Wideband beamforming acoustic doppler velocity system and method based on time delay control

Abstract

The application provides a wideband beamforming acoustic Doppler velocity measurement system and method based on time delay control, which can transmit and receive wideband signals and solves the problem that the measurement accuracy of an existing acoustic Doppler velocity measurement system is affected by bandwidth. The velocity measurement system comprises a transducer module, a beamforming module and a conversion module; the transducer module comprises a planar transducer array and an impedance matching module connected to the planar transducer array; the transducer module is signal-connected to the beamforming module through the conversion module, the beamforming module is used for time delay compensation and weighting processing of the received signals; and the conversion module is used for converting the echo signals collected by the transducer module into digital signals and inputting the digital signals into the beamforming module, or converting the signals to be transmitted received from the beamforming module into analog signals and transmitting the analog signals through the transducer module.

Description

TECHNICAL FIELD

[0001] The present application relates to an acoustic Doppler velocity measurement system and method, in particular to an acoustic Doppler velocity measurement system and method based on time delay control, and belongs to the technical field of underwater acoustic navigation and velocity measurement. BACKGROUND

[0002] A velocity measurement sonar generally transmits and receives acoustic signals through a planar transducer, and calculates the velocity of the sonar carrier relative to the water body or seabed according to the Doppler frequency shift of the echo. The velocity measurement sonar based on acoustic Doppler effect can be used not only for positioning and navigation of ships, submarines, aircraft, etc. Such sonar equipment is generally referred to as Doppler Velocity Log (DVL), but also for flow velocity measurement of rivers, oceans, etc. Such sonar equipment is generally referred to as Acoustic Doppler Current Profiler (ADCP).

[0003] In order to measure three-dimensional velocity information, the acoustic transducer must simultaneously transmit and receive beam signals in at least three different directions; for this purpose, four independent piston acoustic transducers are generally combined together through a mechanical structure to form four spatially symmetric beams (Janus structure). The piston transducers of the Janus structure may interfere with the flow field to be measured near the transducers when measuring the flow velocity, and the measurement accuracy is significantly affected by the sound velocity. In addition, in order to ensure the action distance of the sound wave and the signal-to-noise ratio of the echo, it is generally required that the beam opening angle of the transducer be small, which in turn results in a very large weight and volume of the low-frequency Janus structure transducer, making it difficult to be practically applied.

[0004] The phased array technology can form four spatial beams simultaneously using a planar transducer by adjusting the phase information of a large number of array elements, and effectively avoids the above problems of the piston array, and is currently widely used in the field of acoustic Doppler velocity measurement. The principle of velocity measurement and flow measurement based on Doppler effect is to transmit pulsed acoustic waves to the water body or seabed through multiple obliquely arranged acoustic beams, receive the echoes, and calculate the relative velocity according to the change of the echo frequency (i.e. Doppler shift).

[0005] A typical phased array acoustic Doppler velocity measurement system includes a circular planar transducer, a phase control system, an impedance matching network and other key parts, generally points the beam to a fixed 30°, extracts the same phase row and column degeneracy into a road, to achieve beam transmission and reception with fewer transmitters and receivers. However, the current phased array acoustic Doppler velocity measurement system has the following significant defects: in order to reduce the short-term uncertainty of the velocity measurement result, improve the measurement accuracy and data update rate, in the Doppler velocity measurement system, a phase coded signal with a relative bandwidth of 6.25% ~ 12.5% is generally used, but the beam pointing in the phase shift mode is sensitive to the bandwidth, which leads to the widening of the main lobe of the beam formed by the wide bandwidth phase coded signal, the rising of the side lobe and other problems, which limits the application of the phase coded signal in the high-precision velocity measurement scene; Therefore, the current phased array acoustic Doppler velocity measurement system is only used for the transmission and reception of narrowband signals. SUMMARY

[0006] Therefore, the present application provides a wideband beam forming acoustic Doppler velocity measurement system based on time delay control, which can better adapt to complex signals such as phase coding compared with phase control, can transmit and receive wideband signals, and solves the problem that the measurement accuracy of the existing acoustic Doppler velocity measurement system is affected by the bandwidth.

[0007] The technical scheme of the present application is: a wideband beam forming acoustic Doppler velocity measurement system based on time delay control, comprising: a transducer module, a beam forming module and a conversion module;

[0008] The transducer module includes a planar transducer array and an impedance matching module connected to the planar transducer array;

[0009] The transducer module is signal connected with the beam forming module through the conversion module, and the beam forming module is used for time delay compensation and weighting processing of the received signal;

[0010] The conversion module is used for converting the echo signal collected by the transducer module into a digital signal input to the beam forming module, or converting the signal to be transmitted received from the beam forming module into an analog signal and transmitting it through the transducer module.

[0011] As a preferred mode of the present application, the planar transducer array includes a plurality of transducer units arranged in a multi-row, multi-column structure;

[0012] Each row of the planar transducer array leads to an external interface, and each column leads to an external interface;

[0013] The impedance matching module is a multi-channel impedance matching module, comprising impedance matching circuits corresponding to the multi-channel external interfaces led by the planar transducer array; the external interfaces led by the planar transducer array are connected to the corresponding impedance matching circuits respectively; the impedance matching circuits are used for impedance matching processing of the received signals;

[0014] The multi-channel impedance matching module adopts a distributed common reference method, that is, all the impedance matching circuits in the multi-channel impedance matching module have the same common reference ground and secondary side reference ground.

[0015] The multi-channel impedance matching module is connected to the conversion module.

