respectively on substrate 60 that lead to terminals 37 and 38 respectively at an edge of substrate 38 are also susceptible to this noise pickup from the time varying magnetic field however the amplified high frequency output signal from amplifier 18 is of a high enough level to override the noise picked up by conductive loops 33 and 34 the problem caused by the noise pickup by loops 27 and 28 is that this noise is fed back into the inputs of amplifier 18 for amplification by amplifier 18 by a factor equal to the gain of amplifier 18 of course conductive loops 51 and 52 connecting the power supply leads to amplifier chip 50 are also susceptible to noise pickup but this noise can be easily kept out of the signal path by common mode rejection with respect to differential amplifiers that is well known to those skilled in the art the magnetic flux density of the time varying magnetic field is expressed as the quantity h the time rate of change of the flux density of this magnetic field is expressed as the quantity h the voltage induced into the conductors is equal to the area bounded by the conductors that is perpendicular to the time varying magnetic field multiplied by h that is for the loops shown in fig2 that are perpendicular to the time varying magnetic field with respect to the relatively high frequency noise conductive loops 27 and 28 can be considered to be connected together and connected to ground at terminals 29 and 30 since capacitors 31 and 32 offer a very low impedance path to ground from terminals.