Precision time-domain dielectric spectrometer

A description is given for an automated method for determining dielectric constant and loss by the measurement of the time response of the dielectric to a step voltage. Attention is paid to the circuits necessary to achieve high accuracy (0.1%) and high sensitivity (tan δ=10−5) over audio and subaudio frequencies (104 to 10−4 Hz). These include a 100-V step generator accurate to 5 ppm, a charge detector with a time-independent bias current of 30 fA, and a clock that can control sampling time from 5 μs to 10 s. In addition, a numerical Laplace transform, based on a cubic spline, is described that preserves the accuracy of the time data when they are transformed into the frequency domain.