Showko Shiokawa

New Sensor in Liquid Using Leaky SAW

Utilizing a shear horizontal displacement of a leaky SAW mode, SAW sensors to be used in liquid can be realized. Theoretical and experimental works showed that 36O-rotated Y-cut X-propagation LiTaOj is a promising substrate for a biosensor and a viscosity sensor.

Development of novel atomization system based on SAW streaming

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.

Liquid streaming and droplet formation caused by leaky Rayleigh waves

Various liquid motions such as streaming and droplet formation have been observed when a liquid was put on the surface of a SAW (surface acoustic wave) propagation substrate. Results of experimental and theoretical studies on these so-called SAW streaming phenomena are presented. Surface treatment of the SAW substrate by metallization and by silanization is employed to demonstrate that the liquid motion is strongly influenced by the chemical condition of the substrate surface. Experiments using 128 degrees rotated Y-X LiNbO/sub 3/ at 50 MHz with various pulse widths are described. In a hydrophilic case, such as an Al-deposited metal surface, the pattern of the SAW power flow can be observed. This indicates that one can quickly visualize the SAW radiation by merely putting a small volume of liquid on the surface. If the substrate surface is hydrophobic, small droplets are ejected from the water surface. Using this phenomenon makes it possible to develop new fluid devices. Theoretically, the SAW streaming force can be derived using the theory of acoustic streaming. The calculated SAW streaming force is found to be very large and strong enough to expel the droplet from the liquid surface.<<ETX>>

Experimental Study on Liquid Streaming by SAW

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.

Surface Acoustic Wave Sensors

Acoustic wave sensors are highly sensitive in detecting the properties of solid or fluid materials in contact with their surfaces, including the surface mass change, liquid density, liquid viscosity and electrical conductivity. In this paper, primarily, the commonly used acoustic wave sensors are reviewed and their mass sensitivities are compared. The fundamentals of the sensing system using the shear horizontal surface acoustic wave (SH-SAW) sensor on a 36° rotated Y-cut X-propagating LiTaO3 are described. Since the high sensitivity of the electrical perturbation is a significant advantage of the SH-SAW sensor, its applications based on acoustoelectric interaction are also presented.

Simultaneous Measurements of Liquid Properties Using Multichannel Shear Horizontal Surface Acoustic Wave Microsensor

Surface acoustic waves (SAW) with a shear horizontal polarized displacement (SH-SAW) can be used to determine mechanical and electrical properties of an adjacent liquid. We propose a new multichannel SH-SAW microsensor for liquid characterization. The SH-SAW microsensor, which is fabricated on 36° rotated Y-cut X-propagating LiTaO 3 , consists of three SAW delay lines. The propagating surfaces of two of the delay lines are metallized and electrically shorted, and the other one has a free surface which is an electrically active area. The viscosity, conductivity and permittivity of liquid are obtained simultaneously using the multichannel SH-SAW microsensor.

Design of SAW Sensor in Liquid

A SAW sensor in a liquid medium utilizing a leaky SAW mode having a shear horizontal displacement has been studied, and the device sensitivities have been investigated both theoretically and experimentally. Sensors of liquid viscosity and mass loading have been demonstrated utilizing the present mode on 36° rotated Y-cut X-propagation LiTaO3.

Study on SAW Streaming and its Application to Fluid Devices

Various liquid motions such as streaming and droplet formation on the surface of SAW propagation substrate are called SAW streaming. Experiments on SAW streaming using 128° rot.Y–X LiNbO3 at the frequency of 50 MHz with various pulse widths are described. Surface treatment of SAW substrate by silanization is employed to demonstrate the droplet ejection. Theoretically, SAW streaming force can be derived using the acoustic streaming theory. The calculated SAW streaming force is found to be very large and strong enough to expel a droplet from a liquid surface.

Simulation of Viscoelastic Effects of Polymer Coatings on Surface Acoustic Wave Gas Sensor under Consideration of Film Thickness

In this paper an analysis of the responses of surface acoustic wave (SAW) sensors coated with polymer films is described. Complex bulk and shear moduli are utilized to represent viscoelastic properties of the polymer. Compared with the experimental results, the calculated results strongly suggest that the real part of the shear modulus mostly influences the velocity shift and attenuation change in the sensor responses. In addition, using the real parts of the shear modulus, the polymer films can be classified into three types: glassy films, glassy-rubbery films and rubbery films. Simulations of gas sorption for polymer films are performed. For glassy films, the SAW sensor response increases with increasing film thickness, whereas for glassy-rubbery and rubbery films, the relationship between the sensor sensitivity and film thickness is more complicated. Therefore, an optimization of the properties and thickness of films and the operating frequency is required for designing SAW gas sensors with polymer coatings.

New Biosensor Using Shear Horizontal Surface Acoustic Wave Device

This paper describes a new biosensor to detect an enzyme reaction in liquid using surface acoustic wave (SAW) devices fabricated on 36°-rotated Y-cut, X-propagating LiTaO3. The sensing wave on the substrate is a predominantly shear-horizontal-mode SAW (SH-SAW) and is affected by a strong acoustoelectric interaction between the piezoelectric potential and electrical properties of the materials in the adjacent liquid. As an example of an electrical property, pH change associated with an enzyme reaction leads to measurable perturbation in the wave-propagation characteristic. Taking advantage of this phenomenon we realized a SAW biosensor which consists of an immobilized urease membrane on the surface. Also, highly sensitive detection for the urea solution was obtained in our preliminary experiments.