GB/T 17626 consists of the following parts, under the general title Electromagnetic Compatibility — Testing and Measurement Techniques:
— GB/T 17626.1-2006 Electromagnetic Compatibility — Testing And Measurement Techniques — Overview of Immunity Tests;
— GB/T 17626.2-2018 Electromagnetic Compatibility — Testing And Measurement Techniques — Electrostatic Discharge Immunity Test;
— GB/T 17626.3-2016 Electromagnetic Compatibility — Testing And Measurement Techniques — Radiated, Radio-frequency, Electromagnetic Field Immunity Test;
— GB/T 17626.4-2018 Electromagnetic Compatibility — Testing And Measurement Techniques — Electrical Fast Transient/Burst Immunity Test;
— GB/T 17626.5-2008 Electromagnetic Compatibility — Testing And Measurement Techniques — Surge (Impact) Immunity Test;
— GB/T 17626.6-2017 Electromagnetic Compatibility — Testing And Measurement Techniques — Immunity To Conducted Disturbances, Induced by Radio-frequency Fields;
— GB/T 17626.7-2008 Electromagnetic Compatibility — Testing And Measurement Techniques — General Guide on Harmonics and Interharmonics Measurements And Instrumentation For Power Supply Systems And Equipment Connected Thereto;
— GB/T 17626.8-2006 Electromagnetic Compatibility — Testing And Measurement Techniques — Power Frequency Magnetic Field Immunity Test;
— GB/T 17626.9-2011 Electromagnetic Compatibility — Testing And Measurement Techniques — Pulse Magnetic Field Immunity Test;
— GB/T 17626.10-2017 Electromagnetic Compatibility — Testing And Measurement Techniques — Damped Oscillatory Magnetic Field Immunity Test;
— GB/T 17626.11-2008 Electromagnetic Compatibility — Testing And Measurement Techniques — Voltage Dips, Short Interruptions And Voltage Variations Immunity Tests;
— GB/T 17626.12-2013 Electromagnetic Compatibility — Testing And Measurement Techniques — Oscillatory Waves Immunity Test;
— GB/T 17626.13-2006 Electromagnetic Compatibility — Testing And Measurement Techniques — Harmonics and Interharmonics Including Mains Signalling At A.C. Power Port, Low Frequency Immunity Test;
— GB/T 17626.14-2005 Electromagnetic Compatibility — Testing And Measurement Techniques — Voltage Fluctuation Immunity Test;
— GB/T 17626.15-2011 Electromagnetic Compatibility — Testing And Measurement Techniques — Flickermeter — Functional And Design of Specifications;
— GB/T 17626.16-2007 Electromagnetic Compatibility — Testing And Measurement Techniques — Test For Immunity To Conducted, Common Mode Disturbances In The Frequency Range 0 Hz To 150 kHz;
— GB/T 17626.17-2005 Electromagnetic Compatibility — Testing And Measurement Techniques — Ripple on D.C. Input Power Port Immunity Test;
— GB/T 17626.18-2016 Electromagnetic Compatibility — Testing And Measurement Techniques — Oscillatory Waves Immunity Test;
— GB/T 17626.20-2014 Electromagnetic Compatibility — Testing And Measurement Techniques — Emission And Immunity Testing In Transverse Electromagnetic (TEM) Waveguide;
— GB/T 17626.21-2014 Electromagnetic Compatibility — Testing And Measurement Techniques — Reverberation Chamber Test Methods;
— GB/T 17626.22-2017 Electromagnetic Compatibility — Testing And Measurement Techniques — Radiated Emissions and Immunity Measurements In Fully Anechoic Rooms (FARs);
— GB/T17626.24-2012 Electromagnetic Compatibility — Testing And Measurement Techniques — Test Methods For Protective Devices For HEMP Conducted Disturbance;
— GB/T 17626.27-2006 Electromagnetic Compatibility — Testing And Measurement Techniques — Unbalance Immunity Test;
— GB/T 17626.28-2006 Electromagnetic Compatibility — Testing And Measurement Techniques — Variation of Power Frequency Immunity Test;
— GB/T 17626.29-2006 Electromagnetic Compatibility — Testing And Measurement Techniques — Voltage Dips, Short Interruptions And Voltage Variations On D.C. Input Power Port Immunity Tests;
— GB/T 17626.30-2012 Electromagnetic Compatibility — Testing And Measurement Techniques — Power Quality Measurement Methods;
— GB/T 17626.34-2012 Electromagnetic Compatibility — Testing And Measurement Techniques — Voltage Dips, Short Interruptions And Voltage Variations Immunity Tests For Equipment with Mains Current More Than 16 A Per Phase;
This part is Part 3 of GB/T 17626.
