HARMONIC-GENERATION IN NONLINEAR BIOLOGICAL-SYSTEMS

We describe a high performance, low frequency Fourier Transform based spectrum analyser, with design features particularly suited to the har monic analysis of the non-linear amplitude transfer functions of vario us biological systems. A previous published method, using general purp ose systems to produce reference and signal plus reference ''power'' s pectra, was susceptible to ambiguous interpretation of results. Unlike that design, the present spectrometer derives quantitative complex vo ltage (amplitude and phase) harmonics of sampled voltage data, maintai ning potentially important information. Based on the use of a basic IB M or compatible PC, it features high sensitivity, high speed data proc essing and large dynamic range, is compact, easy to use, flexible in o peration and low in cost. Its precision current signal source eliminat es harmonics generated at the drive electrodes from the measurement. U se of the instrument leads us to conclude that, contrary to previous a ssertions, no repeatable dielectric or conductive non-linearity is exh ibited in the bulk cell suspensions tested under the field and frequen cy conditions reported.