WO2007060109A1

WO2007060109A1 - Method and device for non-destructive analysis by electromagnetic longitudinal waves

Info

Publication number: WO2007060109A1
Application number: PCT/EP2006/068400
Authority: WO
Inventors: Gianpiero Gervino; Giorgio Santucci
Original assignee: Gianpiero Gervino; Giorgio Santucci
Priority date: 2005-11-23
Filing date: 2006-11-13
Publication date: 2007-05-31
Also published as: ITMI20052233A1

Abstract

Method and device for non-destructive analysis using electromagnetic longitudinal waves.

Description

METHOD AND DEVICE FOR NON-DESTRUCTIVE ANALYSIS BY ELECTROMAGNETIC LONGITUDINAL WAVES

The present invention relates to a method and a device for non-destructive analysis in accordance with the introduction to the main claim.

In the present state of the art many devices and methods for non-destructive analysis are available, including many diagnostic procedures. Examples of these are X-ray and ultrasound techniques, nuclear magnetic resonance and computer aided axial tomography. For non-destructive analysis, industry also uses gamma- rays, useful for identifying the presence of corrosion, and heat waves, effectively used for displaying weak points in composite materials. Non-destructive analysis is also commonly used in the security field, for example for checking the presence of explosives in passenger luggage controls prior to boarding an aircraft, or the presence of metal objects of a certain size before entering a bank. In the medical diagnostic field, non-destructive analysis must importantly be as little invasive as possible for the patient.

For example, it is known that high energy ionising radiation such as X-rays can produce serious pathologies in the long term. Besides obtaining an image it is also often important to obtain an indication of the chemical composition of the material or body being analyzed, this not being achievable with conventional X-ray investigation instruments. On the other hand, nuclear magnetic resonance is able to selectively display for example the various tissues on the basis of the different response of the tissues to very intense magnetic fields generated in their proximity. Magnetic resonance imaging instruments are however very bulky and expensive.

An object of the present invention is therefore to provide a method and a device enabling the aforedescribed problems to be overcome.

A particular object is to provide a method and a device for non-destructive analysis that provides information on the presence of a determined material within a body to be analyzed, the word "material" meaning any organic or non-organic material, substance, chemical element or compound or tissue. Another object is to provide a method and a device for non-destructive analysis which is not harmful to human health.

Another object is to provide a tomographic system for non-destructive analysis able to provide images of sections through a body to be analyzed, which enable point-by-point recognition of the material with which it is composed, or at least its basic chemical composition or the type of tissue or its organic structure. Said objects are attained by a method and a device the inventive characteristics of which are defined in the claims.

The invention will be more apparent from the ensuing detailed description of a method and an embodiment thereof provided by way of non-limiting example and illustrated in the accompanying drawings, in which: Fig. 1 shows the wave vector k, the electric vector E and the magnetic vector H of a classical electromagnetic wave in the far radiation field;

Fig. 2 shows a longitudinal electromagnetic wave where the electric vector E is almost parallel to the wave vector k in the near radiation field; Fig. 3 shows a block diagram of the device of the invention for analysing a body. The oscillating electromagnetic fields or electromagnetic waves are described by three vectors: wave vectors k, orientated along the same direction and sense as the electromagnetic wave propagation, electric field vector E and magnetic field vector H (see Fig. 1 ). In classical electromagnetic wave representation these three vectors are perpendicular to each other. The direction of the k vector is provided by the straight line joining the point-antenna (i.e. the source which generates the oscillating electromagnetic field) to a point inside the irradiated region of space. It is likewise known that an electromagnetic wave carries an energy equal to W=hv, where v = frequency and h = Plank's constant. An electromagnetic wave also transfers a pulse p = (hv/c), (c = wave propagation velocity) to the bodies (atoms or molecules) it interacts with during its propagation (Compton's effect). From physics it is also known that every atom and/or molecule has electric and magnetic dipole moments (referred to overall as multiple moments) due to both the electron structure and the charge distribution within the nucleus. When exposed to external fields, these multiple moments undergo a double reaction: the modulus of the electric and/or magnetic multipole vectors increases (Stark and Zeeman effects) and tends to align in accordance with the rules of quantum mechanics. Changing the average value of the total electric and magnetic dipole moment of a body by partial alignment of the atomic/molecular vectors (by just a small percentage) induces substantial variation in the dielectric constant ε and in the magnetic permeability μ. The vector alignment produces a drastic reduction in resistivity p (ε and p directly influence the reflection coefficient R, and all, together with μ, are functions of frequency), ε, μ, p are therefore three parameters which satisfactorily describe the macroscopic electromagnetic properties of matter and are controlled by microscopic phenomena involving atoms/molecules. In this respect, materials having negative values for ε and/or μ are known and hence the refractive index n is also negative. These materials, the existence of which was predicted in 1968 by the Russian physicists Veselago, are known as "metamaterials".

