Patent Application
20060056586
This invention relates to a method and an equipment for detecting dangerous objects such as explosives and illegal objects such as drugs (hereinafter referred to as the explosives, etc. or the explosive, etc., as required).
The luggage inspection at airports, etc. is conducted primarily to detect dangerous objects such as explosives, guns and knives and contraband goods such as narcotics. This inspection is conducted not only at airports but also at event halls, post offices and cargo terminals frequented by people. Such an inspection is intended for not only dangerous objects such as explosives or guns but also contraband goods and substances including drugs and toxic microorganisms such as anthrax.
The X-ray DR is widely used as a detector of metals such as guns and knives. Specifically, the X-ray DR is for specifying an object in a luggage based on the density and the morphologic features of the object and can detect guns and knives with comparative ease by forming an image of the transmittance distribution of the X ray transmitted through the luggage. For example, the density of a substance is detected from the X-ray transmissibility and explosives, guns and knives are identified and displayed in colors based on density difference. Also, the X-ray CT (computer tomography) technique can produce an internal three-dimensional image.
In the baggage inspection at airports, however, dangerous objects such as explosives as well as guns and knives are desirably detected, and the inspection at the custom house is expected to detect contraband goods such as narcotics. The explosives and drugs (hereinafter referred to as the explosives, etc. or the explosive, etc.) assume an unspecified form and have no significant density difference. It is therefore difficult to find them from a transparent image of X ray.
In view of this, various techniques are proposed for identifying a substance such as an explosive by detecting the chemical composition. In an X-ray device, for example, an attempt has been made to identify a substance by radiating a plurality of X rays of different energy levels and calculating the density and the effective atomic number. The density and the effective atomic number alone, however, fail to provide sufficient information to identify a substance and the result is low in reliability. In another approach, a substance is identified by utilizing the correlation which exists between the absorption spectrum of light such as visible light and a substance. The visible light, however, has a low transmissibility through a substance and can produce the information only on the surface of the substance, and though applicable to a thin article such as mail, is not suitable for luggage having some thickness.
The terahertz wave intermediate between radio wave and light, on the other hand, has a high transmissibility and is known to have an absorption spectrum unique to drugs. An application of the terahertz wave to the inspection for a drug in a thin object like a letter, for example, has been suggested by JP-A-2005-114413 and K. Kawase, Y. Ogawa, Y. Watanabe and H. Inoue, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints”, Optics Express, Vol. 11, No. 20, pp. 2549-2554 (2003).
In the luggage check at airports or event halls, explosives, etc. are desirably detected in a very short time (several seconds required for the luggage to pass through the inspection gate) without opening the luggage. The mail inspection, on the other hand, involves a very large volume of mail and therefore is required to be improved in throughput.
In the conventional technique of detecting explosives, etc. using the terahertz wave, however, reduction in inspection time is not considered. Measurement of the absorption spectrum by radiating the terahertz wave requires a considerable time as the whole luggage is required to be scanned by the terahertz wave. An attempt to shorten the inspection time by increasing the scanning rate, on the other hand, requires a high-intensity light source. Under the circumstances, however, a light source of high-intensity terahertz wave is still unavailable. Therefore, the measurement of the absorption spectrum and the scanning of a large area consume a very long time and is not suitable for ordinary luggage check.
The object of this invention is to provide a method and equipment for detecting explosives, etc., in which explosives, etc. in an object to be inspected can be identified within a short inspection time.
In order to achieve the object described above, according to this invention, the high X-ray transmissibility is organically combined with the high performance of the terahertz wave in identifying explosives, etc. thereby to considerably shorten the detection time of explosives, etc.
Specifically, based on an X-ray image obtained by radiating the X ray on an object to be inspected, a specified portion highly likely to contain an explosive, etc. is extracted. The specified portion thus extracted is irradiated with an electromagnetic wave containing the terahertz wave, and based on at least one of the absorption spectrum and the reflection spectrum of the electromagnetic wave at the specified portion, the presence or absence of an explosive, etc. is determined.
