JP5603355B2 - Ultrasonic measuring device - Google Patents

Description

  The present invention relates to an ultrasonic measurement device, and more particularly to an ultrasonic measurement device that measures a target in water.

  An ultrasonic measurement device represented by a sonar or the like measures the position of a target to be measured using ultrasonic waves in water (Patent Documents 1 and 2). Such an underwater ultrasonic measurement device generally includes an array-type transducer, a transmission unit, a reception unit, an image forming unit, and the like. The array-type transducer is composed of, for example, a plurality of conversion elements (a plurality of ultrasonic vibration elements) arranged one-dimensionally. Instead of such a line array type converter, a two-dimensional array type converter may be used. There is also known an ultrasonic measurement apparatus that performs detection or the like by receiving ultrasonic waves from a sound source without performing transmission.

  The above conventional line array type transducer is generally composed of a large number of transducer elements arranged at intervals of 0.5λ as the pitch between the elements, where λ is the wavelength corresponding to the center frequency of the ultrasonic wave. . This is because the directivity width of the main pole and the level of the sub-pole in the directivity characteristics are appropriate.

  FIG. 11 schematically shows general directivity characteristics of a line array type transducer. In the figure, the horizontal axis indicates the azimuth (θ), and the vertical axis corresponds to the amplitude or the response. Here, the amplitude level (dB) is indicated. In the illustrated example, a main pole (main lobe) 54 is formed in the direction of θ = 0 °. That is, this directivity characteristic is generated as a result of applying a phasing process (phasing addition process) to a plurality of received signals output from a plurality of conversion elements while setting the phasing direction to 0 °. is there. A plurality of sub-poles (side lobes) are generated on both sides of the main pole 54, and specifically, a first sub-pole 56 and a second sub-pole 58 are generated on both sides of the main pole 54. In the main pole 54, the directivity width 62 is defined by the beam width when the level is attenuated by 3 dB from the peak 60.

  In addition, if the sound wave from the target arrives in the direction where the main pole exists, the target can be detected, but if the interference sound comes from the direction where the sub-pole exists, it arrives from the main pole direction. Misidentified as a sound wave. That is, a situation of pseudo detection occurs. Therefore, it is desirable to reduce the level of the sub pole as much as possible. In order to improve the image quality when imaging the target or to increase the accuracy of specifying the position of the target, it is desirable to make the directivity width 62 of the main pole 54 smaller. From such a background, conventionally, an array type converter is composed of a number of conversion elements. For example, when the center frequency is 500 kHz, about 100 conversion elements are required to narrow the directivity width to 1.0 degree.

JP 7-225273 A JP-A-8-82664

  In an ultrasonic measurement device, if the number of conversion elements is increased in order to increase measurement accuracy, the configuration of the transmitter / receiver (or receiver) becomes complicated and large, and the number of reception channels also increases. The scale will increase. This causes a problem that the apparatus cost increases. On the other hand, if the number of conversion elements is simply reduced without any treatment, the measurement accuracy is lowered, and problems such as an increase in artifacts and a decrease in azimuth resolution occur on the image.

  An object of the present invention is to make it possible to improve directivity characteristics without increasing the number of conversion elements constituting an array type transducer in an ultrasonic measurement apparatus.

  Alternatively, an object of the present invention is to provide an excellent directivity characteristic by subsequent signal processing even if the number of conversion elements constituting an array type transducer is reduced in an ultrasonic measurement apparatus. .

  An ultrasonic measurement apparatus according to the present invention includes an array type transducer that includes a plurality of transducers arranged in water and outputs a plurality of reception signals by receiving ultrasonic waves, and the plurality of reception signals. By executing the phasing and adding process while changing the phasing direction, a phasing that generates a plurality of phasing signals corresponding to a plurality of phasing directions as a signal sequence reflecting the directional characteristics of the array converter is performed. Adding means; and amplitude difference enlargement processing means for applying an amplitude difference enlargement process for improving the directivity of the array converter afterwards to the plurality of phasing signals.

