APPLICATION OF MEASUREMENT MODELS TO ELECTROHYDRODYNAMIC IMPEDANCE SPECTROSCOPY

The measurement model concept was used to assess both the stochastic a nd bias contributions to the error structure of electrohydrodynamic (E HD) impedance spectra. The stochastic component of the error structure was determined, and a model for the error structure was identified. R egression employing weighting by the stochastic component of the error structure yielded unambiguous values for physical properties such as the Schmidt number, whereas significant ambiguity was observed using o ther weighting strategies. The influence of surface phenomena on the i mpedance response could, through use of the measurement model for asse ssing consistency with the Kramers-Kronig relations, be distinguished from nonstationary effects. The measurement model provided a quantitat ive means for assessing the utility of input signal filtering. The noi se level in the measured impedance was found to be unaffected by use o f input filters and, surprisingly, the time required to collect the da ta was increased slightly by using the filters. The estimated paramete r values and their standard deviations were comparable whether or not filtering was used. The use of the measurement model to assess stochas tic and bias components of the error structure extends the useful freq uency range for EHD measurements and should enhance the application of EHD for assessing surface phenomena.