CN103995262A - MIMO sparse array ultrasonic measurement methods and system for fluctuation interface - Google Patents

Abstract

The invention discloses two ultrasonic measurement methods and system for coded signal transmission on the basis of MIMO sparse array elements, and belongs to the technical field of ultrasonic measurement. The methods are used for measuring irregular fluctuation interfaces similar to fluctuation liquid levels and snow depths, and accuracy of distance measurement under the situation of the fluctuation interface is effectively improved. According to the methods, the sparse array is utilized for conducting ultrasonic measurement on the fluctuation interface at different angles, and two signal transmission modes, namely the time-sharing transmission mode and the simultaneous transmission mode, are adopted. According to the two transmission modes, signals are transmitted through the sparse array, and beam forming processing is carried out after channel separation of the signals is achieved. According to the methods, the echo signals of different virtual array elements can be effectively distinguished, the beam forming processing is facilitated, and accuracy of distance measurement of the fluctuation interface is improved; in addition, the simultaneous transmission mode is adopted to be applied to measurement of rapid changes of the fluctuation interface, distance ambiguity generated by the rapid changes of the fluctuation interface is avoided, and therefore the accuracy of the measurement is improved.

Description

For ultrasonic measurement method and the system of MIMO thinned array at the interface that rises and falls

Technical field

The invention belongs to ultrasonic measurement technical field, especially relate to two kinds for measure fluctuation liquid level, snow depth equal ripple interface MIMO thinned array ultrasonic measurement method and can realize the measuring system of these methods.

Background technology

Ultrasonic measurement is a kind of measuring method of high performance-price ratio, is widely used in all trades and professions.For example, at meteorological field, can realize by ultrasonic liquid-level measurement the measurement of rainfall amount and evaporation capacity, realize the measurement of snow depth by ultrasonic range observation.But in obtaining these meteorological elements with ultrasonic measurement method, due to the fluctuation of liquid level or the fluctuating at interface, traditional some ultrasonic measurement method probably produces larger measuring error.

In order to reduce the measuring error in these application, a simple way is with spatial sampling, then carries out spatial sampling average.Phase-array scanning method is a kind of method wherein, but the port number that the method needs is larger, and system cost is higher, thereby can not be widely adopted.The aspects such as ultrasonic measurement method is estimated in the transit time (TOF), transmitted, echo signal processing are carried out research, and obtain certain progress.Aspect TOF estimation, " the Ultrasonic time-of-flight eatimation through unscented kalman filter " that Angrisani L in 2006 etc. deliver on " IEEE Transactions on Instrumentation and Measurement ", utilize harmless Kalman filtering to process ultrasound echo signal, obtain the envelope of echoed signal, compare with discrete EKF, TOF estimated accuracy has reduced calculated amount when being improved; Aspect transmitting, within 2010, Zang Huai has just waited " the Intelligence Ultrasound tank gage of application linear FM signal " on " sensor and instrument and meter ", delivered, linear frequency modulation ripple is applied in ultrasonic liquid-level measurement, and improves the accuracy of level gauging in conjunction with matched filtering technique; Aspect echo signal processing, " the improving the discussion of aerosphere type ultrasonic water level gauge measuring accuracy " that yellow newly-built grade in 2011 is delivered on " hydrology ", utilizes the hyperacoustic echo frontier of digital sample compensating technique, improves the accuracy of Precipitation measurement.But, above method is mainly made up of one or two ultrasonic transducer, for single channel detection system, these classic methods are only estimated the distance value of a fixed point of whole liquid level, for the range observation at fluctuating interface, above method all easily produces larger measuring error, at present, still lacks a kind of more accurate ultrasonic measurement method for fluctuating interface.

Summary of the invention

For addressing the above problem, the invention discloses the ultrasonic measurement method of two kinds of coded signals based on the sparse array element of MIMO transmitting and can realize the ultrasound measurement system of these methods, for measuring similar fluctuation liquid level, the such random fluctuation interface of snow depth, effectively improve the accuracy of range observation under fluctuating interface conditions.

In order to achieve the above object, the invention provides following technical scheme:

For a ultrasonic measurement method for the MIMO thinned array at the interface that rises and falls, adopt MIMO Sparse Array element array, receive the individual Virtual array of evenly arranging of the equivalent M × N of one-tenth of array element by M transmitting array element and N; Comprise the steps:

Steps A, adopts M transmitting array element timesharing to launch identical linear frequency modulation ripple, transmit into:

S1(t)＝exp{j(2πf ₀t+πμt ²)},0≤t≤T

Wherein, f ₀for the initial frequency of linear frequency modulation ripple, μ=B/T is the chirp rate of linear frequency modulation ripple, and wherein B is modulating bandwidth, and T is signal duration;

Step B, N reception array element receives corresponding Virtual array echoed signal, and echoed signal is:

r1(m,n,t)＝α _mnS1(t-Δt _mn),1≤m≤M,1≤n≤N

Wherein, α _mnfor echoed signal attenuation coefficient, m, n represent respectively m transmitting array element and n reception array element, Δ t _mnfor transmit from m transmitting array element to target, then by target to n reception array element travel-time;

Step C, carries out wave beam formation processing to signal, obtains echo data matrix:

Step C-1, reassembles into corresponding each echoed signal Virtual array the echoed signal of M × N autonomous channel;

Step C-2, utilize r1 in echo data matrix (2,1, t) and r1 (3,4, data t) are carried out matched filtering processing and are obtained corresponding transit time Δ T1 and Δ T2;

Step C-3, by computing formula (Δ T1+ Δ T2) c/2 go out to rise and fall the according to a preliminary estimate distance at interface;

Step C-4, carries out time delay summation wave beam formation processing to echoed signal:

$y\left(t\right)=\underset{m,n}{\mathrm{\Σ}}{\mathrm{\α}}_{\mathrm{mn}}S1(t-\mathrm{\Δ}{t}_{\mathrm{mn}}^c),1\≤m\≤M,1\≤n\≤N$

Wherein for the time delay of different virtual array element after wave beam forms, τ _mnfor different virtual array element is with respect to the delay compensation value of reference point;