  According to the above configuration, the phasing addition processing is sequentially applied to the plurality of received signals output from the plurality of conversion elements while changing the phasing azimuth (main pole azimuth). A plurality of corresponding phasing signals (signals indicating the phasing addition result) are generated. The plurality of phasing signals constitute a signal string reflecting the directivity characteristics of the array converter. By applying the amplitude difference enlargement process to them, the directivity characteristics of the array converter can be improved afterwards. More specifically, in the directional characteristics with the horizontal axis as the azimuth and the vertical axis as the amplitude (signal level), the amplitude difference (signal level difference) is generally between the main pole (main beam) and the sub pole (side lobe). Exists. The amplitude difference enlargement process is a process for further widening such an amplitude difference. An exponential function is given as a function for performing such processing, and a preferred example thereof is N-th power processing described later.

  As a result of the amplitude difference enlargement process, the amplitude of the signal component corresponding to the main pole is relatively larger than that of the main pole, or the amplitude of the sub-pole other than the main pole and other unnecessary signal components is relatively larger than that of the main pole. Get smaller. In addition, in the directivity, the width of the main pole (directivity width) becomes sharper. When multiple phasing signals are imaged, the resolution (azimuth resolution) is improved by the above amplitude difference enlargement process, and unnecessary components such as background and artifacts are reduced, so the image quality is greatly improved. obtain. Alternatively, on the premise of the subsequent improvement of the directivity, it is possible to obtain the same directivity (or image quality) as before even by reducing the number of conversion elements while increasing the pitch between the conversion elements. For the receiving unit, it is possible to obtain advantages such as a reduction in quantity and simplification of configuration. This leads to a reduction in device costs.

  Preferably, the amplitude difference enlargement processing unit applies N-th power processing (where N> 1) to a data string composed of a plurality of pieces of data having the same distance relation taken out from the plurality of phasing signals. N-th power processing means.

  For example, when a sound source at a certain azimuth and a certain distance is assumed, a sound wave coming from the sound reaches the array transducer, and a plurality of reception signals are output from a plurality of transducer elements constituting the array transducer. A plurality of phasing signals are generated by performing phasing addition processing with different phasing directions for them. Usually, each phasing signal is composed of a plurality of data (amplitude values) arranged in the distance direction (time direction). A data string having the same distance relationship (same time relationship) extracted from such a plurality of phasing signals indicates a response characteristic for a plurality of phasing directions, which corresponds to a directivity characteristic. When the N-th power process is applied to such a data string, the other portion is suppressed with respect to the portion corresponding to the main pole, and the amplitude difference between the two increases. As a result, the directivity is improved. N is a numerical value of 1 or more, and it is desirable to adopt an integer such as 2 or 3 as N for convenience of calculation, but a numerical value with a decimal number such as 1.5 may be employed as N. If the configuration is such that N can be variably set, for example, the optimum N can be determined while referring to an image. The adaptive setting of N may be automated.

  Preferably, the amplitude difference enlargement processing unit further performs a normalization process on the data string to generate a normalized data string, and the N-th power process is applied to the normalized data string. And preprocessing means for performing amplitude restoration processing on the normalized data string after the N-th power process to generate a plurality of restored data strings.

  According to the above configuration, normalization processing is applied as preprocessing to data strings extracted from a plurality of phasing signals. For example, a process of dividing other amplitude values by the maximum amplitude value is applied. In that case, the maximum amplitude value is converted to 1.0, and the other amplitude values are converted to numerical values in the range of 0 to 1.0. After that, an N-th power process is applied to the normalized data string to expand the amplitude difference. Thereafter, post-processing for restoring the amplitude is applied to the normalized data string after the N-th power process. The amplitude restoration process is preferably multiplication of the maximum amplitude value for each piece of data. As a result, the maximum amplitude value is restored to the original amplitude value, and the other amplitude values are restored (converted) to an amplitude value lower than the original amplitude value. It should be noted that the amplitude value restoration process may be omitted in a predetermined case where imaging is not performed. Alternatively, it is possible to apply the N-th power process without performing normalization.

  Desirably, the inter-element pitch p in the plurality of conversion elements satisfies the condition of 0.5λ <p <1.0λ, where λ is the wavelength at the center frequency of the ultrasonic wave. In other words, the inter-element pitch is normally 0.5λ, but if the inter-element pitch p is made larger than that, it is possible to reduce the number of conversion elements while ensuring a constant reception aperture. If the pitch between the elements is simply increased, the directional characteristics will deteriorate. However, since the directional characteristics can be improved by applying the amplitude difference enlargement process afterwards, it is possible to obtain the same or higher image quality than before. It becomes. A mechanism for changing the inter-element pitch may be provided, and an optimal inter-element pitch may be set according to the situation. According to the above configuration, since the number of conversion elements can be reduced, it is easy to employ such a pitch variable mechanism.

