Circuits for determining very accurately the position of a device inside biological tissue

Claim 1

A circuit for determining very accurately the position of a device in biological tissue, comprising: a detector means, said detector means having a field coil which, when activated, generates a field, said detector means also having a first receiving coil and a second receiving coil which are both disposed in the field generated by said field coil, said first receiving coil producing a first a.c. output signal and said second receiving coil producing a second a.c. output signal when the field is generated, and an alarm means, said alarm means having a first rectifier means and a first integrator means, said first rectifier means receiving the first a.c. output signal and converting it to a first d.c. signal and said first integrator means converting the first d.c. signal to a first d.c. averaged signal, said alarm means also having a second rectifier means and a second integrator means, said second rectifier means being an active rectifier having an amplifier means and a means for adjusting the output of said amplifier means, said second rectifier means receiving the second a.c. output signal and converting it to a second d.c. signal, the amplitude of which may be varied by said means for adjusting, and said second integrator means converting the second d.c. signal to a second d.c. averaged signal, the amplitude of the second d.c. averaged signal being adjusted by said means for adjusting to be identical with the first d.c. averaged signal when the device is not detected, said alarm means further including an alarm amplifier means which receives the first and second d.c. average signals and produces an alarm output corresponding to any difference between them, as would be caused by the presence of the device inside the field, whereby the alarm output is used to activate an alarm.