Mutual inductance bridge for low-temperature thermometry and susceptibility measurements

Abstract

We describe a solid-state mutual inductance bridge suitable for low-temperature thermometry and susceptibility measurements. The design features an electronically simulated variable mutual inductance. Particular care is taken to reduce spurious capacitive effects. The bridge is highly stable and linear. It has a resolution of 10(-4) over the range 15 microH to 150 mH, and a noise limited sensitivity of 55 I(p) (-1) nH with a l-s time constant, where I(p) is the rms primary current in mA. Application to thermometry is discussed.

An ac susceptometer for the characterization of large, bulk superconducting samples

“…Several methods can be used to reduce this effect. These include either (i) moving the sample from one pick-up coil to the other and the subtracting the signals [2][3][4], or (ii) using passive or active offset adjustment elements [11,[26][27][28]. Achieving a successful compensation process can be difficult due to the variation of the balance point with temperature, applied field and frequency.…”

AC Magnetic Susceptibility Technique for the Characterization of High Temperature Superconductors

“…A typical ac-susceptometer for measuring the magnetic susceptibility of non-ferromagnetic material is often consisting [16,17] of a primary excitation field coil, a secondary pick-up coil, and a secondary compensation coil (known as three-coil system). Next we will be describing the design made in our laboratory as built for low-frequency ac-susceptibility measurement using local facilities.…”

“…While the ac susceptometer relies on inductive coupling between coils, the pick-up coils were winded beneath the field coils with a shield of low temperature silk thread in tape was used to reduce their capacitive coupling [16] and to achieve thermal good stability as well. As the sample is inserted in one of the coils, a change would occur in the self-inductance as well as in the phase, which both are related to the magnetic susceptibility as shown above.…”

Construção de um Susceptômetro AC Autobalanceado e Estudo de Polímeros Condutores Eletrônicos por Susceptibilidade Magnética e Ressonância Magnética.

“…A forma básica da ponte de indutâncias mútuas foi inicialmente introduzida por Hartshorn [23] . Desde então várias outras versões de pontes de indutâncias mútuas foram desenvolvidas [31][32][33][34][35][36] . As pontes mais comuns [37] são compostas Na divisão que adotamos, a ponte de indutâncias mútuas engloba os circuitos utilizados para gerar corrente e balancear a ponte, e também a parte de controle e aquisição de dados, realizado pelo microcomputador.…”

“…Estes acoplamentos capacitivos, somados com o problema de correntes de fuga através de ponto em comum entre os circuitos primário e secundário, provocam defasagens, que inviabilizam a separação correta entre as componentes real e imaginária da susceptibilidade magnética. Para solucionar estes problemas, a partir da década de 80, foram desenvolvidas novas versões de ponte de indutâncias mútuas, onde os transformadores e indutores foram substituídos por componentes eletrônicos [31][32][33][34][35][36] . Além da vantagem quanto ao problema de defasagem, estas pontes eletrônicas têm também a vantagem de serem de baixo custo, de possuírem alta sensibilidade e, principalmente, de facilitar sua automação através de microcomputadores.…”