  According to the present invention, in the ultrasonic measurement apparatus, the directivity can be improved without increasing the number of conversion elements constituting the array type converter. Alternatively, even if the number of conversion elements constituting the array type converter is reduced, it is possible to obtain excellent directivity characteristics by subsequent signal processing.

1 is a block diagram showing the overall configuration of an ultrasonic measurement apparatus according to the present invention. It is a schematic diagram of a line array type transducer. It is a conceptual diagram for demonstrating an amplitude difference expansion process. It is a figure which shows the 1st display example. It is a figure which shows the 2nd example of a display. It is a figure which shows the directional characteristic as a 1st comparative example. It is a figure which shows the directional characteristic as a 2nd comparative example. It is a figure which shows the directional characteristic as a 3rd comparative example. It is a figure which shows an example of the directivity obtained by application of an amplitude difference expansion process. It is a figure which shows the other example of the directivity obtained by application of an amplitude difference expansion process. It is a figure which shows a general directivity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the overall configuration of the ultrasonic measurement apparatus according to this embodiment. This ultrasonic measurement device is a device that performs measurement such as detection and imaging of a fixed target or a moving target in the sea or lake, and in this embodiment, the ultrasonic measurement device constitutes a sonar. Yes. This ultrasonic measurement apparatus is mounted on, for example, a water moving body such as a ship and an underwater moving body such as a submersible craft. Of course, it may be mounted on a floating body, a fixed structure or the like, or may be carried by a diver or the like.

  The ultrasonic measurement device is roughly classified into a line array type transducer 10 composed of a plurality of elements (ultrasonic vibration elements) 10 a, a switch 14 connected to the line array transducer 10, and a switch 14. The connected transmission unit 16, the reception unit 18 also connected to the switch 14, the amplitude difference expansion processing unit 32 provided at the subsequent stage of the reception unit 18, and the subsequent stage of the amplitude difference expansion processing unit 32 The image processing unit 44 includes a display unit 46 connected to the image processing unit 44. The illustrated configuration realizes an active method for transmitting and receiving ultrasonic waves, but the present invention may be applied to a passive method for receiving ultrasonic waves from a sound source.

  The line array type transducer 10 is disposed in water and transmits and receives ultrasonic waves. At the time of transmission, an ultrasonic wave is generally transmitted as a pulse, and an echo from a target is received. In FIG. 1, the azimuth angle is 0 degrees from the central origin of the line array transducer 10 and the phasing azimuth (main pole azimuth) is set to an arbitrary azimuth by a phasing addition process described later with the azimuth angle being 0 degrees. It is possible to set. In FIG. 1, the angle of the phasing direction is represented by θ. The pitch between elements is expressed by p. In this embodiment, when the wavelength corresponding to the center frequency of the transmission ultrasonic wave is λ, the line array transducer 10 is set so that the inter-element pitch p satisfies the condition of 0.5λ <p <1.0λ. It is configured. This is intended to reduce the number of elements constituting the reception aperture while securing a certain reception aperture on the premise of improving the directivity by an amplitude difference enlargement process described later. This will be described in detail later. A two-dimensional array type transducer can be used as the transducer.

  The transmission unit 16 is connected to the line array type transducer 10 via the switch 14, and a transmission pulse is supplied from the transmission unit 16 to n elements at the time of transmission. On the other hand, in the reception period, n reception signals output from the n elements are sent to the reception unit 18 via the switch 14. Each received signal is a continuous waveform signal over a fixed time. The amplitude at each time represents the echo intensity.

  The receiving unit 18 includes n received signal processors and an adder (phased adder) 26. Each received signal processor includes an amplifier 20, a BPF (band pass filter) 30, an A / D converter 22, and a memory 24 in the illustrated example. That is, the reception signal output from each element is amplified, processed into a signal of the same wavenumber band corresponding to the pitch p between elements, converted into a digital signal, and temporarily stored in the memory 24. The plurality of memories 24 may be configured by a single storage device. The BPF band may be variable.

