JP5241295B2 - Underwater image pickup device and underwater image pickup device for identification of buried object - Google Patents

Description

  The present invention relates to an underwater image capturing apparatus, and more particularly, to an underwater image capturing apparatus that irradiates an object with ultrasonic waves in water and captures an image of the object using reflected waves.

  In water, ultrasonic waves are generally less attenuated than electromagnetic waves including visible light, and propagate in muddy water. Therefore, in order to recognize the position, size, and shape of an object in water, imaging using ultrasonic waves is performed.

  As an apparatus that captures an image of an object in water using ultrasonic waves, an underwater acoustic camera that irradiates an object with ultrasonic waves in water and receives the reflected wave to capture an image (acoustic image) of the object, and underwater An underwater acoustic camera for identifying buried objects that emits ultrasonic waves (primary waves) of two different frequencies at the same time, detects objects buried mainly on the sea floor using secondary waves generated by their parametric effects, and identifies them by images. is there.

  Patent Document 1 describes a method of irradiating an object buried in a deposition layer with a secondary wave caused by the parametric effect and obtaining a target detection and image using the reflected wave. In Patent Document 1, when the same object surface is repeatedly scanned while changing the frequency of the secondary wave Δf = | f1-f2 |, the object is identified more accurately due to the difference in the reflectance of the object with respect to the ultrasonic waves of different frequencies. Is disclosed. Further, in Patent Document 1, when transmitting the primary waves f1 and f2, with respect to the method of determining the beam direction, a method of mechanically directing the transmitter in the target direction and a time delay in the signal to each transmitting piezoelectric element And a method of changing the direction by providing the.

  Further, Patent Document 2 discloses that a secondary wave by a parametric effect is irradiated onto a sludge layer on the seabed, a secondary wave echo transmitted through the sludge layer and reflected on a hard seabed, and a primary wave reflected on the top surface of the sludge layer. It shows a method for observing echoes and measuring the thickness of the sludge layer from the difference in detection time between the two.

  Further, in Patent Document 3, when a beam is transmitted in the θ direction in a parametric ultrasonic transmitter, the primary wave f1 is transmitted in the direction of θ + β, and f2 is transmitted in the direction of θ-β. A method for narrowing the beam width of the secondary wave main pole and suppressing the generation level of the sub-pole is described.

JP-A-5-223923 JP 60-192281 A JP-A-10-90410

  When an underwater object is imaged by the frequency sweep method, the ultrasonic wave focused at one point on the receiving surface by the acoustic lens of the underwater acoustic camera is unique to the azimuth direction θ corresponding to the focal position, that is, the ultrasonic frequency fa. Associated with Therefore, ideally, only the ultrasonic wave having the frequency fa corresponding to the position of the point should be detected at the focal point on the piezoelectric element of the underwater acoustic camera.

  However, in reality, sound waves randomly incident from the surrounding environment of the device and ultrasonic waves of different frequencies reflected from points on other channels on the receiving surface are reflected in the device at the focal point on the piezoelectric element of the underwater acoustic camera. Was observed, which was the cause of ghosts appearing especially in the vertical direction of the captured image.

  In addition, in an apparatus that images a buried object by parametric ultrasonic transmission, a circuit that generates signals of two different frequencies for the primary wave and a delay circuit for changing the beam direction of the primary wave or mechanical transmission A mechanism for controlling the orientation of the waver is required, and there is a problem that the circuit scale and the apparatus scale increase.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an ultrasonic underwater image pickup device based on a frequency sweep method that can reduce noise and ghost of an acoustic image and obtain a clearer object image. The purpose is to provide.
It is another object of the present invention to provide a parametric ultrasonic underwater imaging device for buried objects that can control the beam transmission direction with a simple circuit and contribute to the reduction in size and weight of the device.
It is another object of the present invention to provide a parametric ultrasonic underwater image capturing apparatus for an embedded object that can reduce noise and ghost of an acoustic image and obtain a clearer object image.

In order to solve the above-described problems, in the present invention, for receiving waves, the resonance frequency of the piezoelectric element at each focal position on the receiving piezoelectric element matches the frequency of the target ultrasonic wave that converges to the focal point. The thickness of the piezoelectric element was changed continuously or stepwise.
Alternatively, an inductance that resonates with the capacitance component of the receiving piezoelectric element is connected in series to each receiving piezoelectric element, and the resonance frequency is converged to the focal position on the receiving piezoelectric element. The target ultrasonic frequency was adjusted to each.
Alternatively, after the analog electrical signal output from each receiving piezoelectric element is converted into a digital signal, the frequency component included in the digital signal is converged to the focal position on the receiving piezoelectric element. Digital signal processing for transmitting ultrasonic frequency components is performed.
Alternatively, by applying a frequency sweep method and inputting a signal containing two frequencies f1 and f2 corresponding to the primary wave to the piezoelectric element for transmission, a secondary wave due to these parametric effects is generated and the secondary wave is generated. The transmission direction is controlled by changing the values of the frequencies f1 and f2.
Alternatively, by applying a frequency sweep method, an inductance that resonates with the capacitance component of the receiving piezoelectric element is connected in series with each receiving piezoelectric element, and each resonance frequency is used for receiving the wave. The frequency of the target ultrasonic wave that converges at the focal position on the piezoelectric element is adjusted.
Alternatively, after applying the frequency sweep method, the analog electric signal output from each receiving piezoelectric element is converted into a digital signal, and then the receiving piezoelectric element among a plurality of frequency components included in the digital signal. Digital signal processing for transmitting the frequency component of the target ultrasonic wave that converges at the focal position on the element is performed.

