Electrohydrodynamic (EHD) | Power Supply

Electrohydrodynamics (EHD) is a field of science and technology that studies the dynamics of electrically charged fluids. It utilizes the interaction between electric fields and fluids (gases and liquids) for precise transport and control. A key advantage of EHD systems is their lack of mechanical moving parts like fans or pumps, which enables silent operation, compact designs, and maintenance-free performance. A high-voltage power supply is the core component that drives these EHD phenomena. The performance and reliability of EHD-based equipment are critically dependent on the precision, stability, and responsiveness of the applied voltage. Therefore, selecting the optimal high-voltage power supply is crucial for any given application.

This article explains the basic principles of EHD, its fields of application, and the high-voltage power supply requirements for each application.

Basic Principles of EHD

EHD phenomena generate fluid flow by directly imparting momentum to the fluid using electrical forces. It uses electrical forces (such as Coulomb force and dielectrophoretic force) exerted by an electric field on charged particles (ions) or dielectric particles within the fluid. This phenomenon is described by coupling Maxwell's equations from electromagnetism with the Navier-Stokes equations from fluid dynamics.

\mathbf{f}_e = \rho_e \mathbf{E} - \frac{1}{2} E^2 \nabla \epsilon + \frac{1}{2} \nabla \left( E^2 \rho \frac{\partial \epsilon}{\partial \rho} \right)

The EHD body force density, f_e, which drives the fluid motion, is described by the following equation. The first term represents the Coulomb force, which acts on free charges. The second and third terms are forces arising from dielectric polarization: the dielectrophoretic force and the electrostrictive force, respectively.

Some of the most representative phenomena utilized in EHD include ionic wind, dielectrophoresis, and electro-osmotic flow.

Key EHD Phenomena and Required High-Voltage Power Supplies

Ionic Wind (Corona Wind)

Ionic wind, also known as corona wind, is generated by applying a high DC voltage between a sharp, needle-like electrode and a counter electrode. This configuration creates a corona discharge. This produces and accelerates ions, which then generate an airflow through collisions with surrounding neutral gas molecules.

Application Fields: Electronic equipment cooling, air purification, static elimination (ionizers).
Required Power Supply Characteristics: Voltage/Polarity: A stable DC high voltage from several kV to tens of kV. Both positive and negative polarity outputs may be required.; Stability/Ripple: To maintain a stable discharge, a low-ripple, high-stability output is essential. Voltage fluctuations can lead to uneven ion generation and, consequently, unstable airflow velocity.; Controllability: To precisely control the airflow speed, a high-precision output voltage control function via external analog signals or digital communication is required.

Matsusada Precision's Solutions: For basic research, the high-stability, low-ripple digital high-voltage DC power supply HARS series is ideal. For product integration, compact and high-efficiency high-voltage power supply modules are most suitable.

Dielectrophoresis (DEP)

Dielectrophoresis (DEP) is a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field. This force, which arises from polarization, can be used to manipulate and move particles. It is particularly used for the separation and manipulation of microparticles (such as cells, bacteria, and nanoparticles) in liquids.

Application Fields: Cell separation, water quality inspection, drug delivery.
Required Power Supply Characteristics: Output Type: High-frequency AC voltage is necessary to efficiently generate a non-uniform electric field.; Frequency/Waveform: A variable frequency function is important, as the optimal frequency (from several kHz to several MHz) must be selected according to the characteristics (dielectric constant) of the target particles. The ability to output various waveforms, such as sine and square waves, may also be required; Fast Response: For dynamic manipulation of particles, an amplifier-type power supply capable of fast voltage ON/OFF and amplitude modulation is effective.

Matsusada Precision's Solutions: High-voltage amplifiers/fast high-voltage power supplies, which can freely output high-speed, high-voltage waveforms, strongly support dynamic EHD control experiments like dielectrophoresis.

Electro-osmotic Flow (EOF)

This phenomenon drives the bulk fluid by applying an electric field along a microchannel to the electric double layer formed at the interface between the microchannel's inner wall and the liquid.

Application Fields: MEMS, Lab-on-a-Chip, DNA sequencers, micro-volume liquid pumps.
Required Power Supply Characteristics: Voltage/Current: Although the voltage is relatively low (tens of V to several kV), extremely precise control is crucial.; Noise Characteristics: In applications involving minute flows, output noise directly causes flow disturbances. Therefore, ultra-low ripple and low-noise characteristics are essential.; Polarity Switching: A power supply with high-speed polarity switching is often required to enable instantaneous reversal of the flow direction.

Matsusada Precision's Solutions: For precise benchtop experiments, the HJPSS series, which achieves ultra-low ripple, is optimal. It is also possible to provide these performance features in a compact module for OEM integration.

Key Points for Selecting a Power Supply for EHD Applications

To succeed in research and product development applying EHD technology, it is necessary to select a high-voltage power supply from a comprehensive perspective based on the following points.

Selection Criteria	Description
Output Voltage/Current	Does it sufficiently meet the voltage and current range required by the application?
Polarity	Is a positive, negative, or bipolar output required?
Stability/Ripple	This is the most critical item directly affecting the stability and reproducibility of the phenomenon. The required specifications must be clarified.
Response Speed	If dynamic control or fast ON/OFF is needed, a high-speed response power supply such as a high-voltage amplifier is essential.
Controllability/Interface	Does it support external control (analog, digital communication, etc.) from a PC or PLC?
Size/Shape	Is it for product integration (OEM) or benchtop use in a laboratory?
Safety/Reliability	Since it handles high voltage, output protection functions, compliance with safety standards, and reliability for long-term continuous operation are important.

Conclusion

Electrohydrodynamics (EHD) is a technology expected to be utilized in increasingly diverse fields in the future due to its unique characteristics. To unlock the full potential of EHD, the performance of the high-voltage power supply--the heart of the system--is paramount.

At Matsusada Precision, we leverage our long-cultivated high-voltage technology and extensive product lineup to propose optimal high-voltage power supply solutions that meet customer requirements at every phase, from basic EHD research to integration into mass-produced products. If you have any challenges with power supplies for EHD, please do not hesitate to contact us.

Our high-voltage power supplies and high-voltage amplifiers are used in research on electrohydrodynamic.