JP2007121211A - Electromagnetic wave imaging device and electromagnetic wave imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave imaging device of a low price capable of quick scanning using micro wave band or millimeter wave band. <P>SOLUTION: The electromagnetic wave is transmitted to a target 50 from the transmission device, and the electromagnetic wave transmitted through the target 50 is detected by the measurement device provided with a plurality of detectors 12. Thereby, the intensity of multiple electric waves can be measured at once, and the quick scanning becomes possible. The output signals of the plurality of detectors 12 are switched successively by a switch 13. Thereby, a lock-in amplifier 14 of single channel input can be used for measuring the intensity of the electromagnetic wave, and the low price electromagnetic wave imaging device can be provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging technique using an electromagnetic wave in a microwave band or a millimeter wave band.

  The purpose of imaging is to visualize the response of the target to electromagnetic waves with a two-dimensional image. A typical example is a commercially available digital camera.

  A two-dimensional image is a set of fine pixels, and the total number of pixels of an image having resolutions of m and n in the vertical and horizontal directions is m × n. When imaging using a single light receiving element, it is necessary to move and scan the light receiving element about m × n times. Therefore, even with an image of about 100 × 100 pixels, the number of times of moving scanning is 10,000, and imaging takes time.

  In the case of an optical imaging device, in order to capture images having resolutions of m and n in the vertical and horizontal directions, the imaging time is shortened by using an array in which m × n light receiving elements are arranged in advance two-dimensionally. Yes. In addition, there is a method in which m light receiving elements are arranged in a row and n times of moving scanning is performed as in the scanner device.

  When imaging using electromagnetic waves in the microwave band or millimeter wave band, the active method of irradiating the target with electromagnetic waves and detecting the reflected or transmitted waves, or detecting electromagnetic waves emitted spontaneously from the target The passive method is taken. In any system, the imaging time can be shortened by arraying the detectors for detecting electromagnetic waves, as in the case of the optical imaging device.

  In general, a Schottky diode or the like is used as a microwave or millimeter wave electromagnetic wave detector. The intensity of the electromagnetic wave detected by the rectifying action of the Schottky diode is converted into a voltage value. The Schottky diode has a size of sub-millimeters or less, and a detector array for imaging can be realized by arranging a plurality of Schottky diodes.

As an imaging apparatus using millimeter waves, for example, the one described in Patent Document 1 is known.
Japanese Patent Laid-Open No. 2001-50908

  However, in the case of imaging using an electromagnetic wave in the microwave band or the millimeter wave band, a method of measuring signals in parallel when arraying detectors becomes a problem.

  If it is a simple voltage measurement, it can be measured with a commercially available multi-channel input voltmeter, but the voltage output of a Schottky diode that detects electromagnetic waves reflected or transmitted at the target is in the range of several millivolts in the S / N range. The ratio is poor and it is difficult to measure directly with a voltmeter.

  As a measuring instrument for measuring such a signal with a poor S / N ratio, a phase-sensitive detection type lock-in amplifier is known. The lock-in amplifier is effective for extracting a signal buried in noise when a desired electromagnetic wave frequency is known. However, a commercially available lock-in amplifier has a single channel input and cannot cope with an array of detectors. Even if a multi-channel input lock-in amplifier is realized, it is expensive and large-scale.

  The present invention has been made in view of the above, and an object of the present invention is to use an inexpensive microwave band or millimeter wave band electromagnetic wave capable of high-speed scanning of output signals from a plurality of detectors. It is to provide an imaging apparatus.

  An electromagnetic wave imaging apparatus according to the present invention is an electromagnetic wave imaging apparatus that radiates an electromagnetic wave in a microwave band or a millimeter wave band toward a target from a transmission apparatus, and the measurement apparatus measures the response of the electromagnetic wave to the target. The apparatus has generating means for generating electromagnetic waves in the microwave band or millimeter wave band, and radiating means for radiating the generated electromagnetic waves toward the target, and the measuring apparatus detects the electromagnetic waves transmitted or reflected by the target. It is characterized by having a plurality of detectors, a switch for sequentially switching and outputting the output signals from each detector, and a lock-in amplifier to which the output signals from the switches are input in a single channel.

