CN114415162B - System and method for reducing residual vibration and blind area of ultrasonic transducer based on transfer function - Google Patents
System and method for reducing residual vibration and blind area of ultrasonic transducer based on transfer function Download PDFInfo
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Abstract
The invention provides a system and a method for reducing residual vibration and blind area of an ultrasonic transducer based on a transfer function, wherein the system comprises an excitation signal source for providing an excitation signal to an excitation circuit and the transfer function of the ultrasonic transducer at the same time; exciting the ultrasonic transducer based on the exciting circuit to make the ultrasonic transducer emit ultrasonic waves; generating a simulated residual vibration signal according to the excitation signal and the transfer function based on the ultrasonic transducer transfer function module; when the excitation signal source stops providing the excitation signal, generating a residual vibration suppression signal according to the simulated residual vibration signal based on the feedback controller, and inputting the residual vibration suppression signal into the excitation circuit so that the excitation circuit can apply the residual vibration suppression signal to the ultrasonic transducer until the residual vibration signal of the ultrasonic transducer is reduced to a preset threshold value. The system and the method for reducing the residual vibration and the blind area of the ultrasonic transducer based on the transfer function realize weakening of the residual vibration of the ultrasonic transducer by using the transfer function, and reduce the blind area of the ultrasonic transducer for short-distance ranging.
Description
Technical Field
The invention relates to the technical field of ultrasonic transducers, in particular to a system and a method for reducing residual vibration and blind areas of an ultrasonic transducer based on a transfer function.
Background
The ultrasonic detection technology utilizes a transmitting ultrasonic transducer to transmit ultrasonic waves, reflection, refraction, transmission and the like occur in media with different densities and sound speeds, then the ultrasonic waves are received by a receiving ultrasonic transducer, and target information can be obtained through analysis of the received signals. At present, the technology is widely applied to the aspects of non-contact detection, fingerprint identification, medical imaging and the like. Compared with radar ranging, laser ranging, infrared ranging and other ranging modes, the ultrasonic detection technology meets the development requirements of modern non-contact detection, fingerprint identification, imaging of modern medicine and other application scenes, such as refinement, array, micromation, intellectualization and the like.
The ultrasonic ranging mainly transmits ultrasonic waves through an ultrasonic transmitting end, a receiving end receives the ultrasonic waves reflected by an object, and the position of the object is judged by detecting the amplitude or the phase of the echo. The prior art ultrasound transducer system comprises an excitation circuit, an ultrasound transducer and a receiving circuit. The excitation signal excites the ultrasonic transducer to emit ultrasonic waves through the excitation circuit, the ultrasonic waves are reflected back to the ultrasonic transducer after encountering a target, and the receiving circuit receives and processes echo signals received by the ultrasonic transducer to generate distance information. The system belongs to an open loop system, has a simple structure, but has low precision, poor interference suppression capability and is sensitive to system parameter change, so that the effect of the system in the actual use process is often poor.
The TOF (Time of Flight) mode is one of the most commonly used ranging modes, and the distance is calculated by measuring the Time difference between ultrasonic transmission and reception, thereby using the relationship among Time, sound velocity, and distance. The TOF mode is simple to operate and has low system requirements, so that the TOF mode is widely applied to various ranging occasions. One common problem faced by TOF measurement techniques is the dead zone of operation of the ultrasonic transducer at close range measurements. An ultrasonic transducer is a typical electromechanical system that converts an electrical signal into a vibration signal and then into an acoustic signal, or converts an acoustic signal into a vibration signal and then into an electrical signal. As with other vibration systems, after the excitation is stopped, the ultrasonic transducer is not able to stop vibrating on the horse due to inertia, but continues to vibrate for a period of time in the form of free vibration of gradually decaying amplitude, which is commonly referred to as residual vibration or "tailing", until the residual energy is consumed, as shown in fig. 1. If the ultrasonic echo signal is received after the residual amplitude value of the ultrasonic transducer is not attenuated to a certain threshold value, the ultrasonic echo signal is affected by the residual amplitude signal of the ultrasonic transducer, so that the ultrasonic echo signal cannot be detected or the judgment of TOF time is affected. As shown in fig. 2 (a), if the ultrasonic echo signal is received without the amplitude value of the residual oscillation of the ultrasonic transducer being attenuated to be smaller than the maximum amplitude value of the ultrasonic echo signal, the ultrasonic echo signal is buried in the residual oscillation signal of the ultrasonic transducer, and the ultrasonic echo signal cannot be detected. As shown in fig. 2 (b), if the echo signal is received while the residual amplitude value of the ultrasonic transducer is attenuated to be smaller than the maximum amplitude value of the ultrasonic echo signal but not attenuated below the threshold value which is insufficient to affect the echo signal, the echo signal can be detected at this time, but the residual amplitude value is not attenuated below the threshold value which is insufficient to affect the echo signal, at this time, the echo signal is actually the superposition of the real echo signal and the residual amplitude signal, and the superimposed signal is distorted, so that the robustness of the subsequent TOF calculation algorithm is affected, and the judgment of the distance by the sensor is affected. The time from the start of excitation of the ultrasonic transducer to the reduction of the residual amplitude value to a threshold value insufficient to affect the echo signal is called an ultrasonic transducer operation dead zone. The range of ultrasonic waves at close range is limited due to the existence of the working dead zone of the ultrasonic transducer.
