An electronic ‘nose’ model from IIT Bombay

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Electrical Engineering Department of Indian Institute of Technology, Bombay, research is on to develop an “electronic nose”, the “nose” can differentiate between molecules based on their vibrational energies.

Process of Smelling

There are two competing theories that try to explain olfaction or the action of smelling – the shape theory and the vibration theory.According to the shape theory, the shape of a particular molecule acts as a “key” and fits into the “lock” in the nose, thereby stimulating it to perceive a smell.

The vibration theory, on the other hand, proposes that the nose senses not the shape but the vibrational energy of the odorant molecule. Perhaps the actual mechanism is even a combination of the two processes.

The Electronic Nose

It is one-dimensional “resonant tunnelling diode” – a quantum device that conducts only when it is excited by special discrete values of electrical energy. Essentially this is a modification of a quantum wire – a linear array in which the electrons can move in one dimension only.

It takes a quantum wire a little further in a modification without which we do not see room-temperature operation. It adds a double barrier structure — with a [potential] well in the middle — in the transport direction as well

A double potential barrier (like two barricades) is created on the quantum wire, which confines the electrons further to be enclosed in a small region. It is known in quantum mechanics that this allows the confined electrons to possess discrete values of energy.

This device selectively allows electrons with specific resonant incident energies to tunnel through the barriers.

Vibrational mode

The resonant tunnelling diode shows a peak in the current but does not shut down completely away from the peak.

The way the odorant molecule information enters is through the creation of a vibrational mode that modulates the current, specifically by opening up an inelastic channel for tunnelling wherein the electron loses energy in the form of vibration,


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