Thermoelectric Sensors as Microcalorimeter Load

Abstract

Thermoelectric power sensors can now be used as transfer standards, instead of bolometers, in the microcalorimeter technique. This alternative has the technical advantages to be less sensitive to absolute temperature and not downward frequency limited. At INRiM the high frequency power standards are now based on coaxial thermocouples from dc to 34 GHz. Modified commercial thermocouple mounts in 7 mm and 3.5 mm coaxial line are used to realize the national power standard with an accuracy ranging from 0.03 % to 1 % in the mentioned frequency ra nge.

Improving the primary power standard below 10 MHz with thermoelectric sensors

“…All the right terms of (3) can be easily measured with good accuracy, therefore we expect to obtain a low frequency power standard with an accuracy better then the value that we can claim now, [6].…”

“…effective efficiency η e , rather than absolute power. They are based mainly on the bolometric detection but, more recently, thermoelectric detection has been proposed at least for the coaxial systems, [5,6]. Both detection types allow tracing the HF standard to dc standard, a SI quantity, through the dc/1kHz power substitution [1].…”

Millimeter-Wave Thermoelectric Power Transfer Standard

“…2]). For k 1 ( f = 0) = k 2 , which would correspond to a dc substitution via the RF load (only applicable in the case of coaxial sensors [9]), η gen equals the effective efficiency η eff of a coaxial transfer standard according to (2). Even though an optimization of the resistors' shape and location on the membrane toward a symmetrical configuration might reduce the difference between the responses of the transducers, the residual error would still remain substantial.…”

Improvements on INRIM Coaxial Microcalorimeter and Outcome of a Model Comparison

“…where P X is the power loss in the sensor mount [15]- [17]. Operatively, the expected value of η e can be obtained through a mathematical model that has been widely described in [15]- [24] η e = e 2…”

“…The voltage e 1SC corrects the microcalorimeter loss effects that result as dominant error contribution in the whole process of the power standard realization. This voltage is determined by means of the short circuit technique [15], [20], and it has to be halved to take into account the power reflected back by the short circuit. Finally, the term (1 + | S | 2 ) is an additional correction necessary to enhance the accuracy of the power standard when the reflection coefficient S of the power sensor under calibration is not negligible [18].…”