JP5747453B2 - Radio wave imaging method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for imaging a sample by irradiating the sample with radio waves.

In recent years, imaging technology that visualizes the inside of an object safely and non-destructively using radio waves is expected in various fields such as security, civil engineering, and medicine.
In particular, millimeter waves have transmission characteristics similar to terahertz waves, such as being easy to transmit non-metal such as flame, smoke, water vapor, plywood, plaster, board, wall, window, curtain, clothes, plastic, paper, etc. Since the spatial resolution is several millimeters between the terahertz wave and the microwave, various practical objects can be imaged.

There is a passive imaging device that detects and images an electromagnetic wave radiated from an object with a device combining a millimeter wave antenna, an amplifier, a Schottky diode detector, and the like. According to this, for example, a person in the back of a flame can be projected.
In addition, an active imaging apparatus that irradiates an object with millimeter waves and detects and images the transmitted or reflected waves is also being put into practical use. According to this, for example, a knife hidden in clothes can be projected and contributed to the security field.
Since millimeter waves are also sensitive to liquid phase water, it is possible to identify the amount of water and the frozen state of an aqueous solution with high sensitivity. According to this, it is expected to be used for, for example, water monitoring of agricultural products and foods, and observation of thawing processes of frozen foods and biological samples.

Conventional imaging techniques include far-field imaging as in Non-Patent Document 1 and near-field imaging as in Non-Patent Document 2.
In far-field imaging, it is possible to collect a spatially propagated electromagnetic wave with a dielectric lens, etc., and image a distant sample. However, because the electromagnetic wave has a diffraction limit, the resolution is limited in wavelength size. In radio waves, high resolution cannot be expected. In addition, near-field imaging enables surface imaging at a wavelength or less, but it is difficult to image a sample at a position slightly away from the antenna, such as inside a substance.

Patent documents relating to imaging technology using radio waves include Patent Documents 1 and 2 for millimeter waves and Patent Documents 3 to 5 for microwaves.
In Patent Documents 4 and 5, analog phased arrays and binary reflector arrays are used, and the antenna elements are arranged closely in the array so that the spacing between adjacent antenna elements is half the wavelength of the radio wave. It is disclosed to enhance. However, it cannot be said that sensitivity and resolution are sufficient.
The radio wave has not only a wavelength longer than that of light but also has a property of diffracting, so that the resolution of imaging could not be sufficiently improved. Disclosed is a radio wave imaging means capable of acquiring a transmission image of a sample with high resolution below the wavelength.

Related to Patent Document 6, Non-Patent Documents 3 to 4 are related to conventional imaging methods using a monopole antenna, and Non-Patent Document 5 is related to an imaging method using an aperture coaxial probe.
Although it is disclosed to use a monopole type antenna and lens and image by reflected wave from the sample, it is highly sensitive, high resolution and small size reflection considering the characteristics of the antenna and the action of the lens. It has not been disclosed that a type imaging apparatus can be constructed.

JP 2006-250724 “Object fluoroscopy device” Japanese Patent Laid-Open No. 2006-242780 “Millimeter Wave Imaging Device” Japanese Patent Laid-Open No. 7-134174 “Microwave Imaging Device” US Patent Application 10/997422 “A Device for Reflecting Electromagnetic Radiation” US Patent Application 10/99758 “Broadband Binary Phased Antenna” JP 2008-232624 “Radio wave imaging method and apparatus”

David M. Sheen, Douglas L. McMakin, and Thomas E. Hall, “Three-Dimensional Millimeter-Wave Imaging for Concealed Weapon Detection,” IEEETRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol. 49, No. 9, p. 1581 (2001 ) Tatsuo Nozokido, Jongsuck Bae and Koji Mizuno, “Scanning Near-Field Millimeter-Wave Microscopy Using a Metal Slit as a Scanning Probe,” IEEETRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol. 49, No. 3, p. 491 (2001) Maya Mizuno, "Broadband millimeter-wave imaging system," National Institute of Information and Communications Technology, vol. 54, pp. 45-50 (2008) Maya Mizuno, Kaori Fukunaga and Iwao Hosako, "PenetrationMonitoring of Fixation Solution into Tissues Using Millimeter Waves," The joint 33ndinternational conference on infrared and millimeter waves and the 16thinternational conference on Terahertz (IRMMW2008 / THz2008), T5D14, (2008) SK Dutta, CP Vlahacos, DE Steinhauer, Ashfaq S. Thanawalla, BJFeenstra, FC Wellstood, and Steven M. Anlage, "Imaging microwaveelectric fields using a near-field scanning microwave microscope," Applied PhysicsLetters, vol. 74, pp. 156 -8 (1999)

