A method and system for multi-frequency synthesis of time-frequency fusion electromagnetic method transmitting waveforms

Abstract

This application belongs to the field of geophysical exploration technology, and discloses a multi-frequency synthesis method and system for the transmitting waveform of time-frequency fusion electromagnetic method, including: performing Fourier expansion on the time-frequency fusion signal to obtain the DC component represented by the switching angle and each harmonic represented by the switching angle, where one emission period of the time-frequency fusion signal contains two time-domain observation windows; selecting target sub-harmonics from each harmonic to establish an objective function; using a genetic algorithm to calculate the optimal value of the objective function, the switching angle corresponding to the optimal value is the optimal switching angle, and the transmitting waveform is determined according to the optimal switching angle, the length of the time-domain observation window and the starting time interval between the two time-domain observation windows. It solves the problem that multiple signal transmissions are required to complete the detection of a set of frequency points during the electromagnetic exploration process. The generated transmitting waveform can emit a waveform containing multiple frequency combinations in a set of frequency points when detecting a set of frequency points, and multi-frequency joint transmission can reduce the number of transmissions.

Description

Technical Field

[0001] This application belongs to the field of geophysical exploration technology, and more specifically, it is a multi-frequency synthesis method and system for the transmitting waveform of time-frequency fusion electromagnetic method. Background Art

[0002] In the field of electromagnetic exploration, bipolar square waves are often used for time-domain electromagnetic detection or pseudo-random sequences for frequency-domain electromagnetic detection. The two are complementary in the detection range. In the time-domain electromagnetic detection method, at the moment when the pulsed current is turned off, the receiving system receives the attenuated secondary field signal in the near zone. The frequency-domain electromagnetic method emits pseudo-random pulses with adjustable frequencies and observes the superimposed field of the primary field and the secondary field in the far zone. During the process of transmitting the electromagnetic detection signal with the time-frequency fusion signal, a signal containing multiple frequencies and having a time-domain observation window is transmitted, which can fuse the two. At present, the output signal used in the time-frequency fusion detection method is only to add a time-domain observation window to the frequency-domain signal. The signal obtained in this way can only contain the second and fourth harmonics except the fundamental wave. During the detection process, multiple signal transmissions are required to complete the detection of a set of frequency points, which makes the detection process cumbersome, the detection time long, and the concentration degree of the harmonic energy to be utilized low. Summary of the Invention

[0003] The embodiments of this application provide a multi-frequency synthesis method and system for the transmitting waveform of time-frequency fusion electromagnetic method, which solves the problem that multiple signal transmissions are required to complete the detection of a set of frequency points during the electromagnetic exploration process.

[0004] This application is implemented as follows:

[0005] The first aspect of the embodiments of this application provides a multi-frequency synthesis method for the transmitting waveform of time-frequency fusion electromagnetic method, including:

[0006] Performing Fourier expansion on the time-frequency fusion signal to obtain the DC component represented by the switching angle and each harmonic represented by the switching angle. There are two time-domain observation windows within one emission period of the time-frequency fusion signal;

[0007] Selecting target sub-harmonics from each harmonic to establish an objective function, and the objective function is expressed as:

[0008] ,

[0009] Wherein, is the objective function, is the amplitude of the first target sub-harmonic, is the amplitude of the second target sub-harmonic, is the amplitude of the target sub-harmonic, is the amplitude of the sub-harmonic, is the total harmonic number of the low-order harmonics to be optimized, is the amplitude of the DC component, is the average value of the amplitudes of the target sub-harmonics, is the variance of the amplitudes of the target sub-harmonics, is the total energy of the low-order harmonics to be optimized, 、 、 are respectively the weighting coefficient of the energy of the target sub-harmonics, the weighting coefficient of the total energy of the remaining harmonics other than the target sub-harmonics in the low-order harmonics to be optimized, and the weighting coefficient of the variance of the amplitudes of the target sub-harmonics;

[0010] The optimal value of the objective function is calculated using the genetic algorithm. The switching angle corresponding to the optimal value is the optimal switching angle. The transmitted waveform is determined according to the optimal switching angle, the time-domain observation window length, and the starting time interval between two time-domain observation windows.

[0011] In one embodiment, the time-frequency fusion signal includes a first time-domain observation window and a second time-domain observation window within one transmission period. A plurality of first switching angles with equal distribution lengths are set after the first time-domain observation window and before the second time-domain observation window, and a plurality of second switching angles with equal distribution lengths are set after the second time-domain observation window.