Step C-5, detects the echoed signal pre-determining in orientation and whether has carried out wave beam formation processing, wave beam formation processing is proceeded in untreated orientation, until all signals have all carried out, after wave beam formation processing, obtaining new echoed signal matrix;

Step D, the signal after wave beam is formed goes oblique processing, and output signal is:

y1(m,n,t)＝Aexp{j2πφ(m,n,t)}

In formula, phase function φ is $\mathrm{\φ}(m,n,t)=(\mathrm{\μ\Δ}{t}_{\mathrm{mn}}^{c}t+f_0\mathrm{\Δ}{t}_{\mathrm{mn}}^c-\mathrm{\μ}{\left(\mathrm{\Δ}{t}_{\mathrm{mn}}^c\right)}^2/2),$ A is range coefficient;

After trying to achieve processing, signal frequency composition is signal is carried out to FFT processing, obtains range information:

$d_{\mathrm{mn}}=\mathrm{c\Δ}{t}_{\mathrm{mn}}^c=\frac{{\mathrm{cf}}_{\mathrm{mn}}}{\mathrm{\μ}}.$

Further, after described step C-3, also comprise self-adaptation focusing step:

The focal position that the wave beam of each direction of scanning forms is determined at distance and bearing angle by fluctuating interface according to a preliminary estimate.

The present invention also provides the ultrasonic measurement method of the second for the MIMO thinned array at the interface that rises and falls, and adopts MIMO Sparse Array element array, receives the Virtual array that the equivalent M × N of one-tenth of array element evenly arranges by M transmitting array element with N; Comprise the steps:

Steps A, M transmitting array element is launched the linear frequency modulation ripple of different balance Gold pseudo-random code modulation simultaneously, transmit into:

$\begin{array}{c}S{2}_i\left(t\right)=\underset{n=0}{\overset{P-1}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i\mathrm{\δ}(t-n{\mathrm{\τ}}_c)\⊗v\left(t\right)\exp \left[j2\mathrm{\π}(f_{0}t+\frac{1}{2}{\mathrm{\μt}}^2)\right]\\ =S_{\mathrm{Gold}}^i\left(t\right)\⊗S_{\mathrm{LFM}}\left(t\right),i=\mathrm{1,2}...M\end{array}$

In formula, P, τ _cbe respectively code length and the symbol width of balance Gold code; for balance Gold code; f ₀, μ=B/ τ _c, B is respectively chirped initial frequency, chirp rate, modulating bandwidth; V (t) for length be τ _crectangular function; represent convolution algorithm; S _gold(t) impulse function of expression balance Gold code, S _lFM(t) represent linear FM signal;

The echoed signal that receives array element k is:

$r{2}_k\left(t\right)=\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\α}}_{i}S{2}_i(t-{\mathrm{\τ}}_{\mathrm{ki}}),k=\mathrm{1,2}...N$

In formula, α _ifor ultrasound echo signal attenuation amplitude, τ _kithe signal that is the transmitting of i transmitting array element arrives target, then arrives through target the travel-time that receives array element k;

Step B, the echoed signal that each reception array element is received transmits and carries out related operation and realize channel separation with M respectively, obtains the signal of M × N autonomous channel:

$y{2}_{\mathrm{jk}}\left(\mathrm{\τ}\right)=\underset{0}{\overset{T}{\∫}}r{2}_k\left(t\right)S{2}_j^{*}(t-\mathrm{\τ})\mathrm{dt}={\mathrm{\α}}_i{R}_{\mathrm{ii}}+\underset{i\≠j}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\α}}_i{R}_{\mathrm{ij}}$

In formula, * represents to ask complex conjugate; R _iifor signal autocorrelation output; for all possible simple crosscorrelation output of signal sum; Simple crosscorrelation output expression formula is:

$\begin{array}{c}{R}_{\mathrm{ij}}\left(\mathrm{\τ}\right)=\underset{-\∞}{\overset{+\∞}{\∫}}S{2}_i\left(t\right)S{2}_j^{*}(t-\mathrm{\τ})\mathrm{dt}=S{2}_i\left(\mathrm{\τ}\right)\⊗S{2}_j^{*}(-\mathrm{\τ})\\ =[S_{\mathrm{Gold}}^i\left(\mathrm{\τ}\right)\⊗S_{\mathrm{LFM}}\left(\mathrm{\τ}\right)]\⊗[S_{\mathrm{Gold}}^{j*}(-\mathrm{\τ})\⊗S_{\mathrm{LFM}}^{*}(-\mathrm{\τ})]\\ =\underset{m=-(P-1)}{\overset{P-1}{\mathrm{\Σ}}}{R}_{\mathrm{Gold}}^{\mathrm{ij}}\left(m{\mathrm{\τ}}_c\right)\·R_{\mathrm{LFM}}(\mathrm{\τ}-m{\mathrm{\τ}}_c)\end{array}$

Wherein,

$R_{\mathrm{Gold}}^{\mathrm{ij}}\left(m{\mathrm{\τ}}_c\right)=\left\{\begin{array}{cc}\underset{n=0}{\overset{P-1+m}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i{\mathrm{\κ}}_{n-m}^j,& -(P-1)\≤m\≤0\\ \underset{n=m}{\overset{P-1}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i{\mathrm{\κ}}_{n-m}^j,& 0\≤m\≤(P-1)\end{array}\right.,$

$R_{\mathrm{LFM}}(\mathrm{\τ}-m{\mathrm{\τ}}_c)=\left\{\begin{array}{cc}\exp \left[j2\mathrm{\π}(f_0+\frac{1}{2}\mathrm{\μ}{\mathrm{\τ}}_c)(\mathrm{\τ}-m{\mathrm{\τ}}_c)\right]\·& \\ ({\mathrm{\τ}}_c-|\mathrm{\τ}-m{\mathrm{\τ}}_c\left|\right)\sin c\left[\mathrm{\π\μ}{\mathrm{\τ}}_c(\mathrm{\τ}-m{\mathrm{\τ}}_c)(1-\frac{|\mathrm{\τ}-m{\mathrm{\τ}}_c|}{{\mathrm{\τ}}_c})\right],& |\mathrm{\τ}-m{\mathrm{\τ}}_c|\≤{\mathrm{\τ}}_c\\ 0,& |\mathrm{\τ}-m{\mathrm{\τ}}_c|\≥{\mathrm{\τ}}_c\end{array}\right.,$

In formula, for the cross correlation function of balance Gold code; R _lFM(τ) be the cross correlation function of linear FM signal.

