Plasma actuator

Abstract

To provide a high-durability plasma actuator capable of generating a strong induction flow.SOLUTION: A plasma actuator comprises a tabular dielectric, an upstream-side electrode which is disposed on one face of the dielectric, and a downstream-side electrode which is disposed on the other face or inside of the dielectric. The upstream-side electrode and the downstream-side electrode are offset-disposed, the upstream-side electrode includes a projection which protrudes to the side of the downstream-side electrode in an in-plane direction of the dielectric, the dielectric is formed from two kinds of dielectric materials of a first dielectric material and a second dielectric material having a higher dielectric constant and higher plasma resistance than the first dielectric material and includes a location including the second dielectric material and a location of the first dielectric material only in a planar view and a location overlapped with a tip end of the projection is the location including the second dielectric material, thereby providing a plasma actuator by which plasma moves forward and straight in a direction of the dielectric material having higher plasma resistance and which makes generation of a strong induction flow compatible with high durability.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a plasma actuator. [Background technology]

[0002] Plasma actuators are known that generate induced flows using plasma generated by discharge between electrodes. These plasma actuators have no mechanically moving parts and are therefore free from wear due to friction, making them maintenance-free for fluid control.

[0003] Patent Document 1 describes a plasma actuator in which a front electrode plate and a back electrode plate are placed on either side of a dielectric made of a dielectric material such as glass fiber reinforced resin, one end of the front electrode plate is sawtooth-shaped, and plasma is generated in a concentrated manner from the top of the sawtooth, thereby increasing the kinetic energy of the induced flow. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-009796 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the electric field concentrates at each top of the front electrode plate, generating a strong plasma, which etches the dielectric, thereby reducing durability.

[0006] The present invention has been made in view of the problems associated with the prior art, and its object is to provide a highly durable plasma actuator that can generate a strong induced flow. [Means for solving the problem]

[0007] As a result of extensive research into achieving the above-mentioned object, the inventors have found that the above-mentioned object can be achieved by forming a dielectric from two types of dielectric material, namely, a first dielectric material and a second dielectric material having a higher dielectric constant and plasma resistance than the first dielectric material, and arranging the dielectric so that the tip of the electrode convex portion overlaps with the portion containing the second dielectric material, and have thus completed the present invention.

[0008] That is, the plasma actuator of the present invention comprises a plate-shaped dielectric, an upstream electrode arranged on one surface of the dielectric, and a downstream electrode arranged on the other surface of or inside the dielectric. The upstream electrode and the downstream electrode are arranged offset from each other, the upstream electrode has a convex portion that protrudes toward the downstream electrode in the in-plane direction of the dielectric, the dielectric is formed of two types of dielectric materials, a first dielectric material and a second dielectric material that has a higher dielectric constant and plasma resistance than the first dielectric material, and has, in a planar view, a portion that includes the second dielectric material and a portion that is only the first dielectric material, and the portion that overlaps with the tip of the convex portion is the portion that includes the second dielectric material. [Effects of the Invention]

[0009] According to the present invention, the tip of the electrode convex portion is arranged to overlap with the portion formed of the dielectric material having a high dielectric constant and plasma resistance of the dielectric, so that the plasma travels straight in the direction of the dielectric material having high plasma resistance, making it possible to provide a plasma actuator that combines the generation of a strong induced flow with high durability. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view showing the configuration of a plasma actuator. [Figure 2] FIG. 3 is a schematic diagram showing the arrangement of an upstream electrode and a downstream electrode. [Figure 3] FIG. 10 is a diagram showing a state in which the tip of the convex portion of the upstream electrode and the second dielectric material overlap. [Figure 4] 10A and 10B are diagrams showing the positional relationship between the tips of the convex portions of the upstream electrode and the plain weave cloth. [Figure 5] FIG. 10 is a schematic diagram showing an upstream electrode having a small protrusion. DETAILED DESCRIPTION OF THE INVENTION

[0011] The plasma actuator of the present invention will now be described in detail. As shown in FIG. 1, a plasma actuator generally comprises a plate-shaped dielectric 1, an upstream electrode 2 and a downstream electrode 3 that are offset in the in-plane direction (X direction) of the dielectric, with the upstream electrode being exposed on one surface of the dielectric, and the downstream electrode being located on the other surface of the dielectric or inside the dielectric.