  According to the present invention, noise and ghost of an acoustic image can be reduced and a clearer object image can be obtained. Further, the beam transmission direction can be controlled with a simpler circuit than before, which can contribute to the reduction in size and weight of the apparatus. Furthermore, the beam transmission direction can be controlled with a simple circuit, which can contribute to the reduction in size and weight of the apparatus. Furthermore, noise and ghost of the acoustic image can be reduced, and a clearer object image can be obtained.

  Hereinafter, embodiments of the present invention will be described. In order to clarify the features of the present invention, first, a configuration of a general underwater image capturing apparatus and an imaging mechanism will be described with reference to FIGS. 1 to 7.

FIG. 1 is a diagram illustrating a configuration of an entire underwater image capturing system including a general underwater image capturing apparatus.
As shown in FIG. 1, an underwater image capturing system including an underwater acoustic camera that is an underwater image capturing device hangs an underwater acoustic camera 101 from a ship 102 or the like to capture an underwater target object 103. The ship 102 is stationary on the surface of the water, or is traveling at a speed that does not affect the measurement. The underwater acoustic camera 101 radiates a transmission wave 105 from the transmitter 104 in a direction inclined by θ in the horizontal direction (azimuth direction) when viewed from the underwater acoustic camera 101. The frequency of the transmission wave 105 is about several hundreds k to several MHz. The transmission wave 105 has a narrow beam width in the azimuth direction and has high directivity. On the other hand, the beam spreads in the vertical direction (range direction) as viewed from the camera 101, and the transmission wave 105 propagates in water as a fan-shaped beam. A part of the transmission wave 105 is reflected on the surface of the target object 103, and a reflected wave 106 is generated. The underwater acoustic camera converges the reflected wave 106 to one point on a wave receiving surface (not shown) by the acoustic lens 107 of the underwater acoustic camera 101 and converts it into an electric signal to obtain an image of the target object.

Next, the configuration and operation of the transmitter will be described with reference to FIGS.
FIG. 2 is a diagram schematically showing the structure of the transmitter of the frequency sweep type underwater acoustic camera.
First, the frequency sweep method will be described. As a method of inclining a beam in an arbitrary direction θ in the azimuth direction and obtaining high directivity at the time of transmission, in general, the transmission azimuth and focus are applied to the electric signals input to the piezoelectric elements arranged in the transmitter. A method of giving a delay time depending on the distance is often adopted. On the other hand, a method in which the transmission direction changes only by changing the frequency of the input signal, and thus a signal delay circuit is not required, and a high directivity can be obtained is called a frequency sweep method. A brief description will be given below with reference to FIG.

  As shown in FIG. 2, the transmitter of the frequency sweep type underwater acoustic camera is configured by arranging the piezoelectric elements 201 in a line. Piezoelectric ceramics such as PZT (lead zirconate titanate, Pb (Zr-Ti) O3) are generally used for the piezoelectric element 201, and the polarization directions (arrows 202) of adjacent piezoelectric elements are alternately replaced. . Electrodes 203 are deposited on the upper surface of the piezoelectric element 201, and a common electrode 204 is deposited on the lower surface and connected to the power source 205. For example, when an AC electrical signal having a frequency fa is input to these piezoelectric elements 201, a composite wave 206 having directivity in a direction θa depending on the frequency fa is transmitted symmetrically from near both ends of the array of piezoelectric elements 201. . The direction of the synthesized wave can be changed by changing the frequency. When the frequency is increased, for example, fb (> fa), the beam 207 (azimuth θb < θa) is output. Note that a signal waveform including a plurality of frequency components may be input to the piezoelectric element 201. In that case, the transmission wave corresponding to each frequency component is simultaneously transmitted to each corresponding azimuth. This frequency sweep method has an advantage that the circuit scale can be reduced as compared with a general delay circuit method.

  Next, the configuration and operation of the underwater acoustic camera to which the frequency sweep method is applied will be described with reference to FIGS. The content described below is an example, and the configuration and operation of the underwater camera using the frequency sweep method are not limited to the following.

FIG. 3 is a diagram showing an example of a transmitter structure when the frequency sweep method is applied to an underwater acoustic camera.
The transmitter 301 is configured by arranging two piezoelectric element arrays 201 shown in FIG. The acoustic radiation surfaces of the left and right piezoelectric element arrays 302 and 303 are inclined at an angle of 20 to 30 ° with respect to the imaging direction 304, and transmitted waves 305a, 305b, 305c, 305d, and 305e generated from both ends of each array. , 305f, 305g, and 305h, only the transmission waves 305c, 305d, 305e, and 305f from the inner end are directed to the visual field range 306 and contribute to the imaging of the target object 307. The other transmitted waves 305a, 305b, 305g, and 305h are directed away from the visual field range 306 and do not contribute to imaging. In the drawing, the piezoelectric element array 303 on the right side irradiates the left side from the center in the visual field range 306, and the piezoelectric element array 302 on the left side irradiates the right side from the center in the visual field range 306. Of the transmission waves directed toward the target object 307, high-frequency ultrasonic waves 305d and 305e irradiate near the center of the field of view, and low-frequency transmission waves 305c and 305f irradiate the outside. Therefore, the transmission beam width is narrower near the center of the field of view and the spatial resolution is higher.

