Patent ID: 12241961

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure are described with reference to the accompanying drawings.

<Basic Configuration>

First, a basic configuration of a transmission system and a reception system of a target object detection device according to this embodiment is described.

FIG.1(a)is a diagram illustrating a configuration of the transmission system according to a reference example.

According to the configuration illustrated inFIG.1(a), a transmission signal S1may be supplied to a wave source R1, and a transmission wave may be transmitted from the wave source R1. A carrier frequency of the transmission signal S1may be a fixed value f0(single frequency). When the wave source R1is moved in a moving direction D1in this state, the frequency is changed based on the Doppler effect in a transmission wave observed at an observation position separate from the wave source R1by a given distance. That is, when the distance between the wave source R1and the observation position is sufficiently large, at an observation position in front of the center position within a movable range (hereinafter, referred to as a “front observation position”), a transmission wave at the frequency f0similar to the transmission signal S1is generated without occurrence of the frequency change based on the Doppler effect. On the other hand, at an observation position displaced to a direction opposite from the moving direction with respect to the front observation position (hereinafter, referred to as an “upper observation position”), since the wave source R1is moved in a direction away from the upper observation position, a transmission wave at a frequency f0−fd which is lowered from the frequency of the transmission signal S1is generated due to the Doppler effect. “−fd” is an amount of change in the frequency from the frequency f0of the transmission signal S1due to the Doppler effect. Further, at an observation position displaced to a direction same as the moving direction with respect to the front observation position (hereinafter, referred to as a “lower observation position”), since the wave source R1is moved to approach the lower observation position, a transmission wave at a frequency f0+fd which is increased from the frequency of the transmission signal S1is generated due to the Doppler effect. “+fd” is an amount of change in the frequency from the frequency f0of the transmission signal S1due to the Doppler effect.

Such a change in frequency increases as an amount of displacement of each of the upper observation position and the lower observation position with respect to the front observation position becomes larger. That is, according to the displacement angle with respect to the front observation position in a depression-angle direction (the same direction as the moving direction D1) and an elevation-angle direction (the opposite direction from the moving direction D1), the frequency of the transmission wave changes in a positive or negative direction from the frequency f0. Therefore, when a reflection wave of the transmission wave is received by a reception element, magnitude of the depression angle and the elevation angle can be calculated based on a frequency component of a reception signal which is outputted from the reception element. In other words, by extracting a given frequency component from the reception signal, a reception signal at a given angular position in the depression-angle direction and the elevation-angle direction can be acquired. In this embodiment, based on this principle, the reception signal at each angular position in the depression-angle direction and the elevation-angle direction may be acquired.

FIG.1(b)is a diagram illustrating a configuration example for moving the wave source R1.

In this configuration example, a transmission array10in which a plurality of transmission elements10aare lined-up in a row may be used. Although inFIG.1(b)eight transmission elements10aare included in the transmission array10for convenience, the number of transmission elements is not limited to this. InFIG.1(b), the transmission elements10aare numbered in an order from above for convenience.

In this configuration example, connection of an input terminal for the transmission signal S1to each transmission element10amay be switched by a signal switching part20(which may also be referred to as a first switch). The signal switching part20is comprised of, for example, a demultiplexer. Here, the transmission element10awhich is a supply destination of the transmission signal S1may be switched sequentially from above to the next transmission element10a. Therefore, the wave source of the transmission wave may be moved in the direction D1. Also according to this configuration example, similarly to the case illustrated inFIG.1(a), the frequency may be changed by the Doppler effect at each observation position.

However, according to this configuration example, continuity of the transmission waves at the upper observation position and the lower observation position may be interrupted due to the switching of the transmission element10awhich transmits the waves. Waveforms illustrated on the right side inFIG.1(b)illustrate waveforms of the transmission waves at three observation positions. These three observation positions may be the same as the three observation positions (the upper observation position, the front observation position, and the lower observation position) illustrated inFIG.1(a). TD1, TD2, and TD3indicate the transmission waves transmitted by the transmission element10aat the top, the transmission element10aat the second from the top, and the transmission element10aat the third from the top, respectively.

As illustrated inFIG.1(b), since the transmission waves at the front observation position are not affected by the Doppler effect, similarly to the case illustrated inFIG.1(a), the continuity of the transmission waves TD1-TD3is ensured. On the other hand, at the upper observation position, since a phase delay occurs in the transmission waves TD1-TD3, the transmission waves TD1-TD3separate from each other and become discrete. Further, at the lower observation position, since a phase advance is caused in the transmission waves TD1-TD3by the Doppler effect, the transmission waves TD1-TD3approach to each other and become discrete.

As described above, although in this configuration example, similarly to the case illustrated inFIG.1(a), the frequency of the waveform itself is changed at each observation position as the observation position separates from the front observation position in the depression-angle direction or the elevation-angle direction, the phenomenon that the transmission waves transmitted from the respective transmission elements10abecome discrete occurs. As a result, according to this configuration example, unnecessary frequency components may be generated in the transmission waves due to the discrete transmission waves.

FIGS.2(a) to2(c)are charts each illustrating a simulation result in which a resultant waveform of the transmission waves at each of the three observation positions is simulated.

In this simulation, the separated distance of the front observation position from the transmission array10is set to a far field. Further, the upper observation position is set to a position displaced by 30° upward with respect to the front observation position, and the lower observation position is set to a position displaced by 30° downward with respect to the front observation position.FIG.2(b)is the waveform of the transmission waves at the front observation position, andFIGS.2(a) and2(c)are the waveforms of the transmission waves at the upper observation position and the lower observation position, respectively. In each graph, a horizontal axis indicates a data number, and a vertical axis indicates amplitude of the transmission waves. Here, transmission signals of several cycles are supplied to each transmission element10a, and the transmission waves are transmitted. Here, the frequency f0of the transmission signal is set to 150 kHz.

As illustrated inFIG.2(b), at the front observation position, the continuity of the transmission waves TD1, TD2, and TD3is ensured. On the other hand, at the upper observation position, as illustrated inFIG.2(a), since the waveforms of the TD1, TD2, and TD3are separated from each other, flat waveform parts are formed therebetween. Further, at the lower observation position, as illustrated inFIG.2(c), since the waveforms of the TD1, TD2, and TD3overlap with each other, waveform parts with steep amplitude are formed therebetween.

FIGS.3(a) to3(c)are charts illustrating a simulation result in which frequency spectra of the resultant waveforms illustrated inFIGS.2(a) to2(c)at the three observation positions are simulated, respectively.FIG.3(b)illustrates the frequency spectrum of the resultant waveform at the front observation position, andFIGS.3(a) and3(c)illustrate the frequency spectra of the resultant waveforms at the upper observation position and the lower observation position, respectively.

As illustrated inFIG.3(b), in the resultant waveform at the front observation position, the amplitude shows a large peak at near 150 kHz which is the frequency f0of the transmission signal. However, in the frequency spectrum illustrated inFIG.3(b), amplitude appears also in a wide range, other than the normal frequency point at near 150 kHz.

In addition, referring to the frequency spectrum at the upper observation position illustrated inFIG.3(a), the peak appears near a frequency at 145 kHz which is lowered from the frequency f0of the transmission signal due to the Doppler effect, and amplitude appears also in a wide range other than this frequency. Similarly, referring to the frequency spectrum at the lower observation position illustrated inFIG.3(c), the peak appears near a frequency at 155 kHz which is increased from the frequency f0of the transmission signal due to the Doppler effect, and amplitude appears also in a wide range other than this frequency.

As described above, according to the configuration example described above, at each observation position, the amplitude may appear in a wide frequency range other than the frequency caused by the Doppler effect. Such unnecessary frequency components become noise when measuring an original reflection wave for each observation position, and thus, are preferably removed as much as possible.

FIG.4is a diagram illustrating a configuration example for removing unnecessary frequency component.

In this configuration example, a first transmission array11in which a plurality of first transmission elements11aare lined-up in a row, and a second transmission array12in which a plurality of second transmission elements12aare lined-up in a row, may be used. InFIG.4, although each of the first transmission array11and the second transmission array12includes four transmission elements for convenience, the number of transmission elements is not limited to this. Moreover, inFIG.4, the first transmission elements11aand the second transmission elements12aare numbered in an order from above for convenience. The second transmission elements12aare hatched for distinction.

In this configuration example, a second transmission element12amay be disposed between adjacent first transmission elements11a. The plurality of first transmission elements11aand the plurality of second transmission elements12amay be aligned on the same straight line.

