A sensor assembly for the detection of substances by means of nuclear
quadrupolar resonance (NQR) and in the presence of environmental
interference. The sensor assembly has a transmitter T.sub.x which
comprises excitation means which generate excitation signals and a switch
connected at the outlet of the Transmitter. A first phase-shifted signal
divider/adder is connected to the outlet of the T.sub.x/R.sub.x switch.
First and second sensor elements are connected to the respective outlets
of the first phase-shifted signal divider/adder. First and second
coupling circuits, preferably in common, are connected to the outlet of
the first and second sensor elements, respectively. First and second
amplifiers are connected to the outlets of the first and second coupling
circuits, respectively. First and second bandpass filters are connected
to the outlets of the first and second amplifiers, respectively. A second
phase-shifted signal divider/adder is connected to the outlets of the
first and second bandpass filters, respectively. A receiver R.sub.x is
connected to the inlet of the second phase-shifted signal divider/adder.
The method associated to the sensor assembly is also disclosed.
