About Instruments Today No. 230


Be Kind to Others without Asking for Return Dr. Fuh-Sheng Shieu, President of National Chung Hsing University, an Innovative Educator Passing Positive Values

Claire Lin

Special Issue: Principle and Application of Gas Sensor

Special Issue Introduction of “Principle and Application of Gas Sensor”

Sheng-Shian Li

Smart Phone Operated Portable Nitrogen Dioxide Gas Sensor

Hsuan-Ju Shih, Yu-Hsiang Kao, Ting-Wei Chang, Wei-Hsiang Shen, Yi-Hao Lin, Yi-Cheng Lin, Tai-shan Liao, Wen-Tse Hsiao, Heh-Nan Lin

This paper reports on the fabrication of highly sensitive semiconductor-type nitrogen dioxide gas sensing chips, and the construction of a smart phone operated portable gas sensor. The sensing material is a copper oxide/gold/zinc oxide nanocomposite and it is synthesized by low temperature chemical processes on a 4 inch silicon wafer. The sensor is operated by a cell phone with an artificial neural network algorithm for obtaining real-time environmental nitrogen dioxide concentration, and this data can be uploaded to a cloud database. The sensor has a lowest detection limit of 5 ppb and a sensing range between 5 and 1000 ppb. It has been installed in Environmental Protection Administration air quality monitoring station for field test and data comparison. The sensor functions normally in a high temperature and high humidity environment and is suitable for environmental air quality monitoring.

Development and Characteristic Analysis of Nitrogen Oxide Gas Sensor

Ray-Hua Horng, Fu-Gow Tarntair, Wei-Chung Lee

Zinc gallium oxide (ZnGaO, ZGO) single crystal epilayers were grown on sapphire substrates by metalorganic chemical vapor deposition system and applied to gas sensors. Since this ternary oxide semiconductor has a wide energy gap (~5.2 eV) and more oxygen vacancies on the surface. It is more stable in the visible light range after fabrication. Furthermore, the surface will absorb the oxygen due to the the oxygen vacancies. It will interact with the gas as injecting sensing the gas. Compared with other gases with the same concentration, the ZGO film has higher responsivity to nitrogen oxide (NOx) gas, so nitrogen monoxide (NO) is used as the measurement gas. This paper also analyzes the mechanism of gas sensing. The influence of different gallium content of the ZGO on the gas responsivity will be discussed. Moreover, the characteristics and mechanism of the gas sensing reaction will also be studied in details.

High Sensitivity Nitrogen Dioxide Gas Sensing Chip

Ting-Jen Hsueh, Chen-Ming Chang, Shu-Hao Fan

The development of global electronics industry drives the progress of industries and cities. It is advanced technology that makes human life more and more convenient, but it also brings other impacts. Due to population density in high development area is rising, the air quality of the living environment is seriously affected by the exhaust gas of vehicle and locomotives and the air pollution of industrial emissions. In these air pollution, NO2 is a red-brown gas with a pungent smell. It dissolves in water and reacts to form NO and HNO3, which is the main substance causing acid rain and one of the sources of PM2.5. In addition, inhaling NO2 will cause damage to the respiratory system. Living in this environment for a long time will easily cause irreversible respiratory damage. Research on sensor technology is beneficial to prevent and discover pollution sources. Due to the various conditions of open spaces in outdoor, high-sensitivity gas sensors that selectively target NO2 are developed to monitor air pollution quality. The NO2 sensor module of the current research results can measure the concentration of < 120 ppb, the accuracy is ± 30%, and compared with the EPA station, the determination coefficient (R2 ) is up to 0.569.

Surface Acoustic Wave Gas Sensing Device with Array Structure

Ya-Hsin Ke, Cheng-Han Chen, Yu-Jen Hsiao, Sean Wu

In view of air quality and human health, monitoring of gas pollution is a very important topic. The ideal gas sensor needs to meet the following elements: low cost, selection ratio, miniaturization, low power consumption, fast response time, good reproducibility, and high stability. Among many sensors, the surface acoustic wave sensor element can detect different gases due to its advantages of sensitivity, high reliability, small size and low price. It can detect different gases when matched with a specific sensing film. The sensor uses a semiconductor manufacturing process to prepare interdigitated metal electrodes on a piezoelectric substrate and cover the sensing film. The mass of the film increases as its material selectively adsorbs chemicals from the air, which causes the resonance to shift to slightly lower frequencies and thus obtain changes in the concentration of specific gas species in the air.

The Optical Gas Detection System for Nitrogen Dioxide

Jie-Si Jheng, Chun-Kai Wang, Yu-Zung Chiou

Our team develops an optical NO2 gas sensing system based on the demand of “wide deployment” and “simple maintenance” in NO2 gas sensors. The gas sensors are made in our country from structure design, epitaxial growth, chip fabrication, chip packaging, optical path development, and system integration. The cost of our development system is much cheaper than traditional precision instruments, and the gas sensing chips have entered the stage of pilot run. These sensing chips are designed with an epitaxial structure, especially for the light absorption spectrum of NO2 gas. Therefore, the chips can only detect light wavelengths in a specific range and generate corresponding photocurrents, which can exclude the influence of ambient light. Our system is placed in a harsh environment, so it is designed with high specifications and has passed the IPX3 waterproof certification. And our system has been continuously tested at the Tainan station of the Environmental Protection Agency for two years. It has the characteristics of no consumables, easy maintenance, instant response, and a resolution of 2 ppb. Compared with the data from the Tainan station of the Environmental Protection Agency, the coefficient of determination is as high as 0.786.


Improving the Topography Scanning Speed of the Liquid Lens Confocal Module Based on Continuous Triangular Wave Synchronous Drive with Data Acquisition Device

Guo-Hao Lu, Bo-Rong Lu, Chao-Feng Liu, Pi-Ying Cheng, Chun-Jen Weng

The study proposed and applied the innovative confocal optical technique with liquid lens on confocal displacement sensor system. The study proposed the continuously scanning method by using analog triangle mode assisted by DAQ system. Measuring the data of multiple points based on LabVIEW improves the scanning speed while using 20 Hz triangle driving current with this method. The scan speed could reach near 50 ms per scan point, which increases 5.8 times in speed compared with former method. Based on the above method, the topography scanning of standard stepped aluminum blocks was carried out with a two-dimensional mobile platform. The evaluated results demonstrate the improved and practical performance of the confocal displacement sensor system with liquid lens.

Popular Science

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