阅读说明：本技术 一种基于偏转调制的超声相控阵波束形成方法 (ultrasonic phased array beam forming method based on deflection modulation ) 是由 秦云 陈伟 骆英 徐桂东 于 2019-09-10 设计创作，主要内容包括：本发明公开了一种基于偏转调制的相控阵波束形成方法,预先设计偏转调制范围和各偏转波数,并分别确定对于不同偏转波数各阵元所应具备的延迟时间；按预先设定的延迟时间对各阵元接收到的信号分别进行偏转延时处理；对行偏转延时处理的后的各偏转波数所对应的延迟采样数据进行偏转滤波,得到不同偏转角度对应的检测数据序列；利用主响应轴波数分量左右对称偏转调制结果的对称性,对偏转调制输出进行匹配滤波得到系统输出。本发明通过对超声相控阵接收系统阵列输出信号进行偏转调制、解调处理,获得主瓣更窄、旁瓣更低的阵列方向图。(The invention discloses an phased array beam forming method based on deflection modulation, which comprises the steps of designing a deflection modulation range and each deflection wave number in advance, determining delay time which should be possessed by each array element for different deflection wave numbers respectively, conducting deflection delay processing on signals received by each array element according to the preset delay time, conducting deflection filtering on delay sampling data which correspond to each deflection wave number after line deflection delay processing to obtain detection data sequences corresponding to different deflection angles, and conducting matched filtering on deflection modulation output by utilizing the symmetry of a main response axis wave number component bilateral symmetry deflection modulation result to obtain system output.)

The phased array beam forming method based on deflection modulation is 1 and , and is characterized by comprising the following steps:

s1, predefining a deflection modulation range and each deflection wave number, and respectively determining delay time of each array element corresponding to different deflection wave numbers; respectively carrying out deflection delay processing on signals received by each array element according to preset delay time;

s2, performing deflection filtering on the delay sampling data corresponding to each deflection wave number after deflection delay processing to obtain detection data sequences corresponding to different deflection wave numbers;

and S3, performing matched filtering on the deflection modulation output by utilizing the symmetry of the left-right symmetric deflection modulation result of the wave number component of the main response axis to obtain system output.

2. The method of phased array beam forming based on deflection modulation according to claim 1, wherein the array element sampling channel is configured with 1 delay element group, each delay element group comprises m delay elements, the delay elements perform delay processing on the detected data to obtain delay data of m deflection wave numbers, and each delay element performs offset, interpolation and decimation processing on the data queue to realize data delay required by 1 deflection wave number.

3. The method of phased array beam forming based on deflection modulation as claimed in claim 2, wherein the signals received by each array element are represented as:

sampling data sequence: (D)₀(l),D₁(l),…,D_n-1(l))，

Wherein n is the number of array element channels,

the output sequence of each delay unit after delaying the sampling data sequence is as follows:

wherein, tau_ijThat is, the jth delay amount of the ith array element channel, that is, the delay amount corresponding to the jth deflection wave number of the ith array element detection data.

And performing deflection delay processing on the data of each array element sampling channel to obtain delay sampling data corresponding to each deflection wave number.

4. phased array beam forming method based on deflection modulation, according to claim 3, characterized in that, the deflection filtering method is:

the output data corresponding to deflection wave numbers of each delay unit group are input into the filter unit, which substitutes the data into FIR to obtain its weighted sum to obtain y_j(l)：

And finally outputting an m-dimensional detection data sequence: (y)₀(l),y₁(l),…,y_m-1(l) Wherein w)_iAre weights.

5. The phased array beam forming method based on deflection modulation as claimed in claim 4, wherein the matched filtering is to fold the output sequence of the deflection filtering element in half and multiply it with itself one by one and accumulate to obtain the system output:

6. the phased array beam forming method based on deflection modulation as claimed in claim 2, wherein the deflection wavenumber is set such that m deflection angles are symmetrically set at equal intervals on both sides of the main response axis wavenumber to obtain m deflection vectors:

all deflection vectors can be expressed in combination in the form of a deflection modulation matrix

Wherein the content of the first and second substances,

Technical Field

The invention belongs to the processing of ultrasonic receiving signals in ultrasonic phased array imaging detection, and particularly relates to ultrasonic phased array beam forming methods based on deflection modulation.

