JP2009145312A - Inspection apparatus and inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection apparatus that radiates electromagnetic wave to an inspection object, acquires a transmission image or reflection image of an inspection object structure, and non-destructively inspects the inspection object body, structures of different transmittance or reflectivity, and an internal defect. <P>SOLUTION: The electromagnetic wave of about 10 GHz to 1000 GHz (1THz) generated from a diode oscillator such as a TUNNETT diode or the like is fed to a flat antenna capable of selecting an oscillation frequency, a polarization plane or the like to acquire a first resonance, a second resonance is acquired by a hemisphere type dielectric resonator made of high-purity silicon or the like, the intensity of electromagnetic wave radiated is improved by collecting the generated electromagnetic wave, furthermore, the reliability of the inspection is improved by acquiring, as a reference signal, part of the electromagnetic wave before the radiation to the inspection object and canceling the variation of the radiated electromagnetic wave, the reflection of the electromagnetic wave from the inspection object surface is suppressed by arranging an impedance matching film suitable for the inspection object surface on the inspection apparatus side, and the transmission image or reflection image of the inspection object is cleared. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inspection apparatus and an inspection method for obtaining a transmission image or a reflection image of an inspection object structure by irradiating an inspection object with electromagnetic waves.

Terahertz electromagnetic waves, which are expected to be widely used in recent years, have both the characteristics of radio waves and light over the intermediate frequency range between radio waves and light. The frequency is in the 10 ¹² Hz region, and the electromagnetic wave in the 100 micron region in terms of wavelength is characterized by good radio wave transmission to non-polar substances, light straightness, and geometrical optical handling. And it shows strong absorption and reflection characteristics for polar substances such as water. Reflected by metal as a property of radio waves. In this terahertz frequency region, there are characteristic skeletal vibrations related to multiple intermolecular bonds and weak intermolecular vibration frequencies such as hydrogen bonds. By detecting them as fingerprint spectra, bio-related substances, pharmaceuticals, etc. Detection, deterioration, or detection of crystal polymorphism is possible. By obtaining the image of the test object using the specific absorption and reflection, it is possible to know the distribution and internal structure of the test object. This is why a wide range of applications are expected.

Among a wide range of applications, there are building inspections such as concrete that take advantage of high permeability to non-polar materials. Since the origin of cement and concrete goes back to the times of Egypt and Rome, there are many studies and a long history. Research using scientific methods has been carried out by infrared spectroscopy, calorimetric methods, and the like. As a result, the microscopic clarification of the cement / aggregate hydration reaction process and the strength formation process were elucidated, and the strength / deterioration situation was grasped empirically based on many accumulated data. Buildings with strong process control have been created. However, in recent years, there have been many cases where the rule of thumb is threatened. In response to this situation, strength deterioration surveys are being conducted worldwide. However, the current situation is that the technique is based on a destructive technique using X-rays, γ-rays, or neutron rays that are dangerous to the human body, and core removal. Moreover, the location of the reinforcing bar structure in the concrete structure can be easily specified by the high frequency induced current method. This is inexpensive and easy to operate. However, a method using a radiation source such as X-rays or γ-rays is applied in order to grasp a more precise two-dimensional structure of a reinforcing bar. This is harmful to the human body, requires special qualified personnel, requires strict on-site curing, and has poor workability. In response to this background, there is a great need for nondestructive understanding of the extent of building defects or deterioration. In addition, wood has been processed into various products for a long time because of its excellent durability, humidity control, and beautiful appearance, and it is still widely used as a material for buildings and furniture. When wood is used in buildings, there are problems such as damage caused by white ants and the occurrence of madness, cracking and decay due to insufficient drying, but it is very difficult to visually detect defects existing in the wood. From the viewpoint of safety and security of social infrastructure, there is a need for a non-destructive and accurate method for detecting defects and measuring moisture content inside wood. Conventionally, flaw detection equipment using ultrasonic waves or X-rays, electrical resistance type and high frequency capacity type moisture meter, etc. are used for detecting defects and measuring moisture content of wood, but there are problems such as safety and accuracy, structures, etc. There is also a disadvantage that it is difficult to apply to wood incorporated in. Therefore, a small and lightweight inspection device using a tannet, which is a small terahertz light source, has been proposed.
JP2007-132915 JP 2006-145513 JP2007-17419 Unlike ionizing radiation such as X-rays, terahertz electromagnetic waves are harmless to the human body and can be safely inspected. Test results are obtained by imaging, so skill and experience are not required. However, these inspection devices have the following three problems.

