs MMIC process and MEMS technology are used for design and manufacturing. The theoretical model of MEMS dual-channel microwave power sensor with cantilever beam is established. The influence of the size of the cantilever beam on the microwave performance, overload power and sensitivity of the sensor is studied. The microwave performance and sensitivity of three sensors with different cantilever beam sizes were tested. At 8-12 GHz, the return loss of three sensors are -10.6 dB~-57.2 dB@ 200 μm beam length, -10.6 dB~-62.4 dB@300 μm beam length, and -12.0 dB~-62.3 dB@400 μm beam length, respectively. They all show good microwave performance. At 10 GHz, the sensitivities of capacitive detection channel of three sensors are 16.3 fF/W, 65.6 fF/W and 144.4 fF/W respectively. And the sensitivities of thermoelectric detection channel are 142.3 mV/W, 109.5 mV/W and 82.9 mV/W respectively. The sensitivities of dual-channel MEMS microwave power sensors with cantilever beam are improved compared with the traditional microwave power sensor, which has certain reference value for the design of MEMS microwave power sensors.

A circular-arc spiral piezoelectric energy harvester is proposed in this work. It can realize three-dimensional energy harvesting in a low frequency vibration environment. The design of the arc spiral structure can make the cantilever beam absorb energy from vibration in multiple directions, and it can also reduce the resonance frequency. It was found that as the radian increases, the resonance frequency become smaller. The horizontal and vertical vibrations of the circular-arc spiral piezoelectric energy harvester are analyzed. The output performance of the circular-arc spiral piezoelectric energy harvester is measured. The measured results shows that the output characteristic of circular-arc spiral energy harvester with $4\pi $ is the best. When the radian is $4\pi $ , the measured value of the output voltage is 10V. The theoretical value of the output voltage is 10.6V. The relative error is 6%. The best load resistance is 333k $\Omega $ , and the output power can reach $75~\mu \text{W}$ . Therefore, this work has certain reference value for studying energy harvesting technology in the low frequency.

In this work, a pivoted mechanical model of capacitive MEMS microwave power sensor is established to optimize the relative position of the measuring electrode. The pivoted model is divided into four sections in order to more accurately study the vibration of the cantilever beam. The model of the sensitivity and the overload power are obtained. According to the established model, the structure of the sensor is analyzed and optimized, the relationship of the sensitivity and the overload power with the relative position of the measuring electrode is obtained. x3/l=0.9 is the optimal solution for the overload power, x3/l=0.8 is the optimal solution for the sensitivity, and x3/l=0.5 is taken as the trade-off value to verify the accuracy of the model. Finally, the measured results show that this work has certain reference value and guiding significance for capacitive MEMS power sensors.