[0012] In one embodiment, the magnitude of the first switching angle is limited to: ,

[0013] The magnitude relationship of the first switching angles satisfies where, is the time-domain observation window length, is the starting time interval between two time-domain observation windows, represents the th switching angle, represents the total number of the first switching angles, and among the first switching angles ;

[0014] The magnitude of the second switching angle is limited to:

[0015] ,

[0016] The magnitude relationship of the second switching angles satisfies Among the second switching angles , represents the total number of switching angles.

[0017] In one embodiment, calculating the optimal value of the objective function using a genetic algorithm includes: randomly generating a binary code, where the first four bits of the binary code correspond to the start time interval of two time-domain observation windows, and thereafter each six bits of the binary code correspond to a switching angle, and the switching angle includes a first switching angle and a second switching angle;

[0018] After converting the binary code into the start time interval of two time-domain observation windows and the switching angle, calculate the fitness of the objective function;

[0019] Perform selection calculation according to the fitness, and then perform crossover and mutation operations to complete the calculation of one iteration cycle;

[0020] Repeat the calculation for multiple cycles of iteration to obtain the converged binary code, and convert the binary code into the switching angle and the start time interval of two time-domain observation windows.

[0021] In one embodiment, after the calculation of one iteration cycle, adjust the target sub-harmonic energy weighting coefficient, the total energy weighting coefficient of the remaining harmonics in the low-order harmonics to be optimized, and the variance weighting coefficient of the target sub-harmonic amplitude according to the current optimal binary code.

[0022] In one embodiment, the adjustment method is:

[0023] ,

[0024] ,

[0025] ,

[0026] where, 、 … all come from the amplitudes of the corresponding target sub-harmonics in the current iteration cycle calculation, is the length of the time-domain observation window. During the adjustment process, if occurs, then change the value of to 0.1.

[0027] In one embodiment, converting the binary code into the switching angle and the start time interval of two time-domain observation windows includes:

[0028] ,

[0029] ,

[0030] where, is the th switching angle, takes values from 1 to , is the lower limit of the value range, is the upper limit of the value range, ~ is the binary value corresponding to the start time of the second time-domain observation window within one emission period, ~ is the binary value of the corresponding bit of the [[ordinal number]]th switching angle, is the time interval between the start times of two time-domain observation windows.

[0031] The second aspect of the embodiments of the present application provides a time-frequency fusion electromagnetic method transmitting waveform multi-frequency synthesis system, including:

[0032] A harmonic extraction unit, configured to perform Fourier expansion on the time-frequency fusion signal to obtain a DC component represented by a switching angle and each harmonic represented by a switching angle, where two time-domain observation windows are included within one emission period of the time-frequency fusion signal;

[0033] A harmonic selection unit, configured to select target sub-harmonics from each harmonic to establish an objective function, and the objective function is expressed as:

[0034] ,

[0035] where, is the objective function, is the amplitude of the first target sub-harmonic, is the amplitude of the second target sub-harmonic, is the amplitude of the [[ordinal number]]th target sub-harmonic, is the amplitude of the [[ordinal number]]th sub-harmonic, is the total number of harmonics of the low-order harmonics to be optimized, is the amplitude of the DC component, is the average value of the amplitudes of the target sub-harmonics, is the variance of the amplitudes of the target sub-harmonics, is the total energy of the low-order harmonics to be optimized, , , are respectively the energy weighting coefficient of the target sub-harmonic, the energy weighting coefficient of the total energy of the remaining harmonics other than the target sub-harmonic in the low-order harmonics to be optimized, and the variance weighting coefficient of the amplitude of the target sub-harmonic;

[0036] A harmonic optimization unit, configured to calculate the optimal value of the objective function by using a genetic algorithm, where the switching angle corresponding to the optimal value is the optimal switching angle, and the transmitting waveform is determined according to the optimal switching angle, the length of the time-domain observation window, and the time interval between the start times of two time-domain observation windows.

[0037] In the third aspect of the embodiments of the present application, a multi-frequency synthesis system for the emission waveform of the time-frequency fusion electromagnetic method is provided, including: a processor; when the processor calls the computer program or instructions in the memory, the method in the first aspect above is executed.

[0038] In the fourth aspect of the embodiments of the present application, a computer-readable storage medium is provided. The computer-readable storage medium is used to store a computer program, and when the computer program is executed, the method in the first aspect above is executed.