This Part is drafted in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 17626.3-2006 Electromagnetic Compatibility — Testing and Measurement Techniques — Radiated, Radio-frequency, Electromagnetic Field Immunity Test in whole.
The following technical deviations have been made with respect to GB/T 17626.3-2006:
— The original terms 4.11 “stripline” and 4.15 “spurious radiation” are deleted from Clause 4 “Terminology and Definitions”;
— The original Tables 1 and 2 in Clause 5 are merged into Table 1 “Test levels related to general purpose, digital radio telephones and other RF emitting devices”;
— In 5. 2, the high frequency range for test levels related to the protection against RF emissions from digital radio telephones and other RF emitting devices is extend form 2 GHz to 6 GHz;
— In Clause 6, the requirements for power amplifiers are modified;
— In 6.2 “Calibration of field”, the requirements for uniform field area for application of full illumination, partial illumination and independent windows method are added;
— In 6.2.1 “Constant field strength calibration method”, step j) is added to confirm the test system;
— In 6.2.2 “Constant power calibration method”, step m) is added to confirm the test system;
— In Annex B “Field Generating Antennas”, circularly polarized antenna is deleted;
— The original Annex D “Other Test Methods — TEM Cells and Striplines” is deleted;
— The original Annex I is changed to Annex G, and Table G.3 is added;
— The original Annex H is changed to Annex F;
— The original Annex J is changed to Annex H;
— The original Annex K is changed to Annex J;
— The original Annex F and Annex G are merged into Annex E;
— Annex I “Calibration Method for E-field Probes” is added;
— Annex J “Measurement Uncertainty due to Test Instrumentation” is added.
This part is identical with International Standard IEC 61000-4-3:2010 Electromagnetic Compatibility (EMC) — Part 4-3: Testing And Measurement Techniques — Radiated, Radio-frequency, Electromagnetic Field Immunity Test.
The Chinese documents identical to the normative international documents given in this part are as follows:
— GB/T 4365-2003 Electrotechnical Terminology — Electromagnetic Compatibility [IEC 60050 (161):1990, IDT]
— GB/T 17626. 6-2008 Electromagnetic Compatibility — Testing and Measurement Techniques — Immunity To Conducted Disturbances, Induced By Radio-frequency Fields (IEC 61000-4-6:2006, IDT).
This part was proposed by and is under the jurisdiction of the National Technical Committee on Electromagnetic Compatibility of Standardization Administration of China (SAC/TC 246).
Drafting organizations of this part: Shanghai Electrical Apparatus Research Institute, Shanghai Institute of Measurement and Testing Technology, Shanghai Institute of Process Automation & Instrumentation, Beijing Institute of Medical Device Testing, Dongshuo Testing Technology (Suzhou) Co., Ltd. and Shanghai Sanki Electronic Industries Co., Ltd.
Chief drafters of this part: Zheng Junqi, Liu Yuan, Gong Cheng, Wang Ying, Meng Zhiping, Xiao Xiao, Yuan Mingcong, Ye Qiongyu, Shou Jianxia and Qian Feng.
The previous editions of this part are as follows:
— GB/T 17626.3-1992, GB/T 17626. 3-1998, GB/T 17626. 3-2006.
Electromagnetic Compatibility — Testing And Measurement Techniques — Radiated, Radio-frequency, Electromagnetic Field Immunity Test
1 Scope
This part of GB/T 17626 is applicable to the immunity requirements of electrical and electronic equipment to radiated electromagnetic energy. It establishes test levels and the required test procedures.
