Jun Kondoh

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.

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.

Study of Surface Acoustic Wave Streaming Phenomenon Based on Temperature Measurement and Observation of Streaming in Liquids

A longitudinal wave is radiated into a liquid when the liquid is placed on a surface acoustic wave (SAW) propagating surface. The radiated longitudinal wave induces liquid dynamics, such as vibrating and streaming. This phenomenon is called SAW streaming. The liquids temperature increases, as the radiated longitudinal wave becomes attenuated inside the liquid. In this paper, the measurement and observation results of temperature and streaming in liquids are described. First, the sol–gel formation of agar–agar is observed. Second, a highly viscous liquid droplet is placed on the SAW propagation surface. However, the stable measurements are difficult. Therefore, a U-type cell is developed and the pattern of the streaming in this cell is observed. The results show that there is an association between the attenuation of a longitudinal wave and the temperature distribution.

Development of a Shear Horizontal Surface Acoustic Wave Sensor System for Liquids with a Floating Electrode Unidirectional Transducer

The development of sensors using surface acoustic wave (SAW) devices has been attracting attention. A shear horizontal SAW (SH-SAW) sensor can detect the properties and chemical reactions in liquids. To realize practical applications of the SAW sensor, it is necessary to discuss its properties. In this paper, SH-SAW sensors with a floating electrode unidirectional transducer (FEUDT) or an interdigital transducer (IDT) are compared and the insertion loss and phase characteristics are measured. Also, the phase shift between sample and reference liquids is evaluated. The results indicate that the SH-SAW sensor with the FEUDT is suitable for liquid measurements. The SH-SAW sensor with the FEUDT is then mounted in a newly developed SH-SAW sensing system. The system configuration is the same as that of a vector voltmeter measurement system. However, circuits have been developed that reduce its size. Using this system, several liquids are measured. The obtained results agree well with the theoretical values.

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.

Fundamental characteristics of a dual-colour fibre optic SPR sensor

In this paper, we present the fundamental characteristics of a novel dual-colour optical fibre surface plasmon resonance (SPR) sensor for a portable low-cost sensing system. The principle of the proposed SPR sensor is based on the differential reflectance method. Light from two light-emitting diodes (LEDs), which are flashing alternately with different wavelengths, is fed to a sensor via two optical couplers. The reflected light is detected by a photodiode. Changes of reflectance at two wavelengths are proportional to the refractive index change of the medium of interest. Taking the difference in reflectance at two wavelengths improves the sensitivity almost twofold. Measuring ethanol solutions with different refractive indices reveals that the sensor has a linear response to the refractive index change from 1.333 to 1.3616. By measuring the stability in the time response we estimate that the limit of detection (LOD) of the refractive index is 5.2 × 10−4.

Development of practical surface acoustic wave liquid sensing system and its application for measurement of Japanese tea

In this paper, we report on the development of a practical compact and stable sensing system with a shear horizontal surface acoustic wave (SH-SAW) sensor for liquid. First, the oscillation circuits for the liquid-phase sensor based on the SH-SAW device is discussed. Two sensor outputs, i.e., frequency and amplitude, are required for evaluating the liquid properties. To monitor the amplitude, an automatic gain control amplifier (AGC amp) is utilized in the oscillation circuit. The developed sensing system has a low standard deviation of noise that is less than the temperature coefficient of the frequency of the dual SH-SAW sensor and from which the detection limit is estimated. The dynamic range of the developed SH-SAW sensing system is also estimated. The system is applied for the measurement of Japanese tea. The results indicate that the slight differences among teas can be detected by the SH-SAW liquid sensing system.

Deposition of Thin Film Using a Surface Acoustic Wave Device

When a Rayleigh surface acoustic wave (SAW) propagates at a liquid/solid interface, it radiates its energy into the adjacent liquid. If a liquid droplet is loaded on the SAW propagation surface, droplet vibration, streaming, jetting, and atomization are observed. These phenomena are called SAW streaming. In this paper, a novel thin-film deposition method based on the atomization of SAW streaming phenomena is proposed. The liquid with film material is loaded on the SAW propagation surface and the liquid is atomized. The atomization direction depends on the Rayleigh angle, which is determined by the sound velocity in the liquid and the SAW velocity. For easy fabrication of a thin uniform film, the atomization direction is controlled in the perpendicular direction. Using the developed system, the deposition of pigments in ink is carried out. The results observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicate that a pigment layer is formed on a glass plate.