Two degree of freedom vibration based electromagnetic energy harvester for bridge health monitoring system

Abstract

This paper presents an electromagnetic energy harvester to extract low frequency and low acceleration vibration energy available in a bridge environment. The developed harvester is a multi-mode oscillator with dual electromagnetic transduction mechanisms. The harvester consists of two cantilever beams. The first cantilever beam is split into two equal pieces along its length and the second beam placed in between them coming back to the fixed end and attached at outer end to the first beam. This way instead of a long conventional cantilever beam a compact harvester is fabricated. Two magnets as proof masses are attached to each free end of the beam making it a two degree of freedom system (2-DOF). The magnets are positioned to oscillate inside hand wound coils during operation. An analytical model was developed and COMSOL multiphysics was used to simulate the mode shapes of the harvester. The mathematical model was simulated for open circuit voltage in MATLAB and showed closely matching results with the experimental values. The harvester is characterized in lab for its performance under sinusoidal vibrations at low frequency (3 Hz–15 Hz) and low acceleration (0.01–0.09 g) levels. The 2-DOF harvester has two resonant frequencies of 4.4 Hz and 5.5 Hz and a volume of 333 cm3. It produces maximum voltage of 0.6 V at first resonance on coil-1 and maximum voltage of 1.2 V on coil-2 at second resonance at 0.09 g. At acceleration of 0.09 g the harvester produced 2.51 mW at first resonant frequency and 10.7 mW at second resonance. Moreover, the AC output voltage of the harvester is rectified to DC voltage by a three-stage Cockcroft-Walton multiplier type circuit. The DC power output at 0.05 g was 0.939 mW at first resonance and 0.956 mW at second resonance while maximum voltages of 5.4 V on coil-1 and 4 V on coil-2 were produced.

Bridge vibration energy harvesting for wireless IoT-based structural health monitoring systems: A review

“…A two-degree of freedom EM-BEH was developed (Masood Ahmad and Ullah Khan, 2021) and is shown in Figure 24. The overall length of the harvester’s cantilever beam was reduced by the folding beam approach.…”

“…Two degrees of freedom EM energy harvester: (a) design and (b) the prototype. Reproduced with permission (Masood Ahmad and Ullah Khan, 2021). Copyright 2020 SAGE.…”

“…Furthermore, for high power output, huge railway BEHs (Hou et al, 2018) and (Hou et al, 2020) are also developed and reported. Employment of more magnets to increase the power output of the harvesters is also performed (Amjadian et al, 2021) for the same size and in some cases (Masood Ahmad and Ullah Khan, 2021) the overall size of the harvester is reduced (folded beam architecture) for the better power density achievement.…”

A silicone based piezoelectric and electromagnetic hybrid vibration energy harvester

“…in terms of the natural frequency f n , the excitation frequency f, and the total damping ratio, ξ T of the harvester. The magnetic flux density gradient along the center of a cylindrical magnet is represented by [49]:…”

Review of frequency up‐conversion vibration energy harvesters using impact and plucking mechanism

“…When two transduction techniques are combined in the same harvesting device for higher output power then the harvester is categorised as a hybrid energy harvester. 38 There are many harvesters reported in the literature that effectively harvest energy at higher frequencies (greater than 100 Hz).In the harvesters, the resonant configuration 39 is more common and expectations from such harvesters are that these actually will deliver the highest energy output at resonance only. However, during off-resonance operation, when the frequency of excitation is not matching the resonant frequency of the harvester; the difference of the excitation frequency drastically reduces the output power of the harvester.…”