Apparatus and method for detecting weak magnetic fields having a saturable core shaped to cancel magnetic fields parallel to the core

Method of detecting the presence of extraneous magnetic fields having a predetermined weak magnitude comprising:

• providing a transformer having an excitation winding, an output winding, and a saturable core made of amorphous metal alloy which will saturate in a magnetic field of a predetermined saturation magnitude;
• shaping the core to cancel the electromagnetic effects of magnetic fields having flux lines which are substantially parallel with respect to the transformer;
• connecting an excitation signal to the excitation winding and generating a magnetic field having an excitation magnitude of lesser magnitude than the saturation magnitude of the core, the excitation magnitude of the generated magnetic field and the weak magnitude of the extraneous magnetic field combining to create a magnetic field of greater magnitude than the saturation magnitude of the core;
• and
• detecting saturation of the core.

Apparatus which operates on a micropower consumption level for detecting the presence of extraneous magnetic fields having a predetermined weak magnitude, comprising:

• (1) a transformer having an excitation winding, an output winding, and a saturable core which will saturate in a magnetic field of a predetermined saturation magnitude about equal to or less than the magnitude of the earth's magnetic field;
• (2) excitation means, connected to the excitation winding, for generating a magnetic field having an excitation magnitude of lesser magnitude than the saturation magnitude, the excitation magnitude and the weak magnitude of the extraneous magnetic field combining to create a magnetic field of greater magnitude than the saturation magnitude of the core, the excitation means comprising:
• an oscillator;
• a buffer amplifier connected between the oscillator and the excitation winding;
• and
• a capacitor connected in electrical series between the buffer amplifier and the excitation winding in order to prevent direct current coupling between the amplifier and the excitation winding;
• and
• (3) detection means, connected to the output winding for detecting and indicating saturation of the core, comprising:
• a comparator circuit, connected to the output winding of the transformer, for comparing an output signal of the output winding to a reference signal in order to determine whether the core is saturated and for outputting one of a relatively high signal or a relatively low signal when the core is saturated;
• and
• an output amplifier, connected between the output winding and the comparator circuit, for amplifying the output signal of the output winding.

Method of detecting, at a micropower consumption level, the presence of extraneous magnetic fields having a predetermined weak magnitude, comprising:

• (1) providing a transformer having an excitation winding, an output winding, and a saturable core which will saturate in a magnetic field of a predetermined saturation magnitude about equal to or less than the magnitude of the earth's magnetic field;
• (2) connecting an excitation signal to the excitation winding and generating a magnetic field having an excitation magnitude of lesser magnitude than the saturation magnitude of the core, the excitation magnitude of the generated magnetic field and the weak magnitude of the extraneous magnetic field combining to create a magnetic field of greater magnitude than the saturation magnitude of the core, the connecting step comprising the steps of:
• providing an oscillator;
• connecting a buffer amplifier between the oscillator and the excitation winding;
• and
• connecting a capacitor in electrical series between the buffer amplifier and the excitation winding in order to prevent direct current coupling between the buffer amplifier and the excitation winding;
• and
• (3) detecting saturation of the core, comprising the steps of:
• comparing an output signal of the output winding to a reference signal in order to determine whether the core is saturated;
• outputting one of a relatively high signal or a relatively low signal when the core is saturated;
• and
• amplifying the output signal of the output winding before the output signal is compared to the reference signal.