June 2015
14
I
NTERNET
-O
F
-T
HINGS
– A
PPLICATIONS
us to eat smarter and healthier. e e-tongue
measures and compares tastes using sensors
to receive information from target chemicals
which is then sent to a pattern-recognition
system. e result is the detection of taste
based on the human palate. ere are ve
basic types of tastes: sweet, bitter, salty, sour,
and umami (a Japanese word that can be
translated as deliciousness or pleasant, savory
taste). To mimic the human tongue, sensors
are used in multiplexed arrays containing
multiple taste receptors.
E-tongues o en are used in liquid environ-
ments to classify the contents of the liquid,
identify the liquid itself, or sometimes to dis-
criminate between samples. Most e-tongues
are based either on potentiometric or amper-
ometric sensors. e taste sensors have
arti cial polyvinyl chloride (PVC)/lipid mem-
branes that interact with a target solution (e.g.,
ca einated beverages). e membrane poten-
tial of the lipid membrane changes – which is
the sensor output or measurement. Investigat-
ing potential change results in measuring the
taste provided by the output of the chemical
substances. With the array, multiple sensors
provide this output and form a unique nger-
print.
While e-tongue technology has advanced
the past several years, it is taste accuracy that
has become a priority. For example, in 2014
researchers managed to distinguish between
di erent varieties of beer using an electronic
tongue with an accuracy of approximately 82
percent, while other e-tongue prototypes have
demonstrated ability to successfully distin-
guish between wines.
Hearing systems are increasingly being
trained by listening to sounds, detecting
patterns and building models to decompose
sounds. One of the most common applica-
tions for sensors in this segment is in hearing
aids. Digital advances have made s hearing
aids today smaller, smarter and, fortunately,
easier to use. e most advanced hearing aids
are now interacting with other devices, such
as smartphones and digital music players, to
deliver sounds directly and wirelessly to the
listener. Recent improvements are based on
better microprocessors and noise-reduction
so ware so that the hearing aid can be selec-
tive about the types of sound it ampli es, muf-
es, or suppresses.
e focus of current research is on direction-
ality and speech enhancement. Sound systems
can employ digital signal processing to auto-
matically shi between two di erent types
of microphones in order to pick up either a
single speaker voice or sound coming from
all around. Digital-speech enhancement can
now increase the intensity and audibility of
some segments of human speech. Research
projects are underway to reduce the size and
cost of hearing aids, improve their directional
capabilities, and identify and amplify desired
sounds such as a human voice while muting
background noise. Researchers are also work-
ing hard to extend battery life through the
use of tiny microphones mounted on MEMS
chips. ese chips enable multiple micro-
phones to be placed inside a device small
enough to t in a user ear without rapidly
draining the batteries.
For example, while ies ordinarily have no
sense of hearing at all, one subset, the Ormia
ochracea, a parasitic y, can determine the
direction of a sound to within two degrees,
which seems impossible given the tiny size
of the y. Cornell scientists are studying the
extremely tiny insect parasite as the basis of an
e ort to develop a man-made directional-lis-
tening system based on the auditory appa-
ratus of the y, naturally small enough to t
inside a hearing aid.
Sensors that detect sound or hear are essen-
tially microphones with sophisticated sig-
nal-processing capability. In robotics, sound
sensors are used in a myriad of applica-
tions. One sensor particularly well-suited for
sound-based application is the Parallax Sound
Impact Sensor ( gure 2) that provides noise
control to a project and responds to loud
noises such as a clap of the hands. rough
the on-board microphone, this sensor detects
changes in decibel level, which triggers a high
pulse to be sent through the signal pin of the
sensor. is change can be read by an I/O pin
of any Parallax microcontroller. An on-board
potentiometer provides an adjustable range of
detection of up to 3 meters away.
Targeting speech recognition, the STMicro-
electronics MP34DB01MEMS audio sensor
digital microphone (timing waveforms are
presented in gure 3) is an ultra-compact,
low-power, omnidirectional, digital MEMS
microphone built with a capacitive sensing
element and an IC interface with stereo-op-
eration capability. e IC interface is manu-
factured using a CMOS process and features
a single supply voltage, low power consump-
tion, and omni-directional sensitivity. e
MP34DB01 has an acoustic overload point
of120 dBSPL with a 62.6 dB signal-to-noise
ratio and -26 dBFS sensitivity. It is available
in a bottom-port, SMD-compliant, EMI-
shielded package and is guaranteed by the
supplier to operate over an extended tempera-
ture range from -40 °C to +85 °C. In summary,
in the near future there will be more develop-
ments in the smell-, taste-, and hearing-based
sensor technology used a variety of applica-
tions.
n
Figure2. e Parallax Sound Impact sensor
Figure 3. Timing waveforms of the MP34DB01
