Patent Application
20220299602
This application is based on Japanese patent application No. 2021-047049, the content of which is incorporated hereinto by reference.
The present invention relates to an object detection apparatus, an object detection method, and a program for projecting a radio wave onto a detection target object and recognizing or identifying existence of the detection target object by using the radio wave reflected from the target object.
Unlike light, a radio wave (such as a microwave, a millimeter wave, or a terahertz wave) has an excellent ability to penetrate an object. United States Patent Application Publication No. 2014/0167784 (Patent Document 1) proposes an apparatus projecting a radio wave penetrating clothing and a bag onto a hidden article under clothing or in a bag from a radar apparatus, receiving the radio wave reflected by the article by the radar apparatus, and imaging and inspecting the article, based on the received radio wave.
Further, a technology for telemetering the permittivity of a substance by a radio wave has been proposed. Since a permittivity takes an inherent value for each substance, measurement of a permittivity can be used for identification of a substance. A permittivity is particularly useful for identification of an explosive, a drug, and the like.
U.S. Pat. No. 8,946,641 (Patent Document 2) and “K. Haddadi et al, ‘Geometrical Optics-Based Model for Dielectric Constant and Loss Tangent Free-Space Measurement’, IEEE Trans. Instrum. Meas., vol. 63, no. 7, pp. 1818-1823, July 2014” (Non-Patent Document 1) propose methods for projecting a radio wave onto a substance from a radar apparatus, receiving the radio wave reflected from the substance by the radar apparatus, generating an intermediate frequency signal, based on the received radio wave, and estimating the permittivity of the substance by using the intermediate frequency signal. Specifically, geometrical optics modeling having the permittivity of a substance being a measurement target as an unknown variable is used. When a value of a permittivity being an unknown variable is given, a geometrical optics model can compute an intermediate frequency signal. Then, the permittivity of the substance is estimated from a permittivity value of a geometrical optics model best reproducing a measured value of the intermediate frequency signal.
Japanese Patent No. 5260799 (Patent Document 3) proposes a method for measuring a permittivity by an object detection apparatus including a radar and a camera. Specifically, a radio wave is projected onto a substance and a background reflector from a radar apparatus and a three-dimensional microwave image is generated based on radio waves reflected from the substance and the background reflector. The object detection apparatus measures the distances from the object detection apparatus to the substance and the background reflector by using the three-dimensional microwave image and a camera image and further estimates a permittivity from the distances acquired by the measurement.
Further, International Application Publication No. WO 2018/147025 (Patent Document 4) describes projecting a radio wave onto a substance as a transmission signal, receiving the radio wave reflected from the substance as a reception signal, and generating an intermediate frequency signal by mixing the transmission signal and the reception signal. The intermediate frequency signal is used when a spectrum representing a position distribution of an object is computed.
Further, Japanese Patent Application Publication No. 2018-011923 (Patent Document 5) describes a condition detection apparatus for detecting a foreign substance or an abnormal part in a human body by using a standing wave radar. By combining a transmission wave with a reception wave being a received reflected wave reflected by an external measurement target, the condition detection apparatus detects a combined wave. Then, the condition detection apparatus determines a distance spectrum by removing a direct current component from a frequency intensity distribution of the combined wave and Fourier transforming the resulting distribution.
Japanese Patent Application Publication No. 2008-512175 (Patent Document 6) describes using a plurality of antenna elements and collecting reflection coefficient data of a body part of a patient across a frequency range of a microwave in a system generating a three-dimensional image of the body part.
The methods for estimating the permittivity of a substance, based on geometrical optics, in Patent Document 2 and Non-Patent Document 1 are premised on use of a single transmission antenna and a single reception antenna. Use of a single transmission antenna and a single reception antenna has a problem that the method is susceptible to noise of a radar apparatus and precise estimation of the permittivity of a substance is difficult.
In Patent Document 3, a three-dimensional microwave image is generated by an antenna array configured with a plurality of transmission antennas and a plurality of reception antennas. Unlike the methods of using a single transmission antenna and a single reception antenna in Patent Document 2 and Non-Patent Document 1, use of an antenna array is less susceptible to noise of a radar apparatus.