In the prior art, the solution of the residual vibration and the dead zone of the ultrasonic transducer is mainly improved by the following two aspects:
1. improvement of ultrasonic transducer structure
(1) The improvement of the isolation/vibration isolation structure, such as the proposal proposed by the patents CN 203178487U and CN 204422750U, CN 110873873A, WO2019051921A1, weakens the influence of the transmitting end on the receiving end by isolating the transmitting end and the receiving end of the ultrasonic transducer or arranging the vibration isolation structure at the transmitting end.
(2) The back radiation sound wave is absorbed, as in the scheme proposed in the patent CN 103691654B, the reflecting surface of the backing layer is set to be in a bowl shape with continuously changing slope, and the back radiation sound wave is reflected in the backing layer for multiple times along various angles, so that most of the back radiation sound wave is dissipated or absorbed, thereby effectively inhibiting the back radiation sound wave of the transducer and reducing the residual vibration of the transducer.
However, although the improvement in terms of structure can play a role, it cannot completely eliminate the influence of the residual vibration, and greatly increases the complexity of the structure.
2. Improvements in ultrasound transducer systems
(1) The excitation signal intensity is adjusted, as in the solutions proposed in the patents CN 101173986B, CN 102749108B, CN 104180860B, CN 104154961B and CN 107390203B, the higher the excitation voltage is, the stronger the ultrasonic energy generated, but as the vibration of the ultrasonic transducer becomes stronger, the stronger the residual vibration will be brought. The above patent uses the ultrasonic wave with higher intensity during the long-distance ranging and the ultrasonic wave with lower intensity during the short-distance ranging, so as to solve the problem of the large blind area formed by the interference caused by the stronger ultrasonic signal at the short-distance. However, decreasing the energy of the transmission will result in a decrease in the intensity of the transmitted ultrasonic wave, and the energy of the echo will be reduced accordingly, which will result in a decrease in the signal-to-noise ratio of the sensor.
(2) The excitation signal frequency is adjusted, as in the solutions proposed in the patents CN 108333590A, CN 110850416A and US2010036618A1, because the closer the excitation frequency is to the eigenfrequency of the ultrasonic transducer, the stronger the vibration of the ultrasonic transducer, the stronger the generated ultrasonic wave will be, but the stronger the residual vibration will be. According to the method, the blind area error in short distance measurement is reduced and the accuracy of the short distance measurement is improved by adjusting the frequency of the excitation signal and using ultrasonic waves with different frequencies according to different distances. But the lack of excitation with the eigenfrequency of the ultrasonic transducer also results in a reduction in the intensity of the emitted ultrasonic waves, which reduces the signal-to-noise ratio of the sensor.
(3) The composition of the emission signal is adjusted, as in the scheme proposed in patent CN 108519592A, after excitation, a plurality of signals opposite to the excitation signal are applied to the ultrasonic transducer to accelerate the attenuation speed of the residual vibration on the ultrasonic transducer, thereby reducing the dead zone in the ultrasonic ranging. However, the setting of the inversion pulse number is seriously dependent on experience and environment, and incorrect setting of the number can lead to the situation that the inversion signal does not stop after the residual vibration of the transducer stops, and the inversion signal excites the transducer to continue vibrating.
(4) The adjusting circuit structure, such as the solutions proposed in the patents CN 102621552B and CN 102749109B, is used to avoid self-oscillation or to realize accelerated consumption of residual vibration energy caused by the input of the driving signal to the subsequent amplifying circuit. But it increases the complexity of the circuit.
(5) Back-end signal processing, such as proposed in patents CN 104823072B, CN 105699975B, CN 106483526A, CN 108572365A, US10031217B2, is used to extract echo signals by processing the received signals to cancel residual vibration signals. However, the actual signal is very easy to be submerged in noise and residual vibration signals, and the method increases the difficulty of signal acquisition and signal processing.
In summary, the residual vibration of the ultrasonic transducer is a main cause of the blind area of the ultrasonic transducer, but the prior art has no solution for inhibiting the residual vibration of the ultrasonic transducer, so that the problem of the blind area of the ultrasonic transducer cannot be fundamentally solved. Most of the methods in the prior art only weaken the influence of residual vibration, but simultaneously bring the problems of reduced signal-to-noise ratio, increased complexity of a structure/circuit, increased difficulty of signal processing and the like of the sensor.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a system and a method for reducing residual vibration and blind area of an ultrasonic transducer based on a transfer function, which uses the transfer function to weaken the residual vibration of the ultrasonic transducer, thereby reducing the blind area of short-distance ranging of the ultrasonic transducer.
To achieve the above and other related objects, the present invention provides a system for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function, including an excitation signal source, an excitation circuit, an ultrasonic transducer, a receiving circuit, a feedback controller and an ultrasonic transducer transfer function module; the excitation signal source is used for simultaneously providing excitation signals for the excitation circuit and the ultrasonic transducer transfer function; the ultrasonic transducer transfer function module is used for acquiring the transfer function of the ultrasonic transducer and generating a simulated residual vibration signal according to the received excitation signal and the transfer function; the excitation circuit is used for exciting the ultrasonic transducer according to the excitation signal when the excitation signal is input; exciting the ultrasonic transducer according to the residual vibration suppression signal when the residual vibration suppression signal is input; the ultrasonic transducer is connected with the excitation circuit and is used for transmitting signals under the excitation of the excitation circuit; the receiving circuit is connected with the ultrasonic transducer and is used for receiving signals sent by the ultrasonic transducer; the feedback controller is connected with the ultrasonic transducer transfer function module and the excitation circuit, and is used for generating a residual vibration suppression signal according to the simulated residual vibration signal when the excitation signal is stopped, and inputting the residual vibration suppression signal into the excitation circuit so that the excitation circuit can apply the residual vibration suppression signal to the ultrasonic transducer until the residual vibration signal of the ultrasonic transducer is reduced to a preset threshold value.