  In the present invention, a microwave band or millimeter wave band electromagnetic wave is radiated from the transmitting device toward the target, and the electromagnetic wave reflected or transmitted by the target is detected by a plurality of detection means arrayed at a time. Since the intensity of many electromagnetic waves can be measured sequentially, high-speed scanning is possible. Further, by switching the outputs of the plurality of detection means with a switch, a commercially available single channel input lock-in amplifier can be used for measuring the intensity of the electromagnetic wave, so that an inexpensive electromagnetic wave imaging apparatus can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device using the electromagnetic wave of a microwave band or a millimeter wave band which can scan at high speed about the output signal from a several detector and is cheap can be provided.

  FIG. 1 is a schematic diagram showing a configuration of an electromagnetic wave imaging apparatus according to the present embodiment. The electromagnetic wave imaging apparatus of FIG. 1 includes a transmission device including an electromagnetic wave oscillator 23, a low frequency signal device 24, a modulator 22, and a transmission antenna 21, a plurality of reception antennas 11, and a detector 12 connected to each of the reception antennas 11, A measuring device including the switch 13 and the lock-in amplifier 14 and a display 31 are provided.

  The transmission device radiates electromagnetic waves in the microwave band or millimeter wave band toward the target 50. Specifically, the electromagnetic wave in the microwave band or the millimeter wave band output from the electromagnetic wave oscillator 23 is modulated by the modulator 22 with the output signal from the low frequency signal device 24 and radiated from the transmitting antenna 21 to free space. The output signal from the low-frequency signal device 24 is a low-frequency signal having a frequency at which the lock-in amplifier 14 can detect the phase.

  As the electromagnetic wave oscillator 23, for example, a GUNN oscillator that generates an electromagnetic wave in a microwave band or a millimeter wave band is used. A synthesizer that can output a frequency signal in a range in which the lock-in amplifier 14 can detect a phase-sensitive signal is used as the low-frequency signal device 24. The modulator 22 modulates the output of the electromagnetic wave oscillator 23 with the output signal from the low frequency signal device 24, and is realized using a PIN switch or the like. As the transmission antenna 21, for example, a horn antenna or a planar slot antenna is used.

  The measuring device receives microwave or millimeter wave electromagnetic waves transmitted through the target 50, measures the intensity of the electromagnetic waves, and outputs it to the display 31. Specifically, among the electromagnetic waves radiated by the transmission device, the electromagnetic waves that have passed through the target 50 are received by the plurality of receiving antennas 11, and the intensity of the received electromagnetic waves is a detector connected to each of the receiving antennas 11. 12 is converted into a voltage value. Each output of the detector 12 is sequentially switched by the switch 13 and sequentially measured by the lock-in amplifier 14. When measuring the electromagnetic wave intensity, the output signal from the low-frequency signal device 24 of the transmission device is used as a reference signal for the lock-in amplifier 14, so that after removing high-frequency noise by a low-pass filter built in the lock-in amplifier 14, The electromagnetic wave signal modulated by the output signal of the low frequency signal device 24 can be taken out. The output signal from the low frequency signal device 24 is used to determine the timing for switching the switch 13. The measurement result is output to the display 31.

  For example, a horn antenna or a planar slot antenna is used as the reception antenna 11, and the detector 12 is connected to each of the reception antennas 11. By arranging the receiving antennas 11 in a one-dimensional array type and performing uniaxial scanning in parallel to the target surface, it is possible to image like a commercially available office scanner.

  The detector 12 uses a Schottky diode. Due to the rectifying action of the Schottky diode, the intensity of the electromagnetic wave received by the receiving antenna 11 is converted into a voltage value. As the switch 13, an electronic circuit type changeover switch that can arbitrarily select output signals from the plurality of detectors 12 is used. By using an electronic circuit type signal changeover switch, a switching speed of 400 microseconds or less can be realized. For example, even if 100 detectors 12 are arranged to form a detector array, it takes about 40 milliseconds. The outputs of all the detectors 12 can be switched sequentially.