[0039] Compared with the prior art, the embodiments of the present application have at least the following technical effects:

[0040] The generated emission waveform can emit a waveform containing multiple frequency combinations in a set of frequency points when detecting a set of frequency points. The multi-frequency joint emission can reduce the number of emissions and solve the problem of the cumbersome electromagnetic exploration process. Moreover, the energy of the harmonics is higher, and the emitted signal can be received with a higher amplitude, which can avoid the situation where the underground apparent resistivity cannot be calculated due to excessive noise in the subsequent signal processing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic flowchart of a multi-frequency synthesis method for the emission waveform of the time-frequency fusion electromagnetic method provided by the embodiments of the present application;

[0042] Figure 2 It is a structural block diagram of a multi-frequency synthesis system for the emission waveform of the time-frequency fusion electromagnetic method provided by the embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0044] In the field of electromagnetic exploration, the output signal used in the time-frequency fusion detection method only adds a time-domain observation window to the frequency-domain signal. The signal obtained in this way can only contain the second and fourth harmonics except for the fundamental wave. In the detection process, multiple signal emissions are required to complete the detection of a set of frequency points, which makes the detection process cumbersome, the detection time long, and the energy concentration degree of the harmonics to be utilized low.

[0045] In view of the above problems, the embodiments of the present application provide a multi-frequency synthesis method for the time-frequency fusion electromagnetic method emission waveform, which designs a time-frequency fusion signal containing two time-domain observation windows; obtains multiple harmonics through Fourier expansion; according to the detection requirements, selects the target sub-harmonics required, establishes an objective function, and solves the objective function through iteration; equally increases the amplitudes of the required harmonics and reduces the remaining low-frequency harmonics to eliminate them; finally, determines the emission waveform according to the optimal solution obtained by iteration, the optimal switching angle, the length of the time-domain observation window, and the starting time interval between the two time-domain observation windows corresponding to the optimal solution. A multi-frequency synthesis method for the time-frequency fusion electromagnetic method emission waveform can synthesize a combined waveform of arbitrary harmonics, which can improve the detection efficiency and reduce the detection time required during the field electromagnetic exploration process.

[0046] See Figure 1 The schematic flowchart of a multi-frequency synthesis method for the time-frequency fusion electromagnetic method emission waveform shown in the figure. A multi-frequency synthesis method for the time-frequency fusion electromagnetic method emission waveform in the embodiments of the present application includes:

[0047] S1, perform Fourier expansion on the time-frequency fusion signal to obtain the DC component represented by the switching angle and each harmonic represented by the switching angle. One emission cycle of the time-frequency fusion signal contains two time-domain observation windows;

[0048] The time-frequency fusion signal has a fixed duty cycle, contains N switching angles in one emission cycle, and has two time-domain observation windows in one emission cycle. The time-domain observation window refers to the area where the emission signal voltage is 0 within a limited time region. The purpose of setting the time-domain observation window is that when receiving the secondary field signal returned by the earth in the near zone, the primary field intensity emitted by the emission source is too high and will submerge the secondary field signal. Therefore, it is necessary to turn off the primary field power emitted by the emission source to facilitate receiving the secondary field signal returned by the earth.

[0049] The switching angle refers to the angle corresponding to the specific moments of conduction and cutoff in each emission cycle. These angles determine the pulse width and distribution of the emission waveform.

[0050] By performing Fourier expansion on the time-frequency fusion signal, one emission cycle of the time-frequency fusion signal contains two time-domain observation windows. Through Fourier expansion, the periodic time-frequency fusion signal can be decomposed into a DC component and a series of sine and cosine components. These sine wave components are the harmonics in the embodiments of the present application. These harmonics and the DC component have a certain relationship with the switching angle. Through Fourier expansion, the DC component represented by the switching angle and each harmonic represented by the switching angle are obtained.

[0051] It can be understood that Fourier expansion refers to performing a Fourier transform on the time-frequency fused signal to convert a time-domain signal into a frequency-domain representation. After Fourier expansion, the included harmonics, according to their frequencies, include high-frequency harmonics and low-frequency harmonics. In geological exploration, high-frequency harmonics do not play a role, and through Fourier expansion, the low-frequency harmonics that can be used can be separated from the high-frequency harmonics.

[0052] In some embodiments, the time-frequency fused signal is represented within one emission cycle as:

[0053] ,

[0054] It can be understood that within one emission cycle, there are two time-domain observation windows, which are represented here as the first time-domain observation window and the second time-domain observation window. Among them, represents the change in time, is the amplitude of the power supply voltage, represents the voltage varying with time, is the length of the time-domain observation window, is the starting time interval between the two time-domain observation windows. It can be understood that the starting time interval between the two time-domain observation windows ranges from 0 to , The corresponding moment is also the starting time of the second time-domain observation window within one emission cycle, is the switching angle, that is, the voltage value of the emitted voltage waveform jumps at the switching angle at time When it is the switching angle, the voltage changes from positive to negative, or from negative to positive. The number of switching angles before the second time-domain observation window is . For switching angles. And a plurality of switching angles are set after the second time-domain observation window. To distinguish the switching angles in the two distribution regions, the switching angles before the second time-domain observation window are taken as the first switching angles, and the plurality of switching angles set after the second time-domain observation window are taken as the second switching angles.