Step C, carries out wave beam formation processing to signal, obtains range information:

Step C-1, utilize r1 in the echo data matrix of M × N autonomous channel (2,1, t) and r1 (3,4, data t) are carried out matched filtering processing and are obtained corresponding transit time Δ T1 and Δ T2;

Step C-2, by computing formula (Δ T1+ Δ T2) c/2 go out to rise and fall the according to a preliminary estimate distance at interface;

Step C-3, then carries out time delay summation wave beam formation processing to the signal after channel separation;

Step C-4, proceeds wave beam formation processing to untreated orientation, until all signals have all carried out, after wave beam formation processing, obtaining new echoed signal matrix;

Step C-5, is obtained the transit time Δ T of target echo signal by the peak value of the echoed signal after channel separation and wave beam formation processing, calculate Δ Tc and obtain target distance measurement information.

Further, after described step C-2, also comprise self-adaptation focusing step:

The focal position that the wave beam of each direction of scanning forms is determined at distance and bearing angle by fluctuating interface according to a preliminary estimate.

For a ultrasound measurement system for the MIMO thinned array at the interface that rises and falls, comprise supersonic array and signal transmitting and transaction module,

Described supersonic array receives with N the Virtual array that the equivalent M × N of one-tenth of array element evenly arranges by M transmitting array element;

The transmitting of described signal and transaction module comprise timesharing Launching Model and Launching Model simultaneously, and described timesharing Launching Model comprises timesharing transmitter unit, wave beam forming unit, removes oblique processing unit, FFT converter unit;

In described timesharing transmitter unit, linear frequency-modulated wave is launched in the timesharing of M transmitting array element, realizes the channel separation of Virtual array echoed signal by the timesharing transmitting of signal, and N receives array element and receive corresponding Virtual array echoed signal;

Described wave beam forming unit, for after finishing in all echoed signals receptions, reassembles into corresponding each echoed signal Virtual array the echoed signal of M × N autonomous channel, and it is carried out to wave beam formation processing;

Describedly go oblique processing unit for composite signal being gone to oblique processing;

Described FFT converter unit, for to going oblique signal after treatment to carry out FFT processing, calculates corresponding range information;

Described while Launching Model comprises transmitter unit, channel separation unit, wave beam forming unit simultaneously;

In described while transmitter unit, M transmitting array element is launched the linear frequency modulation ripple of different balance Gold pseudo-random code modulation simultaneously, and N receives array element and receive simultaneously;

Described channel separation unit transmits and carries out related operation and realize channel separation with M respectively for echoed signal that each reception array element is received, obtains the signal of M × N autonomous channel,

Described wave beam forming unit is carried out wave beam formation processing for the signal that above-mentioned separation is obtained, and obtains corresponding range information.

Further, in described timesharing Launching Model and simultaneously Launching Model, wave beam forming unit, in the time that signal is carried out to wave beam formation processing, adopts self-adaptation focusing method.

Beneficial effect:

Compared with traditional some ultrasonic measurement, anti-interference and the accuracy of measurement of ultrasonic measurement method provided by the invention obviously improve, can Measurement accuracy fluctuating interface, even in the case of the amplitude of the interfacial wave of about 4cm, still can obtain high accuracy.Utilize when large wide bandwidth signals as transmitting simultaneously, and in conjunction with pulse compression technique, there is good range resolution; When the present invention adopts simultaneously emission mode, still can reliably working in the situation that of be low to moderate in signal to noise ratio (S/N ratio)-30dB.In addition, adopt self-adaptation focusing method, ensured that focus changes with the change at interface, thereby ensured the accuracy of measuring.The present invention is not limited only to the application of meteorological field, and can extensively be generalized to other field, as the measurement of the correlation parameters such as chemical industry, cement, coal, the hydrology, has the value of high application and the prospect of widespread use.

Brief description of the drawings

Fig. 1 is the ultrasound measurement system structural representation for the MIMO thinned array at the interface that rises and falls;

Fig. 2 is the array junctions composition that 4 transmitting array elements and 4 receive array element;

Fig. 34 transmitting array elements when adopting timesharing emission mode pie graph that transmits;

Fig. 4 is adopt timesharing emission mode to rise and fall signal processing flow figure that interface distance measures;

Fig. 5 is embodiment mono-neutral line FM signal excitation, the excitation of balance Gold-LFM composite signal and the pulse pressure result figure of point measurement chirp in the sub-measurement situation of single scattering;

Fig. 6 is that while getting different signal to noise ratio (S/N ratio) in embodiment bis-, wave beam forms the skew of the focus schematic diagram that affects on measuring accuracy;

Fig. 7 is the point target measuring error figure of two kinds of emission modes while getting different signal to noise ratio (S/N ratio) in embodiment tri-, and wherein figure (b) is longitudinal enlarged drawing of figure (a);

Fig. 8 is the Error Graph of interface level measurement of rising and falling under timesharing emission mode in embodiment tetra-, and wherein figure (a) be fluctuating interface, and figure (b) is the Error Graph measuring.

Embodiment

Below with reference to specific embodiment, technical scheme provided by the invention is elaborated, should understands following embodiment and only be not used in and limit the scope of the invention for the present invention is described.

The invention provides a kind of ultrasound measurement system of the MIMO thinned array for the interface that rises and falls, as shown in Figure 1, comprise supersonic array and signal transmitting and transaction module,

Described supersonic array receives with N the Virtual array that the equivalent M × N of one-tenth of array element evenly arranges by M transmitting array element;

The transmitting of described signal and transaction module comprise timesharing Launching Model and Launching Model simultaneously, and described timesharing Launching Model comprises timesharing transmitter unit, wave beam forming unit, removes oblique processing unit, FFT converter unit;

In described timesharing transmitter unit, linear frequency-modulated wave is launched in the timesharing of M transmitting array element, realizes the channel separation of Virtual array echoed signal by the timesharing transmitting of signal, and N receives array element and receive corresponding Virtual array echoed signal;

Described wave beam forming unit, for after finishing in all echoed signals receptions, reassembles into corresponding each echoed signal Virtual array the echoed signal of M × N autonomous channel, and it is carried out to wave beam formation processing;

Describedly go oblique processing unit for composite signal being gone to oblique processing;

Described FFT converter unit, for to going oblique signal after treatment to carry out FFT processing, calculates corresponding range information;

Described while Launching Model comprises transmitter unit, channel separation unit, wave beam forming unit simultaneously;

In described while transmitter unit, M transmitting array element is launched the linear frequency modulation ripple of different balance Gold pseudo-random code modulation simultaneously, and N receives array element and receive simultaneously;

Described channel separation unit transmits and carries out related operation and realize channel separation with M respectively for echoed signal that each reception array element is received, obtains the signal of M × N autonomous channel,

Described wave beam forming unit is carried out wave beam formation processing for the signal that above-mentioned separation is obtained, and obtains corresponding range information.

