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A lot of research has been devoted to creating electrical devices that emulate biological sensors, including:

  • Visual: Cameras, color/light intensity sensors
  • Auditory: Microphones, ultrasonic sensors
  • Tactile: Pressure sensors, temperature sensors
  • Balance: Gyroscopes, accelerometers

However, I have yet to find a comprehensive sensor/processing algorithm to detect and interpret odors. Certainly, there are "olfactory" sensors which are dedicated to a specific purpose, such as carbon monoxide detectors, and other hazardous gas detectors. But I have yet to find a general purpose sensor/processing algorithm that can readily detect and interpret odors within the range and resolution of a human nose.

Do such sensors/algorithms exist? If so, what are they and how do they work? If not, what are the primary obstacles to developing them?

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Odor assessment is usually performed by human sensory analysis using chemosensors:

A chemoreceptor, also known as chemosensor, is a sensory receptor that transduces a chemical signal into an action potential.

Recently I have also heard of a sensor from Honeywell that could potentially be used in smart phones. These sensors are also called electronic noses:

Bio-electronic noses use olfactory receptors - proteins cloned from biological organisms, e.g. humans, that bind to specific odor molecules. One group has developed a bio-electronic nose that mimics the signaling systems used by the human nose to perceive odors at a very high sensitivity: femtomolar concentrations.

The more commonly used sensors for electronic noses include

  • metal–oxide–semiconductor (MOSFET) devices - a transistor used for amplifying or switching electronic signals. This works on the principle that molecules entering the sensor area will be charged either positively or negatively, which should have a direct effect on the electric field inside the MOSFET. Thus, introducing each additional charged particle will directly affect the transistor in a unique way, producing a change in the MOSFET signal that can then be interpreted by pattern recognition computer systems. So essentially each detectable molecule will have its own unique signal for a computer system to interpret.
  • conducting polymers - organic polymers that conduct electricity.
  • polymer composites - similar in use to conducting polymers but formulated of non-conducting polymers with the addition of conducting material such as carbon black.
  • quartz crystal microbalance - a way of measuring mass per unit area by measuring the change in frequency of a quartz crystal resonator. This can be stored in a database and used for future reference.
  • surface acoustic wave (SAW) - a class of microelectromechanical systems (MEMS) which rely on the modulation of surface acoustic waves to sense a physical phenomenon.
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