[0055] In the embodiments of the present application, the starting time interval between the two time-domain observation windows refers to the interval between the starting time of the first time-domain observation window and the starting time of the second time-domain observation window within the same emission cycle.

[0056] In one embodiment, there are limitations on the magnitudes of both the first switching angle and the second switching angle.

[0057] The magnitude of the first switching angle is limited to: ,

[0058] The magnitude relationship of the first switching angle satisfies , where is the length of the time-domain observation window, Indicates the th switching angle, indicates the total number of the first switching angles, among the first switching angles ;

[0059] The magnitude of the second switching angle is limited to:

[0060] ,

[0061] The magnitude relationship of the second switching angle satisfies , among the second switching angles , indicates the total number of switching angles.

[0062] In one embodiment, the DC component represented by the switching angle obtained through Fourier expansion and the harmonics represented by the switching angle are:

[0063] ,

[0064] ,

[0065] ,

[0066] ,

[0067] wherein, is the DC component, is the order of the currently calculated harmonic, that is, the total harmonic order including high-frequency harmonics and low-frequency harmonics, is the sine component of the th harmonic, is the cosine component of the th harmonic,

[0068] It can be understood that the magnitude of each harmonic is related to the switching angle, the length of the time-domain observation window, and the starting time interval between two time-domain observation windows.

[0069] S2 selects the target harmonics from each harmonic to establish the objective function, and the objective function is expressed as:

[0070] ,

[0071] wherein, is the amplitude of the 1st target harmonic, is the amplitude of the 2nd target harmonic, is the amplitude of the target harmonic, is The amplitude of the subharmonic is the total number of low-order harmonics to be optimized. This value is selected according to the amplitude of each harmonic. For high-frequency harmonics, the amplitude of the harmonics is very small. Select a value to remove some harmonics, and the remaining harmonics are used as low-frequency harmonics. is the amplitude of the DC component. is the average value of the target subharmonic amplitude. is the variance of the target subharmonic amplitude. is the total energy of the low-order harmonics to be optimized. , , are the weighted coefficient of the target subharmonic energy, the weighted coefficient of the total energy of the remaining harmonics other than the target subharmonic in the low-order harmonics to be optimized, and the weighted coefficient of the variance of the target subharmonic amplitude, respectively.

[0072] Through step S1, multiple harmonics obtained by Fourier expansion are obtained. For different detection requirements, it may be necessary to select harmonics from multiple harmonics. The amplitudes of the selected harmonics may be relatively high or relatively small among multiple harmonics. When performing electromagnetic detection, the energy of the required harmonics in the transmitted waveform needs to be high, and the amplitudes of the harmonics need to be as equal as possible to ensure

[0073] the consistency of the energy of the

[0074] The selected harmonics are used as target subharmonics, and a target function is established for the target subharmonics.

[0075] The target function includes three terms. The first term represents the energy of the target subharmonics, and a weighted coefficient of the target subharmonic energy is set. The second term is the total energy of the remaining harmonics other than the target subharmonic in the low-order harmonics to be optimized, and a weighted coefficient of the total energy of the remaining harmonics other than the target subharmonic in the low-order harmonics to be optimized is set. The last term is the variance of the target subharmonic amplitude, and a weighted coefficient of the variance of the target subharmonic amplitude is also set.

[0076] S3 uses a genetic algorithm to calculate the optimal value of the objective function. The switching angle corresponding to the optimal value is the optimal switching angle. The transmitted waveform is determined according to the optimal switching angle, the time-domain observation window length, and the starting time interval between two time-domain observation windows.

[0077] The process of optimizing the objective function is to continuously optimize the switching angle and the starting time interval between two time-domain observation windows, so as to make the target sub-harmonics have equal amplitude, increase the energy proportion of the target sub-harmonics, and weaken the amplitudes and energies of other harmonics.

[0078] In the embodiment of the present application, a genetic algorithm is selected to calculate the optimal value of the objective function. After the iteration by the genetic algorithm ends, the switching angle corresponding to the obtained optimal value is used as the optimal switching angle. At this time, the target sub-harmonics are basically of equal amplitude, and the energy proportion of the target sub-harmonics is the highest. The transmitted waveform can be determined according to the optimal switching angle, the time-domain observation window length, and the starting time interval between two time-domain observation windows. Using the determined transmitted waveform for signal transmission can achieve one-time transmission and complete the detection of multiple frequency points. The detection efficiency is improved.