  The first problem is that the tannet oscillator is composed of a cavity resonator. As the electromagnetic wave frequency is increased in order to increase the inspection accuracy, the machining accuracy of the cavity resonator is also required to be higher. At a frequency of 50 GHz, the wavelength is 6 mm, and the machining accuracy is about 1/100 of 0.06 mm (60 microns) or less, but at a frequency of 300 GHz, the wavelength is 1 mm, and the machining accuracy is at least 10 microns or less, and at 1 THz, the wavelength is 300. At micron, the machining accuracy is 3 microns or less, and the machining accuracy degrades the Q of the resonator. This effect becomes more serious as the frequency increases. In addition, terahertz electromagnetic waves extracted from a conventional cavity resonator via a horn antenna need to use a wire grid polarizer or the like to rotate the polarization plane and use a specific polarization. Loss occurs.

  The second problem is that the tannet oscillator is in the form of an open loop without a control loop. Because the tannet device is a transit time effect oscillation element of reverse bias tunnel injection carrier, it has a negative temperature coefficient unlike impat device using avalanche injection, so that runaway of injection current hardly occurs, but electromagnetic wave output When used for imaging without the feedback loop of the oscillator output, there is a drawback that an image that does not reflect the difference in the structure of the test object may be shown in the transmission intensity or reflection intensity of the electromagnetic wave.

The third problem is the heat dissipation structure of the tannet device. The tannet device is characterized in that it operates at room temperature unlike other terahertz semiconductor light sources such as QCL, but the injected DC power is sometimes 6 × 10 ⁵ Wcm ⁻² per unit area. It may also cause characteristic deterioration. Therefore, when assembling a tannet device, the bonding side is bonded to the heat dissipation structure and heat is dissipated from the device bonding using a diamond heat sink or the like with high thermal conductivity, but this has the disadvantage of limiting the characteristics. It was.

The problems to be solved by the present invention are the first problem that machining accuracy limits the resonator performance, the second problem that the tannet oscillator output fluctuates, and the heat dissipation of the tannet device is not enough for natural heat dissipation This is the third issue.

  In order to solve the above problems, the present invention solves the first problem by configuring a tannet oscillator mounted on a planar antenna that can be formed by a lithography process that does not require machining accuracy. In addition, the plane antenna structure can determine the polarization plane of the electromagnetic wave by design, and can irradiate the terahertz electromagnetic wave having a desired polarization plane without using a lossy polarizer. Furthermore, high output and high Q can be realized by the double resonance and condensing resonator structure by a high purity silicon hemisphere lens or the like.

  In order to solve the second problem, in the present invention, the intensity of the terahertz electromagnetic wave irradiated on the specimen is grasped by monitoring the reflected electromagnetic wave from a half mirror or the like having an appropriate transmittance, and acquired imaging Correct image fluctuations.

  In order to solve the third problem, in the present invention, the tannet device is actively dissipated by using a small active cooling device such as a Peltier element. This structure is difficult to apply in the conventional cavity resonator structure, and is made possible by the present invention employing a planar antenna structure.

  By solving the first problem by the apparatus configuration and method of the present invention, it is possible to obtain high-frequency electromagnetic waves having a frequency that can be determined by the planar antenna material system and pattern design up to the high-frequency terahertz electromagnetic wave region. There is an effect of obtaining clear examination object imaging.

  Further, the second problem is solved by the present invention, so that there is an effect of obtaining an accurate inspected body imaging image without error.

  When the third problem is solved by the present invention, there is an effect of configuring an inspection apparatus that operates stably. This active heat dissipation lowers the tannet junction temperature and provides stable device operation. At the same time, the operating voltage can be lowered due to the characteristics of the tannet device, resulting in low power consumption and high terahertz electromagnetic waves. There is an effect of obtaining output.

