A Novel Piezoelectric Energy Harvester for Earcanal Dynamic Motion Exploitation Using a Bistable Resonator Cycled by Coupled Hydraulic Valves Made of Collapsed Flexible Tubes

Abstract

Scavenging energy from the earcanal's dynamic motion during jaw movements may be a practical way to enhance the battery autonomy of hearing aids. The main challenge is optimizing the amount of energy extracted while working with soft human tissues and the earcanal's restricted volume. This paper proposes a new energy harvester concept: a liquid-filled earplug which transfers energy outside the earcanal to a generator. The latter is composed of a hydraulic amplifier, two hydraulic cylinders that actuate a bistable resonator to raise the source frequency while driving an amplified piezoelectric transducer to generate electricity. The cycling of the resonator is achieved using two innovative flexible hydraulic valves based on the buckling of flexible tubes. A multiphysics-coupled model is established to determine the system operation requirements and to evaluate its theoretical performances. This model exhibits a theoretical energy conversion efficiency of 85%. The electromechanical performance of the resonator coupled to the piezoelectric transducer and the hydraulic behavior of the valves are experimentally investigated. The global model was updated using the experimental data to improve its predictability toward further optimization of the design. Moreover, the energy losses are identified to enhance the entire proposed design and improve the experimental energy conversion efficiency to 26%.

Keywords: earcanal; energy harvesting; frequency-up; hydraulic valve; multiphysics.

Figure 1

Earcanal volume variation for one mastication cycle.

Figure 2

Schematic presentation of the frequency-up converted piezoelectric EH exploiting the earcanal’s geometric variation.

Figure 3

Earplug presentation. (a) Earplug schema. (b) Earplug picture.

Figure 4

Amplified piezoelectric generator (APG). (a) APG detailed schema. (b) APG picture.

Figure 5

Details of the contact between an HV and the BR mass.

Figure 6

Kinematic scheme of the electromechanical converter under the mechanical influence of a HV and HC.

Figure 7

Positions of the mass and HCs’s pistons, overlaid with $\Delta V_{ear}\left(t\right)$ , the flow rates in the two parallel branches and the earplug pressure.

Figure 8

Positions of the mass and HCs’s pistons, APG voltage, harvested and source powers and different energies entering and exiting the system.

Figure 9

Test bench of the electromechanical converter (metric units).

Figure 10

APG elastic counter reaction on $\overrightarrow{z}$ axis at $x_m=0$ , depending on the initial structural buckling height $x_0$ .

Figure 11

Schematic view and pictures of the hydraulic characterization test bench for the HVs.

Figure 12

Hydraulic characterization of the HV_T1.

Figure 13

HV_T1 picture for (a) ${\theta }_0(x_m=-x_0)$ and for (b) ${\theta }_f(x_m=x_0$ ).

Figure 14

Experimental measurements and global system simulation with the identified parameters of Table 5. (a) Free oscillations. (b) Oscillations with HV_T1 presence.