Abstract: The invention provides a target object detection system, comprising a plurality of sensing nodes (10) for positioning at respective detection locations with respect to a detection area (12) that is situated within a field generated by an ambient AC source of excitation. Each sensing node has at least one electric potential sensor (22, 42) designed to detect perturbations in said field caused by a target object (14), said one sensor including an electrode (20, 40) responsive to the AC excitation field for generating detection signals, an amplifier (28) connected to the electrode for receiving and amplifying the detection signals to produce AC measurement signals as output, and at least one feedback circuit (30, 36) from an output of the amplifier to an input thereof for enhancing the input impedance of the amplifier.

Abstract: An electrodynamic sensor comprises a high input impedance electrometer adapted to measure small electrical potentials originating from an object under test and having a pair of input probes, characterized in that at least one of said pair of input probes has no direct electrical contact with said object, wherein the circuit arrangement of said electrometer comprises an electrode (1) connected to an amplifier (9), which includes a combination of ancillary circuits cumulatively to increase the sensitivity of said electrometer to said small electrical potentials while not perturbing the electrical field associated therewith.

Abstract: The invention provides a target object detection system, comprising a plurality of sensing nodes (10) for positioning at respective detection locations with respect to a detection area (12) that is situated within a field generated by an ambient AC source of excitation. Each sensing node has at least one electric potential sensor (22, 42) designed to detect perturbations in said field caused by a target object (14), said one sensor including an electrode (20, 40) responsive to the AC excitation field for generating detection signals, an amplifier (28) connected to the electrode for receiving and amplifying the detection signals to produce AC measurement signals as output, and at least one feedback circuit (30, 36) from an output of the amplifier to an input thereof for enhancing the input impedance of the amplifier.

Abstract: An electrodynamic sensor comprises a high input impedance electrometer adapted to measure small electrical potentials originating from an object under test and having a pair of input probes, characterised in that at least one of said pair of input probes has no direct electrical contact with said object, wherein the circuit arrangement of said electrometer comprises an electrode (1) connected to an amplifier (9), which includes a combination of ancillary circuits cumulatively to increase the sensitivity of said electrometer to said small electrical potentials whilst not perturbing the electrical field associated therewith.

Abstract: An electrodynamic sensor comprises a high input impedance electrometer adapted to measure small electrical potentials originating from an object under test and having a pair of input probes, characterized in that at least one of said pair of input probes has no direct electrical contact with said object, wherein the circuit arrangement of said electrometer comprises an amplifier which includes a combination of ancillary circuits cumulatively to increase the sensitivity of said electrometer to said small electrical potentials whilst not perturbing the electrical field associated therewith.