[0016] As a preferred mode of the present application, the impedance matching circuit comprises a transformer, and a primary side circuit on the primary side winding side of the transformer and a secondary side circuit on the secondary side winding side of the transformer;

[0017] The primary side circuit is provided with a first positive connection port and a first negative connection port; the first positive connection port is electrically connected to the corresponding signal led by the planar transducer array, and the first negative connection ports of the primary side circuits of all the impedance matching circuits are connected together to form a common reference ground.

[0018] The secondary side circuit is provided with a second positive connection port and a second negative connection port, the second positive connection port is electrically connected to the corresponding secondary circuit, and the second negative connection ports of the secondary side circuits of all the impedance matching circuits are connected together to form a secondary side reference ground.

[0019] As a preferred mode of the present application, the second positive connection port of the impedance matching circuit corresponds to the positive pole of the transmitted signal.

[0020] When the second positive connection ports of the secondary side circuits of all the impedance matching circuits are connected together, all the transmitted acoustic beam signals are the same.

[0021] When the second positive connection ports of the secondary side circuits of the impedance matching circuits are independently configured, mutually different acoustic beam signals can be transmitted.

[0022] As a preferred mode of the present application, the positive pole of the primary side winding of the transformer is provided with a first positive connection port, and the negative pole is provided with a first negative connection port; the primary side circuit comprises a first resistor, a first inductor, a first capacitor, a second capacitor and a third capacitor, the first resistor, the first inductor and the first capacitor are connected in series; the second capacitor and the third capacitor are connected in parallel between the first capacitor and the first resistor; the first capacitor, the second capacitor and the third capacitor are electrically connected to the first positive connection port; the negative pole of the primary side winding is connected to the other end of the first resistor, the other end of the second capacitor and the other end of the third capacitor.

[0023] The positive pole of the transformer secondary winding is provided with a second positive pole connecting port, and the negative pole is provided with a second negative pole connecting port; the secondary circuit comprises a fourth capacitor, a second inductor and a third inductor, one end of the fourth capacitor is electrically connected with the second positive pole connecting port, and the other end is connected with the third inductor in series; the other end of the third inductor is electrically connected with the positive pole of the secondary winding and one end of the second inductor respectively, and the negative pole of the secondary winding is connected with the other end of the second inductor.

[0024] As a preferred mode of the present application, the planar transducer array comprises a plurality of transducer units arranged in a multi-row, multi-column structure;

[0025] The planar transducer array is divided into a plurality of sub-arrays in rows and in columns respectively, which are row sub-arrays and column sub-arrays respectively;

[0026] Each of the row sub-arrays and each of the column sub-arrays internally performs pre-beamforming in a phase shift manner and then leads out signals;

[0027] The impedance matching module performs impedance matching processing on the signals led out by each of the row sub-arrays and each of the column sub-arrays.

[0028] As a preferred mode of the present application, the effective aperture of the sub-array is , then:

[0029]

[0030] , wherein: is the desired transmit signal bandwidth, is the nominal beam pointing angle, is the medium sound speed;

[0031] According to the above formula, the maximum effective aperture of the sub-array can be obtained.

[0032] As a preferred mode of the present application, the beamforming module comprises a transmitting component and a receiving component;

[0033] The transmitting component comprises an upsampling unit, a first time delay unit, a first phase shift unit, a first weighting unit and an up-conversion unit; the upsampling unit is used for performing digital interpolation filtering on baseband data and raising the sampling rate to the rate required for internal beamforming processing; the first time delay unit and the first phase shift unit sequentially perform time delay compensation and phase compensation on the interpolated baseband data according to the target transmission direction to generate multiple paths of baseband data; the first weighting unit is used for applying amplitude weighting to each path of baseband data; and the up-conversion unit is used for performing up-conversion processing on the weighted baseband data;

[0034] The receiving component comprises a down-conversion unit, a second time delay unit, a second phase shift unit, a second weighting unit and a down-sampling unit; the down-conversion unit performs down-conversion processing on the received signal; the second time delay unit and the second phase shift unit sequentially perform time delay compensation and phase compensation on the down-converted baseband data; the second weighting unit forms beam output data after weighting and accumulation of the baseband data; and the down-sampling unit is used for down-sampling the beam output data to form the digital signal to be processed.

[0035] In addition, based on the speed measurement system, the application provides a wideband beam forming acoustic Doppler speed measurement method based on time delay control, comprising the following steps:

[0036] The baseband data to be transmitted is generated into a baseband signal;

[0037] According to a preset transmission direction, time delay compensation is performed on the baseband signal to form a plurality of signals, and then weighting processing is performed on each signal;

[0038] The data after the weighting processing is up-sampled and mixed to a preset center frequency, and is converted into a real signal;

[0039] After signal conditioning and power amplification are performed on the real signal, a transmission signal is obtained, which is transmitted through the planar transducer array;

[0040] The planar transducer array receives a return signal;

[0041] The received signal is conditioned, and then the conditioned signal is subjected to quadrature mixing processing and down-sampling to obtain a baseband complex signal;

[0042] The baseband complex signal is subjected to inter-channel time delay compensation and amplitude weighting processing to synthesize receiving beam data;

[0043] Doppler frequency shift parameter estimation is performed on the receiving beam data to obtain speed information.

[0044] Advantages:

[0045] (1) The speed measurement system based on the time delay beam forming theory can correct beam distortion caused by wideband signals, and compared with phase control, time delay control can better adapt to complex signals such as phase coding, so that the transmission and reception of wideband signals can be performed, and the problem that the measurement accuracy of the existing acoustic Doppler speed measurement system is affected by the bandwidth is solved.

