Dielectric liquids for enhanced field force in macro scale direct drive electrostatic actuators and rotating machinery

Recently interest towards electrostatic actuators and machinery has increased for use in MEMS, mechatronics and renewable energy applications. Effective electromechanical power conversion using electrostatics requires dielectric liquids whose permittivity and breakdown field strength can facilitate adequate electric shear stress and pressure beyond the capabilities of media such as air or vacuum. This paper discusses design points for practical electrostatic force production and evaluates available off-the-shelf dielectric liquids in terms of electric pressure capability. Key dielectric properties including pressure, breakdown field strength, relative permittivity, and conductivity are measured. A custom test stand measures the attractive force between two electrodes mounted on load cells inside a tank filled with the liquid under test. Measurements demonstrate liquids capable of reaching several psi of electric pressure while correlating with analytical and finite element (FE) models, ultimately forming a basis for electrostatic actuator/machine design. The best liquid candidate, Vertrel XF, was poured into a proof of concept macro scale electrostatic machine demonstrating 0.9 N-m torque and 0.126 N-m/kg. Torque measurements verify the capability of Vertrel XF and the correlation between the electric pressure and shear stress in a rotating machine.