Because forming departing from of focus, wave beam can exert an influence to measurement accuracy, therefore in the wave beam forming unit in timesharing Launching Model and while Launching Model, all adopt a kind of self-adaptation focusing method, ensure that focus changes with the change at interface, thereby ensured the accuracy of measuring.

The present invention utilizes thinned array to carry out from different perspectives ultrasonic measurement to fluctuating interface, two kinds of patterns that transmit are adopted: timesharing emission mode and simultaneously emission mode, can effectively distinguish the echoed signal of different virtual array element, be conducive to carry out wave beam formation processing, improve the accuracy that fluctuating interface distance is measured, in addition, adopt the pattern of transmitting simultaneously can be applied in the fast-changing measurement in fluctuating interface, avoid producing range ambiguity by the quick variation at fluctuating interface, thereby improve the accuracy of measuring.These two kinds of emission modes are all transmitted by thinned array, realize after the channel separation of signal, carry out wave beam formation processing.Under timesharing emission mode, transmitted and realized the channel separation of signal by timesharing, simultaneously under emission mode, the echoed signal by difference being received to array element transmits and carries out relevant treatment and realize the channel separation of signal with M respectively.In the time adopting timesharing emission mode, after wave beam formation processing, also need tiltedly to process and fast fourier transform (FFT).

Specifically, timesharing launching technique provided by the invention, adopts MIMO Sparse Array element array, receives the Virtual array that the equivalent M × N of one-tenth of array element evenly arranges by M transmitting array element with N; Comprise the steps:

Steps A, adopts M of timesharing to launch array element timesharing and launches identical linear frequency modulation ripple, transmit into:

S1(t)＝exp{j(2πf ₀t+πμt ²)},0≤t≤T (1)

Wherein, f ₀for the initial frequency of linear frequency modulation ripple, μ=B/T is the chirp rate of linear frequency modulation ripple, and wherein B is modulating bandwidth, and T is signal duration;

Step B, N reception array element receives corresponding Virtual array echoed signal, and echoed signal is:

r1(m,n,t)＝α _mnS1(t-Δt _mn),1≤m≤M,1≤n≤N (2)

Wherein, α _mnfor echoed signal attenuation coefficient, m, n represent respectively m transmitting array element and n reception array element, Δ t _mnfor transmit from m transmitting array element to target, then by target to n reception array element travel-time;

Step C, reassembles into corresponding each echoed signal Virtual array the echoed signal of M × N autonomous channel; Utilize r1 in echo data matrix (2,1, t) and r1 (3,4, data t) are carried out matched filtering processing and are obtained corresponding transit time Δ T1 and Δ T2; By computing formula (Δ T1+ Δ T2) c/2 go out to rise and fall the according to a preliminary estimate distance at interface; Because forming departing from of focus, wave beam can exert an influence to measurement accuracy, therefore as improving, we adopt self-adaptation focusing method, first determine that by the distance and bearing angle at fluctuating interface according to a preliminary estimate (direction of scanning refers to that coordinate origin forms the direction of focus to wave beam to each " scanning " direction.Scanning is generally that the direction by changing ultrasonic wave acoustic beam realizes, the present invention forms the position of focus by changing wave beam, change the sound beam direction of synthetic ultrasound echo signal, play the effect of " scanning ") the focal position that forms of wave beam, then echoed signal is carried out to time delay summation wave beam formation processing:

$y\left(t\right)=\underset{m,n}{\mathrm{\Σ}}{\mathrm{\α}}_{\mathrm{mn}}S1(t-\mathrm{\Δ}{t}_{\mathrm{mn}}^c),1\≤m\≤M,1\≤n\≤N---\left(3\right)$

Wherein for the time delay of different virtual array element after wave beam forms, τ _mnfor different virtual array element is with respect to the delay compensation value of reference point;

Whether the echoed signal that detection pre-determines in orientation has all carried out wave beam formation processing, if result negate, wave beam formation processing is proceeded in untreated orientation, otherwise, obtain new echoed signal matrix;

Step D, the signal after wave beam is formed goes oblique processing, and output signal is:

y1(m,n,t)＝Aexp{j2πφ(m,n,t)} (4)

In formula, phase function φ is $\mathrm{\φ}(m,n,t)=(\mathrm{\μ\Δ}{t}_{\mathrm{mn}}^{c}t+f_0\mathrm{\Δ}{t}_{\mathrm{mn}}^c-\mathrm{\μ}{\left(\mathrm{\Δ}{t}_{\mathrm{mn}}^c\right)}^2/2),$ A is range coefficient;

After trying to achieve processing, signal frequency composition is therefore, " going tiltedly " signal after treatment is carried out to FFT processing, can obtain range information by following formula:

$d_{\mathrm{mn}}=\mathrm{c\Δ}{t}_{\mathrm{mn}}^c=\frac{{\mathrm{cf}}_{\mathrm{mn}}}{\mathrm{\μ}}---\left(5\right)$

While launching technique provided by the invention, adopts MIMO Sparse Array element array, receives the Virtual array that the equivalent M × N of one-tenth of array element evenly arranges by M transmitting array element with N; Comprise the steps:

Steps A, M transmitting array element is launched the linear frequency modulation ripple of different balance Gold pseudo-random code modulation simultaneously, transmit into:

