Enhanced output power by eigenfrequency shift in acoustic energy harvester

Abstract

In our previous studies, multiple piezoelectric cantilever plates were placed inside a quarter-wavelength straight tube resonator to harvest low frequency acoustic energy. To investigate the modification of eigenmodes in the tube resonator due to the presence of piezoelectric plates, the eigenfrequency shift properties by introducing single and multiple rectangular blockages in open-closed ducts are studied by using 1D segmented Helmholtz equations, Webster horn equation, and finite element simulations. The first-mode eigenfrequency of the duct is reduced when the blockage is placed near the open inlet. The decrease of eigenfrequency leads to the enhancement of absorbed acoustic power in the duct. Furthermore, the first half of the tube resonator possesses high pressure gradient resulting in larger driving forces for the vibration motion of piezoelectric plates. Therefore, in our harvesters, it is better to place the piezoelectric plates in the first half of the tube resonator to obtain high output voltage and power.

Eigenfrequency Shift of Piezoelectric Backplate in Vibro-Acoustic Energy Harvesting

“…The flexible backplate of the resonator can maximise the standing wave inside the resonator, and the piezoelectric can be embedded on the backplate in many ways without affecting the resonant frequency of the resonator tube. The previous researchers who used the resonator with a rigid backplate and attached piezoelectric inside the tube encountered a problem when altering the piezoelectric because the resonant frequency changed [16], [34]. The flexible backplate can be attached with one piezoelectric or several piezoelectrics that can increase the power output without affecting the resonator's resonant frequency.…”

“…The single most striking observation to emerge from the figure was (𝑓 2 ) shows a clear decreasing pattern. Furthermore, the presence of the piezoelectric inside the resonator [34], [44], [45], which can change the acoustic resonant frequency, and the additional masses on the backplate can also shift the resonance frequencies of the resonator and backplate. Due to this behaviour, the structure's resonant frequencies can be tuned close to each other through these additional point masses without affecting other parameters.…”

“…Most previous studies focused on harvesting acoustic energy at relatively high frequencies ranging from a few hundred to kHz and MHz [1], [3], [4], [7], [8], [28], [30]- [32] using an HR as an acoustic resonator. Meanwhile, Bin, Li et al [29], [33], [34] focused on low-frequency acoustic sources using multiple piezoelectric in the rigid quarter wavelength resonator. Bin Li developed a quarter wavelength resonator (QWR) array of several bimorph PZT plates and achieved a maximum power output of 57.4 𝑊. 𝑐𝑚 −2 at 100 dB (199Hz).…”