Patent ID: RE39475

Claim:
A tablet for coupling AC energy to a tuned circuit on an implement adapted to be moved over an external flat surface of the tablet and responsive to AC energy coupled back to the tablet from the tuned circuit, comprising: a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils arranged in two coordinate directions, the loop coils being disposed between the faces for emitting the AC energy coupled to the tuned circuit and responsive to the AC energy coupled from the tuned circuit for generating a signal indicative of the implement position relative to the two coordinate directions; and a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on the loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of the AC energy coupled between the loop coils and tuned circuit.