No abstract

In this paper, we describe a novel atomization system using surface acoustic wave (SAW) devices. The SAW radiates its energy into a liquid, if the liquid is loaded on the SAW propagating surface. The various liquid motions, such as vibration, flow and droplet formation, due to interaction between SAW and liquid are called SAW streaming. The liquid dynamics depends on the SAW input power. First, the relationships between input voltage to the SAW device and water dynamics are observed. For atomization, an input voltage larger than 30 VP-P is required. Second, a stable method of generating a mist is discussed. The thin liquid layer plays an important role in continuous mist generation. The fundamental properties, such as the angle and height of mist, are measured using a filter paper to keep a thin liquid layer on the surface. We also demonstrate the control of mist direction with an electrostatic field. Based on these fundamental experiments, a practical atomization system is designed and performed.

In this paper, we present a liquid-droplet-heating system using a surface acoustic wave (SAW) device. When liquid is placed on a Rayleigh-SAW-propagating surface, a longitudinal wave is radiated into the liquid. If the SAW amplitude increases, the liquid shows nonlinear dynamics, such as vibrating, streaming, small droplet flying, and atomizing. This phenomenon is well known as SAW streaming. The liquid temperature is measured during the longitudinal wave radiation and found to increase. First, the mechanism of the liquid heating effect is discussed on the basis of experimental results. The surface electrical condition is changed to investigate the effect of dielectric heating. The obtained results indicate that the radiated longitudinal wave causes liquid heating and the dielectric heating effect does not. Second, the fundamental properties of the liquid temperature are measured by varying the applied voltage, duty factor, and liquid viscosity. The liquid temperature is found to be proportional to the duty factor and the square of the applied voltage. Therefore, the liquid temperature can be controlled by these applied signals. Also, by using highly viscous solutions, the liquid temperature is increased to more than 100 ˚C. Moreover, for chemical applications, the possibility of periodic temperature control is tested by varying the duty factor. The obtained results strongly suggest that an efficient thermal cycler is realized. A novel application of the SAW device is proposed on the basis of SAW streaming.

Water streaming on the surface of SAW propagating substrate is called SAW streaming. The mechanism of ultrasonic radiation into water due to mode conversion from SAW and the acoustic streaming caused by the sound waves are discussed. The SAW streaming pattern is observed on a metallized surface of SAW propagation. Fundamental experiments for the application of SAW streaming to fluid devices are carried out, and fluid pump and guide are demonstrated.

sented. It is found that the SAW streaming depends on the SAW power, frequency, pulse Various liquid motions such as width, the liquid volume and surface chemstreaming and droplet formation have been ical conditions of the substrate surface. observed when a liquid was put on the If the surface is hydrophobic, liquid surface of SAW propagation substrate. In droplets are effectively ejected from the this report we call these phenomena "SAW surface into the air at an oblique angle. streaming" and experimental and theoreti-Under the proper condition, very fine fogs cal studies are presented. Surface treat-are produced. ment of SAW substrate by metalization and Theoretically, a general differential by silanization is employed to demonstrate equation of second order which is used for that the liquid motion is strongly influ-the acoustic streaming theory3) is develenced by the chemical condition of the oped. It is shown that the calculated substrate surface. Experiments using 128' force of SAW streaming due to leaky rot. Y-X LiNb03 at the frequency of 50 MHz Rayleigh wave is much greater than that of with various pulse width are described.acoustic streaming due to general attenu-Theoretically, SAW streaming force ated plane traveling waves in bulk liquid. can be derived using the acoustic streaming theory. The calculated SAW streaming force is found to be very large and strong enough to expel the droplet from the liquid surface.0090-5607/89/0000-0643 $1 .OO 0 1989 IEEE