Energy Harvesting for Pacemakers

Abstract

A pacemaker runs on a conventional battery that lasts for approximately 6-12 years, after which the pacemaker must be replaced. Converting the heart wall vibrations into electricity through a vibration energy harvester has been considered a promising solution to this problem. However, the complexity of the heart signals on which the energy harvester has to operate is a challenge. The human heart signal is a broadband signal, consisting of a varying acceleration amplitude at low frequencies. Most of the testing signals used in the labs are harmonic signals, Gaussian white noise or Gaussian coloured noise. These signals do not have the same characteristics as a human heart signal. In addition, the dynamical behaviour of an energy harvester differs per input signal. Therefore, it is important to test energy harvesters on the operation signal, in this case human heart acceleration signals. A heart signal differs per person depending on, for instance, someone's age, sex and health. This means that multiple human heart input signals are needed. Ethical requirements make the measurement of these signals with the necessary details a challenge in itself. In order to meet this demand and to avoid this ethical issue, a heart signal generator is developed as a first step towards the testing of energy harvesters on an approximation of human heart signals. Three different sources of heart signals are combined in order to obtain a new source of heart signals, an approximation of reality, which can be used for the testing. Speckle Tracking Echocardiography signals, open-chest pig heart acceleration signals and human chest motion acceleration signals are analysed and their characteristics are used as the source for the heart signal generator. This heart signal generator is able to mimic multiple heartbeats and the influence of the heart rate on the amplitude and signal duration. The disadvantages of accelerometer measurements are compensated with the advantages of Speckle Tracking Echocardiography measurements, and vice versa, in order to obtain an accurate and detailed heart signal. The output of the heart signal generator is a one-dimensional acceleration signal. An energy harvester is tested on multiple generated heart signals for a heart rate range of 120-200 bpm. It was observed that the mean power output and the efficiency of the energy harvester differs per heart signal. This shows that testing on multiple heart signals is crucial in order to validate that enough power is generated for charging the battery.