The object of this part is to establish a common reference for evaluating the immunity of electrical and electronic equipment when subjected to radiated, radio-frequency electromagnetic fields. The test method documented in this part describes a consistent method to assess the immunity of an equipment or system against a defined phenomenon.
Note 1: As described in GB/Z 18509, this is a basic EMC publication for use by product committees. As also stated in GB/Z 18509, the product committees are responsible for determining whether this immunity test standard should be applied or not, and if applied, they are responsible for determining the appropriate test levels and performance criteria. National Technical Committee on Electromagnetic Compatibility of Standardization Administration of China (SAC/TC 246) and its sub-committees are prepared to co-operate with product committees in the evaluation of the value of particular immunity tests for their products.
This part deals with immunity tests related to the protection against RF electromagnetic fields from any source.
Particular considerations are devoted to the protection against radio-frequency emissions from digital radiotelephones and other RF emitting devices.
Note 2: Test methods are defined in this part for evaluating the effect that electromagnetic radiation has on the equipment concerned. The simulation and measurement of electromagnetic radiation is not adequately exact for quantitative determination of effects. The test methods defined are structured for the primary objective of establishing adequate repeatability of results at various test facilities for qualitative analysis of effects.
This part is an independent test method. Other test methods may not be used as substitutes for claiming compliance with this part.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60050(161) International Electrotechnical Vocabulary (IEV) — Chapter 161: Electromagnetic Compatibility
IEC 61000-4-6 Electromagnetic Compatibility (EMC) — Part 4-6: Testing And Measurement Techniques — Immunity To Conducted Disturbances, Induced By Radio-frequency Fields
3 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
3.1
amplitude modulation
process by which the amplitude of a carrier wave is varied following a specified law
3.2
anechoic chamber
shielded enclosure which is lined with radio-frequency absorbers to reduce reflections from the internal surfaces
3.2.1
fully anechoic chamber
shielded enclosure whose internal surfaces are totally lined with anechoic material
3.2.2
semi-anechoic chamber
shielded enclosure where all internal surfaces are covered with anechoic material with the exception of the floor, which shall be reflective (ground plane)
3.2.3
modified semi-anechoic chamber
semi-anechoic chamber which has additional absorbers installed on the ground plane
3.3
antenna
transducer which either emits radio-frequency power into space from a signal source or intercepts an arriving electromagnetic field, converting it into an electrical signal
3.4
balun
device for transforming an unbalanced voltage to a balanced voltage or vice versa
[IEV 60050(161)]
3.5
continuous waves (CW)
electromagnetic waves, the successive oscillations of which are identical under steady-state conditions, which can be interrupted or modulated to convey information
3.6
electromagnetic (EM) wave
radiant energy produced by the oscillation of an electric charge characterized by oscillation of the electric and magnetic fields
3.7
far field
region where the power flux density from an antenna approximately obeys an inverse square law of the distance.
For a dipole this corresponds to distances greater than λ/2π, where λ is the wavelength of the radiation
3.8
field strength
Field strength (namely electric field strength) is the ratio of the electrostatic force to the electric charge at a point in the electric field, which is used to indicate the strength and direction of the electric field.
The term "field strength" is applied only to measurements made in the far field. The measurement may be of either the electric or the magnetic component of the field and may be expressed as V/m, A/m or W/m2; any one of these may be converted into the others.
For measurements made in the near field, the term "electric field strength" or "magnetic field strength" is used according to whether the resultant electric or magnetic field, respectively, is measured. In this field region, the relationship between the electric and magnetic field strength and distance is complex and difficult to predict, being dependent on the specific configuration involved. Inasmuch as it is not generally feasible to determine the time and space phase relationship of the various components of the complex field, the power flux density of the field is similarly indeterminate.
3.9
frequency band
continuous range of frequencies extending between two limits
3.10
Ec
field strength applied for calibration
3.11
Et
carrier field strength applied for testing
3.12
full illumination
test method in which the EUT face being tested fits completely within the UFA (Uniform Field Area, see the test methods covered in 3.27).
This test method may be applied for all test frequencies
3.13
human body-mounted equipment
equipment which is intended for use when attached to or held in close proximity to the human body.
