The urgent demand of wireless sensor nodes for long-life and maintenance-free miniature electrical sources with output power ranging from microwatts to milliwatts has accelerated the development of energy harvesting technologies. For the abundant and renewable nature of wind in environments, flow-induced vibration (FIV)-based wind energy harvesting has emerged as a promising approach. Electromagnetic FIV wind energy harvesters (WEHs) show great potential for realistic applications due to their excellent durability and stability. However, electromagnetic WEHs remain less studied than piezoelectric WEHs, with few dedicated review articles available. This review analyzes the working principle, device structure, and performance characteristics of electromagnetic WEHs based on vortex-induced vibration, galloping, flutter, wake galloping vibration, and Helmholtz resonator. The methods to improve the output power, broaden the operational wind speed range, broaden the operational wind direction range, and enhance the durability are then discussed, providing some suggestions for the development of high-performance electromagnetic FIV WEHs.

Variations in the wind direction over time mean that it is essential to improve the directional adaptability of wind energy harvesters (WEHs) based on wind-induced vibration (WIV) to expand their application potential. Several multi-directional WIV WEHs have been reported in the literature but most of them are not omnidirectional. In particular, no mathematical model has been proposed for omnidirectional WIV WEHs to date. In this Letter, an in-plane omnidirectional piezoelectric WEH with a cylindrical shell, acting as a bluff body and supported by internal piezoelectric composite beams, is proposed. It is deduced that the omnidirectionality of wind energy harvesting can be enhanced by improving the isotropies of the aerodynamic force, stiffness, and electromechanical conversion. For a WEH with three semicircular-shaped supporting beams, a mathematical model suitable for arbitrary wind directions in the horizontal plane was derived. Simulations show that the WEH's stiffness and electromechanical conversion are approximately isotropic. Simulations and experiments demonstrate that the wind direction's effect on the total power is small. The ratio of the experimental minimum to maximum total power is 0.88 at 9 m/s, verifying that the device is an in-plane omnidirectional harvester. An omnidirectionality index including contributions from all directions is proposed with the value of 0.86 at 9 m/s for the prototype. The proposed device configuration and design method may serve as a reference for the development of omnidirectional WIV WEHs.

In this article, a mechanical wind sensor based on additive manufacturing technology is demonstrated for the first time. The sensor is composed of a cylindrical sensing structure vertically placed in the center of a cross-shape cantilever. Four strain gauges are attached to the surface of the beams to monitor the wind-induced cantilever deformation, which can reveal the speed and direction of airflow. Unlike traditional mechanical sensors, the proposed wind sensor is fabricated by additive manufacturing. With this new manufacturing method, the wind sensor can not only be flexibly designed to avoid mechanical wear but also utilize corrosion-resistant organic materials for improved reliability. The designed wind sensor is implemented using a commercially available three-dimensional (3-D) printer and installed in a wind tunnel for the experiment. The test results show that the proposed 3-D printed mechanical wind sensor can achieve a measurement speed range up to 30 m/s, with a maximum error of 0.87 m/s, while the maximum errors for wind direction measurement are ±8°, over the full range of 360°. The proposal of this 3-D printed wind sensor provides a new paradigm for developing small-size, low-cost, and high-reliability wind sensors.

In this paper, the fabrication and characterization of a two-dimensional (2-D) micro-electro-mechanical systems (MEMS) thermal convective accelerometer are demonstrated. This sensor consists of a heater and four thermistors. The central heater warms up the chip to a temperature higher than the ambient, while the four thermistors, which are arranged symmetrically around the heater, monitor the temperature gradients induced by the acceleration. The heater and thermistors are fabricated on one side of a silicon-in-glass (SIG) substrate using a glass reflow process. The utilization of this SIG substrate not only enhances the sensor robustness at low power consumption, but also allows the lead wires of the sensor to be directly soldered to the printed circuit board (PCB), significantly simplifying the sensor packaging. Experimental tests on the fabricated accelerometer indicate that the sensor can measure acceleration exceeding 80 m/s2, with an approximate linear sensitivity of about 150 mV/g. The proposal of this SIG-based device provides a new paradigm for developing high-reliability and low-power-consumption MEMS accelerometers.

The wind-induced vibration energy harvester is a type of ideal power source for wireless sensor nodes. To adapt to the uncertainty of wind direction in natural environments, this paper proposes a three-dimensional multi-directional piezoelectric wind energy harvester (WEH), whose bluff body is an external shell with the shape like a lampshade, supported by three internal piezoelectric composite beams. A harvester prototype was made using 3D printing technology, and its multi-directional energy harvesting characteristics were systematically tested in a wind tunnel. Experiments show that it can harvest wind energy from any direction in three-dimensional space. When the wind speed is about 15 m/s and the wind direction changes in the horizontal plane, the minimum to maximum total average output power ratio is about 0.84. This work provides an experimental basis for the future development of three-dimensional multi-directional WEHs to some extent.