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Qatar University

College of Engineering

Electrical Engineering Department

ELEC - 438

Selected Topics in Electronics

Instructor: Dr. Ahmed Massoud

Teaching Assistant: Eng. Hamid M. Azani

Title: Electronic Nose

[Noor Alam Chowdhury], [200915342]

AC: 2013/2014 Fall 2013

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Introduction

An electronic nose is a device intended to detect odors or flavors. Over the last decade "e-

sensing" technologies have undergone important developments from a technical and commercial

point of view. By observing the mammalian olfaction system of human, researcher undergoes

with different research and succeeded by converting it to electronic nose system. Figure 1comparing the two systems.

Figure 1: Comparison of the human nose system and the e-nose system [1]

Procedure

Electronic nose system converts different gases that diffuse by the sample to signals. Different

gas sensors are use for this conversion. Gas sensors sense the gas and convert it to signal. If we

look into details this signal actually is a time response of sensing the odorant. Figure 2 shows

how the gas has been sensed by the sensor and the time response of the sensor.

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Figure 2: E-nose sensor response to an odorant [1]

There are several gas sensor are used in E-nose like Conducting polymer composite,

intrinsically conducting polymer and metal oxide conductivity gas sensors, SAW and QCM

piezoelectric gas sensors, optical gas sensors and MOSFET gas sensors. MOSFET gas sensor

will be described below.

MOSFET gas sensor works on the principle that the threshold voltage of the MOSFET sensor

changes on interaction of the gate material, usually a catalytic metal, with certain gases, such as

hydrogen, due to corresponding changes in the work functions of the metal and the oxide layers

[1]. In order for the physical changes in the sensor to occur, the metal insulator interface has to

be accessible to the gas. Therefore, a porous gas sensitive gate material is used to facilitate

diffusion of gas into the material [1]. Changes in the drain source current and the gate voltage

have also been used as the response mechanisms for the MOSFET gas sensors as they are also

affected by changes in the work function.

Some key feature of the MOSFET gas sensor:

Response time: 1ms to 300s

Operating temperature: 50-300 degree Celsius

Gate material: polymer

Film thickness: 3-400nm (depending on the gas)

Application of E-nose

1. Identifying the purity of the material

2. To test food and beverage quality3. Hazardous chemical agent detection

References

[1] K. Arshak, E. Moore, G.M. Lyons, J. Harris and S. Clifford.A review of gas sensors

employed in electronic nose applications

[2]Metal Oxide Sensors for Electronic Noses and Their Application to Food Analysis. Retrieved

on October 6, 2013 from

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3274253/

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3274253/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3274253/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3274253/