$\begin{array}{c}S{2}_i\left(t\right)=\underset{n=0}{\overset{P-1}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i\mathrm{\δ}(t-n{\mathrm{\τ}}_c)\⊗v\left(t\right)\exp \left[j2\mathrm{\π}(f_{0}t+\frac{1}{2}{\mathrm{\μt}}^2)\right]\\ =S_{\mathrm{Gold}}^i\left(t\right)\⊗S_{\mathrm{LFM}}\left(t\right),i=\mathrm{1,2}...M\end{array}---\left(6\right)$

In formula, P, τ _cbe respectively code length and the symbol width of balance Gold code; for balance Gold code; f ₀, μ=B/ τ _c, B is respectively chirped initial frequency, chirp rate, modulating bandwidth; V (t) for length be τ _crectangular function; represent convolution algorithm; S _gold(t) impulse function of expression balance Gold code, S _lFM(t) represent linear FM signal;

The echoed signal that receives array element k is:

$r{2}_k\left(t\right)=\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\α}}_{i}S{2}_i(t-{\mathrm{\τ}}_{\mathrm{ki}}),k=\mathrm{1,2}...N$

In formula, α _ifor ultrasound echo signal attenuation amplitude, τ _kithe signal that is the transmitting of i transmitting array element arrives target, then arrives through target the travel-time that receives array element k.

Step B, the echoed signal that each reception array element is received transmits and carries out related operation and realize channel separation with M respectively, obtains the signal of M × N autonomous channel:

$y{2}_{\mathrm{jk}}\left(\mathrm{\τ}\right)=\underset{0}{\overset{T}{\∫}}r{2}_k\left(t\right)S{2}_j^{*}(t-\mathrm{\τ})\mathrm{dt}={\mathrm{\α}}_i{R}_{\mathrm{ii}}+\underset{i\≠j}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\α}}_i{R}_{\mathrm{ij}}$

In formula, * represents to ask complex conjugate; R _iifor signal autocorrelation output; for all possible simple crosscorrelation output of signal sum; Simple crosscorrelation output expression formula is:

$\begin{array}{c}{R}_{\mathrm{ij}}\left(\mathrm{\τ}\right)=\underset{-\∞}{\overset{+\∞}{\∫}}S{2}_i\left(t\right)S{2}_j^{*}(t-\mathrm{\τ})\mathrm{dt}=S{2}_i\left(\mathrm{\τ}\right)\⊗S{2}_j^{*}(-\mathrm{\τ})\\ =[S_{\mathrm{Gold}}^i\left(\mathrm{\τ}\right)\⊗S_{\mathrm{LFM}}\left(\mathrm{\τ}\right)]\⊗[S_{\mathrm{Gold}}^{j*}(-\mathrm{\τ})\⊗S_{\mathrm{LFM}}^{*}(-\mathrm{\τ})]\\ =\underset{m=-(P-1)}{\overset{P-1}{\mathrm{\Σ}}}{R}_{\mathrm{Gold}}^{\mathrm{ij}}\left(m{\mathrm{\τ}}_c\right)\·R_{\mathrm{LFM}}(\mathrm{\τ}-m{\mathrm{\τ}}_c)\end{array}$

$R_{\mathrm{Gold}}^{\mathrm{ij}}\left(m{\mathrm{\τ}}_c\right)=\left\{\begin{array}{cc}\underset{n=0}{\overset{P-1+m}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i{\mathrm{\κ}}_{n-m}^j,& -(P-1)\≤m\≤0\\ \underset{n=m}{\overset{P-1}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i{\mathrm{\κ}}_{n-m}^j,& 0\≤m\≤(P-1)\end{array}\right.$

$R_{\mathrm{LFM}}(\mathrm{\τ}-m{\mathrm{\τ}}_c)=\left\{\begin{array}{cc}\exp \left[j2\mathrm{\π}(f_0+\frac{1}{2}\mathrm{\μ}{\mathrm{\τ}}_c)(\mathrm{\τ}-m{\mathrm{\τ}}_c)\right]\·& \\ ({\mathrm{\τ}}_c-|\mathrm{\τ}-m{\mathrm{\τ}}_c\left|\right)\sin c\left[\mathrm{\π\μ}{\mathrm{\τ}}_c(\mathrm{\τ}-m{\mathrm{\τ}}_c)(1-\frac{|\mathrm{\τ}-m{\mathrm{\τ}}_c|}{{\mathrm{\τ}}_c})\right],& |\mathrm{\τ}-m{\mathrm{\τ}}_c|\≤{\mathrm{\τ}}_c\\ 0,& |\mathrm{\τ}-m{\mathrm{\τ}}_c|\≥{\mathrm{\τ}}_c\end{array}\right.$

In formula, for the cross correlation function of balance Gold code; R _lFM(τ) be the cross correlation function of linear FM signal.After relevant treatment, realized the channel separation of echoed signal, the sharp-pointed characteristic of autocorrelation function is conducive to improve the accuracy of measuring.

Step C, utilize r1 (2 in the echo data matrix of M × N autonomous channel, 1, and r1 (3 t), 4, t) data are carried out matched filtering processing and are obtained corresponding transit time Δ T1 and Δ T2, by computing formula (Δ T1+ Δ T2) c/2 go out to rise and fall the according to a preliminary estimate distance at interface. as improvement, we adopt self-adaptation focusing method, first determine by the distance and bearing angle at fluctuating interface according to a preliminary estimate the focal position that the wave beam of each " scanning " direction forms, again the signal after channel separation is carried out to time delay summation wave beam formation processing, whether the echoed signal that detection pre-determines in orientation has all carried out wave beam formation processing, if result negates, wave beam formation processing is proceeded in untreated orientation, otherwise, obtain new echoed signal matrix.Obtained the transit time Δ T of target echo signal by the peak value of the echoed signal after channel separation and wave beam formation processing, calculate Δ Tc and obtain target distance measurement information.

Embodiment mono-:

As shown in Figure 2, the criterion that the ultrasonic Sparse Array element array in the present embodiment is arranged is: be d if set the spacing of Virtual array, the array element distance of every group of emission array is d ^t=2 × d, the array element distance of receiving array is d ^r=M × d, the spacing at every group of emission array and receiving array edge is d.The invention process example all adopts 4 transmitting array elements, and its coordinate is respectively (135,0), (105,0), (105,0), (135,0) (unit: mm), 4 receive array element, and its coordinate is respectively (90,0), (30,0), (30,0), (90,0) (unit: mm).