[0046] (2) In the speed measurement system of the present invention, when each row and column of the planar transducer array leads out an external interface, a distributed common reference connection is adopted to form a multi-channel impedance matching module for its impedance matching module, which can solve the problem of transducer impedance matching in the complex structure of the time delay array and improve the system energy transmission efficiency. This kind of full time delay speed measurement system takes into account the flexibility of beam pointing control and low distortion. It can control the beam pointing through time delay adjustment. Theoretically, it can achieve precise control of beam pointing at any angle under broadband conditions, significantly reduce the beam broadening error caused by broadband signals, and has the application capability in complex scenarios (non-uniform flow field, unmanned cluster, etc.).

[0047] (3) In the speed measurement system of the present invention, when the planar transducer array is divided into subarrays, after the full array is divided into subarrays, pre-beamforming can be performed in the subarrays in a phase-shift manner, and impedance matching can be performed in a conventional impedance matching manner; time delay compensation and weighting between subarrays are performed outside the subarrays, thereby completing beamforming. This can effectively avoid the beam pointing error generated by the traditional phase-shift method during broadband transmission, and can also greatly reduce the complexity of the engineering implementation of the full time delay control method and simplify the structure of the system. Attached Figure Description

[0048] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.

[0049] Figure 1 This is a structural block diagram of the acoustic Doppler velocimetry system based on time delay control in Embodiment 1 of the present invention;

[0050] Figure 2 This is a schematic diagram of the multi-channel impedance matching network in Embodiment 1 of the present invention;

[0051] Figure 3 In the figure, (a) and (b) are respectively the transmitted waveforms of a single-frequency narrowband signal and a wideband phase-coded signal after impedance matching according to the present invention;

[0052] Figure 4 This is a schematic diagram of the transmission link of the speed measurement system according to Embodiment 1 of the present invention;

[0053] Figure 5 This is a schematic diagram of the receiving link of the speed measurement system according to Embodiment 1 of the present invention;

[0054] Figure 6 This is a flowchart of the acoustic Doppler velocimetry system based on time delay control, which is an embodiment of the present invention.

[0055] Figure 7The subarray division and impedance matching connection diagram in the embodiment 2 of the present application is shown in the figure.

[0056] Figure 8 The beam pointing transmission design diagram after the subarray division in the embodiment 2 of the present application is shown in the figure.

[0057] Figure 9 The beam pointing reception design diagram after the subarray division in the embodiment 2 of the present application is shown in the figure.

[0058] In the figure, 1 represents a planar transducer array, 2 represents an impedance matching circuit, and 21 represents a first positive connection port. DETAILED DESCRIPTION

[0059] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the specific embodiments of the present application will be described below with reference to the drawings. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can be obtained from these drawings without creative labor, and other embodiments can also be obtained.

[0060] In order to make the drawing simple, only the parts related to the present application are shown in each figure, which do not represent the actual structure of the product. In addition, in order to make the drawing simple and easy to understand, in some figures, only one of the parts with the same structure or function is shown, or only one of them is marked. In this paper, "one" not only means "only one", but also means "more than one".

[0061] The wideband beam forming acoustic Doppler velocity measurement system based on time delay control proposed in the present application will be further described in detail below in combination with the drawings and specific embodiments.

[0062] The wideband beam forming acoustic Doppler velocity measurement system based on time delay control proposed in the present embodiment can effectively avoid the beam pointing error caused by the traditional phase shift method in wideband transmission, and solve the problem that the measurement accuracy of the existing acoustic Doppler velocity measurement system is affected by the bandwidth.

[0063] The velocity measurement system comprises a transducer module, a beam forming module and a conversion module; wherein the transducer module comprises a planar transducer array 1 and an impedance matching module connected to the planar transducer array 1. As an example, the planar transducer array 1 is a circular planar array, which comprises a plurality of transducer units arranged in a multi-row and multi-column structure, and each transducer unit is an array element. The impedance matching module is used for impedance matching of the received signal.

[0064] The transducer module is connected with the beam forming module through a conversion module, the beam forming module is used for time delay compensation and weighting processing on the received signal; the conversion module is used for converting the echo signal collected by the transducer module into a digital signal and inputting the digital signal into the beam forming module, or converting the signal to be transmitted received from the beam forming module into an analog signal and transmitting the analog signal through the transducer module.

[0065] Two specific embodiments of the wideband beam forming acoustic Doppler velocity measurement system based on time delay control are given below.

[0066] Embodiment 1:

[0067] The wideband beam forming acoustic Doppler velocity measurement system based on time delay control in this embodiment adopts a full time delay control technology, which can better adapt to complex signals such as phase encoding compared with phase control, and can solve the problem that the measurement accuracy of the existing acoustic Doppler velocity measurement system is affected by the bandwidth; and can control the beam pointing through time delay adjustment, and theoretically can realize beam pointing at any angle.

[0068] As shown in Figure 1 The acoustic Doppler velocity measurement system in this example includes a transducer module, a beam forming module and a conversion module. The transducer module includes a planar transducer array 1 and an impedance matching module; the planar transducer array 1 is a circular planar array, including a plurality of transducer units, the plurality of transducer units are arranged in a multi-row and multi-column structure, and each transducer unit is an array element.

[0069] The planar transducer array 1 is extracted row by row and column by column, and each row and each column is led out through a physical wire; the first column is led out as “H-CH1”, the second column is led out as “H-CH2”, and so on until all columns are led out; the same leading-out mode is adopted for the rows, and all rows are led out, wherein the first row is led out as “V-CV1”, the second row is led out as “V-CV2”, and so on.

[0070] As an example, the planar transducer array 1 leads out 32 rows and 32 columns in total.

[0071] For the full time delay control technology, the main problem to be solved is the transducer impedance matching problem in the complex structure of the time delay array, in this example, through the design of the multi-channel impedance matching network, the transducer impedance matching problem in the complex structure of the time delay array can be solved; and the energy transmission efficiency of the system is improved.

