Object perspective device

Abstract

An object see-through scanning device (100) comprises: a transmission unit (101) that transmits, to a target object (T), transmission radio waves obtained by repeatedly performing frequency sweep which changes a frequency from a first frequency to a second frequency over a frequency sweep time; a reception unit (102) that uses array antenna elements to receive reception radio waves obtained as a result of the transmission radio waves being reflected by the target object (T); a three-dimensional image generation unit (8) that, for each frequency sweep, generates a three-dimensional image from a reception signal from the array antenna elements; and an object detection unit (9) that detects an object on the basis of a plurality of three-dimensional images. At least one of the first frequency, the second frequency, the frequency sweep time, and the number of array antenna elements used in the detection of the object is changed in a time-divided manner.

Description

Object see-through device and object see-through method

[0001] The present disclosure relates to an object see-through device and an object see-through method that use radio waves to see through an object.

[0002] Devices that see through objects to detect foreign objects or dangerous materials are used in food inspections, security gates at airports, and other applications. Conventional object viewing devices generally use X-rays. X-ray-based object viewing devices have the problem of X-ray exposure, limiting their use. As a method that does not involve radiation exposure, object viewing devices that use nuclear magnetic resonance have been put to practical use for medical purposes. However, object viewing devices that use nuclear magnetic resonance require a strong magnetic field, are large, and exert a large force when magnetic materials such as iron are present. Therefore, object viewing devices that use nuclear magnetic resonance require a large space for installation, and there are significant limitations on where the device can be installed, such as the need to control the entry and exit of people and objects into the installation area, limiting their use.

[0003] In contrast, an object see-through device that uses radio waves does not pose the problem of radiation exposure, and there are fewer restrictions on where the device can be installed. When radio waves are used, the resolution limit is limited by the wavelength of the radio waves used. For this reason, object see-through images that use radio waves have traditionally had low resolution and made it difficult to identify objects. However, recent advances in device technology have made it possible to use radio waves of 100 GHz or higher, and improvements in resolution are expected. For example, Patent Document 1 discloses a device that uses microwaves to inspect defects inside tires.

[0004] Japanese Patent Application Laid-Open No. 2018-77192

[0005] However, the above-described conventional technology has a problem in that the detection accuracy decreases when the detection target moves.

[0006] The present disclosure has been made in view of the above, and aims to provide an object see-through device that can suppress a decrease in detection accuracy even when a detection target moves.

[0007] In order to solve the above-mentioned problems and achieve the object, the object visualization device according to the present disclosure includes a transmitting unit that transmits to a target object transmission radio waves that have been repeatedly frequency swept to change the frequency from a first frequency to a second frequency over a frequency sweep time; a receiving unit that receives, using an array antenna element, reception radio waves that are the transmission radio waves reflected by the target object; a three-dimensional image generating unit that generates a three-dimensional image from the reception signal of the array antenna element for each frequency sweep; and an object detection unit that detects an object based on a plurality of three-dimensional images, and is characterized in that at least one of the first frequency, the second frequency, the frequency sweep time, and the number of array antenna elements used to detect the object is changed in a time-division manner.

[0008] The object see-through apparatus according to the present disclosure has the advantage of being able to suppress a decrease in detection accuracy even when the detection target moves.

[0009] 1 is a diagram showing the configuration of an object see-through device according to a first embodiment; FIG. 2 is a diagram showing a first example of a waveform of a transmitted radio wave; FIG. 3 is a diagram showing a second example of a waveform of a transmitted radio wave; FIG. 4 is a diagram showing the configuration of a transmitter shown in FIG. 1; FIG. 5 is a diagram showing the configuration of a receiver shown in FIG. 1;

[0010] An object see-through apparatus and an object see-through method according to embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0011] 1 is a diagram showing the configuration of an object see-through device 100 according to a first embodiment. The object see-through device 100 has a function of seeing through an object using radio waves. The object see-through device 100 is used, for example, to detect dangerous objects such as weapons at airports, or to detect foreign objects mixed into products at production sites.