This term includes hand-held devices which are carried by people while in operation (e.g. pocket devices) as well as electronic aid devices and implants
3.14
independent windows method
test method (using 0.5 m × 0.5 m UFA) in which the EUT face being tested does not fit completely within the UFA.
This test method may be applied for test frequencies greater than 1 GHz
3.15
induction field
predominant electric and/or magnetic field existing at a distance d < λ/2π, where λ is the wavelength, and the physical dimensions of the source are much smaller than distance d
3.16
intentional RF emitting device
device which radiates (transmits) an electromagnetic field intentionally. Examples include digital mobile telephones and other radio devices
3.17
isotropic
having properties of equal values in all directions
3.18
maximum RMS value
highest short-term RMS value of a modulated RF signal during an observation time of one modulation period.
The short-term RMS is evaluated over a single carrier cycle. For example, in Figure 1 b), the maximum RMS voltage is:
(1)
3.19
non-constant envelope modulation
RF modulation schemes in which the amplitude of the carrier wave varies slowly in time compared with the period of the carrier itself. Examples include conventional amplitude modulation and TDMA
3.20
Pc
forward power needed to establish the calibration field strength
3.21
partial illumination
test method (using a minimum sized UFA of 1.5 × 1.5 m) in which the EUT face being tested does not fit completely within the UFA.
This test method may be applied for all test frequencies.
3.22
polarization
orientation of the electric field vector of a radiated field
3.23
shielded enclosure
screened or solid metal housing designed expressly for the purpose of isolating the internal from the external electromagnetic environment. The purpose is to prevent outside ambient electromagnetic fields from causing performance degradation and to prevent emission from causing interference to outside activities
3.24
sweep
continuous or incremental traverse over a range of frequencies
3.25
TDMA (time division multiple access)
time multiplexing modulation scheme which places several communication channels on the same carrier wave at an allocated frequency. Each channel is assigned a time slot during which, if the channel is active, the information is transmitted as a pulse of RF power. If the channel is not active no pulse is transmitted, thus the carrier envelope is not constant. During the pulse, the amplitude is constant and the RF carrier is frequency- or phase-modulated
3.26
transceiver
combination of radio transmitting and receiving equipment in a common housing
3.27
uniform field area (UFA)
hypothetical vertical plane of the field calibration in which variations are acceptably small.
The purpose of field calibration is to ensure the validity of the test result. See 6.2
4 General
Most electronic equipment is, in some manner, affected by electromagnetic radiation. This radiation is frequently generated by such general purpose sources as the small hand-held radio transceivers that are used by operating, maintenance and security personnel, fixed-station radio and television transmitters, vehicle radio transmitters, and various industrial electromagnetic sources.
In recent years there has been a significant increase in the use of radio telephones and other RF emitting devices operating at frequencies between 0.8 GHz and 6 GHz. Many of these services use modulation techniques with a non-constant envelope (e.g. TDMA). See 5.2.
In addition to electromagnetic energy deliberately generated, there is also radiation caused by devices such as welders, thyristors, fluorescent lights, switches operating inductive loads, etc. For the most part, this interference manifests itself as conducted electrical interference and, as such, is dealt with in other parts of the IEC 61000-4 standard series. Methods employed to prevent effects from electromagnetic fields will normally also reduce the effects from these sources.
The electromagnetic environment is determined by the strength of the electromagnetic field. The field strength is not easily measured without sophisticated instrumentation nor is it easily calculated by classical equations and formulas because of the effect of surrounding structures or the proximity of other equipment that will distort and/or reflect the electromagnetic waves.
5 Test Levels
The test levels are given in Table 1.
Table 1 Test Levels Related to General Purpose, Digital Radio Telephones and Other RF Emitting Devices
Level Test field strength (V/m)
1 1
2 3
3 10
4 30
X Special
X is an open test level and the associated field strength may be any value. This level may be given in the product standard.
This part does not suggest that a single test level is applicable over the entire frequency range. Product committees shall select the appropriate test level for each frequency range needing to be tested as well as the frequency ranges. See Annex E for a guidance for product committees on the selection of test levels.
The test field strength column gives values of the unmodulated carrier signal. For testing of equipment, this carrier signal is 80% amplitude modulated with a 1 kHz sine wave to simulate actual threats (see Figure 1). Details of how the test is performed are given in Clause 8.