On the other hand, a camera apparatus is required in addition to a radar apparatus in Patent Document 3. Therefore, there is a problem of cost increase due to use of a camera. Furthermore, a synchronization operation between the radar and the camera is also required. There is a problem that synchronization deviation between the radar and the camera causes a measurement error of a permittivity when a measurement target object moves.
An object of the present invention is to increase measurement precision while suppressing cost increase when the permittivity of an object is measured by using a radio wave.
In one embodiment, there is provided an object detection apparatus for detecting an object by a radio wave, the object detection apparatus including: a transmission unit including a plurality of transmission antennas projecting a radio wave toward the object; a reception unit including a plurality of reception antennas receiving the radio wave reflected from the object and further generating an intermediate frequency signal from a reception signal received by the reception antennas; a three-dimensional reflection amplitude computation unit that computes a distribution of a reflection amplitude of the object in a three-dimensional space from the intermediate frequency signal; a two-dimensional reflection amplitude computation unit that computes a reflection amplitude in a two-dimensional plane from a maximum value possibly taken by the three-dimensional reflection amplitude in a depth direction perpendicular to the two-dimensional plane; and a complex permittivity absolute value computation unit that computes a reflectance of the object by normalizing the two-dimensional reflection amplitude by a maximum value of the two-dimensional reflection amplitude and computing a complex permittivity absolute value of the object from the reflectance.
In another example embodiment, there is provided an object detection method for detecting an object by a radio wave, the object detection method including: a step of projecting a radio wave toward the object from a transmission unit including a plurality of transmission antennas; a step of, by a reception unit including a plurality of reception antennas, receiving the radio wave reflected from the object and further generating an intermediate frequency signal from a reception signal received by the reception antennas; a step of, by a three-dimensional reflection amplitude computation unit, computing a reflection amplitude of the object in a three-dimensional space from the intermediate frequency signal; a step of, by a two-dimensional reflection amplitude computation unit, computing a reflection amplitude in a two-dimensional plane from a maximum value possibly taken by the three-dimensional reflection amplitude in a depth direction perpendicular to the two-dimensional plane; and a step of, by a complex permittivity absolute value computation unit, computing a reflectance of the object by normalizing the two-dimensional reflection amplitude by a maximum value of the two-dimensional reflection amplitude and computing a complex permittivity absolute value of the object from the reflectance.
In still another example embodiment, there is provided a program causing an object detection apparatus including: a transmission unit including a plurality of transmission antennas projecting a radio wave toward an object; a reception unit including a plurality of reception antennas receiving the radio wave reflected from the object and further generating an intermediate frequency signal from a reception signal received by the reception antennas; and a processor to execute: a step of, by a three-dimensional reflection amplitude computation unit, computing a reflection amplitude of the object in a three-dimensional space from the intermediate frequency signal; a step of, by a two-dimensional reflection amplitude computation unit, computing a reflection amplitude in a two-dimensional plane from a maximum value possibly taken by the three-dimensional reflection amplitude in a depth direction perpendicular to the two-dimensional plane; and a step of, by a complex permittivity absolute value computation unit, computing a reflectance of the object by normalizing the two-dimensional reflection amplitude by a maximum value of the two-dimensional reflection amplitude and computing a complex permittivity absolute value of the object from the reflectance.
The present invention can increase measurement precision while suppressing cost increase when the permittivity of an object is measured by using a radio wave.
The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred example embodiments taken in conjunction with the accompanying drawings, in which:
The invention will be now described herein with reference to illustrative example embodiments. Those skilled in the art will recognize that many alternative example embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the example embodiments illustrated for explanatory purposes.
Preferred example embodiments of an object detection apparatus and an object detection method according to the present invention are described below with reference to attached drawings. Note that the same or equivalent parts in the following drawings are given the same sign, and duplicated description thereof is omitted.