  A tannet oscillator structure on which a patch type planar antenna used in the inspection apparatus of the present invention is mounted is shown in FIG. The planar antenna is not limited to a patch antenna, and may be a slot antenna or another planar antenna structure. The patch antenna is configured by creating an antenna pattern 1 and a DC bias feeding pattern 2 by photolithography on an insulating substrate 4 such as quartz, alumina or zirconia. From the DC bias feeding pattern 2 to the antenna pattern, a DC bias is fed to the tannet diode 9 through a high impedance choke in order to prevent radiation of electromagnetic waves to the power source. The antenna pattern includes a stub for impedance matching, a λ / 4 impedance conversion portion, and the like. The long side is the radiation end of the electromagnetic wave, and the short side is the non-radiation end of the electromagnetic wave. In the case of designing with 50Ω impedance matching at 0.2 THz, the irradiation end length is about 300 microns and the non-radiation end length is about 210 microns, and Z / Zo (50Ω) = 0.12 is obtained at 0.2 THz. Good oscillation characteristics with low VSWR can be obtained.

  The tannet diode 9 is mounted on a heat sink 6 made of diamond, ticker aluminum or the like having a high thermal conductivity for heat dissipation, and the heat sink is formed with a metal layer 5 made of gold or the like on both sides thereof, and the tannet diode 9 And improved thermal adhesion. The metal layer 5 uses a relatively thick layer inside and outside 3 microns for bonding the tannet diode.

  The tannet diode on the heat sink composed of 5, 6, 9 and the planar antenna composed of 1, 2, 4 are assembled on the metal block 8 having high conductivity and high thermal conductivity. The metal block is further attached to an electronic cooling element 7 such as Peltier for heat dissipation. By supplying power to the electronic cooling element 7, the heat from the tannet diode 9 is radiated more efficiently. As a result, the efficiency of generation of terahertz electromagnetic waves is increased, and the tannet diode 9 is not deteriorated. The planar antenna and the tannet diode are bonded by a wiring 3 such as gold. Since the wiring 3 has a small inductance component and a low resistance, a ribbon-shaped wiring is used.

Here, the structure of the tannet diode is shown in FIG. A first n ⁺ GaAs buffer layer 13 is epitaxially grown by 50 nm on an n ⁺ GaAs substrate crystal 13 ′ having a plane orientation of {100}, and a high-purity n ⁻ GaAs layer 12 is epitaxially grown to a desired thickness thereon. The n ⁻ GaAs layer 12 is a traveling region. Further, the second n ⁺ GaAs layer 11 and the p ⁺ GaAs layer 10 were epitaxially grown. In order to reduce the diode series resistance, the n ⁺ GaAs substrate crystal is thinned to about 5 to 10 microns. Thereafter, metal electrodes (not shown) are formed on the n ⁺ GaAs substrate crystal and the p ⁺ GaAs layer to form a tannet diode structure. As the metal electrode for the p ⁺ GaAs layer 10, an electrode material having a low contact resistivity such as Ti / Pt / Au and having excellent heat resistance is used. As a metal electrode for the thinned n ⁺ GaAs substrate crystal, a low contact resistivity electrode material such as AuGe / Ni / Au is used. After dicing into a desired shape after electrode formation, the junction area is reduced to about 5 to 30 microns φ to reduce diode parasitic capacitance. The second n ⁺ GaAs layer 11 and the p ⁺ GaAs layer 10 are tunnel junctions, and negative resistance due to the transit time effect that occurs when electrons tunneled with reverse bias are conducted through the n ⁻ GaAs layer transit region 12. As a result, terahertz electromagnetic waves are generated. The tunnel junction composed of the n ⁺ GaAs layer 11 and the p ⁺ GaAs layer 10 is most efficiently tunnel-injected when the sheet carrier density is designed so that the n ⁺ GaAs layer 11 is completely depleted at zero bias voltage. . The first n ⁺ GaAs buffer layer 13 is formed for the purpose of preventing the propagation of defects from the substrate crystal 13 ′, but when an epitaxial growth method such as a molecular layer epitaxial growth method that ensures a sufficient crystal quality is employed. There is no need. The tannet diode does not need to be a GaAs semiconductor, and may be a Ge or GaSb semiconductor having a small forbidden band width and high tunnel injection efficiency. Further, it may be formed of a Si semiconductor from the viewpoint of high thermal conductivity and forbidden band width. In this embodiment, the crystal plane orientation is {100}, but is not limited to {100}. The tannet diode formed in this way is attached to the planar antenna 14 as indicated by 9 in FIG.