In this way, a specified portion highly likely to contain an explosive, etc. is extracted by a density distribution image, for example, using the high transmissibility of X ray, and therefore the scanning area of the terahertz wave can be narrowed. Thus, the whole measurement time is considerably reduced. An explosive, etc. required to be detected has a certain degree of size. In short, therefore, the measurement can be sufficiently conducted by radiating the terahertz wave at a single point of the specified portion, and therefore an explosive, etc. can be detected within a very short time. As a result, the presence or absence of an explosive, etc. in a luggage can be determined without opening it while the luggage passes on the luggage inspection table.
In this case, the electromagnetic wave containing the terahertz wave is selected in the range of 0.1 to 10 THz or preferably 0.5 to 3 THz. The explosive, etc. is defined to include at least one of an explosive, an illegal drug and a toxic microorganism such as anthrax.
The specified portion highly likely to contain an explosive, etc. can be extracted and set by the operator based on an X-ray image through an input means. As an alternative, the specified portion can be determined automatically by determining whether at least one of the density distribution of the X-ray transmissibility determined based on an X-ray image and the effective atomic number is within a set range or not.
An explosive detection equipment according to the invention comprises an X-ray unit for radiating the X ray on an object to be inspected and generating an X-ray transmitted image based on the X ray transmitted through the object, an electromagnetic wave radiator for radiating the electromagnetic wave containing the terahertz wave on a specified portion highly likely to contain an explosive, etc. based on the transmitted image, and a determining unit for measuring at least one of the absorption spectrum and the reflection spectrum of the electromagnetic wave at the specified portion and determining the presence or absence of an explosive, etc. based on a spectrum unique to the explosive, etc. registered in advance.
Also, according to this invention, the type of an explosive, etc. can be identified based on the transmitted images of a plurality of terahertz waves having different frequencies instead of the absorption or reflection spectrum of the terahertz wave.
Specifically, a specified portion highly likely to contain an explosive, etc. is extracted based on an X-ray image obtained by radiating the X ray on an object to be inspected. An electromagnetic wave containing terahertz waves of two or more different frequencies corresponding to a specified explosive, etc. registered in advance is radiated on the extracted specified portion. The terahertz wave image in at least one of the absorbed electromagnetic wave image and the reflected electromagnetic wave image of the specified portion is acquired for each of the two or more frequencies. The size of an area is determined where the absorption rates of the terahertz waves of the terahertz wave images of the respective frequencies are high and coincident with each other, and in the case where the area size thus determined is larger than a reference value, the presence of the specified explosive, etc. is determined.
According to this invention, an explosive, etc. in an object to be inspected can be identified within a shorter inspection time.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
Embodiments of the invention are described below.
A terahertz wave radiator for radiating the terahertz wave toward the luggage 2 is arranged downstream of the X-ray generator 5 on the carriage 1. The terahertz wave radiator is configured of a femt-sec laser light source 9, an optical fiber 10 and a terahertz light source 11. Specifically, the femt-sec laser beam generated by the femt-sec laser light source 9 is radiated on an optical switch in the terahertz light source 11 through the optical fiber 10. A wide-band electromagnetic wave containing the terahertz wave of 0.5 to 3 THz is released from the optical switch according to the principle of time domain spectroscopy. Also, though not shown, a concave mirror or a lens is arranged in the terahertz light source 11 to converge the terahertz wave released from the optical switch at a specified portion of the luggage 2.
Also, a terahertz wave sensor 14 for receiving the terahertz wave reflected from the luggage 2 is arranged in proximity to the terahertz light source 11. The terahertz wave sensor 14 is constituted of a well-known semiconductor optical switch or pyroelectric sensor to detect and disperse the reflected terahertz wave. The spectral data thus obtained is input to an arithmetic unit 12 including a spectrum measuring means. The arithmetic unit 12 includes a determining means for determining the presence or absence of an explosive, etc. based on the measured spectrum and a spectrum unique to the explosive, etc. in registration. The result of this determination is notified by being displayed on the screen 16. The measured spectrum is also displayed on the screen 16 whenever required.
Specifically, the explosive detection equipment according to this embodiment comprises the X-ray generator 5 providing an X-ray radiation means for radiating the X ray on the luggage 2 to be inspected, the line sensor 7 providing an X-ray detection means for detecting the X ray transmitted through the luggage 2 and the arithmetic unit 12 providing an image generating means for generating the X-ray transmitted image based on the detection signal of the X ray detected by the line sensor 7. Also, a specified portion setting means for setting a specified portion highly likely to contain an explosive, etc. based on the X-ray transmitted image includes an input means such as a cursor or a touch panel for setting the specified portion on the X-ray transmitted image displayed on the screen 8.
