Bolometer
Understanding Bolometers
Bolometers are the gold standard for absolute power measurement accuracy. By using DC substitution (replacing the RF power with an equivalent DC power), bolometers provide traceable, frequency-independent measurements.
Bolometer Types
- Thermistor: Temperature-dependent resistor. The most common bolometric power sensor. Negative temperature coefficient (NTC).
- Barretter: Thin wire element. Positive temperature coefficient. Less common today.
- Microbolometer: Array of tiny bolometers for imaging. Used in THz and infrared cameras.
DC Substitution
The bolometer element is first heated by DC current to a known resistance. When RF power is applied, the DC power is reduced to maintain the same resistance. The decrease in DC power equals the absorbed RF power. This is the most accurate power measurement method.
Frequently Asked Questions
What is a bolometer?
A bolometer measures RF power by sensing temperature rise of an absorber. DC substitution provides traceable accuracy. Used as primary power standards in metrology labs and for THz detection. The most accurate broadband power measurement method.
How is a bolometer different from a diode power sensor?
Bolometer: thermal detection, any waveform, limited dynamic range (-15 to +10 dBm), highest accuracy, slow response. Diode: rectification, fast response, wide dynamic range (-70 to +20 dBm), lower accuracy, waveform-dependent above square-law region.
What is a microbolometer?
A microbolometer is a tiny bolometer element (< 50 um) in a large array used for imaging. Each element absorbs radiation and changes resistance. Arrays of 320x240 to 1024x768 pixels create thermal images. Used for THz imaging, security screening, and IR cameras.