Hoyoung Lee

A multilayer PVDF composite cantilever in the Helmholtz resonator for energy harvesting from sound pressure

Although acoustic energy sources are an excellent alternative energy resource for harvesting, studies on harvesting such sources have been rarely investigated because of their lower energy density compared to other resources. For the purpose of efficient acoustic energy harvesting, this study presents a Helmholtz resonator with single-layer and multilayer piezoelectric composite cantilevers. A flexible PVDF piezoelectric composite cantilever is employed in this study due to the simple adjustment of its resonance to the acoustic resonance of the Helmholtz resonator. A multilayer PVDF composite cantilever is considered to improve the power harvested compared to a single-layer harvester. These approaches are investigated and verified by theoretical analysis including finite element simulations and experiments. The results of the current feasibility study show a maximum power of 0.19 μW (0.12 μW cm−2) with sound waves of 15 Pa (~118 dB) at 850 Hz, which can be increased by a factor of 2.3 by adopting the structure of a four-layer PVDF composite cantilever. Theoretically, around seven times more power would be available using the optimal design of a twenty-layer composite structure compared to that of a single-layer composite acoustic energy harvester. Finally, the results of this study can be used in various applications for power generation by means of absorbing and eliminating specific frequency bandwidths of noise in continuously noisy environments.

Sensitivity-Enhanced

This paper presents a sensitivity-enhanced wireless passive LC pressure sensor for monitoring bladder pressure, which can be minimally invasive implanted in the bladder or integrated to a commercial urinary catheter and avoid battery lifetime problem. The proposed sensor design and the theoretical model are useful to increase the pressure sensitivity of a typical air-sealed capacitive pressure sensor, particularly having a flexible diaphragm. The test results of an in vitro evaluation of the prototype LC pressure sensor show a pressure sensitivity of 6385 ppm/kPa (a pressure responsivity of 1.215 MHz/kPa) before encapsulation coating in air at room temperature, whereas 4175 ppm/kPa (0.627 MHz/kPa) and 2679 ppm/kPa (0.304 MHz/kPa) after coating with silicone rubber in air and in water operation, respectively. Finally, the feasibility of the developed sensor is investigated through an animal test and confirmed by comparing with the data of conventional cystometry.

LC

In this letter, we simply fabricate magnetoelectric (ME) composite cantilevers through bonding 30 μm thick Metglas and 52 μm thick polyvinylidene fluoride with an epoxy, and report resonant and energy harvesting characteristics with applied DC and AC magnetic fields ranging from 0 to 3 kA/m. Generated ME voltages from a 40 mm long, 12.3 mm wide, and 112 μm thick cantilever are measured and analyzed as a function of the applied magnetic field. In our experiment, higher ME voltages are generated when both the DC and AC magnetic fields are present and the ME voltages around the second flexural bending mode are approximately five times higher than those around the first mode. The higher ME voltage with the second mode is also confirmed with finite element analysis.