Chatchawal Wongchoosuk

Detection and Classification of Human Body Odor Using an Electronic Nose

An electronic nose (E-nose) has been designed and equipped with software that can detect and classify human armpit body odor. An array of metal oxide sensors was used for detecting volatile organic compounds. The measurement circuit employs a voltage divider resistor to measure the sensitivity of each sensor. This E-nose was controlled by in-house developed software through a portable USB data acquisition card with a principle component analysis (PCA) algorithm implemented for pattern recognition and classification. Because gas sensor sensitivity in the detection of armpit odor samples is affected by humidity, we propose a new method and algorithms combining hardware/software for the correction of the humidity noise. After the humidity correction, the E-nose showed the capability of detecting human body odor and distinguishing the body odors from two persons in a relative manner. The E-nose is still able to recognize people, even after application of deodorant. In conclusion, this is the first report of the application of an E-nose for armpit odor recognition.

Multi-Walled Carbon Nanotube-Doped Tungsten Oxide Thin Films for Hydrogen Gas Sensing

In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of the thin films have been investigated at different operating temperatures and gas concentrations ranging from 100 ppm to 50,000 ppm. The results indicate that the MWCNT-doped WO3 thin film exhibits high sensitivity and selectivity to hydrogen. Thus, MWCNT doping based on E-beam co-evaporation was shown to be an effective means of preparing hydrogen gas sensors with enhanced sensing and reduced operating temperatures. Creation of nanochannels and formation of p-n heterojunctions were proposed as the sensing mechanism underlying the enhanced hydrogen sensitivity of this hybridized gas sensor. To our best knowledge, this is the first report on a MWCNT-doped WO3 hydrogen sensor prepared by the E-beam method.

Au-doped zinc oxide nanostructure sensors for detection and discrimination of volatile organic compounds

Abstract Pure and 10% w/w Au-doped zinc oxide (ZnO) nanostructure sensors were produced and used as sensing devices in a portable electronic nose (E-nose). The nanosensors were prepared using thermal oxidation technique with sintering temperature at 700°C under oxygen atmosphere at a flow rate of 500 mL min–1. The sensors were demonstrated to be sensitive to various volatile organic compounds (VOCs), especially ethanol vapour. The E-nose even with only two sensors was efficient to discriminate a number of selected VOCs. The Au-doped sensor shows a significant improvement of sensitivity. The portable E-nose can detect the difference between alcohol beverages and alcohol solutions and can distinguish the difference of white and red wines having the same percentage of alcohol.

Photoluminescent and gas-sensing properties of ZnO nanowires prepared by an ionic liquid assisted vapor transfer approach

In this work, the ionic liquid assisted technique was used to control the growth characteristic of ZnO nanowires (NWs). The major change after adding ionic liquid into the growth system was the change in NW growth orientation, which was shifted from polar c- to non-polar a-orientation. Room temperature photoluminescence demonstrates a big reduction of the green luminescence which implies an annihilation of deep level emission. We propose two possible mechanisms responsible for the reduction of the green emission: The first mechanism is the passivation of ZnO NWs surface by fractions of ionic liquid employed for the growth, which further reduces the green emission. The second mechanism is the reduction of the defect density by changing the growth orientation. By using a semi-empirical Austin Model 1 method, the formation energy of oxygen vacancies in c- and a-oriented ZnO NWs has been simulated and compared. Accordingly, the gas-sensor constructed from ionic liquid assisted ZnO nanowires does not response ...

Novel Flexible NH3 Gas Sensor Prepared by Ink-Jet Printing Technique

We have fabricated a low-cost and flexible NH3 gas sensor using thermal ink-jet printing. The poly (3,4-ethylene dioxythiophene) doped with polystyrene sulfonated acid (PEDOT/PSS) with thickness of ~ 2 μm was used as a sensing film. The interdigitated electrode using patterned aluminum plate was attached over the sensing film. Atomic force microscopy results show the high homogeneous film and only small roughness is presented on the sensing film. This sensor exhibits high selectivity and sensitivity to NH3 at room temperature. The sensor response works linearly with gas concentrations between 100-1000 ppm. The modulation of conducting polymer/metal electrode interface plays a role in the sensing mechanism of NH3. Changes in the position of interdigitated electrodes can change the dominant sensing mechanism of typical polymer gas sensor.