If the external field is an incident electromagnetic wave, the manner of its interaction, which comprises absorption and/or scattering, is strongly influenced by the value of the multipole moments at the scatter centres and by their alignment. According to Rayleigh's law, which governs this type of interaction, maximum scattering of a non-ionising electromagnetic radiation occurs when the incident electric vector E is parallel to the electric dipole moment d of the scattering body. In the case of an electromagnetic wave with E normal to the propagation direction k, E is alone responsible for alignment of the electric dipoles inside the materials within which the electromagnetic radiation propagates. Likewise H is responsible for alignment of the magnetic dipoles. It is known and predicted by theoretical physics that in proximity to an antenna emitting electromagnetic waves, the electric field vector E is not normal to the propagation direction and hence to the wave vector k, but instead is almost parallel to it ("near field" or longitudinal field), as shown in fig. 2, to produce in this manner an electromagnetic longitudinal wave similar to sound waves. The electromagnetic wave, which is longitudinal in proximity to its emitting antenna, has its electric field vector E gradually becoming normal to the propagation direction as the electromagnetic wave becomes more distant from said antenna ("far field"). The region within which the wave is longitudinal hence presents the characteristic of being evanescent with increasing distance from the antenna which has emitted it. The definition of "evanescent field" derives from the classical theory of electromagnetism, as described for example in "L. Landau - Electrodynamics of continuum media". In general the near field extends as far as λ/10 from the antenna (where λ is the electromagnetic wave wavelength), the region between λ/10 and λ/4 being considered an intermediate region in which "near field" and "far field" coexist. Making a suitable antenna, i.e. a directional antenna, the near field region can be extended up to λ/4. As the near field region can be expressed as a function of the wavelength utilized, it follows that the extent of the near field, i.e. the region in which the electromagnetic wave is substantially longitudinal, is a function of the wave frequency itself, decreasing as the frequency increases. It is also known that within the region in proximity to the antenna by which the electromagnetic wave is propagated, a magnetic field vector H can be obtained substantially parallel to the wave vector k and evidently normal to E. If for example a coil is traversed by an alternating current, the vector H along the coil axis and in proximity thereto is parallel to the coil axis and to the propagation direction of the electromagnetic wave defined by the wave vector k. On moving away from the coil the magnetic field again becomes perpendicular to the electromagnetic wave propagation direction. Reference will be made hereinafter to longitudinal waves in which E is substantially parallel to k, but a similar argument can be made for longitudinal waves in which H is substantially parallel to k. The difference is that E tends to align the electric dipole moments while H tends to align the magnetic dipole moments. Hence generally, if not otherwise specified or evident from the text, the term "longitudinal wave" or "longitudinal electromagnetic wave" refers hereinafter to an electromagnetic wave in which the electric field E or magnetic field H are substantially parallel to the wave vector k which defines the wave propagation direction, by which is meant that the vector E or the vector H form with the wave vector k an angle between 0° and 30° and preferably between 0° and 10°. It has been surprisingly found that if the wave is of longitudinal type, with E substantially parallel to k, it transfers a pulse p = (hv/c) in the same vibration direction as the electric vector E, to the bodies (atoms or molecules) with which it interacts during its propagation, and that the two effects are added together. Likewise, for a longitudinal electromagnetic wave with H substantially parallel to k, the pulse p collaborates with H in aligning the magnetic dipole moments. In other words, taking as reference the longitudinal electromagnetic wave in which E is parallel to k, the wave-matter interaction transfers a pulse and hence kinetic energy to the matter in the direction in which the electromagnetic wave is polarized, and hence in the direction in which the electric vector E oscillates, to facilitate alignment between the dipole moments of the molecules and E. In the case of a "classical" electromagnetic wave, i.e. transverse, E is perpendicular to k, hence the pulse p opposes dipole alignment of the collided molecules (any alignment is due only to the oscillating field E, which has to operate against the disturbance by p).

