Pen harvester for powering a pulse rate sensor

Rapid developments in the area of micro-sensors for various applications such as structural health monitoring, bio-chemical sensors and pressure sensors have increased the demand for portable, low cost, high efficiency energy harvesting devices. In this paper, we describe the scheme for powering a pulse rate sensor with a vibration energy harvester integrated inside a pen commonly carried by humans in the pocket close to the heart. Electromagnetic energy harvesting was selected in order to achieve high power at lower frequencies. The prototype pen harvester was found to generate 3mW at 5 Hz and 1mW at 3.5 Hz operating under displacement amplitude of 16mm (corresponding to an acceleration of approximately 1.14g(rms) at 5Hz and 0.56g(rms) at 3.5 Hz, respectively). A comprehensive mathematical modelling and simulations were performed in order to optimize the performance of the vibration energy harvester. The integrated pen harvester prototype was found to generate continuous power of 0.46-0.66mW under normal human actions such as jogging and jumping which is enough for a small scale pulse rate sensor.