A design method for virtual radiator loaded with metal wire array

Abstract

The present invention discloses a design method for a virtual radiator loaded with a metal wire array, and relates to the technical field of microwave hyperthermia. The present invention can enhance the multipath and complexity of electromagnetic wave propagation in human tissue by loading a metal wire array near a virtual point source, that is, increase the amount of information of the time-reversed electromagnetic wave, so as to reduce the influence of information loss caused by the loss of the inverted electromagnetic wave in the human tissue on the energy focusing accuracy, thereby improving the focusing accuracy of the inverted electromagnetic energy in the human tissue, and can achieve the regulation of the inverted electromagnetic energy focusing spot size by combining the number and spacing of the metal wire array with the source function of the virtual point source, thereby improving the flexibility of the design, and in view of the fact that the increase in the multipath of the time-reversed electromagnetic wave caused by the loading of the metal wire array is not sensitive to small changes in the electromagnetic parameters of the human tissue, when the electromagnetic parameters of the human tissue change due to temperature, the virtual radiator loaded with the metal wire array has the ability to keep the electromagnetic energy stably focused at the original position.

Description

Technical Field

[0001] The invention relates to the technical field of microwave hyperthermia, and in particular to a design method for a virtual radiator loaded with a metal wire array. Background Art

[0002] There are different electromagnetic energy focusing methods according to the type of transmitting antenna used in microwave hyperthermia. Usually, there are two forms of microwave hyperthermia transmitting antennas. One is to use a single transmitting antenna with a lens or a reflective surface. By adjusting the reflective surface of the lens or replacing the lens, the focusing position of the electromagnetic energy can be appropriately adjusted. This method is relatively inflexible and bulky, making it difficult to implement clinical applications. The other is to use multiple radiation units to form an antenna array. By adjusting the amplitude and phase of each unit, the electromagnetic energy is focused on the lesion area. This method is more flexible and has practical clinical application potential. It has been used in the treatment of malignant tumors such as lung cancer, breast cancer, and head and neck cancer.

[0003] However, since human tissue has highly non-uniform electromagnetic parameters, how to quickly obtain the optimal parameters of the external antenna array based on the actual electromagnetic environment so that the electromagnetic energy radiated by it is focused at the expected position is the research focus and difficulty of microwave hyperthermia.

[0004] At present, the theories and optimization algorithms used to obtain the best array antenna parameters mainly include beamforming method, particle swarm algorithm, genetic algorithm, energy optimization transmission theory of power transmission network and time inversion method. Among them, the beamforming method has energy sidelobes when directly applied to highly inhomogeneous human tissue, and needs to be used in conjunction with other optimization algorithms. Although optimization algorithms such as particle swarm algorithm and genetic algorithm can obtain ideal dissipated power, a large number of iterative calculations are required to converge the results. Although the energy optimization transmission theory based on power transmission network can effectively reduce the number of iterative calculations and achieve good focusing effects on cylindrical phantoms, this method still needs to be further verified in highly inhomogeneous human models.

[0005] The time reversal method uses the time reversal invariance of electromagnetic wave propagation to achieve the focusing of electromagnetic energy. Since this method only requires one forward calculation to obtain the ideal parameters of the focusing antenna, it has received widespread attention in microwave hyperthermia and has achieved certain results. However, most previous studies have ignored the important issue that the perfect time reversal characteristics of electromagnetic waves are destroyed in lossy human tissues, and only the simplest point source is used in the setting of the virtual radiator that plays an important role in the time reversal process, resulting in the existence of secondary energy points in the obtained inverted electromagnetic energy distribution, which seriously limits its further application in microwave hyperthermia.