Hence for equal frequency, the longitudinal electromagnetic wave has the maximum probability of interacting with matter (Rayleigh's law), as by interacting with the electric or magnetic dipole moments of the irradiated body it utilizes the transported energy (W = hv, where v = frequency, to align them, via these interactions (Compton's effect), with its propagation direction and hence with E (or H). For equal irradiated power the power scattered by the body is maximized. As the scattered waves are strictly related to the electromagnetic properties of the scattering body, by using frequencies within the micro-wave range or lower, where the wavelength is much greater than the molecular dimensions, a collective response of all the individual constituent materials of the body is obtained, correlated with its macroscopic characteristics such as ε, n, p and μ. For equal incident power the increase in scattered power can be evaluated to one order of magnitude. If the frequency of the longitudinal wave is equal to the electrical (or magnetic) dipole resonance frequency, the refractive index n becomes negative, to transform the irradiated object into a "metamaterial", which behaves as a "perfect mirror" for the incident wave, i.e. it almost totally reflects the power of the incident wave (greater than 90% if perpendicular). This effect hence enables the presence of a material to be identified, even if it occupies a physical space considerably less than the wavelength with which it is irradiated, as each material has its own response to the interaction with the longitudinal wave.

This property of longitudinal electromagnetic waves can be utilized, on the basis of the irradiated material and the incident electromagnetic wave frequency, to selectively modify the average value of the electrical or magnetic dipole moment within a body to be analyzed. This enables the dielectric constant ε and magnetic permeability μ to be varied, so reducing the resistivity p and increasing the reflection coefficient R. The longitudinal electromagnetic wave which strikes the body temporarily modifies its properties, in particular its reflection coefficient, so that the wave is then reflected or scattered, a sensor positioned about the irradiated body being able to receive a signal modified on the basis of interference between the incident wave emitted by the antenna and the wave scattered or reflected by the body. The relative position of the emitting antenna, sensor and body to be analysed is evidently important and can provide useful information.

By varying the longitudinal electromagnetic wave frequency, different energy levels of the substance under examination can be excited: for example the roto- vibrational levels of complex organic molecules can be excited (these all having a high electrical dipole moment due to spatial asymmetry of the charge), or the nuclear quadrupole resonance of a particular nucleus can be excited. The frequency can therefore be utilized as the selecting agent between the various chemical elements and/or compounds. A further selection factor is represented by the generated interference figure. In the case of a well focused field, the electric field generated by polarization (the term polarization is limited herein to considering the alignment of electric dipoles, however a similar reasoning can be made for magnetic dipole moments) increases more rapidly than the "elastic" return force related for example to thermal disturbances. A very large polarization can be observed locally ("polarization catastrophe"), but this needs to be maintained merely for the time required to irradiate just a small percentage of atoms of the sample with the dipole moment axis aligned and with the refractive index n able to reach a negative value, so that perpendicular incident rays are reflected back out of phase by π, by a percentage of 95%-97% of the incident power. In this manner a characteristic and easily recognizable interference figure is generated for each substance. The power required for the longitudinal electromagnetic wave to determine a dipole alignment is extremely low, of the order of a fraction of one watt, hence it is easy to generate.

The present invention relates to a method of non-destructive analysis composed of a calibration stage and a measurement stage. Hereinafter the term "body to be analysed" indicates a body which is to be analysed to identify its composition in terms of materials or substances. The term "sample" indicates a body consisting essentially of a single known material which is used for calibration. The calibration stage (performed only once for the different materials) consists of the following steps: a) a sample composed of a known material is irradiated with a longitudinal electromagnetic wave at a predetermined frequency; b) the electromagnetic field is measured about the sample, to obtain a response signal at the predetermined frequency; c) this response signal is stored on a suitable support, for example a RAM (random access memory); d) the same sample composed of a known material is again irradiated with a longitudinal electromagnetic wave of a predetermined frequency different from the preceding; e) the electromagnetic field is measured about the sample, to obtain a response signal at this frequency; f) this response signal is also stored on a suitable support, for example a RAM; g) steps d), e) and f) are repeated until the material has been sufficiently characterised, for example until the intrinsic resonance frequency of the tested material has been identified; h) the electromagnetic "fingerprint" of the known material defined by the response signal measured at the different frequencies is stored on a suitable support, for example a non-volatile magnetic memory.

