A Self-Propelled Mechanism to Increase Range of Bistable Operation of a Piezoelectric Cantilever-Based Vibration Energy Harvester

Abstract

In our previous works, we presented a method to increase the harvested energy from vibrations using a piezoelectric cantilever and to increase the frequency range of operation by introducing bistability with the use of magnetic repulsion. However, for small excitations, the cantilever may not be able to overcome the magnetic repulsive force but vibrate at one of its two equilibrium positions with reduced amplitude. This work introduces a method of increasing the range of excitations over which the operation remains bistable. This is achieved by spring loading one of the magnets, previously on a fixed support, allowing motion in one dimension only, toward and away from the cantilever in the horizontal plane. Configured so, as the cantilever moves toward this magnet, the repulsion due to the cantilever-mounted magnet pushes the spring-loaded magnet away, increasing distance, and thus, reducing magnetic force between them, required to be overcome by external excitations for bistable operation. Similarly, as the cantilever moves away, the spring pushes the magnet closer to the cantilever-mounted magnet, increasing vibration amplitude. Thus, the spring introduces a negative feedback which favors bistable operation over an increased range of excitations. This completely mechanical method requires no additional energy cost. Peak power gains of up to 90 and a decrease in excitation voltage of up to 60% were observed over the fixed magnet.

Pre-Biased Synchronous Charge Extraction for Triboelectric Nanogenerator

“…Then, inserting the value of Q II+ C T from (21) into (22), and invoking the definition of β, we arrive at:…”

“…Similarly, using (24) and (21) and taking into consideration the switch leakage charge between the States II+ and I-(Q II L ), the charge flowing through the load in the second half cycle is given by,…”

A broadband bistable piezoelectric cantilever-based vibration energy harvester with nonlinear high power extraction

“…Various extraction schemes for the piezoelectric generator have been proposed [48][49][50][51][52]. This section presents methods we have utilized to optimize power extraction from our nonlinear bistable transducer [29][30][31], and compares them to a standard extraction circuit comprising an AC to DC converter. Since the extracted energy is required to charge a battery, all circuits analyzed have a battery as the load.…”

“…The synchronous charge extraction (SCE) circuit [50,51], employed in our work [29][30][31], allows charge to build up on the piezoelectric capacitance C e until it reaches a maximum, corresponding to the maximum displacement of the cantilever. At this point, all the charge is extracted from the capacitor and transferred to the battery, thereby dropping the piezoelectric voltage to zero.…”

“…The parallel synchronized switch harvesting on inductor (SSHI) circuit [50,51], employed in our work [29][30][31], also involves switching at displacement extrema for synchronized extraction. Unlike SCE, however, the switch is turned on at the extrema to invert charge polarity on the piezoelectric capacitor, while the charge developed on C e flows to the battery during the rest of the period.…”