Comprehensive performance evaluation method of absorption type electromagnetic shielding material

Abstract

The invention relates to the technical field of performance evaluation of electromagnetic shielding materials, in particular to a comprehensive performance evaluation method of an absorption type electromagnetic shielding material. The method comprises the following steps: constructing a comprehensive evaluation index system; the total shielding effectiveness, the reflection loss and the absorption loss of the material are obtained through a far field test, and an absorption coefficient, a reflection coefficient and an absorption dominant factor are determined; through a cavity effect test, comparing the internal field intensity of the cavity with the incident field intensity when the shielding body exists, and determining a cavity field intensity attenuation factor; determining an effective absorption bandwidth according to the absorption coefficient changing curve along with the frequency; determining a near-field absorption coefficient through a near-field test; integrating the indexes into a multi-dimensional evaluation vector, setting a weight according to an application scene, calculating a comprehensive score, and dividing grades. According to the method, multi-dimensional quantitative evaluation of the comprehensive performance of the absorption type electromagnetic shielding material is realized, and research, development and model selection of the material can be effectively guided.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding material performance evaluation technology, and in particular to a comprehensive performance evaluation method for an absorptive electromagnetic shielding material. Background Technology

[0002] As electronic devices develop towards higher density and higher power, electromagnetic interference (EMI) problems are becoming increasingly prominent. Traditional electromagnetic shielding materials are mainly metals (such as aluminum, copper, and steel), and their shielding mechanism is primarily based on reflection, using impedance mismatch on the material surface to reflect electromagnetic waves back into space. However, this reflective shielding has inherent drawbacks in practical applications: on the one hand, the reflected electromagnetic waves are reflected multiple times within the device cavity, easily forming standing waves, leading to local field strength amplification and secondary interference to sensitive circuits; on the other hand, metallic materials have extremely low shielding effectiveness against near-field low-frequency magnetic fields, and their high density makes it difficult to meet the requirements for lightweight equipment.

[0003] To address these issues, absorption-based electromagnetic shielding materials have emerged. These materials fundamentally reduce the risk of secondary interference by converting electromagnetic energy into heat. However, existing evaluation systems for electromagnetic shielding materials still use the evaluation standards for traditional reflective materials, which have the following shortcomings: First, the evaluation indicators are singular, focusing only on total shielding effectiveness and failing to distinguish between absorption and reflection contributions, thus obscuring the core advantages of absorption-based materials. Second, the risk of secondary interference cannot be quantified; materials with high total shielding effectiveness may still have strong reflected waves, leading to a deterioration of the electromagnetic environment within the cavity. Third, there is a lack of evaluation on the degree of absorption dominance; no indicator can reflect whether the material's shielding mechanism is primarily absorption-based or reflection-based. Fourth, near-field and far-field evaluations are confused; existing standards mainly target far-field plane waves, while near-field interference is dominant in practical applications, resulting in significant differences in evaluation results. Fifth, they cannot effectively guide material optimization and selection; engineers cannot determine whether a material is suitable for absorption-dominant application scenarios based solely on total shielding effectiveness. Summary of the Invention

[0004] The purpose of this invention is to provide a comprehensive performance evaluation method for absorbing electromagnetic shielding materials, which realizes multi-dimensional quantitative evaluation of the comprehensive performance of absorbing electromagnetic shielding materials and can effectively guide material research and development and selection.

[0005] To achieve the above objectives, this invention provides a comprehensive performance evaluation method for absorbing electromagnetic shielding materials, comprising the following steps: A comprehensive evaluation index system for absorption-type electromagnetic shielding materials is constructed, which includes absorption coefficient, reflection coefficient, absorption dominance factor, cavity field strength attenuation factor, effective absorption bandwidth, and near-field absorption coefficient. The total shielding effectiveness, reflection loss, and absorption loss of the material are obtained through far-field testing. The absorption coefficient is determined based on the ratio of the absorption loss to the total shielding effectiveness, the reflection coefficient is determined based on the ratio of the reflection loss to the total shielding effectiveness, and the absorption dominance factor is determined based on the ratio of the absorption loss to the sum of the absorption loss and the reflection loss. By measuring the cavity effect test, the comparison between the field strength inside the cavity with a shield and the incident field strength without a shield is measured, and the cavity field strength attenuation factor is determined. Based on the absorption coefficient versus frequency curve, an absorption coefficient threshold is set, and the continuous frequency range in which the absorption coefficient is consistently higher than the threshold is determined as the effective absorption bandwidth. The total shielding effectiveness and reflection loss of the material under near-field conditions are measured through near-field testing, and the difference between the two is determined as the near-field absorption coefficient. The total shielding effectiveness, absorption dominance factor, cavity field strength attenuation factor, near-field absorption coefficient, and effective absorption bandwidth are integrated into a multi-dimensional evaluation vector. Weights are assigned to each indicator according to the target application scenario, a comprehensive score is calculated, and the material grade is classified based on the comprehensive score.

