Magnetic Resonance and Microwave Techniques for Security Applications

Detection and discrimination of various liquid substances is a very important problem with respect various security and industrial applications. The techniques, which provide a possibility of the chemical-specific identification of various materials, look prospective for practical implementation. Among various techniques of liquid identification, the time-domain nuclear magnetic resonance (TD-NMR) is considered as very promising for detection of energetic, flammable, and other dangerous liquids. TD NMR looks very attractive because of its high selectivity as well as relatively low price and maintenance expenses. However, for a reliable discrimination in a large set of various substances there is a need to obtain additional parameters for discriminations (e.g., the real and imaginary permittivities by dielectric spectroscopy, the
¹⁴
N NMR signal, diffusion constant or T
₁
/T
₂
relaxation times distribution). Dielectric spectroscopy which can measure the dielectric constant and the loss tangent of liquids in the broad range of frequencies (in general, from DC to sub-THz) looks as especially prospective technique for the combined use with TD NMR. In this work, we review possible approaches in TD NMR as well as in MW detection based on probing dielectric permittivities (i.e., dielectric spectroscopy) to probe additional information about liquid content and to shorten the scanning time. Technical approaches for realization of MW detection device as well as construction of TD NMR instrument for obtaining versatile discrimination parameters of the tested liquids are also presented.