Connection of an input terminal for a first transmission signal S11to the first transmission element11amay be switched by a first signal switching part21(which may also be referred to as a first switch). Further, connection of an input terminal for a second transmission signal S12to the second transmission element12amay be switched by a second signal switching part22(which may also be referred to as a second switch). The first signal switching part21and the second signal switching part22are comprised of, for example, demultiplexers. Here, the first transmission element11awhich is a supply destination of the first transmission signal S11may be switched sequentially from above to the next first transmission element11a. In addition, the second transmission element12awhich is a supply destination of the second transmission signal S12may be switched sequentially from above to the next second transmission element12a.

After the first transmission signal S11is supplied to one first transmission element11a, the second transmission signal S12may be supplied to the second transmission element12anext to the one first transmission element11aat a timing when half a supplying period of the first transmission signal S11lapsed. That is, the supply timing of the first transmission signal S11and the supply timing of the second transmission signal S12may be deviated from each other by half the length of the first transmission signal S11or the second transmission signal S12. In this manner, the wave source of the transmission waves may be moved in the direction D1. As a result, also according to this configuration example, similarly to the case illustrated inFIG.1(a), the frequency may be changed based on the Doppler effect at each observation position.

In this configuration example, a carrier frequency of the first transmission signal S11and a carrier frequency of the second transmission signal S12may be set to a fixed and identical value f0. However, in this configuration example, the first transmission signal S11and the second transmission signal S12may be modulated in a given modulation method. In detail, amplitudes of the first transmission signal S11and the second transmission signal S12may be modulated so as to avoid generation of unnecessary frequency components in the resultant waveform at each observation position. As a method of the amplitude modulation, a method based on a triangular window function, or a method based on a Hanning window function may be used.

Waveforms on the right side illustrated inFIG.4illustrate waveforms of the transmission waves at the three observation positions. The three observation positions are the same as the three observation positions (the upper observation position, the front observation position, and the lower observation position) illustrated inFIG.1(b). TD11and TD12indicate the transmission waves transmitted by the first transmission elements11aof the first transmission array11at the top and the second from above, respectively. Further, TD21and TD22indicate the transmission waves transmitted by the second transmission elements12aof the second transmission array12at the top and the second from above, respectively.

In this configuration example, similarly to the case illustrated inFIG.1(b), the transmission waves TD11and TD12at the upper observation position are separated from each other. However, since the transmission wave TD21exists at this separated part, the flat part does not appear at the concerned part in the resultant waveform where the transmission waves are synthesized. Therefore, the generation of unnecessary frequency components based on the flat part is suppressed.

Moreover, in this configuration example, similarly to the case illustrated inFIG.1(b), the transmission waves TD11and TD12at the lower observation position partially overlap with each other. However, since the transmission wave TD21exists at this overlapping part, the steep amplitude part does not appear at the concerned part in the resultant waveform where the transmission waves are combined. Therefore, the generation of unnecessary frequency components based on the steep amplitude part is suppressed.

FIG.5(a)is a chart illustrating a simulation result in which states of the transmission waves TD11, TD12, and TD21at the upper observation position are simulated. Further,FIG.5(b)is a chart illustrating a simulation result in which the resultant waveform synthesizing the transmission waves TD11, TD12, and TD21illustrated inFIG.5(a)is simulated.

The vertical axis and the horizontal axis inFIGS.5(a) and5(b)are similar to the vertical axis and the horizontal axis inFIG.2(a), respectively. The upper observation position is set similarly to the case illustrated inFIG.2(a). InFIG.5(a), the transmission waves TD11and TD12are illustrated by solid lines, and the transmission wave TD21is illustrated by a broken line.

In this simulation, the first transmission signal S11is modulated so that the amplitude becomes the largest at the middle of the supplying period to each first transmission element11a, and gradually approaches zero at a start timing and an end timing of the supplying period. The second transmission signal S12is modulated similarly. The frequencies of the first transmission signal S11and the second transmission signal S12are set to be identical. The length of the supplying period of the first transmission signal S11to the first transmission element11aand the length of the supplying period of the second transmission signal S12to the second transmission element12aare identical with each other.

As illustrated inFIG.5(b), although the amplitude slightly changes in the resultant waveform at the upper observation position, there is no flat part in the resultant waveform as shown in the graph inFIG.2(a), and the continuity of the resultant waveform is ensured.

FIG.6(a)is a chart illustrating a simulation result in which states of the transmission waves TD11, TD12, and TD21at the front observation position are simulated. Further,FIG.6(b)is a chart illustrating a simulation result in which the resultant waveform synthesizing the transmission waves TD11, TD12, and TD21illustrated inFIG.6(a)is simulated.

The vertical axis and the horizontal axis inFIGS.6(a) and6(b)are similar to the vertical axis and the horizontal axis inFIGS.5(a) and5(b), respectively. The front observation position is set similarly to the case illustrated inFIG.2(b). InFIG.6(a), the transmission waves TD11and TD12are illustrated by solid lines, and the transmission wave TD21is illustrated by a broken line. Also in this simulation, the first transmission signal S11and the second transmission signal S12similar to the simulation illustrated inFIGS.5(a) and5(b)are used.

As illustrated inFIG.6(b), in the resultant waveform at the front observation position, the amplitude is maintained to be substantially fixed similarly to the case illustrated inFIG.2(b), and the continuity of the resultant waveform is ensured.

FIG.7(a)is a chart illustrating a simulation result in which states of the transmission waves TD11, TD12, and TD21at the lower observation position are simulated. Further,FIG.7(b)is a chart illustrating a simulation result in which the resultant waveform synthesizing the transmission waves TD11, TD12, and TD21illustrated inFIG.7(a)is simulated.

The vertical axis and the horizontal axis inFIGS.7(a) and7(b)are similar to the vertical axis and the horizontal axis inFIGS.5(a) and5(b), respectively. The lower observation position is set similarly to the case illustrated inFIG.2(c). InFIG.7(a), the transmission waves TD11and TD12are illustrated by solid lines, and the transmission wave TD21is illustrated by a broken line. Also in this simulation, the first transmission signal S11and the second transmission signal S12similar to the simulation illustrated inFIGS.5(a) and5(b)are used.

As illustrated inFIG.7(b), although the amplitude slightly changes in the resultant waveform at the lower observation position, there is no steep amplitude part in the resultant waveform as shown in the graph inFIG.2(c), and the continuity of the resultant waveform is ensured.

FIGS.8(a) to8(c)are charts illustrating a simulation result in which frequency spectra of the resultant waveforms illustrated inFIG.5(b),FIG.6(b), andFIG.7(b)are simulated, respectively.

As illustrated inFIG.8(a), similarly to the frequency spectrum illustrated inFIG.3(a), the frequency spectrum of the resultant waveform at the upper observation position has a large peak near 145 kHz which is the frequency shifted based on the Doppler effect. Moreover, compared to the frequency spectrum illustrated inFIG.3(a), unnecessary peaks are removed in the frequency spectrum illustrated inFIG.8(a), and the frequency range where the amplitude appears is limited to a significantly narrow range centering around 150 kHz.

As illustrated inFIG.8(b), similarly to the frequency spectrum illustrated inFIG.3(b), the frequency spectrum of the resultant waveform at the front observation position has a large peak near 150 kHz which is similar to the frequency of the first transmission signal S11and the second transmission signal S12. Moreover, compared to the frequency spectrum illustrated inFIG.3(b), in the frequency spectrum illustrated inFIG.8(b), the frequency range where the amplitude appears is limited to a significantly narrow range centering around 150 kHz.

As illustrated inFIG.8(c), similarly to the frequency spectrum illustrated inFIG.3(c), the frequency spectrum of the resultant waveform at the lower observation position has a large peak near 155 kHz which is the frequency shifted based on the Doppler effect. Moreover, compared to the frequency spectrum illustrated inFIG.3(c), unnecessary peaks are removed in the frequency spectrum illustrated inFIG.8(c), and the frequency range where the amplitude appears is limited to a significantly narrow range centering around 150 kHz.

As described above, by using the configuration illustrated inFIG.4, unnecessary frequency component of the transmission waves, which may be noise at each observation position, may effectively be removed. As a result, the reflection waves can be measured accurately.

Meanwhile, the change in frequency based on the Doppler effect as illustrated inFIG.1(b)andFIG.4occurs not only at the front observation position, the upper observation position, and the lower observation position described above, but also at other observation positions within a range where the transmission waves are transmitted. However, since a positional relation of each observation position with respect to the wave source varies, the way of occurrence of the Doppler effect varies at every observation position. That is, observation positions in a plane having a given elevation or depression angle with respect to the front direction have mutually different heights from a horizontal plane including the front direction. Therefore, when the wave source is moved, the observation positions approach or separate to/from the wave source at speeds different from each other. As a result, a plane in which the frequency of the transmission waves becomes equal is not the flat plane having the given elevation or depression angle with respect to the front direction, but a curved surface formed by curving the flat plane in a circumferential direction.