An object detection apparatus, an object detection method, and a program according to example embodiments of the present invention are described below referring to
First, a configuration of an object detection apparatus according to a first example embodiment is described by using
Next,
Next,
Next, operation of the object detection apparatus according to the first example embodiment illustrated in
In the apparatus configuration illustrated in
The reception unit 1102 in
In the transmission unit 1101 illustrated in the internal configuration in
In the reception unit 1102 illustrated in the internal configuration in
In the arithmetic apparatus 1211 illustrated in the internal configuration in
The three-dimensional reflection amplitude p(x, y, z) computed by the three-dimensional reflection amplitude computation unit 1301 is input to the target object depth position computation unit 1308. The target object depth position computation unit 1308 computes a depth position zd(x, y) indicating a position of the target object 1003 in the z-axis direction at a two-dimensional position (x, y). Specifically, the depth position zd(x, y) is computed as a position in the z-axis direction maximizing the three-dimensional reflection amplitude p(x, y, z) at each point of the two-dimensional position (x, y) as indicated in equation (1).
z
d(x, y)=argmaxz[p(x, y, z)], (1)
The three-dimensional reflection amplitude p(x, y, z) computed by the three-dimensional reflection amplitude computation unit 1301 is input to the two-dimensional reflection amplitude computation unit 1302. Based on the input three-dimensional reflection amplitude p(x, y, z), the two-dimensional reflection amplitude computation unit 1302 computes a two-dimensional reflection amplitude pd(x, y) of the target object 1003 with a two-dimensional position (x, y) as an argument. Specifically, the two-dimensional reflection amplitude pd(x, y) is computed as a maximum value of the three-dimensional reflection amplitude p(x, y, z) when z is changed at each point of the two-dimensional position (x, y) as expressed in equation (2).
p
d(x, y)=maxz[p(x, y, z)]=p(x, y, zd(x, y)), (2)
The two-dimensional reflection amplitude pd(x, y) computed by the two-dimensional reflection amplitude computation unit 1302 is input to the complex permittivity absolute value computation unit 1303. Based on the input two-dimensional reflection amplitude pd(x, y), the complex permittivity absolute value computation unit 1303 computes the absolute value |εc(x, y)| of the complex permittivity of the target object 1003 at a two-dimensional position (x, y).
Specifically, the complex permittivity absolute value computation unit 1303 first computes the reflectance R(x, y) of the target object 1003 from a value acquired by normalizing the two-dimensional reflection amplitude pd(x, y) by the maximum value thereof in accordance with the following equation (3).
R(x, y)=pd(x, y)/max(x,y)[pd(x, y)], (3)
Next, the complex permittivity absolute value computation unit 1303 computes the absolute value |εc(x, y)| of the complex permittivity of the target object 1003 from the reflectance R(x, y) of the target object 1003 in accordance with the following equation (4).
|εc(x, y)|=[1+R(x, y)]2/[1−R(x, y)]2, (4)
The depth position zd(x, y) computed by the target object depth position computation unit 1308 is input to the target object thickness computation unit 1304. Based on the input depth position zd(x, y), the target object thickness computation unit 1304 computes a target object thickness d(x, y) and a reference depth position zref(x, y) at a two-dimensional position (x, y).
First, a specific computation method of a reference depth position zref(x, y) is described below. A case of the positional relation between the object detection apparatus 1000 and target objects 1003 being a placement illustrated in
The same number of numerical values of depths zd as the number of points in the domain (x, y) are acquired from the depth positions zd(x, y) input to the target object thickness computation unit 1304. The target object thickness computation unit 1304 computes a distribution state of numerical values of the depths zd by using a histogram N(zd) of the depths zd. An example of the histogram N(zd) related to the placement in
z
ref(x, y)=zi (5)
Then, the target object thickness computation unit 1304 computes a target object thickness d(x, y) in accordance with the following equation (6) by using the depth position zd(x, y) and the reference depth position zref(x, y).
d(x, y)=zref(x, y)−zd(x, y) (6)
In the example described above, the target object thickness computation unit 1304 detects the positions z1, z2, . . . , zK at the surface of the target objects 10031, 10032, . . . , 1003K in the z-axis direction from peak values in the histogram counting the number N(zd) of depth positions zd included in the x-y plane. As another means, the target object thickness computation unit 1304 may detect the positions z1, z2, . . . , zK at the surface of the target objects 10031, 10032, . . . , 1003k in the z-axis direction from positions in the z-axis direction where peaks of a function g(z)=Σ(x, y)[p(x, y, z)] acquired as the sum of three-dimensional reflection amplitudes p(x, y, z) in the x-y plane in the x-y plane are acquired.
