Most wind energy harvesters (WEHs) that have been reported in the literature collect wind energy using only one type of wind-induced vibration, such as vortex-induced vibration (VIV), galloping, and flutter or wake galloping. In this letter, the interaction between VIV and galloping is used to improve the performance of WEHs. For a WEH constructed by attaching a bluff body with a rectangular cross-section to the free end of a piezoelectric cantilever, the measures to realize the interaction are theoretically discussed. Experiments verified the theoretical prediction that the WEHs with the same piezoelectric beam may demonstrate either separate or interactive VIV and galloping, depending on the geometries of the bluff bodies. For the WEHs with the interaction, the wind speed region of the VIV merges with that of the galloping to form a single region with high electrical outputs, which greatly increases the electrical outputs at low wind speeds. The interaction can be realized even when the predicted galloping critical speed is much higher than the predicted VIV critical speed. The proposed interaction is thus an effective approach to improve the scavenging efficiencies of WEHs operating at low wind speeds.

Previous works verified experimentally that interactions between vortex-induced vibration (VIV) and galloping may greatly improve the performance of piezoelectric wind energy harvesters (PWEHs) at low wind speeds. However, no mathematical model has been available to date to predict the responses or optimize the structures of PWEHs. In this paper, a distributed-parameter electromechanical coupling model of a VIV-galloping interactive PWEH was derived and was then experimentally validated using two harvester prototypes. For the first prototype, while the theoretical critical galloping speed is approximately 2.1 times the theoretical critical VIV speed, the experiments verified the proposed model’s prediction that this harvester involves full interaction between VIV and galloping because there is only one wind speed region (in the wind speed range of interest) that offers high electrical output. For the second prototype, whose theoretical galloping speed is about 2.3 times the critical VIV speed, the model indicates that there are two completely separate wind speed regions that have relatively high electrical outputs, implying that this is a harvester without the interaction between VIV and galloping, coinciding with the experimental results. For both prototypes, the model is accurate enough to predict the onset reduced speeds for the wind speed regions with high electrical outputs, and can be used to obtain the output voltage in the wind speed range of interest. The proposed model can thus be used to design VIV-galloping interactive PWEHs with enhanced performance in the collection of low speed airflows.

This letter proposes an impact-based piezoelectric energy harvester that uses a rolling bead contained in a bracket that is supported by a spring. Under either translational or rotational base excitation, the bead moves within the bracket and collides with piezoelectric cantilevers that are located around the bracket; these collisions cause the piezoelectric beams to vibrate and thus produce electrical outputs. The low rolling friction and the motion amplification effect of the spring make the resulting device suitable for collection of low-level vibration energy. Experiments show that the proposed harvester is promising for use in scavenging of energy from the multidimensional, low-level, broadband, and low-frequency vibrations that occur in natural environments.

A wireless temperature sensor node composed of a piezoelectric wind energy harvester, a temperature sensor, a microcontroller, a power management circuit and a wireless transmitting module was developed. The wind-induced vibration energy harvester with a cuboid chamber of 62 mm × 19.6 mm × 10 mm converts ambient wind energy into electrical energy to power the sensor node. A TMP102 temperature sensor and the MSP430 microcontroller are used to measure the temperature. The power management module consists of LTC3588-1 and LT3009 units. The measured temperature is transmitted by the nRF24l01 transceiver. Experimental results show that the critical wind speed of the harvester was about 5.4 m/s and the output power of the harvester was about 1.59 mW for the electrical load of 20 kΩ at wind speed of 11.2 m/s, which was sufficient to power the wireless sensor node to measure and transmit the temperature every 13 s. When the wind speed increased from 6 m/s to 11.5 m/s, the self-powered wireless sensor node worked normally.