In order to identify the type of the explosive, etc., on the other hand, the explosive detection equipment according to this embodiment comprises the terahertz light source 11 providing an electromagnetic wave radiation means for radiating the electromagnetic wave containing the terahertz wave on a specified portion, the terahertz wave sensor 14 providing an electromagnetic wave detector for detecting the electromagnetic wave reflected from the specified portion, the spectrum measurement means for measuring the spectrum of the reflected wave and the arithmetic unit 12 providing a determining means for determining the presence or absence of an explosive, etc. based on the measured spectrum and a spectrum unique to the explosive, etc. registered in advance.
With reference to the embodiment having this configuration, the operation of detecting an explosive, etc. is explained. The luggage 2 transported on the carriage 1 enters the interior 3b from the inlet 3a of the X-ray shield case 3. The luggage 2 is detected the optical sensor 4, and an X ray beam 6 is radiated at the timing of the luggage 2 reaching the position of the X-ray generator 5. The X ray that has been transmitted through the luggage 2 is detected by the line sensor 7, and the image data corresponding to the X ray transmissibility is input to the arithmetic unit 12. The arithmetic unit 12 generates an X-ray transmitted image based on the input image data and displays it on the screen 8. The luggage 2 on the carriage 1 is moved through the position just under the X-ray beam 6. Thus, the X-ray transmitted image shown in
As shown in
Once the specified portion is set by the operator, the arithmetic unit 12, as shown in
The relation between an explosive, etc. and the reflection spectrum unique to the terahertz wave is explained. First, an explosive and a drug are known to exhibit a spectrum unique to the composition thereof against the terahertz wave of 0.5 to 3 THz. The millimeter wave with the frequency lower than 0.1 THz, however, exhibits no spectrum having a significant feature in spite of its high transmissibility. The infrared ray area with a frequency higher than 10 THz, on the other hand, has a spectrum of a significant feature but low in transmissibility. Since many substances have a spectrum of a significant feature, it may be difficult to identify a specified substance. For example, RDX which is a main chemical component of the plastic bomb C4 exhibits a spectrum of a significant feature having a peak at about 0.75 THz, 1.4 THz and 1.9 THz. Many substances including wood, paper, cloth and leather used for cases and bags such as luggage exhibit no spectrum of a significant feature against the terahertz wave. Explosives and illegal drugs, on the other hand, normally exhibit a spectrum of a significant feature in two or more areas against the terahertz wave of 0.5 to 3 THz, and therefore the type of an explosive or an illegal drug can be identified.
Further, the logic to identify the type of explosives and illegal drugs can be formed by combining a plurality of features on the spectrum. By doing so, in the case where a given substance happens to have a spectrum in the same area as another substance, an identification error can be considerably reduced by combining a plurality of features. Also, even in the absence of a spectrum having a significant feature, the base line 25 of the spectrum 24 shown in
Once a doubtful object in the luggage 2 is found to be an explosive, etc., as shown in
In the case where the integrated value fails to satisfy any one of the reference values of the registered objects to be detected, on the other hand, the wording “not detected” is displayed. In this case, the operator can change the place of the specified portion and by setting the cursor, can inspect another doubtful portion with a similar operation. At the end of the detecting operation, an end command 28 on the screen 16 is selected. Then, the carriage 1 begins to move again and the luggage 2 having been inspected is delivered out from the outlet 3c, and the next luggage 2 is ready for inspection.
As explained above, according to this embodiment, utilizing the high transmissibility of the X ray, a specified portion highly likely to contain an explosive, etc. is extracted by a density distribution image, for example, and an inspection for identifying an explosive, etc. is conducted with the terahertz wave in the extracted narrow area. Thus, the total inspection time can be considerably reduced. An explosive, etc. required to be searched has some degree of size, and therefore, in short, measurement is possible by radiating the terahertz wave at a single point of the specified portion. Also, only a very small area is scanned, if required, and therefore an explosive, etc. can be detected within a short time. As a result, the presence or absence of an explosive, etc. in the luggage can be determined without opening the luggage while being transported on the carriage 11 like the inspection table.
