Patent ID: 8841903

Claim:
A metal detection apparatus comprising: a transmitter unit adapted to provide transmitter signals to a transmitter coil that is coupled to a receiver coil, the receiver coil connected to the input of a receiver unit; a frequency generator associated with the transmitter unit, the frequency generator for providing an operating frequency to the input of an amplifier stage whose output is connected via a transformer to the transmitter coil and to a first tap of a first transformer winding; a second tap of the same first transformer winding connected to the transmitter coil, the transformer winding having a number of n winding coils between the first tap and a common potential and a number of n+m winding coils between the second tap and the common potential; wherein the transmitter coil comprises a number of q winding coils and is connected in parallel to a capacitor, thus forming a resonant circuit that is tuned to the operating frequency; and wherein the ratio (n+m)/q of the winding coils of the first transformer winding and the winding coils of the transmitter coil is selected such that the inductance of the first transformer winding is at least ten times higher than the inductance of the transmitter coil.