Abstract: The present invention contributes to the resolution of the problem of detecting, for example, plastic explosives, which are not easily detected by conventional inspection techniques, as those based on X-ray apparatuses; or those using more sophisticated means from traces of explosive material which may remain, “contaminating” the external surface of luggage. As regards the first technique, the invention has an additional advantage in that it is fully automatic, that is, it is independent from the operator's ability to interpret low contrast images. As regards the second technology, the main advantage of the present invention consists of its speed and safety when inspecting luggage.

Abstract: 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 Tx 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 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 of common mode, 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.