[0006] Most existing time reversal methods ignore the important issue that the perfect time reversal characteristics of electromagnetic waves are destroyed in lossy human tissues, and the virtual radiator setting that plays an important role in the time reversal process only uses the simplest point source, resulting in the inverted electromagnetic energy distribution losing some information due to the dissipation of electromagnetic waves in human tissues and being unable to be accurately refocused to the original source position, resulting in the existence of secondary energy points, affecting the safety of patients. Moreover, the use of simple virtual point sources cannot control the size of the inverted electromagnetic energy focus spot, and does not have design flexibility.

[0007] Therefore, a new solution to the above problems needs to be proposed. Summary of the invention

[0008] The object of the present invention is to provide a design method for a virtual radiator loaded with a metal wire array to solve the problems raised in the prior art.

[0009] To achieve the above object, the present invention provides the following technical solution: a method for designing a virtual radiator loaded with a metal wire array, comprising at least the following steps:

[0010] S1: After placing a series of metal wire array structures around the virtual point source, the electromagnetic waves excited by the virtual point source will reach the human tissue after multipath scattering through the metal wire array, and then reach the external receiving antenna along multiple paths in the human tissue;

[0011] S2: Since the receiving antenna records the complex propagation path of the electromagnetic wave in the human tissue after passing through the metal wire, after the signal on the receiving antenna is time-reversed and resent, even though the metal wire and the virtual point source have been removed, the time-reversed electromagnetic wave will still tend to return to the original virtual radiator position through the human tissue along the original path and form a focus at this position;

[0012] S3: In order to analyze the influence of the metal wire array on the focusing of the time-reversed electromagnetic wave in the S2 process, we start from a simple one-dimensional time-reversal model to obtain the key parameters of the metal wire array affecting the propagation process of the time-reversed electromagnetic wave;

[0013] S4: Load the virtual radiator with a metal wire array in the three-dimensional electromagnetic field model and obtain the geometric dimensions [a, b, r] of the metal wire array loaded by the virtual radiator req ;

[0014] S5: Based on S4, the electromagnetic energy focusing concentration obtained by the virtual radiator loaded with a metal wire array has been greatly improved. The reason is that the metal wire array can increase the multipath of electromagnetic wave propagation, thereby improving the accuracy of the inversion process. Given that the increase in multipath is not sensitive to small changes in the electromagnetic parameters of human tissue, when the electromagnetic parameters of human tissue change due to temperature, it can be seen that the virtual radiator loaded with a metal wire array has the potential to keep the electromagnetic energy stably focused at the original position.

[0015] Preferably, S3 at least includes the following steps: after obtaining the expression of the transmission coefficient of the metal wire array with respect to its geometric dimensions [a, b, r] by using the metal wire array equivalent dielectric model, the time inversion electromagnetic field distribution in region I can be established. Mathematical relationship with the geometric dimensions of the wire array [a, b, r] in a one-dimensional model:

[0016] Preferably, S4 at least includes the following steps:

[0017] First, based on the optimization of the one-dimensional time-reversal electromagnetic field distribution in the previous step, the initial parameters [a, b, r] of the virtual radiator loaded wire array in the three-dimensional electromagnetic field model are obtained. int ;

[0018] The above initial parameters are quantitatively adjusted to obtain the external antenna array parameters and time-inversion electromagnetic dissipated power distribution corresponding to different wire array sizes in a three-dimensional electromagnetic field simulation;

[0019] The difficulty in calculating the electromagnetic field caused by the small size of the metal wire is solved by using the equivalent dielectric model or transformation optics method;

[0020] The relationship between the size of the metal wire array and the external antenna array parameters and the gain and size of the electromagnetic energy focus spot radiated by it is established using fitting software such as MATLAB, as shown below:

[0021]

[0022] in, represents the time-reversed electromagnetic energy dissipation power distribution; Am represents the focal spot amplitude; R represents the focal spot radius; a, b, r represent the spacing and radius of the metal wires respectively;

[0023] Txop, dxop, Axop, t represent the period, peak width and peak size of the signal source, respectively, and represent the amplitude and phase of the external antenna array 1-n;

[0024] Based on the above formula, the expected focal spot size is set, and the geometric size of the virtual radiator loaded wire array [a, b, r] can be obtained by using the response surface method. req .