5.1 Test Levels Related to General Purposes
The tests are normally performed without gaps in the frequency range 80 MHz to 1000 MHz.
Note 1: Product committees may decide to choose a lower or higher transition frequency than 80 MHz between IEC 61000-4-3 and IEC 61000-4-6 (see Annex G).
Note 2: Product committees may select alternative modulation schemes for equipment under test.
Note 3: IEC 61000-4-6 also defines test methods for establishing the immunity of electrical and electronic equipment against radiated electromagnetic energy. It covers frequencies below 80 MHz.
5.2 Test Levels Related to the Protection Against RF Emissions from Digital Radio Telephones and Other RF Emitting Devices
The tests are normally performed in the frequency ranges 800 MHz to 960 MHz and 1.4 GHz to 6 GHz.
The frequencies or frequency bands to be selected for the test are limited to those where mobile radio telephones and other intentional RF emitting devices actually operate. It is not intended that the test needs to be applied continuously over the entire frequency range from 1.4 GHz to 6 GHz. For those frequency bands used by mobile radio telephones and other intentional RF emitting devices, specific test levels may be applied in the corresponding frequency range of operation.
Also if the product is intended to conform only to the requirements of particular countries, the measurement range 1.4 GHz to 6 GHz may be reduced to cover just the specific frequency bands allocated to digital mobile telephones and other intentional RF emitting devices in those countries. In this situation, the decision to test over reduced frequency ranges shall be documented in the test report.
Note 1: Annex A contains an explanation regarding the decision to use sine wave modulation for tests related to protection against RF emissions from digital radio telephones and other intentional RF emitting devices.
Note 2: Annex E contains guidance with regard to selecting test levels.
Note 3: The measurement ranges for Table 2 are the frequency bands generally allocated to digital radio telephones (Annex G contains the list of frequencies known to be allocated to specific digital radio telephones at the time of publication).
Note 4: The primary threat above 800 MHz is from radio telephone systems and other intentional RF emitting devices with power levels similar to that of radio telephones. Other systems operating in this frequency range, e.g. radio LANs operating at 2.4 GHz or higher frequencies, are generally very low power (typically lower than 100 mW), so they are much less likely to present significant problems.
Foreword II
1 Scope
2 Normative References
3 Terms and Definitions
4 General
5 Test Levels
5.1 Test Levels Related to General Purposes
5.2 Test Levels Related to the Protection Against RF Emissions from Digital Radio Telephones and Other RF Emitting Devices
6 Test Equipment
6.1 Description of the Test Facility
6.2 Calibration of Field
7 Test Setup
7.1 Arrangement of Table-top Equipment
