JP5137103B2 - 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.

  Since radio waves often penetrate wood, plastic, paper, etc., techniques for imaging other substances inside these substances have been expected in the past.

Long-wave radio waves are not significantly affected by substances other than metal, but short-wave millimeter waves closest to light waves are also affected by substances other than metal. However, since it is not perfect light, a material that does not transmit light does not transmit millimeter waves.
In recent years, a microwave imaging system capable of generating a two-dimensional or three-dimensional image of a human body or an object with a microwave having a longer wavelength than millimeter waves has been developed.

  However, radio waves not only have a longer wavelength than light waves but also have the property of being diffracted, so that the imaging resolution could not be sufficiently improved.

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.
David M. Sheen, Douglas L. McMakin, and Thomas E. Hall, “Three-Dimensional Millimeter-WaveImaging for Concealed Weapon Detection,” IEEE TRANSACTIONS ON MICROWAVE THEORYAND TECHNIQUES, Vol. 49, No. 9, p. 1581 (2001)

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 aperture, such as inside a substance.
Tatsuo Nozokido, Jongsuck Bae and Koji Mizuno, “Scanning Near-Field Millimeter-Wave Microscopy Using a Metal Slit as aScanning Probe,” IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol. 49, No. 3, p. 491 (2001)

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.
JP 2006-250724 “Object fluoroscopy device” Japanese Patent Application 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 No. 10 / 997,583 "Broadband Binary Phased Antenna"

  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, the resolution is still around the wavelength.

  Therefore, the present invention provides a radio wave imaging method capable of acquiring a transmission image of a sample with a high resolution below the wavelength while suppressing the cause of resolution reduction with a simple configuration, and an apparatus for implementing the method. The issue is to provide.

 In order to solve the above problems, the radio wave imaging apparatus of the present invention has the following configuration. That is, an apparatus for irradiating a sample with radio waves and imaging the sample with the transmission signal thereof, a source of radio waves, a line for guiding an output signal from the radio wave source to an external terminal and an arithmetic processing unit, and an external A measuring instrument having at least a line for guiding a signal from an external sample received at the terminal to the arithmetic processing unit, an arithmetic processing unit for imaging based on the signal from the sample, and an external terminal of the measuring device And two probes having coaxial connectors connected to each other and provided with a coaxial connector on which a projecting plug of the central conductor is disposed, and the interval between the two central conductors is set to be equal to or less than the wavelength of the output signal from the radio wave source. A sample is disposed between two central conductors.

  Here, a network analyzer is preferably used as the measuring instrument.

  An aperture having a wavelength equal to or smaller than the wavelength of the output signal from the radio wave source may be attached to the center conductor on the detection side to suppress interference of diffracted radio waves and contribute to an improvement in resolution.

  Provide a sample moving member that supports the sample and moves it in a direction substantially perpendicular to the signal emission direction, and irradiates the output signal from the radio wave source over the entire desired part of the sample to contribute to a wide range of imaging of the sample. Also good.

  Further, the radio wave imaging method of the present invention is a method of irradiating a sample with radio waves and imaging the sample by the transmitted signal, and the radio wave generation source and the output signal from the radio wave source are connected to an external terminal and arithmetic processing. A measuring instrument comprising at least a line that leads to a part, a line that guides a signal from an external sample received by an external terminal to the arithmetic processing part, and an arithmetic processing part that performs imaging based on the signal from the sample; In a configuration having two probes connected to an external terminal of the measuring instrument and having a coaxial connector provided with a protruding plug of the central conductor, the distance between the two central conductors is determined from the radio wave source. The sample is placed between the two center conductors, and the signal emitted from the output signal connector from the radio wave source is Before diffusing irradiated to the sample, the transmitted signal samples, characterized by receiving at the detection side connector.

  Here, a network analyzer may be used for the measuring instrument.

  An aperture having a wavelength equal to or smaller than the wavelength of the output signal from the radio wave source may be used for the center conductor on the detection side to suppress the interference of the diffracted radio wave and contribute to an improvement in resolution.

  An aperture may be brought close to the central conductor on the detection side to several millimeters to contribute to detection of leakage waves from the aperture.

