A PARALLEL-PLATE CAPACITOR USED TO DETERMINE THE COMPLEX PERMITTIVITYOF SUPERCOOLED AQUEOUS-SOLUTIONS IN THE 1 MHZ RANGE

To evaluate temperature-dependent stretching experiments of biological cells down to sub-zero temperatures in a high-frequency electric fiel d, knowledge of the electrical parameters of the suspension is necessa ry. A measuring system was developed to determine the relative permitt ivity epsilon(r)(f,T) and the ionic conductivity gamma(f,T) of superco oled aqueous solutions and suspensions in the frequency range 0.1-2 MH z. A parallel-plate capacitor was used in connection with an impedance analyser and a cryostat. The errors caused by the cables needed betwe en analyser and cooled capacitor were minimized. Field homogenization within the measuring space is realized by correcting the reference pot ential at the guard ring. The starting capacitance at each temperature was reproduced by testing the 0 degrees C value after re-assembling t he capacitor. Damaging of the capacitor by ice formation is prevented. For testing, a comparison was made with literature data and first mea surements of supercooled aqueous solutions.