The calibration procedure described herein is repeated for different materials in order to achieve a characteristic fingerprint for each material. The band within which the frequency of the longitudinal wave is varied must be sufficiently wide and the measurements within the band must be sufficiently dense, to succeed in characterising the material. When calibration is complete and the fingerprints of various materials have been stored, a body in which the presence of one or more of the materials of which the fingerprint has already been stored can be analysed. This measurement stage consists of the following steps:

1 ) a body to be analyzed, composed of one or more materials the presence of which is to be identified, is irradiated with a longitudinal electromagnetic wave at a predetermined frequency; 2) the electromagnetic field is measured about the body to be analyzed, to obtain a response signal at the predetermined frequency;

3) this response signal is stored on a suitable support, for example a RAM;

4) the body to be analysed is irradiated with a longitudinal electromagnetic wave of a predetermined frequency different from the preceding; 5) the electromagnetic field is measured about the sample, to obtain a response signal at this new frequency;

6) this response signal is also stored on a suitable support, for example a RAM;

7) steps 4), 5) and 6) are repeated until the "overall fingerprint" of the materials present, for example the various resonance peaks or figures, has been determined with sufficient precision;

8) the fingerprint obtained is compared with the fingerprints stored for different materials during the calibration stage, to determine the material or materials with which the body to be analysed is composed.

If no sample or body to be analyzed is positioned close to the antenna which generates longitudinal waves, the electromagnetic field is given by the undisturbed longitudinal wave alone. If instead a body is exposed to the longitudinal wave, from the macroscopic viewpoint the alignment of a minimal percentage of dipole moments results, within the irradiated region, in a drastic variation in the values ε, μ, p and n, hence in the incident wave reflection coefficient R. In this manner nearly total reflection of the incident power is obtained, so that the electromagnetic field about the body to be analyzed or about the sample is modified on the basis of the constituent material of the sample. As each substance or material responds to the intrinsic resonance frequency of its own electric dipoles, the most convenient manner of characterising a material is hence to find its resonance frequency by continuously varying the frequency of the longitudinal wave within a predetermined band. This band can be limited for example by the requirement not to use too high a frequency, resulting in radiation harmful to man, even if, as is currently the case with many investigation techniques, a certain level of radiation harmfulness can be tolerated because of the advantages deriving therefrom. The fingerprint of a material can advantageously be defined by the peak corresponding to its resonance frequency. If the body to be analyzed is not homogeneous but composed of different materials, during analysis its fingerprint will appear as the composition of several known fingerprints, this enabling the constituent materials of the body to be determined. For example, the characteristic resonance peaks or the interference figures of its various constituent materials can be recognized at the different frequencies. From the aforegoing, it is particularly advantageous to measure the electromagnetic wave reflected rearwards by the body to be analyzed or by the sample, because by varying the frequency of the longitudinal wave, when the longitudinal wave frequency is equal to the dipole resonance frequency the refractive index n becomes negative and the irradiated body behaves as a mirror. As the longitudinal electromagnetic wave can totally pass through the body to be analyzed, it can be interesting to determine not only of which materials the body is composed, but also their arrangement within its interior. To achieve a good spatial resolution, the longitudinal electromagnetic wave must be focused on a sufficiently small region. As it penetrates to the interior of the body to be analyzed starting from its surface, the body can be made to gradually enter the "near field" region in which the wave is longitudinal, by gradually making the body to be analyzed gradually approach the antenna emitting the longitudinal electromagnetic waves. In this manner the longitudinal wave penetrates gradually and increasingly into the interior of the body to be analyzed. The data collected as the longitudinal wave gradually penetrates increasingly deeply can then be analyzed by using a common inversion technique, to hence obtain information not only regarding the substances or materials present in the body, but also regarding their position. The body to be analyzed can maintain its position fixed relative to the points in which the electromagnetic field is measured while these are moved to penetrate into the near field region, or the points at which this electromagnetic field is measured can remain fixed relative to the antenna generating the longitudinal electromagnetic field while the body to be analyzed is moved to penetrate into the near field region. The same result can be obtained by causing the body to be analyzed to emerge from the near field region. Information on the position of the material activated by a particular longitudinal wave in the body to be analyzed can also be obtained by the direction along which the incident wave is preferably scattered or reflected and by its position along a predetermined direction.