Background

The design of the traditional array signal processing algorithm is realized by adopting FIR classical design methods such as a window function method, a frequency sampling method, an equal ripple optimization method and the like. By using the method, a feasible array wave number forming algorithm can be conveniently designed. On the basis, proper time delay processing is introduced to the output signal of each array element, so that the translation of the signal in the wave number domain can be realized, and signals with different central wave numbers are converted into 0 wave number for filtering, namely:

in the formula:

is the delay weight of each array element signal.

By utilizing the traditional array signal processing algorithm, the system design process is simple, the prior information of the tested sound field is not depended on, and the algorithm computation amount is small. However, the filtering effect is limited by the aperture of the array element, and taking an 8-array element standard linear array as an example, the minimum sine of the half width of the main lobe angle can reach about 0.12. Therefore, the traditional array signal processing algorithm has low transverse resolution and limited interference suppression capability.

In order to improve the interference suppression capability of a data processing algorithm, a statistical optimal filter can be formed by using a statistical signal processing theory, namely, an optimal weight is designed according to the actual conditions of a signal to be detected, an interference signal and noise in a sound field, for example, the MVDR algorithm can realize the minimum output total power under the condition of constant power of the signal to be detected, so that the algorithm has the optimal suppression capability on the interference and the noise, but the design of the weight of the algorithm depends on the priori knowledge of the sound field, so that the sound field needs to be sampled and detected for many times, the sampled data are processed to obtain the statistical characteristics of the sampled data, the conditions of the signal to be detected, the interference and the noise in the sound field are estimated, and on the basis, step estimation of the optimal weight can be further realized.

The method has the defects and limitations in the process of spatial filtering, and the invention designs algorithms which do not depend on sound field priori knowledge and have small calculation amount and can obtain narrower main lobes aiming at the defects of the current algorithms.

Disclosure of Invention

According to the problems in the prior art, the invention provides phased array beam forming methods based on deflection modulation, which can obtain a narrower main lobe without relying on sound field priori knowledge and an algorithm with a smaller computation amount, and can improve the detection space resolution in the ultrasonic nondestructive inspection application.

The technical scheme adopted by the invention is as follows:

A phased array beam forming method based on deflection modulation, comprising the steps of:

s1, predefining a deflection modulation range and each deflection wave number, and respectively determining delay time of each array element corresponding to different deflection wave numbers; respectively carrying out deflection delay processing on signals received by each array element according to preset delay time;

s2, performing deflection filtering on the delay sampling data corresponding to each deflection wave number after the line deflection delay processing to obtain detection data sequences corresponding to different deflection angles;

and S3, performing matched filtering on the deflection modulation output by utilizing the symmetry of the left-right symmetric deflection modulation result of the wave number component of the main response axis to obtain system output.

And , configuring 1 delay cell group in the array element sampling channel, wherein each delay cell group comprises m delay cells, respectively performing delay processing on the detection data to obtain delay data of m deflection wave numbers, and each delay cell performs offset, interpolation and extraction processing on the data queue to realize data delay required by 1 deflection wave number.

And , the signals received by the array elements are expressed as:

sampling data sequence: (D)₀(l),D₁(l),…,D_n-1(l))，

Wherein n is the number of array element channels,inputting a sampling data sequence for a delay cell group of an ith array element sampling channel, wherein l is a sampling sequence number, and l is 0,1, …_iIs array element position, k is signal wave number;

the output sequence of each delay unit after delaying the sampling data sequence is as follows:

wherein, tau_ijThat is, the jth delay amount of the ith array element channel, that is, the delay amount corresponding to the jth deflection wave number of the ith array element detection data;

deflection delay processing is carried out on the data of each array element sampling channel to obtain delay sampling data corresponding to each deflection wave number, and an nxm data sequence is output:

where m is the number of deflection wavenumbers.

