|Budget Amount *help
¥7,200,000 (Direct Cost: ¥7,200,000)
Fiscal Year 2002: ¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 2001: ¥5,300,000 (Direct Cost: ¥5,300,000)
A solid electrolyte CO_2 sensor, nondispersive infrared (NDIR) CO_2 sensor, liquid electrolyte CO sensor, phthalocyanine-film NO_2 sensor, and their signal processing interfaces are developed for atmospheric air quality assessment. The solid electrolyte CO_2 sensor developed consists of the detection, reference, and base electrodes screen-printed on the sodium super ion conductor (Nasicon). The durability of the Nasicon sensor is greatly improved by using such non-aqueous carbonates as LiCO_2 and CaCO_3. The drift mechanism has also been exploited by impedance measurements and the correlation between the voltages appeared at the detection and base electrodes. From these measurements, an electrical equivalent circuit including the electromotive force and drift voltage has successfully been derived to design its signal processing circuit.
The NDIR CO_2 sensor is composed of one IR source and two IR detectors. To split the IR beam into the two detectors, a silicon wafer is used. The signal
processing interface is also developed which accommodates the algorithm to cancel the temperature dependence of the IR detectors and the aging effect of the IR source. With these configurations, a high resolution and low temperature dependence quite satisfactory for practical applications are achieved.
The liquid electrolyte CO sensor consists of the working, counter, and reference electrodes immersed in an electrolyte H_2SO_4. To characterize this amperometric sensor, the interface circuit is developed which allows simultaneous measurements of the gas sensitivity and impedance while keeping the voltage across the working and reference electrodes constant. The characterization has revealed the linear relation between the gas sensitivity and the impedance which is available for in-situ calibration of the sensitivity.
As NO_2 gas sensors, substituted copper- and aluminumfluaro- (AIFPc) phthalocyanine thin films are synthesized and their performances are evaluated. Among such thin-film sensors, mono-methyl substituted AIFPc is found to have a high-sensitivity at low NO_2 concentration below 1 ppm and an excellent reproducibility. Less