FIG. 4 is a diagram three-dimensionally showing the process until the transmission wave emitted from the transmitter is reflected by the surface of the target object.
The azimuth azimuth θ of the transmission wave 403 emitted from one end of the piezoelectric element array of the transmitter 401 toward the target object 402 is determined depending on the frequency of the transmission wave 403 based on the frequency sweep method. The closer to the front direction 404, the higher the frequency. The transmission wave 403 propagates in water in a fan shape that is narrow in the azimuth direction and spreads in the range direction. When the fan beam reaches the surface of the target 402 and is irregularly reflected by fine irregularities on the surface of the object, the ultrasonic wave is reflected from the position as a spherical wave (not shown). Reference numeral 405 denotes a receiving system that measures a reflected wave from an object. Next, the function of the receiving system 405 will be described.

FIG. 5 is a diagram three-dimensionally illustrating a process in which the wave receiving system 405 of the underwater acoustic camera receives a reflected wave from an object.
The wave receiving system 405 includes an acoustic lens 501 and a wave receiver 502. The acoustic lens 501 is designed to converge the plane wave to one point. In the figure, the acoustic lens 501 is drawn as a single lens, but in reality, two or three acoustic lenses are used to eliminate aberrations and adjust the focal position. May be configured in combination. The acoustic lens 501 is made of a material such as acrylic resin or polymethylpentene. The receiver 502 is a one-dimensional array of piezoelectric elements 503 that are channel-divided in the range direction. On the other hand, the receiver is not divided into channels in the azimuth direction, and each piezoelectric element 503 is elongated in the azimuth direction.
When the reflected wave 504 from the object reaches the vicinity of the acoustic lens 501, since the distance between the object and the underwater acoustic camera is sufficiently large, the reflected wave 504 can be considered as a plane wave. For this reason, the reflected wave 504 is converged to one point 505 on the surface of the receiver 502 by the acoustic lens 501 and converted into an electric signal by the corresponding piezoelectric element.

Next, a method for obtaining the spatial resolution in the range direction will be described with reference to FIG.
FIG. 6 is a diagram illustrating a method for obtaining the spatial resolution in the range direction.
In FIG. 6, for the reflected wave 601 (solid line) arriving from the front of the apparatus and the reflected wave 602 (dotted line) arriving from the lower side of the apparatus (range azimuth φ), the receiving process is performed from the side of the receiving system (azimuth direction (From) shows the case. The wave receiver 603 is divided into channels 1, 2,..., N piezoelectric elements in the range direction, and is arranged so as to be curved in accordance with the focal position (field curvature). Reference numeral 604 denotes one piezoelectric element. Reference numeral 605 denotes an acoustic lens, which is represented by a single biconcave lens in the figure. The frequency of the reflected waves 601 and 602 is arbitrary.
The reflected wave 601 incident from the front of the apparatus is connected to the focal point 606 at the center of the receiver by the acoustic lens 605 and converted into an electric signal 607 by the corresponding piezoelectric element (channel i). Note that the horizontal axis of the electrical signal is time (starting from the start of transmission wave output), and the vertical axis is voltage. On the other hand, the reflected wave incident from the lower side of the apparatus forms a focal point 608 slightly above and in front of the receiver, and is similarly converted into an electric signal 609 by the corresponding piezoelectric element (channel j). As described above, the direction of the reflected wave can be known by distinguishing the channel receiving the signal in the range direction.

Next, a method for obtaining the spatial resolution in the azimuth direction will be described with reference to FIG.
FIG. 7 shows the process of receiving a reflected wave 701 (solid line) coming from the front of the apparatus and a reflected wave 702 (dotted line) coming from the right side of the apparatus (azimuth azimuth θ) from the upper side of the receiving system (range From the direction). The receiver is not divided as a channel in the azimuth direction, and only one arbitrary piezoelectric element 703 is shown in FIG. Reference numeral 704 denotes an acoustic lens, which is a biconcave lens as in FIG. 6 (axisymmetric with respect to the sound axis). Further, the frequency of the reflected wave 701 coming from the front is assumed to be fb, and the frequency of the reflected wave 702 coming from the right side of the apparatus is assumed to be fa (fb> fa). In the frequency sweep method, the frequencies fb and fa of the reflected waves 701 and 702 are related to the azimuth transmission directions of the respective ultrasonic waves.
Since the reflected waves 701 and 702 are both converted into an electric signal 705 by the same piezoelectric element 703, the electric signal 705 includes both frequency components of the two reflected waves 701 and 702. Therefore, the direction of the reflected wave can be known by detecting peaks 707 and 708 corresponding to the frequencies of the reflected waves 701 and 702 in the spectrum 706 obtained by Fourier transforming the spectrum, and associating the frequencies with the azimuth transmission directions.
As described above, the direction of the reflected wave in the range direction and the azimuth direction, that is, the direction of the object is analyzed, and an image of the underwater object is obtained.