The embodiment is explained above with reference to a case in which the electromagnetic wave containing the terahertz wave has a wide frequency band of 0.5 to 3 THz. Nevertheless, the invention is not limited to the frequency range, and a wide-band electromagnetic wave of 0.1 to 10 THz can be selected. Also, although RDX is taken up as an example of the explosive, etc., the invention is not limited to RDX and various explosives, illegal drugs and toxic microorganisms such as anthrax can be detected. Of course, the features of the terahertz wave spectrum of the object to be detected are required to be analyzed and the reference values for identification are required to be registered beforehand in the arithmetic unit 12.
Also, according to this embodiment, the explanation has been made about a case in which the operator sets a specified portion highly likely to contain an explosive, etc. on the screen 8 through the input means. The invention is not limited to such a case, but the specified portion can be set automatically. For example, upon determination that at least one of the density distribution of the X-ray transmitted image and the effective atomic number is included in a set range as a reference value, a specified portion can be set automatically.
Also, instead of using the reflection spectrum based on the wave reflected from a specified portion of the luggage as in the embodiment described above, an explosive, etc. can be identified and detected with equal effect by use of the absorption spectrum absorbed into a specified portion. The absorption spectrum has an inverted waveform of the spectrum 24 shown in
As shown in
In the case where the operator determines that a doubtful portion exists, on the other hand, a conveyor 38 is activated by button operation, and as shown in
The operation of this embodiment having the configuration described above is explained with reference to
The embodiment is explained above taking a transmitted image as an example. It is also possible to use a reflected image or both an absorbed image and a reflected image in combination. Also, as long as bacteria such as anthrax are in powder form, a spectrum having a significant feature is measured and a detection logic is created to make detection possible.
As described above, according to this embodiment, a drug or anthrax contained in mail can be detected reliably without opening the mail.
The X ray can be radiated from two directions from a vertical X-ray radiator 51 and a horizontal X-ray radiator 52. Also, vertical and horizontal X-ray line sensors 53 correspond to the vertical X-ray radiator 51 and the horizontal X-ray radiator 52, respectively. The vertical and horizontal X-ray line sensors 53 are moved together with the vertical X-ray radiator 51 and the horizontal X-ray radiator 52, respectively, and can scan the container 50 from the ends thereof.
Also, the X-ray energy can be switched between high and low levels alternately. The vertical and horizontal X-ray transmitted images are picked up, and from these transmitted images, the density distribution and the effective atomic number are calculated. Based on the density and the effective atomic number thus calculated, an area 54, if found, coincident with the range of density and effective atomic number of the explosive etc. set in advance is set as a specific portion.
Then, the terahertz wave is radiated and focused automatically from terahertz wave radiators 55 at the set area 54 of the specific portion. In this case, the terahertz wave is radiated from at least three points. The reflection spectrum of the terahertz wave is acquired by terahertz wave detectors 56 corresponding to each terahertz wave radiator 55. Like in the embodiment shown in
A substance resistant to the terahertz wave may exist in the container 50. Therefore, the terahertz wave radiators 55 and the terahertz wave detectors 56 are arranged in such a manner that the detection is possible from at least three directions. The radiation and detection from at least three directions makes the detection possible even in the case where the terahertz wave is blocked by some substance.
Also, by measuring the difference of time from the radiation of the terahertz wave on the area 54 of the specified portion to the return of the reflected terahertz wave, it is possible to determine whether terahertz wave is reflected from the focused area 54 of the specified portion. In the case where the reflected wave returns through a shorter distance than the focused area 54, for example, the presence of an obstacle midway can be estimated. In the case where the result is the same for all the three directions, on the other hand, an alarm is issued indicating that an explosive, etc. may be shielded.
Instead of radiating the X ray from horizontal and vertical directions, each set of the X-ray radiator 51 and the X-ray detector 53 can be configured to rotate around the container 50. Alternatively, the X-ray radiator and the X-ray detector can be fixed while the container 50 is rotated. As a result, an X-ray CT image is obtained, and the presence or absence of the area 54 coincident with the range of the density and the effective atomic number of the explosive, etc. is inspected on the CT image. Thus, the position of the explosive, etc. can be easily determined with a higher reliability.
According to this embodiment, an explosive, etc. in a bulky object can be automatically detected.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-268174 | Sep 2004 | JP | national |