FIG.9is a diagram illustrating a simulation result in which a surface where the frequency becomes equal (hereinafter, referred to as an “equal-frequency surface”) is simulated.

InFIG.9, the unit of each axis is “meter.” The transmission array is disposed at the middle position in a Y-axis direction (a position where the distance becomes zero) to extend in an X-axis direction. The transmission waves are transmitted in a Z-axis direction from the center position in Y-axis direction. That is, a direction from the center position in the Y-axis direction to the Z-axis direction is the front direction.

InFIG.9, equal-frequency surfaces EP1-EP5within an upper range with respect to the front direction are illustrated. The equal-frequency surfaces EP1, EP2, EP3, EP4, and EP5are frequency surfaces at f0−fd1, f0−fd2, f0−fd3, f0−fd4, and f0−fd5, respectively. “f0” is the frequency in the front direction and equal to the frequency of the transmission signal supplied to the transmission element. A relationship between fd1to fd5is fd1<fd2<fd3<fd4<fd5.

Although inFIG.9five equal-frequency surfaces EP1to EP5are illustrated for convenience, many equal-frequency surfaces exist between the equal-frequency surfaces EP1to EP5. For example, frequencies between the equal-frequency surfaces EP1and EP2continuously transit from f0−fd1to f0−fd2. By inversing the equal-frequency surfaces EP1to EP5symmetrically with respect to a Y-Z plane, equal-frequency surfaces within a lower range with respect to the front direction are formed.

FIG.10is a diagram schematically illustrating a configuration example of the transmission system and a reception system.

In this configuration, other than the configuration of the transmission system illustrated inFIG.4, a reception array31having a plurality of reception elements31amay be provided as a reception system. Similarly toFIG.4, the configuration of the transmission system may include the first transmission array11and the second transmission array12which are disposed along an X-axis. The reception array31may be disposed immediately above the first transmission array11. In this configuration example, a direction in which the reception elements31aare aligned may be perpendicular to the direction in which the first transmission elements11aand the second transmission elements12aare aligned.

By actuating the first transmission elements11aof the first transmission array11and the second transmission elements12aof the second transmission array12in the method described with reference toFIG.4, a transmission beam TB1may be formed forward (Z-axis direction) of the first transmission array11and the second transmission array12.

That is, when the first transmission signal S11is supplied to the first transmission element11a, the transmission waves may be transmitted from the first transmission element11ahaving a comparatively wide directivity. Similarly, when the second transmission signal S12is supplied to the second transmission element12a, the transmission waves may be transmitted from the second transmission element12ahaving a comparatively wide directivity. When the first transmission signal S11and the second transmission signal S12for one scanning are supplied to the first transmission elements11aof the first transmission array11and the second transmission elements12aof the second transmission array12sequentially from above, a range where all the transmission waves transmitted from the respective transmission elements are stacked on top of each other may be a formation range of the transmission beam TB1. In this formation range, many equal-frequency surfaces may be formed as described above with reference toFIG.9.

By performing a phase control (beamforming) to a reception signal outputted from each reception element31a, a reception beam RB1with a narrow width may be formed in the circumferential direction centering on the X-axis. Accordingly, a reception signal within a range where the reception beam RB1and the transmission beam TB1intersect with each other may be extracted. By the reception beam RB1being rotated in a θ1-direction centering on the X-axis by the phase control, the reception signal at each rotating position may be extracted. The rotating position of the reception beam RB1may define an incoming direction, in the horizontal direction, of the reflection wave which is a reflection of the transmission wave from a target object. Moreover, depending on the frequency of the reception signal, the equal-frequency surface (seeFIG.9) at which the reflection wave is generated may be defined.

Therefore, by extracting the reception signal at a frequency corresponding to each equal-frequency surface from the reception signal extracted by the reception beam RB1, and plotting on each equal-frequency surface an intensity of the extracted reception signal, a distribution of intensity data of the reception signal in the range where the reception beam RB1and the transmission beam TB1intersect with each other may be obtained. Then, when the reception beam RB1is rotated in the horizontal direction within a detection range, by obtaining the distribution of the intensity data at each rotating position, intensity data (volume data) distributed three dimensionally in the entire detection range in the horizontal direction and the vertical direction can be acquired. By turning the intensity data (volume data) into an image, an image indicative of a state of the target object in the detection range can be obtained.

<Concrete Configuration>

FIG.11is a block diagram illustrating a concrete configuration of a target object detection device1.

The target object detection device1may include the first transmission array11and the second transmission array12as the transmission system. The configuration of the first transmission array11and the second transmission array12may be similar toFIG.10. The target object detection device1may be provided with a first transmission signal generating module111(which may also be referred to as a first transmission signal generator), a first transmission amplifier112, and a first signal switching part113(which may also be referred to as a first switch) as a configuration to supply the first transmission signal S11to each first transmission element11aof the first transmission array11. The target object detection device1may further be provided with a second transmission signal generating module121(which may also be referred to as a second transmission signal generator), a second transmission amplifier122, and a second signal switching part123(which may also be referred to as a second switch) as a configuration to supply the second transmission signal S12to each second transmission element12aof the second transmission array12.

The first transmission signal generating module111may generate the first transmission signal S11according to control from a control part101(which may also be referred to as a controller). The first transmission signal S11may have a waveform with a fixed frequency and a modulated amplitude. The first transmission signal S11may be set to have a waveform similarly to the transmission wave TD11illustrated inFIG.6(a). The first transmission amplifier112may amplify the first transmission signal S11inputted from the first transmission signal generating module111according to the control from the control part101. The first signal switching part113may supply the first transmission signal S11sequentially to the plurality of first transmission elements11aincluded in the first transmission array11according to the control from the control part101. The first signal switching part113may have a similar structure to the first signal switching part21illustrated inFIG.4. The first signal switching part113is comprised of, for example, a demultiplexer.

The second transmission signal generating module121may generate the second transmission signal S12according to the control from the control part101. The second transmission signal S12may have a waveform with a fixed frequency and a modulated amplitude. The second transmission signal S12may be set to have a waveform similarly to the transmission wave TD21illustrated inFIG.6(a). The second transmission signal S12may be a signal similar to the first transmission signal S11. The second transmission amplifier122may amplify the second transmission signal S12inputted from the second transmission signal generating module121according to the control from the control part101. The second signal switching part123may supply the second transmission signal S12sequentially to the plurality of second transmission elements12aincluded in the second transmission array12according to the control from the control part101. The second signal switching part123may have a similar structure to the second signal switching part22illustrated inFIG.4. The second signal switching part123is comprised of, for example, a demultiplexer.

The control part101may be provided with an arithmetic processing circuit such as a CPU (Central Processing Unit), and a storage medium such as a ROM (Read Only Memory), a RAM (Random Access Memory), and/or a hard disk. The control part101may be comprised of an integrated circuit, such as an FPGA (Field-Programmable Gate Array). The control part101may control the first signal switching part113and the second signal switching part123so that the supplying period of the second transmission signal S12to the second transmission element12aadjacent to the first transmission element11ais delayed by half the supplying period of the first transmission signal S11to the first transmission element11a. According to this, the transmission waves as illustrated inFIGS.5(b),6(b), and7(b)may be transmitted, and the equal-frequency surfaces (seeFIG.9) may be formed in the transmission beam TB1.

The target object detection device1may be provided with the reception array31as the reception system. A structure of the reception array31may be similar structure toFIG.10. “m” reception elements31amay be arrayed in the reception array31. The reception signal may be outputted from the reception elements31ato channels CH1to CHm corresponding to the reception elements31a.

As a configuration to process the reception signal outputted from the reception elements31aof the reception array31to generate a detection image, the target object detection device1may be provided with a plurality of reception processing modules131, a plurality of AD converters132, a reception signal processing module133(which may also be referred to as processing circuitry), and an image signal processing module134.

The plurality of reception processing modules131may be connected to the channels CH1to CHm, respectively. Each reception processing module131may process the inputted reception signal, for example, to remove an unnecessary band, to amplify the reception signal to a level suitable for AD conversion, and to remove signal components within a band at half a sampling cycle of the AD conversion or higher. The plurality of AD converters132may be provided so as to correspond to the plurality of reception processing modules131. Each AD converter132may convert the analog reception signal inputted from the corresponding reception processing module131to a digital signal at a given sampling cycle.

The reception signal processing module133may process the reception signal of the channels CH1to CHm inputted from the plurality of AD converters132, respectively, to calculate the intensity data (volume data) of the reception signal distributed three-dimensionally in the detection range. The reception signal processing module133may be comprised of a single integrated circuit (e.g., an FPGA) together with the control part101.