[0012] The object see-through device 100 includes a transmitter 1, a transmitting antenna 2, a receiving antenna 3, a receiver 4, an analog-to-parallel serial conversion unit 5, an analog-to-digital converter 7, a three-dimensional image generation unit 8, an object detection unit 9, and an oscillator 10. The transmitter 1 and the transmitting antenna 2 are collectively referred to as a transmitting unit 101. The receiving antenna 3, the receiver 4, the analog-to-parallel serial conversion unit 5, and the analog-to-digital converter 7 are collectively referred to as a receiving unit 102.

[0013] The transmitter 1 generates a transmission radio wave W1 to be transmitted toward the target object T, and transmits the generated transmission radio wave W1 using the transmission antenna 2. Here, the waveform of the transmission radio wave W1 will be described. The transmitter 1 generates the transmission radio wave W1 having a waveform obtained by repeatedly performing a frequency sweep that changes the frequency from a first frequency to a second frequency. Here, the length of time it takes to change the frequency from the first frequency to the second frequency is referred to as the frequency sweep time. The transmitter 1 can change at least one of the frequency sweep parameters, namely the first frequency, the second frequency, and the frequency sweep time, in a time-division manner.

[0014] FIG. 2 is a diagram illustrating a first example of the waveform of the transmission radio wave W1. In the first example illustrated in FIG. 2, the first frequency is 270 GHz and the second frequency is 290 GHz. While the values ​​of the first and second frequencies are fixed, the frequency sweep time is changed for each frequency sweep. In the first frequency sweep, the frequency sweep time is 10 μsec, in the second frequency sweep, the frequency sweep time is 20 μsec, in the third frequency sweep, the frequency sweep time is 40 μsec, and in the fourth frequency sweep, the frequency sweep time is 80 μsec. In addition, in the fifth frequency sweep, the frequency sweep time is 10 μsec, in the sixth frequency sweep, the frequency sweep time is 20 μsec, in the seventh frequency sweep, the frequency sweep time is 40 μsec, and in the eighth frequency sweep, the frequency sweep time is 80 μsec.

[0015] 3 is a diagram showing a second example of the waveform of the transmission radio wave W1. In the second example shown in FIG. 3, the frequency sweep time is a constant value of 10 μsec, while the first frequency and the second frequency are changed for each frequency sweep. In the first frequency sweep, the first frequency is 278 GHz and the second frequency is 282 GHz. In the second frequency sweep, the first frequency is 276 GHz and the second frequency is 284 GHz. In the third frequency sweep, the first frequency is 274 GHz and the second frequency is 286 GHz. In the fourth frequency sweep, the first frequency is 272 GHz and the second frequency is 288 GHz. In the fifth frequency sweep, the first frequency is 270 GHz and the second frequency is 290 GHz. In the sixth frequency sweep, the first frequency is 278 GHz and the second frequency is 282 GHz. In the seventh frequency sweep, the first frequency is 276 GHz and the second frequency is 284 GHz. In the eighth frequency sweep, the first frequency is 274 GHz and the second frequency is 286 GHz. In the ninth frequency sweep, the first frequency is 272 GHz and the second frequency is 288 GHz. In the tenth frequency sweep, the first frequency is 270 GHz and the second frequency is 290 GHz.

[0016] 4 is a diagram showing the configuration of the transmitter 1 shown in FIG. A constant envelope signal is input to the transmitter 1 from an oscillator 10. The transmitter 1 has an N-multiplier 11 and a transmission amplifier 12. The transmitter 1 multiplies the constant envelope signal input from the oscillator 10 by N using the N-multiplier 11. Therefore, the oscillator 10 generates a signal having a frequency that is 1 / N times the frequency of the transmission radio wave W1. The output of the N-multiplier 11 is amplified by the transmission amplifier 12, and the transmission radio wave W1 is emitted from the transmission antenna 2.

[0017] Returning to the explanation of Fig. 1, the receiving antenna 3 receives a received radio wave W2, which is a radio wave that is a transmission radio wave W1 transmitted by the transmitting unit 101 and reflected by a target object T. The receiving antenna 3 is an array antenna element arranged in a two-dimensional array.

[0018] A receiver 4 is provided for each receiving antenna 3, and has a function of processing the analog signal of the radio wave received by the corresponding receiving antenna 3. The receiver 4 outputs the processed analog signal to an analog-parallel-serial converter 5.

