Tech Briefs Magazine - November 2023 - PIT-6

Comparing
Sensitivity
of Thermal
Imaging
Cameras
Modules
T
hermal imagers make pictures
from heat, also called infrared
(IR) or thermal energy. They
capture IR energy and use that
energy to create images through digital
or analog video outputs, with the details
defined by differences in temperature.
Heat is a separate part of the electromagnetic
spectrum from typical visible light.
A camera that can detect visible light
won't see thermal energy, and vice versa.
Infrared camera detectors are made of
an array of individual detector elements.
Because the wavelengths of energy in the
IR spectrum are longer than those of visible
light, each IR detector element must
be correspondingly larger than elements
on visible light detectors to absorb the
larger wavelength. As a result, a thermal
camera usually has a lower resolution
(fewer pixels) than a visible light sensor
Sensitivity (mK)
of the same mechanical size. Microthermal
cameras, small enough to be in rugged
mobile phones, often have a resolution
between 80x60 and 160x120 pixels.
Thermal cameras used by firefighters
and for industrial inspection can have a
resolution of 320x256 to 640x512 pixels,
providing many times more pixels and
significantly better thermal imagery but
at a notably higher cost.
Initially developed for surveillance
and military operations, thermal cameras
are now widely used for industrial applications
such as building inspections
(e.g., moisture, insulation, roof, etc.),
firefighting, autonomous vehicles, automatic
emergency braking (AEB) systems,
industrial inspections, scientific
research, and much more. These cameras
come in a variety of form factors,
from handheld cameras to uncrewed
Description
<30 Excellent
40 - 49
50 - 59
60 - 69
70 - 80
Great
Good
Acceptable
Satisfactory
Table 1. Thermal sensor sensitivity range and description.
6
drones to scientific instruments sent
into outer space.
Engineers developing products or systems
incorporating thermal cameras
need to clearly understand the critical
design specifications, including scene
dynamic range, field of view, resolution,
sensitivity, and spectral range, to name a
few. Different cameras can excel at different
things, so engineers need to understand
the tradeoffs between different
types of thermal camera modules and
the impact those differences will have on
the final product performance.
Sensitivity: A Key Variable
That Affects Thermal Imaging
Clarity and Utility
One crucial specification often overlooked
at the expense of resolution is
thermal sensitivity, which defines the
smallest temperature difference a camera
can detect. A thermal camera's sensitivity
will directly impact the image clarity
and sharpness that the camera can
produce. A camera with a low NETD
probably isn't necessary if the targets
measured typically have wide temperature
differences. However, better sensitivity
is required for more subtle applications,
like detecting moisture issues,
security and surveillance, and automotive
applications.
Thermal devices measure sensitivity in
milliKelvins (mK). The lower the numPhotonics
& Imaging Technology, November 2023
Tech Briefs Magazine - November 2023

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