[0006] In the comprehensive evaluation index system, the absorption coefficient is used to reflect the proportion of absorption loss to total shielding effectiveness, the reflection coefficient is used to reflect the proportion of reflection loss to total shielding effectiveness, the absorption dominance factor is used to normalize and characterize the absorption dominance of the material, the cavity field strength attenuation factor is used to quantify the secondary interference suppression effect of the material in the cavity environment, the effective absorption bandwidth is used to evaluate the absorption stability of the material in a wide frequency range, and the near-field absorption coefficient is used to reflect the material's ability to absorb near-field magnetic fields.

[0007] The far-field test includes: using a vector network analyzer to measure the reflected signal strength and transmitted signal strength of the material in the target frequency band; determining the total shielding effectiveness by comparing the transmitted signal strength before and after the sample is installed; determining the reflection loss by measuring the amplitude of the reflected wave on the material surface; and determining the absorption loss as the difference between the total shielding effectiveness and the reflection loss.

[0008] The cavity effect test includes: making the material to be tested into a shielded cavity of standard size, placing an electric field probe inside the cavity, applying an incident electromagnetic wave from the outside, measuring the field strength at a specified position inside the cavity when there is a shield, and comparing it with the theoretical incident field strength at the same point when there is no shield. The ratio of the two is converted into a cavity field strength attenuation factor. When the factor is negative, it indicates that the field strength inside the cavity is lower than the incident field strength.

[0009] The effective absorption bandwidth is determined as follows: on the absorption coefficient versus frequency curve, a threshold is set based on the maximum value of the absorption coefficient. The starting frequency point where the absorption coefficient first reaches and remains above the threshold, and the ending frequency point where the absorption coefficient first drops below the threshold are identified. The difference between the ending frequency and the starting frequency is determined as the effective absorption bandwidth.

[0010] The near-field test includes: using a near-field magnetic field testing device to measure the total shielding effectiveness and reflection loss of the material under near-field conditions, and determining the difference between the total shielding effectiveness and the reflection loss as the near-field absorption coefficient, which is used to characterize the absorption loss of the material under near-field magnetic field conditions.

[0011] The data fusion and comprehensive evaluation includes: normalizing the total shielding effectiveness, absorption dominance factor, cavity field strength attenuation factor, near-field absorption coefficient, and effective absorption bandwidth to eliminate dimensional differences; setting weight coefficients for each indicator according to the target application scenario; and summing the scores of each normalized indicator with their corresponding weight coefficients to obtain the comprehensive score of the material.

[0012] The weighting coefficients are adjusted according to the emphasis on material performance in the target application scenario. For inverter housing application scenarios, the weights of the absorption dominance factor and near-field absorption coefficient are increased; for communication equipment chassis application scenarios, the weight of the effective absorption bandwidth is increased; and for scenarios with high requirements for the absolute value of shielding effectiveness, the weight of the total shielding effectiveness is increased.

[0013] The material grades are classified as follows: based on the comprehensive score, the materials are divided into excellent absorption type, good absorption type, mixed type, predominantly reflective type, and unsuitable type.

[0014] This invention discloses a comprehensive performance evaluation method for absorptive electromagnetic shielding materials. The method includes: constructing a comprehensive evaluation index system comprising absorption coefficient, reflection coefficient, absorption dominance factor, cavity field strength attenuation factor, effective absorption bandwidth, and near-field absorption coefficient; obtaining the material's total shielding effectiveness, reflection loss, and absorption loss through far-field testing to determine the absorption coefficient, reflection coefficient, and absorption dominance factor; determining the cavity field strength attenuation factor by comparing the internal field strength of the cavity with the incident field strength using cavity effect testing; determining the effective absorption bandwidth based on the absorption coefficient versus frequency curve; determining the near-field absorption coefficient through near-field testing; integrating the above indicators into a multi-dimensional evaluation vector, calculating a comprehensive score based on weights set according to the application scenario, and classifying the levels. This invention solves the technical problems of existing evaluation systems, such as single indicators, inability to distinguish between absorption and reflection contributions, inability to quantify secondary interference risks, and confusion between near-field and far-field evaluations. It achieves multi-dimensional quantitative evaluation of the comprehensive performance of absorptive electromagnetic shielding materials, effectively guiding material research and development and selection. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0016] Figure 1 This is a schematic diagram illustrating the steps of a comprehensive performance evaluation method for an absorptive electromagnetic shielding material according to the present invention.

[0017] Figure 2 This is a flowchart illustrating a comprehensive performance evaluation method for an absorptive electromagnetic shielding material provided by the present invention. Detailed Implementation

[0018] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0019] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0020] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0021] Please see Figures 1-2 This invention provides a comprehensive performance evaluation method for absorption-type electromagnetic shielding materials, comprising the following steps: S1. Construct a comprehensive evaluation index system for absorption-type electromagnetic shielding materials. The index system includes absorption coefficient, reflection coefficient, absorption dominance factor, cavity field strength attenuation factor, effective absorption bandwidth, and near-field absorption coefficient.

[0022] Specifically, when constructing a comprehensive evaluation index system for absorptive electromagnetic shielding materials, it is first necessary to clarify that the object of evaluation is a material whose shielding mechanism is mainly based on absorption. Its core advantage lies in converting electromagnetic energy into thermal energy, thereby reducing secondary interference caused by reflection. Therefore, the design of the index system should revolve around four dimensions: "absorption capacity," "reflection suppression capacity," "secondary interference suppression effect," and "wideband adaptability," to ensure that the evaluation results can comprehensively reflect the material's absorption-dominant characteristics and its overall performance in practical applications.