[0019] Fig. 5 is a diagram showing the configuration of the receiver 4 shown in Fig. 1. The receiver 4 receives a constant envelope signal from the oscillator 10 and receives an analog signal of the radio wave received from the receiving antenna 3. The receiver 4 has a receiving amplifier 41, an N multiplier 42, a frequency mixer 44, an LPF (Low Pass Filter) 45, and a sample and hold 46, denoted as "S&H" in the figure.

[0020] An analog signal input from the receiving antenna 3 is amplified by the receiving amplifier 41 and then input to the frequency mixer 44. In addition, the constant envelope signal input from the oscillator 10 is multiplied by N by the N multiplier 42, and the N-multiplied signal is also input to the frequency mixer 44. The frequency mixer 44 mixes and down-converts the signals input from the receiving amplifier 41 and the N multiplier 42, and outputs the result to the LPF 45.

[0021] The LPF 45 is a filter with a variable cutoff bandwidth, and cuts off signals above a set frequency to remove unnecessary high frequencies before outputting the signal to the sample and hold 46. The sample and hold 46 samples and holds the analog signal. The sample and hold process is performed simultaneously in all of the receivers 4. The output of the sample and hold 46 is connected to the analog-parallel-serial conversion unit 5.

[0022] Returning to the explanation of Fig. 1, the analog signals sampled and held in each of the multiple receivers 4 are converted into serial analog signals in the analog parallel-serial conversion unit 5. The serial analog signals are output to the analog-digital converter 7.

[0023] FIG. 6 is a diagram showing the configuration of the analog-parallel-serial conversion unit 5 shown in FIG. 1 . The analog-parallel-serial conversion unit 5 is composed of multiple analog switches 51. By turning on the analog switches 51, the analog-parallel-serial conversion unit 5 can select the signal that the receiving unit 102 outputs to the 3D image generation unit 8, in other words, the signal used for generating a 3D image and detecting an object. Therefore, the array antenna element of the receiving antenna 3 connected to an analog switch 51 that is turned on can also be called the array antenna element used for object detection. Note that only one of the multiple analog switches 51 is turned on at a time, and the analog-parallel-serial conversion unit 5 can perform parallel-serial conversion by sequentially switching the analog switches 51 that are turned on. Furthermore, the analog-parallel-serial conversion unit 5 can change the array antenna element to be used by changing the switching pattern of the analog switches 51, i.e., the parallel-serial conversion pattern. The analog-parallel-serial conversion unit 5 changes the parallel-serial conversion pattern in a time-division manner synchronized with the frequency sweep of the transmission radio wave W1, thereby changing the number of array antenna elements used for object detection for each frequency sweep. Note that the analog-parallel-serial conversion unit 5 does not necessarily need to turn on all of the analog switches 51. By changing the parallel-serial conversion pattern and limiting the number of analog switches 51 that are turned on, the analog-parallel-serial conversion unit 5 can limit the number of array antenna elements used. For example, the larger the frequency sweep width, the fewer array antenna elements the analog-parallel-serial conversion unit 5 can use.

[0024] The analog-to-digital converter 7 converts the serial analog signal output by the analog-parallel-serial conversion unit 5 into a digital signal and outputs the converted digital signal to the 3D image generation unit 8. Thus, by including the analog-to-serial conversion unit 5, the multiple analog signals received by the multiple array antenna elements are converted into serial analog signals by parallel-to-serial conversion, so the receiving unit 102 only needs to include one analog-to-digital converter 7. Furthermore, by using the analog-to-serial conversion unit 5 to limit the number of array antenna elements used, the bandwidth of the analog-to-digital converter 7 can be reduced. When the object see-through device 100 sees a moving target object T, such as a walk-through security gate, the receiving unit 102 must process a large amount of data at high speed, so the analog-to-digital converter 7 must be very fast and expensive. By including the analog-to-serial conversion unit 5 in the receiving unit 102, the number of analog-to-digital converters 7 can be reduced, and the bandwidth of the analog-to-digital converters 7 can be reduced, thereby reducing the overall cost of the object see-through device 100.

[0025] For each frequency sweep, the three-dimensional image generator 8 generates a three-dimensional image from the digital signal output by the receiver 102. The three-dimensional image generator 8 outputs the generated three-dimensional image to the object detector 9.