[0072] That is, in this example, the impedance matching module is a multi-channel impedance matching module, the planar transducer array 1 is connected with the multi-channel impedance matching module, the multi-channel impedance matching module is connected with the beam forming module through the conversion module, and after the signal is subjected to phase shift, time delay and other operations in the beam forming module, the emission and reception of the beam signal with any pointing direction are realized.

[0073] The multi-channel impedance matching module includes impedance matching circuits that correspond one-to-one with the multiple interfaces led out from the planar transducer array; the signals led out from the planar transducer array 1 are respectively connected to the corresponding impedance matching circuits.

[0074] like Figure 1 As shown, in this example, the multi-channel impedance matching module includes a V-channel multi-channel impedance matching network and an H-channel multi-channel impedance matching network. The V-channel multi-channel impedance matching network has impedance matching circuits 2 (32 in this example) that correspond one-to-one with the rows led out of the planar transducer array 1. The H-channel multi-channel impedance matching network has impedance matching circuits 2 (32 in this example) that correspond one-to-one with the columns led out of the planar transducer array 1. All rows led out of the planar transducer array 1 are sequentially connected to the corresponding impedance matching circuits 2 in the V-channel multi-channel impedance matching network, and all columns are sequentially connected to the corresponding impedance matching circuits 2 in the H-channel multi-channel impedance matching network.

[0075] In acoustic Doppler velocimeters, the impedance matching method of the planar transducer array directly affects the overall power transmission efficiency, bandwidth performance, and phase consistency. In order to form arbitrary beam pointing, distributed impedance matching is adopted. On this basis, the multi-channel impedance matching module adopts a common reference connection, thus forming a distributed common reference connection transformer matching network. This matching network is an impedance matching scheme that takes into account both system complexity and performance consistency.

[0076] Impedance matching circuit 2 includes a transformer, and primary and secondary circuits located on either side of the transformer. The primary circuit has a first positive connection port and a first negative connection port. The first positive connection port is electrically connected to the corresponding row or column pin of the planar transducer array 1; that is, the first positive connection port of any impedance matching circuit 2 is connected to the corresponding row or column pin of the planar transducer array 1. The negative connection ports of the primary windings of all transformers in all impedance matching circuits 2, i.e., the first negative connection ports, are all connected together (i.e., the negative terminals of the primary windings of all transformers in all impedance matching circuits 2 are commonly connected), forming a common reference ground, equivalent to the system's virtual ground / zero potential reference plane. This structure ensures that the primary input current of each transformer in the multi-channel impedance matching module references the same potential, enhancing the phase consistency and driving stability between rows and columns of the planar transducer array 1. It can be understood that "all impedance matching circuits 2" mentioned here refers to all the impedance matching circuits corresponding to rows and columns of the planar transducer array 1.

[0077] The secondary side circuit is provided with a second positive electrode connecting port and a second negative electrode connecting port, the second positive electrode connecting port is electrically connected with the corresponding later stage circuit; the negative electrode connecting port of the transformer secondary side winding in all impedance matching circuits 2, namely the second negative electrode connecting port, is connected together (namely the negative electrode of the transformer secondary side winding in all impedance matching circuits is commonly connected), thereby forming a secondary side reference ground; in this way, while ensuring isolation, the secondary side reference is kept consistent, thereby providing a standard potential reference for subsequent circuit processing.

[0078] Specifically, as shown in Figure 2 , the circuit structure of the impedance matching circuit 2 will be described, and since the structure of each impedance matching circuit 2 is the same, any one circuit will be described:

[0079] The impedance matching circuit 2 comprises a transformer TR1, a primary side circuit located at the side of the primary side winding N1 of the transformer TR1, and a secondary side circuit located at the side of the secondary side winding N2 of the transformer TR1; the positive electrode of the primary side winding N1 is provided with a first positive electrode connecting port 21, and the negative electrode is provided with a first negative electrode connecting port J1. The primary side circuit comprises a first resistor R1, a first inductor L1, a first capacitor C1, a second capacitor C0 and a third capacitor C3. The first resistor R1, the first inductor L1 and the first capacitor C1 are connected in series, and the second capacitor C0 and the third capacitor C3 are connected in parallel between the first capacitor C1 and the first resistor R1. Among them, the first capacitor C1, the second capacitor C0 and the third capacitor C3 are electrically connected with the first positive electrode connecting port 21. The pins of the row or column of the planar transducer array 1 corresponding to the impedance matching circuit 2 are electrically connected with the first positive electrode connecting port 21. The negative electrode of the primary side winding N1 is connected with the first resistor R1, the other end of the second capacitor C0 and the other end of the third capacitor C3. The first negative electrode connecting port J1 of the primary side winding N1 in all impedance matching circuits 2 is connected together, thereby forming a primary side reference ground, that is, a common reference ground, which is equivalent to a virtual ground / zero potential reference surface of the system.

[0080] The secondary side circuit comprises a fourth capacitor C2, a second inductor L2 and a third inductor L3; the positive electrode of the secondary side winding N2 of the transformer TR1 is provided with a second positive electrode connecting port J0, and the negative electrode is provided with a second negative electrode connecting port J2. One end of the fourth capacitor C2 is electrically connected with the second positive electrode connecting port J0, the other end of the fourth capacitor C0 is connected with the third inductor L3 in series, and then the other end of the third inductor L3 is electrically connected with the positive electrode of the secondary side winding N2 and one end of the second inductor L2, respectively, the negative electrode of the secondary side winding N2 and the other end of the second inductor L2 are electrically connected with the second negative electrode connecting port J2. The negative electrode connecting port J2 of the secondary side winding N2 in all impedance matching circuits 2 is connected together, thereby forming a secondary side reference ground.