  Next, a description will be given of a conventional technique in the case where an image is picked up by ultrasonic waves on an object buried in a seabed sediment layer such as a seabed cable. For underwater objects, high frequencies on the order of hundreds of k to several MHz are used to obtain high spatial resolution, but when such frequencies are used for the sediment layer on the seabed, most of them are reflected on the seafloor surface. The transmitted wave is attenuated with almost no propagation, and an effective reflected wave from the buried object cannot be obtained. Therefore, it is necessary to use an ultrasonic wave having a low frequency of several k to 10 kHz, which is more easily propagated in the deposition layer, for imaging the buried object in the deposition layer.

On the other hand, there is a relationship of d = λ / L between the diameter d of the transmission beam, the wavelength λ of the ultrasonic wave, and the aperture length (array length) L of the transmitter. Therefore, if the frequency of the ultrasonic wave is lowered and the wavelength λ is made longer, the beam diameter d increases with the same aperture length L, and a beam with high directivity cannot be obtained, resulting in a reduction in spatial resolution. If the aperture length L is increased, d becomes smaller and the beam becomes highly directional. However, there is a limit to the size and weight of a transmitter that can be mounted on an actual device, and the spatial resolution is increased beyond this. I can't.
Therefore, in an application for imaging an object buried in a sediment layer on the seabed by using an ultrasonic wave, a secondary wave generated by a parametric effect in the medium is used. The parametric effect is that when strong ultrasonic waves (primary waves) of two different frequencies f1 and f2 are transmitted so that they overlap each other in space, the secondary wave (the sum of f1 and f2) is generated by the interaction of the two waves. The frequency f1 + f2 and the difference frequency | f1-f2 |) are excited. The beam width of the secondary wave (the width of the main pole) conforms to that of the primary wave, and the generation level of the sub pole is also reduced, so that good directivity can be obtained.
Therefore, the primary wave frequencies f1 and f2 are set high enough to obtain the target spatial resolution, and the difference between f1 and f2 Δf = | f1-f2 | is suitable for propagation in the deposition layer. The secondary wave of the difference frequency △ f = | f1-f2 | can propagate through the sedimentary layer with high directivity and observe reflection from the buried object. Can do. On the other hand, the waves having the frequencies f1, f2 and the sum frequency f1 + f2 are quickly attenuated in the deposited layer.

A problem when an underwater object is imaged by an acoustic camera using the above-described frequency sweep method will be described with reference to FIG.
FIG. 8 shows the process of receiving the reflected wave 801 (dotted line) coming from the right side of the device (azimuth direction θ) as seen from the upper side of the receiving system (from the range direction), as in FIG. . The reflected wave 801 is converged at a point 804 on the piezoelectric element 803 by the acoustic lens 802. In the frequency sweep method, the ultrasonic wave focused at one point on the receiving surface by the acoustic lens is uniquely associated with the azimuth direction θ corresponding to the focal position, that is, the ultrasonic frequency fa. Therefore, ideally, at the focal point 804 on the piezoelectric element 803, only the ultrasonic wave 801 having the frequency fa corresponding to the position of the point should be detected.
However, in reality, a sound wave 805 randomly incident from the surrounding environment of the apparatus or an ultrasonic wave 806 of a different frequency reflected from a point on another channel on the receiving surface is also observed at the point 804 as reverberation in the apparatus. In other words, a ghost appears in the vertical direction of the captured image.

  In addition, in an apparatus that images a buried object by parametric ultrasonic transmission, a circuit that generates signals of two different frequencies for the primary wave and a delay circuit for changing the beam direction of the primary wave or mechanical transmission A mechanism for controlling the orientation of the waver is required, and there is a problem that the circuit scale and the apparatus scale increase.

  Examples of the present invention that solve these problems will be described below.

FIG. 9 is a diagram for explaining a receiver structure applied in an embodiment of the present invention.
In this figure, the wave receiving process is viewed from the upper side of the apparatus as in FIGS.
In FIG. 9, a reflected wave 901 (solid line, frequency fb) is incident from the front of the apparatus and converges at a point 904 on the receiving piezoelectric element 903 by an acoustic lens (not shown). The reflected wave 902 (dotted line, frequency fa, fa <fb) is incident obliquely from the right side of the apparatus and converges at a point 905 on the receiving piezoelectric element 903.
For example, as shown in FIG. 9, the thickness of the receiving piezoelectric element 903 changes continuously or stepwise, and the resonance condition (resonance filter thickness is an integral multiple of a half wavelength) corresponding to the thickness at each point. Is equal to). That is, for example, in FIG. 9, at the point 904 where the ultrasonic wave of the reflected wave 901 (frequency fb) incident from the front converges, the piezoelectric element 903 has a thickness corresponding to the half wavelength λb / 2 in the piezoelectric element 903 having the frequency fb. If the element 903 is set, the frequency fb becomes the resonance frequency and can be efficiently converted into an electric signal. On the other hand, many ultrasonic waves of other frequencies are attenuated because they do not satisfy the resonance condition. Similarly, the thickness of the piezoelectric element 903 at the focal point 905 is set so as to resonate with the ultrasonic wave having the frequency fa even with respect to the reflected wave 902 (frequency fa) incident obliquely from the right side of the apparatus. Only efficiently converted into electrical signals. The converted electric signal is taken out by the output line 906.

