We have prepared nanocomposites of polymers and platelet CMK-5-like carbon and have demonstrated their superior performance for gravimetric gas detection. The zirconium-containing platelet SBA-15 was used as hard template to prepare CMK-5-like carbon, which was then applied as a lightweight and high-surface-area scaffold for the growth of polymers by radical polymerization. Mesoporous nanocomposites composed of four different polymers were used as sensing materials for surface acoustic wave devices to detect ppm-level ammonia gas. The sensors showed much better sensitivity and reversibility than those coated with dense polymer films, and the sensor array could still generate a characteristic pattern for the analyte with a concentration of 16 ppm. The results show that the nanocomposite sensing materials are promising for highly sensitive gravimetric-type electronic nose applications.

A surface acoustic wave (SAW) sensor array was developed for sensing amino gas. Poly-N-vinylpyrrolidone (PNVP) composite film as a sensitive interface material was deposited onto a 128° YX-LiNbO 3 substrate by the spin coating technique. Moreover, we have developed an improved portable electronic noise based on a 2x2 non-continuously working oscillators equipped with coated SAW sensor array. This gas sensor array system consists of SAW sensors, polymers with different polarity of function groups, signal readout electronics with quick connector, miniature sensing chamber made by acrylic, and aluminum plates. The adsorption of amino gas by the sensitive coating material modulates the phase velocity of the acoustic wave due to the mass loading and acoustoelectric effect. Thus, the targeted amino gas can be evaluated by recording the frequency shift of the SAW device. The fast response time (49 s) and recovery time (64 s), and larger frequency response of 800 Hz were observed from the fabricated SAW sensor under 150 ppm concentration of amino gas. The detection response and large frequency shift have been improved under current generation of SAW sensing array system.

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An electronic nose (E-Nose) is one of the applications for surface acoustic wave (SAW) sensors. In this paper, we present a low-noise complementary metal–oxide–semiconductor (CMOS) readout application-specific integrated circuit (ASIC) based on an SAW sensor array for achieving a miniature E-Nose. The center frequency of the SAW sensors was measured to be approximately 114 MHz. Because of interference between the sensors, we designed a low-noise CMOS frequency readout circuit to enable the SAW sensor to obtain frequency variation. The proposed circuit was fabricated in Taiwan Semiconductor Manufacturing Company (TSMC) 0.18 μm 1P6M CMOS process technology. The total chip size was nearly 1203 × 1203 μm2. The chip was operated at a supply voltage of 1 V for a digital circuit and 1.8 V for an analog circuit. The least measurable difference between frequencies was 4 Hz. The detection limit of the system, when estimated using methanol and ethanol, was 0.1 ppm. Their linearity was in the range of 0.1 to 26,000 ppm. The power consumption levels of the analog and digital circuits were 1.742 mW and 761 μW, respectively.

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