As shown in FIG. 3, the tannet diode attached to the planar antenna 14 is further attached to a hemispherical lens 15 made of a material having a low refractive index and a low absorption of terahertz electromagnetic waves such as high-purity silicon. When using silicon,
In the 0.2 THz band tannet oscillator, the radius of the hemispherical lens is about 3 mm. In the planar antenna 14, the tannet diode forms a first resonator and forms a second resonator in the silicon hemispherical lens 15. This two-stage resonator structure constitutes a high-output and high-Q tannet oscillator. The radiated terahertz electromagnetic wave becomes parallel light in a substantially vertical direction with respect to the planar antenna and has a high radiation density.

  The inspection apparatus of the present invention is configured using the tannet oscillator configured as described above. However, the terahertz electromagnetic wave generation source is not limited to the tannet diode. The tannet diode can oscillate to a high frequency at room temperature, has a low operating voltage and low noise, but may be a Gunn diode, an impat diode, a mitten diode, a resonant tunnel diode, a quantum cascade laser diode, or the like. FIG. 4 shows the configuration of the inspection apparatus of the present invention. The terahertz electromagnetic wave beam 27 radiated from the tannet oscillator 20 passes through a terahertz beam splitter 26 made of, for example, high-purity silicon having high transmittance with respect to the terahertz electromagnetic wave, and further to an arbitrary depth of the test body 16. The specimen 16 is irradiated through a converging optical system 29 such as a Fresnel lens for focusing. Inside the test body 16, there are, for example, a cavity defect inside the cement structure, a reinforcing bar or water infiltrating part, or a defect part 17 to be inspected such as a hydrate formation defect. A part of the terahertz electromagnetic wave 27 passing through the beam splitter 26 is reflected by the beam splitter 26 to generate a reflected terahertz electromagnetic wave 25, which is measured by the detector 23, and changes in the intensity of the terahertz electromagnetic wave irradiated to the specimen 16 are detected. Monitor. On the other hand, the terahertz electromagnetic wave 28 reflected or scattered from the structure defect 17 in the test body 16 is focused and enhanced again by the condensing optical system 29 and then reflected by the beam splitter 26 to generate a reflected wave 30. It is measured by the detector 24. The detector 23 of the irradiation electromagnetic wave intensity monitor and the detector 24 for measuring the reflected / scattered electromagnetic wave intensity from the defect are simultaneously measured, and the electromagnetic wave intensity signal is signal-processed by the measurement control device 18 to irradiate the electromagnetic wave 27 to the specimen 16. Cancel intensity fluctuations. Therefore, it is possible to accurately detect the structural defect 17.

  The tannet oscillator 20, detectors 23 and 24, and beam splitter 26 focusing optical system 29 are integrally formed, and are mounted on XY scanning drive devices 21 and 22 that scan the specimen 16. The XY scanning driving devices 21 and 22 can simultaneously drive in the Z direction, and can change the focusing depth of the irradiation terahertz beam 27 into the test body 16. The XY scanning driving devices 21 and 22 that can be driven in the Z direction are controlled by the scanning control device 19 and driven according to the measurement sequence from the measurement control device 18.

  FIG. 5 shows an inspection apparatus and method when the specimen is relatively small. When the test body is small, the apparatus is configured to inspect by testing the test body itself with the XYZ moving mechanism 31. In this case, the test body is installed on the XYZ moving mechanism 31. The XYZ moving mechanism 31 is scanned by the position control device 32 controlled by the measurement control device 18 to obtain an image of the structural defect 17 in the specimen 16. Other components are the same.

  When terahertz electromagnetic waves are incident on an insulating specimen, reflection occurs on the surface of the specimen due to differences in the dielectric constant and extinction coefficient between air and the specimen, that is, differences in refractive index, and terahertz electromagnetic waves entering the specimen The osmotic strength of is attenuated. In this case, if there is a dielectric material that impedance matches with the electromagnetic wave on the surface of the test object, the surface reflected wave can be effectively suppressed and the terahertz electromagnetic wave can penetrate into the test object.

