Tools for Analytical and Numerical Analysis of Electrostatic Vibration Energy Harvesters: Application to a Continuous Mode Conditioning Circuit

This paper reports the application of different analytical tools to a basic continuous conditioning (CC) circuit for electrostatic vibration energy harvesters (e-VEHs). We address the fundamental issues of this conditioning circuit and give design advice that enhances the performance of e-VEHs employing this circuit. This circuit is widely used for harvesters with or without an electret layer. Despite its wide use, its fundamental problems have been weakly addressed even for simple configurations of e-VEHs since it is impossible to solve the corresponding equations in closed form. As a consequence, appropriate semi-analytical methods that provide an insight into the physics of the system are required. 1. Introduction Vibration energy harvesting is a promising technique for the generation of electricity from ambient vibrations for the supply of autonomous microsystems. Capacitive (electrostatic) vibration energy harvesters appear to be the best candidates for miniatuarization. They are not as bulky as electromagnetic harvesters, and they do not suffer from fatigue or depolarization like piezoelectric devices. A large number of studies have investigated electrostatic vibration energy harvesters, and many have focused on the design of a transducer device including a mechanical resonator and a capacitive transducer. However, the main challenge of e-VEH implementation is related to the design of conditioning and interface electronics. Currently, there are several families of circuits for the conditioning of capacitive energy converters. We can group them into three categories. (i) Constant-charge or constant-voltage operation mode [1], (ii) Circuits employing a charge pump [2, 3] and (iii) " Basic " conditioning circuit obtained by connecting a capacitive transducer to a source of voltage in series with a load resistor [4]. The first two families of circuits require complex control electronics in order to correctly sequence different phases of energy conversion. They are considered to be an encouraging prospect for the implementation of smart adaptive e-VEH systems, able to react to a variation in the input vibrations. On the other hand, the operation of a basic conditioning circuit does not require any smart electronics. Its cost is low, however its efficiency is also lower in comparison with the other families. The basic conditioning circuit shown in fig. 1a has been extensively used in two contexts. Firstly, when the main research or design work is focused on a transducer or a resonator, this circuit is used for the testing of the device [4]. Secondly, this circuit is often used in e-VEH employing an electret …