An interactive security screening system includes a main housing, a contact pad provided on the main housing and a sample sheet positioned upon the contact pad. Electrical position detection circuitry, which may be substantially time-multiplexed or frequency-multiplexed, comprises a differential charge integrator with input-sensed output-driven common mode feedback. The evacuating system includes a vacuum pump, a high-temperature trapping device disposed above the vacuum pump with respect to the flowing direction of a gas, and a low-temperature trapping device disposed below the vacuum pump with respect to the flowing direction of a gas.