The test object is close to an insulator such as concrete or wood having a very low electrical conductivity. Incident medium (usually air), respectively the refractive index of the impedance matching film and inspected present on inspected, n _{o, n,} and n _m. Consider a case where a terahertz electromagnetic wave is perpendicularly incident on an impedance matching film having a thickness d. In this case, the characteristic matrix M of the impedance matching film is

It becomes. However, here

δ = (2π / λ) nd
It is a phase shift of the terahertz electromagnetic wave. λ is the wavelength of the terahertz electromagnetic wave. The characteristic matrix of the membrane system is

It is represented by Then Fresnel's reflection coefficient ρ and reflectance R are

Therefore, in order for the reflectance to become zero, the condition that the numerator of R becomes zero, that is,

_{n o m 11 -n m m 22} = cosδ = 0 of _(n o -n _m)
And

Is required. When this condition is satisfied, the reflection of the electromagnetic wave becomes zero, and the electromagnetic wave transmission intensity to the inside of the test body becomes maximum. In general, the refractive index of the test subject different from the refractive index of the surrounding environment (usually air), so n _o ≠ n _m

This is called the impedance matching phase condition. Furthermore, since sin δ = ± 1 under this condition, after all,

Is obtained. This is called an impedance matching amplitude condition. The third embodiment of the present invention shows an inspection apparatus in which an impedance matching film having a refractive index n satisfying this condition and a film thickness d is mounted between the inspection objects.

  FIG. 6 shows an inspection apparatus equipped with an impedance matching film. The inspection object 33 has a defect 17 inside the building. The generation source of terahertz electromagnetic waves and the configuration of the detection apparatus are the same as those in the first and second embodiments. Around the inspection apparatus, a flexible dielectric layer 35 satisfying appropriate impedance matching phase conditions and amplitude conditions is supported and rotated by a roller 34, and the inspection apparatus moves and scans on the surface of the inspection body 33. is there. The scanning device including the terahertz electromagnetic wave generation source, the detection device, and the roller 34 is controlled by a measurement control device and a scanning control device which are not drawn in the drawing. Since the terahertz irradiation beam 27 is always perpendicularly irradiated to the inspection body 33 through the impedance matching film 35 in contact with the inspection body 33, the inspection body can be selected by appropriately selecting the refractive index and the thickness satisfying the phase condition and the amplitude condition. Since reflection on the surface 33 is suppressed and the incident intensity to the inside of the inspection body 33 is increased, the defect 17 located at a deeper location inside the inspection body 33 can be detected.

The example which test | inspected the adhesion state of the ceramic tile arrange | positioned on the concrete wall surface with the above structures is shown in FIG. The right figure of FIG. 7 is an optical image of the test body, and the left figure is an image of terahertz electromagnetic waves. In this example, since the size of the inspection body 39 is as small as about 12 cm square, the apparatus configuration of the embodiment 2 shown in FIG. The inspection body 39 is obtained by fixing nine ceramic tiles 41 of about 4 cm square on the concrete surface of about 12 cm square with an organic adhesive for exterior tile sticking. The reflection image of the terahertz electromagnetic wave was performed on a 4 cm square ceramic tile in the central portion of the test body 39. The test body was intentionally provided with a poor adhesion region 36. As shown in FIG. 7, when a reflection image of terahertz electromagnetic waves is picked up by the inspection apparatus of the present invention, a region image 38 corresponding to the poor adhesion region 36 is clearly recognized as shown in the left diagram of FIG. It was. Further, the tile adhesion good region image 40 corresponding to the good adhesion region 37 could be clearly recognized.

  By using the inspection apparatus and method of the present invention, it is possible to safely and efficiently inspect structures and defects inside structures such as concrete and wood that could not be inspected so far without requiring skilled experience. it can. In addition, it is possible to safely and efficiently inspect the adhesion of the outer wall and tile of the building and the adhesion state of the inner wall of the tunnel without requiring skilled experience. And the infiltration state of water which has a big influence on building strength deterioration can be inspected.