And , the deflection filtering method comprises:

the output data corresponding to deflection wave numbers of each delay unit group are input into the filter unit, which substitutes the data into FIR to obtain its weighted sum to obtain y_j(l)：

And finally outputting an m-dimensional detection data sequence: (y)₀(l),y₁(l),…,y_m-1(l) Wherein w)_iAre weights.

And , folding the output sequence of the deflection filtering link in half, multiplying the output sequence by itself one by one, and accumulating to obtain the system output:

and , setting the deflection wave number as m deflection angles symmetrically arranged at equal intervals on two sides of the main response axis wave number to respectively obtain m corresponding deflection vectors:

i＝0,1,…,m-1

all deflection vectors can be expressed in combination in the form of a deflection modulation matrix

Wherein the content of the first and second substances,

delay weights for each array element signal under different deflection wavenumbers, wherein (k)_j+k_c)p_iIs the jth delay quantity tau of the ith array element channel_ij，p_iIs the ith array element position, k_jIs the jth deflection wavenumber, k_cThe dominant response axis wavenumber.

The invention has the beneficial effects that:

the invention provides array directional diagrams with narrower main lobe and lower side lobe by carrying out deflection modulation and demodulation processing on array output signals of an ultrasonic phased array receiving system.

Drawings

FIG. 1 is a block diagram of an algorithm implementation system;

FIG. 2 is a block diagram of a delay cell structure;

FIG. 3 is an 8-element array response using the basic FIR algorithm;

FIG. 4 is a modulation response of an 8-element array for 3 different wavenumber components;

fig. 5 is an 8-array element array matched filter output.

Detailed Description

For purposes of making the objects, aspects and advantages of the present invention more apparent, the present invention will be described in detail below with reference to the accompanying drawings and examples.

In order to realize the ultrasonic phased array beam forming methods based on deflection modulation, an array space filter is constructed, as shown in fig. 1, system hardware is formed by driving a high-speed ADC through an FPGA, and an internal circuit of the FPGA is designed by using a hardware description language to realize links such as deflection delay, deflection filtering, matched filtering and the like, the basic structure parameters of the system are that an acoustic wave medium is an aluminum plate, the sound velocity is about 6260m/s, the signal frequency is 100kHz, the wavelength 0.0626m, the array adopts a standard linear array of 8 array elements, the spacing of the array elements is set to be 0.0313m, namely half of the signal wavelength, the system sampling rate is set to be 32 times of the ultrasonic signal frequency, namely 3.2MHz modulation deflection wave number is 17, the modulation range of the deflection angle sine is +/-1/5, and the angle sine corresponds to-1/5, -7/40, -3/20, -1/8, -1/10, -3/40, -1/20, -1/40, 0, 1/40, 1/20, 3/40, 1/10, 1/8, 3/20, 7/40 and 1/5.

As shown in FIG. 2, during operation, the deflection delay element inputs n-dimensional sampling data sequence (D)₀(l),D₁(l),…,D_n-1(l) N is the number of array element channels, l is a sampling sequence number, and the ith array element channel delay unit group inputs a sampling data sequence:

in this embodiment, the FPGA samples 8 array elements of sample data, and samples 8 channels of sample data (D)₀(l),D₁(l),…,D₇(l) To the deflection delay stage.

Each delay unit realizes the delay processing of the data sequence, wherein the jth delay unit obtains the output:

wherein, tau_ijThat is, the jth delay amount of the ith array element channel, that is, the delay amount corresponding to the jth deflection wave number of the ith array element detection data.

