Microscale Plasma Actuator for Active Flow Control
Yoshinori Mizuno, Marius Blajan, and Kazuo Shimizu
Organization for Innovation and Social Collaboration, Shizuoka University,
3-5-1 Jyouhoku, Hamamatsu, 432-8561, JAPAN; E-mail：shimizu@cjr.shizuoka.ac.jp
Introduction
In various mechanical systems, flow control byactive method is an important factor to improvethe efficiency or decrease the environmental
load. To control the air flow, many mechanicalactuators have been developed and usedeffectively. Recently, Plasma actuator has
attracted attention due to the its advantages
such as no moving parts, simple construction,high frequency compared with mechanicalactuators.

(3) Air flow visualization and investigation

Results and discussions(1)Electrical characteristics
When discharge voltage was 2 kV and pulse
width was 500 ns, discharge current and power
could be up to 8 A and 12 kW, respectively.
Energy consumption by applying one shot pulse
was about 550 µJ at both polarity. Average
power consumption was calculated by theproduct of 550 µJ and pulse frequency of 1 kHzand was estimated at about 550 mW.

The plasma actuator consists in a groundedelectrode, a high voltage energized electrodeand thin dielectric layer. When a plasma actuatoris energized by high voltage, a high electric field
ionizes the air near the plasma actuator. Ions
are drifted by the Coulomb force. While travelingthrough the air, ions collide with neutral gas
molecules and transfer their momentum toneutral molecules induced air.

Fig. 1 Principle of air flow induced by plasma actuator.
In this study, the microscale plasma actuator
was developed and investigated. Due to themicro scale gap, our microplasma actuator could
be driven at 1 kV, relativity low voltage.

Experimental Setup(1) Microplasma actuator

Air flow was visualized by using tracer particle
and laser. High-speed camera was used for theobserving the air flow. Without driving themicroplasma actuator, there is no flow. Whenthe electrodes are energized and plasma turned
on a time resolved air flow movement causedby the microplasma actuator is observed.
Discharge voltage was negative 2 kV, pulse
width was 500 ns and pulse frequency was 1kHz. Air flow caused by the microplasma
actuator changed its state from transition one
to stationary one 1 second after driving themicroplasma actuator. At the center of themicroplasma actuator, scattering lights oftracer particles were concentrated near the 1
mm from the microplasma actuator. This showsthat air flow induced by the microplasma
actuator could reach up to 1 mm height fromthe microplasma actuator. At edge of themicroplasma actuator, a vortex was developedwith time (left side: clockwise rotation, rightside: anticlockwise rotation). Air flow velocitywas about 0.1 m/s at 1 mm height and edge ofthe microplasma actuator.

Fig. 4 Waveforms of discharge voltage andcorresponding discharge current and power.

(2) Emission spectra
Light emission was observed by applying
pulsed negative 2 kV to the microplasmaactuator. Emission spectra of microplasma in
atmospheric air were measured by an emission
spectrometer.

Fig. 7 Air flow Before driving the microplasma actuator.

(a) 100 ms after driving the microplasma actuator

Fig. 2 Geometry of microplasma actuator.

(2) Experimental SetupPlasma actuator was energized by a pulsed
negative high-voltage. Air flow caused by themicroplasma actuator wasvisualized
andmeasured by Particle Imaging Velocity (PIV)
method. Alumina 5 µm diameter were used as
tracer particles. Nd YVO4 laser 532 nm was usedfor irradiation.

(a) Without discharge(b) While discharge
Fig.4 Light emission from the microplasma
N2 Second Positive Band System and weremeasured at 315, 337, 357, 375, and 380 nm.
And, Nitrogen First Negative System 391 and427 nm was observed.

(b) 300 ms after driving the microplasma actuator

5Emission intensity [a. u.]

The microplasma actuator developed and usedin this study consists in dielectric layer wasplaced between two metallic electrodes. Due tothe electrode configuration, the microplasma
actuator is capacitive load of 200 pF. Discharge
gap was set at 25 µm. As a result, atmospheric
air plasma could be generated at about 1 kV,
relatively low discharge voltage. Such low
voltage is easily controlled by semiconductor
switches without step-up transformer. This
contributes to theminiaturization of thesystem.

432(c) 500 ms after driving the microplasma actuator

10250300

350

400450

Wavelength [nm]Fig.5 Emission peaks from microplasma.

Fig. 2 The experimental setup for visualization theAir flow induced by the microplasma actuator.

Knowing behavior of ions and electrons, excitedspecies in the microscopic region could be very
important for driving or optimization of plasma
actuator. Furthermore, time resolved emission
intensity from the microplasma was measured
byanemission
spectrometeranda
photomultiplier tube. Emission of N2 second
positive system 337.1 nm is shown in Fig. 6.
Lifetime emission signal was only 50 ns.
Lifetime emission signals from other N2 SPS
peaks at 315 nm, 353 nm, 357 nm, 375 nm and380 nm were also for 50 ns.

A pulsed negative high-voltage supply used inthis study. Negative2 kV is easily controlled by a
5 V signal.

Fig. 6 Time resolved emission intensity fromNitrogen Second Positive System, 337.1 nm.
Fig. 3 Schematic of pulsed negative high-voltage supply.

(d) 1000 ms after driving the plasma actuator
Fig. 8 Time resolved air flow induced by the microplasma.

Conclusions
In this study, air flow induced by microscale
plasma actuator was investigated and following
conclusions were obtained.
1) When microplasma actuator energized bypulsed negative high-voltage, 2 kV and 1 kHz,power consumption was 550 mW.
2) Air flow made the transition to stationary
state 1 second after driving the microplasma
actuator.
3) At center of the microplasma actuator, airflow induced by the microplasma actuator
could reach up to 1 mm height from themicroplasma actuator.
4) At edge of the microplasma actuator, air flow
vortex was generated and its velocity wasabout 0.1 m/s at 1 mm height.

Acknowledgement
The authors would like to thank Prof. Toshiyuki
Sanada of Shizuoka University and Prof. Hitoki
YonodaofTheUniversityofElectrocommunications for the fruitful discussions.