[0026] The object detection unit 9 detects objects based on the multiple 3D images output from the 3D image generation unit 8. The objects detected by the object detection unit 9 are, for example, objects of a predetermined type, such as a foreign object or a weapon. The object detection unit 9 is configured with a neural network or the like, and can detect the set object using a trained model that has been trained in advance for the object to be detected. When detecting an object using a neural network, the object detection unit 9 inputs multiple 3D images to the trained model, and the trained model outputs a detection result indicating whether the target object T includes a predetermined type of object to be detected, such as a foreign object or a weapon. When a set object is detected, the detection result may include, for example, the type of the detected object.

[0027] As described above, the object see-through apparatus 100 according to the first embodiment includes a transmitting unit 101 that transmits to a target object T a transmission radio wave W1 that has been repeatedly subjected to a frequency sweep in which the frequency is changed from a first frequency to a second frequency over a frequency sweep time; a receiving unit 102 that receives, using an array antenna element, a reception radio wave W2 that is the transmission radio wave W1 reflected by the target object T; a three-dimensional image generating unit 8 that generates a three-dimensional image from the reception signal of the array antenna element for each frequency sweep; and an object detecting unit 9 that detects an object based on a plurality of three-dimensional images, and at least one of the first frequency, the second frequency, the frequency sweep time, and the number of array antenna elements used for object detection is changed in a time-division manner.

[0028] The frequency sweep rate can be changed by changing at least one of the first frequency, the second frequency, and the frequency sweep time. The frequency sweep width can be changed by changing the first frequency or the second frequency. When the first frequency and the second frequency are the same, the shorter the frequency sweep time, the faster the frequency sweep rate. Furthermore, when the frequency sweep time is the same, the larger the frequency sweep width, the faster the frequency sweep rate. Increasing the frequency sweep rate can suppress degradation in the quality of the acquired 3D image, even when the target object T is moving. However, increasing the frequency sweep width and increasing the frequency sweep rate results in a broadband output from the receiver 4. In this case, reducing the number of array antenna elements used to detect an object can reduce the bandwidth of the analog-to-digital converter 7, but reducing the number of array antenna elements used to detect an object reduces the angular resolution. Furthermore, shortening the frequency sweep time to increase the frequency sweep rate reduces the distance resolution. Therefore, by changing at least one of the first frequency, the second frequency, the frequency sweep time, and the number of array antenna elements used to detect the object in a time-division manner, multiple three-dimensional images with different distance resolutions and angular resolutions can be obtained, and by combining these to detect the object, it is possible to suppress a decrease in detection accuracy even when the target object T moves.

[0029] In the first embodiment, the waveforms shown in FIG. 2 and FIG. 3 are shown as examples of the waveform of the transmission radio wave W1. Therefore, when the transmission radio wave W1 having the waveform shown in FIG. 2 is used, the transmitter 101 changes the frequency sweep time in a time-division manner, and the receiver 102 changes the number of array antenna elements used for object detection in a time-division manner. Furthermore, when the transmission radio wave W1 having the waveform shown in FIG. 3 is used, the transmitter 101 changes the first frequency and the second frequency in a time-division manner, and the receiver 102 changes the number of array antenna elements used for object detection in a time-division manner. However, these are merely examples, and the object see-through imaging device 100 may change at least one parameter among the first frequency, the second frequency, the frequency sweep time, and the array antenna elements used for object detection in a time-division manner. Furthermore, in the first embodiment, the above parameters are changed for each frequency sweep. However, the parameters do not need to be changed for each frequency sweep; they may be changed for each frequency sweep, or they may be changed for multiple frequency sweeps.

[0030] Furthermore, in the object see-through system 100, the receiving unit 102 has a plurality of array antenna elements, and performs parallel-to-serial conversion on a plurality of analog signals for each array antenna element, and converts them into digital signals by a single analog-to-digital converter 7. This makes it possible to reduce the number of analog-to-digital converters 7, and thus the cost of the object see-through system 100 can be reduced.

[0031] Furthermore, the object see-through apparatus 100 can limit the number of array antenna elements used for object detection by changing the parallel-to-serial conversion pattern, thereby making it possible to change the angular resolution of object detection.