[0079] In one embodiment, using a genetic algorithm to calculate the optimal value of the objective function includes: randomly generating a binary code, and the first four bits of the binary code correspond to the starting time interval between two time-domain observation windows, and each subsequent six bits of the binary code correspond to a switching angle. The switching angle includes a first switching angle and a second switching angle;

[0080] After converting the binary code into the starting time interval between two time-domain observation windows and the switching angle, calculate the fitness of the objective function;

[0081] Perform selection calculation according to the fitness, and then perform crossover and mutation operations to complete the calculation of one iteration cycle;

[0082] Repeat the calculation of multiple cycles of iteration to obtain the converged binary code, and convert the binary code into the switching angle and the starting time interval between two time-domain observation windows.

[0083] The core idea of the genetic algorithm is to optimize the objective function by simulating natural selection and genetic mechanisms. It mainly includes: encoding, initializing the population, fitness evaluation, selection, crossover, mutation, and iteration. Among them, encoding is to represent the solution of the optimization problem in a form suitable for genetic operations. Encoding has various forms, such as binary encoding, real number encoding, permutation encoding, tree encoding, etc. Initializing the population is to generate an initial population, and each individual is a possible solution. The population size is usually selected according to the problem scale and complexity. Fitness evaluation is to calculate the fitness of each individual, and the fitness function is usually directly related to the objective function. The higher the fitness, the greater the probability of an individual being selected. Selection is to select individuals for reproduction according to fitness, exchange part of the genes of two individuals to generate new individuals; mutation is to randomly change some genes of an individual to increase the diversity of the population; iteration is to repeat the steps of fitness evaluation, selection, crossover, and mutation until the termination condition is met.

[0084] In the embodiment of the present application, the genetic algorithm is used for the optimization of the emission waveform. By combining the established objective function, the switching angle and the starting time interval of two time-domain observation windows are binary encoded. After being converted into the starting time interval of two time-domain observation windows and the switching angle through binary encoding, the fitness of the objective function is calculated, and the fitness is , the minimum value of the calculated objective function. is the objective function.

[0085] In one embodiment, the formula for converting binary encoding into the starting time interval of two time-domain observation windows and the switching angle is:

[0086] ,

[0087] ,

[0088] where is the th switching angle, takes values from 1 to , is the lower limit of the value range, is the upper limit of the value range, ~ is the binary value corresponding to the starting time of the second time-domain observation window within one emission period, ~ is the binary value corresponding to the number of bits of the th switching angle.

[0089] According to the calculated starting time interval and switching angle of the two time-domain observation windows, as well as the expression of the objective function, the fitness of the objective function can be obtained.

[0090] Objective function Calculate the fitness in the genetic algorithm:

[0091] ,

[0092] is the minimum value of the calculated objective function.

[0093] By performing the selection operation, the selection probability of each individual is related to the fitness. The greater the fitness, the greater the selection probability, and the probability size is:

[0094] ,

[0095] is the selection probability of the th individual, is the fitness of the th individual, is the fitness of the

[0096] The selection process is: generate a random number , and judge and size relationship, is the selection probability of the represents the serial number of the individual currently being judged whether to be selected during the selection process, starts from 1. If is less than , then select the current individual as an individual of the next-generation population. If is greater than , it means that the current individual is not selected. Judge whether the next individual meets the conditions until the next-generation individuals are selected. Repeat this process until all the next-generation individuals are selected, where is the number of individuals in the population. After selection, the next-generation population is formed. Here, the individual refers to the binary encoding.

[0097] After each iteration, the current optimal binary encoding is obtained, and then the binary encoding is converted into the switching angle and the starting time interval of the two time-domain observation windows. Adjust the weighting coefficient of the target subharmonic energy, the weighting coefficient of the total energy of the remaining harmonics in the low-order harmonics to be optimized, and the weighting coefficient of the variance of the target subharmonic amplitude.

[0098] The adjustment process is:

[0099] ,

[0100] ,

[0101] ,

[0102] Among them, and … all come from the amplitudes of the corresponding target sub-harmonics in the current iteration cycle calculation. is the time-domain observation window length. During the adjustment process, if occurs, then is changed to 0.1.

[0103] The adjusted weighting coefficient participates in the next iteration to improve the optimization efficiency.

[0104] To further analyze and explain the calculation of the optimal value of the objective function using the genetic algorithm in the embodiments of the present application, refer to the following application embodiments. Include:

[0105] Initialize the population, set the population size. The population is a set of individuals. The population size is the number of individuals in a population, the binary coding length, i.e., the length of an individual, the crossover probability, the mutation probability, and the weight coefficient for initializing the objective function.

