About Instruments Today No. 218

Air Quality Sensors

Introduction of the Domestic and International Situation on Air Quality Sensor

Kuo-Cheng Huang, Yi-Hsuan Chen, Ching-Ching Yang, Wen-Tse Hsiao

With the advancement of information networks and sensing technologies, networking technology is driving a wave of novel technologies. Air quality affects people’s daily lives. This paper introduces the current status of domestic/outside air quality sensors, the technical energy developed by the niche market. Moreover, the National Applied Research Laboratories, Taiwan Instruments Research Institute (TIRI) and Taiwan Semiconductor Research Institute (TSRI) on gas sensor components and integrated test platforms (i.e., thin film process, micro-electromechanical system process technology, and system circuit design and production and verification test platform established). From the front-end air quality sensing component module to the back-end data information integration analysis and other applications, the localization technology of gas sensor components is established to vertically integrate the industry and establish an overall system team to promote the empty goods internet of things (IoT) integration system.

Introduction of Solid-state Gas Sensor

Li-Yan Yang, Ting-Syun Ke, Wenjea J. Tseng

Solid-state gas sensors are commonly used to detect flammable and toxic gases. Depending on the sensing mechanisms, the sensors possess different advantages and disadvantages. For example, catalytic combustion gas sensors are less likely to be affected by ambient temperature and humidity. Solid electrolytes gas sensors present good selectivity, high conductivity and sensitivity. Semiconducting oxide gas sensors have advantages such as high sensitivity, capability of detecting gas in low concentration, miniaturization, and capability of cost-effective, scaleup production. This article is intended to give a brief introduction of the above gas sensors together with materials and processes commonly used for preparing the solid-state gas sensors.

Application of Nanoparticle Modified Zinc Oxide Nanowires for Nitrogen Oxides Gas Sensing under Ambient Environment

Wen-Chung Lu, Yu-Chieh Chen, Hsien-Wen Ke, Heh-Nan Lin

We report on the fabrication of nanoparticle modified zinc oxide nanowire resistive sensing chips for nitrogen oxides gas sensing under ambient environment. A sensing chip is made of two electrodes with grown nanomaterial. The chip resistance increases when NOx gas molecules adsorb on the nanomaterial surface. The gas concentration can thus be deduced from the resistance change. Using the UV-activation mode, responses of around 110% and 590% at 0.5 ppm NO and NO2, respectively, have been obtained under ambient environment. A cell phone operated portable gas sensor has also been constructed. The resistance change of the sensing chip due to NOx gas is recorded in an App program and the gas concentration in the surrounding environment can be obtained.

Investigation of Solid-State Electrochemical NOχ Sensors for Euro 6 Emissions Standard

Shu-Yi Tsai, Chen-Ta Chen, Kuan-Zong Fung

In recent years, exhaust emissions management has played an important role in the Internet of Vehicles (IoV). The scandal of computer software for the emission of diesel vehicles from the Volkswagen of Germany, which has caused an uproar in the global auto industry. It is to cope with increasingly strict emission standards. How to monitor gas quality and feedback the electronic signal to the vehicle computer has attracted much attention in recent years.The project is based on oxygen ion conductor materials combined with nanomaterials as sensing electrode materials and alteration of the chemical composition to enhance the gas sensing characteristics. In this study also using mass-produced ceramic molding technology, sequentially the design and preparation of materials for layer patterns to develop new products that meet the air pollution regulations and also enhance the international competitiveness of domestic manufacturers for market demand.

Development of Semiconductor Chip-Type Gas Sensor

Ting-Jen Hsueh, Wen-Tse Hsiao

Global technology industry has been driven the development of industry and cities. With the increasing factors of vehicles and factories, the air quality was significantly affected. These air pollutants cause diseases and disasters. For example, in the evening of July 31, 2014, Kaohsiung's gas explosion accident. At that time, if we can develop the integration of each gas sensor into a common mobile device, achieve the purpose of environmental monitoring and action the detection with "people" as the center of it. The concept has got the whole world's attention. Such as this year (2016), International Yole Development estimated the usage of gas sensor will increase from 1.2 million in 2014 to 350 million in 2021. The number increasing is about 300 times and the output value will be more than $ 2 billion. The most usage will smart phones. However, to be integrated in mobile devices, gas sensors must be miniaturized and low power consumption. At present, there are micro-electro-mechanical systems (MEMS) technology developed by the semiconductor chip-type gas sensor to achieve the smallest, lowest energy and low cost, which caught people's attention. In this study, based on the MEMS integrated technology platform we develop metal oxide semiconductor gas sensors by using the different sensing fi lms such as SnO2 and nano gas sensing fi lm. Therefore, NO2 gas concentration, SO2 gas concentration and alcohol gas concentration were measured.