[0032] Furthermore, the object see-through imaging device 100 can change the number of array antenna elements used by changing the parallel-serial conversion pattern in a time-division manner at a timing synchronized with the frequency sweep, thereby making it possible to change the angular resolution of object detection for each 3D image.

[0033] Furthermore, the object detection unit 9 can detect an object using a neural network.

[0034] Furthermore, the object visualization device 100 can reduce the number of array antenna elements used for object detection as the difference between the first frequency and the second frequency increases. As a result, even when the frequency sweep width is large and the output of the receiver 4 is broadband, the bandwidth of the analog-to-digital converter 7 can be reduced by reducing the number of array antenna elements used for object detection.

[0035] Each unit of the object perspective imaging apparatus 100 can be realized using a processing circuit. The processing circuit may be realized by dedicated hardware, or may be a control circuit using a CPU (Central Processing Unit).

[0036] When the processing circuitry is implemented by dedicated hardware, the processing circuitry may be a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

[0037] When the processing circuit is realized by a control circuit using a CPU, the control circuit includes, for example, a processor and a memory. The processor is a CPU, which is also called an arithmetic unit, a microprocessor, a microcomputer, or a DSP (Digital Signal Processor). The memory may be, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), or an EEPROM (Electrically EPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, or a DVD (Digital Versatile Disk).

[0038] When the processing circuit is realized by a control circuit, the processor reads and executes a program corresponding to the processing of each component stored in memory. The memory is also used as a temporary memory for each process executed by the processor.

[0039] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, and parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0040] 1 transmitter, 2 transmitting antenna, 3 receiving antenna, 4 receiver, 5 analog parallel serial conversion unit, 7 analog digital converter, 8 three-dimensional image generation unit, 9 object detection unit, 10 oscillator, 11, 42 N multiplier, 12 transmitting amplifier, 41 receiving amplifier, 44 frequency mixer, 45 LPF, 46 sample and hold, 51 analog switch, 100 object see-through device, 101 transmitting unit, 102 receiving unit, T target object, W1 transmitted radio wave, W2 received radio wave.

Claims

1. a transmission unit that transmits to a target object a transmission radio wave that has been repeatedly subjected to a frequency sweep in which the frequency is changed from a first frequency to a second frequency over a frequency sweep time; a receiving unit that receives, by using an array antenna element, a received radio wave that is the transmitted radio wave reflected by the target object; a three-dimensional image generating unit that generates a three-dimensional image from the received signals of the array antenna elements for each frequency sweep; an object detection unit that detects the target object based on a plurality of the three-dimensional images; Equipped with changing at least one of the first frequency, the second frequency, the frequency sweep time, and the number of the array antenna elements used for detecting the target object in a time division manner; The receiving unit is A method for converting a plurality of analog signals from each of the array antenna elements into digital signals by a single analog-to-digital converter, comprising: The number of the array antenna elements used for detecting the target object is limited by changing a conversion pattern of the parallel-to-serial conversion. An object visualization device comprising:

2. A transmitting unit that transmits to a target object a transmission radio wave that has been repeatedly subjected to a frequency sweep in which the frequency is changed over a frequency sweep time from a first frequency to a second frequency; a receiving unit that receives, by using an array antenna element, a received radio wave that is the transmitted radio wave reflected by the target object; a three-dimensional image generating unit that generates a three-dimensional image from the received signals of the array antenna elements for each frequency sweep; an object detection unit that detects the target object based on a plurality of the three-dimensional images; Equipped with changing at least one of the first frequency, the second frequency, the frequency sweep time, and the number of the array antenna elements used for detecting the target object in a time division manner; The receiving unit is A method for converting a plurality of analog signals from each of the array antenna elements into digital signals by a single analog-to-digital converter, comprising: The number of the array antenna elements used for detecting the target object is changed for each frequency sweep by changing the conversion pattern of the parallel-serial conversion in a time division manner at a timing synchronized with the frequency sweep. An object visualization device comprising:

3. The object detection unit detects the target object using a neural network.

3. An object viewing apparatus according to claim 1 or 2.

4. The greater the difference between the first frequency and the second frequency, the smaller the number of the array antenna elements used to detect the target object.

3. An object viewing apparatus according to claim 1 or 2.