The two-dimensional reflection amplitude pd(x, y) computed by the two-dimensional reflection amplitude computation unit 1302, the absolute value |εc(x, y)| of the complex permittivity and the reflectance R(x, y) that are computed by the complex permittivity absolute value computation unit 1303, and the target object thickness d(x, y) and the reference depth zref(x, y) that are computed by the target object thickness computation unit 1304 are input to the permittivity computation unit 1305. Based on the input data, the permittivity computation unit 1305 computes the permittivity εr(x, y) of the target object 1003 at a two-dimensional position (x, y). The permittivity εr(x, y) corresponds to the real part of the complex permittivity εc(x, y).
A specific computation method of a permittivity εr(x, y) is described below. The permittivity computation unit 1305 computes a radio wave absorption amount Δa(x, y) at a two-dimensional position (x, y) in accordance with the following equation (7) by using the input two-dimensional reflection amplitude pd(x, y), the input reference depth zref(x, y), and the input reflectance R(x, y).
Δa(x, y)=pd(x, y)/p[x, y, zref(x, y)]/[1−R(x, y)]2, (7)
Next, the permittivity computation unit 1305 computes an absorption coefficient α(x, y) at a two-dimensional position (x, y) in accordance with the following equation (8) by using the computed radio wave absorption amount Δa(x, y) and the input target object thickness d(x, y).
α(x, y)=−ln(Δa(x, y))/2d(x, y), (8)
Next, the permittivity computation unit 1305 computes a permittivity εr(x, y) at a two-dimensional position (x, y) in accordance with the following equation (9) by using the computed absorption coefficient α(x, y) and the input absolute value |εc(x, y)| of the complex permittivity.
εr(x, y)=|εc(x, y)|−2(λα(x, y)/2π)2 (9)
Note that λ in equation (9) denotes the wavelength of a radio wave transmitted by the transmission unit 1101.
The absolute value |εc(x, y)| of the complex permittivity computed by the complex permittivity absolute value computation unit 1303 and the permittivity εr(x, y) computed by the permittivity computation unit 1305 are input to the dielectric loss computation unit 1306. Based on the input data, the dielectric loss computation unit 1306 computes the dielectric loss εi(x, y) of the target object 1003 at a two-dimensional position (x, y). The dielectric loss εi(x, y) corresponds to the imaginary part of the complex permittivity εc(x, y).
A specific computation method of a permittivity εi(x, y) is described below. The dielectric loss computation unit 1306 computes a dielectric loss εi(x, y) at a two-dimensional position (x, y) in accordance with the following equation (10) by using the input absolute value |εc(x, y)| of the complex permittivity and the input permittivity εr(x, y).
εi(x, y)=sqrt(|εc(x, y)|2−εr(x, y)2). (10)
Each of the absolute value |εc(x, y)| of the complex permittivity computed by the complex permittivity absolute value computation unit 1303, the permittivity εr(x, y) computed by the permittivity computation unit 1305, and the dielectric loss εi(x, y) computed by the dielectric loss computation unit 1306 may be output as a two-dimensional image.
At least one of the absolute value |εc(x, y)| of the complex permittivity computed by the complex permittivity absolute value computation unit 1303, the permittivity εr(x, y) computed by the permittivity computation unit 1305, and the dielectric loss εi(x, y) computed by the dielectric loss computation unit 1306 is input to the substance identification unit 1307. The substance identification unit 1307 includes a database storing a value of the complex permittivity absolute value, the permittivity, or the dielectric loss of each of various substances. The substance identification unit 1307 identifies a constituent substance of the target object 1003 by checking at least one of the absolute value |εc(x, y)| of the complex permittivity, the permittivity εr(x, y), or the dielectric loss εi(x, y) input to the substance identification unit 1307 against a value in the database.