In an embodiment of the present invention, the transfer function module of the ultrasonic transducer obtains the transfer function of the ultrasonic transducer by any one of the following modes:
1) Applying different types of excitation signals to the ultrasonic transducer to obtain response signals of the ultrasonic transducer in an excitation stage and a residual vibration stage; identifying the excitation signal and the response signal based on a preset identification algorithm, and acquiring the transfer function of the ultrasonic transducer;
2) And obtaining ultrasonic transducer displacement, speed and acceleration of the ultrasonic transducer under different input signals, and obtaining the ultrasonic transducer transfer function by identifying the input signals and the ultrasonic transducer displacement, speed and acceleration.
In an embodiment of the present invention, the feedback controller is a proportional controller, a proportional-derivative controller, a proportional-integral controller, or a proportional-integral-derivative controller.
In an embodiment of the present invention, the excitation signal is a sine signal, a cosine signal or a square wave signal; the simulated residual vibration signal is a vibration voltage signal, a vibration displacement signal, a vibration speed signal or a vibration acceleration signal.
In an embodiment of the present invention, the apparatus further includes a switch module, wherein the switch module connects the excitation signal source and the excitation circuit when the excitation signal is input, and connects the feedback controller and the excitation circuit when the excitation signal is stopped.
The invention provides a method for reducing residual vibration and blind areas of an ultrasonic transducer based on a transfer function, which comprises the following steps:
Acquiring a transfer function of an ultrasonic transducer;
when the excitation signal source provides an excitation signal, the excitation signal is provided for the excitation circuit and the ultrasonic transducer transfer function module simultaneously; exciting an ultrasonic transducer based on the exciting circuit so that the ultrasonic transducer emits ultrasonic waves for receiving by a receiving circuit; generating a simulated residual vibration signal according to the excitation signal and the transfer function based on an ultrasonic transducer transfer function module;
When the excitation signal source stops providing the excitation signal, generating a residual vibration suppression signal according to the simulated residual vibration signal based on a feedback controller, and inputting the residual vibration suppression signal into the excitation circuit so that the excitation circuit can apply the residual vibration suppression signal to the ultrasonic transducer until the residual vibration signal of the ultrasonic transducer is reduced to a preset threshold value.
In an embodiment of the present invention, the transfer function module of the ultrasonic transducer obtains the transfer function of the ultrasonic transducer by any one of the following modes:
1) Applying different types of excitation signals to the ultrasonic transducer to obtain response signals of the ultrasonic transducer in an excitation stage and a residual vibration stage; identifying the excitation signal and the response signal based on a preset identification algorithm, and acquiring the transfer function of the ultrasonic transducer;
2) And obtaining ultrasonic transducer displacement, speed and acceleration of the ultrasonic transducer under different input signals, and obtaining the ultrasonic transducer transfer function by identifying the input signals and the ultrasonic transducer displacement, speed and acceleration.
In an embodiment of the present invention, the feedback controller is a proportional controller, a proportional-derivative controller, a proportional-integral controller, or a proportional-integral-derivative controller.
In an embodiment of the present invention, the excitation signal is a sine signal, a cosine signal or a square wave signal; the simulated residual vibration signal is a vibration voltage signal, a vibration displacement signal, a vibration speed signal or a vibration acceleration signal.
In an embodiment of the present invention, the switching between the connection of the excitation circuit to the excitation signal source and the connection of the excitation circuit to the feedback controller is implemented based on a switching module.
As described above, the system and method for reducing residual vibration and blind area of ultrasonic transducer based on transfer function of the invention has the following beneficial effects:
(1) A feedback suppression system for reducing the residual vibration and the blind area of the ultrasonic transducer is constructed based on the transfer function, and the transfer function is driven while the ultrasonic transducer is excited by the excitation signal, so that an analog residual vibration signal capable of reflecting the residual vibration of the ultrasonic transducer is obtained; the simulated residual vibration signal generates a residual vibration suppression signal through the feedback controller, so that the residual vibration of the ultrasonic transducer can be suppressed, and the vibration of the ultrasonic transducer is quickly attenuated to be below a threshold value;
(2) Compared with the ultrasonic transducer system in the prior art, the feedback inhibition method based on the transfer function forms a closed loop system by using the transfer function, is insensitive to the change of input signals, and has stronger anti-interference capability; meanwhile, compared with a system for performing feedback inhibition by directly utilizing an output signal of an ultrasonic transducer, the system has low requirement on hardware and is easier to popularize and apply industrially;
(3) The transfer function of the ultrasonic transducer is obtained in a self-calibration mode, namely, a plurality of excitation signals of different types are applied to the ultrasonic transducer in an initialization stage, response signals of the ultrasonic transducer in an excitation stage and a residual vibration stage are obtained, and the built-in system identification algorithm is utilized to identify the excitation signals and the feedback signals so as to obtain the transfer function of the ultrasonic transducer; compared with the method for identifying by utilizing the ultrasonic transducer test result, the method considers the influence of the environment on the ultrasonic transducer, improves the accuracy of the transfer function obtained by identification, and improves the accuracy of feedback control;
(4) The residual vibration of the ultrasonic transducer can be quickly attenuated after the excitation signal is stopped, and the residual vibration suppression signal does not excite the ultrasonic transducer to vibrate again after the residual vibration is stopped, so that the problem of a short-distance range finding blind zone caused by the residual vibration of the ultrasonic transducer is solved; this is because the analog residual vibration signal of the ultrasonic transducer itself is used as the feedback input, and the residual vibration suppression signal generated by the feedback controller according to the residual vibration signal is also a gradually attenuated signal because the analog residual vibration signal itself is a gradually attenuated signal, so that the residual vibration suppression signal always attenuates the residual vibration of the ultrasonic transducer gradually, and the problem that the residual vibration is stopped but the suppression signal is not stopped, and the ultrasonic transducer is re-excited by the suppression signal is avoided.