[0081] In impedance matching circuit 2, the positive terminal of the secondary winding N2 corresponds to the positive terminal of the transmitted signal. When the second positive terminal J0 of the secondary winding N2 in all impedance matching circuits 2 is connected together, all transmitted acoustic beam signals are the same. When the second positive terminal J0 of the secondary winding N2 in impedance matching circuit 2 is configured independently, the row transmission signal and the column transmission signal can drive the corresponding transducer array elements respectively. Different beams can transmit different signal modes, realizing the differentiation of signal waveforms in the spatial domain, thereby improving the anti-interference performance of the system.

[0082] Figure 3 Images (a) and (b) show a single-frequency narrowband signal and a wideband phase-coded signal, respectively, when using... Figure 2 The transmitted waveform obtained after impedance matching network is shown. Results show that for single-frequency narrowband signals, this design performs consistent with traditional schemes in waveform preservation; while for wideband phase-coded signals, this design can better preserve phase flip information while maintaining amplitude characteristics. The common reference ground structure effectively reduces phase mismatch caused by reference drift between columns or rows of the planar transducer array 1, and facilitates use with phase shifters or fractional delay modules, thereby supporting full-delay beam control at the subarray level.

[0083] In this system, beamforming, upsampling, and downsampling are performed through beamforming and conversion modules. Specifically, the system includes two beamforming modules and two conversion modules. A V-channel multi-channel impedance matching network corresponds to one beamforming module and one conversion module, while an H-channel multi-channel impedance matching network corresponds to one beamforming module and one conversion module. Figure 1 As shown.

[0084] The beamforming module is connected to the corresponding impedance matching network (V-channel multi-channel impedance matching network or H-channel multi-channel impedance matching network) in the multi-channel impedance matching module through the conversion module. It is used to perform delay, phase shift and weighting processing on the signal. The conversion module is used to convert the acquired echo signal (analog signal) into a digital signal and input it to the beamforming module, or to convert the signal to be transmitted (digital signal) received from the beamforming module into an analog signal and transmit it through the planar transducer array 1.

[0085] Specifically: the beamforming module includes a transmitting component and a receiving component; the transmitting component includes an upsampling unit, a first delay unit, a first phase shift unit, a first weighting unit, and an upconversion unit (i.e., a digital upconverter, DUC); for example... Figure 4As shown, the upsampling unit performs digital interpolation filtering on the baseband data to increase the sampling rate to a higher rate required by the internal beamforming processing, thereby achieving finer fractional delay resolution and reducing delay quantization error; according to the target transmission direction, the first time delay unit and the first phase shift unit respectively apply accurate delay (i.e. time delay compensation) and phase compensation to the interpolated baseband data to generate multiple paths of baseband data; the first weighting unit applies amplitude weighting (beam weighting coefficient) to each path of baseband data to optimize the beam shape characteristics such as main lobe width and side lobe suppression. Each path of weighted baseband data enters the up-conversion unit (DUC) to be interpolated by an integer multiple to the working sampling rate of the DAC unit in the conversion module, and is mixed to a specified center frequency to generate a real signal; the real signal is sent to the DAC unit for digital-to-analog conversion to form an analog signal to be transmitted.

[0086] When high-precision time delay compensation is used in the first time delay unit, the first phase shift unit can also be omitted in the transmitting assembly, i.e. only accurate time delay compensation is applied to the interpolated baseband data to generate multiple paths of baseband data.

[0087] The receiving assembly includes a down-conversion unit (i.e. digital down-converter DDC), a second time delay unit, a second phase shift unit, a second weighting unit and a downsampling unit; as shown, Figure 5 As shown, the receiving signal from the ADC unit in the conversion module first enters the down-conversion unit (DDC) and is mixed to shift the signal around the specified center frequency to the complex baseband; then, low-pass filtering is performed to suppress the image and out-of-band noise, and the signal is down-sampled by an integer multiple to the sampling rate required by the beamforming processing. The baseband data is subjected to accurate delay (i.e. time delay compensation) and phase compensation in the second time delay unit and the second phase shift unit, respectively, to achieve wavefront alignment. Each path of baseband data after delay and phase shift compensation is subjected to amplitude weighting (beam weighting coefficient) in the second weighting unit to optimize the main lobe width and side lobe suppression performance; then, the weighted signals are accumulated to form beam output data; the beam output data is subjected to low-pass filtering and integer multiple downsampling again to form a digital signal to be processed.

[0088] When high-precision time delay compensation is used in the first time delay unit, the first phase shift unit can also be omitted in the transmitting assembly, i.e. only accurate time delay compensation is applied to the interpolated baseband data to generate multiple paths of baseband data.

[0089] As an example, the planar transducer array 1 has 32 rows and 32 columns in total; in the transmitting assembly, the upsampling unit, the first time delay unit, the first phase shift unit, the first weighting unit and the up-conversion unit are each correspondingly provided with 32 paths. In the receiving assembly, the down-conversion unit, the second time delay unit, the second phase shift unit, the second weighting unit, the second weighting unit and the downsampling unit are each correspondingly provided with 32 paths.

[0090] The conversion module comprises a DAC unit and an ADC unit; the DAC unit is configured to convert the digital signal processed by the up-conversion unit in the transmitting assembly into an analog signal, and send the analog signal as a signal to be transmitted to the planar transducer array 1; the ADC unit is configured to convert the collected echo data into a digital signal and deliver the digital signal to the down-conversion unit.

