Mitsunori Sugimoto

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.

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.

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.

Measurements of Standard-Viscosity Liquids Using Shear Horizontal Surface Acoustic Wave Sensors

A shear horizontal surface acoustic wave (SH-SAW) sensor can be used to detect the properties of liquids. We propose one application of the SH-SAW sensor as a viscosity sensor. The Japanese Industrial Standards Committee (JISC) has determined the standard liquids used to calibrate a viscometer. If the SH-SAW sensor is to be commercialized, it is necessary that the viscosities of these liquid can be measured. In this study, the standard-viscosity liquids are measured using the SH-SAW sensor operating at different frequencies. The sensor responses to the standard-viscosity liquids are less than those for a glycerol/water mixture. This is due to the viscoelasticity of the standard-viscosity liquids. A simple viscoelastic model is applied to explain the experimental results.

Development of SAW thermocycler for small liquid droplets

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 liquid heating phenomenon is discussed. 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. Finally, 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.

Development of a dual-color optical fiber SPR sensor

This paper presents a dual-color optical fiber surface plasmon resonance (SPR) sensor for a portable and low cost sensing system with high resolution. Principle of the proposed SPR sensor is based on the differential reflectance method. Light from two light emitting diodes (LEDs), which are alternately flashed with a constant cycle, is fed to a sensing part 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 a sensed medium. Taking the difference of reflectance at these two wavelengths makes the sensitivity almost twice. Measuring ethanol solutions with different refractive indices reveals that this sensor responds to the refractive index change linearly over the range of from 1.333 to 1.3616. From the noise analysis of the output signal of the sensor, the limit of detection (LOD) of the refractive index is estimated to be 5.2 times 10-4

A novel integrated system of sensor and actuator for droplets on sensor plate/matching layer/piezoelectric substrate structure

With the continuing development of biotechnology and nanotechnology, a miniaturized and integrated device that is capable of controlling and measuring a small droplet has become desirable. Using a surface acoustic wave (SAW), a droplet is manipulated. If the sensor is fabricated onto the SAW propagating surface, a novel sensor and actuator integrated system, namely digital microfluidic system, is realized. The integrated device is called a “micro-laboratory.” In this paper, to actualize a disposable micro-laboratory, three-layer structure of sensor plate/ matching layer/ piezoelectric substrate is examined. Droplet manipulation, mixing and measurement are succeeded using the proposed novel micro-laboratory.

Refractive Index Measurement of Liquids Using A Dual-color Optical Fiber SPR Sensing System

In this paper we present practical capability of a dual-color optical fiber surface plasmon resonance (SPR) sensing system for measuring the refractive index (RI) of liquids. The sensor system consists of two LEDs, two optical couplers, a photodiode and an electronics followed by a laptop computer via an A/D converter. Features of the developed system are compact, portable and inexpensive. Principle of the proposed SPR sensing system is based on the differential reflectance method. Changes of reflectance at two wavelengths are proportional to the refractive index change of a sensed medium. Differential of two reflectance gives two-folded sensitivity. Three liquids with different RI ranges were tested. Also the reproducibility of measured data was checked. As a result, it was demonstrated experimentally that the dual-color optical fiber SPR sensing system is capable of measuring the RI of liquids over the range of from 1.329 to 1.36 with the RI resolution of 2.35 X 10-4.

Temperature-control system for small droplet using surface acoustic wave device

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. 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, 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