[0023] The first dimension is the evaluation of absorption capacity, used to characterize the efficiency of a material in converting electromagnetic energy into thermal energy. Under this dimension, the "absorption coefficient" is set as the core indicator. The absorption coefficient is defined as the proportion of absorption loss to the total shielding effectiveness, reflecting the degree to which the material consumes electromagnetic energy through absorption during the overall shielding process. The closer the absorption coefficient is to 1, the more likely the material relies almost entirely on absorption to achieve shielding, with minimal contribution from reflection, which conforms to the ideal characteristics of an absorbing material.

[0024] The second dimension is the reflection suppression capability evaluation, used to measure the degree to which a material reduces electromagnetic wave reflection. Under this dimension, the "reflection coefficient" is set as the core indicator, defined as the proportion of reflection loss to total shielding effectiveness. The lower the reflection coefficient, the weaker the reflection of electromagnetic waves on the material surface, which helps reduce the risk of secondary interference formed by reflected waves within the system. To further comprehensively reflect the dominant relationship between absorption and reflection, this dimension also includes an "absorption dominance factor," defined as the ratio of the absorption coefficient to the sum of the absorption coefficient and the reflection coefficient. The absorption dominance factor normalizes absorption and reflection suppression capabilities to between 0 and 1. When the factor is close to 1, it indicates that the material's shielding mechanism is dominated by absorption; when it is close to 0, it is dominated by reflection. This factor can serve as a core criterion for determining whether a material is suitable for absorption-dominant scenarios.

[0025] The third dimension is the evaluation of secondary interference suppression effectiveness, used to assess the degree of electromagnetic field change caused by the material in a real cavity environment. Traditional material-level shielding effectiveness tests cannot reflect the impact of the material on the electromagnetic environment inside the cavity after it is assembled into a shell. Therefore, it is necessary to introduce the "cavity field strength attenuation factor" as an indicator. This factor quantifies the material's ability to suppress the cavity field strength under operating conditions by comparing the ratio of the field strength inside the cavity with a shield to the incident field strength without a shield. A negative value of this factor indicates that the field strength inside the cavity is lower than the incident field strength; the larger the absolute value, the more significant the material's suppression effect on secondary interference. The introduction of this indicator fills the technical gap in existing evaluation methods that cannot predict the risk of secondary interference.

[0026] The fourth dimension is broadband absorption characteristic evaluation, used to measure the consistency of a material's absorption dominance over a wide frequency range. Under this dimension, "effective absorption bandwidth" is set as the core indicator, defined as the continuous frequency range within the target frequency band where the absorption coefficient is consistently above a set threshold (e.g., absorption coefficient not lower than 0.7 or absorption dominance factor not lower than a certain set value). This indicator reflects whether the material consistently maintains absorption-dominant shielding characteristics within the target application frequency band, avoiding problems such as significant decreases in absorption capability and increased reflection in certain frequency bands.

[0027] The fifth dimension evaluates near-field magnetic field absorption capacity, supplementing the limitations of traditional far-field testing in low-frequency magnetic field applications. This dimension uses the "near-field absorption coefficient" as a core indicator. Through shielding tests under near-field conditions, the absorption loss component is separated to characterize the material's ability to absorb near-field magnetic field energy. This indicator is crucial for evaluating the material's performance in applications where near-field interference is dominant, such as inverters and wireless charging.

[0028] The above six indicators together constitute a complete comprehensive evaluation index system. These indicators complement each other, characterizing the material's overall performance from multiple perspectives, including absorption capacity, reflection suppression, secondary interference suppression, broadband characteristics, and near-field adaptability. In subsequent evaluation processes, testing and data fusion will be conducted based on this index system to provide quantitative evidence for material classification, selection, and optimization.

[0029] S2. Obtain the total shielding effectiveness, reflection loss, and absorption loss of the material through far-field testing, and determine the absorption coefficient based on the ratio of the absorption loss to the total shielding effectiveness, determine the reflection coefficient based on the ratio of the reflection loss to the total shielding effectiveness, and determine the absorption dominance factor based on the ratio of the absorption loss to the sum of the absorption loss and the reflection loss.

[0030] Specifically, after constructing the comprehensive evaluation index system, the basic shielding parameters of the material are first obtained through far-field testing, providing data support for the subsequent calculation of the absorption coefficient, reflection coefficient, and absorption dominance factor. The purpose of far-field testing is to quantitatively measure the overall shielding capability of the material against electromagnetic waves under plane wave conditions, and to separate the contributions of absorption loss and reflection loss.

[0031] Before testing, standard-sized annular or flat specimens are prepared, ensuring that the specimen surface is flat and uniform, representing the typical shielding performance of the material under test. A vector network analyzer is used as the testing equipment, along with a dedicated shielding effectiveness testing fixture or coaxial testing device, enabling the testing system to generate a stable plane wave field within the target frequency band, while simultaneously and accurately acquiring the material's reflected and transmitted signals.

