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A black gauze cap-shaped bistable energy harvester (abbreviated as the BGCBEH) with a movable design is raised to broaden frequency bandwidth. The proposed BGCBEH is composed of two harvesting units which like the ancient Chinese cap wings. Under lower frequency vibrations, they can not only reciprocate in the horizontal direction, but also vibrate in the vertical direction. Each harvesting unit can realize adaptive potential by reciprocating sliding of cap wings, and achieving inter-well oscillation to get more energy, which are verified by theoretical analyzing and numerical simulating. Under harmonic excitation, the energy obtained by BGCBEH is greater than that by unmovable bistable energy harvester (abbreviated as the UBEH) within 69.7% of the given frequency bandwidth. The energy acquisition frequency domain is broadened by 373.8% and the corresponding rms voltage is increased by 81%. Under random excitation, the rms voltage of the proposed BGCBEH is increased by 396.4% compared to that of the UBEH. The proposed design is further verified by the experiments. Under harmonic excitation, the energy obtained by BGCBEH is greater than that by the UBEH within 71% of the given frequency bandwidth. The energy acquisition frequency domain is broadened by 44% and the corresponding rms voltage is increased by 111.1%. Under random excitation, the rms voltage of the proposed BGCBEH is increased by 81.7% compared to that of the UBEH, and this increase is distributed over the entire frequency domain. The experimental results are greatly consistent with those observed in the above numerical simulating. The output can be further improved when the sum of movable distance and initial magnetic spacing are optimized. The proposed BGCBEH is expected to be applicable to the early-stage warning and accurate detection of passive acceleration due to its snap-through amplitude response characteristics, which needs to be further explored.

An oscillating-type MEMS dc current sensor integrated with piezoelectric actuating and sensing elements was proposed to be utilized for monitoring electricity consumption by a one-wire or two-wire appliance cord. It enabled non-contact and constant measurement and could be applicable to two-wire appliances without using a cord separator. It was found experimentally that the relative change in the maximum value of the output voltage was approximately proportional to the applied dc current. Theoretical models are developed in this work to analyze the relationship between the relative change in the maximum value of the output voltage and the applied dc current. We find that as the applied dc current increases, the oscillating-type sensing system exhibits three response areas: a linear increase area, an abrupt increase area and a decrease area. A linear increase area is defined as the sensing area where the equations on the linear relationship and the sensitivity are derived. In addition, theoretical considerations are outlined on the effect of the displacement of the cantilever during the vibration on the nonlinear response, the restoring forces of the cantilever as the applied current increases, and the factors affecting sensitivity. Theoretical models can be utilized to predict the applicable magnetic forces and piezoelectric output voltage as well as guide the optimization of the sensor design.