DC-biased dielectric measurements using an existing frequency-domain spectroscopy (FDS) instrument and series battery

Resumé

We present a simple method for adding DC bias to frequency-domain spectroscopy (FDS) measurements by inserting a battery in series in the ‘high’ lead to the device under test. An instrument designed for FDS measurements with pure AC can be used in this way without modification, even for DC voltages above the instrument’s AC range. Issues and limitations of the method are discussed, along with some alternative methods. Experimental results from FDS measurements on well defined linear objects are compared with/without the DC bias, to check that the measurement is not disturbed by the DC source. The only detected difference was the expected effect of including the battery impedance in series with the specimen in the measurement. This effect was negligible for typical lab-specimen capacitances, around and below power frequency. The nature of battery impedance is further described, as multiple small batteries in series can strongly affect the results for large specimens and at high frequencies.