A phase comparison-based negative group velocity detection method

Abstract

The application relates to the field of acoustic detection, and particularly discloses a negative group velocity detection method based on phase comparison. The method comprises the following steps: emitting a pulse string acoustic wave signal to a region to be detected; selecting two detection points on the propagation path of the acoustic wave signal, and collecting acoustic wave signals at the two detection points; and judging the positive and negative of the group velocity by comparing the phases of the collected signals at the two points, wherein the specific judgment method is as follows: if the signal phase of the point reached by the acoustic wave first is in the front, the group velocity is positive; and if the signal phase of the point reached by the acoustic wave last leads, the group velocity is negative. The signal used in the method has clear characteristics, the excitation, collection and analysis methods are simple, and the method is not easily disturbed by amplitude changes.

Description

Technical Field

[0001] This invention relates to the field of acoustic detection, and in particular to a method for detecting negative group velocities based on phase comparison. Background Technology

[0002] Group velocity refers to the speed at which signal energy propagates. Under certain specific conditions, the direction of the signal group velocity is opposite to the direction of the phase velocity, which is the phenomenon of negative group velocity, also known as a backswing wave. Negative group velocity can occur in plates, rods, and multi-layered plate structures, and can also be obtained by controlling the propagation of artificial material waves. It has broad application prospects in material testing and super-resolution imaging. Currently, the main methods for observing negative group velocity include wave packet comparison, transfer function method, and photoelastic imaging. Among these, the wave packet comparison method mainly compares the wave packet positions of two points on the signal propagation path. In actual measurements, especially manual measurements, the peak position of the wave packet is greatly affected by the measurement conditions, and it is sometimes difficult to accurately determine its peak time. The transfer function method requires a reference point signal and involves complex calculations, resulting in relatively unclear final characteristics. The photoelastic imaging method provides the most intuitive results, but requires the observed object to be a transparent medium, and the instrument is complex and difficult to operate, making it unsuitable for field applications. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems of cumbersome signal processing or poor detection results caused by easy interference of features in negative group velocity detection methods, and to propose a negative group velocity detection method based on phase comparison.

[0004] To address the above problems, this invention proposes a negative group velocity discrimination method based on phase comparison. This method is simple to operate, has clear characteristics, requires no complex instruments or processing techniques, and can quickly determine the positive or negative sign of the measured signal group velocity.

[0005] To address the aforementioned technical problems, this invention proposes a negative group velocity detection method based on phase comparison, the method comprising the following steps:

[0006] (1) Transmit a pulse train of acoustic signals to the area to be detected;

[0007] (2) Select two detection points along the propagation path of the sound wave signal and collect the sound wave signals at the two detection points;

[0008] (3) The positive or negative group velocity is determined by comparing the phase of the signals collected at the two points.

[0009] As an improvement to the above technical solution, in step (2) of the detection method, the two detection points selected on the propagation path of the acoustic signal are on the same straight line as the excitation position, and the excitation position is the position where the acoustic signal is emitted.

[0010] As another improvement to the above technical solution, the formula for calculating the group velocity in step (3) of the detection method based on the phase of the acoustic signals collected at the two detection points is as follows:

[0011]

[0012] Among them, C g For group velocity, For the phase of the acoustic signal, This represents the phase change propagating from a detection point closer to the excitation location to a more distant one, where k is the wave vector, dk is the wave vector change of the acquired acoustic signal, and t is the propagation time. For two defined detection points, t is a constant, and clearly tdk > 0. When That is, when the signal phase of the detection point closer to the excitation position is in front, the sound wave group velocity is positive; when That is, when the signal phase of the detection point that is farther away from the excitation position is in front, the sound wave group velocity is negative.

[0013] Compared with existing technologies, the negative group velocity detection method based on phase comparison described in this invention has the following advantages:

[0014] 1. The method described in this invention directly compares the phases of signals collected at two points along the sound wave propagation path. The sign of the group velocity can be determined by the phase comparison, and the operation is simple.