The centre frequency of linear FM signal is made as 300KHZ, and bandwidth is 60KHZ, and balance Gold code adopts the coding in following table 1.

The balance Gold code that the code length that table 1 optimization obtains is 127

Adopt respectively that timesharing emission mode is carried out in linear FM signal excitation, while emission mode is carried out in the excitation of balance Gold-LFM composite signal and point measurement chirp carries out single channel emission mode.

While adopting timesharing emission mode to rise and fall interface distance measurement, 4 the 4 ultrasonic thinned arrays of receipts in employing Fig. 2 obtain the echo data of 16 autonomous channels, and 4 transmitting array elements transmit pie graph as shown in Figure 3, be organized into after echo data matrix, follow-up signal processing procedure comprises the following steps (as shown in Figure 4): 1. utilize r1 (2 in echo data matrix, 1, and r1 (3 t), 4, t) data go out to rise and fall the according to a preliminary estimate distance at interface, then determine that by the distance and bearing angle at fluctuating interface according to a preliminary estimate the position coordinates that 2. focal position that wave beam forms forms focus according to ultrasonic array element and wave beam calculates time delay and relative delay corresponding to each Virtual array for how much, each echoed signal in echo data matrix is carried out to corresponding time delay equalization, then sue for peace and obtain the composite signal that this side up, change focus orientation repeats above processing procedure and 3. directive composite signal is removed to tiltedly processing and FFT until obtain the directive composite signal of institute, obtain the distance to fluctuating interface of supersonic array center in respective direction, according to the position angle interface shape sample range information that can obtain rising and falling, it is averaged and obtains range information accurately.

Adopt when emission mode rises and falls interface distance measurement simultaneously, 4 transmitting array elements are launched the linear frequency modulation ripple of different balance Gold pseudo-random code modulation simultaneously, 4 receive array element and receive simultaneously, the echoed signal that each reception array element receives transmits and carries out related operation and realize channel separation with 4 respectively, obtain the signal of 4 × 4=16 autonomous channel, then carry out wave beam formation processing, obtain corresponding range information.

The pulse compression result figure that aforementioned three kinds of emission modes obtain in the situation that single scattering is measured as shown in Figure 5, as can be seen from Figure 5, the main secondary lobe of transmitted waveform under two kinds of emission modes provided by the invention after pulse compression is higher, there is good range resolution, pulsewidth after balance Gold-LFM composite signal pulse pressure compares the narrower of linear FM signal but secondary lobe improves slightly, and the Range resolution effect of point measurement chirp in the sub-measurement situation of multiple scattering is relatively poor.

Embodiment bis-:

Ultrasonic array element array arrangement as shown in Figure 2, getting array center's point is coordinate axis initial point, the centre frequency of linear FM signal is made as 300KHZ, bandwidth is 60KHZ, point target position is located at (14 °, 1.2m), the location test wave beam that forms focus by changing wave beam forms the impact that measurement accuracy is produced that departs from of focus, wherein wave beam form the skew of focus be divided into along synthetic wave beam axially and position angle both direction be offset.Be 20mm when wave beam forms focus along synthetic wave beam axle offset scope, echo signal to noise ratio (S/N ratio) was higher than 5 o'clock, measuring error is stabilized in 0.6mm, but, position angle skew can cause sizable wave beam to form focal shift, cause serious measuring error, corresponding emulation (adopting timesharing emission mode) result is as Fig. 6.From Fig. 6, we can find out, echo signal to noise ratio (S/N ratio) is 15, when the position angle of wave beam formation focus is 0.245 radian (14 °), measuring error is less than 0.5mm, in the time that the position angle of wave beam formation focus is reduced to 0.241 radian (13.45 °) or is increased to 0.253 radian (14.55 °), measuring error is increased to 1.2mm; Echo signal to noise ratio (S/N ratio) is reduced to 5, and when the position angle of wave beam formation focus is reduced to 0.242 radian (13.85 °) or is increased to 0.247 radian (14.2 °), measuring error exceedes 1.2mm.From Fig. 6, it can also be seen that, when wave beam formation focus is offset along azimuth direction, measuring error near symmetrical, along with the reduction of echo signal to noise ratio (S/N ratio), wave beam forms focus and is limited in the interior measuring error that can guarantee expectation among a small circle along azimuth direction deviation range.Although wave beam in method forms departing from of focus and can exert an influence to measurement accuracy,, the present invention, owing to having adopted self-adaptation focusing method, has ensured that focus changes with the change at interface, thereby ensures the accuracy of measuring.

Embodiment tri-:

Ultrasonic array element array arrangement is as Fig. 2, getting array center's point is coordinate axis initial point, the centre frequency of linear FM signal is made as 300KHZ, bandwidth is 60KHZ, balance Gold code adopts the coding in table 1, adopt respectively timesharing, while emission mode under different state of signal-to-noise, to carry out single-point target measurement, get-30～15dB of the scope of signal to noise ratio (S/N ratio), point target position is located at (0 °, 0.5m), steps flow chart, with embodiment mono-, obtains the Error Graph (Fig. 7) of two kinds of emission modes under different state of signal-to-noise.

From Fig. 7 (a), can find out, the method for the invention can Measurement accuracy in low signal-to-noise ratio situation target range, especially at the same time under emission mode, still can reliably working in the situation of be low to moderate-30dB of signal to noise ratio (S/N ratio).Fig. 7 (b) is longitudinal enlarged drawing of Fig. 7 (a), can find out that at the same time under emission mode, measuring error is in 0.1mm, and the method has good noiseproof feature.

Embodiment tetra-:

Ultrasonic array element array arrangement is as Fig. 2, getting array center's point is coordinate axis initial point, the centre frequency of linear FM signal is made as 300KHZ, bandwidth is 60KHZ, fluctuating interface is as shown in Fig. 8 (a), adopt the rise and fall measurement at interface of timesharing emission mode, steps flow chart, with embodiment mono-, obtains measuring error figure as Fig. 8 (b).