Design and Fabrication of Low Power Consumption Gas Sensor

Yu-Jen Hsiao, Wei-Zhi Lin, Chien-Wei Liu, Wen-Tse Hsiao

Metal oxide semiconductor gas sensors have attracted a lot of attention because of their low cost, long life, miniaturization, mass production, and easy integration into Si processes. A common metal oxide semiconductor gas sensor is in the form of a two-dimensional sensor provided by a micro-heater. The heating and sensing electrodes are designed in the same process, resulting in a relatively low temperature peripheral temperature and a temperature distribution. Both are generated and consume a lot of power. The three-dimensional structure produced this time is to separate the heating from the sensing electrode and optimize the pattern of the heating electrode, which contributes to the uniformity of heating and the improvement of power.

Real-time Optical-type Air Quality Index System Application in Industrial Flue Gas

Yu-Zung Chiou

This article introduces the manufacturing and design of the real-time optical-type air quality index system application in industrial flue gas. The system consists of a band-pass photodetector, a laser and a 220 cm light path. The wavelength of absorption of the band-pass photodetector is forecasted from 390 nm to 420 nm. The detect limit of nitrogen dioxide is estimated to be approximately 5 ppm. We have to emphasize that there is no need to replace sensor head in our system as compare to the traditional gas sensor.

A Wireless Temperature, Humidity, and Optical Aerosol Sensor System for Three-Dimensional Space Monitoring

Yi-Cheng Lin, Cheng-Ru Li, Chih-Ning Hsu, Ching-Ching Yang, Kuo-Cheng Huang, Wen-Tse Hsiao

Atmospheric particulate matter (PM), also called aerosols, refers to solid particles or droplets suspended in the air. The existence of these particles cannot be easily detected by people because they are too small to be identified with the naked eyes. The concentration of ambient PM2.5 has been attracting considerable research attention because of its adverse effect on human health, as revealed by many epidemiological studies. To protect public health, PM2.5 air quality standards have been promulgated in many countries, and various measurement methods for defining the particle size exist. In this study, temperature, humidity, and optical aerosol sensors were integrated with a wireless transmission module for developing a portable multisensor monitoring module. The developed module was tested using a thermohygrometer and laser particle counter in a dry box to establish a regression equation by using the least squares method. To discuss the environmental condition and spatial dimension affect, the monitoring module was then placed in the bottom, middle, and upper layers of the dry box, and the relative humidity was controlled between 20% and 90% to monitor the performance of the optical aerosol sensor under various environmental conditions and spatial dimensions. Experimental results indicated that the aerosol count provided by the optical aerosol sensor increased with the relative humidity level. Temperature did not have a substantial effect on the particle sensor. The aerosol counter had a higher aerosol count in the upper layer than in the middle and bottom layers under various environmental conditions.

Surface Profiling Measurement and Model Reconstruction of Micro Object Using Varifocal System Based on Multi-Focus Image Fusion

Chen-Liang Fan, Jing-Xuan Lin, Pi-Ying Cheng, Chun-Jen Weng

The purpose of this thesis is about to integrate and develop a method of surface profiling measurement that based on the image processing technique into varifocal microscope system. The method of measuring surface profile based on the image processing technique is call shape from focus or multi-focus image fusion. It can measure the surface profile of sample and create an image with large depth of field at same time. If the surface of sample is out of depth of field, the image is blurry. Using focus algorithm can calculate the sharpness of image and help the varifocal microscope systems to determine the best focus setting. The multi-focus image fusion method is established based on focus algorithm and integrated into the varifocal microscope systems in this research. Even in the case of poorly depth of field, our systems are capable to get the all in-focus image with the multi-focus image fusion method and this research can also achieve the functionality of surface profiling in the microscopy scale. The surface profiling method in this research is passive measurement, it does not cause any physically contact to the sample. It can prevent the risk of damaging the sample.