| 摘要 |
The metal detection apparatus comprises a transmitter unit (1), which provides transmitter signals to a transmitter coil (21) that is coupled to a receiver coil (3), which is connected to the input of a receiver unit (4), said transmitter unit (1) comprises a frequency generator (11) that provides an operating frequency (f TX ) to the input of an amplifier stage (12), whose output is connected via a transformer (13) to the transmitter coil (21). According to the invention the output of the amplifier stage (12) is connected to a first tap (141; 142; 143) and the transmitter coil (21) is connected to a second tap (151; 152; 153; 154) of the same transformer winding (131) of the transformer (13), 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 (151; 152; 153; 154) and the common potential, wherein the transmitter coil (21) comprises the number of q winding coils and is connected in parallel to a capacitor (221) thus forming a resonant circuit that is tuned to the operating frequency (f TX ) and wherein the ratio (n+m)/q of the winding coils of the transformer winding (131) and the winding coils of the transmitter coil (21) is selected such that the inductance of the transformer winding (131) is at least ten times higher than the inductance of the transmitter coil (21). |
