阅读说明：本技术 一种非线性超声混频最佳激励频率的选取方法 (Method for selecting optimal excitation frequency of nonlinear ultrasonic frequency mixing ) 是由 李一博 王晢 芮小博 綦磊 刘嘉玮 于 2019-08-26 设计创作，主要内容包括：本发明涉及一种非线性超声混频最佳激励频率的选取方法,其特征在于：所述方法的步骤为：1)搭建非线性超声混频最佳激励频率的实验系统；2)第一信号激励传感器信号激励；3)第二信号激励传感器信号处理；4)第二信号激励传感器信号激励；5)第一信号激励传感器信号处理；6)最佳激励频率获取。本发明设计科学合理,对混频信号进行频谱分析,确定了最佳频率,对于信号后续分析有着重要意义。(The invention relates to a method for selecting the optimal excitation frequency of nonlinear ultrasonic frequency mixing, which is characterized by comprising the following steps: the method comprises the following steps: 1) building an experimental system of nonlinear ultrasonic frequency mixing optimal excitation frequency; 2) a first signal excitation sensor signal excitation; 3) the second signal stimulates the sensor to process the signal; 4) a second signal excitation sensor signal excitation; 5) the first signal stimulates the sensor signal processing; 6) and obtaining the optimal excitation frequency. The invention has scientific and reasonable design, performs frequency spectrum analysis on the mixing signals, determines the optimal frequency and has important significance for subsequent analysis of the signals.)

1. A method for selecting the optimal excitation frequency of nonlinear ultrasonic frequency mixing is characterized in that: the method comprises the following steps:

1) an experimental system of the optimal excitation frequency of the nonlinear ultrasonic mixing is built: the system comprises a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, a signal excitation sensor, an experimental piece, a duplexer, a high-pass filter and an oscilloscope, the computer is connected with the nonlinear ultrasonic instrument which is provided with two paths of radio frequency output ends and one path of radio frequency input end, the two paths of radio frequency output ends are respectively connected with attenuators which are respectively connected with a low pass filter and a duplexer, the two sides of the experimental piece are symmetrically provided with a first signal excitation sensor and a second signal excitation sensor, the low-pass filter is connected to the first signal excitation sensor, the diplexer is connected to a second signal excitation sensor, the other end of the diplexer is connected to the high pass filter, the high-pass filter is connected to the radio frequency input end of the nonlinear ultrasonic instrument, and the nonlinear ultrasonic instrument is connected to the oscilloscope;

2) first signal excitation sensor signal excitation: enabling the first signal excitation sensor to excite a sine signal with the center frequency f1 through the nonlinear ultrasonic instrument, enabling the second signal excitation sensor to excite a frequency sweep signal, and enabling the second signal excitation sensor to receive signals through the duplexer;

3) and the second signal stimulates the sensor to perform signal processing: performing fast Fourier transform on the signal received by the second signal excitation sensor, and taking the difference between the frequency with the maximum amplitude in the sum frequency band and the fundamental frequency f1 of the first signal excitation sensor in the spectrogram of the received signal as the fundamental frequency f2 of the second signal excitation sensor;

4) second signal excitation sensor signal excitation: enabling the second signal excitation sensor to excite a sine signal with the center frequency f2 through the nonlinear ultrasonic instrument, enabling the first signal excitation sensor to excite a frequency sweep signal, and enabling the second signal excitation sensor to receive signals through the duplexer;

5) the first signal stimulates sensor signal processing: performing fast Fourier transform on the signal received by the second signal excitation sensor, and taking the difference between the frequency with the maximum amplitude in the sum frequency band and the fundamental frequency f2 of the second signal excitation sensor as the fundamental frequency f3 of the first signal excitation sensor in the spectrogram of the received signal;

6) optimal excitation frequency acquisition: the resulting optimal frequency combination is the sum of the frequencies f2, f 3.

Technical Field

The invention belongs to the technical field of signal processing, and relates to a method for selecting an optimal excitation frequency of nonlinear ultrasonic frequency mixing.

Background

The metal plate is widely applied to the fields of military affairs, industry, medical treatment, aerospace and the like, the material is inevitably influenced by external factors such as repeatedly applied load, temperature change, corrosion and the like in the using process, fatigue is further generated, and when the fatigue is accumulated to a certain degree, a macrocrack is developed, so that safety accidents and great economic loss are caused.