[0015] 2. The method described in this invention does not require signal processing, the signal characteristics are easy to identify, the results are clear, and it is less susceptible to interference. Attached Figure Description

[0016] Figure 1 This is a flowchart of the implementation steps of the detection method described in this invention;

[0017] Figure 2 This is a schematic diagram of simulating the excitation of sound waves in a flat plate and a schematic diagram of the selection of detection points;

[0018] Figure 3 These are signal waveforms measured at each detection point, where... Figure 3 (a) shows the signal waveforms collected at points A and B. Figure 3 (b) shows the signal waveforms collected at points C and D. Detailed Implementation

[0019] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0020] This invention aims to solve the problem of observing negative group velocities by proposing a negative group velocity detection method based on phase comparison.

[0021] like Figure 1The diagram shown is a flowchart illustrating the implementation steps of the detection method described in this invention. The specific steps are as follows:

[0022] Transmit a burst of acoustic signals to the area to be detected;

[0023] Two detection points are selected along the propagation path of the sound wave signal, and the sound wave signals at the two detection points are collected.

[0024] The presence of a negative group velocity is determined by comparing the phases of the signals acquired at two points. Specifically, if the signal phase of the point where the sound wave arrives first is ahead, the group velocity is positive; if the phase of the point farther from the excitation position is ahead, the group velocity of the signal propagation is negative.

[0025] In this embodiment, the experimental subject selected was 3mm thick K9 glass, such as... Figure 2 As shown, according to the literature [“Dynamic Photoelastic Observation of Backward Waves” by An Zhiwu, Hu Zhongtao, and Cui Hanyin [C] / / Proceedings of the 2016 National Conference on Acoustics], for this structure, when excited at a specific angle in the frequency band of approximately 970kHz, the acoustic wave in the plate will exhibit a negative group velocity propagation phenomenon behind the excitation position. In this experiment, 967kHz was selected as the frequency of the excitation signal, and the excitation position and detection point were selected as follows: Figure 2 As shown, the excitation position is the location where the excitation probe emits the acoustic signal.

[0026] According to the formula

[0027]

[0028] It can be seen that if That is, if the signal phase of the detection point closer to the excitation position is in front, then the sound wave group velocity is positive; otherwise, if That is, if the signal phase of the detection point that is farther away from the excitation position is in front, then the sound wave group velocity is negative.

[0029] like Figure 3 The image shows the signal waveforms measured at each detection point; the time-domain signal waveforms measured at points A and B are shown below. Figure 3 As shown in (a), it can be observed that the signal phase at point B, which is farther from the excitation location, leads the signal phase at point A. This result indicates the presence of a negative group velocity in this region. Figure 3 (b) is a waveform diagram of the detection signals at points C and D. It can be found that the phase of the signal at point D, which is farther from the excitation position, lags behind the phase of the signal at point C, indicating that there is no negative group velocity in this region.

[0030] The above results are consistent with those in the literature [“Dynamic Photoelastic Observation of Backward Waves” by An Zhiwu, Hu Zhongtao, and Cui Hanyin [C] / / Proceedings of the National Conference on Acoustics (2016)].

[0031] As can be seen from the above, the method of the present invention does not require signal processing, is simple to operate, the signal features are easy to identify, the results are clear, and it is less susceptible to interference. It solves the problems of cumbersome signal processing or poor detection results caused by easy interference of features in existing methods.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A negative group velocity detection method based on phase comparison, the method comprising the following steps: (1) Transmit a pulse train of acoustic signals to the area to be detected; (2) Select two detection points on the propagation path of the sound wave signal and collect the sound wave signals at the two detection points; the two detection points are on the same straight line as the excitation position, and the excitation position is the position where the sound wave signal is emitted; (3) Determine the sign of the group velocity by comparing the phase of the signals collected at the two points; The formula for calculating the group velocity is: in, For group velocity, For the phase of the acoustic signal, To propagate the phase change from a detection point closer to the excitation location to a detection point farther away, k For wave vector, dk The wave vector variation of the acquired acoustic signal, For the transmission time; for the two identified testing sites, It is a constant; when That is, when the signal phase of the detection point closer to the excitation position is in front, the sound wave group velocity is positive; when... That is, when the signal phase of the detection point that is farther away from the excitation position is in front, the sound wave group velocity is negative.

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