Next, a second example embodiment is described. The second example embodiment provides an object detection method in a case of a surface of a target object 1003 not being parallel to an aperture plane 1400 formed by a transmission antenna 1202 and a reception antenna 1203 in an object detection apparatus 1000, as illustrated in
An apparatus configuration according to the second example embodiment is illustrated in
In a placement illustrated in
A computation method of the value of the angle θ0 is described below. A target object depth position computation unit 1308 sets a z(θ) axis and an x(θ) axis being axes acquired by tilting the z-axis and the x-axis at an angle θ. The target object depth position computation unit 1308 computes a depth position zd[x(θ), y. θ] as a position in the z(θ) axis direction maximizing a three-dimensional reflection amplitude p(x, y, z) input from a three-dimensional reflection amplitude computation unit 1301.
z
d[x(θ), y. θ]=argmaxz(θ)[p(x, y, z)], (11)
The computed depth position zd[x(θ), y. θ] is input to the target object orientation computation unit 1309.
Next, based on the input depth position zd[x(θ), y. θ], the target object orientation computation unit 1309 computes a histogram counting the number N[zd(θ)] of depth positions zd[x(θ), y. θ] included in an x(θ)-y plane.
Similarly to the first example embodiment, a function g(z(θ))=Σ(x(θ), y)[p(x(θ), y, z(θ))] acquired as the sum of three-dimensional reflection amplitudes p(x(θ), y, z(θ)) in the x(θ)-y plane may be used in place of the histogram N[zd(θ)] of depth positions zd[x(θ), y. θ] in the second example embodiment also.
A target object thickness computation unit 1304 computes a histogram N[zd(θ0)] of depth positions zd[x(θ0), y. θ0] for the tilt angle θ0 from the computed value of the tilt angle θ0 of the target object 1003 computed by the target object orientation computation unit 1309 and the depth position computed by the target object depth position computation unit 1308. Furthermore, the target object thickness computation unit 1304 computes a reference depth position zref(x(θ0), y) and a target object thickness d(x(θ0), y) from the peak value of the histogram N[zd(θ0)] by a procedure similar to that according to the first example embodiment.
Furthermore, based on the three-dimensional reflection amplitude p(x, y, z) input from the three-dimensional reflection amplitude computation unit 1301 and the computed value of the tilt angle θ0 of the target object 1003 computed by the target object orientation computation unit 1309, a two-dimensional reflection amplitude computation unit 1302 computes a two-dimensional reflection amplitude pd[x(θ0), y] as expressed in equation (12) as a maximum value of a three-dimensional reflection amplitude when z(θ0) is changed at each point of a two-dimensional position (x(θ0), y).
p
d(x(θ0), y)=maxz(θ0)[p[x(θ0), y, z(θ0)]] (12)
Subsequently, a complex permittivity absolute value computation unit 1303, the target object thickness computation unit 1304, a permittivity computation unit 1305, and a dielectric loss computation unit 1306 compute a complex permittivity absolute value, a permittivity, and a dielectric loss by performing processing identical to that in the first example embodiment with the depth position zd[x(θ0), y. θ0] based on the tilt angle θ0, the two-dimensional reflection amplitude pd[x(θ0), y], the target object thickness d(x(θ0), y), and the reference depth position zref(x(θ0), y) in place of a depth position zd(x, y), a two-dimensional reflection amplitude pd(x, y), a target object thickness d(x, y), and a reference depth position zref(x, y) as input data.
A substance identification unit 1307 according to the second example embodiment also identifies a constituent substance of the target object 1003 by checking at least one of the complex permittivity absolute value, the permittivity, and the dielectric loss input to the substance identification unit 1307 against a value in the aforementioned database.
When the target object 1003 faces the object detection apparatus 1000 as illustrated in
Whether the target object 1003 faces the object detection apparatus 1000 can be determined by using the position of the target object 1003 estimated from the reflection amplitude p(x, y, z) of the target object 1003 acquired by the three-dimensional reflection amplitude computation unit 1301 and the value of the angle θ0 estimated by the two-dimensional reflection amplitude computation unit 1302 and the target object thickness computation unit 1304.
