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Thermal Imaging Sensors for Fever Detection

produced by bulk-silicon thermopile
technology.
2. The displayed core body temperature
is calculated in the device, based on
the measured skin temperature, the
ambient temperature, and a heat transfer
equation.
3. The thermometer must be placed very
close to the skin (i.e., a couple of centi-
meters away at most), even if physical
contact between the skin and the detec-
tor is not necessary.
Figure 3: Boots contact thermometer Figure 4: Braun forehead thermometer
(Source: Meridian Innovation) (Source: Meridian Innovation) THERMAL IMAGING CAMERA FOR
DETECTION OF ELEVATED TEMPERATURE
A thermal imaging camera, on the other hand,
MEASUREMENT OF CORE BODY the rectal temperature readout), or the armpit is built around a multipixel thermal imaging
TEMPERATURE (axillary thermometers, about 0.6°C lower sensor as described earlier. The design and
We stated earlier that thermal imagers mea- than the rectal temperature readout). manufacturing process used in the formation
sure the surface temperature of the objects or The practical limitations of the contact of the detectors not only allows miniaturiza-
subjects in the field of view. The question now thermometers have been overcome by the tion, which favors packing more detectors
is whether, and how, we can use the informa- development of different types of non- per die (e.g., 5,000 pixels or more), but also
tion in a thermal image to determine the core contact, infrared-sensing thermometers, results in more sensitive detectors with a
body temperature of a human subject. which can be distinguished by their form short response time, which allows one to cap-
Before answering that, let us recall that factor and the way they must be positioned ture not just static scenes but thermal video
traditionally, core body temperature is mea- to perform the measurement — for example, streams at frame rates anywhere from
sured by a mercury or digital thermometer tympanic thermometers, positioned in the 1 to 30 frames per second.
(Figure 3) that must be in physical contact distal ear canal; temporal artery thermome- Together with a specialized lens that typ-
with a concealed area of the body that has ters, slid across the superficial temporal artery ically has an angular field of view of at least
a temperature very close to or the same as on the side of the forehead; or forehead ther- 40°, the technology allows one to capture
that of the internal organs. Typical places mometers (Figure 4), placed right in front of complex, dynamic thermal scenes, including
of contact are inside the rectum (rectal the forehead. There are three common factors multiple people at the same time, at distances
thermometers, which are the most accurate of among these thermometers: ranging between 50 cm and several meters.
the contact thermometers), under the tongue 1. They have a single LWIR detector that All this seems to make it possible to quickly
(oral thermometers, about 0.3°C lower than senses the skin temperature, and it is measure body temperature for groups of

Figure 5: Meridian Innovation multiple-people fever-detection camera solution (Source: Meridian Innovation)

NOVEMBER 2021 | www.eetimes.eu