  In the present embodiment, the receiving unit 18 repeats the phasing addition processing while changing the phasing direction with a predetermined angular pitch for the n reception signals stored in the n memories 24, thereby A phasing signal (a signal indicating a phasing addition result) is generated. More specifically, for example, assuming that the central azimuth is 0 degrees, the phasing azimuth is changed at a pitch of 0.5 degrees, for example, at a azimuth range of -90 degrees to +90 degrees, and the phasing addition processing is performed for each phasing Is running. Thereby, for example, 360 phasing signals are obtained. Each phasing signal is composed of a plurality of data (amplitude addition values) arranged in the time axis (distance axis on the main pole direction) direction. The adder 26 adds n received signals under the control of a phasing addition control unit (not shown). Various processes are applied to these received signals as necessary.

  The amplitude difference enlargement processing unit 32 applies processing for improving the directivity characteristics afterwards to a plurality of phasing signals generated corresponding to a plurality of phasing angles. That is, in the directivity characteristics, the amplitude difference enlargement process is performed so that the directivity width of the main pole is narrowed and, at the same time, sub-poles other than the main pole are suppressed. For this reason, in the illustrated example, the amplitude difference expansion processing unit 32 normalizes a memory 34 that stores a plurality of phasing signals and a data string that is extracted from the plurality of phasing signals so as to traverse it. A processor 36, an N-th power processor 38 that performs N-th power processing (where N> 1) on the normalized data sequence, a restoration processing device 40 that restores the amplitude of the data sequence after the N-th power processing, And a memory 42 in which the restored data sequence is sequentially stored and thereby a plurality of processed phasing signals are reconstructed. Details of the processing will be described later with reference to FIG.

  The image processing unit 44 forms an image based on a plurality of phasing signals stored in the memory 42. The image data is sent to the display unit 46. As a result of improving the directivity by the amplitude difference enlargement process, it is possible to improve the image quality even with a small number of elements. That is, azimuth | direction resolution can be improved and unnecessary components, such as an artifact, can be suppressed.

  FIG. 2 schematically shows the line array transducer 10 described above. The line array type transducer 10 includes n elements (ultrasonic vibration elements) 10a arranged in a straight line, and an insulating material 48 that acoustically and electrically separates the elements is provided between adjacent elements. Is provided. As indicated by reference numeral 50, ultrasonic waves are transmitted by the line array type transducer 10, and echoes that arrive sequentially immediately after that are received by the line array type transducer 10. As a result, n reception signals are output from the n elements constituting the reception aperture. In FIG. 2, a backing material, a substrate, and the like are not shown.

  When the element pitch variable configuration is adopted, a slide mechanism such as a pantograph and a drive source such as a motor for driving the pantograph are disposed, and the element pitch is changed by a user operation or automatically. In that case, the insulating material 48 between the elements may be changed to an air layer, or an insulating material 48 having elasticity may be used. When the element pitch is changed, it is desirable to vary the BPF band accordingly.

  Incidentally, the directivity obtained by the phasing addition process can be obtained by computer simulation. Assuming a line array transducer, the number of elements n, the center frequency f of transmitted ultrasonic waves (for example, 500 kHz), the pitch p between elements (for example, 0.817λ), the azimuth angle γ, and the underwater sound velocity c (1500 m / s) Can be expressed as follows. Equation (1) shows the relationship between the center frequency f and the wavelength λ. Expression (2) is an expression for obtaining the directivity characteristic R. Equation (3) indicates a directivity characteristic T obtained by logarithmic conversion of the directivity characteristic R.

  When the phasing azimuth θ = 0 ° as in the following equation (4), the directivity characteristics R and T can be expressed as the following equations (5) and (6), respectively.

  It is possible to set the inter-element pitch p in advance or variably set according to the situation based on the computer simulation result using the above calculation formula. Further, it is possible to set the numerical value of N in the N-th power process in advance using such a computer simulation result or to variably set it according to the situation.

  FIG. 3 schematically shows the contents of the process by the amplitude difference enlargement processing unit 32 shown in FIG. 1, that is, the contents of the amplitude difference enlargement process for improving the directivity afterwards.