If the body to be analyzed is of considerable dimensions, its surface can be scanned to analyze it by parts.

Figure 3 shows an embodiment of the device according to the invention. It can be seen that the longitudinal electromagnetic wave generator 1 is connected to a directional emitting antenna 2, which emits electromagnetic waves at the desired frequency. The "near field" region, which presents an electric field E (or H) sufficiently parallel to the field vector k, and hence parallel to the wave propagation direction, is bounded by the line L. The body to be analyzed or the sample 3 is disposed in proximity to the antenna within the longitudinal wave field. A detector 4 is positioned in proximity to the body or sample 3, and in the embodiment of the figure comprises a reception antenna 5, an adjustable pass band filter 6 and a receiver 7. Figure 3 also shows a comparator 8 connected to the detector 4 to store the signals obtained by the detector 4 and compare them with other reference signals previously stored on a suitable support. The comparator function can be provided for example by a normal computer with an acquisition card, hence able to acquire, store and compare signals. To better characterise the response of a material, a body to be analyzed or a sample, it is useful to locate several detectors within the test region, positioned at different points, although for descriptive simplicity only one of these will be considered.

Any antenna from which electromagnetic waves propagate generates about it (near field) a field of longitudinal waves which dissolve at a certain distance from it. The emitting antenna is preferably of directional type and made such that the near field, i.e. the region in which the waves are substantially longitudinal, extends as far from the emitting antenna as possible, is directed in a predefined direction and is concentrated within a small a region as possible, in order to improve the spatial resolution of the instrument. The further the region in which the waves are longitudinal extends from the antenna, the greater the test region and hence the greater the size of the body which can be analyzed. The generator 1 must be able to modify both the frequency and the amplitude of the generated electromagnetic wave. Varying the frequency serves to identify the resonance frequencies useful for characterising the different materials. The frequency also influences the size of the near field region. Varying the power and hence the amplitude of the waves is useful for obtaining a stronger signal which can be better distinguished from background noise. The comparator 8 possesses all the stored fingerprints for which the device was initially calibrated and is hence able to recognize.

The device has firstly to be calibrated by following, for each material which is to be identified, the steps from a) to h) of the calibration procedure. The electromagnetic fingerprints of the different materials are stored in the comparator 8 and are then ready to be compared with the overall fingerprints determined for the bodies to be analyzed.

In operation, the body to be analyzed is inserted into the "near field" region in proximity to the emitting antenna 2. The body to be analyzed is then irradiated with longitudinal waves of predetermined frequency while simultaneously the detector 4 (normally more than one) measures the electromagnetic field at the longitudinal wave frequency with which the body is being irradiated, and the result is stored. The pass band filter 6 enables the detector 4 to select this frequency and as far as possible filter out noise and undesirable signals. The frequency of the longitudinal wave is varied and the measurement with the detector 4 is repeated, again storing the result. The frequency of the longitudinal wave is varied within a predetermined band while taking a number of measurements sufficient to characterise the constituent material of the body to be analyzed on the basis of its response. The fingerprint of the body to be analyzed, determined at the various frequencies and stored for example in digital form, is compared by the comparator 8 with the fingerprints determined during calibration with known materials. In this manner the comparator 8 is able to establish which materials are present in the body to be analyzed.

The position of the reception antenna 5 of the receiver 4 relative to the body 3 under examination is very important, as the interaction between longitudinal waves and matter aligns the dipoles to vary the reflection coefficient of the waves. For this reason it is important to position several detectors 4 about the body 3 under examination, or to be able to move the reception antenna 5 of the receiver 4 about the body 3 under examination. The wave striking the body to be analyzed 3 can be reflected or scattered in preferential directions relative to the direction of incidence of the longitudinal wave on the body to be analyzed. In addition to the direction, the position in which this reflected or scattered wave is detected can also give useful information on the constituent materials of the body to be analyzed and on their arrangement or aggregation within it.