[0012] In such a plasma actuator, an atmospheric pressure barrier discharge occurs between the upstream electrode 2 and the downstream electrode 3 when an AC voltage is applied between the electrodes, generating plasma in the in-plane direction of the dielectric from the upstream electrode toward the downstream electrode, thereby generating an induced flow 5 on the surface of the dielectric.

[0013] As shown in FIG. 2, in a plan view (XY plane), the plasma actuator of the present invention has an upstream electrode 2 and a downstream electrode 3 on the back side, indicated by the dashed line in FIG. 2, arranged in parallel, and the upstream electrode 2 has a protrusion 21 that protrudes toward the downstream electrode in the in-plane direction of the dielectric 1. Therefore, an electric field is concentrated at the tip of the convex portion of the upstream electrode 2, and a strong plasma is generated from the tip of the convex portion, causing a strong induced flow.

[0014] The apex angle of the convex portion is preferably equal to or less than 90 degrees. The sharply pointed tip of the convex portion 21 makes it possible to generate a strong plasma.

[0015] Furthermore, in the plasma actuator of the present invention, the dielectric 1 is formed of two types of dielectric materials: a first dielectric material 11 and a second dielectric material 12 that has a higher dielectric constant and plasma resistance than the first dielectric material, and in a planar view (XY plane), it has areas formed only by the first dielectric material 11 and areas formed by both the first dielectric material and the second dielectric material 12.

[0016] In plan view (XY plane), as shown in Figure 3, the tip of the convex portion of the upstream electrode 2 is positioned so as to overlap the portion of the dielectric containing the second dielectric material 12, so that the strong plasma generated from the tip of the convex portion travels straight toward the portion of the dielectric containing the second dielectric material 12 having a high dielectric constant, and the traveling direction of each plasma coincides with the direction in which the induced flow is generated, thereby generating a strong induced flow.

[0017] In addition, the second dielectric material 12 not only has a high dielectric constant but also has high plasma resistance, so that etching of the dielectric due to collision with plasma can be suppressed, improving durability.

[0018] It is preferable that the second dielectric material is present on the surface of the dielectric, but it does not necessarily have to be exposed on the surface of the dielectric; as long as it is contained somewhere in the thickness direction (Z direction) of the dielectric, it can be prevented from being etched to a depth greater than that.

[0019] Furthermore, even if the upstream electrode has a convex portion, a barrier discharge is not generated only at the tip of the convex portion, but a weak discharge is also generated at locations other than the tip of the convex portion, resulting in power consumption.

[0020] 3, the plasma actuator of the present invention has a portion in plan view (XY plane) where the dielectric is made only of a first dielectric material with a low dielectric constant, and portions other than the tips of the convex portions overlap with the portion made only of the first dielectric material. Because barrier discharge is unlikely to occur in this portion, the generation of weak plasma that does not contribute to the generation of a strong induced flow is suppressed, making it possible to achieve both the generation of a strong induced flow and reduced power consumption.

[0021] In the present invention, "plasma resistance" refers to the resistance to loss of insulating performance due to thermal decomposition or melting caused by heat when exposed to discharge. Generally, the stronger the bonding strength of the molecules constituting the dielectric material and the harder the dielectric material, the higher the plasma resistance. Table 1 shows examples of plasma resistance of resin materials according to the ASTM D495 test.

[0022] [Table 1]

[0023] The dielectric material can be a resin substrate containing a glass material or a ceramic material. The resin used as the first dielectric material constituting the resin substrate can be, for example, a fluororesin such as PTFE, PFA, FEP, or PCTFE.

[0024] The glass or ceramic material used as the second dielectric material may be glass or ceramic beads embedded in positions that overlap the tips of the convex portions of the upper electrode, as shown in Figure 3, but plain woven glass cloth is preferably used because it improves the strength of the dielectric.

[0025] Plain weave is a weaving method in which warp and weft threads cross each other alternately, and even though the fabric is thin, it is strong because there are many points where the threads cross.