Drawings
FIG. 1 is a schematic waveform diagram of an ultrasonic transducer during an excitation phase in one embodiment;
FIG. 2 (a) is a schematic waveform diagram showing an echo signal being submerged in an embodiment by a residual signal;
FIG. 2 (b) is a schematic diagram showing waveforms of the echo signal distorted by the residual oscillation signal in one embodiment;
FIG. 3 is a schematic diagram of a system for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function according to an embodiment of the present invention;
FIG. 4 is a flow chart of a method of reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function according to one embodiment of the present invention;
FIG. 5 (a) is a schematic diagram of an ultrasonic signal emitted by an open-loop ultrasonic transducer system according to the prior art in one embodiment;
Fig. 5 (b) is a schematic diagram of an ultrasonic signal emitted by a system for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function according to the present invention in one embodiment.
FIG. 6 (a) is a schematic diagram of an echo signal received by an open loop ultrasound transducer system according to the prior art in one embodiment;
Fig. 6 (b) is a schematic diagram of an embodiment of echo signals received by a system for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function according to the present invention.
Description of element reference numerals
1. Excitation signal source
2. Excitation circuit
3. Ultrasonic transducer
4. Receiving circuit
5. Feedback controller
6. Transfer function module of ultrasonic transducer
7. Switch module
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be noted that the following embodiments and features in the embodiments may be combined with each other without conflict.
It should be noted that the illustrations provided in the following embodiments merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complicated.
The system and the method for reducing the residual vibration and the blind area of the ultrasonic transducer based on the transfer function are characterized in that a closed-loop feedback control system is constructed, the transfer function is driven while the ultrasonic transducer is excited by an excitation signal, and an analog residual vibration signal capable of reflecting the residual vibration of the ultrasonic transducer is obtained; the simulated residual vibration signal generates a residual vibration suppression signal through the feedback controller, and the residual vibration suppression signal can enable the ultrasonic transducer to generate acceleration opposite to the movement of the residual vibration stage, so that the residual vibration of the ultrasonic transducer is suppressed, and the vibration of the ultrasonic transducer is quickly attenuated to be below a threshold value, so that the ultrasonic transducer has high practicability.
As shown in fig. 3, in one embodiment, the system for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function of the present invention includes an excitation signal source 1, an excitation circuit 2, an ultrasonic transducer 3, a receiving circuit 4, a feedback controller 5 and an ultrasonic transducer transfer function module 6.
The excitation signal source 1 is used for simultaneously providing excitation signals to the excitation circuit and the ultrasonic transducer transfer function. In an embodiment of the present invention, the excitation signal is a sine signal, a cosine signal or a square wave signal, so the excitation signal source may be a sine generator, a cosine generator or a square wave generator.
The ultrasonic transducer transfer function module 6 is configured to obtain a transfer function of the ultrasonic transducer 3, and generate an analog residual vibration signal according to the received excitation signal and the transfer function.
In particular, the ultrasonic transducer transfer function may reflect the motion of the ultrasonic transducer at the aftershock stage after the excitation has ceased. Therefore, in the initialization stage of the system operation for reducing the residual vibration and the blind area of the ultrasonic transducer based on the transfer function, the transfer function of the ultrasonic transducer 3 needs to be acquired first. In the present invention, the transfer function is obtained by the following two ways:
(1) Self-calibration mode
Applying different types of excitation signals to the ultrasonic transducer 3 to obtain response signals of the ultrasonic transducer 3 in an excitation stage and a residual vibration stage; and identifying the excitation signal and the response signal based on a preset identification algorithm to acquire the transfer function of the ultrasonic transducer.
(2) Test mode
And obtaining ultrasonic transducer displacement, speed and acceleration of the ultrasonic transducer 3 under different input signals, and obtaining the ultrasonic transducer transfer function by identifying the input signals and the ultrasonic transducer displacement, speed and acceleration.
After the excitation signal is input to the ultrasonic transducer 3, an analog residual vibration signal can be generated through the transfer function. The simulated residual vibration signal reflects the motion condition of the ultrasonic transducer in the residual vibration stage after the excitation is stopped, and can be used for subsequent residual vibration suppression processing.
The excitation circuit 2 is used for exciting the ultrasonic transducer according to the excitation signal when the excitation signal is input; and exciting the ultrasonic transducer according to the residual vibration suppression signal when the residual vibration suppression signal is input. Specifically, the excitation circuit 2 can drive the ultrasonic transducer 3 to emit ultrasonic waves when receiving an excitation signal; upon receiving the residual vibration suppression signal, the residual vibration suppression signal can be applied to the ultrasonic transducer 3 to suppress residual vibration of the ultrasonic transducer 3.
The ultrasonic transducer 3 is connected to the excitation circuit 2 for emitting a signal under excitation of the excitation circuit 2.
The receiving circuit 4 is connected with the ultrasonic transducer 3 and is used for receiving signals sent by the ultrasonic transducer.
Specifically, when the ultrasonic transducer 3 stops ultrasonic wave transmission, the receiving circuit 4 can receive the residual vibration signal of the ultrasonic transducer 3. Meanwhile, the receiving circuit 4 is also capable of receiving and processing echo signals received by the ultrasonic transducer 3.