[0032] During testing, the sample is mounted at the window position of the test fixture, ensuring good electrical contact between the sample and the fixture to prevent electromagnetic wave leakage from the edges. The test system is first calibrated without the sample installed, and the transmission signal under no-load conditions is recorded as a reference. Subsequently, the sample is installed, and a vector network analyzer is used to measure the intensity of the reflected electromagnetic wave signal on the material surface and the intensity of the transmitted signal after passing through the material.

[0033] By comparing the transmitted signal strength before and after the sample installation, the overall shielding effectiveness of the material can be calculated. Overall shielding effectiveness reflects the material's overall ability to block electromagnetic waves; a higher value indicates less electromagnetic wave transmission. However, overall shielding effectiveness alone cannot distinguish whether the shielding effect originates from absorption or reflection; therefore, further analysis of the reflected signal is required.

[0034] The intensity of the reflected signal directly reflects the material's ability to reflect electromagnetic waves. In testing, the magnitude of reflection loss can be determined by measuring the amplitude of the reflected wave at the material's surface and comparing it with the amplitude of the incident wave. A greater reflection loss indicates that the material surface reflects more electromagnetic waves back into space; this energy does not enter the material's interior and therefore is not converted into heat.

[0035] After obtaining the total shielding effectiveness and reflection loss, the remaining shielding contribution is the absorption loss. Absorption loss represents the portion of electromagnetic waves that are converted into heat energy after entering the material. Since the total shielding effectiveness is composed of reflection loss, absorption loss, and multiple reflection corrections, the multiple reflection corrections can be ignored when the absorption loss is large. Therefore, the absorption loss can be approximately determined by subtracting the reflection loss from the total shielding effectiveness.

[0036] Based on the above three parameters, the core indicators characterizing the material's absorption capacity are further calculated. The absorption coefficient is determined by the ratio of absorption loss to total shielding effectiveness, reflecting the proportion of absorption loss in the total shielding effectiveness. The reflection coefficient is determined by the ratio of reflection loss to total shielding effectiveness, reflecting the proportion of reflection loss. The absorption dominance factor is determined by the ratio of absorption loss to the sum of absorption loss and reflection loss. This factor normalizes the contributions of absorption and reflection, intuitively reflecting whether the material's shielding mechanism is dominated by absorption or reflection. When the absorption dominance factor is close to its maximum value, it indicates that the material relies almost entirely on absorption to achieve shielding; when it is close to its minimum value, it indicates that the shielding effect mainly depends on reflection.

[0037] Through the aforementioned far-field tests and parameter calculations, complete data on the material's total shielding effectiveness, reflection loss, absorption loss, absorption coefficient, reflection coefficient, and absorption dominance factor as a function of frequency under plane wave conditions can be obtained. These data form the basis for the two dimensions of absorption capacity and reflection suppression capacity in the comprehensive evaluation system, and provide key inputs for subsequent integration with near-field test and cavity effect test results.

[0038] S3. By measuring the cavity effect test, the comparison between the field strength inside the cavity with a shield and the incident field strength without a shield is measured to determine the cavity field strength attenuation factor.

[0039] Specifically, after obtaining the basic shielding parameters of the material through far-field testing, it is necessary to further evaluate the impact of the material on the electromagnetic environment inside the cavity after it is actually assembled into a shell. Traditional material-level shielding effectiveness testing only reflects the shielding capability of the material under infinite plane wave conditions and cannot predict the risk of secondary interference that may be caused when the material is used in a finite space. To this end, this invention introduces cavity effect testing, which quantifies the material's suppression effect on secondary interference by simulating the cavity usage state of the material in actual applications.

[0040] The core principle of cavity effect testing lies in the following: When electromagnetic waves are incident on a shielded cavity made of the material under test, some of the electromagnetic waves are reflected by the material surface, some are absorbed inside the material, and some pass through the material into the cavity. If the material is primarily reflective, the reflected waves will undergo multiple reflections inside the cavity, leading to an increase in the field strength and secondary interference. If the material is primarily absorbent, the energy of the electromagnetic waves entering the cavity is effectively dissipated, and the field strength inside the cavity is significantly reduced. By measuring the actual field strength inside the cavity with shielding and comparing it with the incident field strength without shielding, the material's ability to suppress secondary interference in a cavity environment can be directly observed.

[0041] Before testing begins, the material under test is first fabricated into a standard-sized shielded cavity. The shape and size of the cavity are determined based on the target application scenario, typically using a rectangular cavity structure to ensure that an electric field probe can be placed inside. All surfaces of the cavity are made of the material under test to accurately reflect the shielding effect of the material in its actual assembled state. The cavity seams are treated with good conductivity to prevent electromagnetic waves from leaking through gaps and affecting test accuracy.

[0042] The testing system includes a signal generator, a transmitting antenna, an electric field probe, and a field strength receiving device. The transmitting antenna is placed outside the cavity to generate incident electromagnetic waves of known intensity. The electric field probe is installed at a designated location inside the cavity to measure the actual field strength at that location. During the test, without installing a shielded cavity, the transmitting antenna first generates electromagnetic waves, and the electric field probe directly receives the incident waves, recording the incident field strength at that location as a reference.