In this embodiment, the deflection delay link allocates 1 delay cell group including 16 signal delay cells to each array element channel; and 8 delay unit groups are used for completing signal delay processing of all channels under various modulation deflection wave number requirements. The structure of the signal delay unit is shown in fig. 2. Each array element channel is continuously sampled, and the sampling result D_i(l) Into data queue D_i(-32)～D_i(32) The queue depth is 65, the middle position serial number is 0, and the forward and backward positions are positive or negative serial numbers, respectively. Each unit firstly carries out coarse delay operation, namely carries out address offset forwards or backwards by taking the middle position of the queue as a reference, and takes out two adjacent sampling data. And carrying out 32-equal division interpolation calculation between the two coarse delay data to obtain a fine delay result.

For the deflection angle θ, the delay time of the ith array element can be obtained as:

depending on the sample rate setting, the amount of delay can be expressed as an offset of the sampled data:

Δ＝16×(i-3.5)sinθ (4)

wherein: f is the frequency of the ultrasonic signal, the integer part of delta is the coarse delay, namely the offset of the sampled data sequence, the decimal part of delta corresponds to the fine delay, the extraction offset after 32-fold interpolation calculation is obtained by amplifying by 32 times, and then the corresponding deflection modulation delay can be calculated as follows:

in the deflection delay step, each array element channel data is processed to obtain delay sampling data corresponding to each deflection wave number, and an 8 × 17 data sequence is output: :

the deflection filtering link comprises 17 filtering units, and each filtering unit obtains delay output of each channel corresponding to offset angles

The output data of each channel are summed to obtain 17 deflection modulation data y of sampling time l₀(l)～y₁₆(l)。

And the matched filtering step multiplies the modulation output of the ith deflection wave number by the modulation output of the 16 th-i deflection wave number, and accumulates and sums all products to obtain the final output of the system. The output of the ith sample is:

the fundamental principle of ultrasonic nondestructive inspection is that an appropriate ultrasonic generating device is used for transmitting beams of ultrasonic waves to a certain direction, when a defect is encountered in the propagation process, the ultrasonic waves are reflected to a transmitting end by the surface of the defect, the transmitting end receives reflected echoes by an appropriate device (transducer), the size of the defect is determined by the intensity of the echoes, and the echo time indicates the spatial position of the defect.

The algorithm solves the main problems and contradictions that the array element spacing is limited, the array cannot be too sparse, the filtering effect is better when the overall size of the array is larger, namely, the system has strong response to signals in a specific direction, and signals slightly deviating from a desired direction are completely inhibited as much as possible, so that the signals cannot be interfered by other damages except a detection direction in the flaw detection process.

FIG. 4 shows the modulation response of the inventive line array system to 3 different wave number components, 1# being the main response axis component, 2# being the 0.1 pi/d wave number component, 3# being the-0.15 pi/d wave number component, where d is the array element spacing. As is readily apparent from fig. 2, the modulation responses of the system to the 2# and 3# wavenumber components are not characterized by bilateral symmetry, and only the modulation response of the 1# wavenumber component corresponding to the main response axis is bilaterally symmetric.

As shown in FIG. 5, the 8-element array matched filter output of the present invention has no bilateral symmetry, the wavenumber component in the non-main response axis direction is greatly suppressed, the wavenumber component in the main response axis can obtain higher gain, and the matched filter output of different wavenumber components can be seen in FIG. 5. the filtering effect of the system of the present invention on different wavenumber components is obviously improved, and the sine of the half width of the main lobe angle is only about 0.067, which is reduced to about half of the basic FIR algorithm.

The core of the invention is to use a proper algorithm to obtain a better filtering effect under the condition of relatively few array elements, and the cost is higher data processing capacity, but the cost is worthy for the application occasions with limitations in the aspects of detection system volume, process and the like. Meanwhile, according to the embodiment provided by the invention, the main cost of the increase required by the 8-element system is 9 multipliers, which can be satisfied by most of the FPGAs on the current market. Therefore, the invention has feasibility and practical value.

The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes and modifications made in accordance with the principles and concepts disclosed herein are intended to be included within the scope of the present invention.