The feedback controller 5 is connected with the ultrasonic transducer transfer function module 6 and the excitation circuit 2, and is configured to generate a residual vibration suppression signal according to the analog residual vibration signal when the excitation signal is stopped, and input the residual vibration suppression signal into the excitation circuit, so that the excitation circuit applies the residual vibration suppression signal to the ultrasonic transducer until the residual vibration signal of the ultrasonic transducer is reduced to a preset threshold.
Specifically, when the excitation signal is stopped, the feedback controller 5 generates a residual vibration suppression signal from the analog residual vibration signal, and inputs the residual vibration suppression signal to the excitation circuit 2, and the excitation circuit 2 applies the residual vibration suppression signal to the ultrasonic transducer 3. Since the residual vibration suppression signal can cause the ultrasonic transducer 3 to generate acceleration opposite to the movement of the residual vibration stage, the residual vibration of the ultrasonic transducer 3 can be suppressed. The feedback adjustment is performed until the residual vibration signal of the ultrasonic transducer 3 is reduced to a preset threshold value, i.e. the residual vibration signal amplitude is reduced below a threshold value which is insufficient to influence the echo signal.
An ultrasonic transducer is a typical electromechanical system, taking piezoelectric micromachined ultrasonic transduction (pMUT, piezoelectric Micromechanical Ultrasonic Transducer) as an example, pMUT can be equivalently a mass-spring-damper system, while considering its piezoelectric effect, its kinetic equation is:
Wherein M is equivalent mass, b m is damping coefficient, K is spring coefficient, w b (t) is deformation (relative displacement between components) generated by inverse piezoelectric effect in the system, and w (t) is displacement output from the system to the outside; the piezoelectric unit is connected with the driving circuit, the voltage at two ends of the piezoelectric unit is set as V (t), the piezoelectric unit is connected with the load R in parallel, Θ bc V (t) is the piezoelectric coupling force generated by the voltage V (t), and Θ bc is called a backward coupling constant.
PMUT generally works in bending mode, mainly using d 31 mode of piezoelectric material, corresponding to e-type piezoelectric equation, and its expression is:
σ1＝Ypδ1-d31YpE3 (2)
Wherein σ 1 is mechanical stress, δ 1 is mechanical strain, Y p is young's modulus of the piezoelectric material, E 3 is electric field strength, D 3 is electric displacement (charge density), ε 33 S is dielectric constant of the piezoelectric material under mechanical clamping condition, E 31 and D 31 are piezoelectric stress, strain constant, and E 31＝d31Yp, respectively. When the piezoelectric cantilever beam is bent and deformed, the piezoelectric material stress expression (2) comprises two parts of forces, one is the spring restoring force acting on the mass block in the equivalent model, and the other is the backward coupling force generated by the electric field in turn.
Wherein, stress sigma bc＝-d31YpE3 generated by backward coupling force is set as the corresponding coupling force:
Wherein, κ a represents a relation constant between the backward coupling stress and the coupling force, V represents the output voltage of the device, and t p is the thickness of the piezoelectric layer. Thus, the back coupling constant Θ bc can be expressed as
From (3) and q=d 3Ape, it is possible to obtain
Wherein, Q is the charge collected by the device, A pe represents the effective area of the piezoelectric layer, i.e. the coverage area of the electrode layer. The above two sides differentiate with respect to time t. Since dQ/dt=i (t), it is possible to obtain
The current i (t) in the above formula can be represented by V (t)/R. Let κ b be the displacement versus strain constant, δ 1＝κbwb (t). Can be obtained by substituting (6)Wherein the method comprises the steps ofAn effective capacitance between the piezoelectric layer electrodes; Θ fc is the forward coupling constant, and its expression is Θ fc＝d31YpApeκb.
Differential equations (1) and (7) represent the dynamics equation of pMUT, and the Laplacian transformation is performed on (1) and (7), respectively, to obtain
w(s)(Ms2+bms+K)+ΘbcV(s)＝-wb(s)Ms2 (8)
The relation between the obtainable displacement and the voltage in the pull domain is arranged as follows
So that the transfer function of displacement and voltage can be expressed as
From equation (11), it can be seen that the transfer function of the excitation voltage to pMUT displacement is a second order system with 2 zeros and 2 poles, and that the transfer function can reflect the vibration conditions of the excitation phase and the residual vibration phase of pMUT. With the excitation signal and pMUT transfer function known, an analog residual vibration signal reflecting the vibration of pMUT during the residual vibration phase can be obtained.
While equation (11) is exemplified by pMUT to derive the transfer function of the ultrasound transducer, it can be seen that equation (11) is too complex and it is difficult to physically derive the transfer function of the ultrasound transducer. However, the ultrasonic transducer can test certain response information of the ultrasonic transducer by a proper method, and with certain response data of the system, the transfer function of the ultrasonic transducer can be obtained according to the response information, and the process of obtaining the transfer function of the ultrasonic transducer is called system identification. The ultrasonic transducer transfer function is obtained through system identification, and the specific method is that the ultrasonic transducer response is obtained through self-calibration of a feedback system based on the transfer function or testing of the ultrasonic transducer, and then the ultrasonic transducer response is obtained through a system identification algorithm. When the transfer function of the ultrasonic transducer is obtained through self-calibration of a feedback system based on the transfer function, the feedback system applies a plurality of types of excitation signals to the ultrasonic transducer in an initialization stage, response signals of the ultrasonic transducer in an excitation stage and a residual vibration stage are obtained, and then the excitation signals and the feedback signals are identified by utilizing a system identification algorithm built in the system to obtain the transfer function of the ultrasonic transducer. When the transfer function of the ultrasonic transducer can be obtained through testing the ultrasonic transducer, signals such as displacement, speed, acceleration and the like of the ultrasonic transducer under the excitation of different input signals can be obtained through testing the ultrasonic transducer, and the transfer function of the ultrasonic transducer can be obtained through identifying the input signals and the signals such as displacement, speed, acceleration and the like output by the ultrasonic transducer.
