Bidirectional electrical tuning of FR4 based electromagnetic energy harvesters

We report the bidirectional electrical tuning of electromagnetic energy harvesters using two different complex load topologies: capacitive load to tune in the lower frequency range and inductive load to tune in the higher frequency range respectively. A theoretical model has been developed to address the bidirectional tuning capabilities using complex loads and the model has been successfully validated against the experimental results. Four electromagnetic harvesters with different spring configurations and thus operating at different frequencies have been developed on FR4 using laser micromachining technique and a comparison of their untuned output performances has been reported. Varying the load capacitance, the resonant frequency has been tuned up to almost 1.8 Hz for both prototype 1 and 2 and up to almost 0.16 Hz for prototype 3 and 4 in the lower frequency directions. Similarly, varying the load inductance, the resonant frequency has been tuned up to 0.6 Hz for prototype 1 and 2 and up to 0.13 Hz for prototype 3 and 4 in the higher frequency directions. This tuning comes with the reduction in the output power; however the comparative experimental study shows that the tuning range can be further widened by using devices with larger electromagnetic coupling values.