Tannet oscillator mounted on a planar antenna Multilayer structure of tannet diode Planar antenna resonator mounted on hemispherical lens type resonator Schematic configuration diagram of an inspection device using a tannet oscillator Schematic configuration diagram of an inspection device for small inspection objects Schematic configuration diagram of inspection equipment with impedance matching film An image of tile adhesion with this inspection device

Explanation of symbols

1. . . Antenna pattern 2. . . 2. Power feeding pattern . . Ribbon-like wiring4. . . 4. Insulating substrate . . Metal layer 6. . . 6. High thermal conductivity heat sink . . Electronic cooling element8. . . 8. High conductivity and high thermal conductivity metal stem . . Tannet diode element 10. . . p + anode layer 11. . . n + tunnel barrier layer 12. . . High purity traveling layer 13. . . n + buffer layer 13 '. . . n + substrate crystal 14. . . Planar antenna 15. . . Hemispherical lens resonator 16. . . Test specimen 17. . . Specimen defect 18. . . Measurement control device 19. . . XYZ scanning control device 20. . . Terahertz electromagnetic wave oscillator 21. . . XYZ scanning drive device 22. . . Second XYZ scanning drive device 23. . . Reference electromagnetic wave detector 24. . . Reflected electromagnetic wave detector 25. . . Reference reflected electromagnetic wave beam 26. . . Beam splitter 27. . . Irradiated electromagnetic wave beam 28. . . Reflected / scattered electromagnetic wave beam from defect 29. . . Condensing device 30. . . Reflected / scattered electromagnetic wave beam from defect reflected by beam splitter 31. . . XYZ driving apparatus for scanning an inspection object 32. . . Inspection object drive control device 33. . . Inspection object 34. . . Roller 35. . . Impedance matching film 36. . . Tile adhesion failure area 37. . . Tile adhesion good region 38. . . Tile adhesion failure area image 39. . . Tile adhesion inspection body 40. . . 41. Tile adhesion good region image 41. . . tile

Claims (5)

  Using an electromagnetic wave generator of a wide range of about 10 GHz to 1000 GHz (1 THz) composed of a diode oscillator mounted on a planar antenna structure, the electromagnetic wave generating means, the generated electromagnetic wave condensing means, the electromagnetic wave dividing means, and the dividing means A combination of a means for detecting electromagnetic waves reflected from the means and a means for detecting electromagnetic waves reflected or scattered from the inspection body is formed as an integral structure, and the integral structure is scanned three-dimensionally on the inspection body, Inspection of a structure using electromagnetic waves, wherein the internal structure and defects of the inspection body are imaged by measuring the intensity of electromagnetic waves from the surface and inside of the inspection body to obtain a reflection image of the inspection body Apparatus and method.   Using an electromagnetic wave generator of a wide range of about 10 GHz to 1000 GHz (1 THz) composed of a diode oscillator mounted on a planar antenna structure, the electromagnetic wave generating means, the generated electromagnetic wave condensing means, the electromagnetic wave dividing means, and the dividing means A combination of a means for detecting electromagnetic waves reflected from the object and a means for detecting electromagnetic waves reflected or scattered from the inspection object is formed as an integral structure, and the inspection object surface and A structure inspection apparatus and method using electromagnetic waves, wherein the internal structure and defects of the inspection object are imaged by measuring the intensity of electromagnetic waves from the inside to obtain a reflection image of the inspection object. The flexible structure is covered with a flexible dielectric film so as to surround at least the electromagnetic wave radiation portion of the wavelength λ of the integral structure according to claim 1, and the dielectric film moves in close contact with the surface of the test object,
A structure using electromagnetic waves characterized in that the internal structure and defects of the inspection body are imaged by measuring the intensity of electromagnetic waves from the surface of the inspection body and from inside to obtain a reflection image of the inspection body Inspection apparatus and method.   4. The diode oscillator mounted on the planar antenna structure is any one of a tannet diode, a Gunn diode or an impat diode, a mitten diode, a resonant tunnel diode, and a quantum cascade laser diode. Inspection apparatus and method of structure using electromagnetic wave of description.   4. A structure inspection apparatus and method using electromagnetic waves according to claim 1, wherein the diode oscillator mounted on the planar antenna structure is mounted on a second oscillator made of a hemispherical dielectric lens.