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention can enhance the multipath and complexity of electromagnetic wave propagation in human tissue by loading a metal wire array near a virtual point source, that is, increase the amount of information of the time-reversed electromagnetic wave, so as to reduce the influence of information loss caused by the loss of the inverted electromagnetic wave in human tissue on the energy focusing accuracy, thereby improving the focusing accuracy of the inverted electromagnetic energy in human tissue;

[0027] 2. The present invention can realize the regulation of the focus spot size of the inversion electromagnetic energy by combining the number and spacing of the metal wire arrays with the source function of the virtual point source, thereby improving the flexibility of the design;

[0028] 3. In view of the fact that the improvement of the multipath of the time-reversed electromagnetic wave caused by the loading of the metal wire array is not sensitive to small changes in the electromagnetic parameters of human tissue, when the electromagnetic parameters of human tissue change due to temperature, the virtual radiator loaded with the metal wire array has the ability to keep the electromagnetic energy stably focused at the original position. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0030] Figure 1 is a schematic diagram of a metal wire array of the present invention;

[0031] Figure 2 It is a schematic diagram of the process of establishing the relationship between the size of the metal wire loaded by the virtual radiator based on electromagnetic field simulation and the electromagnetic energy focusing spot of the present invention;

[0032] Figure 3 A schematic diagram of the corresponding relationship between the waveform function of a virtual point source loaded with a metal wire array and the focus spot size according to the present invention;

[0033] Figure 4 A schematic diagram of a microwave thermotherapy device for treating head and neck cancer and the distribution of the array antenna inside;

[0034] Figure 5 Schematic diagram of electromagnetic energy focusing based on time reversal. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] In the prior art, multiple radiating units are used to form an antenna array. The amplitude and phase of each unit are adjusted to focus the electromagnetic energy on the lesion area. This method has good flexibility and practical clinical application potential. It has been applied to the treatment of malignant tumors such as lung cancer, breast cancer, and head and neck cancer. Figure 4 As shown;

[0037] The time reversal method uses the time reversal invariance of electromagnetic wave propagation to focus electromagnetic energy, such as Figure 5 As shown in Figure 2. Since this method only requires one forward calculation to obtain the ideal parameters of the focusing antenna, it has received widespread attention in microwave hyperthermia and has achieved certain results. However, most previous studies have ignored the important issue that the perfect time reversal characteristics of electromagnetic waves in lossy human tissues are destroyed, and the virtual radiator setting that plays an important role in the time reversal process only uses the simplest point source, resulting in the existence of secondary energy points in the inverted electromagnetic energy distribution (such as Figure 5 (circled in (b)), which seriously limits its further application in microwave hyperthermia therapy.

[0038] It should be noted that Figure 5 (a) is the forward process, and (b) is the inverse process.

[0039] The present invention increases the amount of information of the inverted electromagnetic wave by loading a metal wire array near a virtual point source on the basis of the original time inversion technology, so as to improve the focusing accuracy of the time inverted electromagnetic energy in human tissue.

[0040] In addition, the size of the inversion electromagnetic energy focus spot can be controlled by combining the number and spacing of the metal wire arrays with the source function of the virtual point source.

[0041] A method for designing a virtual radiator loaded with a metal wire array comprises the following specific steps:

[0042] (1) Place a series of metal wire array structures (such as Figure 1 After that, the electromagnetic waves excited by the virtual point source will reach the human tissue after multipath scattering by the metal wire array, and then reach the external receiving antenna along multiple paths in the human tissue.

[0043] (2) At this time, since the receiving antenna records the complex propagation path of the electromagnetic wave in the human tissue after passing through the metal wire, after the signal on the receiving antenna is time-reversed and resent, even though the metal wire and the virtual point source have been removed, the time-reversed electromagnetic wave will still tend to return to the original virtual radiator position through the human tissue along the original path and form a focus at this position.

