Vibration power generation harnesses weak environmental vibrations and converts them into electrical energy. In this study, a vibration power generator based on a magnetostrictive material (Fe-Ga) was investigated. The generator was designed with a cantilever beam structure, offering advantages in simplicity, robustness, and high-power generation capacity compared with piezoelectric systems. The change in magnetic flux within the coil is attributed to two factors: the change in the magnetoresistance of the magnetostrictive material owing to applied stress, and the variation in air-gap reluctance caused by fluctuations in the air-gap length. In our previous research, we focused on air-gap magnetoresistance variation and proposed a vibro-generator with a narrower air gap. Modifying the air-gap structure increased the generator’s air-gap magnetoresistance variation at the same amplitude, enhancing power generation. In this study, we introduced an auxiliary magnetic circuit to a narrow-gap-type vibration power generator. The main and auxiliary magnetic circuits had opposing flux directions and trends, which maximized the change in flux in the coil. Based on the study’s experimental results, the maximum output power generated by the multiple magnetic circuit vibro-generator was 149% and 46.3% higher than that of conventional vibro-generators and narrow-gap-type vibration generators, respectively. The multiple magnetic-circuit structure can enhance the power generation efficiency of the vibration generator, thereby increasing the application potential of the equipment.
The periodic inspection of a bridge requires visual observation and hammering, which is very costly. In addition, the inspection is sometimes difficult, depending on the place of installation. Consequently, there is a need for remote health monitoring of structures using wireless modules. However, nowadays, these monitoring systems use batteries for power supply and need periodic battery replacement. As a solution, we investigate vibration generators using magnetostrictive materials (Fe-Ga alloy) as a power source for remote health monitoring. Using this system, we can inspect infrastructures without maintenance such as changing batteries. The generator features a simple structure, robustness, and high output and is close to practical application. In this paper, we propose an extra-large magnetostrictive vibration power generator that can generate practical power using a low frequency (10~20 Hz), such as bridge vibration. It is 300 mm in length, 5 kg in weight, and uses a Fe-Ga alloy plate with dimensions of 40 × 4 × 125 mm3 . First, we improve the output of the generator by adding a reinforcing plate and adjusting the bias magnetic field. Next, we confirmed the generation of an instantaneous maximum power of 0.58 W and effective power of 0.22 W under sinusoidal vibration (18.5 Hz, 0.2 G). Furthermore, we reproduced bridge vibration and evaluated the characteristics of the extra-large generator. Finally, we confirmed that 88 mJ of energy was stored in the storage capacitor from reproduced vibration of the bridge in 5 s.
In recent years, the periodic inspection of aging transport infrastructure has become a global problem incurring significant costs and requiring the extensive use of manpower. As a solution, we propose a magnetostrictive vibration power generator that makes use of vehicle-induced highway vibrations to power a battery-free low power wide area (LPWA) module incorporating a titanium wire sensor. This system makes use of an LPWA module with a transmission range of over 1 km, and a titanium wire sensor which was inexpensive, easy to install, and could be used to inspect aging infrastructure. Using this system, infrastructure inspection, can be conducted without the need for conventional maintenance on the system, such as battery replacement. Our main research objective was the magnetostrictive vibration power generator. The generator was suitable for supplying power to the system because it was simple, robust, and was capable of high power output. First, the generator was scaled up to increase the output power in order to generate practically useful electric power with highway vibrations. The large generator was 150 mm×60 mm×50 mm in size and 0.6 kg in weight, incorporating a 16 mm×2 mm×50 mm plate of iron-gallium (Fe-Ga) alloy. We then reproduced the highway vibrations experimentally in a laboratory to ascertain the generator characteristics. We confirmed that it generated a peak voltage of 7 V, instantaneous maximum power of 36 mW, and total energy output of 52 mJ from the simulated highway vibrations over a period of 5 min. Finally, we field tested the system and succeeded in activating the battery-free LPWA modules within 16.5 min using vehicleinduced highway vibrations.
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