Frequency-dependent stability of parallel-plate electrostatic actuators in conductive fluids

Abstract

We present an electromechanical stability analysis of passivated parallel-plate electrostatic actuators in conductive dielectric media and show that the pull-in instability can be eliminated by tuning the applied frequency below a design-dependent stability limit. A partial instability region is also obtained, where the actuator jumps from the pull-in displacement to another stable position within the gap. The results predict that the stability limit is always greater than the critical actuation frequency, and therefore any device that is feasible to actuate in a conductive fluid can be operated with stability over the full range of motion.

Review: Electrostatically actuated nanobeam-based nanoelectromechanical switches – materials solutions and operational conditions

“…The charge accumulation issue may be partially resolved by using bipolar AC rather than DC voltage actuation [ 191 ]. However, it would require complex electronics [ 192 – 193 ] to drive the NEM switch in dielectric charging-free mode.…”

An in vivo study of electrical charge distribution on the bacterial cell wall by atomic force microscopy in vibrating force mode

“…15 . In search of quantitative imaging of local dielectric properties in electrolyte solutions with nanoscale spatial resolution, most of studies have been done by applying high frequency voltages 16 between the cantilever and sample. By working at frequencies greater than the dielectric relaxation frequency of the medium (in the MHz range for 1mM KCl 17 ) and by scanning the probe at distances much larger than the Debye length (typically 10 nm in 1mM monovalent electrolytes), spatially resolved mapping of the dielectric properties of patterned samples are feasible 18 .…”

“…13,14 The presence of mobile ions and bias voltage applied between the tip and the sample led to induced charge dynamics, ion diffusion and a capacitive coupling between them depending on the electrochemical properties of the solution (ionic strength, etc.). 15 In search of a quantitative imaging of local dielectric properties in electrolyte solutions with nanoscale spatial resolution, most of the studies have been done by applying high frequency voltages 16 between the cantilever and the sample. By working at frequencies greater than the dielectric relaxation frequency of the medium (in the MHz range for 1 mM KCl 17 ) and by scanning the probe at distances much larger than the Debye length (typically 10 nm in 1 mM monovalent electrolytes), spatially resolved mapping of the dielectric properties of patterned samples is feasible.…”

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“…As discussed below, various studies have recently been conducted to measure the charge, surface potential, dielectric constant, Stern potential, Debye length and other electrical surface properties in solution. 39,42,[61][62][63] Key to recent advances are the studies carried out by Sounart et al and Panchawagh et al 41,64 on the electromechanical stability of passivated parallel plate electrostatic actuators in conductive dielectric media. They show that by appropriately choosing the frequency of the AC signal one can control the forces between the various components of the actuator.…”

“…They further found a relation between the AC frequency and the actuation stability and the thickness and dielectric constant of the electret layer on the parallel plates. 41,64 The plate-solution system was modeled by the equivalent RC circuit as shown in Fig. 6 by including the leakage resistance of the solution R s , capacitance of the solution C s and capacitance of the electret layer C d .…”