It is particularly advantageous to have a detector 4 in a position suitable for measuring the longitudinal wave reflected back from the body under examination, in order in this manner to easily determine the frequency at which the material under examination is transformed into metamaterial, reflecting the incident wave rearwards.

The device is advantageously provided with a support to locate the body to be analyzed 3 in a position identical to that of the sample relative to the emitting antenna 2 generating the longitudinal wave and to the reception antennas 5 of the detectors 4.

This support could be movable to be able to move the body to be analyzed into and out of the longitudinal field region, in order to be able to analyze voluminous body parts of dimensions greater than those of the near field region or to better locate the sought material within the body to be analyzed. In this respect, two possibilities exist: the emitting antenna 2 could be moved relative to the body to be analyzed 3, by making it gradually enter or leave the longitudinal field while the reception antennas 5 remain fixed relative to the body to be analyzed 3, or alternatively the body to be analyzed 3 can be moved into or out of the longitudinal field while the reception antennas 5 remain fixed relative to the emitting antenna 2. With a known inversion technique applied before comparison with the stored fingerprints, the device is able to carry out a tomography on the body to be analyzed. This comparison can be improved by storing the fingerprints of the samples taken in different positions within the longitudinal field.

Various fields of application exist for the method and device of the present invention, for example the biomedical sector, the analysis of tissues or substances, the security sector and industrial non-destructive testing. The potential of this analysis technique is its rapid response to constituent substances and its ability to determine the chemical organization of a sample, without having to use destructive methods while still obtaining a rapid response, by comparison with interference signals (fingerprints) stored on a suitable support (a "library"). In principle, the electromagnetic waves utilized can be at any frequency, however the most interesting applications, in particular in the biomedical field, are those using frequencies between kHz frequencies and GHz frequencies. As stated, the power consumed is also low, being just a fraction of a watt. The body to be analyzed must be irradiated with longitudinal waves and the electromagnetic interference field created by the even partial alignment of electric and magnetic dipole moments be detected preferably by at least three detectors disposed in suitable positions about the body to be analyzed. Said detectors must be connected to a spectrum analyser comprising at least one band pass filter 6, to analyze the signal received. This signal is compared with previously stored signals by a comparator 8. To identify a determined substance, the longitudinal wave must preferably scan the frequency band previously defined as characteristic of the substance to be tested for its presence. In the medical field the applications are particularly interesting: certain pathologies present concentrations of ions or of particular substances in such quantities that the relaxation time characteristic of the tissue is altered thereby. This results in substantially different responses for the same incident longitudinal wave frequencies, enabling a healthy tissue to be distinguished from an unhealthy tissue. All organic molecules have a high dipole moment, and depending on the type of tissue there is a different ion concentration and composition which heavily affects the relaxation time τ. Different relaxation times correspond to a different type of tissue or a different pathological situation for the same tissue. In particular pathologies, healthy tissues can be distinguished from unhealthy tissues, the discrimination being observed in the resonant alignment of the electric dipole axis, which may or may not result in the attainment of a state of negative refractive index n. Certain pathologies, including carcinomas and melanomas, have a heavy alteration in the calcium cycle and present a drastic increase in the local concentration of Ca⁺⁺ ions and hyaluronic acid in the intercellular matrix. Ca⁺⁺ and hyaluronic acid have one of the highest electric dipole moments and present a large probability of interacting with the oscillating field: this results in a considerable tendency to align their electric dipole axis with the vector E. The local field generated by the induced alignment is sufficient to trigger a chain action so that other dipole moments are induced to align (including locally present ions and molecules other than Ca⁺⁺), such that for example the Ca⁺⁺ ion acts as catalyst in creating a region with ε and μ values totally different from the surrounding tissue where its concentration does not reach the critical values. This peculiarity of the ε and μ values leads for certain frequencies to negative n values, easily recognizable by measuring the power scattered through 180° and the phase displacement from the incident wave (about π, deducible from the resultant interference wave). This principle is particularly promising for noninvasive medical diagnostics.