  FIG. 10 shows another embodiment of the present invention. In the above description, the receiving piezoelectric element is assumed to be elongated in the azimuth direction. However, when it is difficult to mount such elongated piezoelectric elements or to arrange materials, the piezoelectric elements may be divided into M pieces in the azimuth direction as shown in FIG. Since the signal lines 1002 to which the electric signals from the divided piezoelectric elements 1001 are respectively output are connected to the common signal line 1003, the electric signals including frequency components from the piezoelectric elements are decomposed in the azimuth direction by frequency analysis. To be served.

  The thickness of each of the divided piezoelectric elements 1001 is adjusted so as to resonate at the frequency of the target ultrasonic wave that converges to the corresponding focal position. Thereby, each piezoelectric element functions as a mechanical filter that efficiently converts only the target ultrasonic wave into an electric signal and removes other unnecessary ultrasonic waves.

Next, an example of the receiver structure applied in another embodiment of the present invention will be described with reference to FIG. The piezoelectric element for receiving waves is divided into M pieces in the azimuth direction, and all of the divided piezoelectric elements 1101 have the same dimensions (thickness, surface area).
In FIG. 11, when the impedance from the electrical end of each piezoelectric element 1101 to the piezoelectric element side is measured, the reactance component is capacitive and is set to Ci (i = 1, 2,..., M), respectively. Now, since the dimensions of the piezoelectric element 1101 are the same, the values of the capacitances Ci are substantially equal. On the other hand, signal output lines 1102 from which electric signals are output from the respective piezoelectric elements 1101 are connected to a common signal line 1104 via respective inductances Li (i = 1, 2,..., M) 1103 in series. (The ground wire from the piezoelectric element is not shown). Any value can be selected as the inductance value.
Therefore, for example, the inductance La is set so as to satisfy the well-known resonance condition fa = 1 / {2π√ (La Ca)} with respect to the frequency fa of the target ultrasonic wave 1105 that is known to converge to the position of the piezoelectric element a. If this value is set, only the component of the target ultrasonic wave can be efficiently converted into an electric signal and extracted into an electric circuit. Unwanted ultrasonic waves that do not satisfy the resonance condition are attenuated and removed.

  In this embodiment, since the signal line 1102 from each piezoelectric element 1101 is connected to the common signal line 1104, different frequency components from each piezoelectric element 1101 are superimposed on the final output signal. Therefore, in order to separate and detect each frequency component, it is necessary to perform frequency analysis on the final output signal. However, a configuration is also conceivable in which signal lines from each piezoelectric element are not combined into a common line, but are individually amplified and A / D converted, and then signal processed by a computer or dedicated hardware. In that case, frequency analysis is unnecessary, but the circuit scale becomes large.

Next, the example of the receiver structure in another Example is demonstrated using FIG.
In FIG. 12, the receiving piezoelectric element is divided into M pieces in the azimuth direction. The signal output lines 1202 from each piezoelectric element 1201 are not combined into a common line as shown in FIG. 11, and are individually connected to an amplifier 1203, an A / D converter (ADC) 1204, and a digital bandpass filter (BPF) 1205. It is connected. The digital BPF 1205 is a digital signal processing device that equalizes only a designated frequency band among frequency components included in an input digital signal. The transmission frequency can be arbitrarily set.
Therefore, for example, if the digital BPF a connected to the piezoelectric element a is set so that only the frequency (fa) component of the target ultrasonic wave 1206 known to converge at the position of the piezoelectric element a is transmitted, Only the target ultrasound can be extracted into the digital signal, and other unwanted ultrasound can be removed.

Below, the Example in the underwater acoustic camera for buried object identification is described.
FIG. 13 shows an example of the structure of the piezoelectric element array for transmitting in one embodiment of the present invention.
In FIG. 13, the structure of the piezoelectric element array 1301 for transmission is the same as that described with reference to FIG. 2, and the piezoelectric elements 1302 are arranged in a line with their polarization directions (arrows 1303) interchanged. For simplicity, electrodes and power supply are not shown. In order to obtain a parametric effect, a signal having components of two frequencies f1 and f2 corresponding to the primary wave is synthesized and input to each piezoelectric element. Thereby, the primary wave 1304 corresponding to the component of the frequency f1 is transmitted to the azimuth direction θ1, and the primary wave 1305 corresponding to the frequency f2 is simultaneously transmitted to the azimuth direction θ2. A secondary wave 1306 due to the parametric effect is generated in the direction in which both waves overlap.

