Electronic Gate Detection for the Counting and Sizing of Cells or Colloidal Particles in Liquids: Front-end Characteristics, Specific Problems and their Remediation. Part 1: Physical Model and Equivalent Circuits.

DC, RF and LF operated gating for cell/particle counting and sizing in liquids are hindered by unstable gate impedance. Most problematic appear transients and fluctuations due to varying flow patterns of the carrier liquid. Their effects, largely hidden in DC-operated gating, cause broadening and shift of cell/particle size distributions. RF/LF-operated gating, more specifically the demodulation of the AM-encoded gate signal, is much more disturbed. For a systematic study of these effects, an equivalent circuit is presented along with a procedure to determine the system parameters