Analytical model of droplet based electrostatic energy harvester performance

An analytical model for electrostatic energy harvesters that use translating conductive droplets as proof masses is presented. These devices generate power from the variable capacitance that results from droplet motion across an interdigitated electrode array. Model predictions are compared with numerical and experimental results. Comparison with numerical simulation supports the validity of the model and suggests that capacitance scales with contact diameter, not droplet diameter. Comparison with experimental results shows that the model captures the shape of the evolution of transient output energy and voltage from the device. These comparisons suggest that the contact diameter of mercury droplets tested experimentally was similar to the diameter of the droplet. Evaluation of the Bond number in these cases supports this result. Model predictions based on a contact diameter equal to the observed droplet diameter correctly predict the width and spacing of output voltage peaks as the droplet translates through the device. However, underprediction of the magnitude of voltage peaks resulted in an underprediction of the accumulated energy output (36 %). This discrepancy suggests that the contact area may not remain constant as the droplet moves through the device. A deeper understanding of the evolution of the contact area is required to optimize device parameters to maximize energy output.