  Since the ultrasonic waves are radiated symmetrically from both ends of the piezoelectric element array 1301 as shown in FIG. 13, the piezoelectric element array is arranged obliquely with respect to the direction facing the apparatus as shown in FIG. A configuration in which only the emitted secondary wave is used for imaging can be considered. When changing the transmission direction of the secondary wave, the values of the frequencies f1 and f2 are changed. At this time, if the difference frequency Δf is constant, when receiving the reflected wave of the secondary wave, the azimuth direction decomposition cannot be performed by frequency analysis, so that the difference frequency Δf changes corresponding to the transmission direction uniquely. And change f2.

It is not practical to apply the embodiment described with reference to FIGS. 9 and 10 to the embodiment described with reference to FIG. This is because the secondary wave generated by the parametric effect is set at a low frequency (several k to 10 kHz) so as to be suitable for propagation in the deposited layer, so that the receiving piezoelectric element that resonates with it is too thick. Because.
Therefore, a configuration in which the embodiment described in FIGS. 11 and 12 is applied to the embodiment described in FIG. Each will be described below.

  First, the case where the embodiment of FIG. 11 is applied to the embodiment of FIG. 13 will be described. In this embodiment, the transmission wave applied to the buried object is a parametric secondary wave by a frequency sweep method, and the receiver is connected in series with an electric analog filter similar to the receiver of FIG. 11 to each piezoelectric element. Thus, unnecessary signal components are removed, noise and ghost in the image are reduced, and the circuit scale is reduced.

  Next, the case where the embodiment of FIG. 12 is applied to the embodiment of FIG. 13 will be described. In this embodiment, the transmission wave applied to the buried object is a parametric secondary wave by a frequency sweep method, and a digital bandpass filter similar to the receiver of FIG. 12 is connected in series to each piezoelectric element. Thus, unnecessary signal components are removed, noise and ghost in the image are reduced, and the circuit scale is reduced.

  FIG. 14 is an apparatus block diagram in an embodiment in which FIG. 11 is applied to FIG. 11, FIG. 12, and FIG. The transmission control device 1401 sets the frequency, pulse time width, etc. of the transmission signal to the waveform generator 1402 and instructs the output timing. Also, the transmission control device 1401 controls the switch 1403 to instruct which of the amplifiers (AMP) 1404 and 1405 the signal is input to. The waveform generator 1402 generates a signal waveform having a single frequency or a signal waveform having a plurality of frequency components based on the setting, and inputs the signal waveform to the amplifier 1404 or 1405 connected via the switch 1403. The amplifier 1404 is connected to the left piezoelectric element array 1406, for example, and the amplifier 1405 is connected to the right piezoelectric element array 1407. The amplifier 1404 or 1405 amplifies the input signal and transmits the amplified signal to the piezoelectric element array 1406 or 1407 connected thereto. As described with reference to FIG. 2, the piezoelectric elements for transmission included in the piezoelectric element arrays 1406 and 1407 have their polarization directions interchanged between adjacent elements, so that the transmission wave is transmitted in the direction depending on the frequency component in the input waveform. Is output.

  The receiver is composed of N receiving piezoelectric elements (No. 1, 2,..., N) 1408 divided as channels in the range direction as described with reference to FIG. In the tenth embodiment, the thickness of each receiving piezoelectric element is set to resonate at a target frequency. In the embodiment of FIG. 11 and the embodiment in which FIG. 11 is applied to FIG. 13, the thickness of each receiving piezoelectric element is the same, but an inductance (not shown) is connected in series with each other. The reflected wave is converted into an electric signal by the receiving piezoelectric element 1408, and unnecessary signals are removed by the filter action in each invention. Further, the electric signal is amplified by an amplifier (AMP) 1409 of each channel and then converted into a digital signal by an A / D converter (ADC) 1410. The digital signal is stored in a memory 1412 in a computer 1411. In an arithmetic processing unit 1413 in the computer, an azimuth azimuth direction analysis of an object by frequency analysis, a range azimuth analysis by channel decomposition, and an apparatus-object difference due to a transmission / reception time difference. An image is generated by analyzing the distance. The frequency analysis may be separately performed on dedicated hardware (not shown). Finally, the generated image is output to the display device 1414. The operation panel 1415 provides an interface with the user and includes a keyboard and a mouse. The user sets specifications of the transmission signal, analysis conditions, image display conditions, and the like for the transmission control device 1401 and the computer 1411 via the operation panel 1415.

  FIG. 15 is an apparatus block diagram in an embodiment in which FIG. 12 is applied to FIGS. It consists of a total of N × M receiving piezoelectric elements 1408 for N channels in the receiver range direction and M channels in the azimuth direction. The reflected wave is converted into an electric signal by each receiving piezoelectric element, and then amplified and A / D converted for each channel. In the embodiment in which FIG. 12 is applied to FIG. 12 and FIG. 13, for each digital signal after A / D conversion, only a target frequency component is extracted by a digital bandpass filter (BPF) 1501 and a noise component is removed. Each digital signal is stored in the memory 1412 in the computer 1411. The arithmetic processing unit 1413 in the computer 14 performs range azimuth analysis by channel decomposition, azimuth azimuth analysis, device-object distance analysis by transmission / reception time difference, and the like. And generate an image. Other components are the same as those in FIG.