  As the lock-in amplifier 14, a commercially available single-channel input phase-sensitive detection lock-in amplifier is used.

  For example, a personal computer is used as the display 31 to visualize the measurement result sent from the measurement device as, for example, a two-dimensional image. Alternatively, an image may be printed directly on paper using a plotter or the like.

  Next, referring to the timing chart of the present embodiment shown in FIG. 2 and the timing chart of the comparative example shown in FIG. 3, the state of the switch 13 of the electromagnetic wave imaging apparatus shown in FIG. The signal strength will be described.

  Each figure shows a state in which the output signal Sb1 from the i-th detector 12 is selected when the switch 13 sequentially switches and outputs the output signal from the detector 12 in the electromagnetic wave imaging apparatus shown in FIG. FIG. 6 is a timing chart when switching to a state in which the output signal Sb2 from the (i + 1) th detector 12 is selected, the state Sa of the switch 13, the output signal Sb1 from the i-th detector 12, and the i + 1-th detector. The output signal Sb2 from the detector 12, the output signal Sc from the switch 13, and the signal strength Sd measured by the lock-in amplifier 14 are shown.

  Here, the time required for the switch 13 to fall is Δt1, the time required for the switch 13 to rise is Δt2, the total time required for switching including the fall time Δt1 and the rise time Δt2 of the switch 13 is ΔT, and the lock-in amplifier 14 Let f be the frequency of the output signal from the low-frequency signal device 24 input as the reference signal.

  FIG. 2 is a timing chart when the switch 13 is switched from the output signal Sb1 of the i-th detector 12 to the output signal Sb2 of the i + 1-th detector 12 in the present embodiment. Specifically, FIG. 2A shows the state Sa of the switch 13. FIG. 2B shows the output signal Sb1 from the i-th detector 12 and the output signal Sb2 from the i + 1-th detector 12 adjacent to each other. FIG. 2C shows the output signal Sc from the switch 13. FIG. 2D shows the signal intensity Sd measured by the lock-in amplifier 14.

  In the present embodiment, as shown in FIG. 2A, when the switch 13 is switched from the i-th detector 12 to the i + 1-th detector 12, the total time (ΔT ) Longer than the period (1 / f) of the output signal from the low-frequency signal device 24. At this time, the switch 13 may be gradually lowered and raised so that Δt1 ≠ 0 and Δt2 ≠ 0. By making ΔT longer than 1 / f, the signal intensity Sd measured by the lock-in amplifier 14 becomes as shown in FIG. 2D, and shot noise is reduced.

  If ΔT is too long, the time for measuring all the outputs of the arrayed detectors 12 increases, making it difficult to perform high-speed scanning. For example, when 100 detectors 12 are arranged and ΔT is 1 second, it takes 100 seconds or more to measure the outputs of all the detectors 12.

  Next, the switching timing of the switch 13 of the comparative example and the signal intensity measured by the lock-in amplifier 14 will be described with reference to FIG. 3 shows that when the switch 13 is switched from the i-th detector 12 to the (i + 1) -th detector 12, ΔT << 1 / f and the switch switching time (ΔT) are simply obtained from the low-frequency signal device 24. FIG. 5 is a timing diagram when switching is performed under a condition shorter than a cycle (1 / f) of an output signal.

  FIG. 3A shows the state of the switch 13. FIG. 3B shows the output signal Sb1 from the i-th detector 12 and the output signal Sb2 from the i + 1-th detector 12 adjacent to each other. FIG. 3C shows the output signal Sc from the switch 13. FIG. 3D shows the signal intensity Sd measured by the lock-in amplifier 14.

  When the switch 13 is in the state indicated by reference numeral 301 in FIG. 3, the output signal Sb1 from the i-th detector 12 is selected, and in the state indicated by reference numeral 302 in FIG. 3, the i + 1-th detector. The output signal Sb2 from 12 is selected. As shown in FIG. 3C, the output signal Sc from the switch 13 corresponds to the output signal from the selected detector 12.