The image signal processing module134may process the intensity data (volume data) inputted from the reception signal processing module133so as to generate image data for creating the image of the state of the target object in the detection range. The image signal processing module134is comprised of, for example, a CPU. A display part135is comprised of a monitor etc., and may display the detection image corresponding to the image data inputted from the image signal processing module134.

FIG.12(a)is a functional block diagram of a configuration example of the reception signal processing module133.

The reception signal processing module133may be provided with an arithmetic processing circuit and a storage medium. The reception signal processing module133may implement functions of the respective functional blocks illustrated inFIG.12(a)by executing a program stored in the storage medium. A part of the functions illustrated inFIG.12(a)may be implemented by hardware instead of software.

The reception signal processing module133may be provided with a plurality of digital filters201, a buffer202, a plurality of bandpass filters203, and a plurality of beam synthesizing modules204.

The plurality of digital filters201may be provided so as to correspond to the plurality of AD converters132illustrated inFIG.11. Each digital filter201may be a filter having a filtering function sharper than that of the reception processing module131illustrated inFIG.11, and may remove a signal in an unnecessary band from the reception signal.

The buffer202may temporarily store the reception signal of the channels CH1to CHm outputted from the plurality of digital filters201. The buffer202may store the reception signal (hereinafter, referred to as “one-scanning reception signal”) from a start of the actuation of the plurality of first transmission elements11aof the first transmission array11and the plurality of the second transmission elements12aof the second transmission array12from the top to the bottom (this actuation is referred to as “scanning”), until the reflection wave from the maximum distance within the detection range is received by the reception array31, for a plurality of scannings in a chronological order. The buffer202may sequentially supply the one-scanning reception signal to each of the plurality of bandpass filters203. When the buffer202supplies the one-scanning reception signal to the plurality of bandpass filters203, the buffer202may delete the one-scanning reception signal.

The plurality of bandpass filters203may extract, from the inputted one-scanning reception signal of the channels CH1to CHm, the frequency components (equal-frequency reception signals) at frequencies F1to Fn, respectively. The frequencies F1to Fn of the bandpass filters203may define the equal-frequency surfaces illustrated inFIG.9, respectively. That is, the equal-frequency surfaces can be defined by the number of the bandpass filters203. As the number of the bandpass filters203increases, a resolution of the reception signal in a stacking direction of the equal-frequency surfaces may be increased. Each bandpass filter203may extract a frequency component (equal-frequency reception signal) at a frequency Fk set to itself from the one-scanning reception signal of the channels CH1to CHm, and supply it to the beam synthesizing module204.

The plurality of beam synthesizing modules204may be provided so as to correspond to the plurality of bandpass filters203. The beam synthesizing module204may form the reception beam RB1by beamforming based on a phase control or a delay control, and isolate the equal-frequency reception signal at a given resolution in the θ1-direction illustrated inFIG.10. Accordingly, the equal-frequency reception signal within a range where the reception beam RB1intersects with the equal-frequency surface defined by the bandpass filter203may be acquired. That is, the beam synthesizing module204at the top may acquire the equal-frequency reception signal within the range (intersection range) in which the equal-frequency surface corresponding to the frequency F1intersects with the reception beam RB1in each azimuth in the direction parallel with the horizontal plane (θ1-direction inFIG.10).

An intensity of the acquired equal-frequency reception signal may vary on a time axis according to the intensity of the refection wave from the intersection range. The time axis may correspond to a distance from the reception array31within the intersection range. Therefore, by mapping each intensity on the time axis at a position corresponding to the distance from the reception array31within the intersection range, the distribution of the intensity data in the intersection range can be obtained. In this manner, by integrating the distribution of the intensity data for the respective azimuths outputted from the beam synthesizing modules204, the volume data in which the intensity data is distributed three-dimensionally in the detection range can be acquired.

FIG.12(b)is a functional block diagram of another configuration example of the reception signal processing module133.

In this configuration example, the bandpass filters203may be substituted by an FFT (Fast Fourier Transform)211and a frequency extracting module212. The FFT211may calculate frequency spectra based on the one-scanning reception signal of the channels CH1to CHm. The frequency extracting module212may extract frequency components (equal-frequency reception signals) at the frequencies F1to Fn from the frequency spectrum of each channel calculated by the FFT211, and supply the extracted frequency components to the corresponding beam synthesizing modules204. The processing of the beam synthesizing modules204is similar to the case illustrated inFIG.12(a).

Also according to this configuration, similarly to the configuration illustrated inFIG.12(a), by integrating the distribution of the intensity data for the respective azimuths outputted from the beam synthesizing modules204, the volume data in which the intensity data is distributed three-dimensionally in the detection range can be acquired. Note that, according to the configuration example illustrated inFIG.12(b), the frequency at which the equal-frequency reception signal is extracted can be set more finely compared to the configuration example illustrated inFIG.12(a). Therefore, the number of equal-frequency surfaces to be processed can be increased, and the resolution of the equal-frequency reception signal in the stacking direction of the equal-frequency surfaces can be increased.

FIGS.13(a) and13(b)are flowcharts each illustrating a wave transmission processing executed by the control part101illustrated inFIG.11. This processing may be executed continuously during detecting operation, and finished in response to the end of the detection operation.

Referring toFIG.13(a), the control part101may cause the first transmission signal generating module111to generate the first transmission signal S11(S111). Then, at a given switching timing (S112: YES), the control part101may switch the first transmission element11ato which the first transmission signal S11is to be supplied, to the adjacent first transmission element11a(S113). Here, the switching timing may be a timing when one unit of the first transmission signal S11with the modulated amplitude (the first transmission signal S11corresponding to the transmission wave TD11illustrated inFIG.6(a)) comes to an end. Then, the control part101may return the processing to Step S112, and wait for the arrival of the next switching timing. Accordingly, the first transmission element11ato which the first transmission signal S11is to be supplied, can be switched to the adjacent first transmission element11aat the start timing of one unit of the first transmission signal S11.

Referring toFIG.13(b), the control part101may cause the second transmission signal generating module121to generate the second transmission signal S12at a timing delayed from the generation start timing of the first transmission signal S11by half the period of one unit of the first transmission signal (S121). As described above, the second transmission signal S12may have the same frequency and amplitude modulation as the first transmission signal S11. Then, at a given switching timing (S122: YES), the control part101may switch the second transmission element12ato which the second transmission signal S12is to be supplied, to the adjacent second transmission element12a(S123). Here, the switching timing may be a timing at a middle position of one unit of the first transmission signal S11which is being supplied to the first transmission element11aimmediately above the second transmission element12awhich is the current supply destination. Then, the control part101may return the processing to Step S122, and wait for the next switching timing. Therefore, the second transmission element12ato which the second transmission signal S12is to be supplied, can be switched to the adjacent second transmission element12aat a timing delayed from the first transmission signal S11by half the period for one unit of the first transmission signal S11.

According to the processing illustrated inFIGS.13(a) and13(b), the first transmission elements11aand the second transmission elements12ato which the first transmission signal S11and the second transmission signal S12are supplied, may be sequentially switched from above. When the supply destinations are switched to the bottom first transmission element11aand the bottom second transmission element12a, and one scanning is finished, the control part101may again return the supply destinations to the top first transmission element11aand the top second transmission element12a, and execute the next scanning by similar processing. In each scanning, the wave transmission may be performed as described with reference toFIG.4. In this manner, the transmission beam TB1in which the equal-frequency surfaces are stacked as described above may be formed.

FIG.13(c)is a flowchart illustrating processing of displaying the detection image by processing the reception signal. This processing may be continuously executed during the detection operation, and finished in response to the end of the detection operation.

The one-scanning reception signal may be supplied to the plurality of bandpass filters203from the buffer202(S201). Each bandpass filter203may extract frequency components (equal-frequency reception signal) at the frequency set to itself from the inputted reception signal of the respective channels, and supply the extracted frequency components to the corresponding beam synthesizing module204(S202). The beam synthesizing module204may extract, from the inputted frequency components (equal-frequency reception signal), the signal component of each azimuth in the horizontal direction (θ1-direction) by beamforming (S203). Therefore, the distribution of the intensity data in which the intensity data of the reception signal is mapped on the equal-frequency surface defined by each frequency, can be obtained. The reception signal processing module133may integrate the intensity data from all the beam synthesizing modules204so as to constitute the volume data where the intensity data is distributed three-dimensionally in the detection range (S204). The reception signal processing module133may supply the volume data to the image signal processing module134.

The image signal processing module134may process the volume data to generate the image data for displaying the detected state of the target object in the detection range, and supply the generated image data to the display part135(S205). The display part135may display the image based on the inputted image data (S206). Therefore, the detected state of the target object in the detection range may be displayed.