[0044] (3) In order to analyze the influence of the metal wire array on the focusing of the time-reversed electromagnetic wave in this process, we start with a simple one-dimensional time-reversal model, such as Figure 1 As shown in (b), the key parameters of the metal wire array that affect the time-reversal electromagnetic wave propagation process are obtained.

[0045] based on Figure 1 (b) One-dimensional time reversal model, the focus distribution of the time-reversed electromagnetic wave is related to the transmission coefficient of the metal linear array. Figure 1 After obtaining the expression of the transmission coefficient of the wire array with respect to its geometric dimensions [a, b, r] from the equivalent dielectric model of the wire array in (a), the time-reversed electromagnetic field distribution in region I can be established. Mathematical relationship with the geometric dimensions of the wire array [a, b, r] in a one-dimensional model:

[0046] (4) Load a metal wire array onto the virtual radiator in the three-dimensional electromagnetic field model, such as Figure 2 First, based on the optimization of the one-dimensional time-reversal electromagnetic field distribution in the previous step, the initial parameters [a, b, r] of the virtual radiator loaded metal wire array in the three-dimensional electromagnetic field model are obtained. int . Quantitatively adjust the above parameters, and obtain the external antenna array parameters and time-reversed electromagnetic dissipated power distribution corresponding to different wire array sizes in the three-dimensional electromagnetic field simulation. In view of the difficulty in electromagnetic field calculation caused by the small size of the wire, the equivalent dielectric model or transformation optics method is used to solve it. The relationship between the wire array size and the external antenna array parameters and the gain and size of the electromagnetic energy focus spot radiated by it is established using fitting software such as MATLAB, as shown below:

[0047]

[0048] in, represents the time-reversed electromagnetic energy dissipation power distribution; Am represents the focal spot amplitude; R represents the focal spot radius; a, b, r represent the spacing and radius of the metal wires, respectively. Figure 1 As shown;

[0049] Txop, dxop, Axop, t represent the period, peak width and peak size of the signal source respectively. Figure 3As shown, they represent the amplitude and phase of the external antenna array 1-n respectively;

[0050] Based on the above formula, the expected focal spot size is set, and the geometric size of the virtual radiator loaded wire array [a, b, r] can be obtained by using the response surface method. req The research steps of this part are shown in Figure 2 .

[0051] Depend on Figure 2 The preliminary calculation results in show that the electromagnetic energy focusing concentration obtained by the virtual radiator loaded with the metal wire array has been greatly improved. This is because the metal wire array can increase the multipath of electromagnetic wave propagation, thereby improving the accuracy of the inversion process. Given that the increase in multipath is not sensitive to small changes in the electromagnetic parameters of human tissue, when the electromagnetic parameters of human tissue change due to temperature, the virtual radiator loaded with the metal wire array has the potential to keep the electromagnetic energy stably focused at the original position.

[0052] It should be noted that Figure 1 (a) is a schematic diagram of the metal wire array structure; (b) is a one-dimensional time inversion model of the metal wire array (the virtual radiators including the metal wires and virtual point sources will be removed during the inversion process).

[0053] The present invention proposes to load a metal wire array near the virtual point source in the time reversal method, such as Figure 1 As shown, by enhancing the multipath and complexity of electromagnetic wave propagation in human tissue, that is, increasing the amount of information of the time-reversed electromagnetic wave, the influence of information loss caused by the loss of the inverted electromagnetic wave in human tissue on the energy focusing accuracy is reduced, thereby improving the focusing accuracy of the inverted electromagnetic energy in human tissue. In addition, the present invention proposes that the source function of the virtual point source and the number and spacing of the metal wire array can be combined to optimize the size of the focus spot. For example, under a certain metal wire structure, the peak width of the virtual source function has a corresponding relationship with the size of the focus spot, such as Figure 3 As shown, adjusting the virtual source function waveform function can correspondingly change the size of the focus spot.

