Vibration Energy Harvester Based on Torsionally Oscillating Magnet

Most of the miniaturized electromagnetic vibrational energy harvesters (EVEHs) are based on oscillating proof mass suspended by several springs or a cantilever structure. Such structural feature limits the miniaturization of the device’s footprint. This paper presents an EVEH device based on a torsional vibrating magnet over a stack of flexible planar coils. The torsional movement of the magnet is enabled by microfabricated silicon torsional springs, which effectively reduce the footprint of the device. With a size of 1 cm × 1 cm × 1.08 cm, the proposed EVEH is capable of generating an open-circuit peak-to-peak voltage of 169 mV and a power of 6.9 μW, under a sinusoidal excitation of ±0.5 g (g = 9.8 m/s2) and frequency of 96 Hz. At elevated acceleration levels, the maximum peak-to-peak output voltage is 222 mV under the acceleration of 7 g (±3.5 g).

A Nonlinear Calibration Method Based on Sinusoidal Excitation and DFT Transformation for High-Precision Power Analyzers

For most high-precision power analyzers, the measurement accuracy may be affected due to the nonlinear relationship between the input and output signal. Therefore, calibration before measurement is important to ensure accuracy. However, the traditional calibration methods usually have complicated structures, cumbersome calibration process, and difficult selection of calibration points, which is not suitable for situations with many measurement points. To solve these issues, a nonlinear calibration method based on sinusoidal excitation and DFT transformation is proposed in this paper. By obtaining the effective value data of the current sinusoidal excitation from the calibration source, the accurate calibration process can be done, and the calibration efficiency can be improved effectively. Firstly, through Fourier transform, the phase value at the initial moment of the fundamental frequency is calculated. Then, the mapping relationship between the sampling value and the theoretical calculation value is established according to the obtained theoretical discrete expression, and a cubic spline interpolation method is used to further reduce the calibration error. Simulations and experiments show that the calibration method presented in this paper achieves high calibration accuracy, and the results are compensation value after calibration with a deviation of ± 3 × 10 − 4 .

Improving Power Density Of A Class Of Piezoelectic Power Harvesters Through Proof Mass Optimization

This thesis presents a method to optimize the proof mass of the cantilever piezoelectric power harvester. With this novel proof mass, a lower fundamental frequency and a higher power density (output power per unit volume) were achieved. Prototypes of 0.242 cm³ in volume were fabricated and tested and a power density of 1446 μW/cm³ was achieved for sinusoidal excitation of 0.75 g. It was experimentally shown that the new power harvester lowered the fundamental frequency by 26% and increased the power density by 68% in comparison with the conventional harvesters. When tested on a shoe, the new power harvester generated an average power of 48.4 μW at 3.0 mph walking speed on a treadmill.

Improving Power Density Of A Class Of Piezoelectic Power Harvesters Through Proof Mass Optimization

This thesis presents a method to optimize the proof mass of the cantilever piezoelectric power harvester. With this novel proof mass, a lower fundamental frequency and a higher power density (output power per unit volume) were achieved. Prototypes of 0.242 cm³ in volume were fabricated and tested and a power density of 1446 μW/cm³ was achieved for sinusoidal excitation of 0.75 g. It was experimentally shown that the new power harvester lowered the fundamental frequency by 26% and increased the power density by 68% in comparison with the conventional harvesters. When tested on a shoe, the new power harvester generated an average power of 48.4 μW at 3.0 mph walking speed on a treadmill.