Utilize r1 (2 in echo data matrix, 1, and r1 (3 t), 4, go out to rise and fall the according to a preliminary estimate distance at interface of data t) is 1.0063m, and the distance at the interface that finally obtains rising and falling is 1.0002, maximum error of measuring is 0.1867mm, therefore, the method for the invention is not only feasible, and can further improve the accuracy of fluctuating interface level measurement.

The disclosed technological means of the present invention program is not limited only to the disclosed technological means of above-mentioned embodiment, also comprises the technical scheme being made up of above technical characterictic combination in any.It should be pointed out that for those skilled in the art, under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications are also considered as protection scope of the present invention.

Claims (6)

1. for a ultrasonic measurement method for the MIMO thinned array at the interface that rises and falls, it is characterized in that, adopt MIMO Sparse Array element array, receive the individual Virtual array of evenly arranging of the equivalent M × N of one-tenth of array element by M transmitting array element and N; Comprise the steps:

Steps A, adopts M transmitting array element timesharing to launch identical linear frequency modulation ripple, transmit into:

S1(t)＝exp{j(2πf ₀t+πμt ²)},0≤t≤T

Wherein, f ₀for the initial frequency of linear frequency modulation ripple, μ=B/T is the chirp rate of linear frequency modulation ripple, and wherein B is modulating bandwidth, and T is signal duration;

Step B, N reception array element receives corresponding Virtual array echoed signal, and echoed signal is:

r1(m,n,t)＝α _mnS1(t-Δt _mn),1≤m≤M,1≤n≤N

Wherein, α _mnfor echoed signal attenuation coefficient, m, n represent respectively m transmitting array element and n reception array element, Δ t _mnfor transmit from m transmitting array element to target, then by target to n reception array element travel-time;

Step C, carries out wave beam formation processing to signal, obtains echo data matrix:

Step C-1, reassembles into corresponding each echoed signal Virtual array the echoed signal of M × N autonomous channel;

Step C-2, utilize r1 in echo data matrix (2,1, t) and r1 (3,4, data t) are carried out matched filtering processing and are obtained corresponding transit time Δ T1 and Δ T2;

Step C-3, by computing formula (Δ T1+ Δ T2) c/2 go out to rise and fall the according to a preliminary estimate distance at interface;

Step C-4, carries out time delay summation wave beam formation processing to echoed signal:

$y\left(t\right)=\underset{m,n}{\mathrm{\Σ}}{\mathrm{\α}}_{\mathrm{mn}}S1(t-\mathrm{\Δ}{t}_{\mathrm{mn}}^c),1\≤m\≤M,1\≤n\≤N$

Wherein for the time delay of different virtual array element after wave beam forms, τ _mnfor different virtual array element is with respect to the delay compensation value of reference point;

Step C-5, detects the echoed signal pre-determining in orientation and whether has carried out wave beam formation processing, wave beam formation processing is proceeded in untreated orientation, until all signals have all carried out, after wave beam formation processing, obtaining new echoed signal matrix;

Step D, the signal after wave beam is formed goes oblique processing, and output signal is:

y1(m,n,t)＝Aexp{j2πφ(m,n,t)}

In formula, phase function φ is $\mathrm{\φ}(m,n,t)=(\mathrm{\μ\Δ}{t}_{\mathrm{mn}}^{c}t+f_0\mathrm{\Δ}{t}_{\mathrm{mn}}^c-\mathrm{\μ}{\left(\mathrm{\Δ}{t}_{\mathrm{mn}}^c\right)}^2/2),$ A is range coefficient;

After trying to achieve processing, signal frequency composition is signal is carried out to FFT processing, obtains range information:

$d_{\mathrm{mn}}=\mathrm{c\Δ}{t}_{\mathrm{mn}}^c=\frac{{\mathrm{cf}}_{\mathrm{mn}}}{\mathrm{\μ}}.$

2. the ultrasonic measurement method of the MIMO thinned array for the interface that rises and falls according to claim 1, is characterized in that, also comprises self-adaptation focusing step after described step C-3:

The focal position that the wave beam of each direction of scanning forms is determined at distance and bearing angle by fluctuating interface according to a preliminary estimate.

3. the second, for the ultrasonic measurement method of the MIMO thinned array at the interface that rises and falls, is characterized in that, adopts MIMO Sparse Array element array, receives the Virtual array that the equivalent M × N of one-tenth of array element evenly arranges by M transmitting array element with N; Comprise the steps:

Steps A, M transmitting array element is launched the linear frequency modulation ripple of different balance Gold pseudo-random code modulation simultaneously, transmit into:

$\begin{array}{c}S{2}_i\left(t\right)=\underset{n=0}{\overset{P-1}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i\mathrm{\δ}(t-n{\mathrm{\τ}}_c)\⊗v\left(t\right)\exp \left[j2\mathrm{\π}(f_{0}t+\frac{1}{2}{\mathrm{\μt}}^2)\right]\\ =S_{\mathrm{Gold}}^i\left(t\right)\⊗S_{\mathrm{LFM}}\left(t\right),i=\mathrm{1,2}...M\end{array}$

In formula, P, τ _cbe respectively code length and the symbol width of balance Gold code; for balance Gold code; f ₀, μ=B/ τ _c, B is respectively chirped initial frequency, chirp rate, modulating bandwidth; V (t) for length be τ _crectangular function; represent convolution algorithm; S _gold(t) impulse function of expression balance Gold code, S _lFM(t) represent linear FM signal;

The echoed signal that receives array element k is:

$r{2}_k\left(t\right)=\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\α}}_{i}S{2}_i(t-{\mathrm{\τ}}_{\mathrm{ki}}),k=\mathrm{1,2}...N$

In formula, α _ifor ultrasound echo signal attenuation amplitude, τ _kithe signal that is the transmitting of i transmitting array element arrives target, then arrives through target the travel-time that receives array element k;

Step B, the echoed signal that each reception array element is received transmits and carries out related operation and realize channel separation with M respectively, obtains the signal of M × N autonomous channel:

$y{2}_{\mathrm{jk}}\left(\mathrm{\τ}\right)=\underset{0}{\overset{T}{\∫}}r{2}_k\left(t\right)S{2}_j^{*}(t-\mathrm{\τ})\mathrm{dt}={\mathrm{\α}}_i{R}_{\mathrm{ii}}+\underset{i\≠j}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\α}}_i{R}_{\mathrm{ij}}$

