Hsu-Chao Hao

A Portable Electronic Nose Based on Bio‐Chemical Surface Acoustic Wave (SAW) Array with Multiplexed Oscillator and Readout Electronics

We have developed a new portable electronic nose based on a SAW sensor array and its readout electronics. The SAW array is based on 2×2 non‐continuously working oscillators for sensors coated with different polymer/mesoporous carbon composite materials. Signals of the SAW array can be obtained by a readout PCB and a microprocessor. Experiments indicate good results for this portable system to perform gas detection and recogntion applications.

Polymer-coated surface acoustic wave sensor array for low concentration NH 3 detection

Surface acoustic wave sensors are famous for its low cost, high resolution, and quick response time. In this paper, the SAW gas sensor for detecting low concentration of NH3 was presented. The gas sensor array is composed of 2×2 non-continuously working oscillators equipped with one reference SAW sensor and three SAW sensors coated with different polymers. To improve the selectivity and sensitivity, ten kinds of polymers with special functional group were coated on the sensing area as the sensing film. The gas recognition database was established by collecting and normalizing the results of interplay between polymers and target gas. The miniaturized SAW chip was developed for low cost and portability, more capacities of polymer-coated SAW sensors mounted on a limited region of sensor array chip. The PNVP-coated miniaturized SAW sensor has been successfully developed to detecting low concentration ammonia of 16 ppm. Compared with the original SAW sensor, the miniaturized SAW sensor coated with PNVP film shows larger frequency shift but similar performance for low concentration of NH3 detection after normalizing the results of interaction between polymer and ammonia.

A chemical surface acoustic wave(SAW) sensor array for sensing different concentration of NH 3

Surface acoustic wave (SAW) sensor is generally known as high-resolution mass-sensitive transducers. We developed a novel SAW sensing array based on 2×2 non-continuously working oscillators equipped with differently coated SAW sensors, respectively, which is used to analyze organic compound gases. The sensing array consisting of four two-port SAW resonator sensors with a fundamental frequency at 99.8 MHz was fabricated on LiNbO3 substrate. Four different polymers were coated on the surface of sensing regions. The gas sensing array was put into 10L reaction chamber with temperature and humidity controllable environment. The frequency outputs from each sensor were used to compare with the frequency from a reference device for eliminating the environmental effects. The results suggest that frequency shift of the designed gas sensor array changes with different concentration of the target gas(NH3).

Gas sensor array based on surface acoustic wave devices for rapid multi-detection

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-LiNbO3 substrate by the spin coating technique. Moreover, we have developed an improved portable electronic noise based on a 2×2 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.

An electronic-nose sensor node based on polymer-coated surface acoustic wave array for environmental monitoring

We report an electronic-nose sensor node based on polymer-coated surface acoustic wave (SAW) sensor array for environmental monitoring applications. The sensor node consists of a SAW sensor array, its readout circuitry and a Wireless Sensor Network (WSN) platform. The 2 × 2 non-continuous gas SAW sensor array is coated with different polymer composite materials for different gas detection. The frequency signals from the SAW array are processed by the frequency readout circuitry to obtain frequency shift information. The sensor data is transmitted from sensor nodes by Octopus II WSN platform. Experimental results have shown good performance of gas detection and recognition. In order to achieve a high efficient environmental monitoring sensing network, the decision supporting system by implementing weighted voting system (WVS) has also been considered.

Surface acoustic wave gas sensor for monitoring low concentration ammonia

A surface acoustic wave (SAW) gas sensor coated with poly-N-vinylpyrrolidone (PNVP) film for monitoring low concentration ammonia was developed. By miniaturization of SAW chip and employment of polymer as sensing material, the sensitivity of SAW gas sensor can be improved. A dual-device configuration was applied to construct SAW gas sensor for eliminating detection deviation from environment such as temperature and humidity. Frequency shifts of SAW sensor were measured to monitor the presence of different concentration ammonia. The as-developed SAW gas sensor presented good repeatability and response to low concentration ammonia detection, even though the ammonia was below 10 ppm. The sensitivity of PNVP-coated SAW sensor for ammonia detection was 6.91 Hz/ppm, and the frequency shift of the as-developed SAW sensor to monitor 8 ppm ammonia was 27.5 Hz.

Rapid cigarette detection by using surface acoustic wave gas sensor with non-polymer sensing film

The surface acoustic wave (SAW) gas sensor is coated with modified hollow mesoporous carbon nanosphere to replace generally used polymer as new type sensing material, which is used to detect the secondhand smoke marker, 3-ethenylpyridine. This non-polymer sensing layer is more sensitive than poly-acrylic acid due to the much more carboxyl group bonded by treating with nitric acid and the large specific surface area caused by porous structure is leading to rapid detection at low flow rate. Finally, the SAW sensor successfully detects real cigarette smoke with good repeatability, having great potential as real time monitoring for smoking in actual environment.

Handheld Gas Sensing System

Handheld gas sensing systems have drawn attentions recently for personal use and daily applications. However, commercially available gas detection devices are yet to satisfy the needs due to the challenging issues of system miniaturization, such as insufficient selectivity and sensitivity. In this chapter, we introduce an approach to achieve this goal. Based on an array of surface acoustive wave (SAW) gas sensors, a bio-inspired gas sensing system (also called electronic nose) could be realized to construct a robust system to identify gases. To increase the gas sensitivity, nanocomposites of polymers and ordered mesoporous carbons (OMCs) is introduced. The polymers are directly grown on the carbon material through a radical polymerization process, thus forming interpenetrating and inseparable composite frameworks with carbon. Furthermore, to reduce the system size and power consumption, the integrated circuits (IC) technology is adopted to implement the readout interface circuit to replace bulky instruments, such as frequency counter. Finally, several odor classification algorithms are introduced to perform gas classification.

Detection of hazardous vapors including mixture in different conditions using surface acoustic wave device array

In this research, a surface acoustic wave (SAW) sensor was used for chemical compounds detection such as ammonia, methane, and ammonia/methane mixture gases. The detection results of ammonia/methane mixture gases by polymer deposited on 128° YX-LiNbO3 SAW delay lines were presented. To enhance the sensitivity and accuracy of the surface acoustic wave sensors, the sensing chamber and polymer films was improved. Very low concentration of ammonia (~250 ppb) and methane(~9 ppm) could be detected by this SAW sensor. From the sensing database of ammonia and methane, we Figured out that the frequency shift of ammonia/methane mixtures was equal to the sum of frequency shift of ammonia and methane. Besides, the signal loss of ammonia was much stronger than methane in high relative humidity conditions. Here, superposition effect between ammonia and methane sensing signals could be used for the signal intensity prediction of different concentrations ammonia/methane mixture gases.