Abstract: A search coil assembly for an inductive search device is described having a hield formed from a carrier layer and a thin metal coating applied thereupon, in which the coating is arranged into a plurality of parallel circuit tracks. The circuit tracks are electrically connected to one another by connecting tracks and to a reference potential. The described search coil assembly can be advantageously constructed by multi-layer circuit board technology.

Abstract: A wire loop of almost negligible inductance is coupled with the excitation and receiver coils of metal object detection apparatus which is opened and closed to produce signals in phase with noise signals produced by poorly conductive soils. Enhanced suppression of noise signals is achieved.

Abstract: A wire loop reference transmitter is coupled with the excitation winding and the receiver winding of metal detection apparatus and which can be alternately opened and closed through a switch. In another version the separation of the reference phase transmitter reference signal from other signals is accomplished by periodically turning the reference signal off and on at a predetermined switching frequency. According to a further version this separation is achieved by a phase control demodulator controlled by a switched-on reference signal of a first controllable phase and by a switched-off reference signal with a control signal to obtain a 180 degree second control phase. Still further, control signals of a phase controlled rectifier can be at 90 degrees to the reference signal of the reference phase transmitter.