There exists interest in the measurement of small forces for applications such as microtopography of semiconductor devices and atomic force microscopy. A new method is introduced here in which a small silicon beam, that is acted on by the external force of interest, has its position sensed by an rf phase shift technique. The position information in turn is fed back via electrostatic forces to continuously rebalance the beam about its central support. This force-feedback approach provides high sensitivity, submillisecond response, inherent force calibration, and electronically controlled stiffness.

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A simple technique has been developed for the high resolution measurement of small changes in capacitors which have one grounded electrode. The capacitor is arranged to be the tuning element in a series resonant LC tank circuit that is driven by a transistor emitter follower. Signal information is provided by observing the phase shift in the transistor collector current that results from any small change in the capacitor value. Implementation is simple, readily analyzable, provides good diagnostics, is easily multiplexed into arrays, and has potential applications in a number of areas including high resolution proximity sensing, capacitive topography, atomic force microscopy, and capacitor microphones.

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