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The purpose of this paper is to introduce a rapid method for calculating capacitive sensor signal variations for any small permittivity or electrode modifications at any position in space.

When a capacitive sensor is probing its surrounding, the modification of the permittivity, the displacement or the deformation of one or more electrodes induce a signal variation which depends on the position of the modification. Seeing that modification as a small perturbation and using Gauss identity, it is possible to find integral expressions of the sensor sensitivity map.

Capacitive sensor sensitivity map expressions depend only on the perturbation to measure, on the electric field before the perturbation, and on a sensitivity field which is the electric field produced by the sensor when the measuring electrode is held to 1 V while the others, except the floating ones, are grounded. The sensitivity field is a kind of Green's function for the capacitive sensor. The knowledge of the electric and sensitivity fields makes it possible to obtain the whole sensor sensitivity map at once without requiring time consuming parametric calculations.

The sensitivity field calculation provides a simple and direct view of the capacitive sensor capabilities. That should improve capacitive sensor design.

The Federal Motor Vehicle Safety Standards No. 208 includes directives rendering the morphological estimation of passengers mandatory for advanced air bag systems. The dynamic automatic suppression system uses both the morphological and positional information about the passenger to allow or prevent air bag deployment. Various solutions have been proposed to obtain these information by using capacitive sensors. This paper presents a method, that makes possible use of such sensors in the car industry by correcting their responses from these perturbing parameters.