[0106] The target sub-harmonics are selected as the fundamental harmonic, the second harmonic, the third harmonic, and the fourth harmonic, i.e., , and and and are the amplitudes of the fundamental harmonic, the second harmonic, the third harmonic, and the fourth harmonic respectively. Take , , . The population size of the genetic algorithm binary coding is . The binary coding length is 100. The first four bits of the binary coding correspond to the starting time interval of two time-domain observation windows. After that, every six-bit binary code corresponds to a switching angle. The genetic algorithm exits the loop after 4000 executions. Each individual is a binary coding containing bits.

[0107] Take the crossover probability = 0.1, the mutation probability = 0.05. The weight coefficients for initializing the objective function include the target sub-harmonic energy weighting coefficient, the total energy weighting coefficient of the remaining harmonics in the low-order harmonics to be optimized, and the variance weighting coefficient of the target sub-harmonic amplitude, which are = 1, = 1、 = 10。

[0108] Assign an initial value to the binary code. The number of groups of binary codes depends on the set population size;

[0109] Randomly generate binary codes and convert the binary codes into the start time interval of two time-domain observation windows and the switching angle ~ to generate an initial value that satisfies and calculate the fitness of the objective function;

[0110] The start time interval of two time-domain observation windows and the switching angle ~ The corresponding conversion formula is

[0111] ,

[0112] ,

[0113] where is the switching angle of the current conversion, takes values from 1 to , is the lower limit of the value range, is the upper limit of the value range, ~ is the binary value corresponding to the start time of the second time-domain window, ~ is the binary value of the th bit corresponding to the switching angle.

[0114] Calculate the fitness of the genetic algorithm and perform selection, crossover, and mutation operations.

[0115] Calculate the fitness based on the start time interval of two time-domain observation windows and the switching angle obtained by converting the binary code.

[0116] Perform the selection operation. The selection probability of each individual, i.e., the binary code, is related to its fitness. The greater the fitness, the greater the selection probability.

[0117] After the selection process, form the next-generation population.

[0118] Perform the crossover operation. Select two adjacent individuals within the population and generate a random number between 0 and 1. If the random number is less than the crossover probability, perform the crossover operation, that is, randomly select a binary code and swap all the subsequent binary codes.

[0119] Perform mutation operation. For each individual in the population, generate a random number between 0 and 1. If the random number is less than the mutation probability, perform the mutation operation, which is to randomly select a binary code and reverse it.

[0120] After each iteration cycle of the genetic algorithm, dynamically adjust the weight coefficient of the objective function according to the current optimal individual situation.

[0121] Repeat the fitness calculation, selection, crossover, mutation, and dynamic adjustment of the weight coefficient until the number of loops meets the set value.

[0122] After the loop ends, the binary code of the genetic algorithm converges, and convert the binary code into switching angles. For example, in one embodiment, it corresponds to 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 , , , The calculated value of the objective function is 2.4654.

[0123] If the values of two adjacent switching angles are equal, then there are two instantaneous jumps, which actually shows no jump, that is, they cancel each other out.

[0124] Calculate the finally obtained time-frequency fusion waveform. The amplitudes of the first harmonic, second harmonic, third harmonic, and fourth harmonic of the target sub-harmonic are respectively 、 、 、 。The target sub-harmonic accounts for 80.7% of the total energy of the time-frequency fusion signal, and the energy utilization rate is high. In actual exploration, by changing in the objective function to the amplitudes of other harmonics, it can be calculated with any combination of sub-harmonic frequencies, which can achieve faster detection, reduce the time required for the detection process, and improve the detection efficiency.

[0125] The embodiment of the present application also provides a time-frequency fusion electromagnetic method transmitting waveform multi-frequency synthesis system, and the time-frequency fusion electromagnetic method transmitting waveform multi-frequency synthesis system and the time-frequency fusion electromagnetic method transmitting waveform multi-frequency synthesis method can be mutually referenced.

[0126] See Figure 2As described above, a multi - frequency synthesis system for the time - frequency fusion electromagnetic method emission waveform in an embodiment of the present application includes:

[0127] A harmonic extraction unit, configured to perform Fourier expansion on the time - frequency fusion signal to obtain a DC component represented by switching angles and each harmonic represented by switching angles. One emission period of the time - frequency fusion signal contains two time - domain observation windows;

[0128] A harmonic selection unit, configured to select target sub - harmonics from each harmonic to establish an objective function, and the objective function is expressed as:

[0129] ,

[0130] where, is the amplitude of the first target sub - harmonic, is the amplitude of the second target sub - harmonic, is the amplitude of the target sub - harmonic, is the amplitude of the sub - harmonic, is the total number of harmonics of the low - order harmonics to be optimized, is the amplitude of the DC component, is the average value of the amplitudes of the target sub - harmonics, is the variance of the amplitudes of the target sub - harmonics, is the total energy of the low - order harmonics to be optimized, , , are respectively the energy weighting coefficient of the target sub - harmonics, the total energy weighting coefficient of the remaining harmonics other than the target sub - harmonics in the low - order harmonics to be optimized, and the variance weighting coefficient of the amplitudes of the target sub - harmonics;

[0131] A harmonic optimization unit, configured to calculate the optimal value of the objective function by using a genetic algorithm. The switching angles corresponding to the optimal value are the optimal switching angles, and the emission waveform is determined according to the optimal switching angles, the length of the time - domain observation window, and the start - time interval between the two time - domain observation windows.