  The sample holding member supports the sample and moves it in a direction substantially perpendicular to the signal emission direction, irradiates the output signal from the radio wave source over the entire desired part of the sample, and contributes to a wide range of imaging of the sample. Also good.

According to the present invention, the distance between the center conductors of the two probes is equal to or less than the wavelength of the radio signal, the sample is irradiated before the signal is dispersed, and the signal transmitted through the sample is received by the center conductor of the probe. A transmission image of the sample can be acquired with a high resolution below the wavelength while suppressing the cause of the reduction in resolution.
In particular, if an aperture having a wavelength equal to or smaller than the wavelength of the output signal from the radio wave source is attached to the central conductor of the detection side probe, interference of diffracted radio waves can be suppressed and resolution can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing an outline of a 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 transmission signal.

In the illustrated example, a network analyzer (eg, Agilent E8363B) is used as a measuring instrument. As a measuring instrument, in general, a radio wave generation source, a line for guiding an output signal from the radio wave source to an external terminal and an arithmetic processing unit, and a signal from an external sample received by the external terminal are guided to the arithmetic processing unit. It is possible to use an apparatus including at least a line to be processed and an arithmetic processing unit that performs imaging based on a signal from a sample.
Since the radio wave imaging apparatus according to the present invention is an imaging apparatus that does not use a waveguide, a horn antenna, or the like, the frequency is not limited, and it is possible to perform imaging at various frequencies by using a broadband light source.

FIG. 2 is a circuit diagram showing a main circuit of the network analyzer.
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 transmitted or reflected signal from the sample are controlled by the directional coupler and processed by the arithmetic processing unit.

The directional coupler classifies and outputs the direction of a signal coming from one of the two ports. In the directional coupler on the left side in FIG. 2, a signal entering from the signal source side port is output to the terminal a1, and a signal entering from the sample side port is output to the terminal b1. The same applies to the right directional coupler.
Not all the power input to the signal line is led from the signal line to the terminal a1 or b1, and usually about 1/100 (−20 dB) of power is extracted with directionality. In an actual network analyzer, the terminals a1 and a2 are measured by distributing the power of the signal source without using a directional coupler to increase the measurement accuracy, and the signal power from the sample is also as high as possible at the terminals b1 and b2. Often a directional coupler leading to
The signals output to the terminals a and b of the directional coupler include a type in which only amplitude is detected and a type in which both amplitude and phase are detected. In a vector network analyzer that can also measure the phase, the S parameter can be obtained from the amount of transmission or reflection at the input / output part of the sample and the phase.

To the external terminal of the network analyzer, two probes (for example, Agilent 85133) having a coaxial connector in which a plug (male) with a protruding central conductor is disposed are connected.
BNC, SMA type and N type connectors are also available as connector types.

  The two connectors are installed so that the distance between the central conductors at each end is less than the wavelength of the output signal from the radio wave source, such as about 4 mm. The sample is placed in the gap, and the signal emitted from the connector on the transmission side of the output signal from the radio wave source is irradiated to the sample before being dispersed, and the signal transmitted through the sample is received by the connector on the detection side. To detect.

The detection side connector has an aperture made of φ2 mm aluminum. As the aperture, a metal having a size equal to or smaller than the wavelength of the output signal from the radio wave source is used.
By bringing the aperture close to the center conductor on the detection side up to several millimeters, it is possible to suppress the interference of diffracted radio waves and improve the resolution. At this time, by adjusting how close or how far the tip of the central conductor is inserted into the aperture, leakage waves from the aperture can be detected to reduce diffraction, improve detection efficiency, and improve resolution.

  A member that supports the sample is attached with a mechanism that allows it to move in a direction substantially perpendicular to the signal emission direction, so that the output signal from the radio wave source is irradiated over the entire desired part of the sample so that the sample can be imaged over a wide range. It may be. As described above, a conventionally known member such as a stage moving mechanism can be appropriately used as the sample holding member that supports the sample so as to be movable.