[0043] A shielded cavity made of the material under test is then placed between the transmitting antenna and the electric field probe, allowing electromagnetic waves to pass through the cavity walls and enter the cavity. The transmitting antenna transmits electromagnetic waves at the same power and frequency, and the electric field probe measures the field strength at the same location inside the cavity. By comparing the field strength inside the cavity with that of the shield with that of the unshielded cavity, the actual impact of the material on the electromagnetic environment inside the cavity can be determined.

[0044] If the field strength inside the cavity is lower than the incident field strength, it indicates that the material effectively absorbs the electromagnetic energy entering the cavity, reducing the electromagnetic field level inside the cavity and exhibiting good secondary interference suppression. If the field strength inside the cavity is equal to or even higher than the incident field strength, it indicates severe material reflection, with the reflected waves forming a superposition and enhancement within the cavity, leading to a significant increase in the risk of secondary interference.

[0045] Logarithmically transforming the ratio of the intracavity field strength to the incident field strength yields an index used to quantify the effectiveness of secondary interference suppression. A negative value indicates that the intracavity field strength is lower than the incident field strength; the larger the absolute value, the stronger the material's ability to suppress secondary interference. A positive value indicates that the intracavity field strength is higher than the incident field strength; the larger the positive value, the higher the risk of secondary interference.

[0046] Cavity effect testing allows for the measurement and recording of this indicator's variation with frequency at different points, thus comprehensively evaluating the material's secondary interference suppression performance within the target operating frequency band. The test results, along with indicators such as the absorption coefficient and absorption dominance factor obtained from far-field testing, corroborate each other, forming a crucial dimension for comprehensive material evaluation. For applications sensitive to secondary interference, such as inverter housings and communication equipment chassis, this indicator can serve as a core basis for material selection.

[0047] S4. Based on the absorption coefficient versus frequency curve, set an absorption coefficient threshold and determine the continuous frequency range where the absorption coefficient is consistently higher than the threshold as the effective absorption bandwidth.

[0048] Specifically, after obtaining data on the frequency variation of the material's absorption coefficient through far-field testing, it is necessary to further evaluate the material's absorption stability over a wide frequency range. While the absorption coefficient reflects the material's absorption capability at specific frequencies, it cannot intuitively represent the width of the material's dominant absorption performance across a continuous frequency range. For practical applications, electromagnetic interference is often distributed within a certain frequency range; only by maintaining high absorption capability across the entire target frequency band can the material effectively suppress interference and reduce the risk of secondary interference. Therefore, this invention introduces the indicator of effective absorption bandwidth to quantify the bandwidth through which the material stably exerts its absorption capability across a continuous frequency range.

[0049] The effective absorption bandwidth is determined based on the absorption coefficient versus frequency curve. This curve is obtained by converting the absorption coefficients of a series of discrete frequency points obtained from far-field testing into a continuous curve, clearly showing the trend of the absorption coefficient across the entire test frequency band. The horizontal axis of the curve represents frequency, and the vertical axis represents the absorption coefficient. The absorption coefficient ranges from its minimum to its maximum value; the closer it is to the maximum value, the stronger the material's absorption capacity at that frequency.

[0050] The first step in determining the effective absorption bandwidth is to set a threshold for the absorption coefficient. This threshold depends on the minimum requirements for the material's absorption capacity, typically using the maximum value of the absorption coefficient as a benchmark, and taking a certain percentage of that maximum value as the threshold. For example, when the absorption capacity corresponding to the maximum absorption coefficient is considered ideal, a range where the absorption coefficient is not lower than a certain percentage of that maximum value can be set as the effective absorption range. This percentage can be adjusted according to the absorption capacity requirements of the target application scenario; a higher percentage is used for scenarios with high absorption requirements, while a lower percentage can be used for scenarios with relatively relaxed requirements.

[0051] Identify the frequency range on the curve where the absorption coefficient first reaches and remains above the threshold. Since the absorption coefficient may fluctuate with frequency, not all frequencies above the threshold are continuously distributed. Therefore, starting from the beginning of the test frequency band, check each frequency in the increasing frequency direction to see if the absorption coefficient reaches or exceeds the threshold, and record the starting frequency points that continuously meet the condition. When the absorption coefficient first drops below the threshold, record the frequency corresponding to that point as the end frequency of the current continuous interval. If the absorption coefficient exceeds the threshold again at a higher frequency band and remains above it for a certain period, record the starting and ending frequency points of each continuous interval.

[0052] For absorptive electromagnetic shielding materials, their absorption capacity typically performs optimally within a specific frequency band, gradually decreasing towards either end of that band. Therefore, the effective absorption bandwidth is usually defined as the continuous interval from when the absorption coefficient first rises above the threshold until it first falls below the threshold. The width of this continuous interval is obtained by subtracting the starting frequency from the ending frequency, reflecting the bandwidth range within which the material maintains its dominant absorption characteristics in the target frequency band.

[0053] For materials whose absorption coefficient is consistently above the threshold throughout the entire test frequency band, the effective absorption bandwidth is the total width of the entire test frequency band; for materials whose absorption coefficient is consistently below the threshold, the effective absorption bandwidth is zero. In practical applications, a wider effective absorption bandwidth indicates that the material can stably exert its absorption effect over a wider frequency range, making it suitable for scenarios that cover a wider range of interference frequencies.

