Currently, most wireless sensor networks (WSNs) are powered by batteries. When energy stored in batteries is exhausted, the life of the WSNs goes to the end. The concept of energy harvesting provides a practical solution to the problem of the energy limitation. In this article, the feasibility and performance of a simple and low-cost analog solar energy harvesting circuit with the function of maximum power point tracking (MPPT) are investigated. The technique provided is based on the approximately linear relationship between the maximum power point (MPP) voltage and the open-circuit voltage of a solar panel under different irradiation levels. Several experiments have been carried out regarding the accuracy and efficiency of MPPT as well as the working process of the circuit. Results show that the maximum power point with different loads can be effectively tracked by the self-powered MPPT circuit, and in the meantime, a stable output voltage can be generated. The efficiency of energy conversion is guaranteed by a commercial off-the-shelf DC-DC chip. The detailed description of the circuit design and the comprehensive analysis of the circuit performance will provide a useful guide for the future applications.

The stable range of MEMS electrostatically actuated beam during the pull-in process is crucial to the device performance. Different devices have specific requirements for stable pull-in region based on their applications. In this paper, Rayleigh-Ritz energy method is used to establish dynamic pull-in model of electrostatic cantilever actuated by a step voltage. Modified trial function is derived according to different position of bottom electrode. The model takes into account the effects of fringe capacitance and variable cross-sectional beam. Published numerical methods and experimental data are used to verify the model . The impact of bottom electrode position on pull-in parameters is analyzed in present model. With fitting empirical equations, pull-in parameters can be easily satisfied through the distribution of bottom electrode, which provide an effective reference for the design of MEMS electrostatically actuated beam under given pull-in parameters .

This paper presents a new type of micro self-powered wireless analog sun sensor. The mask with aperture of the sun sensor, developed by glass coated process, reduces the impact on accuracy caused by second reflection of the light, and also promotes system’s external thermal radiation ability. With aluminum substrate process, the processing circuit is integrated on the bottom cover of the sun sensor, which saves the conventional processing circuit needed space and reduces the complexity of system’s structure. Self-powered and wireless data transmission improve the system’s application flexibility. The simulation results and preliminary experiments show that the accuracy of the system has the ability to reach 0.2° in the whole 120°×120° FOV and the solar cells’ minimum output power is 90mW which is able to meet the power consumption requirements of the system circuits.