[0054] It can be seen from the above embodiments that:

[0055] 1. A metal wire array is loaded near the virtual point source of the original time reversal method to increase the multipath and complexity of the time reversal electromagnetic wave, thereby improving the focusing accuracy of the electromagnetic energy. The metal wire array does not have to be made of metal material, but can also be other non-wave-absorbing dielectric materials.

[0056] 2. By combining the number, spacing and arrangement of the metal wire array with the source function of the virtual point source, the size of the time-reversal electromagnetic energy focus spot in human tissue can be regulated.

[0057] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A design method for a virtual radiator loaded with a metal wire array, characterized in that: At least the following steps are included: S1: After placing a series of metal wire array structures around the virtual point source, the electromagnetic waves excited by the virtual point source will reach the human tissue after multipath scattering through the metal wire array, and then reach the external receiving antenna along multiple paths in the human tissue; S2: Since the receiving antenna records the complex propagation path of the electromagnetic wave in the human tissue after passing through the metal wire, after the signal on the receiving antenna is time-reversed and resent, even though the metal wire and the virtual point source have been removed, the time-reversed electromagnetic wave will still tend to return to the original virtual radiator position through the human tissue along the original path and form a focus at this position; S3: In order to analyze the influence of the metal wire array on the focusing of the time-reversed electromagnetic wave in the S2 process, we first start from a one-dimensional time-reversal model to obtain the key parameters of the metal wire array affecting the propagation process of the time-reversed electromagnetic wave, and the key parameters are [a, b, r]; The S3 at least comprises the following steps: after obtaining the expression of the transmission coefficient of the metal wire array with respect to its geometric dimensions [a, b, r] by using the metal wire array equivalent dielectric model, establishing the time inversion electromagnetic field distribution in region I Mathematical relationship with the geometric dimensions of the wire array [a, b, r] in a one-dimensional model: S4: Load the virtual radiator with a metal wire array in the three-dimensional electromagnetic field model and obtain the geometric dimensions [a, b, r] of the metal wire array loaded by the virtual radiator req ; The S4 at least comprises the following steps: First, based on the optimization of the one-dimensional time-reversal electromagnetic field distribution in the previous step, the initial parameters [a, b, r] of the virtual radiator loaded wire array in the three-dimensional electromagnetic field model are obtained. int ; The above initial parameters are quantitatively adjusted to obtain the external antenna array parameters and time-inversion electromagnetic dissipated power distribution corresponding to different wire array sizes in a three-dimensional electromagnetic field simulation; The difficulty in calculating the electromagnetic field caused by the small size of the metal wire is solved by using the equivalent dielectric model or transformation optics method; The relationship between the size of the metal wire array and the external antenna array parameters and the gain and size of the electromagnetic energy focus spot radiated by it is established using MATLAB fitting software, as shown below: in, represents the time-reversed electromagnetic energy dissipation power distribution; Am represents the focal spot amplitude; R represents the focal spot radius; a, b, r represent the spacing and radius of the metal wires respectively; Txop, dxop, Axo, t represent the period, peak width, peak size and time of the signal source, respectively. (ζ1, θ1), ..., (ζn, θn) represent the amplitude and phase of the external antenna array 1-n, respectively. Based on the above formula, the expected focal spot size is set, and the geometric size [a, b, r]req of the virtual radiator loaded wire array can be obtained by using the response surface method; S5: Based on S4, the electromagnetic energy focusing concentration obtained by the virtual radiator loaded with a metal wire array is improved. The reason is that the metal wire array can increase the multipath of electromagnetic wave propagation, thereby improving the accuracy of the inversion process. Given that the increase in multipath is not sensitive to changes in the electromagnetic parameters of human tissue, when the electromagnetic parameters of human tissue change due to temperature, it can be seen that the virtual radiator loaded with a metal wire array has the potential to keep the electromagnetic energy stably focused at the original position.

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