It is a figure which shows the structure of the whole underwater image imaging system containing a general underwater image imaging device. It is a figure which shows typically the structure of the transmitter of a frequency sweep type underwater acoustic camera. It is the figure which showed an example of the transmitter structure in the case of applying a frequency sweep system to an underwater acoustic camera. It is a figure explaining the process until the transmission wave emitted from the transmitter is reflected by the surface of a target object. It is a figure explaining the process in which the receiving system of an underwater acoustic camera receives the reflected wave from an object. It is the figure which showed the method which decomposes | disassembles the incident direction of a reflected wave about a range azimuth | direction. It is the figure which showed the method of decomposing | disassembling the incident direction of a reflected wave about an azimuth direction. It is a figure explaining the subject in the ultrasonic type underwater image pick-up device using a frequency sweep system. It is a figure explaining the receiver structure in one Example of this invention. It is a figure explaining the receiver structure in one Example of this invention. It is a figure explaining the receiver structure in one Example of this invention. It is a figure explaining the receiver structure in one Example of this invention. It is a figure explaining the structure of the piezoelectric element arrangement | sequence for wave transmission in one Example of this invention. [BRIEF DESCRIPTION OF THE DRAWINGS] It is a block diagram of the whole apparatus to which one Example of this invention is applied. [BRIEF DESCRIPTION OF THE DRAWINGS] It is a block diagram of the whole apparatus to which one Example of this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Underwater acoustic camera 102 Ship etc. 103 Target object 104 Transmitter 105 Transmission wave 106 Reflected wave 107 Acoustic lens 201 Piezoelectric element 202 Polarization direction 203 of piezoelectric element Electrode 204 Common electrode 205 Power supply 206 Transmission wave 207 of frequency fa Transmission of frequency fb Wave 301 Transmitter 302 Left-side transmitting piezoelectric element array 303 Right-side transmitting piezoelectric element array 304 Imaging directions 305a to 305h Transmitting wave 306 Field of view 307 Target object 401 Transmitter 402 Target object 403 Transmitting wave 404 Imaging direction 405 Reception system 501 Acoustic lens 502 Receiver 503 Receiver piezoelectric element 504 Reflected wave 505 Focus 601 Reflected wave 602 incident from the front of the apparatus Reflected wave 603 incident from below the apparatus (range azimuth φ) Receiver 604 For receiving waves Piezoelectric element 605 Acoustic lens 606 Reflected wave incident from the front of the device Focal point 607 Electric signal 608 from channel i Focal point 609 of reflected wave incident from below device (range azimuth φ) Reflected wave 701 incident from front of device 702 Reflected wave 702 incident from front of device azimuth azimuth θ Reflected wave 703 Received piezoelectric element 704 Acoustic lens 705 Electrical signal 706 converted by received piezoelectric element Spectrum 707 obtained by Fourier transform of electrical signal Peak 708 corresponding to reflected wave of frequency fa Corresponding to reflected wave of frequency fb Peak 801 Reflected wave 802 incident from azimuth azimuth θ Acoustic lens 803 Received piezoelectric element 804 Focus 805 Noise arriving from surrounding environment 806 Wave reflected from received piezoelectric element of other channel 901 Frequency fb incident from front of apparatus Wave 902 Wave 903 of frequency fa incident from obliquely receiving piezoelectric element 9 4 Focal point 905 of wave incident from front 906 Focal point 906 of wave incident obliquely Signal output line 1001 Divided piezoelectric element 1002 Signal line 1003 Common signal line 1101 Divided piezoelectric element 1102 Signal line 1103 Inductance 1104 Common signal line 1105 Target ultrasonic wave 1201 Received piezoelectric element 1202 Signal line 1203 Amplifier 1204 A / D converter 1205 Digital band pass filter 1206 Target ultrasonic wave 1301 Transmitted piezoelectric element array 1302 Transmitted piezoelectric element 1303 Polarization direction 1304 Transmission primary corresponding to frequency f1 Wave 1305 Transmission primary wave 1306 corresponding to frequency f2 Secondary wave 1401 due to parametric effect of transmission waves of frequencies f1 and f2 Transmission wave control device 1402 Waveform generator 1403 Switch 1404, 1405 Amplifier 1406, 1407 Piezoelectric element for transmission Sub array 1408 Receiver 1409 Receiver amplifier 1410 A / D converter 1411 Computer 1412 Memory 1413 Processing unit 1414 Display unit 1415 Operation panel 1501 Digital band pass filter

Claims (6)

