A. Saitoh

Passive strain sensor using SH-SAW reflective delay line

A shear horizontal-mode surface acoustic wave (SH-SAW) has the unique characteristic of complete reflection at a free edge normal to the direction of propagation, making it possible to construct a reflective delay line. A passive SAW strain sensor based on such a reflective delay line is presented. The reflective delay line is constructed on a 36° YX LiTaO 3 substrate. The SH-SAW velocity is shown to provide a reliable measure of the strain of a propagation surface, and incorporation of an oscillator circuit is demonstrated to allow wireless remote monitoring of strain using this sensor.

Liquid sensing system based on two port SH-SAW resonator

A new liquid flow sensing system constructed with SH-SAW resonator was used to characterize liquid properties. Surface acoustic waves with the shear horizontal displacement (SH-SAW) have been used for sensing the properties in liquid phase. The SH-SAW resonator having two port was fabricated on a 36° rotated Y cut X prop. LiTaO3 (36YX LiTaO3) substrate. The flow of a sample liquid was precisely controlled by a liquid chromatography system. The transient responses were detected as sensor response by the two-port SAW resonator. The results showed a specific feature and are used to determine the liquid properties.

Mass Flow Sensor Using Dual SAW Device

The application of SAW devices to a thermometric mass flow rate meter with a reference channel for temperature compensation is presented. The sensor is composed of a delay line device with two channels, namely a reference channel that does not come in contact with the fluid and a sensing channel that makes contact with the fluid. The mass flow rate of gases can be obtained by measuring the temperature change of the device caused by drawing heat from the surface with constant temperature due to the fluid. The results obtained from flow rate measurements of several gases demonstrate that the proposed device is effective as a flow rate meter. Moreover, it is also shown that the response characteristics to mass flow rate changes and the response stability for fluids were improved by taking the phase difference between the signals of the reference channel and the sensing channel as the gas flow rate.

SAW sensor for liquid chromatography using 2-port resonator

The propagation characteristics of surface acoustic waves (SAW) along a solid surface vary considerably depending on the ambient environment. Therefore, SAW devices are used as sensors in a variety of fields. In particular, surface acoustic waves propagating in the shear horizontal (SH) mode only possess components for which particle displacements are parallel to the surface, which means that, even in a liquid, they propagate without loss of energy. Sensors that utilize such waves are thus suitable for sensing the characteristics of liquids. A flow-type liquid sensor using a 2-port SH-SAW resonator was constructed and used to measure properties, such as electrical characteristics, density and viscosity, of various liquids. Results of measurements using this liquid flow sensing system on a variety of liquids are presented. Finally, this sensing system is demonstrated to be an effective sensor in liquid chromatography, due to its small size, enabling measurement on a very small amount of liquid, and its highly stable operation.

Optimization of sensing film for quartz crystal microbalance odor sensor using self-assembly deposition method

We demonstrated a new self-assembly method using thiol compounds for making a sensing film with a desired specific response property, using the interaction between odor molecules and sensing film molecules due to their affinity. The sensing film was deposited self-assembly on a QCM with gold electrode in the mixed solution of sensing film materials and odor molecules. This method realizes easy fabrication of the sensor with a desired response property. In addition, we investigated response property of the sensor having a surface function group controlled sensing film by self-assembly method. In this experiment, amino group, hydroxyl group, and -CH/sub 3/ group were used for the function group. The results of a series of the sensor response measurement indicated the importance of the function groups on the sensing film surface and the necessity of controlling the surface.

Methanol sensor using a surface acoustic wave

The propagation characteristics of a surface acoustic wave (SAW) that travels along the surface of a solid object can vary significantly depending on the surrounding environment. SAW devices are employed in sensors that measure many different kinds of environments and their changes. This paper discusses a SAW sensor used to measure the concentration of methanol, a fuel required by methanol fuel cells. The permittivity of methanol exhibits significant variation depending on the concentration and the temperature. Two SAW resonators were used to measure the permittivity of a liquid; one with the cavity surface as an electrically open circuit, and the other short-circuited. Two resonating systems were constructed from an amplifier and a SAW resonator, and fluid was allowed to run through the cavities of the two resonators to measure the difference in the oscillation frequency. This difference in frequency changed in proportion to the permittivity of the liquid, so that its concentration could be measured. It was also experimentally demonstrated that the use of SAW resonators can stabilize measurements and improve reproducibility. A sensing system made of liquid flow cells and SAW sensors was then proposed. The proposed system is able to measure the real time concentration of methanol independently of the temperature and with good reproducibility.

Surface acoustic wave vapor sensor using ultrathin multilayer films

A surface acoustic wave (SAW) sensor incorporating an ultrathin selective film is presented. The ultrathin films were made by both self-assembled (SA) method and by Langmuir-Blodgett (LB) method. SAW delay lines coated with SA film and LB film has been used as vapor sensor. Rapid and totally reversible sensor responses were obtained by using the thin monolayer film.

Surface acoustic wave gas phase sensor using self-assembled monolayer film

A surface acoustic wave (SAW) sensor for measuring environment is presented. SAW devices respond to changes in the mass on its surface with a shift in frequency, and offer many attractive features for applications as a gas and liquid phase sensor. In the most gas phase sensor, the device surface is coated with a thin selective film. In this paper a SAW delay line coated with self-assembled (SA) film has been used as environment sensor. A dual delay line was fabricated on a single lithium niobate (128/spl deg/ Y cut X propagating LiNbO/sub 3/) substrate and the propagation path was coated with the selective polymer film deposited by SA transfer technique. The polystyrene sulfonic acid sodium was used as a gas sensing material. Due to sorption of molecules, the electrical conductivity of the SA film changes. The effects caused to reduce the velocity of the SAW. Experimental results showed that the SAW velocity change was quite linear in proportion to the concentration of organic gases. Rapid and totally reversible responses were obtained by using a SA monolayer film.

Multi-channel chemical sensor using surface acoustic wave device

Multi-channel SAW chemical sensor is used as an analytical system for organic gas detection. SAW sensors show a high frequency property, and can become multi-channel devices on a substrate. The features improve sensor sensitivity and enable integration of the sensor. In this paper, we propose a new chemical sensor system using multi-channel SAW devices. A four channel SAW delay line was designed and fabricated on one piezoelectric substrate. Each channel was coated by a different selective organic film and the output of each channel was used to make a response pattern. The response to odorant solvents showed different analyte specific patterns.