[0091] The main working process of the velocity measurement system is divided into two parts of transmission and reception, and the transmission link and the reception link will be described in detail:

[0092] As an example, in the transmission link: the baseband data to be transmitted (in complex I / Q form) is first transmitted to the upsampling unit for preprocessing. The upsampling unit combines FIR digital filtering with zero insertion to upsample the baseband data to a higher rate (typical value: 4 times to 8 times). The upsampling multiple needs to satisfy the delay resolution ≤ 1 / 4 sampling interval to ensure the accuracy of the delay and the phase shift. After upsampling, the signal enters the beamforming preprocessing stage: the first delay unit calculates the time delay of each column or row according to the set beam pointing angle is the inter-element spacing, is the medium sound speed, typical value 1500 m / s, is the sound wave transmission direction), to perform accurate time delay compensation. The first delay unit sends the calculated time delay signal to the first phase shift unit. The first phase shift unit performs complex multiplication phase compensation on the received time delay signal to ensure the phase alignment of each column or row signal, and then sends it to the first weighting unit. The first weighting unit applies amplitude weighting coefficients (such as Taylor weighting) to suppress sidelobes, and the dynamic range of the weighting coefficients is 0.1-1.0 to balance the main lobe gain and sidelobe suppression. Subsequently, the signal is upsampled to the carrier sampling rate by the digital up-conversion unit (DUC), and the sampling rate meets the Nyquist criterion.

[0093] Finally, the complex mixer moves the baseband signal processed by the transmitting module to the preset center frequency, converts it into a real signal after Hilbert transform, and then completes digital-to-analog conversion by the DAC unit to output an analog signal. After signal conditioning and power amplification, the planar transducer array 1 is driven to form a beam in a specified direction.

[0094] ​As an example, in the receiving link: the ADC unit collects echo signals at a sampling rate greater than 4 times the center frequency, and the down-conversion unit (DDC) mixes the signals near the specified frequency to the baseband: the digital down-conversion process uses a local oscillator matched with the transmitting end to realize frequency shift, and preserves the baseband signal through low-pass filtering. The baseband data after down-conversion is sent to the second weighting unit after being processed by the second time delay unit and the second phase shift unit in turn; wherein the time delay calculation is symmetrical with the transmitting end, and the phase shift amount (the negative sign indicates that the direction of receiving phase compensation is opposite to that of transmission) ensures the space-time alignment of multi-element signals; the second weighting unit uses the same weighting coefficient (such as Taylor weighting) as the transmitting end to perform amplitude weighting and accumulation on the baseband data, synthesizes the beam data, and then reduces the sampling rate twice to a lower sampling rate through the down-sampling unit, and finally transmits to the CPU for beam synthesis post-processing. The conventional method is to estimate the Doppler shift parameter of the beam data to obtain the speed information.

[0095] The system control and signal processing part is one of the key components of the acoustic Doppler velocity measurement device, mainly responsible for coordinating the transmission and receiving processes, completing the tasks of echo signal preprocessing (data interception, filtering, etc.), echo detection, Doppler frequency estimation (phase estimation, time delay estimation, etc.), and speed solution.

[0096] The acoustic Doppler velocity measurement system in this example is based on the time delay beam forming theory (full time delay technology), and solves the impedance matching problem of complex structure of time delay array and planar transducer through the transformer matching network of distributed common reference method, improving the energy transmission efficiency of the system.

[0097] The speed measurement method of the wideband beam forming acoustic Doppler velocity measurement system based on the above time delay control is as shown in Figure 6 , including the following steps:

[0098] First, generate the baseband signal to be transmitted;

[0099] Then, according to the preset transmission direction, sequentially perform time delay compensation and phase shift processing on the baseband signal to form multiple (such as 32) signals;

[0100] Perform weighting processing on each signal to control the beam shape; then up-sample and mix the weighted data to the preset center frequency to convert it into a real signal suitable for transmission;

[0101] After signal conditioning and power amplification on the real signal, it is transmitted through the planar transducer array 1;

[0102] The planar transducer array 1 receives the echo signal; performs front-end conditioning on the received signal, including low-pass filtering to suppress high-frequency noise, low-noise preamplification to improve signal-to-noise ratio, and time-varying gain control to compensate for signal attenuation;

[0103] The conditioned received signal is subjected to quadrature mixing downconversion and downsampling to obtain the baseband complex signal;

[0104] The baseband complex signal is subjected to inter-channel delay compensation, phase compensation and amplitude weighting processing to synthesize the received beam data;

[0105] The Doppler frequency shift is estimated based on the phase change of the received beam data, and the velocity information of the target is finally calculated.

[0106] Example 2:

[0107] The full-time delay technology used in the above embodiment 1 can solve the problem that the measurement accuracy of the existing acoustic Doppler velocities is affected by the bandwidth, but the full-time delay array has a complex structure. This embodiment provides a simplified design with a specific orientation based on time delay control for acoustic Doppler velocities.

[0108] In this example, the planar transducer array 1 is divided into several subarrays by row and column, namely row subarrays and column subarrays; the subarray division follows the following principles:

[0109] Maximum bandwidth of transmitted signal Aperture of planar transducer array 1 (For a circular planar array, aperture) (approximately its diameter) and nominal beam pointing angle The mathematical relationship between them satisfies the following formula:

[0110] (1)

[0111] in: The velocity of sound in the medium is typically 1500 m / s.

[0112] The subarray design involves dividing the entire array (planar transducer array 1) into multiple subarrays by rows and columns, with each subarray having an effective aperture. This will significantly reduce and relax bandwidth restrictions, effectively reducing the number of transmitters and receivers while meeting the broadband signal transmission requirements of the acoustic Doppler velocimetry system.

