JP2013099734A - Surface acoustic wave liquid spray device having directivity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid spray device using a surface acoustic wave in which the directivity of the spray is improved.SOLUTION: Though the atomization of the liquid using the surface acoustic wave is characterized by miniaturizing a device and saving energy, the generated mist is non-directional and atomized with large scattering. On the basis of the fact, a groove is formed between opposed type surface acoustic wave elements to separate the opposed surface acoustic waves and thereby, the width of the generated atomization flow is remarkably reduced to give directivity.

Description

The present invention relates to a droplet atomization spray device, and more particularly to a spray device using a surface acoustic wave element.

Known devices for spraying liquid in fine particles include a device for spraying from a nozzle using pressure energy, and a device for spraying by the action of ultrasonic waves by vibrating a piezoelectric element.

Among them, an apparatus has been developed in which a comb electrode is arranged on a piezoelectric body, a surface acoustic wave is driven by applying a high-frequency voltage, and an ultrasonic wave is applied to a liquid to spray it. In comparison, it is expected to reduce costs by making it small, energy-saving, and using a semiconductor process. (For example, Non-Patent Document 1)

Conventional atomizers using surface acoustic waves are intended to generate a large amount of uniform mist, and it has been reported that a liquid holding mechanism is provided so that mist can be stably and continuously supplied. For example, Patent Document 1 describes a sprayer in which a porous water retention material is disposed on a piezoelectric substrate. Patent Document 2 describes a sprayer that holds a liquid in a hole arranged on a substrate.

Furthermore, in Patent Document 3, by using a counter-type comb-tooth electrode, the liquid can be held in the central portion between the electrodes without having a special holding mechanism due to the action of the surface acoustic wave propagating oppositely. Have been described.

JP2011-112050 JP 7-116574 A Patent Publication 2008-238058 Qi et. al. Physics of Fluids, Vol. 20,074103 (2008)

However, in any case, the generated mist is greatly scattered from the liquid holding part and does not have a function of controlling the direction of the generated mist.

An object of the present invention is to generate a spray flow that has a simple structure and is greatly scattered in a conventional surface acoustic wave sprayer so as to converge in one direction.

Opposite comb electrodes drive the surface acoustic waves facing each other and act on the liquid droplets arranged in the center to generate acoustic flows due to leaky surface acoustic waves in the droplets. If it is large, the atomized liquid is sprayed from the droplet surface.

The acoustic flow driven by the leaky surface acoustic wave has an inclination from the vertical direction of the substrate surface to the traveling direction of the surface acoustic wave, and its angle is determined by the propagation speed of the surface acoustic wave and the speed of sound in the liquid, and is called the Rayleigh angle ( (See FIG. 2). For example, the Rayleigh angle is about 22 degrees for a combination of 128-degree rotated Y-plate X-propagating lithium niobate substrate and water.

When surface acoustic waves are incident on the liquid from one direction, the acoustic flow generated in the liquid is generated along the direction of the Rayleigh angle, so that the sprayed mist is also generated around this direction. In other words, it has a considerable directivity in the same direction as the surface acoustic wave traveling direction.

[0006] Even when an opposing comb electrode is used as described in [0006], an acoustic flow having an opposing Rayleigh angle is generated in the liquid between the electrodes, and the generated spray flow is shown in FIG. Scattered greatly as shown.

According to the first aspect of the present invention, a discontinuous surface that inhibits the propagation of surface acoustic waves is disposed between the opposing comb electrodes, and the opposing acoustic streams act independently on the droplets to generate the generated spray. It is to give directionality to the flow.

In the invention of claim 2, by providing a groove between the opposing comb electrodes, the propagation of the opposing surface acoustic wave is inhibited, and as shown in FIG. Only an acoustic stream having a vector directed upward in the center is generated, and the generated spray stream is converged in the vertical direction of the droplet center.

The invention of claim 3 is to impart directivity to the resulting spray flow by controlling the voltage applied to the opposing comb electrodes. For example, in FIG. 2B, when the voltage applied to the right comb electrode is stronger than the left comb electrode, the resultant vector of the acoustic flow generated in the droplet is tilted to the left from the vertical direction of the droplet center. Therefore, the generated spray flow can also be generated in the left direction from the vertical.