[0054] The effective absorption bandwidth is a key indicator for quantitatively evaluating the broadband absorption characteristics of materials. This indicator, along with other metrics such as the absorption coefficient and absorption dominance factor, forms a comprehensive description of a material's absorption capability. The absorption coefficient reflects the absorption intensity at a specific frequency, while the effective absorption bandwidth reflects the absorption stability over a wide frequency range. Combining these two metrics provides more comprehensive guidance for the selection and application of materials in broadband interference environments.

[0055] S5. Through near-field testing, measure the total shielding effectiveness and reflection loss of the material under near-field conditions, and determine the difference between the two as the near-field absorption coefficient.

[0056] Specifically, after obtaining the shielding parameters of a material under plane wave conditions through far-field testing, it is necessary to further evaluate the material's absorption capacity under near-field magnetic field conditions. Far-field testing, using plane wave illumination, is suitable for evaluating the shielding effect of a material against long-distance electromagnetic interference. However, in practical applications, interference sources inside electronic devices are often close to the shielding enclosure, such as the power modules of inverters and the inductors of switching power supplies. The electromagnetic fields generated by these interference sources are predominantly near-field, with the magnetic field component dominating. Traditional far-field test results cannot accurately reflect the shielding performance of the material under near-field magnetic field conditions; therefore, specialized near-field testing is needed to evaluate the material's absorption capacity against near-field magnetic fields.

[0057] The core principle of near-field testing lies in the fact that, under near-field conditions, the wave impedance of electromagnetic waves differs from that of far-field plane waves, causing changes in the reflection characteristics of the material surface and its internal absorption characteristics. For electromagnetic shielding materials that primarily rely on absorption, their absorption capacity under near-field magnetic field conditions may differ significantly from that under far-field conditions. Using a near-field testing device, the physical scenarios of near-field magnetic field interference in practical applications can be simulated, the shielding parameters of the material under near-field conditions can be quantitatively obtained, and the absorption loss component can be separated to evaluate the material's absorption capacity against near-field magnetic fields.

[0058] Before testing, standard-sized samples are prepared. The samples should be flat, uniform, and representative of the typical shielding performance of the material under test. The testing setup employs a specially designed near-field magnetic field testing system, which includes a signal generator, a near-field magnetic field probe, a receiving device, and sample clamps. The near-field magnetic field probe generates or receives electromagnetic fields dominated by magnetic field components, simulating the near-field magnetic field characteristics of actual interference sources. The testing setup is calibrated before formal testing to ensure the accuracy and repeatability of the test results.

[0059] The testing process is divided into two parts. The first part measures the material's overall shielding effectiveness under near-field conditions. The sample is installed at the window position of the testing apparatus, ensuring good electrical contact between the sample and the apparatus to prevent electromagnetic wave leakage from the edges. A near-field magnetic field probe generates a near-field magnetic field of known intensity, and a receiving probe on the other side of the sample measures the magnetic field strength after it passes through the sample. By comparing the magnetic field strength before and after sample installation, the material's overall shielding effectiveness under near-field conditions can be determined. This overall shielding effectiveness comprehensively reflects the sum of the material's reflection loss and absorption loss of electromagnetic waves under near-field magnetic field conditions.

[0060] The second part measures the reflection loss of the material under near-field conditions. Using the same testing apparatus, the reflection magnetic field strength on the sample surface is measured and compared with the incident magnetic field strength to determine the material surface's ability to reflect near-field magnetic fields. Reflection loss reflects the proportion of electromagnetic waves reflected back into space by the material surface; this portion of energy does not enter the material's interior and therefore is not converted into heat.

[0061] After obtaining the total shielding effectiveness and reflection loss under near-field conditions, subtracting the two yields the absorption loss under near-field conditions, which is defined as the near-field absorption coefficient. The near-field absorption coefficient reflects the material's ability to convert electromagnetic energy into thermal energy under near-field magnetic field conditions and is a core indicator for evaluating the absorption performance of materials in near-field interference scenarios.

[0062] A larger near-field absorption coefficient indicates that the material can effectively absorb electromagnetic energy under near-field magnetic field conditions, reducing electromagnetic interference that penetrates the material into sensitive areas and minimizing the impact of reflected waves on surrounding circuits. Conversely, a smaller near-field absorption coefficient indicates weaker absorption capacity under near-field magnetic field conditions, with the shielding effect relying primarily on reflection, potentially leading to secondary interference issues in near-field interference scenarios.

[0063] The near-field absorption coefficient obtained through near-field testing complements the absorption coefficient and absorption dominance factor obtained through far-field testing, together forming a complete description of the material's absorption capability. The far-field absorption coefficient reflects the material's absorption performance under plane wave conditions and is suitable for evaluating the material's shielding effect against long-distance electromagnetic interference. The near-field absorption coefficient reflects the material's absorption performance under near-field magnetic field conditions and is suitable for application scenarios where near-field interference is dominant, such as inverter housings, wireless charging devices, and switching power supplies. The combination of these two factors allows the evaluation system of this invention to comprehensively cover various electromagnetic environments in practical applications, providing a more scientific basis for material research, selection, and optimization.

