Naoya Iwata

Evaluation of Response Time in Ball Surface-Acoustic-Wave Hydrogen Sensor using Digital Quadrature Detector

Hydrogen leak detection sensors must have high sensitivity and a short response time of 1 s or less. A ball surface-acoustic-wave (SAW) hydrogen sensor has a high sensitivity and can detect hydrogen in a very wide concentration range of 10 ppm to 100%. Moreover, a fast response can be expected because of the very thin sensitive film used. In this study, we developed a digital quadrature detector (DQD) to measure responses of less than 1 s, and measure phases in 1 ms intervals with excellent sensitivity. We evaluated the response time of the ball SAW hydrogen sensor where the signal was averaged 256 times in 0.256 s using the DQD. As a result, the response time was found to be 1 s or less for 3.0 vol % hydrogen gas in nitrogen.

Development of Microseparation Column for Ball Surface Acoustic Wave Gas Chromatograph

For the safety and security of a society, ubiquitous multiple-gas sensors are required. The gas chromatograph (GC) based on the separation of gases according to the elution time is frequently used for multiple-gas sensing, but it is not portable. In this situation, we have developed a ball surface acoustic wave (SAW) sensor, where SAW on a sphere with a specific width is naturally collimated and makes multiple roundtrips without diffusing by diffraction. In this study, in order to develop a portable GC, we developed a gas separation column using micro-electro-mechanical-system (MEMS) technology and evaluated it, combining it with a ball SAW sensor.

Analysis of ball surface acoustic wave sensor response to wide variety of gases using gas chromatography

It is necessary to detect a wide variety of dangerous gases for environment assessment and security. Gas chromatography using a gas separation column has been used for this purpose; however, a compact and high-performance system has not yet been established. Thus, we propose a new approach to measure gases using a ball surface acoustic wave (SAW) sensor, after separating them using gas separation columns. In this work, amplitude responses were observed for mixed alcohol gases. With water–ethanol mixed gas, both delay time and amplitude responses were observed, and different response and recovery times were found for these responses. Also, an amplitude response reflecting the leaky loss of SAW was observed and an approximate equation of leaky loss was derived to quantitatively evaluate the roles of leaky loss and other parameters observed in the ball SAW sensor. These results suggest that the proposed approach is promising for developing compact and high-performance multigas sensors.

One-Millimeter Diameter Harmonic Ball Surface Acoustic Wave Gas Sensor with Temperature Compensation by Itself

A newly designed 1-mm diameter harmonic ball surface acoustic wave (SAW) gas sensor has a double-electrode interdigital transducer (IDT) for driving multiple frequencies. The fundamental frequency is 80 MHz. The difference in delay time between a fundamental frequency component and a high harmonics was used to compensate temperature drift. A temperature coefficient of about 0.1 ppm/°C was obtained after compensation.

Acoustic dispersion in a ball-shaped surface acoustic wave device

Theoretical model for ball surface acoustic wave (SAW) sensors has been developed. Wave front distortion encountered in planar SAW sensors caused by diffraction or reflection can be neglected because of the diffraction-free propagation of a naturally collimated beam. Wave form at each turn is expressed by an integral of terms defined by the array factor and the elementary charge density of electrodes as well as the frequency-dependent velocity and attenuation caused by the sensitive film. Irrespective of the significant simplicity of the theory, excellent agreement has been observed between the simulated and experimental wave forms of a double-electrode ball SAW sensor.

2E-4 Temperature Compensation Method of phi 1mm Ball SAW Gas Sensor Using Harmonics

Newly designed phi 1 mm ball SAW device with a double electrode IDT has a fundamental frequency of 80[MHz], third and fifth harmonics. A difference of the delay time between the fundamental frequency component and a higher harmonic was used to compensate the temperature drift. A temperature coefficient of about 1[ppm/degC ] was obtained after compensation.

Ball Surface Acoustic Wave Hydrogen Sensor with Widest Sensing Range and Fast Response

SAW(surface acoustic wave) excited on a spherical surface under a specific condition is naturally collimated, realizing ultra-multiple roundtrips along an equator of the sphere. The ball SAW hydrogen gas sensor is based on this newly discovered phenomenon, and uses a very thin Pd-Ni alloy sensitive film. The detection range for hydrogen gas was 10 ppm to 100% and the response time was less than Is for 3.0% hydrogen concentration in nitrogen gas, evaluated by using a newly developed digital quadrature detector (DQD).