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

  • US 4,445,501 A
  • Filed: 05/07/1981
  • Issued: 05/01/1984
  • Est. Priority Date: 05/07/1981
  • Status: Expired due to Fees
First Claim
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1. A circuit for determining very accurately the position of a device in biological tissue, comprising:

  • a detector circuit,said detector circuit having a field coil which, when activated, generates a field, said detector circuit also having a first receiving coil and a second receiving coil which are both disposed in the field generated by said field coil,whereby said first receiving coil produces a first output signal and said second receiving coil produces a second output signal when the field is generated,a variable resistor having a wiper, a differential amplifier having first and second inputs and an output,a first side of said first receiving coil and a first side of said second receiving coil being connected to a common reference, a second side of said first receiving coil being connected to said first input of said amplifier, a second side of said second receiving coil being connected to said variable resistor, said wiper of said resistor being connected to said second input of said amplifier so that the magnitude of said second output signal may be varied so as to make it equal to the magnitude of said first output signal when no device is detected in the field,whereby said amplifier provides an output signal when there is a difference between said first and said second output signals from said first and said second receiving coils, andan alarm,said alarm being connected to receive the signal from said amplifier output to produce an alarm signal when there is an output signal, as would be caused by the presence of the device inside the field.

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