Abstract: Process and apparatus for determination of permeability of porous media by measurement at finite frequency of streaming potential and electro-osmotic induced voltage and pressure due to applied finite frequency pressure oscillations and alternating current, respectively. The inter-electrode distance between points of application and measurement of the alternating signals at a finite frequency is small compared to the wavelength of the pressure oscillations and alternating current voltage.

Abstract: A force-generating actuator connected at or across points of a structure capable of relative motion at an exciting frequency is operated to input a predetermined load into the structure and the response of the structure is measured for analysis. In one form of the invention the actuator is one of a plurality of actuators of an active vibration control system which is isolated and operated independently in a shake test mode. Advantageously, especially in a helicopter application, the remaining actuators can continue to be operated to reduce background vibration.