FIG.14is a diagram schematically illustrating a configuration when the target object detection device1described above is used as a sonar which detects an underwater target object.

A transducer300may be installed in a bottom of a ship2. The transducer300may be provided with the first transmission array11, the second transmission array12, and the reception array31. The first transmission array11and the second transmission array12may transmit transmission waves underwater through the processing described above. Here, sound waves (e.g., ultrasonic waves) may be transmitted as the transmission waves. Accordingly, the transmission beam TB1may be formed within a range of an angle θ2 in parallel with a vertical plane such that the equal-frequency surfaces are stacked in the angular direction.

Among the configuration illustrated inFIG.11, the configuration other than the first transmission array11, the second transmission array12, the reception array31, and the display part135may be equipped in a control device installed in a wheelhouse2aof the ship2. The display part135may be installed in the wheelhouse2aseparately from the control device. The display part135may be integrated with the control device.

According to this configuration, a detection image indicative of states of a bottom of water3and a school of fish4may be displayed on the display part135, and thus, a user can grasp the underwater state. Note that four transducers300oriented forward, rearward, leftward, and rightward, respectively, may be installed in the ship bottom. In this case, the configuration of the transmission system and the reception system illustrated inFIG.11may be provided to each transducer300. As a result, the detection image of the entire circumference of the ship can be displayed on the display part135.

Further, when the target object detection device1is used as a radar which detects a target object in the air, for example, a transducer400is installed in a side wall of the wheelhouse2a. The transducer400may be comprised of the first transmission array11, the second transmission array12, and the reception array31. The first transmission array11and the second transmission array12may transmit transmission waves in the air through the processing described above. Here, radio waves may be transmitted as the transmission waves. A configuration of a circuit part may be installed in the wheelhouse2a, similarly to the case of the sonar.

According to this configuration, a detection image indicative of states of an obstacle and a flock of birds may be displayed on the display part135, and thus, a user can grasp the midair state. Note that the transducers400may be installed in front, rear, left, and right side walls of the wheelhouse2a, respectively. In this case, the configuration of the transmission system and the reception system illustrated inFIG.11may be provided to each transducer400. As a result, the detection image of the entire circumferential space of the ship can be displayed on the display part135.

Effects of Embodiment

According to this embodiment, the following effects can be obtained.

Since the first transmission element11ato which the first transmission signal S11is supplied is switched from the first element to the second element in the first transmission array11, the wave source of the transmission waves may be moved in the lined-up direction of the first transmission elements11a. Therefore, the frequency of the transmission beam TB1may change in the moving direction of the wave source due to the Doppler effect, and the plurality of equal-frequency surfaces may be formed in the transmission beam TB1. As a result, by extracting the frequency component corresponding to each equal-frequency surface from the reception signal from the reception element31a, the reception signal (equal-frequency reception signal) based on the reflection wave from each equal-frequency surface can be obtained. As described above, according to this embodiment, by the switching of the first transmission elements11ato which first transmission signal S11is supplied in the first transmission array11, the equal-frequency reception signals for all of the to-be-observed equal-frequency surfaces can be generated simultaneously. Thus, the target object can be promptly detected with the simple configuration.

Further, in this embodiment, since the first transmission signal S11is supplied sequentially to the adjacent first transmission element11a, the wave source of the transmission waves can be finely moved in the lined-up direction of the first transmission elements11a. Therefore, the frequency change caused by the Doppler effect can be smooth.

Further, in the configuration example illustrated inFIGS.4and10, the second transmission array12having the plurality of second transmission elements12amay be provided, and the second transmission signal S12may be sequentially supplied to the plurality of second transmission elements12a. Therefore, by adjusting the first transmission signal S11and the second transmission signal S12, unnecessary frequency components superimposed in the transmission waves can be suppressed. As a result, the processing based on the reception signal can be performed more accurately.

Further, since the second transmission element12ais located adjacent to the first transmission element11a, while the wave source of the transmission wave, which is based on the first transmission signal S11, is moved from the first element to the second element in the first transmission array11, the second transmission element12ain the second transmission array12may transmit the transmission wave, which is based on the second transmission signal S12, at the position between the first element and the second element in the first transmission array11. As a result, it becomes easier to maintain the continuity of the transmission waves, and thus, the superimposition of unnecessary frequency components in the transmission waves can be suppressed.

Further, in this configuration, by modulating the amplitude of the first transmission signal S11and the second transmission signal S12, for example, to be like the waveforms illustrated inFIG.5(a), the superimposition of unnecessary frequency components in the transmission waves can be suppressed effectively. As a result, a quality of the reception signal for each equal-frequency surface can be enhanced.

Further, as described with reference toFIGS.12(a) and12(b), the reception signal processing module133may extract, on the basis of the frequency component of the reception signal, the reception signal which is based on the reflection wave from the equal-frequency surface corresponding to the concerned frequency. Therefore, the equal-frequency reception signal for each equal-frequency surface can be acquired smoothly.

Further, as illustrated inFIG.10, the reception beam RB1generated based on the reception signal from the reception elements31amay be configured to intersect with the transmission beam TB1generated by the first transmission array11. Therefore, within the range where the reception beam RB1and the transmission beam TB1(equal-frequency surface) intersect with each other, the distribution of the intensity data based on the intensity of the reflection waves can be calculated. As a result, by changing the directivity of the reception beam within the detection range by beamforming, the intensity data distributed three-dimensionally in the detection range can be constituted.

<Modifications>

The present disclosure is not limited to the embodiment described above. Moreover, other than the above configuration, the embodiment of the present disclosure can be changed variously.

For example, in the embodiment described above, as illustrated inFIGS.12(a) and12(b), the frequency component at each frequency is extracted from the reception signal, and then, the extracted frequency component is separated for the respective azimuths by beamforming. However, the reception signal may first be separated for the respective azimuths by beamforming, and then, the frequency component at each frequency may be extracted from the separated signal of each azimuth. That is, the bandpass filters203and the beam synthesizing modules204illustrated inFIG.12(a)may be interchanged with each other, or the FFT211and the frequency extracting module212, and the beam synthesizing modules204illustrated inFIG.12(b)may be interchanged with each other.

Further, although in the embodiment described above the plurality of reception elements31aare provided as illustrated inFIG.10, the reflection waves may be received by a single reception element31a. However, in this case, since the intensity data of the reception signal cannot be divided for the respective azimuths to be mapped on the equal-frequency surfaces, the state of the detection range cannot be displayed as the 3D image like the above embodiment. In such a configuration, the azimuth of the reception beam (the azimuth in the θ1-direction inFIG.10) may be fixed. The intensity data in each direction in the vertical direction can be acquired by extracting the frequency component of the reception signal from the reception beam in the fixed azimuth. Therefore, by mapping the intensity data in each direction in the vertical direction, a two-dimensional detection image can be displayed.

Further, although in the embodiment described above the first transmission signal S11and the second transmission signal S12are the same signal, the first transmission signal S11and the second transmission signal S12may be different signals from each other, as long as the unnecessary frequency components in the transmission waves can be reduced. Further, although in the embodiment described above the carrier frequency of the transmission signal S1, the first transmission signal S11, and the second transmission signal S12is fixed, the frequency of the carrier signal may be modulated like a chirp signal. Alternatively, the first transmission signal S11may be burst waves, or the second transmission signal S12may be burst waves.

Further, the switching timing of the first transmission element11ato which the first transmission signal S11is to be supplied, and the switching timing of the second transmission element12ato which the second transmission signal S12is to be supplied, are not limited to the timings described with reference toFIGS.13(a) and13(b). The timings may be other timings, as long as the unnecessary frequency components caused in the transmission waves can be reduced.

Further, the configuration of the first transmission array11and the second transmission array12is not limited to the configuration of the embodiment described above, but may be another configuration, as long as the frequency may be changed based on the Doppler effect in the transmission beam TB1.

For example, as illustrated inFIG.15(a), the first transmission array11and the second transmission array12may be configured such that the second transmission element12ais located at a side of a border between the two adjacent first transmission elements11a. Also in this case, the first transmission signal S11and the second transmission signal S12may be supplied to the first transmission elements11aand the second transmission elements12a, respectively, at timings similarly to the case illustrated inFIG.10. Therefore, unnecessary frequency components generated in the transmission waves can be reduced.

Alternatively, as illustrated inFIG.15(b), the plurality of transmission elements10amay be divided into a plurality of groups, the plurality of transmission elements in each group are connected to each other so that they are supplied simultaneously, and the supply destination of the transmission signal S1may be switched between the groups. Also according to this configuration, the wave source can be moved in the moving direction D1, and thus, the frequency may change based on the Doppler effect in the transmission beam TB1. Moreover, since the transmission waves are transmitted per group, an output of the transmission waves can be raised. The number of transmission elements10amade into one group is not limited to two, but may be three or more.