[0064] S6. Integrate the total shielding effectiveness, absorption dominance factor, cavity field strength attenuation factor, near-field absorption coefficient and effective absorption bandwidth into a multi-dimensional evaluation vector. Set weights for each indicator according to the target application scenario, calculate the comprehensive score, and classify the material grade according to the comprehensive score.

[0065] Specifically, after completing far-field testing, near-field testing, cavity effect testing, and determining the effective absorption bandwidth, the test results from each dimension need to be integrated to form a comprehensive evaluation of the material's overall performance. Since different indicators reflect the material's performance in different aspects, a single indicator cannot fully characterize the material's comprehensive value in practical applications. Therefore, data fusion and comprehensive evaluation are needed to organically unify multi-dimensional information, providing a quantitative basis for material research, selection, and optimization.

[0066] The first step in data fusion and comprehensive evaluation is to construct a multi-dimensional evaluation vector. This involves integrating five core indicators: total shielding effectiveness and absorption dominance factor obtained from far-field testing; cavity field strength attenuation factor obtained from cavity effect testing; and near-field absorption coefficient and effective absorption bandwidth obtained from near-field testing. This forms a multi-dimensional data structure describing the comprehensive performance of the material. Each indicator reflects the material's performance characteristics from different perspectives: total shielding effectiveness characterizes the material's overall shielding capability; absorption dominance factor characterizes the degree of absorption dominance in the material's shielding mechanism; cavity field strength attenuation factor characterizes the material's actual effect in suppressing secondary interference; near-field absorption coefficient characterizes the material's absorption capability in near-field low-frequency application scenarios; and effective absorption bandwidth characterizes the material's absorption stability over a wide frequency range. These five indicators complement each other, together forming a complete evaluation dimension.

[0067] The second step is to determine the weighting coefficients of each indicator based on the target application scenario. Different application scenarios have different focuses on material performance, so it is necessary to assign different importance to each indicator according to specific needs. For example, in the application scenario of inverter housing, since the inverter generates strong near-field magnetic field interference during operation and the internal space of the housing is limited, the risk of secondary interference caused by reflection is high. Therefore, the weights of the absorption dominance factor and the near-field absorption coefficient should be appropriately increased. In the application scenario of communication equipment chassis, more attention may be paid to the stable absorption performance of the material over a wide frequency range. Therefore, the weight of the effective absorption bandwidth should be increased accordingly. For scenarios with high requirements for the absolute value of shielding effectiveness, the weight of the total shielding effectiveness needs to be increased. The weighting coefficients can be determined based on engineering experience, industry standards, or scientific methods such as the analytic hierarchy process (AHP) to ensure that the weight allocation matches the needs of the target application scenario.

[0068] The third step is to normalize the various indicators. Because the indicators have different dimensions and significantly different numerical ranges, direct weighted summation is not feasible. Therefore, the test results of each indicator need to be converted into dimensionless scores on a unified scale. The normalization benchmark can be selected from the performance values ​​of reference materials, or it can be set according to industry standards or the theoretical upper limit of material performance. Through normalization, the scores of each indicator fall within the same range, eliminating the impact of differences in dimensions and orders of magnitude on the comprehensive evaluation, making the performance comparison between different materials more intuitive and fair.

[0069] The fourth step is to calculate the overall score. The normalized scores of each indicator are weighted and summed according to the weighting coefficients determined in the second step to obtain the material's overall score. The overall score reflects the material's overall performance level within a multi-dimensional evaluation framework. It reflects both the material's performance on each individual indicator and, through weighting, the differentiated performance requirements of different application scenarios. A higher overall score indicates stronger overall adaptability of the material to the target application scenario.

[0070] The fifth step is to classify materials based on their overall scores. To facilitate engineering applications and selection decisions, the overall scores are divided into several levels, each corresponding to a different performance level and applicable scenarios. Materials with the highest overall scores are rated as excellent absorbers, suitable for scenarios with extremely high requirements for secondary interference, such as near high-sensitivity circuits or inside equipment with strict electromagnetic environment requirements. Materials with the second-highest overall scores are rated as good absorbers, suitable for general absorption-dominant scenarios. Materials with overall scores in the middle range are rated as mixed absorbers, still usable in scenarios where some reflection is acceptable. Materials with lower overall scores are rated as primarily reflective, only suitable for scenarios where secondary interference is not a concern. Materials with the lowest overall scores are rated as unsuitable and not recommended for absorption-dominant applications.

[0071] Through the aforementioned data fusion and comprehensive evaluation steps, the previously scattered test indicators are integrated into a unified comprehensive score and grade determination result. This evaluation result retains the physical meaning of each dimension indicator, facilitating targeted optimization of material formulations and structures by R&D personnel, while also providing an intuitive comprehensive assessment, enabling engineers to make rapid decisions during selection. This method overcomes the limitations of traditional evaluation methods that rely solely on a single indicator of total shielding effectiveness, achieving a quantitative, comprehensive, and scientific evaluation of the overall performance of absorbing electromagnetic shielding materials.