  Therefore, the present invention provides a radio wave imaging method capable of imaging a sample with high sensitivity and high resolution while taking a characteristic of the vicinity of an antenna into a small and simple configuration, and an apparatus for implementing the method. This is the issue.

  In order to solve the above problems, the radio wave imaging method of the present invention comprises the following arrangement. That is, a method of irradiating a sample with radio waves and imaging the sample by the reflected signal, a radio wave source that generates radio waves, an external output means for radiating an output signal from the radio wave source to the outside, and an external output An output lens that converges radio waves emitted from the means, an input lens that accepts and converges radio waves emitted from the output lens and reflected by the sample, and an external input that accepts radio waves emitted from the input lens And a pole-shaped antenna in which the external output means and the external input means are surrounded by a metal cylinder in a configuration comprising at least a means and an arithmetic processing means for processing an input signal received by the external input means to image a sample In addition, the input lens and the output lens are short focal length lenses, and the intensity distribution characteristics and relativity of radio waves in the vicinity of the antenna. By setting the sample so that the full width at half maximum of the radio wave intensity distribution is about the wavelength of the radio wave from the lens to the farther than the radio wave wavelength. It is characterized by detecting a direct wave from a sample with high sensitivity.

  Here, the input lens that receives and converges the radio wave radiated from the output lens and transmitted through the sample, the external input means that receives the radio wave radiated from the input lens, and the input received by the external input means An arithmetic processing means for processing the signal and imaging the sample may be provided so that the sample can also be imaged by a transmission signal of the sample.

  As the radio wave applied to the sample, millimeter waves can be preferably used.

  A broadband light source may be used as the radio wave source, and spectral multivariate analysis in the frequency domain or time domain may be performed.

  The radio wave imaging apparatus of the present invention is an apparatus that irradiates a sample with radio waves and images the sample by the reflected signal, and radiates a radio wave source that generates radio waves and an output signal from the radio wave source to the outside. External output means, an output lens for converging radio waves radiated from the external output means, an input lens for receiving and converging radio waves radiated from the output lens and reflected by the sample, and radiated from the input lens An external input means for receiving the received radio wave and an arithmetic processing means for imaging the sample by processing the input signal received by the external input means, and the external output means and the external input means are surrounded by a metal tube In addition to the pole-shaped antenna, the input lens and the output lens are lenses with a short focal length. The full width at half maximum of the radio wave intensity distribution is set to about the radio wave wavelength from the lens to the farther than the radio wave wavelength, and the sample is placed in the area where the radio wave intensity is increased. Thus, a direct wave from the sample is detected with high sensitivity.

  Here, the input lens that receives and converges the radio wave radiated from the output lens and transmitted through the sample, the external input means that receives the radio wave radiated from the input lens, and the input received by the external input means Arithmetic processing means for processing the signal and imaging the sample may be provided so that the sample can be imaged by the transmission signal of the sample.

  A network analyzer may be used for input / output of radio waves so that the external output means and the external input means can be shared, and the output lens and the input lens can be shared.

  As the external output means and the external input means, a monopole antenna whose center conductor surrounded by a metal tube has a length equal to or shorter than the wavelength of the irradiated radio wave can be used effectively.

  Further, as the external output means and the external input means, coaxial connectors in which the central conductor protrudes for a length equal to or shorter than the wavelength of the irradiation radio wave can be used effectively.

  While supporting the sample, the sample may be moved in a two-dimensional direction substantially perpendicular to the signal emission direction, and a sample holding means for two-dimensionally scanning the sample may be provided to contribute to acquisition of a two-dimensional image.