  (A) shows the storage space of the memory 34. The vertical direction corresponds to the phasing direction, and the horizontal direction (right direction) indicates time (corresponding to the distance of the main pole direction). A plurality of phasing signals 66 are stored in the memory 34. As described above, for example, when the phasing addition processing is sequentially executed while setting the phasing direction in increments of 0.5 ° from −90 ° to + 90 °, 360 phasing signals are generated and stored in the memory. 34 is stored. Each phasing signal is composed of a plurality of data 66a arranged in the time axis direction. Each data is a phasing addition value. As indicated by S10, a plurality of data 68 corresponding to the designated time (data number) is extracted from the plurality of phasing signals so as to cross them. That is, a plurality of data having the same distance relationship is extracted. Basically, one data is extracted from one phasing signal. A plurality of extracted data (for example, 360 pieces of data) form a data string.

  In (B), the data string 70 is shown as a waveform (profile). The horizontal axis indicates the direction, and the vertical axis indicates the amplitude. The same applies to the horizontal and vertical axes of other waveforms described later. In the example shown in (B), for example, a sound source (target) is present at an azimuth of 0 °, and the maximum amplitude occurs when the phasing azimuth coincides with the sound source azimuth. That is, the amplitude of the data extracted from the phasing signal corresponding to the phasing direction 0 ° constitutes the maximum value. When the phasing azimuth shifts from the sound source azimuth and the sound source azimuth matches the azimuth corresponding to the sub-pole, a certain amount of amplitude is generated. That is, when a data string is expressed as an amplitude waveform, it corresponds to a directivity characteristic.

  A normalization process is applied to the data string as shown in S12. That is, a process of dividing individual amplitude values by the maximum value is applied. Thereby, the normalized data string 72 shown in (C) is generated. There, the maximum value is converted to 1, and the other values take values between 0 and 1.0. This normalization processing corresponds to pre-processing for preventing the N-th power processing result from being divided due to a difference in amplitude value in the next N-th power processing. S14 represents the Nth power process. That is, the individual data constituting the normalized data string is subjected to the Nth power process. For example, if N is 2, the data is squared, and if N is 3, the data is cubed. An N-th power process with a decimal value such as a power of 1.5 may be executed.

  (D) shows the result of the N-th power process. That is, the normalized data string 74 after the Nth power process is shown. After the Nth power process, the maximum value is 1 and is unchanged, but the levels other than the portion corresponding to the main pole are considerably lowered, that is, unnecessary components are suppressed. The shoulder corresponding to the part corresponding to the main pole is also lowered, and the directivity width is narrowed. Such an amplitude difference enlargement process corresponds to a subsequent improvement of the directivity. Theoretically, the higher the value of N, the larger the amplitude difference between the portion corresponding to the main pole and the other portion. In practice, it is desirable to set an integer such as 2 or 3 as N from the viewpoint of calculation convenience and practical effects. Of course, N may be variably set to find an optimum numerical value.

  After that, as shown in S16, the restoration process is applied to the normalized data string after the Nth power process. (E) shows a restored data string 76 after the restoration process is applied. In the restoration process, each data is multiplied by the maximum value used in the normalization process. Thereby, the maximum value is restored to the original amplitude value. The other values are restored to values lower than the original amplitude value according to the amplitude difference from the maximum value.

  The above processing is executed step by step in the time axis direction from the reception origin. That is, data sequences are sequentially extracted in the distance direction, and the above processing is applied to each of them. However, it is possible to change the extraction sequence of the data string.

  (F) schematically shows the storage space of the memory 42. As shown in S18, the restored data string after the restoration process is written in the memory 42. A plurality of data strings are sequentially processed, a plurality of restored data are sequentially stored in the memory 42, and finally, a plurality of phasing signals subjected to the amplitude difference expansion processing are reconstructed in the storage space. Each phasing signal 80 is composed of a plurality of data, and each data 80a has an amplitude value after the N-th power process is applied.

  In the above example, the sound source (target) is present at the azimuth of 0 °. Of course, the same processing as described above can be applied even when the sound source is present in another azimuth. Even if there are a plurality of sound sources, processing can be basically performed in the same manner as described above. However, if a plurality of sound sources interfere with each other and the calculation cannot be performed properly, the target signal component may be narrowed down by a band pass filter, for example.