Solving the differential equations (1) and (7), the integrated equations (1) and (7) can be obtained
After the excitation is stopped, pMUT is in the free oscillation phase, where V (t) =0, equation (12) can be:
Solution of formula (13) Wherein the method comprises the steps ofA 0 is the initial displacement of pMUT.
When voltage excitation is applied to pMUT after excitation is stopped, cosine signal same as free vibration phase of pMUT is used as excitation, and the excitation is set asSubstituted into (12) to obtain
Order theFormula (15) may be:
Reams the Is available in the form of The solution of the second order differential equation is: Wherein, A 0 is the initial displacement of pMUT,
When pMUT is operated at resonant frequencyAt this time, the vibration amplitude isAt this time the displacement is
As can be seen from comparison of the formulas (14) and (19), after stopping excitation, pMUT vibration displacement can be used as a feedback signal, and vibration suppression signals can be generated by appropriately gain the displacement signal. Then, excitation of the pMUT with the vibration suppression signal can suppress vibration of the pMUT in real time. At this time, the liquid crystal display device,Is the free vibration term of pMUT after stopping excitation,Is an additional attenuation term for pMUT displacement generated by the vibration suppression signal. Because the displacement signal of the pMUT is generally not easy to obtain in practical application, the obtained signal is generally a voltage signal, but because the voltage signal obtained by the ultrasonic transducer is positively correlated with the acceleration of the vibration of the ultrasonic transducer, the acceleration of the vibration of the ultrasonic transducer is in a second derivative relation with the displacement of the vibration of the ultrasonic transducer. Therefore, in practical application, the vibration displacement signal, the vibration velocity signal, the vibration acceleration signal and the vibration voltage signal of the ultrasonic transducer can be used as analog residual vibration signals, and only the non-displacement signal needs to be subjected to certain phase inversion and delay treatment, and then the non-displacement signal has the same effect as the effect of taking displacement as feedback. However, the working frequency of the ultrasonic transducer is generally higher, so that in order to ensure the real-time performance of the whole system, if the residual vibration signal output by the receiving circuit is directly used as a feedback signal, the hardware requirement of the whole system is very high. If the transfer function of the ultrasonic transducer is input into the system, the analog residual vibration signal which is output by the transfer function of the ultrasonic transducer and can reflect the vibration condition of the ultrasonic transducer is used as a feedback signal, and at the moment, as all the calculation is carried out in the main control chip, the time delay brought by the excitation circuit and the receiving circuit is not needed to be considered, and the hardware requirement of the system can be greatly reduced.
In an embodiment of the present invention, the feedback controller is a proportional controller, a proportional-derivative controller, a proportional-integral controller, or a proportional-integral-derivative controller. Thus, the analog residual signal may be one or more of proportional amplification, inverse, differential, integral, and the residual suppression signal.
In an embodiment of the present invention, the system for reducing residual vibration and blind area of an ultrasonic transducer based on a transfer function further comprises a switch module 7, wherein the switch module 7 communicates the excitation signal source 1 with the excitation circuit 2 when the excitation signal is input, and communicates the feedback controller 5 with the excitation circuit 2 when the excitation signal is stopped. Specifically, the switch module is a switchable switch, one end of the switch module is connected with the excitation circuit 2, the other end of the switch module is connected with the excitation signal source 1 when the excitation signal is input, and the switch module is connected with the feedback controller 5 when the excitation signal is stopped, so that the switching of the excitation signal and the residual vibration suppression signal input on the excitation circuit 2 is realized.
In one embodiment, the method for reducing residual vibration and blind area of an ultrasonic transducer based on a transfer function comprises the following steps:
And S1, acquiring a transfer function of the ultrasonic transducer.
Specifically, the ultrasound transducer response is obtained by self-calibration of a transfer function-based feedback system or testing of the ultrasound transducer, and then obtained by a system identification algorithm. When the transfer function of the ultrasonic transducer is obtained through self-calibration of a feedback system based on the transfer function, the feedback system applies a plurality of types of excitation signals to the ultrasonic transducer in an initialization stage, response signals of the ultrasonic transducer in an excitation stage and a residual vibration stage are obtained, and then the excitation signals and the feedback signals are identified by utilizing a system identification algorithm built in the system to obtain the transfer function of the ultrasonic transducer. When the transfer function of the ultrasonic transducer can be obtained through testing the ultrasonic transducer, signals such as displacement, speed, acceleration and the like of the ultrasonic transducer under the excitation of different input signals can be obtained through testing the ultrasonic transducer, and the transfer function of the ultrasonic transducer can be obtained through identifying the input signals and the signals such as displacement, speed, acceleration and the like output by the ultrasonic transducer.
Step S2, when an excitation signal source provides an excitation signal, the excitation signal is provided for an excitation circuit and an ultrasonic transducer transfer function module at the same time; exciting an ultrasonic transducer based on the exciting circuit so that the ultrasonic transducer emits ultrasonic waves for receiving by a receiving circuit; and generating an analog residual vibration signal according to the excitation signal and the transfer function based on an ultrasonic transducer transfer function module.
Specifically, when the excitation signal source works, the excitation signal is simultaneously provided to an excitation circuit and an ultrasonic transducer transfer function module; the ultrasonic transducer emits ultrasonic waves under the excitation of the excitation circuit; and the ultrasonic transducer transfer function module generates a simulated residual vibration signal according to the excitation signal and the transfer function.
