Apparatus and method for detecting a designated group of materials and apparatus and method for determining if a designated group of materials can be distinguished from one or more other materials.

A method of interrogating a subject for presence of any material that is a member of a designated group of materials and for distinguishing comprising;

• exposing each material selected to belong to said class to terahertz radiation;
• detecting the reflected radiation from each of said materials;
• determining a frequency signature set for which PCA classification has been determined that is sufficiently clustered;
• carrying out a principle component analysis of the reflected radiation in each instance;
• determining a signature frequency set in the reflected radiation which permits the analysis to construct a PCA classification for the materials belonging to the class;
• storing data defining said classification;
• detecting reflected terahertz radiation from a subject;
• carrying out a principle component analysis on said reflected terahertz radiation to obtain PCA classification data characterizing the subject;
• and
• comparing that classification data with the previously stored classification data for determining whether or not the material that reflected the THz radiation is in the designated group of materials.

A method of determining whether or not a suspect material is a member of a designated group of materials which has been characterized by a signature frequency set of absorption spectra for which a PCA classification has been determined;

• exposing the suspect material to terahertz radiation beam comprising said signature set of frequencies;
• detecting reflected terahertz absorption spectra at the signature set of absorption spectral frequencies from the suspect material;
• carrying out a principle component analysis on said reflected absorption spectra for constructing a PCA classification characterizing the suspect material;
• and
• comparing the PCA classification characterizing the suspect material with the PCA classification characterizing the members of the designated group in a manner to determine whether or not there is a match therebetween.

Apparatus for detecting the presence of a material as belonging to a designated group of materials, said apparatus comprising;

• a source of a beam of terahertz radiation comprising a set of frequencies having been previously determined to permit PCA classification data that is distinguishable from that of non-target material;
• said apparatus including means for storing said PCA classification data and means responsive to reflected terahertz radiation to determine PCA classification data for the suspect material;
• means for comparison of the PCA classification data of the suspect material with the previously stored PCA classification data of target and
• means for determining a threat level based on analysis of the closeness of match of the PCA classification data of the suspect material to that of the target material.

The method of determining whether or not a suspect material is a member of a predefined class of members each characterized by a frequency signature set constructed by principle component analysis (PCA) at each of a plurality of frequencies at which the members share an identifiable absorbance feature, said method comprising;

• exposing the suspect material to terahertz radiation beam comprising said plurality of frequencies;
• detecting reflected terahertz radiation from the suspect material;
• carrying out a principle component analysis on said reflected radiation for determining PCA classification data for the suspect material and
• comparing the PCA classification data of the suspect material with the PCA classification data of the members of the predefined class in a manner to determine a threat level from the suspect material.

A method for determining the likely presence of a material that is a member of a class of materials comprising;

• a) determining classification data for distinguishing the material as a member of a designated group comprising;
• i) exposing each material of the designated group to terahertz radiation;
• ii) detecting in a detector reflected radiation from each prospective member;
• iii) selecting frequencies in the reflected radiation at which a plurality of members of the group share an identifiable absorbance characteristic and storing the frequency data in a specially programmed computer;
• iv) in a specially programmed computer, carrying out a principle component analysis on said selected frequencies for obtaining PCA classification data for the class and storing said PCA classification data in a specially programmed computer.
• b) determining the presence or absence of a suspected material comprising;
• i) exposing a suspect material to terahertz radiation comprising said selected frequencies;
• ii) using a detector detecting reflected radiation from said suspect material;
• iii) in a specially programmed computer carrying out a principle component analysis on said radiation at said selected frequencies for constructing a signature set characteristic of the suspect material;
• iv) in a specially programmed computer comparing the signature set characteristic of the suspect material to said stored signature set;
• v) and providing in a display or output device a determination of the likelihood of presence of a suspect material.

A method of determining whether or not a suspect material is a member of a designated group of materials which has been characterized by a signature frequency set of absorption spectra for which a PCA classification has been determined;

• detecting reflected terahertz absorption spectra at the signature set of absorption spectral frequencies from the suspect material;
• carrying out a principle component analysis on said reflected absorption spectra for constructing a PCA classification characterizing the suspect material;
• and
• comparing the PCA classification characterizing the suspect material with the PCA classification characterizing the members of the designated group in a manner to determine whether or not there is a match therebetween.