Identification of people from armpit odor region using networked electronic nose

Homeland security basically needs devices that can detect, track, and identify a terrorist from a distance. Body odor recognition offers an opportunity to confirm a persons identity based on ones unique odor pattern. In this paper, we have reported how to invent a networked electronic nose (E-nose), which can detect and recognize human odors from the armpit region. An array of metal oxide sensors was used to detect human odor. Principal component analysis (PCA) was employed to perform pattern recognition and discrimination. The method for correction of the sensor drift has been proposed. The results show that the networked E-nose has a capability to detect human body odor and can create the unique smell print of each person. Based on PCA with 95% confidence ellipse, this E-nose can identify a person from four persons by detecting odor from armpit region.

Portable electronic nose for beverage quality assessment

A portable electronic nose (e-nose) was appropriately designed for investigating quality of beverages such as juice or wine, etc. The e-nose system comprises of sample and reference containers, air flow unit, sensing unit and data acquisition unit. All of the hardware units were controlled by in-house software under LABVIEW program via USB port of a DAQ card. The sensing unit includes eight different metal oxide gas sensors from Figaro Engineering Inc. Principal component analysis (PCA) was used as a statistical method in order to discriminate and assess the experimental data as defined by the percentage change in sensor resistances that correlates directly to difference in the aroma characteristics. Drift compensation model was applied to the raw data that sometimes suffer from the effects of sensor drift. Constructed portable e-nose has been tested on-field in a winery to evaluate wine aroma during process of wine bottling. The e-nose using PCA algorithm can distinguish the wine bottling under nitrogen from the bottling under partial vacuum. We also demonstrated that e-nose can be used to help wine maker to design the appropriate process of wine bottling achieving a high quality of wine product.

Correction of humidity effect for detection of human body odor

Humidity strongly effects the sensitivity of odor sensors. It is therefore a major problem in the use of electronic nose (E-nose) for most applications including detecting human body odor from armpits, where humidity at the armpits can varies to a large extent due to various human activities. In this paper, we propose both hardware and software approaches to correct the humidity effect. The E-nose was designed to efficiently measure volatile organic compounds generated from human body and was most optimized if both the hardware and software corrections were employed. Principle component analysis (PCA) method was used for pattern recognition and discrimination of human body odor. After humidity correction, our special designed E-nose not only shows the capability in detecting human body odor, but it is also able to classify two different persons who have the same life style and activities.

Development of networked electronic nose based on multi-walled carbon nanotubes/polymer composite gas sensor array

In this paper, we have presented the design and invention of an electronic nose (E-nose) that can work and analyze the results via a network system such as LAN or WiFi. The MWCNTs/polymer composites were used as a gas sensor array. The constant current circuit was newly designed for gas sensor measurement. The fabricated E-nose showed a high performance for indoor air monitoring with very low noise.

Flexible alternating current electroluminescent ammonia gas sensor

In this work, the fabrication and performance of flexible alternating current electroluminescent (AC-EL) devices for ammonia (NH3) detection at room temperature are presented for the first time. The AC-EL gas sensor was fabricated by the screen-printing of a ZnS:Cu,Cl phosphor and PEDOT:PSS sensing layers. The effects of parameters including applied voltage, excitation frequency and waveform on light emission and luminance intensity of the AC-EL gas sensor were systematically investigated. From gas-sensing characterization, the AC-EL gas sensor exhibited very high selectivity and a linear response to NH3 in the concentration range of 100–1000 ppm at room temperature. A sensing mechanism of the EL gas sensor was proposed based on the resistance change of the PEDOT:PSS sensing layer via a charge-transfer process.