Considerable applications are possible in the security sector. For example plastic explosives, which are the most difficult to identify, present a chemical composition formed from organic substances with a high electrical and magnetic dipole moment. TNT has a chemical structure of ¹H-¹⁴N type, with the nitrogen nucleus presenting high nuclear quadrupole resonance (NQR) excitable with frequencies within the range 3-5 MHz by the indirect method (by which the excitation is transferred to the nitrogen nucleus via the hydrogen atom chemically bonded to it). By using focused oscillating fields even if of relatively low power, and with the characteristic of presenting a vector E parallel to the propagation pulse p, a polarization phenomenon occurs in the case of plastic explosive which leads to a special fingerprint determinable by the receiving antennas, while in the case of TNT in addition to electrical polarization, the further advantage of NQR excitation can be utilized, by which scattering is nearly zero at π/2 to the propagation direction of the oscillating field. By comparison with a "library" containing fingerprints of known materials, the present technique is able to selectively identify the materials present in a body to be analyzed. Moreover, as the frequency of the radiations used is low, they are not harmful to human health. Finally, as the location of materials identified as present can be determined, a body to be analyzed can be subjected to tomographic analysis.

Claims

1. A method for non-destructive analysis using electromagnetic waves, characterised in that said electromagnetic waves are of longitudinal type.

2. A method for non-destructive analysis as claimed in claim 1 , characterised by comprising the following steps: a) a body to be analyzed is irradiated with a longitudinal electromagnetic wave at a predetermined frequency; b) the electromagnetic field is measured about the body to be analyzed, to obtain a response signal at the predetermined frequency; c) said response signal is compared, relative to the predetermined frequency, with at least one reference signal associated with a material the presence of which is to be identified in the body to be analyzed.

3. A method for non-destructive analysis as claimed in claim 2, characterised in that each reference signal associated with a material is acquired by the following calibration procedure: a) a sample composed essentially of a known material is irradiated with a longitudinal electromagnetic wave at a predetermined frequency; b) the electromagnetic field is measured about the sample, to obtain a response signal at the predetermined frequency; c) this response signal is stored as the reference signal relative to the predetermined frequency for the material with which the sample is essentially composed.

4. A method for non-destructive analysis as claimed in claim 2, characterised in that said response signal is stored prior to its comparison with the reference signals (step c).

5. A method for non-destructive analysis as claimed in claim 4, characterised in that the procedure consisting of irradiating the body to be analyzed, measuring the electromagnetic field and storing the response signal, is repeated for a plurality of different frequencies, to acquire an assembly of signals known as the "overall fingerprint" of the materials present in the body to be analyzed.

6. A method for non-destructive analysis as claimed in claim 3, characterised in that the described calibration procedure is repeated for a plurality of different frequencies, the stored response signals obtained for each frequency forming the fingerprint of the material with which the sample is essentially composed.

7. A method for non-destructive analysis as claimed in claims 5 and 6, characterised in that the overall fingerprint obtained for the body to be analyzed is compared with the fingerprints relative to known materials, in order to determine the presence of such materials in the body to be analyzed.

8. A method for non-destructive analysis as claimed in one or both of claims 5 and 6, characterised in that the overall fingerprint for the body to be analyzed and the fingerprints of known materials comprise the resonance peaks at the different frequencies.

9. A method for non-destructive analysis as claimed in claim 2, characterised in that the longitudinal electromagnetic wave irradiates the body to be analyzed by originating from a certain direction, and that the electromagnetic field the measurement of which generates the response signal is measured in one or more predetermined directions relative to the body to be analyzed and to the direction from which the longitudinal electromagnetic wave originates.

10. A method for non-destructive analysis as claimed in claim 3, characterised in that during the calibration procedure the longitudinal electromagnetic wave irradiates the sample by originating from a predetermined direction, and that the electromagnetic field the measurement of which generates the response signal is measured in one or more predetermined directions relative to the body to be analyzed and to the direction from which the longitudinal electromagnetic wave originates.

