June 2015
12
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NTERNET
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HINGS
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PPLICATIONS
Five Senses of Sensors - Part 1:
smell, taste, and hearing
By Rich Miron,
Digi-Key
This article is the first of a two-part
series on the “Five Senses of Sensors”.
The discussion looks at advances in
sensor technology that mimic and
mirror human smell, taste, and hea-
ring. The focus is on changes in the
underlying sensors and how applica-
tions have grown, particularly in the
light of the Internet of Things (IoT).
Part 2 will examine touch and vision
sensors.
n
An arti cial olfaction device, an electro-
mechanical or e-nose, is an array of chem-
ical gas sensors, a sampling system, and a
pattern-classi cation algorithm to recognize,
identify, and compare gases, vapors, or odors.
ese devices mimic the human olfactory sys-
tem and have been successfully used in a wide
variety of applications including detection of
food quality, wastewater management, mea-
surement, and detection of air and water pol-
lution, in health care, and in warfare. One of
their strengths is that the data gathered can be
interpreted without bias.
In food safety, the most common use is to
determine the quality of tea, milk, alcoholic
beverages, fruits, meats and sh, cheese, and
other dairy products. Gas sensors include
methane, ethanol, toluene, o-xylene (an aro-
matic hydrocarbon based on benzene), CO2,
and CH4. For medical applications, e-nose
devices are being explored for the detection
of the cancer biomarkers necessary for early
diagnosis and fast treatment. For example,
researchers at the University of Tampere in
Finland have used a device that conducts
molecular analysis of the air above urine
samples, testing it for the volatile organic
compounds associated with prostate cancer.
In a study, published last year, the scientists
claimed the method had a detection rate of 78
percent.
e use of nano-materials in e-nose applica-
tions is gaining ground along with the capa-
bility of creating sensors with ultra-high
sensitivities and fast response (due in part to
a smaller structure). e smaller sensor size
also promotes integration into a larger num-
ber of devices. An attractive class of materi-
als for functional nano-devices is metal-oxide
semiconductors. ey o er simple operation,
ease of fabrication and the potential for com-
patibility with microelectronic processing, as
well as low cost and low power consumption.
ere are still many challenges to be overcome,
including fully understanding the nano-ma-
terial growth mechanism to assure su cient
quality. Aligning nano-materials between
prede ned electrodes and forming proper
contacts that directly in uence device perfor-
mance is also not an easy feat.
ere have been recent sensor breakthroughs
with devices that could give smartphones
a sense of smell. Developed by Honeywell
ACS Labs, the new device utilizes a new type
of MEMS vacuum pump, hundreds of times
smaller than previously available. In human
olfaction, lungs bring odor to the olfactory
epithelium layer inside the nose, while the
e-nose uses a pump. e Honeywell devices
promise to initially provide an add-on sense
of smell for spectrometers, but it may also end
up in smartphones that can sense everything
from toxic chemicals to pollen to general air
quality.
e classes of e-noses include those with con-
ductive polymer, surface acoustic wave, calo-
rimetric, and polymer composite. O en there
are several types or classes of sensors used in
these applications, including optical-sensor
systems, mass and ion mobility spectrometry,
gas chromatography, infrared spectrometry,
and chemical sensors. An example of a gas
sensor used for CO2detection is Amphenol’s
Telaire 6613 CO2 module ( gure 1). e small,
compact module is designed to integrate into
existing controls and equipment to meet the
volume, cost, and delivery expectations of
OEMs. All units are factory calibrated to mea-
sure concentration levels to 2000 and 5000
ppm. Dual-channel sensors are also available
for higher concentrations. e a ordable,
reliable, exible sensor platform is designed
to interact with other MPU devices.
e electronic tongue (e-tongue) uses an array
of liquid sensors that mimic the human sense
of taste, without the intrusion of other senses
such as human vision and olfaction that o en
interfere with taste perception. Within a few
years, researchers anticipate that a machine
that experiences avor will determine the
precise chemical structure of food and why
people like it. Digital taste-buds also will help
Figure 1. e Telaire 6613 C02
module