There are four major categories of currently mature methods for nondestructive testing of metals: ultrasonic flaw detection, which mainly detects metallurgical defects such as slag inclusion, holes, cracks and the like; x-ray flaw detection, detecting high-density inclusions in parts, such as defects of tungsten inclusion and the like; a fluorescent penetrant inspection method for detecting surface opening defects; eddy current inspection, the detection of surface and near-surface defects. These conventional non-destructive inspection methods are feasible and effective for conventional open cracks, but do nothing to the microcracks caused by fatigue damage. With the development of lamb wave theory and nonlinear ultrasonic frequency mixing theory, a new idea is provided for the nondestructive testing of the microcracks of the sheet metal structure.

According to a Dun clear team, the generation condition of secondary lamb waves in a plate structure is researched by a waveguide excitation mode analysis method on the basis of a second order perturbation theory, the result shows that the generation efficiency of the secondary harmonic waves is related to the constant of an interface, and the result lays a foundation for the application of the secondary harmonic waves of the lamb waves in the aspect of nondestructive testing of a thin plate structure. ChristohpPruell experimentally demonstrated that lamb wave nonlinearity has similar results in interaction with plastic materials as longitudinal and transverse waves, thus indicating that lamb wave higher harmonics can be used to evaluate plastic-driven material damage. Thereafter, Christoph Pruell continues to excite and receive lamb waves and second harmonics by using a pair of wedge-shaped sensors, and the results show that the acoustic nonlinearity measured based on the lamb waves is directly related to fatigue damage, so that an experimental program for representing the fatigue damage of the metal sheet by using the nonlinearity of the lamb waves is developed. H Xu et al studied the evaluation of lamb nonlinear effect characterization structural damage, and proposed a time-frequency analysis algorithm to process the acquired nonlinear lamb signals. When the X Wan utilizes a finite element analysis method for simulation, the fact that the lamb wave generates second harmonic when acting with the micro-size cracks in the thin plate is found, and further, a structural damage detection method of applying the nonlinear lamb wave to the thin plate is provided. In the same year, Z Su extracts linear and nonlinear signals by extracting almost invisible fatigue cracks of the metal plate, and proves the feasibility, accuracy and practicability of the nonlinear lamb wave for detecting the micro-damage structure. In 2017, the team of the worship article completes the frequency mixing ultrasonic detection of the closed cracks by utilizing body waves, and makes a positive search for the evaluation of the microcracks in the structure.

The metal fatigue damage detection based on the nonlinear frequency mixing theory can effectively avoid the nonlinear interference brought by the system, and the energy of a target frequency mixing signal which needs to be extracted and analyzed in the process is weak, so that the excitation frequency needs to be selected in the experimental process so as to find the frequency mixing signal with the optimal frequency and obvious display.

Through a search for a patent publication, no patent publication that is the same as the present patent application is found.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for selecting an excitation frequency, which is used for carrying out spectrum analysis on a mixing signal to determine the optimal frequency and has important significance for subsequent analysis of the signal.

The technical problem to be solved by the invention is realized by the following technical scheme:

a method for selecting the optimal excitation frequency of nonlinear ultrasonic frequency mixing is characterized in that: the method comprises the following steps:

1) an experimental system of the optimal excitation frequency of the nonlinear ultrasonic mixing is built: the system comprises a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, a signal excitation sensor, an experimental piece, a duplexer, a high-pass filter and an oscilloscope, the computer is connected with the nonlinear ultrasonic instrument which is provided with two paths of radio frequency output ends and one path of radio frequency input end, the two paths of radio frequency output ends are respectively connected with attenuators which are respectively connected with a low pass filter and a duplexer, the two sides of the experimental piece are symmetrically provided with a first signal excitation sensor and a second signal excitation sensor, the low-pass filter is connected to the first signal excitation sensor, the diplexer is connected to a second signal excitation sensor, the other end of the diplexer is connected to the high pass filter, the high-pass filter is connected to the radio frequency input end of the nonlinear ultrasonic instrument, and the nonlinear ultrasonic instrument is connected to the oscilloscope;

2) first signal excitation sensor signal excitation: enabling the first signal excitation sensor to excite a sine signal with the center frequency f1 through the nonlinear ultrasonic instrument, enabling the second signal excitation sensor to excite a frequency sweep signal, and enabling the second signal excitation sensor to receive signals through the duplexer;