A computer (arithmetic apparatus) providing an object detection apparatus by executing a program according to each example embodiment of the present invention is described by using
As illustrated in
The CPU 111 performs various computations by loading programs (codes) according to each example embodiment stored in the storage 113 into the main memory 112 and executing the programs in a predetermined order. The main memory 112 is typically a volatile storage such as a dynamic random access memory (DRAM). Further, the program according to each example embodiment is provided in a state of being stored in a computer-readable storage medium 120. The program according to each example embodiment may be distributed on the Internet connected through the communication interface 117.
Further, specific examples of the storage 113 include semiconductor storages such as a flash memory in addition to a hard disk drive. The input interface 114 mediates data transmission between the CPU 111 and input equipment 118 such as a keyboard and a mouse. The display controller 115 is connected to a display apparatus 119 and controls display at the display apparatus 119. The computer 110 may include a graphics processing unit (GPU) or a field-programmable gate array (FPGA) in addition to or in place of the CPU 111.
The data reader-writer 116 mediates data transmission between the CPU 111 and the storage medium 120 and executes readout of a program from the storage medium 120 and writing of a processing result in the computer 110 into the storage medium 120. The communication interface 117 mediates data transmission between the CPU 111 and another computer.
Specific examples of the storage medium 120 include general-purpose semiconductor storage devices such as a CompactFlash [(CF) registered trademark] and a secure digital (SD), magnetic storage media such as a flexible disk, and optical storage media such as a compact disk read only memory (CD-ROM).
The object detection apparatus according to each example embodiment may be provided by use of hardware equivalent to the components instead of by a computer installed with a program. Furthermore, part of the object detection apparatus may be provided by a program, and the remaining part may be provided by hardware.
Effects of the example embodiments of the present invention are summarized below.
The object detection apparatus and object detection method according to the example embodiments of the present invention can measure a complex permittivity absolute value, a permittivity, and a dielectric loss that are substance-specific characteristics of a target object 1003 while reducing an effect of noise of a radar apparatus constituting the object detection apparatus 1000, by using antenna arrays configured with a plurality of transmission antennas 1202 and a plurality of reception antennas 1203, respectively. Furthermore, the object detection apparatus 1000 is configured without using a sensor other than a radar and therefore can measure the complex permittivity absolute value, the permittivity, and the dielectric loss of the target object 1003 without accompanying a cost and an error that result from a sensor other than the radar. Furthermore, the object detection apparatus 1000 can identify a substance constituting the target object 1003 from the value of the complex permittivity absolute value, the permittivity, or the dielectric loss of the target object 1003 acquired by measurement.
Configurations of preferred example embodiments of the present invention have been described above. However, the disclosure of the aforementioned patent literatures and the like may be incorporated herein by reference thereto. The example embodiments may be changed and adjusted within the scope of the entire disclosure of the present invention (including the claims) and on the basis of the basic technological concept thereof Further, various disclosed elements may be combined and selected in a variety of ways within the scope of the claims of the present invention. In other words, it is apparent that the present invention includes various modifications and changes that may be made by a person skilled in the art on the basis of the entire disclosure including the claims, and the technological concept.
It is apparent that the present invention is not limited to the above embodiment, and may be modified and changed without departing from the scope and spirit of the invention.
110: computer
111: CPU
112: main memory
113: storage
114: input interface
115: display controller
116: data reader-writer
117: communication interface
118: input equipment
119: display apparatus
120: storage medium
121: bus
1000: object detection apparatus
1001: transmission-reception apparatus
1002: radio wave(transmission signal)
1003: target object (object as detection target)
1004: radio wave(reception signal)
1005: target object placement plane
1101: transmission unit
1102: reception unit
1201: oscillator
1202: transmission antenna
1203: reception antenna
1204: mixer
1205: interface circuit
1207: variable amplitude phase shifter
1208: terminal
1211: arithmetic apparatus
1301: three-dimensional reflection amplitude computation unit
1302: two-dimensional reflection amplitude computation unit
1303: complex permittivity absolute value computation unit
1304: target object thickness computation unit
1305: permittivity computation unit
1306: dielectric loss computation unit
1307: substance identification unit
1308: target object depth position computation unit
1309: target object orientation computation unit
1400: aperture plane
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-047049 | Mar 2021 | JP | national |