  Here, when the switch 13 is simply switched at high speed, the output signal Sc from the switch 13 is the output signal from the i-th to (i + 1) -th detector 12 as indicated by reference numeral 303 in FIG. Since the output signal Sb1 from the i-th detector 12 and the output signal Sb2 from the i + 1-th detector 12 are superimposed, the signal measured by the lock-in amplifier 14 is instantaneously switched. The intensity Sd is as shown in FIG. 3D, and shot noise occurs.

  On the other hand, in the present embodiment, by making ΔT longer than 1 / f, the signal intensity Sd measured by the lock-in amplifier 14 becomes as shown in FIG. 2D, and shot noise is reduced. The

  Therefore, according to the present embodiment, an electromagnetic wave is radiated from the transmitting device toward the target 50, and the electromagnetic wave transmitted through the target 50 is detected by a measuring device including a plurality of detectors 12, thereby many Since the intensity of the electromagnetic wave can be measured, high-speed scanning is possible. Further, by sequentially switching the output signals from the plurality of detectors 12 with the switch 13, the lock-in amplifier 14 having a single channel input can be used for measuring the electromagnetic wave intensity, so that an inexpensive electromagnetic wave imaging apparatus is provided. Can do.

  According to the present embodiment, an output signal from the low-frequency signal device 24 modulated with electromagnetic waves is used as a reference signal for the lock-in amplifier 14, and the total time required for switching the switch 13 is output from the low-frequency signal device 24. By making it longer than the signal cycle, it is possible to reduce shot noise appearing in the signal intensity Sd measured by the lock-in amplifier 14.

  In the present embodiment, the transmission antenna 21 and the reception antenna 11 are opposed to the target 50, and the transmission imaging apparatus that measures the transmitted electromagnetic wave among the electromagnetic waves radiated toward the target 50 is used. On the other hand, if the transmitting antenna 21 and the receiving antenna 11 are installed on the same side, a reflection type imaging apparatus that measures the reflected wave of the radiated electromagnetic wave can be realized.

It is a schematic diagram which shows the structure of the electromagnetic wave imaging device in one embodiment. It is a timing diagram which shows switching of the switch in one embodiment, and the measured signal strength. It is a timing diagram which shows switching of the switch of a comparative example, and the measured signal strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Reception antenna 12 ... Detector 13 ... Switch 14 ... Lock-in amplifier 21 ... Transmission antenna 22 ... Modulator 23 ... Electromagnetic wave oscillator 24 ... Low frequency signal device 31 ... Display device 50 ... Target

Claims (4)

An electromagnetic wave imaging device that emits an electromagnetic wave in a microwave band or a millimeter wave band from a transmission device toward a target, and the measurement device measures the response of the electromagnetic wave to the target,
The transmitter is
Generating means for generating electromagnetic waves in the microwave band or millimeter wave band;
Radiation means for radiating the generated electromagnetic wave toward the target,
The measuring device is
A plurality of detectors for detecting electromagnetic waves transmitted or reflected by the target;
A switch that sequentially switches and outputs the output signal from each detector;
An electromagnetic wave imaging apparatus comprising: a lock-in amplifier to which an output signal from the switch is input through a single channel. The radiating means modulates an electromagnetic wave with a signal having a frequency capable of phase-sensitive detection by the lock-in amplifier, and a total time required for switching including a rise time and a fall time of the switch is calculated from a cycle of the signal. The electromagnetic wave imaging apparatus according to claim 1, wherein the electromagnetic wave imaging apparatus is longer. Generating microwave or millimeter wave electromagnetic waves;
Radiating the generated electromagnetic wave toward the target;
Detecting electromagnetic waves transmitted or reflected by the target with a plurality of detectors;
A step of sequentially switching and outputting the intensity of each detected electromagnetic wave;
And measuring the intensity of the electromagnetic waves that are sequentially switched and output by a single channel input lock-in amplifier. The step of radiating the electromagnetic wave comprises modulating the electromagnetic wave with a signal having a frequency capable of phase-sensitive detection by the lock-in amplifier, and in the step of sequentially switching the voltage value, the total time required from the start of switching to the completion of switching. The electromagnetic wave imaging method according to claim 3, wherein a period of the signal is longer than a period of the signal.

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