3) and the second signal stimulates the sensor to perform signal processing: performing fast Fourier transform on the signal received by the second signal excitation sensor, and taking the difference between the frequency with the maximum amplitude in the sum frequency band and the fundamental frequency f1 of the first signal excitation sensor in the spectrogram of the received signal as the fundamental frequency f2 of the second signal excitation sensor;

4) second signal excitation sensor signal excitation: enabling the second signal excitation sensor to excite a sine signal with the center frequency f2 through the nonlinear ultrasonic instrument, enabling the first signal excitation sensor to excite a frequency sweep signal, and enabling the second signal excitation sensor to receive signals through the duplexer;

5) the first signal stimulates sensor signal processing: performing fast Fourier transform on the signal received by the second signal excitation sensor, and taking the difference between the frequency with the maximum amplitude in the sum frequency band and the fundamental frequency f2 of the second signal excitation sensor as the fundamental frequency f3 of the first signal excitation sensor in the spectrogram of the received signal;

6) optimal excitation frequency acquisition: the resulting optimal frequency combination is the sum of the frequencies f2, f 3.

The invention has the advantages and beneficial effects that:

1. the invention has scientific and reasonable design, establishes a nonlinear ultrasonic different measurement excitation experiment platform, performs frequency spectrum analysis on the mixing signal by applying a single frequency and frequency sweep mode, determines the optimal frequency, and has important significance for subsequent analysis of the signal.

Drawings

FIG. 1 is a flow chart of the present invention;

FIG. 2 is a schematic connection diagram of an optimal excitation frequency experimental system for nonlinear ultrasonic mixing according to the present invention.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.

A method for selecting the optimal excitation frequency of nonlinear ultrasonic frequency mixing is innovative in that: the method comprises the following steps:

1) an experimental system of the optimal excitation frequency of the nonlinear ultrasonic mixing is built: the system comprises a computer, a nonlinear ultrasonic instrument, an attenuator, a low-pass filter, a signal excitation sensor, an experimental piece, a duplexer, a high-pass filter and an oscilloscope, the computer is connected with the nonlinear ultrasonic instrument which is provided with two paths of radio frequency output ends and one path of radio frequency input end, the two paths of radio frequency output ends are respectively connected with attenuators which are respectively connected with a low pass filter and a duplexer, the two sides of the experimental piece are symmetrically provided with a first signal excitation sensor and a second signal excitation sensor, the low-pass filter is connected to the first signal excitation sensor, the diplexer is connected to a second signal excitation sensor, the other end of the diplexer is connected to the high pass filter, the high-pass filter is connected to the radio frequency input end of the nonlinear ultrasonic instrument, and the nonlinear ultrasonic instrument is connected to the oscilloscope;

2) first signal excitation sensor signal excitation: enabling the first signal excitation sensor to excite a sine signal with the center frequency f1 through the nonlinear ultrasonic instrument, enabling the second signal excitation sensor to excite a frequency sweep signal, and enabling the second signal excitation sensor to receive signals through the duplexer;

3) and the second signal stimulates the sensor to perform signal processing: performing fast Fourier transform on the signal received by the second signal excitation sensor, and taking the difference between the frequency with the maximum amplitude in the sum frequency band and the fundamental frequency f1 of the first signal excitation sensor in the spectrogram of the received signal as the fundamental frequency f2 of the second signal excitation sensor;

4) second signal excitation sensor signal excitation: enabling the second signal excitation sensor to excite a sine signal with the center frequency f2 through the nonlinear ultrasonic instrument, enabling the first signal excitation sensor to excite a frequency sweep signal, and enabling the second signal excitation sensor to receive signals through the duplexer;

5) the first signal stimulates sensor signal processing: performing fast Fourier transform on the signal received by the second signal excitation sensor, and taking the difference between the frequency with the maximum amplitude in the sum frequency band and the fundamental frequency f2 of the second signal excitation sensor as the fundamental frequency f3 of the first signal excitation sensor in the spectrogram of the received signal;

6) optimal excitation frequency acquisition: the resulting optimal frequency combination is the sum of the frequencies f2, f 3.

Although the embodiments of the present invention and the accompanying drawings are disclosed for illustrative purposes, those skilled in the art will appreciate that: various substitutions, changes and modifications are possible without departing from the spirit and scope of the invention and the appended claims, and therefore the scope of the invention is not limited to the disclosure of the embodiments and the accompanying drawings.