&nbsp;In Japan, the lack of manpower for maintenance and inspection of the aging degradation of bridges has become an increasingly serious issue. To this end, structural health monitoring (SHM) systems based on Internet-of-Things (IoT) technology are being developed actively, and energy harvesters are expected to be the power sources for such SHM systems. Although solar power generation can produce higher energy than other sources, solar panels must be kept exposed on the surface of bridges and have a greater risk of receiving an external force from passing vehicles, flying objects, and wind. Thus, vibration-based energy harvesters (VEHs) often tend to be employed in SHM systems of bridges. However, it is difficult to generate a large amount of energy from bridge vibrations by using VEHs because the bridge vibration has a small amplitude and is composed of low-frequency vibrations. Moreover, the accelerations of the bridge vibrations reported in the literature are only in the range of 0.01–0.38G. Therefore, we propose a novel, small-sized energy-harvester device (EHD) that utilizes the tread force of vehicles passing over the EHD as the input. We applied electromagnetic induction to the EHD because electromagnetic-induction-based structures are more durable to impact forces than piezoelectric-based structures. A large amount of power can be obtained even with a small EHD if the tread force of passing cars is utilized to achieve rapid variations in the magnetic flux density. This is possible because the generated voltage is proportional to the variation in magnetic flux density per unit time. The developed device can also detect the number of car passages, which affects the structural soundness of bridges. 
&nbsp;Our previous research confirmed that the length of a generated-voltage time series of &gt;2,050,000s required to accurately detect the natural frequencies of a bridge. Assuming that the natural frequencies are measured once a day, the minimum energy required for data collection and wireless transmission over Bluetooth low energy (BLE) using a wireless communication module every day is 522 mJ. The average traffic volume per day on the bridge considered in the previous study is approximately 48,000. Therefore, the target amount of power to be generated by every car passage at 30 km/h was &gt;11 uJ. In the present study, we designed the EHD with a 4 cm2 footprint, a 7.5 mm thickness, and a volume of 2.4 cm3. These dimensions render the device extremely small and thin when compared with EHDs designed in previous studies; this is an advantage of the EHD because the smaller devices require smaller construction costs. 
&nbsp;In the experiment, we measured the generated power when a bicycle, instead of a car, passed over the EHD. We conducted the experiment 34 times with various bicycle speeds and obtained a regression curve using the least-squares method. The power generated while using the car was estimated considering the difference between the characteristics of car tires and bicycle tires. The results confirmed that, even with the small size of the EHD, a car can generate energies of 100 uJ and 1.0 mJ when it is passing over the EHD at a speed of 17 and 52 km/h, respectively.

Electromagnetic Energy Harvester for Transportation Infrastructure Using Vehicle-Tread Force

Paper Proceedings: https://asmedigitalcollection.asme.org/ISPS/ISPS2021/volume/84799

ASME 2021 Information Storage and Processing Systems (ISPS2021)

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