  According to the present invention, the sample is placed in a region where the radio wave intensity is increased by the intensity distribution characteristic of the radio wave in the vicinity of the antenna and the convergence characteristic by the lens, and the direct wave from the sample is detected with high sensitivity. A small device capable of imaging a sample is obtained.

An explanatory diagram showing the intensity distribution characteristics of radio waves in the vicinity of a pole-shaped antenna (a) When no lens is attached (b) When a lens is attached Explanatory drawing which shows the angle characteristic of the reflected wave from the sample in the pole-shaped antenna surrounded by the metal cylinder which attached the lens Explanatory drawing which shows the outline | summary of the radio wave imaging apparatus by this invention Photo showing the image of a sample of wood board and plaster

Embodiments of the present invention will be described below with reference to the drawings. The embodiment can be appropriately changed in design without departing from the gist of the present invention, and the above-mentioned patent documents and conventionally known techniques can be used as appropriate.
As an extension of Patent Document 6, Non-Patent Documents 3 to 4 and the like, the present inventor has investigated the characteristics in the vicinity of the antenna in detail, and thereby uses a reflection-type imaging apparatus using a pole-shaped antenna surrounded by a metal cylinder. I found an optimization method.

1A and 1B are explanatory views showing the intensity distribution characteristics of radio waves in the vicinity of a pole-shaped antenna. FIG. 1A shows a case where no lens is attached, and FIG. 1B shows a case where a lens is attached.
In a pole-shaped antenna such as a coaxial cable, the radio wave intensity is high only in the vicinity of the antenna end as shown in FIG. 1A. However, as shown in FIG. When a lens of a distance is attached, a region with a high radio wave intensity can be increased from the end of the lens to a distance according to the convergence characteristics of the lens.

FIG. 2 is an explanatory diagram showing angle characteristics of a reflected wave from a sample in a pole-shaped antenna surrounded by a metal cylinder provided with a lens.
Reflected waves not directed to the lens direction from the sample and scattered waves on the sample surface can be removed by the convergence property of the lens, and direct waves from the sample are detected with high sensitivity.

Therefore, considering the distribution characteristics of the radio wave intensity and the convergence characteristics of the lens, the full width at half maximum of the radio wave intensity distribution is set to be about the wavelength of the radio wave from the end of the lens beyond the wavelength of the radio wave used. By arranging the sample in a region where the intensity is increased, a direct wave from the sample can be detected with high sensitivity.
Normally, when performing imaging, a condensing optical system is used to increase the spatial resolution. However, since the condensing optical system also detects scattered waves from the sample at the same time, it is spatially directly I could n’t separate it from the waves. In the case where it cannot be decomposed in the time domain, the detection ability of the sample, such as the accuracy of distinguishing the state of the substance, has been reduced. In contrast, in the present invention, with a resolution equivalent to the focusing optical system, and it is possible to detect predominantly direct wave as parallel light science-based, etc., such that sensitively distinguish the state of the material, High sensitivity and high resolution detection is possible.

As compared with the prior arts of Patent Document 6 and Non-Patent Documents 3 to 4 by the present inventor, in the present invention, reflection imaging is performed by utilizing the characteristics in the vicinity of a pole-shaped antenna surrounded by a metal tube. In addition, by using a lens and optimizing the installation position, the area that can be imaged with high sensitivity and high resolution has been increased.
In addition, since scattered waves and reflected waves from inclined surfaces can be removed spatially during detection, by using multivariate analysis of the entire spectrum in the frequency domain and time domain, it is possible to detect substances with high sensitivity and high resolution. It became possible to distinguish the state. For multivariate analysis in the frequency domain and time domain, it is useful to use a broadband light source. In the time domain, information in the depth direction of the sample can be obtained simultaneously, and three-dimensional imaging can be performed. It is.

