In this paper, a spiral-shaped piezoelectric cantilever structure is proposed to harvest the energy from the vibration of the heartbeat. The proposed cantilever structure is 14 μm thin with the outer dimension of 5 mm × 5 mm. The spiral structure reduces the stiffness of the cantilever beam which reduces the resonant frequency. A proof mass is introduced in the spiral structure to further reduce the resonant frequency of the cantilever beam. Due to biocompatibility nature, Zinc oxide (ZnO) has been used as the piezoelectric material for the design. The proposed structure has a resonant frequency of 45.8 Hz which is suitable for harvesting energy from the human heartbeat. The harvester generates peak output open circuit voltage of 3.2 V and peak output power of 3.5 μW at the resonant frequency of 45.8 Hz for a sinusoidal acceleration of 1g.

In this paper, a spiral-shaped piezoelectric cantilever structure is proposed to harvest the energy from the vibration of a heartbeat. The proposed cantilever structure is 14 μm thin and has outer dimensions of 6 mm × 6 mm. The spiral structure reduces the stiffness of the cantilever beam, which reduces the resonant frequency. A proof mass is introduced in the spiral structure to reduce further the resonant frequency of the cantilever beam. Due to its biocompatible nature, zinc oxide (ZnO) is used as the piezoelectric material for the design. The proposed structure has a resonant frequency of 30·6 Hz, which is suitable for harvesting energy from the human heartbeat. The resonant frequency of the proposed 3-turn spiral cantilever beam is 33·18% lower than that of the 2·5-turn spiral cantilever beam and 54·93% lower than that of the 2-turn spiral. The proposed harvester generates a peak output open-circuit voltage of 4 V and a peak output power of 5·3 μW at a resonant frequency of 30·6 Hz for a sinusoidal acceleration of 1g (1g = 9·8 m/s²).

The principle of piezoelectricity has been used to design the micro-electro-mechanical system-based piezoelectric energy harvester for generating electrical energy from the surrounding vibration. The huge popularity of these energy harvesters (EHs) is due to their small size. This paper designs the EH for the heating, ventilation, and air conditioning system. Different cantilever structures with different shapes of the same fabricated area have been designed and investigated at an excited acceleration of 1 g (9.8 ms⁻²). The multi-perforated cantilever structure has the better stress distribution within the cantilever structure and generates better output voltage and power than their basic design. The proposed tapered multi-perforated cantilever structure has the least value of the resonant frequency of 98.59 Hz which is 31.13% less than the rectangular cantilever structure. The proposed structure generates the output voltage of 14 V which is 91.78% higher than the basic rectangular cantilever structure. It also generates the average output power of 7.15 µW which is 213.59% higher than basic rectangular cantilever structure.

Microelectromechanical system (MEMS)-based piezoelectric energy harvesters have been successful in harvesting optimum power output from the low-frequency vibrations in the environment. Their ability to operate over a wide range of frequencies is quite essential because the vibrations occurring in the environment are random and occur at different frequencies. In this paper, we try to increase the operating bandwidth of a MEMS-based energy harvester using parallel connection of multiple cantilever beam structures. The operating bandwidth of the energy harvester increases as the number of beams is increased, provided the resonant frequencies of the beams differ from each other by a sufficient margin. Here we consider the operating bandwidth of the energy harvesters to be the range of frequencies over which they generate an output voltage greater than or equal to 1 V. The single beam, parallelly connected two-beam, three-beam and four-beam structures has an operating bandwidth of 26 Hz, 27 Hz, 28 Hz, and 31 Hz, respectively. Thus, the bandwidth of parallelly connected four-beam structure is wider than that of single beam structure by 5 Hz.

Piezoelectric energy harvesters have high power density and are simpler to fabricate as compared to other low power energy harvesters. There are certain issues which need to be addressed while designing a piezoelectric energy harvester. These are the requirements of maintaining a high output voltage, low resonant frequency, small size and wide bandwidth of operation. Achieving a wide bandwidth is one of the most prominent issues. It is because most of the vibrations occur over a range of frequencies. So, the challenge is to design an energy harvester which generates high output voltage over a wide range of frequencies. In this paper, a Microelectromechanical system (MEMS) based multi-beam energy harvester has been proposed. This energy harvester has been designed using two single cantilever beams and the top electrodes of both the beams are connected by a metal layer. The peak output voltage of the proposed structure is 18 V at 142 Hz. The multi-beam structure generates an output voltage of more than or equal to 5 V for a bandwidth of 15 Hz which is 1.5 times wider as compared to that of a single beam energy harvester.