[0072] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0073] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A comprehensive performance evaluation method for an absorptive electromagnetic shielding material, characterized in that, Includes the following steps: A comprehensive evaluation index system for absorption-type electromagnetic shielding materials is constructed, which includes absorption coefficient, reflection coefficient, absorption dominance factor, cavity field strength attenuation factor, effective absorption bandwidth, and near-field absorption coefficient. The total shielding effectiveness, reflection loss, and absorption loss of the material are obtained through far-field testing. The absorption coefficient is determined based on the ratio of the absorption loss to the total shielding effectiveness, the reflection coefficient is determined based on the ratio of the reflection loss to the total shielding effectiveness, and the absorption dominance factor is determined based on the ratio of the absorption loss to the sum of the absorption loss and the reflection loss. By measuring the cavity effect test, the comparison between the field strength inside the cavity with a shield and the incident field strength without a shield is measured, and the cavity field strength attenuation factor is determined. Based on the absorption coefficient versus frequency curve, an absorption coefficient threshold is set, and the continuous frequency range in which the absorption coefficient is consistently higher than the threshold is determined as the effective absorption bandwidth. The total shielding effectiveness and reflection loss of the material under near-field conditions are measured through near-field testing, and the difference between the two is determined as the near-field absorption coefficient. The total shielding effectiveness, absorption dominance factor, cavity field strength attenuation factor, near-field absorption coefficient, and effective absorption bandwidth are integrated into a multi-dimensional evaluation vector. Weights are assigned to each indicator according to the target application scenario, a comprehensive score is calculated, and the material grade is classified based on the comprehensive score.

2. The comprehensive performance evaluation method for the absorptive electromagnetic shielding material as described in claim 1, characterized in that, In the comprehensive evaluation index system, the absorption coefficient is used to reflect the proportion of absorption loss to total shielding effectiveness, the reflection coefficient is used to reflect the proportion of reflection loss to total shielding effectiveness, the absorption dominance factor is used to normalize and characterize the absorption dominance of the material, the cavity field strength attenuation factor is used to quantify the secondary interference suppression effect of the material in the cavity environment, the effective absorption bandwidth is used to evaluate the absorption stability of the material in a wide frequency range, and the near-field absorption coefficient is used to reflect the material's ability to absorb near-field magnetic fields.

3. The comprehensive performance evaluation method for the absorptive electromagnetic shielding material as described in claim 1, characterized in that, The far-field test includes: using a vector network analyzer to measure the reflected signal strength and transmitted signal strength of the material in the target frequency band; determining the total shielding effectiveness by comparing the transmitted signal strength before and after the sample is installed; determining the reflection loss by measuring the amplitude of the reflected wave on the material surface; and determining the absorption loss as the difference between the total shielding effectiveness and the reflection loss.

4. The comprehensive performance evaluation method for the absorptive electromagnetic shielding material as described in claim 1, characterized in that, The cavity effect test includes: making the material under test into a shielded cavity of standard size, placing an electric field probe inside the cavity, applying an incident electromagnetic wave from the outside, measuring the field strength at a specified location inside the cavity when there is a shield, and comparing it with the theoretical incident field strength at the same point when there is no shield. The ratio of the two is converted into a cavity field strength attenuation factor. When the factor is negative, it indicates that the field strength inside the cavity is lower than the incident field strength.

5. The comprehensive performance evaluation method for the absorptive electromagnetic shielding material as described in claim 1, characterized in that, The effective absorption bandwidth is determined as follows: on the absorption coefficient versus frequency curve, a threshold is set based on the maximum value of the absorption coefficient. The starting frequency point where the absorption coefficient first reaches and remains above the threshold, and the ending frequency point where the absorption coefficient first drops below the threshold are identified. The difference between the ending frequency and the starting frequency is determined as the effective absorption bandwidth.

6. The comprehensive performance evaluation method for the absorptive electromagnetic shielding material as described in claim 1, characterized in that, The near-field test includes: using a near-field magnetic field testing device to measure the total shielding effectiveness and reflection loss of the material under near-field conditions, and determining the difference between the total shielding effectiveness and the reflection loss as the near-field absorption coefficient, which is used to characterize the absorption loss of the material under near-field magnetic field conditions.

7. The comprehensive performance evaluation method for the absorptive electromagnetic shielding material as described in claim 1, characterized in that, Data fusion and comprehensive evaluation include: normalizing the total shielding effectiveness, absorption dominance factor, cavity field strength attenuation factor, near-field absorption coefficient, and effective absorption bandwidth to eliminate dimensional differences; setting weight coefficients for each indicator according to the target application scenario; and summing the scores of each normalized indicator with their corresponding weight coefficients to obtain the comprehensive score of the material.

8. The comprehensive performance evaluation method for the absorptive electromagnetic shielding material as described in claim 7, characterized in that, The weighting coefficients are set according to the emphasis on material performance in the target application scenario. For inverter housing application scenarios, the weights of the absorption dominance factor and near-field absorption coefficient are increased; for communication equipment chassis application scenarios, the weight of the effective absorption bandwidth is increased; for scenarios with high requirements for the absolute value of shielding effectiveness, the weight of the total shielding effectiveness is increased.

9. The comprehensive performance evaluation method for the absorptive electromagnetic shielding material as described in claim 1, characterized in that, The material grades are classified as follows: based on the comprehensive score, the materials are divided into excellent absorption type, good absorption type, mixed type, predominantly reflective type, and unsuitable type.

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