FIG. 3 is a graph showing experimental results obtained by measuring a 35 GHz beam.
The shape of a 35 GHz beam (wavelength of about 8 mm) was examined by the knife edge method using an aluminum plate at a position about 1 mm away from the end of the transformer-side connector. FIG. 3A is a graph when no aperture is used, and FIG. 3B is a graph when an aperture is used.
As shown in FIG. 3A, when the aperture is not used, the beam diameter is about 2 mm, which seems to be small, but the interference with the diffracted radio wave is large. On the other hand, when an aperture is used as shown in FIG. 3B, the beam diameter is about 3 mm, but the influence of interference is reduced.

FIG. 4 is an explanatory diagram simply showing experimental results of imaging a card.
The card (JR Suica) shown in FIG. 4 (a) was imaged with a 35 GHz beam. FIG. 4B shows a case where no aperture is used, and FIG. 4C shows a case where an aperture is used.
In both cases, metal distribution within the card was observed. As shown in FIG. 4B, it is possible to perform imaging at a wavelength or less even when no aperture is used. However, when an aperture is used as shown in FIG. 4C, the influence of radio wave diffraction is suppressed. And a clearer image was obtained.

Similarly, pig meat was imaged.
It was observed that the absorption of radio waves differed depending on the amount of moisture and fat in the meat and the solution added to it (DMSO). From this experimental result, it was found that there is a possibility that the uniformity of the biological sample can be evaluated by imaging.

 According to the present invention, a transmission image of a sample can be obtained with a high resolution below the wavelength even with a simple configuration, so that it can be widely used in security fields such as metal detection and biochemistry fields such as biological tissue observation. High utility value.

The schematic diagram which shows the outline | summary of the radio wave imaging apparatus by this invention Circuit diagram showing the main circuit of the network analyzer Graph showing the experimental results of measuring 35 GHz beam Explanatory drawing which shows the experimental result which imaged the card simply

Claims (9)

A device for irradiating a sample with radio waves and imaging the sample using the transmission signal,
A source of radio waves, a line for guiding an output signal from the radio wave source to the external terminal and the processing unit, a line for guiding a signal from an external sample received by the external terminal to the processing unit, and a line from the sample A measuring device including at least an arithmetic processing unit that performs imaging based on a signal;
Two probes having a coaxial connector connected to an external terminal of the measuring instrument and provided with a protruding plug of a central conductor;
A radio wave imaging apparatus characterized in that a distance between the two central conductors is set to be equal to or less than a wavelength of an output signal from a radio wave source, and a sample is disposed between the two central conductors. The radio wave imaging apparatus according to claim 1, wherein the measuring instrument is a network analyzer. The radio wave imaging apparatus according to claim 1, wherein an aperture having a wavelength equal to or less than a wavelength of the output signal from the radio wave source is attached to the center conductor on the detection side. The radio wave imaging apparatus according to any one of claims 1 to 3, further comprising a sample moving member that supports the sample and moves the sample in a direction substantially perpendicular to a signal emission direction. A method of irradiating a sample with radio waves and imaging the sample using the transmission signal,
A source of radio waves, a line for guiding an output signal from the radio wave source to the external terminal and the processing unit, a line for guiding a signal from an external sample received by the external terminal to the processing unit, and a line from the sample A measuring device including at least an arithmetic processing unit that performs imaging based on a signal;
In a configuration having two probes connected to an external terminal of the measuring instrument and provided with a coaxial connector provided with a protruding plug of a central conductor,
The distance between the two central conductors is set to be equal to or less than the wavelength of the output signal from the radio wave source, and a sample is disposed between the two central conductors.
A signal emitted from a connector on the transmission side of an output signal from a radio wave source is irradiated to the sample before the signal is dispersed, and the signal that has passed through the sample is received by the connector on the detection side. Imaging method. The radio wave imaging method according to claim 5, wherein a network analyzer is used for the measuring instrument. The radio wave imaging method according to claim 5, wherein an aperture having a wavelength equal to or smaller than a wavelength of an output signal from the radio wave source is attached to the center conductor on the detection side to suppress interference of diffracted radio waves. The radio wave imaging method according to claim 7, wherein the leaking wave from the aperture is detected by bringing the aperture close to the central conductor on the detection side up to several millimeters. The radio wave imaging according to claim 5, wherein the sample is supported by the sample holding member and moved in a direction substantially perpendicular to the signal emission direction to irradiate the output signal from the radio wave source over the entire desired part of the sample. Method.

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