  In the Nth power process, the Nth power process may be performed by exponential calculation using a floating point function, instead of repeating multiplication of the same numerical value. In the following formula (7), a calculation example of x = 15 ^ 1.1 is shown. By using the logarithm in the exponent calculation, multiplication turns into addition and division turns into subtraction. In the manual calculation, the true number x can be obtained by interpolation on a logarithmic table. It is desirable to set the numerical value of N so as to reduce the accumulation of errors and digits loss in the amplitude difference enlargement process.

  FIG. 4 shows an image 82 as a first display example. The origin 84 indicates the transmission / reception origin of the array-type transducer, and a plurality of display lines 86 corresponding to a plurality of phasing signals are displayed side by side in the arc direction, that is, the azimuth direction based on the origin, thereby generating an image 82. The L indicates the distance direction, and reference numeral 88 indicates a target as a sound source. One display line 86 corresponds to one phasing signal, and each amplitude value constituting it is expressed by luminance. It is also possible to adopt a color expression. For example, a portion having a predetermined amplitude or more may be expressed in color. FIG. 5 shows an image 90 as a second display example. A line indicated by reference numeral 92 corresponds to the transmission / reception origin position, and each position on the line corresponds to each direction. A plurality of display lines corresponding to a plurality of phasing signals are displayed in parallel from above the line. t indicates a time axis, which corresponds to a distance axis. Reference numeral 96 indicates a target as a sound source. Display modes other than the above display examples may be adopted.

  6 to 8 show comparative examples, and each figure shows the directivity characteristics in the line array type receiver. Note that the normalization is performed with the maximum value in any directivity.

  The directivity shown in FIG. 6 is created under the conditions that the number of elements is 100, the center frequency is 500 kHz, and the pitch p between elements is 0.5λ. The main pole exists at an azimuth of 0 °. The N-th power process described above is not applied, in other words, N = 1. Since a large number of elements are used, a considerably narrowed main pole is generated, and a directivity width of 1 ° is realized. The levels of the plurality of sub-poles formed on both sides of the main pole are also considerably low. For reference, the first sub-pole level is −29 dB, the second sub-pole level is −33 dB, and the third sub-pole is −36 dB with respect to the maximum value. Since the sub pole level is sufficiently low, false detection due to the sub pole can be reduced.

  FIG. 7 shows directivity characteristics when the number of elements is intentionally reduced to 11 elements. This is created under the conditions of a center frequency of 500 kHz and an element pitch p of 0.5λ. In this example as well, the main pole is formed in the 0 ° direction, and the above-mentioned Nth power process is not applied. The directivity width has increased to 10 °, and the subpolar level has increased. For reference, with respect to the maximum value, the level of the first sub-pole is −13 dB, the level of the second sub-pole is −17 dB, and the level of the third sub-pole is −19 dB. Compared to the case of 100 elements shown in FIG. 6, the first subpolar level is increased by 16 dB, and there is a concern about an increase in false detection. As a result of the pointing width expanding to 10 °, the target detection resolution is also lowered.

  FIG. 8 shows the directivity characteristics when the number of elements is further intentionally reduced to 5 elements. This was created under the conditions of a center frequency of 500 kHz and an element pitch p of 0.817λ. In this example as well, the main pole is formed in the 0 ° direction, and the above-mentioned Nth power process is not applied. The pointing width has increased considerably, and the subpolar level has further increased. For reference, with respect to the maximum value, the first sub-pole is −12 dB, the second sub-pole is −14 dB, and the directivity width is 12.8 °.

  In FIG. 9, the directivity according to the present embodiment is indicated by a solid line. This is obtained by applying N-th power processing to the directivity characteristics as a comparative example shown in FIG. The phasing direction is 0 ° as described above. A directivity characteristic (corresponding to a first power process) created under the condition of a center frequency of 500 kHz, five elements, and an inter-element pitch p of 0.817λ is indicated by a broken line in FIG. The processed directivity after application of is indicated by a solid line in FIG. In the directivity characteristics after the squaring process, the subpolar level is greatly lowered and the directivity width is also improved as compared with the case of the squaring process indicated by the broken line. The part with the larger amplitude difference from the maximum value is more suppressed. For reference, the first subpole is −24 dB, the second subpole is −28 dB, and the directivity width is 9.2 ° with respect to the maximum value.

