= Microbolometer
{wiki}
A \b[microbolometer] is a miniaturized <bolometer> in which absorbed <electromagnetic radiation> heats a thermally isolated sensing element and the readout detects the resulting change in <electrical resistance>. Arrays of microbolometers can form an <infrared> image without cryogenic detector cooling. A pixel commonly has an absorbing membrane suspended above its readout circuit on narrow supports.<Microbolometer Basics: Structure, Operating Principle, and Key Parameters by Automation Technology>[Detector Structure of a Microbolometer Pixel; operating principle]{ref}
An elementary small-signal <heat transfer> model writes
$$
C\frac{d\theta}{dt}+G\theta=\eta P(t),\qquad \theta=T-T_b.
$$
Here $C$ is the sensing element's <heat capacity>, $G$ its <thermal conductance> to a fixed-temperature substrate $T_b$, $P$ incident <radiant power> and $\eta$ its absorbed fraction. The model treats the element as having a single <temperature> and neglects changes in readout self-heating. A step to constant incident power $P_0$ gives
$$
\theta(t)=\frac{\eta P_0}G\left(1-e^{-t/\tau}\right),\qquad \tau=\frac CG.
$$
The <thermal time constant> therefore connects sensitivity to response speed. Lowering $G$ increases the steady temperature rise, but at fixed $C$ also lengthens the response.<Microbolometer Basics: Structure, Operating Principle, and Key Parameters by Automation Technology>[How a Microbolometer Converts Infrared Radiation into a Signal, thermal conductance and time constant]{ref}
For an original example, choose $C=10^{-9}\,\mathrm{J\,K^{-1}}$, $G=10^{-7}\,\mathrm{W\,K^{-1}}$, $\eta=0.8$ and $P_0=1\,\mathrm{nW}$. Then $\tau=10\,\mathrm{ms}$ and the final sensing-element rise is $8\,\mathrm{mK}$; after $30\,\mathrm{ms}$ it has reached about $95\%$ of that rise. If the initial resistance is $100\,\mathrm{k\Omega}$ and the <temperature coefficient of resistance> is $\alpha=-0.02\,\mathrm{K^{-1}}$, the linear approximation $\Delta R\approx\alpha R\theta$ gives $\Delta R=-16\,\Omega$ at steady state. These stipulated values illustrate the model, not a particular camera's specification.
The sensing element's temperature rise is not the observed object's temperature rise. Inferring object temperature from the measured <infrared> signal additionally depends on <emissivity>, reflected radiation, the optical path and <measurement calibration>. “Uncooled” also permits temperature stabilization of the array; it describes the absence of required cryogenic operation, not the absence of thermal design.
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