In formula, * represents to ask complex conjugate; R _iifor signal autocorrelation output; for all possible simple crosscorrelation output of signal sum; Simple crosscorrelation output expression formula is:

$\begin{array}{c}{R}_{\mathrm{ij}}\left(\mathrm{\τ}\right)=\underset{-\∞}{\overset{+\∞}{\∫}}S{2}_i\left(t\right)S{2}_j^{*}(t-\mathrm{\τ})\mathrm{dt}=S{2}_i\left(\mathrm{\τ}\right)\⊗S{2}_j^{*}(-\mathrm{\τ})\\ =[S_{\mathrm{Gold}}^i\left(\mathrm{\τ}\right)\⊗S_{\mathrm{LFM}}\left(\mathrm{\τ}\right)]\⊗[S_{\mathrm{Gold}}^{j*}(-\mathrm{\τ})\⊗S_{\mathrm{LFM}}^{*}(-\mathrm{\τ})]\\ =\underset{m=-(P-1)}{\overset{P-1}{\mathrm{\Σ}}}{R}_{\mathrm{Gold}}^{\mathrm{ij}}\left(m{\mathrm{\τ}}_c\right)\·R_{\mathrm{LFM}}(\mathrm{\τ}-m{\mathrm{\τ}}_c)\end{array}$

Wherein,

$R_{\mathrm{Gold}}^{\mathrm{ij}}\left(m{\mathrm{\τ}}_c\right)=\left\{\begin{array}{cc}\underset{n=0}{\overset{P-1+m}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i{\mathrm{\κ}}_{n-m}^j,& -(P-1)\≤m\≤0\\ \underset{n=m}{\overset{P-1}{\mathrm{\Σ}}}{\mathrm{\κ}}_n^i{\mathrm{\κ}}_{n-m}^j,& 0\≤m\≤(P-1)\end{array}\right.,$

$R_{\mathrm{LFM}}(\mathrm{\τ}-m{\mathrm{\τ}}_c)=\left\{\begin{array}{cc}\exp \left[j2\mathrm{\π}(f_0+\frac{1}{2}\mathrm{\μ}{\mathrm{\τ}}_c)(\mathrm{\τ}-m{\mathrm{\τ}}_c)\right]\·& \\ ({\mathrm{\τ}}_c-|\mathrm{\τ}-m{\mathrm{\τ}}_c\left|\right)\sin c\left[\mathrm{\π\μ}{\mathrm{\τ}}_c(\mathrm{\τ}-m{\mathrm{\τ}}_c)(1-\frac{|\mathrm{\τ}-m{\mathrm{\τ}}_c|}{{\mathrm{\τ}}_c})\right],& |\mathrm{\τ}-m{\mathrm{\τ}}_c|\≤{\mathrm{\τ}}_c\\ 0,& |\mathrm{\τ}-m{\mathrm{\τ}}_c|\≥{\mathrm{\τ}}_c\end{array}\right.,$

In formula, for the cross correlation function of balance Gold code; R _lFM(τ) be the cross correlation function of linear FM signal;

Step C, carries out wave beam formation processing to signal, obtains range information:

Step C-1, utilize r1 in the echo data matrix of M × N autonomous channel (2,1, t) and r1 (3,4, data t) are carried out matched filtering processing and are obtained corresponding transit time Δ T1 and Δ T2;

Step C-2, by computing formula (Δ T1+ Δ T2) c/2 go out to rise and fall the according to a preliminary estimate distance at interface;

Step C-3, then carries out time delay summation wave beam formation processing to the signal after channel separation;

Step C-4, proceeds wave beam formation processing to untreated orientation, until all signals have all carried out, after wave beam formation processing, obtaining new echoed signal matrix;

Step C-5, is obtained the transit time Δ T of target echo signal by the peak value of the echoed signal after channel separation and wave beam formation processing, calculate Δ Tc and obtain target distance measurement information.

4. the ultrasonic measurement method of the MIMO thinned array for the interface that rises and falls according to claim 3, is characterized in that, also comprises self-adaptation focusing step after described step C-2:

The focal position that the wave beam of each direction of scanning forms is determined at distance and bearing angle by fluctuating interface according to a preliminary estimate.

5. for a ultrasound measurement system for the MIMO thinned array at the interface that rises and falls, it is characterized in that: comprise supersonic array and signal transmitting and transaction module,

Described supersonic array receives with N the Virtual array that the equivalent M × N of one-tenth of array element evenly arranges by M transmitting array element;

The transmitting of described signal and transaction module comprise timesharing Launching Model and Launching Model simultaneously, and described timesharing Launching Model comprises timesharing transmitter unit, wave beam forming unit, removes oblique processing unit, FFT converter unit;

In described timesharing transmitter unit, linear frequency-modulated wave is launched in the timesharing of M transmitting array element, realizes the channel separation of Virtual array echoed signal by the timesharing transmitting of signal, and N receives array element and receive corresponding Virtual array echoed signal;

Described wave beam forming unit, for after finishing in all echoed signals receptions, reassembles into corresponding each echoed signal Virtual array the echoed signal of M × N autonomous channel, and it is carried out to wave beam formation processing;

Describedly go oblique processing unit for composite signal being gone to oblique processing;

Described FFT converter unit, for to going oblique signal after treatment to carry out FFT processing, calculates corresponding range information;

Described while Launching Model comprises transmitter unit, channel separation unit, wave beam forming unit simultaneously;

In described while transmitter unit, M transmitting array element is launched the linear frequency modulation ripple of different balance Gold pseudo-random code modulation simultaneously, and N receives array element and receive simultaneously;

Described channel separation unit transmits and carries out related operation and realize channel separation with M respectively for echoed signal that each reception array element is received, obtains the signal of M × N autonomous channel,

Described wave beam forming unit is carried out wave beam formation processing for the signal that above-mentioned separation is obtained, and obtains corresponding range information.

6. the ultrasound measurement system of the MIMO thinned array for the interface that rises and falls according to claim 5, it is characterized in that: in described timesharing Launching Model and simultaneously Launching Model, wave beam forming unit, in the time that signal is carried out to wave beam formation processing, adopts self-adaptation focusing method.