FIG. 3 is an explanatory diagram showing an outline of the radio wave imaging apparatus according to the present invention.
The present invention is basically based on irradiating a sample with radio waves and imaging the sample using the reflected signal. It is also possible to image the sample using the transmission signal. In this embodiment, a case where a sample is imaged using a transmission signal is illustrated. When imaging a sample using a reflection signal, a similar lens is disposed at the reflection position. The main parts of the device include a radio wave source that generates radio waves, an external output means that radiates an output signal from the radio wave source to the outside, an output lens that converges the radio waves emitted from the external output means, and an output An input lens that receives and converges a radio wave radiated from the lens and reflected by the sample, an external input unit that receives the radio wave radiated from the input lens, and a sample that processes the input signal received by the external input unit And at least arithmetic processing means for performing imaging.
In the illustrated example, a network analyzer (Agilent E8363B, 10 MHz-70 GHz) is used as a light source and a detector.

In general, a network analyzer is a device that outputs high-frequency waves such as microwaves to circuits and elements, and measures the reflection and passage states from the circuits to determine the electrical characteristics of the circuits and elements.
The signal source provided in the network analyzer sweeps the frequency in the range to be measured. A directional coupler is provided between the signal source and the external output terminal. The sample is disposed between two external output terminals. A signal given to the sample from the signal source and a reflected or transmitted signal from the sample are controlled by the directional coupler and processed by the arithmetic processing unit. A signal output to the terminal of the directional coupler includes a type in which only amplitude is detected and a type in which both amplitude and phase are detected. In a vector network analyzer of a type that can also measure the phase, the S parameter can be obtained from the reflection or transmission amount and phase of the input / output part of the sample.

Two probes (Agilent 85133E, 2.4 mm) having a coaxial connector in which a plug (male) with a protruding central conductor is disposed are connected to an external terminal of the network analyzer. As the connector type, BNC, SMA type and N type connectors can also be used.
In the vicinity of the end of the probe, a silicon hemispherical lens (focal length 6.3 mm, refractive index 3.4, diameter 30 mm) is arranged to suppress the spread of the millimeter wave in and out. The lens arrangement was set at a position 6.8 mm away from the end of the probe.

  Also, by facing the two lenses, the reflected wave from the sample can be input at the same port as the transmission port, and the transmitted wave from the sample can be input at the reception port via the mirror.

A member that holds the sample may be provided with a mechanism that can move at least in a direction substantially perpendicular to the signal emission direction, and radio waves may be irradiated over the entire desired portion of the sample so that the sample can be imaged over a wide range. . As described above, a conventionally known member such as a biaxial or triaxial stage moving mechanism can be appropriately used as the sample holding member that movably supports the sample.
Such a stage position control and a control of a detector such as a network analyzer may be controlled by a common control device, and a display or the like for displaying an imaging image may be provided.

FIG. 4 is a photograph showing a result of differential imaging of a sample in which a wooden board and gypsum are overlapped by a millimeter wave reflection type apparatus (time domain) according to the present invention.
A cross-shaped pattern is drawn with a gold leaf on the wooden board, and plaster (thickness less than 13 mm) is laminated on it. There is an air gap (thickness d) between the wood board and the plaster, which corresponds to an aged deterioration model such as a tempera.

As reference data, a time waveform at a position where there is no air gap (point A) was used. When the air gap d was 0 mm, the time waveform difference was greater at point B than at point A. This indicates that a gap of several tens of microns has occurred at point B, and the time waveform has changed due to multiple reflections, changes in the optical path, and the like. Further, when the air gap d was 0.5 and 1 mm, the difference in time waveform was further increased. As the air gap d increases, not only multiple reflection but also the beam diameter increases, and the difference in time waveform increases. Therefore, it is easier to detect the presence of the air gap.
From these results, it has been found that by using the present invention, it is possible to detect the presence of an air gap between gypsum and a wooden board. Similarly, according to the present invention, various objects can be imaged.

    According to the present invention, a sample image can be obtained with high sensitivity and high resolution even though it is a small and simple configuration, and can be widely used in fields such as security, civil engineering, food, medicine, and biochemistry, and has high industrial utility value. .