[0113] If the system requires a transmit signal bandwidth (i.e., the desired bandwidth) of Then we have:

[0114] (2)

[0115] With a center frequency of 75 kHz, the desired bandwidth Taking a 15 kHz acoustic Doppler velocimetry system as an example, the speed of sound is measured. 1500 m / s, nominal beam pointing angle Given an angle of 30°, substituting this into formula (2) yields a maximum aperture of approximately 0.18 m for the subarray. In this example, the total aperture is... The value is 0.35 m, and the number of subarrays is 2. That is, the entire array (planar transducer array 1) is evenly divided into two column subarrays (left half and right half) along the horizontal direction. At this time, each column subarray contains 16 columns. The entire array is evenly divided into two row subarrays (upper half and lower half) along the vertical direction. At this time, each row subarray contains 16 rows.

[0116] Within each row subarray and each column subarray, pre-beamforming is performed using phase shifting before signal extraction. For example, for row or column subarrays, based on the phase relationship of the array elements during transmission or reception, array elements with the same or equivalent phase (meaning achieving phase equivalence through polarity adjustment, etc., by utilizing phase change laws such as opposite phases) can be extracted in one path, thereby reducing the number of signal channels and lowering hardware design costs.

[0117] In this example, the planar transducer array 1 is designed with subarray division and array element polarity to realize the transmission and reception of broadband signals with a fixed beam direction of 30° in the acoustic Doppler velocimetry system.

[0118] like Figure 7 As shown, taking a half-wavelength array with a beam pointing angle of 30° as an example, under this condition, the phases of the transmitted or received signals of the array elements within each subarray are sequentially spaced at 90° intervals. Therefore, the polarities of the array elements can be arranged sequentially by column or row as positive, positive, negative, negative, and array elements with the same or equivalent phase of transmitted or received signals are led out as one path. This achieves pre-beamforming within the group through phase shifting, followed by conventional impedance matching. Specifically, in this example, each row subarray can be grouped into four rows, with the transducer elements within each group arranged sequentially as positive, positive, negative, negative; each column subarray can be grouped into four columns, with the transducer elements within each group arranged sequentially as positive, positive, negative, negative. This achieves pre-beamforming within each row subarray group and each column subarray group through phase shifting, followed by two signal outputs; then, impedance matching is performed on the signals output from each row subarray and each column subarray.

[0119] It should be noted that, Figure 7 The illustrated implementation is merely a specific example of grouping and channel merging using the phase relationship of array elements. This invention is not limited to this specific array spacing, beam pointing angle, or the number of array elements within a group. Under different array designs and beam pointing conditions, array elements with the same or equivalent phase can still be extracted into a single signal based on the phase relationship of the transmitted or received signals, thereby achieving pre-beamforming within the group through phase shifting, thus simplifying hardware and reducing costs.

[0120] Thus, in this embodiment, after the subarray division of the full array according to the limiting condition of formula (2), the beam forming is performed in the subarray in a fixed phase shift manner and the impedance matching is performed in a conventional impedance matching manner, because the beam direction is fixed; then the time delay compensation and weighting processing between the subarrays are performed outside the subarrays, as shown in Figure 8 , without performing the wideband time delay compensation at the full array level; thus, the beam pointing error caused by the conventional phase shift manner in wideband transmission can be effectively avoided, and the complexity of the engineering implementation of the time delay control method can be greatly reduced.

[0121] In this example, the beam forming module includes a transmitting component and a receiving component; the transmitting component includes an upsampling unit, a first time delay unit, a first weighting unit and an up-conversion unit (i.e. a digital up-converter DUC). In the transmitting stage, the upsampling unit performs digital interpolation filtering on the baseband data, and up-samples to a higher rate, so as to realize finer fractional delay resolution and reduce delay quantization error; according to the target transmission direction, the first time delay unit applies accurate time delay compensation to the interpolated baseband data to generate multiple paths of baseband data; the first weighting unit applies amplitude weighting (beam weighting coefficient) to each path of baseband data to optimize the beam shape characteristics such as main lobe width and side lobe suppression. Each path of weighted baseband data enters the up-conversion unit (DUC) to be interpolated to an integer multiple of the working sampling rate of the DAC unit in the conversion module, and is mixed to a specified center frequency to generate a real signal; the real signal is sent to the DAC unit for digital-to-analog conversion to form an analog signal to be transmitted, as shown in Figure 8 .

[0122] The receiving component includes a down-conversion unit (i.e. a digital down-converter DDC), a second time delay unit, a second weighting unit and a downsampling unit; in the receiving stage, after the signal received from the ADC unit in the conversion module is converted into a digital signal, the digital signal enters the down-conversion unit (DDC) and is mixed to shift the signal around the specified center frequency to the complex baseband; then, after the internal subarray receiving beam forming (phase compensation and accumulation summation) is performed, the second time delay unit and the second weighting unit are used for the external subarray beam forming, i.e. accurate time delay compensation is applied in the second time delay unit to realize wavefront alignment. Each path of baseband data after time delay compensation is amplitude weighted (beam weighting coefficient) in the second weighting unit to optimize the main lobe width and side lobe suppression performance. The downsampling unit performs integer multiple downsampling on the beam output data to form a digital signal to be processed, as shown in . Figure 9

[0123] ​The embodiments of the present application are explained in detail above with reference to the accompanying drawings, but the present application is not limited to the above-described embodiments. Even if various changes are made to the present application, if the changes fall within the scope of the claims of the present application and equivalents thereof, they are still within the protective scope of the present application.