[0132] In an embodiment, the time - frequency fusion signal containing two time - domain observation windows processed by the harmonic extraction unit includes a first time - domain observation window and a second time - domain observation window within one emission period. A plurality of first switching angles with equal distribution lengths are set after the first time - domain observation window and before the second time - domain observation window, and a plurality of second switching angles with equal distribution lengths are set after the second time - domain observation window.

[0133] In one embodiment, the harmonic optimization unit calculates the optimal value of the objective function using a genetic algorithm, including: randomly generating binary codes, where the first four bits of the binary code correspond to the start time interval between two time-domain observation windows, and each subsequent six bits of the binary code correspond to a switching angle, and the switching angle includes a first switching angle and a second switching angle;

[0134] After converting the binary code into the start time interval between two time-domain observation windows and the switching angle, calculate the fitness of the objective function;

[0135] Perform selection calculation based on the fitness, and then perform crossover and mutation operations to complete the calculation of one iteration cycle;

[0136] Repeat the calculation for multiple cycles of iteration to obtain the converged binary code, and convert the binary code into the switching angle and the start time interval between two time-domain observation windows.

[0137] In one embodiment, the harmonic optimization unit is further configured to, after the calculation of one iteration cycle is completed, adjust the target sub-harmonic energy weighting coefficient, the total energy weighting coefficient of the remaining harmonics in the low-order harmonics to be optimized, and the variance weighting coefficient of the target sub-harmonic amplitude according to the current optimal binary code.

[0138] An embodiment of the present application further provides an electronic device, including a processor; when the processor calls a computer program or instruction in the memory, a multi-frequency synthesis method for a time-frequency fusion electromagnetic method emission waveform is executed. The processor completes mutual communication with the communication interface and the memory through a communication bus. The processor can call the logical instructions in the memory to execute the following method: perform Fourier expansion on the time-frequency fusion signal to obtain the DC component represented by the switching angle and each harmonic represented by the switching angle, and two time-domain observation windows are included within one emission cycle of the time-frequency fusion signal; select the target sub-harmonic from each harmonic to establish an objective function, calculate the optimal value of the objective function using a genetic algorithm, the switching angle corresponding to the optimal value is the optimal switching angle, and determine the emission waveform according to the optimal switching angle, the length of the time-domain observation window, and the start time interval between two time-domain observation windows.

[0139] On the other hand, an embodiment of the present application further provides a computer-readable storage medium for storing a computer program, and when the computer program is executed, the method in the above embodiment is executed.

[0140] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included within the protection scope of the present application.

Claims

1. A multi - frequency synthesis method for the emission waveform of time - frequency fusion electromagnetic method, characterized in that, Including: Performing Fourier expansion on the time-frequency fusion signal to obtain a DC component represented by switching angles and each harmonic represented by switching angles, where two time-domain observation windows are included within one emission period of the time-frequency fusion signal; Selecting a target sub-harmonic from each harmonic to establish an objective function, and the objective function is expressed as: ， Among them, is the objective function, is the amplitude of the first target sub - harmonic, is the amplitude of the second target sub - harmonic, is the amplitude of the target sub - harmonic, is the amplitude of the sub - harmonic, is the total number of harmonics of the low - order harmonics to be optimized, is the amplitude of the DC component, is the average value of the amplitudes of the target sub - harmonics, is the variance of the amplitudes of the target sub - harmonics, is the total energy of the low - order harmonics to be optimized, , , are the weighted coefficients of the target sub - harmonic energy, the weighted coefficient of the total energy of the harmonics other than the target sub - harmonics in the low - order harmonics to be optimized, and the weighted coefficient of the variance of the amplitudes of the target sub - harmonics respectively; Using a genetic algorithm to calculate the optimal value of the objective function, the switching angle corresponding to the optimal value is the optimal switching angle, and the emission waveform is determined according to the optimal switching angle, the length of the time-domain observation window, and the starting time interval between the two time-domain observation windows.