Further, the number of transmission elements are not limited to the number illustrated in the embodiment described above, but may be another number as long as it is more than one. Moreover, although in the embodiment described above the transmission array and the reception array are disposed to be perpendicular to each other, the transmission array and the reception array may be disposed having an angle therebetween slightly deviated from perpendicular.

Further, althoughFIG.11illustrates the case where the first transmission array11and the second transmission array12are used, only the first transmission array11may be used. In this case, the second transmission array12, the second transmission signal generating module121, the second transmission amplifier122, and the second signal switching part123may be omitted fromFIG.11.

Further, althoughFIG.14illustrates the case where the target object detection device1(the sonar or the radar) is disposed on the ship2, the target object detection device1(the sonar or the radar) may be installed in a moving body other than the ship2. Alternatively, the target object detection device1(the sonar or the radar) may be installed in a structure (e.g., a buoy) other than the moving body.

Embodiment 2

In the embodiment described above, by actuating the plurality of transmission elements of the transmission array from the top to the bottom only once (scanning), the wave transmission for one pulse corresponding to one unit of detection (1 ping) is performed. In this case, the transmission waves are transmitted from each transmission element only during the actuation of the concerned transmission element. Therefore, a transmission energy of one pulse may be low, and the maximum detectable range may be limited.

In this respect, in Embodiment 2, control for improving the transmission energy of one pulse is performed. In detail, during one unit of detection, the scanning in which the plurality of first transmission elements11aof the first transmission array11and the plurality of second transmission elements12aof the second transmission array12are actuated sequentially in one direction in the method as described with reference toFIG.4may be performed a plurality of times so as to generate the pulse. In more detail, in the configuration illustrated inFIG.4, in a first sequence, the signal switching parts21and22may be controlled to sequentially supply the transmission signals to the plurality of transmission elements11aand12abetween a start element and an end element, from the start element to the end element, and in a second sequence subsequent to the first sequence, the signal switching parts21and22may be controlled to sequentially supply the transmission signals to the plurality of transmission elements11aand12abetween the start element and the end element, from the start element to the end element. As a result, the transmission energy of one pulse may be increased.

FIG.16is a diagram schematically illustrating a state of a sound field when the scanning is performed for the first transmission array11and the second transmission array12in one direction a plurality of times. InFIG.16, the lined-up direction of the first transmission elements11aof the first transmission array11and the second transmission elements12aof the second transmission array12is set as an x-axis, and the front direction of the first transmission array11and the second transmission array12is set as a y-axis. Moreover, inFIG.16, wavefronts of the sound field are illustrated.

After the scanning of the first transmission array11and the second transmission array12by sequentially actuating the plurality of first transmission elements11aof the first transmission array11and the plurality of second transmission elements12aof the second transmission array12in order from one end (the transmission element at the start position) to the other end (the transmission element at the end position), control to repeat similar scanning may be performed without a time interval. According to this, a state may be created, in which, after a sound source S which transmits at the frequency f0is moved from the start position to the end position, the sound source S is moved from the start position to the end position without the time interval. By repeating this control a given times during one unit of detection, a period of pulse transmission may be extended, thus the transmission energy may be increased.FIG.16illustrates the sound field in a case where the scanning is performed four times during one unit of detection for convenience.

Note that, in the following description, as illustrated inFIG.1(a), it is assumed that there is no discontinuity in the sound waves in each direction. That is, the influence of the discontinuity of the sound waves illustrated inFIG.1(b)may be suppressed by the control using the first transmission array11and the second transmission array12as illustrated inFIG.4, and the influence of the spurious (unnecessary) peaks illustrated inFIGS.8(a) and8(c)is canceled by the frequency filtering by the bandpass filters203illustrated inFIG.12(a)or the frequency extracting module212illustrated inFIG.12(b). The wave transmission by the first transmission array11and the second transmission array12may also be treated equivalently to the state where the continuity of the sound waves is maintained in all the directions as illustrated inFIG.1(a)by the frequency filtering being applied to the reception system. Therefore, below, description is made supposing that the discontinuity of the sound waves does not occur in all the directions for convenience.

As illustrated inFIG.16, a transmission packet in each scanning is time-compressed according to a direction θ in an in-plane direction of a x-y plane with reference to the front direction (hereinafter, referred to as the “direction θ” in Embodiment 2), and the carrier frequency changes. Further, according to this time compression, a gap (a section where a sound pressure is zero) is generated between the transmission packets according to the direction θ. InFIG.16, the transmission packets in the front direction (y-axis direction), and the transmission packets in the scanning direction of the first transmission array11and the second transmission array12(x-axis direction) are indicated along the y-axis and the x-axis, respectively, and the transmission packets in an arrowed direction are indicated at a tip end of the arrow. A character “T” given to each transmission packet indicates a period of time spent for the sound source S to move from the start position to the end position, that is, a period of time for one scanning of the first transmission array11and the second transmission array12.

As illustrated inFIG.16, in the front direction (y-axis direction), since there is no influence of the Doppler effect, the waveform of the transmission packets is maintained to be similar to that of the transmission signal. Therefore, in the front direction, there is no gap between the transmission packets. On the other hand, in the scanning direction (x-axis direction) of the first transmission array11and the second transmission array12, since the waveform of the transmission packets is largely compressed due to the Doppler effect, a large gap occurs between the transmission packets. Further, in the arrowed direction, since the influence of the Doppler effect is smaller than in the x-axis direction, the compression of the waveform of the transmission packets is smaller, and thus, the gap between the transmission packets is reduced.

As described above, since the state of the compression and gap of waveforms is different according to the direction, a frequency spectrum of the sound waves varies according to the direction. That is, in a direction where phase discontinuity is caused by the gap, a spectral intensity decreases, and in a direction where the phase discontinuity is not caused by the gap, the spectral intensity increases. Specifically, in a direction where the gap is an integral multiple of the wavelength, the phase discontinuity does not occur, and therefore the spectral intensity becomes high.

FIGS.17(a) and17(b)are diagrams each illustrating a simulation result in which a relation between the spectrum of the sound field and the direction is simulated.

The simulation is performed under the following conditions.Transmission Frequency: f0=150 kHzPulse Width: PW=100 msecScanning Period: τ=1 msec

That is, continuous waves CW at the fixed transmission frequency f0are transmitted in each packet. The scanning period τ of each transmission packet is set to 1 msec, and the sound source S is scanned 100 times to form a pulse. That is, the pulse width PW is 100 msec.

FIG.17(a)illustrates the simulation result in a 3D contour display, andFIG.17(b)is a 3D bird's eye view from the angle axis.

Referring toFIGS.17(a) and17(b), it is apparent that peaks of the spectral intensity (i.e., the transmission beam) are formed at a 1 kHz interval. This mechanism is as follows.

The number of waves transmitted in the front direction (θ=0) during one scanning is “f0·τ”, and this packet of the scanning period τ is repeated so that continuous waves CW having continuous phase and a long pulse width are transmitted in the front direction. On the other hand, in the direction other than the front direction, discontinuity of the phase is caused by the gap according to the direction. However, in a direction where the following relational expression is satisfied, the initial phases are maintained between the packets.
f0·τ+n=fn·τ(n=0,1, . . . )  (1)

When the gap period (i.e., a phase stop period) is an integral multiple of a carrier cycle in the concerned direction, since the initial phases are the same between the packets, the influence of the gap becomes insignificant. This condition may be represented by the following formula based on Formula (1).

fn=f0+nτ(2)

From Formula (2), it can be understood why the continuous phase (i.e., the direction of sharpening of the spectrum) is formed every 1/τ (i.e., 1 kHz) inFIGS.17(a) and17(b).

Next, beam spacing (a gap formed between the transmission beams) is examined.

As described above, the direction where the transmission beam is formed is the direction in which the initial phases are continuous and the carrier frequency satisfies Formula (2). Such a direction θnis associated with other variables by the following formulas.

A gap period in the θ-direction is calculated based on the following formula.

τ-τθ=τ-τ·r⁡(θ)=τ⁢V⁢sin⁢⁢θc(3)

Here, “V” is a moving velocity of the sound source S, “c” is a sound velocity, and “r(θ)” is a compression rate of the transmission waves propagated in the θ-direction.

Since a direction where the gap period becomes an integral multiple of the cycle of the carrier frequency in the θ-direction is θn, θnmay be defined by the following formula.

τ⁢V⁢sin⁢⁢θnc=n·1f⁡(θn)=n·1f0·c-V⁢sin⁢⁢θnc(4)

Therefore, θnmay be calculated based on the following formula.

