Superconducting submillimeter and millimeter wave detectors Page: 10 of 135
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Chapter 2: Principles of Antenna Coupled Bolometers
2.1 Introduction
A bolometer is a thermal detector which in principle, can detect radiation from de to y
rays. Bolometers are the most sensitive direct detectors of radiation for frequencies
between 3 GHz to 1 THz, and have also been used extensively up to 10 THz. All
bolometers include an absorbing element which converts the incident radiation to heat, and
a thermal link between the active region and the heat sink. The rise in temperature of the
thermally active region is measured by a resistive thermometer. Bolometric detectors for
infrared and millimeter waves are used extensively in laboratory and astronomical
applications. Bolometers that operate between LHe temperature and room temperature are
mainly used for laboratory far infrared spectroscopy, while bolometers operating between
0.02 K and 4.2 K are used for very sensitive ground and space-based astronomical and
astrophysics observations. The design parameters of the bolometer depend on the
particular application, and in most cases, the optimization of the bolometer performance
involves a complicated tradeoff between sensitivity, speed of response, dynamic range, etc.
In what follows, I will give an overview of the basic operating principles of bolometers,
and will then motivate the concept of antenna coupled bolometers (also referred to as
microbolometers). I will conclude this chapter with a discussion of the properties of planar
antennas.
2.2 Bolometer Theory
As previously mentioned, a bolometer consists of a thermally active region of heat
capacity C coupled to a temperature bath through a thermal conductance G (Fig. 2.1). The
thermally active region includes an absorber and a thermometer. The temperature rise
AT=To+Tlexp(iwt) of the active region due to a modulated radiant power input
P=Po+Plexp(iot) is found from simple energy considerations4
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Nahum, M. Superconducting submillimeter and millimeter wave detectors, thesis or dissertation, October 20, 1992; California. (https://digital.library.unt.edu/ark:/67531/metadc1311365/m1/10/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.