Claims (10)

A method of irradiating a sample with radio waves and imaging the sample with the reflected signal,
A radio wave source that generates radio waves, an external output means that radiates an output signal from the radio wave source to the outside, an output lens that converges the radio waves radiated from the external output means, and a radiation emitted from the output lens and reflected by the sample Lens for receiving and focusing received radio waves, external input means for receiving radio waves radiated from the input lens, and arithmetic processing means for processing the input signal received by the external input means and imaging the sample In a configuration comprising at least
The external output means and the external input means are pole-shaped antennas surrounded by a metal cylinder, and both the input lens and the output lens are determined by the intensity distribution characteristics of the radio waves in the vicinity of the antenna and the convergence characteristics of the lenses. In the direction from the lens toward the sample, from the end of the convex portion of the lens to a distance greater than or equal to the wavelength of the radio wave, approximately twice the half width at half maximum of the radio wave intensity distribution is set equal to the wavelength of the radio wave,
By placing the sample in a region that starts from the end of the convex portion of both the input lens and the output lens, and where approximately half the half width of the radio wave intensity distribution is kept equal to the wavelength, A radio wave imaging method characterized by detecting a direct wave from a wave with high sensitivity. An input lens for a transmitted radio wave that receives and converges a radio wave radiated from the output lens and transmitted through the sample, an external input unit that receives the radio wave radiated from the input lens for the transmitted radio wave, and the external input unit Computation processing means for processing the received input signal and imaging the sample,
The radio wave imaging method according to claim 1, wherein the sample is imaged by a transmission signal of the sample. The radio wave imaging method according to claim 1, wherein millimeter waves are used as radio waves irradiated to the sample. The radio wave imaging method according to any one of claims 1 to 3, wherein a broadband light source is used as a radio wave source, and spectral multivariate analysis in a frequency domain or a time domain is performed. A device that irradiates a sample with radio waves and images the sample using the reflected signal,
A radio wave source that generates radio waves, an external output means that radiates an output signal from the radio wave source to the outside, an output lens that converges the radio waves radiated from the external output means, and a radiation emitted from the output lens and reflected by the sample Lens for receiving and focusing received radio waves, external input means for receiving radio waves radiated from the input lens, and arithmetic processing means for processing the input signal received by the external input means and imaging the sample And at least
The external output means and the external input means are pole-shaped antennas surrounded by a metal tube, and both the input lens and the output lens have a radio wave intensity distribution characteristic near the antenna and a convergence characteristic by the lens. In the direction from the lens toward the sample, from the end of the convex portion of the lens to a distance greater than or equal to the wavelength of the radio wave, approximately twice the half width at half maximum of the radio wave intensity distribution is set equal to the wavelength of the radio wave,
By placing the sample in a region that starts from the ends of the convex portions of both the input lens and the output lens, and approximately twice the half-value half-width of the radio wave intensity distribution is kept equal to the wavelength, A radio wave imaging device characterized in that a direct wave from a sample is detected with high sensitivity. An input lens for a transmitted radio wave that receives and converges a radio wave radiated from the output lens and transmitted through the sample, an external input unit that receives the radio wave radiated from the input lens for the transmitted radio wave, and the external input unit Computational processing means for processing the received input signal and imaging the sample,
The radio wave imaging apparatus according to claim 5, wherein imaging of a sample by a transmission signal of the sample is also possible. Network analyzers are used for radio input and output,
The radio wave imaging apparatus according to claim 5 or 6, wherein the external output means and the external input means can be shared, and the output lens and the input lens can be shared. The radio wave imaging apparatus according to any one of claims 5 to 7, wherein the external output unit and the external input unit are monopole antennas having a central conductor surrounded by a metal tube and having a length equal to or shorter than the wavelength of the irradiation radio wave. The radio wave imaging apparatus according to any one of claims 5 to 7, wherein the external output means and the external input means are coaxial connectors whose center conductor protrudes a length equal to or shorter than the wavelength of the irradiation radio wave. 10. The radio wave imaging apparatus according to claim 5, further comprising a sample holding unit that supports the sample and moves the sample in a two-dimensional direction substantially perpendicular to the signal emission direction to perform two-dimensional scanning of the sample.

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