  FIG. 10 shows another directivity characteristic according to this embodiment. This is a result of applying the cube process to the directivity created under the conditions of a center frequency of 500 kHz, five elements, and an element pitch p of 0.817λ. Compared to the case of the square process, the sub-pole level is greatly lowered, and the directivity width is also improved. For reference, the first subpole is −37 dB and the second subpole is −42 dB with respect to the maximum value, and the directivity width is 8.2 °. That is, the characteristics are further improved compared to the case of the square process.

  As simulation conditions for directivity, the number of elements is varied between 5 and 50, the pitch p between elements is varied between 0.5λ and 1.0λ, while the phasing direction is set to 0 °, and the number of N power processes Was varied from the first power to the third power in 0.5 power steps, and the following relational expression (8) was obtained.

  Here, w is the directivity width, N is the number of multiplication processes, p is the pitch between elements, and n is the number of elements. According to the above equation (8), even if the inter-element pitch p is increased and the number of elements n is decreased, the directivity width w can be decreased by increasing the number of multiplication processes. However, the upper limit of the inter-element pitch p is less than one wavelength (λ). From the simulation results of the present inventor, it has been found that practically usable Nth power processing should preferably be limited to about 3 to 5th power in consideration of floating-point arithmetic accuracy and processing speed. .

  According to the above method, when the amplitude difference expansion process is applied while maintaining the number of elements as in the conventional case, it is possible to significantly improve the directivity. Alternatively, on the premise of such amplitude difference enlargement processing, even if the number of elements is reduced, it is possible to obtain the same directivity characteristics as a result. In that case, it is desirable to increase the pitch between the elements from 0.5 λ from the viewpoint of securing a constant reception aperture, and even if so, it is possible to obtain a satisfactory directional characteristic.

  In adopting the above-described embodiment, it is desirable that the inter-element pitch, the phasing azimuth angle pitch, and the numerical value N can be automatically or manually varied in accordance with various measurement situations. For example, if the number of elements is designated on the assumption that a certain directivity width is obtained, an optimum inter-element pitch and an optimum value of N may be automatically determined.

10-line array type transducer, 10a element, 14 switch, 16 transmitter, 18 receiver, 20 amplifier, 22 A / D converter, 24, 34, 42 memory, 26 adder, 30 band pass filter, 32 Amplitude difference expansion processing unit, 36 normalization processing unit, 38 N power processing unit, 40 restoration processing unit, 44 image processing unit, 46 display unit.

Claims (4)

An array type transducer configured by a plurality of transducer elements arranged in water and outputting a plurality of received signals by receiving ultrasonic waves;
By executing the phasing addition process while changing the phasing direction with respect to the plurality of received signals, a plurality of phasings corresponding to the plurality of phasing directions are obtained as a signal string reflecting the directivity characteristics of the array converter. Phasing addition means for generating a phase signal;
Amplitude difference enlargement processing means for applying an amplitude difference enlargement process for improving the directivity of the array converter afterwards with respect to the plurality of phasing signals;
Only including,
The amplitude difference enlargement processing means is
Means for extracting a data string composed of a plurality of data having the same distance relationship across the plurality of phasing signals for each distance from the array type converter;
Means for enlarging an amplitude difference of other data with respect to maximum data in the extracted data sequence;
An ultrasonic measurement apparatus comprising: The apparatus of claim 1.
Wherein the means for expanding, N-th power to the retrieved data string processing (where N> 1) is an N-th power processing means to apply ultrasonic measuring apparatus characterized by.
An ultrasonic measurement apparatus characterized by that. The apparatus of claim 1 .
The amplitude difference enlargement processing means further includes:
Pre-processing means for generating a normalized data string by performing a normalization process on the data string, and applying the N-th power process to the normalized data string;
Post-processing means for performing an amplitude restoration process on the normalized data string after the N-th power process to generate a plurality of restored data strings;
An ultrasonic measurement apparatus comprising: The device according to any one of claims 1 to 3,
The inter-element pitch p in the plurality of conversion elements satisfies the condition of 0.5λ <p <1.0λ, where λ is the wavelength at the center frequency of the ultrasonic wave.