θn=sin-1(n·cf0·V·1τ+nf0)(5)

Accordingly, the transmission beam is formed in the direction θncalculated based on Formula (5). Therefore, by extracting the carrier frequency in the direction θnby the bandpass filters203illustrated inFIG.12(a)or the frequency extracting module212illustrated inFIG.12(b), the reception signal for each transmission beam can be extracted.

Embodiment 3

Referring toFIG.17(b), the gap between the transmission beams is large to continuously image the detection range in the θ-direction. That is, the reception signal may be missing within an angular range between the transmission beams, thus generation of the favorable detection image may be difficult. In this respect, in Embodiment 3, control for forming other transmission beams between the transmission beams illustrated inFIG.17(b)is performed.

In a direction at the middle between the adjacent transmission beams, the phase is inversed every transmission packet. Therefore, by transmitting the transmission signal which is inversed in its polarity per transmission packet, the initial phases in the concerned direction should be phased.

FIGS.18(a) and18(b)are diagrams each illustrating a simulation result in which a relation between the spectrum of the sound field and the direction when transmitting the transmission signal which is inversed in its polarity per transmission packet is simulated. Conditions for the simulation are similar to the conditions for the simulation illustrated inFIGS.17(a) and17(b), except for inverting the polarity of the transmission signal every transmission packet.

Referring toFIGS.18(a) and18(b), in the direction at the middle between the transmission beams illustrated inFIGS.17(a) and17(b), the transmission beam is formed. That is, inFIGS.18(a) and18(b), the transmission beam which interpolates the direction between the transmission beams illustrated inFIGS.17(a) and17(b)is formed. Therefore, for example, during one unit of detection, by performing a first transmission process in which the transmission packet is repeatedly transmitted without inversing the polarity every transmission packet, and performing a second transmission process in which the transmission packet is repeatedly transmitted while inversing the polarity every transmission packet, the processes can mutually interpolate the direction where the transmission beam is omitted. Thus, the detection range can be imaged continuously in the θ-direction. Also in this case, by applying the carrier frequency of each transmission beam to the bandpass filters203illustrated inFIG.12(a)or the frequency extracting module212illustrated inFIG.12(b), the reception signal for each transmission beam can be extracted.

Note that, in the first transmission process and the second transmission process, the polarity of the transmission signal may be inversed in one of an odd number or an even number. Therefore, the transmission processes can mutually interpolate the direction where the transmission beam is omitted.

Embodiment 4

In Embodiment 3 described above, when the first transmission process and the second transmission process are performed in two transmission/reception steps, the frame rate is halved. On the other hand, when the first transmission process and the second transmission process are performed simultaneously, the transmission packets with the inversed polarity between the transmission processes interfere with each other, thus, deleting the transmission waves. Therefore, performing the first transmission process and the second transmission process simultaneously may be equivalent to suspending the transmission in the odd-numbered or the even-numbered transmission packets. In this respect, in Embodiment 4, the suspension of the transmission in the odd-numbered or the even-numbered transmission packets is examined.

Based on Formula (2), it is apparent that by repeating the transmission at a cycle twice the scanning period τ (i.e., 2τ), the gap between the transmission beams can be reduced by half. In this case, for example, by transmitting only the even-numbered transmission packets or the odd-numbered transmission packets among the series of transmission packets illustrated inFIG.16, the scanning cycle becomes twice. Therefore, when only the even-numbered or odd-numbered transmission packets are transmitted in this manner, the gap between the transmission beams should be halved.

FIGS.19(a) and19(b)are diagrams each illustrating a simulation result in which a relation between the spectrum of the sound field and the direction when only the even-numbered transmission packets are transmitted is simulated. Conditions for the simulation are similar to the conditions for the simulation illustrated inFIGS.17(a) and17(b), except for transmitting only the even-numbered transmission packets.

Referring toFIGS.19(a) and19(b), compared to the case illustrated inFIGS.17(a) and17(b), the gap between the transmission beams is halved. Therefore, when the first transmission array11and the second transmission array12are controlled to transmit only the even-numbered or odd-numbered transmission packets, the gap between the transmission beams can be narrowed. That is, by transmitting only the even-numbered or odd-numbered transmission packets, the gap between the transmission beams can be narrowed while reducing the pulse width of the pulse transmitted in one unit of detection and improving the range resolution. As a result, the detection range can be imaged continuously in the θ-direction.

Further, according to Embodiment 4, since information for one unit of detection can be obtained by one transmission/reception, the frame rate during the generation of the detection image can be increased. Note that, when the frame rate can be made low, the first transmission process and the second transmission process may be divided into two transmission/reception steps as described in Embodiment 3.

Further, the information for one unit of detection may be obtained by one transmission/reception in which the first transmission process and the second transmission process are carried out sequentially without an interval.

Embodiment 5

When the transmission packets are transmitted repeatedly more than once in one unit of detection like Embodiment 2, the transmission energy is increased, and thus, a signal-to-noise (S/N) ratio rises. On the other hand, since the transmission period (pulse width) in one unit of detection becomes longer, the range resolution decreases. In this respect, in Embodiment 5, the improvement in the range resolution using pulse compression is examined.

The present inventors examined the sound field by simulation under a condition in which the sound source S, which transmits a linear-frequency-modulated (LFM) chirp signal with the pulse width at 100 msec and a chirp sweeping width at 1 kHz, is uniformly moved at a velocity V repeatedly from the start position to the end position. In this examination, parameters of the linear chirp signal (LFM) are set as follows.

<LFM Parameters>

Sweep Start Frequency: fs=150 kHzSweep Frequency: fsweep=1 kHzSweep Period (LFM pulse width)=100 msecWindow Function: Hanning (applied to the pulse of 100 msec)Sound Source Sweep Length: L=16λo (λo: wave length at sweep startfrequency)Sound Source Sweep Period (scanning period): τ=1 msec

That is, the linear chirp signal of which the frequency linearly shifts from 150 kHz to 151 kHz in 100 msec is sectioned every 1 msec to actuate the transmission array, and transmit one pulse.

FIGS.20(a) and20(b)are diagrams each illustrating the simulation result in which the relation between the spectrum of the sound field and the direction is simulated when the transmission is performed by the linear chirp signal of the above conditions.

As illustrated inFIGS.20(a) and20(b), also in the case where the transmission is performed by the linear chirp signal of the above conditions, the transmission beams can be formed at a pitch similar to the case illustrated inFIGS.17(a) and17(b).

Next, in order to examine a time response after the pulse compression, an autocorrelation function of the direction in which the transmission beam is formed inFIGS.20(a) and20(b)is calculated.

FIGS.21(a) and21(b)are graphs each illustrating the autocorrelation function at the angle 0°, andFIGS.21(c) and21(d)are graphs each illustrating the autocorrelation function at the angle 7°.FIGS.21(b) and21(d)are enlarged graphs of a range between 1-4,000 μsec in the graphs illustrated inFIGS.21(a) and21(c), respectively.

From the result illustrated inFIGS.21(a) to21(d), by using the transmission waveform in the transmission beam direction as a compression filter coefficient, it is possible to achieve good pulse compression with few time-axis side lobes. InFIGS.21(a) to21(d), the pulse width of 100 msec is compressed to about 3 msec. Therefore, by further providing the reception signal processing module133illustrated inFIG.11for processing the reception signal with a compression filter having a coefficient corresponding to the waveform of the transmission beam in each direction, the range resolution can be increased in the direction of each transmission beam.

Further, also in this embodiment, similarly to Embodiment 2, the gaps between the transmission beams is large. Therefore, in order to interpolate the transmission beams at the gaps, similarly to Embodiment 3, application of the method of inversing the polarity every transmission packet is examined.

FIGS.22(a) and22(b)are diagrams each illustrating a simulation result in which the relation between the spectrum of the sound field and the direction is simulated in the case where the linear chirp signal of the above conditions is transmitted.

In this simulation, under the simulation conditions illustrated inFIGS.20(a) and20(b), the polarity of the linear chirp signal is inversed every scanning period τ. Other simulation conditions are similar to those inFIGS.20(a) and20(b).

Referring toFIGS.22(a) and22(b), it can be seen that transmission beams for interpolating directions between the adjacent transmission beams illustrated inFIGS.20(a) and20(b)are formed. Therefore, by combining a first transmission process where the linear chirp signal with the polarity inversed every scanning period τ is used for the wave transmission, and a second transmission process where the linear chirp signal with the polarity not inversed every scanning period τ is used for the wave transmission, the transmission processes can mutually interpolate the direction between the transmission beams. As a result, the detection range can be imaged continuously in the θ-direction.

