《现代传感器》课件Lecture11

Garlic and enchiladas produce a slightly different collective response in the entire set of sensors in your nose, and your brain has stored an extensive collection of these patterns which are used for comparisons.
An important lesson is that a multi-functional system will probably need to use a small set of distinct sensors and a pattern-matching algorithm to identify odors accurately.
A responsive matrix
Pattern-Matching algorithm
Identify Odors
Department of ptical Engineering
Zhejiang University
Detectors of Particular Molecules
If a chemical sensing application requires detection of a particular molecule, several techniques are available. These techniques are based on the unique properties of particular molecules.
Metal oxide sensors are more accurate and are the common type of sensor employed in home models. This type of sensor uses solid state tin-dioxide circuits, which clear quickly and continually monitor the air for presence of carbon monoxide.
Most vibrations and rotations are "optically active", meaning that they may be excited by absorption of a photon, or may relax by emission of a photon. These photon absorptions are generally most likely to occur in the infrared, so infrared spectroscopy is a generally useful way to identify molecules.
Modern Sensors Lecture 11
X. Wu
Department of Optical Engineering
Zhejiang University
A Review of Lecture 10
Two types of commonly used acoustic sensors:
Department of Optical Engineering
Zhejiang University
Commercial CO Detectors
The bio-mimetic gel sensor : designed to mimic the body's response to carbon monoxide by continually absorbing gas.
Department of Optical Engineering
Zhejiang University
Human Nose
The human nasal sensing apparatus contains a remarkably flexible and sensitive detection capability.
In addition to vibrations, molecules also can have rotational energy.
In the spectrum of NH3 (ammonia), the rotational spectrum contributes a series of closely-spaced lines centered about the vibrational peaks.
Zhejiang University
On-chip Optical Detection
Micro-ring resonator: n Pressure
Department of Optical Engineering
Zhejiang University
Rotational energy: NH3
Instant Detection and Response (IDR) electrochemical sensing technology, which is claimed to be the most effective detection method.
Optical?
Department of Optical Engineering
the line connecting the atoms).
In quantum mechanics,
a vibration is represented as a single frequency
En
(n
1) 2
Quantum mechanics includes "Selection Rules" which strongly favor relaxation a single step of h/2 at a time. This feature shows up in the infrared spectrum as a single absorption.
Department of Optical Engineering
Zhejiang University
Chemical Sensing System
Chemical sensing system designers need to draw lessons from these biological systems.
Department of Optical Engineering
Zhejiang University
For example, CO detection
CO: A very simple molecule ( 2 balls and a spring),
capable of oscillating at a single frequency rotations about 2 axes (both perpendicular to
Psychologists have found that these odor patterns can be among the strongest of memories, and smells are often used to aid in the reconstruction of memories.
Department of Optical Engineering
Zhejiang University
CO detection (cont.)
In the spectrum of the absorption of CO, we see a pair of absorption peaks.
This peak splitting is due to the fact that Carbon exists in isotopes which have atomic mass of 12 or 13.
Bimorph ceramic--- like bimetal thermistor/piezoelectric
Crystal: ADP, sodium-potassium tartrate tetrahydrate ---- piezoelectric
Limitations to acoustic sensing
You are capable of detecting and distinguishing thousands of different smells with almost instantaneous recognition.
Odor detection is made very complicated because of the lack of actual uniqueness in the chemical basis of most smells.
The additional mass of the C13 reduces the vibrational energy simply because it lowers the resonant frequency:
k
m
2150-2180 wave-number Or ~4.5m (mid infrared)
There is no "garlic molecule" that is distinct from the
"enchilada molecule"; yet you can easily distinguish
these smells.
Department of Optical Engineering