According to the present invention, a fine spray flow can be controlled and generated in a desired direction without using a mechanical movable part.

The perspective view explaining the composition concept of the surface acoustic wave spraying device concerning the embodiment of the present invention. The fragmentary sectional view explaining the convergence of the spray flow in a surface acoustic wave spray apparatus same as the above. The graph of the change of the surface acoustic wave transmission coefficient and the reflection coefficient depending on the groove depth in the surface acoustic wave spraying apparatus. The photograph which shows that a spray flow is actually converged using the surface acoustic wave spray apparatus same as the above.

Embodiments of a surface acoustic wave liquid spraying apparatus according to the present invention will be described below with reference to the accompanying drawings.

The configuration of one embodiment of a surface acoustic wave liquid spraying apparatus according to the present invention is shown in FIG. The liquid spraying device 1 includes a piezoelectric 128-degree rotated Y-plate X-propagating lithium niobate substrate 2, opposing comb-shaped electrodes 3 formed of aluminum on the substrate, and grooves on the substrate between the opposing comb-shaped electrodes. 4. It has the droplet 5 and the high frequency alternating current power supply 6 which were distribute | arranged on the groove | channel.

When an AC voltage having a resonance frequency determined by the comb electrode interval is applied to the comb electrode 3 by the high frequency AC power source 6, a surface acoustic wave is driven on the substrate. In this embodiment, since the comb frequency is 0.1 mm and the resonance frequency is 19.9 MHz, a sine wave having a frequency of 19.9 MHz and an amplitude of about 100 Vpp is applied by the high-frequency AC power supply 6.

The transmission coefficient and reflection coefficient of the generated surface acoustic wave vary depending on the presence / absence and depth of the groove 4 on the substrate as shown in FIG. When the depth of the groove is deeper than one wavelength of the surface acoustic wave of 200 μm, the transmission coefficient is 0.1 or less, which is about 1/5 of the case where there is no groove.

This means that, as shown in FIG. 2, the acoustic flow having opposing vectors driven by opposing surface acoustic waves is separated on both sides of the groove, thereby A vector is formed and the spray flow generated on the droplet surface is also converged in the direction of this vector, i.e. upward from the groove.

By forming the groove from the photograph of the spray flow formed when there is no groove (FIG. 4 (a)) and when the groove depth is 136 μm (FIG. 4 (b)) shown in FIG. It can be seen that the width of can be reduced from 3 mm to 0.8 mm.

In this embodiment, a 128-degree rotated Y-plate X-propagating lithium niobate substrate is used as the piezoelectric substrate, but the same applies to piezoelectric substrates that drive Rayleigh waves, such as lithium tantalate and quartz.

In addition to the aluminum of this embodiment, for example, the material for forming the comb-teeth electrode can have the same function as long as it is a conductive substance such as gold or copper.

DESCRIPTION OF SYMBOLS 1 Surface acoustic wave spraying device 2 Piezoelectric substrate 3 Comb electrode 4 Groove 5 Droplet 6 High frequency power supply 7 Rayleigh angle

Claims (3)

In a droplet spraying apparatus that includes a piezoelectric substrate having piezoelectric characteristics and a comb electrode fabricated on the substrate, and generates a surface acoustic wave to atomize and spray droplets on the substrate, the comb electrode includes: A droplet spraying device that is arranged so as to face each other with a droplet interposed therebetween and has a discontinuous surface that inhibits surface acoustic wave propagation in the middle thereof. By disposing a groove between the opposed comb electrodes, an opposing acoustic flow generated in the droplet by the surface acoustic waves facing each other is generated separately on both sides of the groove, thereby generating a spray flow generated from the droplet. The droplet spraying apparatus according to claim 1, wherein the spraying width of the droplets is greatly reduced. 3. The spray flow generated from the liquid droplets has directivity by controlling the voltage applied to the opposed comb electrodes and changing the intensity of the opposing acoustic flow generated in the liquid droplets. The droplet spraying apparatus described in 1.