Claims

1. A time-delay controlled wideband beamforming acoustic Doppler velocity system, characterized in that, The application relates to an ultrasonic imaging system, which comprises a transducer module, a beam forming module and a conversion module. The transducer module comprises a planar transducer array and an impedance matching module connected with the planar transducer array. The transducer module is signal-connected with the beam forming module through the conversion module, and the beam forming module is used for time delay compensation and weighting processing of received signals. The conversion module is used for converting echo signals collected by the transducer module into digital signals and inputting the digital signals into the beam forming module, or converting signals received from the beam forming module into analog signals and transmitting the analog signals through the transducer module. The planar transducer array comprises a plurality of transducer units arranged in a multi-row and multi-column structure. Each row of the planar transducer array leads to an external interface, and each column leads to an external interface. The impedance matching module is a multi-channel impedance matching module, which comprises impedance matching circuits corresponding to the multi-channel external interfaces led by the planar transducer array; the external interfaces led by the planar transducer array are connected with the corresponding impedance matching circuits respectively; and the impedance matching circuits are used for impedance matching processing of received signals. The multi-channel impedance matching module adopts a distributed common reference method, that is, all the impedance matching circuits in the multi-channel impedance matching module have the same common reference ground and secondary side reference ground. The multi-channel impedance matching module is signal-connected with the conversion module. The impedance matching circuit comprises a transformer, a primary side circuit on the primary side winding side of the transformer and a secondary side circuit on the secondary side winding side of the transformer.

2. The time delay control based wideband beamforming acoustic Doppler velocity system of claim 1, wherein, The primary side circuit is provided with a first positive connection port and a first negative connection port; the first positive connection port is electrically connected with the corresponding signal led by the planar transducer array; the first negative connection ports of the primary side circuits in all the impedance matching circuits are connected together to form a common reference ground; The secondary side circuit is provided with a second positive connection port and a second negative connection port; the second positive connection port is electrically connected with the corresponding subsequent circuit; and the second negative connection ports of the secondary side circuits in all the impedance matching circuits are connected together to form a secondary side reference ground. The second positive connection port of the impedance matching circuit corresponds to the positive pole of a transmitting signal.

3. The time delay control based wideband beamforming acoustic Doppler velocity system of claim 2, wherein, When the second positive connection ports of all the secondary side circuits in all the impedance matching circuits are connected together, all the acoustic beam signals are the same; When the second positive connection ports of the secondary side circuits in the impedance matching circuits are independently configured, different acoustic beam signals can be transmitted. The positive pole of the primary side winding of the transformer is provided with the first positive connection port, and the negative pole is provided with the first negative connection port; the primary side circuit comprises a first resistor, a first inductor, a first capacitor, a second capacitor and a third capacitor; the first resistor, the first inductor and the first capacitor are connected in series; the second capacitor and the third capacitor are connected in parallel between the first capacitor and the first resistor; the first capacitor, the second capacitor and the third capacitor are electrically connected with the first positive connection port; and the negative pole of the primary side winding is connected with the first resistor, the other end of the second capacitor and the other end of the third capacitor.

4. A latency control based wideband beamforming acoustic Doppler velocity system according to claim 2 or 3, characterized in that, ​ The positive pole of the transformer secondary winding is provided with a second positive pole connecting port, and the negative pole is provided with a second negative pole connecting port; the secondary side circuit comprises a fourth capacitor, a second inductor and a third inductor, one end of the fourth capacitor is electrically connected with the second positive pole connecting port, and the other end is connected with the third inductor in series; the other end of the third inductor is electrically connected with the positive pole of the secondary winding and one end of the second inductor respectively, and the negative pole of the secondary winding is connected with the other end of the second inductor.

5. The time delay control based wideband beamforming acoustic Doppler velocimetry system according to claim 1 or 2 or 3, characterized in that, The beam forming module comprises a transmitting assembly and a receiving assembly; The transmitting assembly comprises an upsampling unit, a first time delay unit, a first phase shift unit, a first weighting unit and an up-conversion unit; the upsampling unit is used for performing digital interpolation filtering on baseband data and raising the sampling rate to the rate required by internal beam forming processing; the first time delay unit and the first phase shift unit sequentially perform time delay compensation and phase compensation on the interpolated baseband data respectively according to the target transmission direction, generating multiple paths of baseband data; the first weighting unit is used for applying amplitude weighting to each path of baseband data; and the up-conversion unit is used for performing up-conversion processing on the weighted baseband data. The receiving assembly comprises a down-conversion unit, a second time delay unit, a second phase shift unit, a second weighting unit and a downsampling unit; the down-conversion unit performs down-conversion processing on the received signal, the second time delay unit and the second phase shift unit sequentially perform time delay compensation and phase compensation on the down-converted baseband data; the second weighting unit forms beam output data after weighting and accumulation of the baseband data, and the downsampling unit is used for downsampling the beam output data to form a digital signal to be processed.

6. A time-delay controlled wideband beamforming acoustic Doppler velocimetry method, characterized in that, The speed measurement system according to any one of claims 1-5, comprising the following steps: generating a baseband signal from the baseband data to be transmitted; performing time delay compensation on the baseband signal according to a preset transmission direction to form multiple paths of signals, and then performing weighting processing on each path of signal; upsampling and mixing the data after weighting processing to a preset center frequency, and converting to a real signal; obtaining a transmission signal after signal conditioning and power amplification of the real signal, and transmitting the transmission signal through the planar transducer array; receiving a return signal by the planar transducer array; conditioning the received signal, and then performing quadrature mixing processing and downsampling on the conditioned signal to obtain a baseband complex signal; performing inter-channel time delay compensation and amplitude weighting processing on the baseband complex signal to synthesize received beam data; performing Doppler frequency shift parameter estimation on the received beam data to obtain speed information.

Images