[0026] As shown in Figure 4, when the intersection of the warp and weft threads of the glass cloth overlaps with the tip of the convex portion of the upper electrode, not only is the resistance to plasma etching improved, but the ratio of the second dielectric material to the first dielectric material is higher at the intersection, increasing the dielectric constant at the intersection, allowing the plasma to travel straight toward the intersection.

[0027] The upstream electrode may have different numbers of protrusions and different protruding lengths depending on the location where the induced flow is to be generated and the strength of the induced flow to be generated, but it is preferable that the upstream electrode be a sawtooth electrode with multiple protrusions of uniform protruding lengths.

[0028] When the protruding lengths of the convex portions of the upstream electrode are uniform, the distance between the tips of the convex portions and the downstream electrode becomes the same, generating a strong and uniform plasma.This, combined with the fact that the tips of the convex portions overlap with the areas containing the second dielectric material and the plasma advances in a straight line in the same direction, can generate a strong induced flow.

[0029] Furthermore, if the protruding lengths of the convex portions of the upstream electrode are uniform, as shown in Figure 4, by aligning the tips of the convex portions of the upstream electrode with the warp yarns extending in the Y direction of the plain weave glass cloth, the tips of the convex portions of the upstream electrode can be easily overlapped with the portion of the dielectric containing the second dielectric material regardless of the spacing of the weft yarns extending in the X direction, making it easy to control the positioning.

[0030] The spacing between the convex portions of the upstream electrode is preferably 0.1 mm to 1 mm, which increases the number of locations where the electric field is concentrated and strong plasma is generated, thereby generating a strong induced flow.

[0031] Furthermore, if the protrusions on the upper electrode are spaced at equal intervals and the intervals are a natural number multiple of the intervals between the warp threads or weft threads of the glass cloth, the period of the protrusions will match the period of the glass cloth, and discharge will occur equally from each protrusion, generating plasma in a balanced manner, thereby generating a strong induced flow.

[0032] As shown in FIG. 5, the upstream electrode may further have small convex portions between the convex portions, the small convex portions having a protruding length shorter than the convex portions.

[0033] By having the small convex portion, when the tip of the convex portion becomes dirty or deteriorated due to the etched first dielectric material or the like, making it difficult to discharge, discharge can occur from the small convex portion instead of the convex portion, generating plasma, and the device can be used for a long period of time. [Explanation of symbols]

[0034] 1 Dielectric 11 First dielectric material (resin) 12 Second dielectric material (glass) 2 Upstream electrode 21 Convex part 22 Small convex part 3 Downstream electrode 4 AC power supply 5 Induced flow

Claims

1. a plate-shaped dielectric; an upstream electrode disposed on one surface of the dielectric; a downstream electrode disposed on the other surface of or inside the dielectric body, a plasma actuator in which the upstream electrode and the downstream electrode are arranged in an offset manner, the upstream electrode has a protrusion protruding toward the downstream electrode in an in-plane direction of the dielectric, the dielectric is formed of two types of dielectric materials, namely, a first dielectric material and a second dielectric material having a higher dielectric constant and plasma resistance than the first dielectric material, and has, in plan view, a portion including the second dielectric material and a portion including only the first dielectric material; A plasma actuator characterized in that the portion overlapping the tip of the convex portion is a portion containing the second dielectric material.

2. 2. The plasma actuator according to claim 1, wherein the dielectric is a resin substrate containing a glass material.

3. 3. The plasma actuator according to claim 2, wherein the second dielectric material is a plain woven glass cloth.

4. 4. The plasma actuator according to claim 3, wherein the tip of the convex portion overlaps with a point where the warp and weft of the glass cloth intersect.

5. the upstream electrode has a plurality of the protrusions, 2. The plasma actuator according to claim 1, wherein the plurality of protrusions have the same protruding length.

6. 6. The plasma actuator according to claim 5, wherein the interval between the projections is 0.1 mm or more and 1 mm or less.

7. 7. The plasma actuator according to claim 6, wherein the upper electrode has protrusions spaced at equal intervals.

8. 8. The plasma actuator according to claim 7, wherein the upstream electrode further includes a small protrusion between the adjacent protrusions, the small protrusion having a protruding length shorter than that of the adjacent protrusions.

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