And S3, when the excitation signal source stops providing the excitation signal, generating a residual vibration suppression signal based on the feedback controller according to the simulated residual vibration signal, and inputting the residual vibration suppression signal into the excitation circuit so that the excitation circuit can apply the residual vibration suppression signal to the ultrasonic transducer until the residual vibration signal of the ultrasonic transducer is reduced to a preset threshold value.
Specifically, when the excitation signal source stops working, the feedback controller generates a residual vibration suppression signal according to the analog residual vibration signal, and inputs the residual vibration suppression signal into the excitation circuit. The excitation circuit applies the residual vibration suppression signal to the ultrasonic transducer, and the ultrasonic transducer generates acceleration opposite to the movement of the residual vibration stage, so that the residual vibration of the ultrasonic transducer can be suppressed. And performing feedback adjustment until the residual vibration signal is reduced to a preset threshold value, namely the amplitude of the residual vibration signal is reduced to a value which is insufficient to influence the echo signal.
In one embodiment of the present invention, as shown in fig. 4, the switching of the communication between the excitation circuit and the excitation signal source and the communication between the excitation circuit and the feedback controller is implemented based on a switching module. Specifically, the switch module is a switchable switch, one end of the switch module is connected with the excitation circuit, the other end of the switch module is switched to the excitation signal when the excitation signal is input, and is switched to the feedback controller when the excitation signal is stopped, so that the switching of the excitation signal and the residual vibration suppression signal input on the excitation circuit is realized.
The method for reducing the residual vibration and the dead zone of the ultrasonic transducer based on the transfer function is practically applied to the ultrasonic sensor. As can be seen from fig. 5 (a) and fig. 5 (b), compared with the conventional open-loop ultrasonic transducer system, the system for reducing the residual vibration and the dead zone of the ultrasonic transducer based on the transfer function can quickly attenuate the residual vibration, so that the amplitude of the residual vibration is attenuated to a smaller value in a shorter time. The system for reducing the residual vibration and the blind area of the ultrasonic transducer based on the transfer function can reduce the blind area of the ultrasonic transducer because the residual vibration is attenuated rapidly. Fig. 6 (a) and 6 (b) show actual signals received by an ultrasonic transducer when the conventional open-loop ultrasonic transducer system and the system for reducing residual vibration and dead zone of the ultrasonic transducer based on the transfer function of the present invention are applied to the TOF ranging of an ultrasonic sensor. Fig. 6 (a) shows ultrasonic signals acquired by using a conventional open loop ultrasonic transducer system, and it can be seen from the figure that echo signals are distorted. The distortion is generated after the superposition of echo signals and residual vibration signals due to the tailing generated by ultrasonic residual vibration, and the distortion can influence the accuracy of TOF judgment, thereby influencing the ranging accuracy. As shown in fig. 6 (b), in order to use the ultrasonic signal acquired when the system for reducing the residual vibration and the dead zone of the ultrasonic transducer based on the transfer function of the present invention is adopted, it can be seen from the figure that the waveform of the ultrasonic echo is complete and has no distortion, and the arrival time of the echo can be determined according to the waveform of the echo, so as to calculate the distance. Therefore, when the distance is measured in a short distance, the distance information cannot be accurately obtained by the traditional open-loop ultrasonic transducer system due to the influence of residual vibration, and the system for reducing the residual vibration and the blind area of the ultrasonic transducer based on the transfer function can enable the distance which cannot be detected by the traditional open-loop ultrasonic transducer system to be detected due to the fact that the residual vibration is restrained, so that the blind area of the ultrasonic transducer is reduced. The above results illustrate the effectiveness of the system and method for reducing residual vibration and dead zone of ultrasonic transducer based on transfer function in actual sensor near distance measurement.
In summary, the system and the method for reducing the residual vibration and the blind area of the ultrasonic transducer based on the transfer function construct a feedback suppression system for reducing the residual vibration and the blind area of the ultrasonic transducer based on the transfer function, and drive the transfer function while exciting the ultrasonic transducer by the excitation signal, thereby obtaining the simulated residual vibration signal capable of reflecting the residual vibration of the ultrasonic transducer; the simulated residual vibration signal generates a residual vibration suppression signal through the feedback controller, so that the residual vibration of the ultrasonic transducer can be suppressed, and the vibration of the ultrasonic transducer is quickly attenuated to be below a threshold value; compared with the ultrasonic transducer system in the prior art, the feedback inhibition method based on the transfer function forms a closed loop system by using the transfer function, is insensitive to the change of input signals, and has stronger anti-interference capability; meanwhile, compared with a system for performing feedback inhibition by directly utilizing an output signal of an ultrasonic transducer, the system has low requirement on hardware and is easier to popularize and apply industrially; the transfer function of the ultrasonic transducer is obtained in a self-calibration mode, namely, a plurality of excitation signals of different types are applied to the ultrasonic transducer in an initialization stage, response signals of the ultrasonic transducer in an excitation stage and a residual vibration stage are obtained, and the built-in system identification algorithm is utilized to identify the excitation signals and the feedback signals so as to obtain the transfer function of the ultrasonic transducer; compared with the method for identifying by utilizing the ultrasonic transducer test result, the method considers the influence of the environment on the ultrasonic transducer, improves the accuracy of the transfer function obtained by identification, and improves the accuracy of feedback control; the residual vibration of the ultrasonic transducer can be quickly attenuated after the excitation signal is stopped, and the residual vibration suppression signal does not excite the ultrasonic transducer to vibrate again after the residual vibration is stopped, so that the problem of a short-distance range finding blind zone caused by the residual vibration of the ultrasonic transducer is solved; this is because the analog residual vibration signal of the ultrasonic transducer itself is used as the feedback input, and the residual vibration suppression signal generated by the feedback controller according to the residual vibration signal is also a gradually attenuated signal because the analog residual vibration signal itself is a gradually attenuated signal, so that the residual vibration suppression signal always attenuates the residual vibration of the ultrasonic transducer gradually, and the problem that the residual vibration is stopped but the suppression signal is not stopped, and the ultrasonic transducer is re-excited by the suppression signal is avoided. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (8)