FIGS.23(a) and23(b)are graphs each illustrating the autocorrelation function at the angle 2° where the transmission beam illustrated inFIGS.22(a) and22(b)is formed, andFIGS.23(c) and23(d)are graphs each illustrating the autocorrelation function at the angle 16° where the transmission beam illustrated inFIGS.22(a) and22(b)is formed.FIGS.23(b) and23(d)are enlarged graphs of a range between 1-4,000 μsec in the graphs illustrated inFIGS.23(a) and23(c), respectively.

Also from the result illustrated inFIGS.23(a) to23(d), similarly toFIGS.21(a) to21(d), by using the transmission waveform in the transmission beam direction as the compression filter coefficient, it is possible to achieve good pulse compression with few time-axis side lobes. Also inFIGS.23(a) to23(d), the pulse width of 100 msec is compressed to about 3 msec. Therefore, also in this case, similarly to the case described above, the range resolution can be increased in the direction of each transmission beam by using the compression filter.

Note that in Embodiment 5, as in Embodiment 4, instead of the control for sequentially performing the first transmission process and the second transmission process, the control for transmitting only the odd-numbered or even-numbered transmission packets (scanning period) may be performed.

Note that, when a chirp signal is transmitted as the transmission signal, as described above, parts of the signal to be supplied to a first element and a second element may differ from each other, and therefore, a first part of the transmission signal may be supplied to the first element, and a second part of the transmission signal different from the first part may be supplied to the second element. Without any limitation to a chirp signal, for example for a single frequency transmission signal or any other transmission signal, a first part of the transmission signal may be supplied to the first element, and a second part of the transmission signal different from the first part may be supplied to the second element.

Embodiment 6

Although in Embodiments 2 to 4 all of the transmission packets are scanned in only one direction, the scanning direction of the transmission packets is not limited to this. In Embodiment 6, the moving direction of the sound source S (i.e., the scanning direction) may be reversed between the odd-numbered transmission packet and the even-numbered transmission packet.

In this case, after the sound source S performs scanning in one direction, it may perform the scanning in the other direction without a time interval. That is, the sound source S may be reciprocated a plurality of times. In detail, the first transmission array11and the second transmission array12may be sequentially actuated in the order from the transmission element at one end to the transmission element at the other end, and then, sequentially actuated in the order from the transmission element at the other end to the transmission element at the one end without a time interval.

FIG.24is a diagram schematically illustrating a state of the sound field when the first transmission array11and the second transmission array12are reciprocally scanned a plurality of times.

The transmission packet of each scanning is time-compressed according to the direction θ, thus the carrier frequency is changed. Moreover, since the scanning direction is opposite between the odd-numbered transmission packet and the even-numbered transmission packet, the compression rates are different between the odd-numbered and even-numbered transmission packets. Assuming that the velocity of each scanning is Voddand Veven, compression rates rodd(θ) and reven(θ) of the odd-numbered and even-numbered transmission packets are represented by the following formulas, respectively.

ro⁢d⁢d⁡(θ)=c-Vo⁢d⁢d⁢sin⁢⁢(θ)c(6)re⁢v⁢e⁢n⁡(θ)=c+Ve⁢v⁢e⁢n⁢sin⁢⁢(θ)c(7)

As can be seen fromFIG.24and Formulas (6) and (7), compression and expansion are alternately performed in the direction θ.

Further, the transmission frequencies may be different between the odd-numbered transmission packet and the even-numbered transmission packet. In this case, the transmission frequency of the odd-numbered transmission packet and the transmission frequency of the even-numbered transmission packet may be set to frequencies that do not affect the transmission of the other transmission packet.

FIG.25is a diagram illustrating a simulation result in which a relation between a spectrum of the sound field and the direction is simulated in a case where the reciprocating scanning is performed ten times while changing the transmission frequencies between the odd-numbered transmission packets and the even-numbered transmission packets.

Conditions for the simulation is as follows.Sound Source Sweep Length: L=16λo (λo: wave length at 150 kHz)Scanning Period (per scanning): τ=1 msecOdd-numbered Transmission Packet: f0=150 kHz, Vodd=160 msecEven-numbered Transmission Packet: f0=170 kHz, Veven160 msec

Under the above conditions, the sound source S is reciprocated ten times. That is, the odd-numbered transmission packets are formed by the motion of the sound source S in the forward path, and the even-numbered transmission packets are formed by the motion of the sound source S in the return path. The moving velocity of the sound source S in the forward and return paths is set to be the same.

As illustrated inFIG.25, two frequency components are included in one direction. Also in Embodiment 6, similarly to Embodiments 2 to 5 described above, by separating the frequencies by the bandpass filters (or the compression filters) or the FFT, the reception signal in each direction can be acquired.

Note that, in this transmission method, since the period of the odd-numbered transmission packet and the period of the even-numbered transmission packet are separated by the frequencies, similarly to Embodiment 4, the transmission cycle of the odd-numbered transmission packets becomes longer, which narrows the gap between the transmission beams. Similarly, the transmission cycle of the even-numbered transmission packets becomes longer, which narrows the gap between the transmission beams. As a result, the gap between the transmission beams can be narrowed, and the detection range can be imaged continuously in the θ-direction.

In Embodiment 6, since transmission is performed even in the transmission packets whose transmissions are suspended in Embodiment 4, the transmission energy of the pulse in one unit of detection is remarkably improved.

Note that although in the simulation illustrated inFIG.25the sound source S is reciprocated, the moving direction of the sound source S (i.e., the scanning directions of the transmission packets) may be the same between the odd-numbered transmission packets and the even-numbered transmission packets. Also in this case, the transmission frequency of the odd-numbered transmission packets and the transmission frequency of the even-numbered transmission packets may be set to a frequency that does not affect the transmission of the other transmission packet. Accordingly, a frequency spectrum in which two frequency components are included in one direction can be formed, and the transmission energy of the pulse in one unit of detection can be remarkably enhanced.

Further, also in Embodiment 6, similarly to Embodiment 5, the pulse compression may be performed by using a chirp signal as the transmission signal.

Terminology

It is to be understood that not necessarily all objects or advantages may be achieved in accordance with any particular embodiment described herein. Thus, for example, those skilled in the art will recognize that certain embodiments may be configured to operate in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

All of the processes described herein may be embodied in, and fully automated via, software code modules executed by a computing system that includes one or more computers or processors. The code modules may be stored in any type of non-transitory computer-readable medium or other computer storage device. Some or all the methods may be embodied in specialized computer hardware.

Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and/or computing systems that can function together.

The various illustrative logical blocks and modules described in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a processor. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuitry configured to process computer-executable instructions. In another embodiment, a processor includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor (DSP) and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, some or all of the signal processing algorithms described herein may be implemented in analog circuitry or mixed analog and digital circuitry. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

Conditional language such as, among others, “can,” “could,” “might” or “may,” unless specifically stated otherwise, are otherwise understood within the context as used in general to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment.

Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present.

Any process descriptions, elements or blocks in the flow diagrams described herein and/or depicted in the attached figures should be understood as potentially representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or elements in the process. Alternate implementations are included within the scope of the embodiments described herein in which elements or functions may be deleted, executed out of order from that shown, or discussed, including substantially concurrently or in reverse order, depending on the functionality involved as would be understood by those skilled in the art.

Unless otherwise explicitly stated, articles such as “a” or “an” should generally be interpreted to include one or more described items. Accordingly, phrases such as “a device configured to” are intended to include one or more recited devices. Such one or more recited devices can also be collectively configured to carry out the stated recitations. For example, “a processor configured to carry out recitations A, B and C” can include a first processor configured to carry out recitation A working in conjunction with a second processor configured to carry out recitations B and C. The same holds true for the use of definite articles used to introduce embodiment recitations. In addition, even if a specific number of an introduced embodiment recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations).

It will be understood by those within the art that, in general, terms used herein, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.).

For expository purposes, the term “horizontal” as used herein is defined as a plane parallel to the plane or surface of the floor of the area in which the system being described is used or the method being described is performed, regardless of its orientation. The term “floor” can be interchanged with the term “ground” or “water surface.” The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms such as “above,” “below,” “bottom,” “top,” “side,” “higher,” “lower,” “upper,” “over,” and “under,” are defined with respect to the horizontal plane.

As used herein, the terms “attached,” “connected,” “mated,” and other such relational terms should be construed, unless otherwise noted, to include removable, moveable, fixed, adjustable, and/or releasable connections or attachments. The connections/attachments can include direct connections and/or connections having intermediate structure between the two components discussed.

Numbers preceded by a term such as “approximately,” “about,” and “substantially” as used herein include the recited numbers, and also represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 10% of the stated amount. Features of embodiments disclosed herein preceded by a term such as “approximately,” “about,” and “substantially” as used herein represent the feature with some variability that still performs a desired function or achieves a desired result for that feature.

It should be emphasized that many variations and modifications may be made to the above-described embodiments, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.