Page 48 - EE Times Europe Magazine | June2020

48 EE|Times EUROPE — Sensors Insert

Monitor Carbon Dioxide Level by Photoacoustic Sensing

the energy of the photon is first transferred
to the CO 2 molecule and subsequently to the
surrounding molecules. The absorbed energy
results in a microscopic pressure increase.
Since millions of absorption events take place
inside the optical cavity, the pressure increase
becomes a macroscopic phenomenon. By
modulating the IR emitter, we induce a pres-
sure increase and decrease with a well-defined
frequency, which is nothing other than an
acoustic sound wave. While the frequency of
Figure 5: Functioning of PASens Technology. There are dust filters on the top of the the sound is given by the IR-emitter modula-
sensor. (Image: Sensirion) tion frequency, the amplitude of the sound is
proportional to the CO 2 concentration.
“This amplitude of the photoacoustic signal
can be measured with a MEMS microphone.
The CO 2 concentration is then calculated
using the built-in processor by means of
advanced signal-processing algorithms.”
The SCD40 represents a combination of
sensing and MEMS technology by combining
minimum size and maximum performance,
according to Sensirion (Figure 6). The SCD40
offers a measurement range of 0 ppm to
40,000 ppm, fully calibrated and linearized
output, and a digital I C interface.
2
“Maybe the biggest asset with the SCD40
Figure 6: SCD40 sensor features (Image: Sensirion) is that we design and produce all the critical
components in-house,” said Gysel. “This
allows us to realize highest performance while
With a photoacoustic detection approach enclosed space. The CO 2 molecules in the keeping a cost-effective BOM structure. For
such as Sensirion’s PASens Technology, the measuring cell absorb part of the irradiated example, the actively regulated IR emitter,
sensitivity of the sensor is independent of the light. The absorbed light excites molecular which is based on our CMOSens technology,
size of the optical cavity. Sensirion combined vibrations. The result is an increase in trans- ensures the highest long-term stability and is
that approach with its CMOSens Technology lational energy that causes a periodic change significantly more cost-effective than existing
for miniaturization to create a new type of in pressure in the measuring cell. The change off-the-shelf products.”
sensor (Figure 4). can be measured with a microelectromechan- Sensor accuracy “enables our customers to
The photoacoustic principle is relatively ical system (MEMS) microphone to calculate design products with superior performance”
simple. A modulated narrowband light signal the CO 2 concentration (Figure 5). and allows customers in certain sectors to
at 4.26 µm, corresponding to the absorption Gysel described the process as it relates to meet industry norms and standards, he added.
bands of CO 2 molecules, is emitted in a small, the PASens Technology: “Upon absorption, Standards compliance “is very critical in the
HVAC market, for example,” he said.
Sensirion specifies the accuracy of the
SCD40 as ±30 ppm (+3% of reading), which
NEWS Gysel said “is among the best accuracy that
can be found on the market. Rated sensor
New Technique Embeds Sensors in lifetime is 10 years.”
The CO 2 problem is very much felt. Accord-
Clothing for Vital Sign Monitoring ing to the World Health Organization, more
than 5.5 million people worldwide die from
air pollution each year. Many cities have
Researchers at the Massachusetts Institute of Technology (MIT) have developed a technique integrated sensors to map air quality into
to embed sensors into stretchy clothing fabric, paving the way to monitor vital signs such as existing infrastructures. Indoor air pollution
temperature, respiration, and heart rate as you go about your day. The form-fitting, sensor- can have negative consequences on economic
embedded garments are machine-washable. Researchers said that the garments could be used to health as well as human health. To keep the
remotely track a patient’s health, ranging from checking in on those ill at home or in a hospital concentration of contaminants low, even the
to monitoring an athlete’s physical activity. It can also be useful for telemedicine, which is par- most airtight buildings must swap out stale
ticularly useful now, during the Covid-19 pandemic, for doctors who are increasingly connecting air and bring in fresh air. Intelligent indoor
with patients remotely. “We can have any commercially available electronic parts or custom and outdoor sensors are critical components
lab-made electronics embedded within the textiles that we wear every day, creating conformable in this effort. ■
garments,” said Canan Dagdeviren, the LG Electronics Career Development assistant professor
of Media Arts and Sciences at MIT, in a statement. “These are customizable, so we can make Maurizio Di Paolo Emilio is a staff
garments for anyone who needs to have some physical data from their body like temperature, correspondent at AspenCore, editor of Power
respiration rate, and so forth.” Electronics News, and editor-in-chief of EEWeb.

JUNE 2020 | www.eetimes.eu