Dielectric elastomer generators (DEG) are well suited to harvest energy from natural motion sources (e.g. water, human locomotion). DEG require a source of high voltage charge to generate energy. In low cost, low power DEG, a high voltage charge source is expensive and impractical to implement. The Self Priming Circuit (SPC) can be used to remove the high voltage charge source and replace it with a low voltage one. The SPC works by moving charge onto and off the DEG in synchrony with DEG compression to enable voltage boosting. For the initial cycle a low voltage source is still required in the form of a battery or similar device which in some instances can completely discharge, rendering the DEG useless. Another approach is to include an electret into the DEG design. The electret acts as a permanent voltage source for the DEG and SPC. This allows the DEG to receive a medium voltage (much higher than a battery) from the electret and then boost this voltage up to a high voltage where generation efficiency is improved. This paper presents an integrated SPC with an electret charge source that is capable of boosting quickly to a high voltage without the addition of external charge.
Among the main issues with the implementation of Dielectric Elastomer Generators (DEGs) is the need for pre-charging to perform mechanical-to-electrical energy conversion. In cases when energy harvesting has to be performed in an environment with unpredictable characteristics (e.g., wind, waves, human walking), defining the best times for charge injection and energy extraction in a cycle is a non-trivial problem. In this paper, we present a novel Self-Sensing with Peak Detection (SSPD) method to control the charges on the material using capacitive self-sensing techniques, which defines an optimal cycle and requires no knowledge of the mechanical excitation amplitude or frequency. The effectiveness of the approach is proved by means of numerical simulations based on an highly accurate model of the DEG device.
Dielectric Elastomer Generators (DEGs) are an emerging energy harvesting technology based on a the cyclic stretching of a rubber-like membrane. However, most design processes do not take into account different excitation frequencies; thus limits the applicability studies since in real-world situations forcing frequency is not often constant. Through the use of a practical design scenario we use modeling and simulation to determine the material frequency response and, hence, carefully investigate the excitation frequencies that maximize the performance (power output, efficiency) of DEGs and the factors that influence it.
One of the main challenges for the practical implementation of dielectric elastomer generators (DEGs) is supplying high voltages. To address this issue, systems using self-priming circuits (SPCs) — which exploit the DEG voltage swing to increase its supplied voltage — have been used with success. A self-priming circuit consists of a charge pump implemented in parallel with the DEG circuit. At each energy harvesting cycle, the DEG receives a low voltage input and, through an almost constant charge cycle, generates a high voltage output. SPCs receive the high voltage output at the end of the energy harvesting cycle and supply it back as input for the following cycle, using the DEG as a voltage multiplier element. Although rules for designing self-priming circuits for dielectric elastomer generators exist, they have been obtained from intuitive observation of simulation results and lack a solid theoretical foundation. Here we report the development of a mathematical model to predict voltage boost using self-priming circuits. The voltage on the DEG attached to the SPC is described as a function of its initial conditions, circuit parameters/layout, and the DEG capacitance. Our mathematical model has been validated on an existing DEG implementation from the literature, and successfully predicts the voltage boost for each cycle. Furthermore, it allows us to understand the conditions for the boost to exist, and obtain the design rules that maximize the voltage boost.