11. A method for non-destructive analysis as claimed in claim 9, characterised in that the electromagnetic field the measurement of which generates the response signal is measured in one or more predetermined directions relative to the body to be analyzed and to the direction from which the longitudinal electromagnetic wave originates.

12. A method for non-destructive analysis as claimed in claim 10, characterised in that the electromagnetic field the measurement of which generates the response signal is measured in one or more predetermined positions relative to the body to be analyzed and to the direction from which the longitudinal electromagnetic wave originates.

13. A method for non-destructive analysis as claimed in one or both of claims 9 and 10, characterised in that the sample and the body to be analyzed are disposed substantially in the same position relative to the direction from which the longitudinal electromagnetic wave originates and to the predetermined directions in which the electromagnetic field generating the response signal is measured.

14. A method for non-destructive analysis as claimed in one or both of claims 11 and 12, characterised in that the sample and the body to be analyzed are disposed substantially in the same position relative to the direction from which the longitudinal electromagnetic wave originates and to the predetermined positions in which the electromagnetic field generating the response signal is measured.

15. A method for non-destructive analysis as claimed in one or both of claims 9 and 10, characterised in that the response signal is generated by measuring the electromagnetic wave reflected substantially rearwards from the body to be analyzed and hence forming about 180° with the direction and sense of the longitudinal electromagnetic wave which irradiates the body to be analyzed.

16. A method for non-destructive analysis as claimed in one or both of claims 2 and 3, characterised in that the body to be analyzed or the sample is gradually inserted into or extracted from the region in which the electromagnetic wave is longitudinal.

17. A method for non-destructive analysis as claimed in the preceding claim, characterised in that the measured response signals are processed by an inversion technique.

18. A device for non-destructive analysis, comprising an electromagnetic wave generator (1 ) connected to an emitting antenna (2), to generate electromagnetic waves for irradiating a body to be analyzed or a sample (3), and further comprising at least one detector (4) for detecting the electromagnetic field about the body to be analyzed by means of a reception antenna (5), to obtain a response signal, and also comprising a comparator (8) for comparing said response signal with at least one reference signal, each associated with a material of which the presence in the body to be analyzed is to be determined, characterised in that said electromagnetic waves are of longitudinal type.

19. A device for non-destructive analysis as claimed in claim 18, characterised in that said emitting antenna (2) is of directional type.

20. A device for non-destructive analysis as claimed in claim 18, characterised in that said detector (4) comprises a receiver (7) and an adjustable band pass filter (6).

21. A device for non-destructive analysis as claimed in claim 18, characterised in that the generator (1 ) and the emitting antenna (2) emit longitudinal electromagnetic waves at different frequencies.

22. A device for non-destructive analysis as claimed in the preceding claim, characterised by being arranged to obtain an overall fingerprint from the body to be analyzed.

23. A device for non-destructive analysis as claimed in claim 18, characterised in that said comparator (8) compares said overall fingerprint with one or more reference fingerprints, each associated with a material of which the presence in the body to be analyzed is to be determined.

24. A device for non-destructive analysis as claimed in claim 18, characterised in that the generator (1 ) and the emitting antenna (2) emit longitudinal electromagnetic waves of different amplitudes.

25. A device for non-destructive analysis as claimed in claim 18, characterised in that the detectors (4) are arranged to measure the electromagnetic field about the body to be analyzed at the same frequency as the longitudinal electromagnetic wave generated by the antenna (2), to obtain a response signal.

26. A device for non-destructive analysis as claimed in claim 18, characterised in that the reception antennas (5) for the detectors (4) are disposed in predetermined positions relative to the emitting antenna (2).

27. A device for non-destructive analysis as claimed in claim 18, characterised in that the reception antennas (5) for the detectors (4) are disposed in predetermined positions relative to the body to be analyzed or the sample (3).

28. A device for non-destructive analysis as claimed in claim 18, characterised in that at least one reception antenna (5) for a detector (4) is disposed in a position such as to receive the longitudinal electromagnetic wave reflected substantially at 180° by the body to be analyzed.

29. A device for non-destructive analysis as claimed in claim 18, characterised in that the body to be analyzed (3) is movable relative to the emitting antenna (2).

30. A device for non-destructive analysis as claimed in the preceding claim, characterised by comprising means for processing the obtained signals by an inversion technique.