EHD effects were first discovered in 1629 by Cabeo, who observed that electric fields could attract sawdust, after noticing repulsion following physical contact [1]. However, Cabeo did not understand the rationale behind this phenomenon. Over the next few hundred years, Wilson investigated the EHD effect, coining the term electric wind, and attempted to find practical applications [2]. In 1961, a theory relating to ionic wind was developed by Robinson, who proposed the possibility of developing functional electrostatic blowers, namely EHD gas pumps [3]. Although this electrostatic blower had the advantages of low wear, quiet operation, and no requirement for lubrication as compared to conventional fans (i.e., a mechanical pump), Robinson was disappointed by the inability to overcome the extremely low operating efficiency (the conversion efficiency was less than 1% from corona discharge to mechanical energy). The low conversion efficiency from electrical to mechanical energy represented a primary limitation of EHD pumps. Many researchers attempted to improve the device structure using EHD pumps, and there have been some experimental studies focused on improving the flow rate and efficiency of EHD pumps. In 2008, Moreau et al. made substantial improvements [4]. Morrow et al. increased the electrical energy conversion efficiency to 1.72% via the pin-ring and pin-grid electrode configuration, which provided more than twice the conversion efficiency compared to previous EHD effect studies. In recent times, the higher energy conversion efficiency of EHD pumps has also been demonstrated by June et al. [5]. June et al. experimentally tested a five-needle mesh-like EHD pump prototype and found static efficiencies of up to 14%.

In addition to EHD air pumps, functional fluidic EHD pumps have also been developed in recent decades. Sharbaugh et al. [6] were the first to use media other than air in EHD pumps, attempting to apply EHD pumps to transformers. However, this was deemed impractical owing to subsequent contamination of the collector electrode after hundreds of hours of operation. Five-years later, Crowley et al. were the first researchers to publish an experimental study on the behavior of multiple working fluids using a rectangular EHD pump with a parallel strip-to-strip electrode [7]. This paper develops a basic EHD pumping model to illustrate the working fluid’s material properties. They applied the model to several experimental pumps reported earlier and found good agreement. Examples of this model demonstrate several new fluids suitable for EHD pumping. The authors concluded that there are considerable differences in the maximum velocity that can be achieved for different fluids and that the maximum velocity for a given fluid cannot determine the maximum efficiency. The basic geometry of a functional fluidic EHD pump is depicted in Figure 1. Several years later, a multi-stage EHD pump using transformer oil as the working fluid was designed as a practical solution for motor cooling [8,9]. There are also studies using a dielectric fluid (dibutyl sebacate, an organic plasticizer) as a medium, both as a single-stage and a multi-stage configuration of the same geometry. Researchers in other studies also employed a dielectric fluid (such as dibutyl sebacate) as a medium, both as single- and multi-stage configurations of the same geometry [10,11].

Despite the computational conditions, the flawed theories of physics and materials science, and the limitations of experimental equipment, previous explorations built the foundation for future research, as these results retain the majority of their validity even today.

2. Pump Structure and Material