Design of a spiral-shaped piezoelectric energy harvester for powering pacemakers

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).