2. A multi-frequency synthesis method for a time-frequency fusion electromagnetic method transmitting waveform according to claim 1, characterized in that, The time-frequency fusion signal includes a first time-domain observation window and a second time-domain observation window within one emission period. A plurality of first switching angles with equal distribution lengths are set after the first time-domain observation window and before the second time-domain observation window, and a plurality of second switching angles with equal distribution lengths are set after the second time-domain observation window.

3. A multi-frequency synthesis method for time-frequency fusion electromagnetic method transmitting waveforms according to claim 2, characterized in that The magnitude of the first switching angle is limited to: , The magnitude relationship of the first commutation angle satisfies , where is the time-domain observation window length, is the start time interval between two time-domain observation windows, represents the th commutation angle, represents the total number of the first commutation angles, and among the first commutation angles ; The magnitude of the second switching angle is limited to: ， The magnitude relationship of the second switching angle satisfies , among the second switching angles , represents the total number of switching angles.

4. A multi - frequency synthesis method for the time - frequency fusion electromagnetic method transmitting waveform according to claim 2, characterized in that, The step of using a genetic algorithm to calculate the optimal value of the objective function includes: randomly generating binary codes, where the first four bits of the binary code correspond to the starting time interval between the two time-domain observation windows, and each subsequent six-bit binary code corresponds to a switching angle, and the switching angle includes a first switching angle and a second switching angle; Converting the binary code into the starting time interval between the two time-domain observation windows and the switching angle, and then calculating the fitness of the objective function; Performing selection calculation according to the fitness, and then performing crossover and mutation operations to complete the calculation of one iteration cycle; Repeating the calculation for multiple iteration cycles to obtain the converged binary code, and converting the binary code into the switching angle and the starting time interval between the two time-domain observation windows.

5. A method for multi - frequency synthesis of a time - frequency fusion electromagnetic method transmitting waveform according to claim 4, characterized in that, After the calculation of one iteration cycle is completed, adjust the weighted coefficient of the target sub-harmonic energy, the weighted coefficient of the total energy of the remaining harmonics in the low-order harmonics to be optimized, and the weighted coefficient of the variance of the target sub-harmonic amplitude according to the current optimal binary code.

6. A method for multi-frequency synthesis of a time-frequency fusion electromagnetic method transmitting waveform according to claim 5, characterized in that The adjustment method is: ， ， ， Among them, , … are all from the amplitudes of the corresponding target sub-harmonics in the current iteration cycle calculation. is the time-domain observation window length. During the adjustment process, if occurs, then will be changed to 0.

1.

7. A method for multi - frequency synthesis of time - frequency fusion electromagnetic method transmitting waveforms according to claim 4, characterized in that, Converting the binary code into the switching angle and the starting time interval between the two time-domain observation windows includes: ， ， Among them, is the th switching angle, takes values from 1 to , is the lower limit of the value range, is the upper limit of the value range, ~ is the binary value corresponding to the start time of the second time-domain observation window within a transmission period, ~ is the binary value corresponding to the number of bits of the th switching angle, is the time interval between the start times of two time-domain observation windows.

8. A multi-frequency synthesis system for the emission waveform of time-frequency fusion electromagnetic method, characterized in that, Including: A harmonic extraction unit for performing Fourier expansion on the time-frequency fusion signal to obtain a DC component represented by switching angles and each harmonic represented by switching angles, where two time-domain observation windows are included within one emission period of the time-frequency fusion signal; A harmonic selection unit for selecting a target sub-harmonic from each harmonic to establish an objective function, and the objective function is expressed as: ， Among them, is the objective function, is the amplitude of the first target harmonic, is the amplitude of the second target harmonic, is the amplitude of the target harmonic, is the amplitude of the harmonic, is the total number of harmonics of the low-order harmonics to be optimized, is the amplitude of the DC component, is the average value of the amplitudes of the target harmonics, is the variance of the amplitudes of the target harmonics, is the total energy of the low-order harmonics to be optimized, , , are the weighting coefficients of the target harmonic energy, the weighting coefficient of the total energy of the harmonics other than the target harmonics in the low-order harmonics to be optimized, and the weighting coefficient of the variance of the amplitudes of the target harmonics, respectively; A harmonic optimization unit for using a genetic algorithm to calculate the optimal value of the objective function, the switching angle corresponding to the optimal value is the optimal switching angle, and the emission waveform is determined according to the optimal switching angle, the length of the time-domain observation window, and the starting time interval between the two time-domain observation windows.

9. An electronic device, characterized in that, Including: A processor; When the processor calls the computer program or instruction in the memory, the method described in any one of claims 1-7 is executed.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium is used to store a computer program, and when the computer program is executed, the method described in any one of claims 1-7 is executed.

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