Planar linear inductive position sensor having edge effect compensation

A planar linear inductive position sensor system comprising:

• a substrate;
• an oscillating coil;
• a first sensing coil having opposing edges extending beyond opposing edges of the oscillating coil along a linear axis along which a linear position of a conductive target is to be sensed;
• a second sensing coil having opposing edges extending beyond opposing edges of the oscillating coil along the linear axis;
• the first and second sensing coils having geometries selected such that equal opposing magnetic fields are induced in the first and second sensing coils in the presence of a magnetic field generated by the oscillating coil when no conductive target is proximate to the first and second sensing coils and unequal opposing magnetic fields are induced in the first and second sensing coils when the conductive target is proximate to the first and second sensing coils, a difference in the unequal opposing magnetic fields induced in the first and second sensing coils correlated to the position of the conductive target;
• a capacitor coupled to the oscillating coil to form a resonant LC circuit at a resonant frequency;
• a signal generator generating a signal at the resonant frequency coupled to the oscillator coil;
• and
• sensor circuits coupled to the first and second sensing coils.

A method for detecting the linear position of a conductive target with respect to a substrate comprising:

• providing an oscillating coil on the substrate;
• providing first and second sensing coils on the substrate, the first and second sensing coils having geometries selected such that equal opposing magnetic fields are induced in the first and second sensing coils in the presence of a magnetic field generated by the oscillating coil when no conductive target is proximate to the first and second sensing coils and unequal opposing magnetic fields are induced in the first and second sensing coils when the conductive target is proximate to the first and second sensing coils, a difference in the unequal opposing magnetic fields induced in the first and second sensing coils correlated to the position of the conductive target, the provided first and second sensing coils having opposing edges extending beyond opposing edges of the oscillating coil along a linear axis along which the linear position of the conductive target is to be sensed;
• exciting the oscillating coil with a generated oscillator signal;
• measuring voltages induced in the first and second sensing coils from the generated oscillator signal;
• and
• determining presence and position of the conductive target as a function of a difference in the voltages induced in the first and second sensing coils.