An underwater imaging device that irradiates an object with ultrasonic waves in water and images the object by reflected waves from the object,
A transmitter applying a frequency sweeping method capable of controlling the direction of a transmission wave by changing the frequency of an electric signal input to the piezoelectric element for transmission ;
An acoustic lens for converging the reflected wave from the object;
Receiving a reflected wave converged by the acoustic lens and converting it into an electrical signal;
The wave receiver includes a wave receiving piezoelectric element, and the ultrasonic waves having different frequencies arriving at the points on the wave receiving piezoelectric element are related by the positions of the points on the wave receiving piezoelectric element. An underwater image capturing apparatus comprising: a filter that transmits a target frequency component to be transmitted; and the frequency component transmitted through the filter is converted into an electrical signal. An underwater imaging device that irradiates an object with ultrasonic waves in water and images the object by reflected waves from the object,
A transmitter applying a frequency sweeping method capable of controlling the direction of a transmission wave by changing the frequency of an electric signal input to the piezoelectric element for transmission ;
An acoustic lens for converging the reflected wave from the object;
Receiving a reflected wave converged by the acoustic lens and converting it into an electrical signal;
The wave receiver has a piezoelectric element for reception, by continuously or stepwise changing the thickness of the piezoelectric element for the reception, change the resonant frequency at each position of the piezoelectric element for receiving waves and, a resonance frequency at each point on the piezoelectric element for receiving waves, set to match the frequency of advance before Symbol object that has been determined for each point, into an electrical signal ultrasonic frequencies that purpose conversion to Rukoto underwater imaging apparatus characterized. An underwater imaging device that irradiates an object with ultrasonic waves in water and images the object by reflected waves from the object,
A transmitter applying a frequency sweeping method capable of controlling the direction of a transmission wave by changing the frequency of an electric signal input to the piezoelectric element for transmission ;
An acoustic lens for converging the reflected wave from the object;
Receiving a reflected wave converged by the acoustic lens and converting it into an electrical signal;
The receiver has a plurality of receiving piezoelectric elements divided into a plurality, and an inductance is connected in series to each of the receiving piezoelectric elements, and the value of the inductance is changed, whereby the receiving change the resonance frequencies of the piezoelectric element, the resonance frequency of each of the piezoelectric elements for the wave reception is ultrasound extracted set to meet the purpose of the frequency coming to the piezoelectric element for receiving waves An underwater imaging device characterized by converting into an electrical signal. An underwater imaging device that irradiates an object with ultrasonic waves in water and images the object by reflected waves from the object,
A transmitter applying a frequency sweeping method capable of controlling the direction of a transmission wave by changing the frequency of an electric signal input to the piezoelectric element for transmission ;
An acoustic lens for converging the reflected wave from the object;
Receiving a reflected wave converged by the acoustic lens and converting it into an electrical signal;
The wave receiver is provided with the reception piezoelectric element that will receive the reflected wave of the transmission wave, and means for converting the analog signal waveform into digital signal waveform outputted from the piezoelectric element for respective reception, respective a digital signal processing means for transmitting the component of a specific frequency band Chi sac frequency component included in a digital signal waveform, and means for setting a translucent over-frequency in each optionally set for each piezoelectric element for the reception permeate frequency is set to match the purpose of the frequency coming to the piezoelectric element for receiving waves, it you transmitting underwater imaging apparatus wherein an ultrasonic wave of a frequency the set as a digital signal . Simultaneously transmitting ultrasonic waves of two different frequencies in water, meet their parametric equation buried object identification for underwater imaging device for imaging buried objects deposited layer in water using a secondary wave generated by parametric effect And
A frequency sweep method is adopted as a transmission method, and an electric signal including two different frequency components f1 and f2 is input to a transmission piezoelectric element, whereby a parametric secondary wave having a difference frequency Δf = | f1−f2 | a wave transmitter which is generated and controlled by the transmission direction of the parametric secondary wave to change the value of the input frequency components f1, f2,
An acoustic lens for converging the reflected wave from the object;
Receiving a reflected wave converged by the acoustic lens and converting it into an electrical signal ;
Receiving duplexer has possess a piezoelectric element for reception, which is divided into a plurality, the inductance connected in series with the piezoelectric element for the respective reception, by changing the value of the inductance, receiving waves use piezoelectric elements to change the respective resonant frequencies, the resonant frequency of each of the piezoelectric elements for the reception, and set to match the frequency of interest coming to the piezoelectric element for receiving waves, and the set frequency ultrasound underwater imaging apparatus for parametric ultrasonic implant which was characterized by conversion to Rukoto into an electric signal. Simultaneously transmitting ultrasonic waves of two different frequencies in water, meet their parametric equation buried object identification for underwater imaging device for imaging buried objects deposited layer in water using a secondary wave generated by parametric effect And
A frequency sweep method is adopted as a transmission method, and an electric signal including two different frequency components f1 and f2 is input to a transmission piezoelectric element, whereby a parametric secondary wave having a difference frequency Δf = | f1−f2 | a wave transmitter which is generated and controlled by the transmission direction of the parametric secondary wave to change the value of the input frequency components f1, f2,
An acoustic lens for converging the reflected wave from the object;
Receiving a reflected wave converged by the acoustic lens and converting it into an electrical signal ;
Receiving duplexer includes a piezoelectric element for reception, which is divided into a plurality, and means for converting the analog signal waveform into digital signal waveform outputted from the piezoelectric element for the respective reception, the respective digital signal waveform Among the included frequency components, there are digital signal processing means for transmitting a component in a specific frequency band , and means for arbitrarily setting the transmission frequency, and the transmission frequency set for each of the receiving piezoelectric elements is the set to match the frequency of the object coming to the piezoelectric element for receiving waves, a parametric ultrasonic implant for underwater imaging apparatus, wherein the retrieving the ultrasound with a frequency the set as a digital signal .

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