1. A system for reducing residual vibration and blind area of an ultrasonic transducer based on a transfer function is characterized in that: the device comprises an excitation signal source, an excitation circuit, an ultrasonic transducer, a receiving circuit, a feedback controller and an ultrasonic transducer transfer function module;
the excitation signal source is used for simultaneously providing excitation signals for the excitation circuit and the ultrasonic transducer transfer function module;
The ultrasonic transducer transfer function module is used for acquiring the transfer function of the ultrasonic transducer and generating a simulated residual vibration signal according to the received excitation signal and the transfer function;
the excitation circuit is used for exciting the ultrasonic transducer according to the excitation signal when the excitation signal is input; exciting the ultrasonic transducer according to the residual vibration suppression signal when the residual vibration suppression signal is input;
the ultrasonic transducer is connected with the excitation circuit and is used for transmitting signals under the excitation of the excitation circuit;
The receiving circuit is connected with the ultrasonic transducer and is used for receiving signals sent by the ultrasonic transducer;
The feedback controller is connected with the ultrasonic transducer transfer function module and the excitation circuit, and is used for generating a residual vibration suppression signal according to the simulated residual vibration signal when the excitation signal is stopped, and inputting the residual vibration suppression signal into the excitation circuit so that the excitation circuit can apply the residual vibration suppression signal to the ultrasonic transducer until the residual vibration signal of the ultrasonic transducer is reduced to a preset threshold value;
The ultrasonic transducer transfer function module obtains the transfer function of the ultrasonic transducer by adopting any one of the following modes:
1) Applying different types of excitation signals to the ultrasonic transducer to obtain response signals of the ultrasonic transducer in an excitation stage and a residual vibration stage; identifying the excitation signal and the response signal based on a preset identification algorithm, and acquiring the transfer function of the ultrasonic transducer;
2) And obtaining ultrasonic transducer displacement, speed and acceleration of the ultrasonic transducer under different input signals, and obtaining the ultrasonic transducer transfer function by identifying the input signals and the ultrasonic transducer displacement, speed and acceleration.
2. The system for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function of claim 1, wherein: the feedback controller adopts a proportional controller, a proportional-differential controller, a proportional-integral controller or a proportional-integral-differential controller.
3. The system for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function of claim 1, wherein: the excitation signal is a sine signal, a cosine signal or a square wave signal; the simulated residual vibration signal is a vibration voltage signal, a vibration displacement signal, a vibration speed signal or a vibration acceleration signal.
4. The system for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function of claim 1, wherein: the device also comprises a switch module, wherein the switch module is used for communicating the excitation signal source with the excitation circuit when the excitation signal is input and communicating the feedback controller with the excitation circuit when the excitation signal is stopped.
5. A method for reducing residual vibration and blind area of an ultrasonic transducer based on a transfer function is characterized by comprising the following steps: the method comprises the following steps:
Acquiring a transfer function of an ultrasonic transducer;
When the excitation signal source provides an excitation signal, the excitation signal is provided for the excitation circuit and the ultrasonic transducer transfer function module simultaneously; exciting an ultrasonic transducer based on the exciting circuit so that the ultrasonic transducer emits ultrasonic waves for receiving by a receiving circuit; generating a simulated residual vibration signal according to the excitation signal and the transfer function based on an ultrasonic transducer transfer function module;
When the excitation signal source stops providing the excitation signal, generating a residual vibration suppression signal according to the simulated residual vibration signal based on a feedback controller, and inputting the residual vibration suppression signal into the excitation circuit so that the excitation circuit can apply the residual vibration suppression signal to the ultrasonic transducer until the residual vibration signal of the ultrasonic transducer is reduced to a preset threshold value;
The ultrasonic transducer transfer function module obtains the transfer function of the ultrasonic transducer by adopting any one of the following modes:
1) Applying different types of excitation signals to the ultrasonic transducer to obtain response signals of the ultrasonic transducer in an excitation stage and a residual vibration stage; identifying the excitation signal and the response signal based on a preset identification algorithm, and acquiring the transfer function of the ultrasonic transducer;
2) And obtaining ultrasonic transducer displacement, speed and acceleration of the ultrasonic transducer under different input signals, and obtaining the ultrasonic transducer transfer function by identifying the input signals and the ultrasonic transducer displacement, speed and acceleration.
6. The method for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function of claim 5, wherein: the feedback controller adopts a proportional controller, a proportional-differential controller, a proportional-integral controller or a proportional-integral-differential controller.
7. The method for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function of claim 5, wherein: the excitation signal is a sine signal, a cosine signal or a square wave signal; the simulated residual vibration signal is a vibration voltage signal, a vibration displacement signal, a vibration speed signal or a vibration acceleration signal.
8. The method for reducing residual vibration and dead zone of an ultrasonic transducer based on a transfer function of claim 5, wherein: and the switching between the communication of the excitation circuit and the excitation signal source and the communication of the excitation circuit and the feedback controller is realized based on a switch module.
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