7.2 Arrangement of Floor-standing Equipment
7.3 Arrangement of Wiring
7.4 Arrangement of Human Body-mounted Equipment
8 Test Procedure
8.1 Laboratory Reference Conditions
8.2 Execution of the Test
9 Evaluation of Test Results
10 Test Report
Annex A (Informative) Rationale for the Choice of Modulation for Tests Related to the Protection against RF Emissions from Digital Radio Telephones
Annex B (Informative) Field Generating Antennas
Annex C (Informative) Use of Anechoic Chambers
Annex D (Informative) Amplifier Non-linearity and Example for the Calibration Procedure According to
Annex E (Informative) Guidance for Product Committees on the Selection of Test Levels
Annex F (Informative) Selection of Test Methods
Annex G (Informative) Description of the Environment
Annex H (Normative) Alternative Illumination Method for Frequencies Above 1 GHz (“Independent Windows Method”)
Annex I (Informative) Calibration Method for E-field Probes
Annex J (Informative) Measurement Uncertainty due to Test Instrumentation
电磁兼容试验和测量技术
射频电磁场辐射抗扰度试验
1范围
GB/T 17626的本部分适用于电气、电子设备的电磁场辐射抗扰度要求,规定了试验等级和必要的 试验程序。
本部分的目的是建立电气、电子设备受到射频电磁场辐射时的抗扰度评定依据。在本部分中给出 的试验方法描述了评估设备或系统抵抗一定环境的抗扰度的符合性方法。
注1：如GB/Z 18509所述.本部分是供冇关专业标准化技术委员会使用的基础EMC出版物。同时在GB/Z 18509 中规定,有美专业标准化技术委员会负责确定此抗扰度测试标准是否适用.如适用，他们右责任确定适合的试 验等级及性能判据。全国电磁兼容标准化技术委员会(S/\C/TC 246＞及其分会与右美专业标准化技术委员会 合作.以评估对其产品的特定抗扰度试验的试验等级及性能判据。
本部分适用丁 •防止所有发射源的射频电磁场的抗扰度试羚。
特别关注对防止数字无线电话和其他射频发射装置的射频辐射。
注2：本部分规定了 if EUT在电磁辐射状况卜受影响程度的试验方法。电磁辐射的模拟和测政对定拭确定这种 影响程度是不够准确的。所定义试缱方法的宗旨是为定性分析建立一个对各种EUT均可获得度好重复性洲I 员结果的方法。
本部分是一个独立的试验方法。不可使用其他试验方法替代来声称符合本部分。
2规范性引用文件
下列文件对于本文件的应用是必不町少的。凡是注日期的引用文件，仅注日期的版本适用于本文 件。凡是不注日期的引用文件，其最新版本(包括所有的修改单)适用于本文件。
IEC 60050(161) 国际电工词汇(IEV) 第 161 章：电磁兼容 International Electrotechnical Vo¬cabulary (IEV)—Chapter 161: Electromagnetic compatibility]
IEC 61000-4-6电磁兼容 第4-6部分 试验与测最技术-射頻场感应的传导干扰抗扰度[Elec¬tromagnetic compatibilitity ( EM(')一Part 4-6 : Testing and measurement techniques—Immunity to conducted di st ur bances. induced by radio frequency fields]
3术语和定义
下列术语和定义适用于本文件。
3. 1
调幅 amplitude modulation
载波幅度按给定规律变化的过程。
3.2
电波暗室 anechoic chamber
安装吸波材料用以降低内表面电波反射的屏蔽室。
3.2. 1
全电波暗室 fully anechoic chamber
内表而全部安装吸波材料的屏蔽室。
3.2.2
半电波暗室 scnii-ancchoic chamber
除地面安装反射接地平板外.其余内表面均安装吸波材料的屏蔽室。
3.2.3
可调式半电波暗室 modified semi-anechoic chamber
在地面反射接地平板上附加吸波材料的半电波暗室。
3.3
天线 antenna
-•种将信号源射频功率发射到空间或截获空间电磁场转变为电信号的转换器。
3.4
平衡•不平衡转换器balun
用来将不平衡电压与平衡电压相互转换的装置。
| IEC 60050(161)]
3.5
连续波(CW) continuous waves (CW)
在稳态条件下，完全相同的连续振荡的电磁波，可以通过中断或调制来传递信息•
3.6
电磁波 electromagnetic (EM) wave
由电荷振荡所产生的辐射能员.其特征是电磁场的振荡。
3.7
远场 far field
由天线发射的功率通量密度近似地与距离的平方呈反比关系的场域。
对于偶极子天线来说，相当丁大于"臨的距离的场域，A为辐射波长。
3.8
场强 field strength
场强即电场强度.是放入电场中某点的电荷所受静电力与它的电荷量的比值.用来表示电场的强弱 和方向的物理量。
••场强I”一词仅适用于远场测虽。测虽的可以是电场分星或磁场分垦,可用V/m.A/m或W/m2表 示.单位间可相互换算。
近场测址时•术语“电场强度”或“磁场强度"的使用取决于是否分别测量电场或磁场的分量。近场 中.电场强度和磁场强度与距离的关系是复杂的.并旦很难预测.它涉及场中特定的布置。因此.一般不 可能确定复合场的分虽在时间和空间相位上的变化，功率通虽密度同样也是不确定的。
3.9
频带 frequency band
两个限定的频率点之间频率延伸的连续区间。
3. 10
校准用场强。
3. 11
&
测试用的载波场强。
3. 12
完全照射 full illumination
EUT的被测试面完全被UFA（均匀场域.见3. 27所覆盖的试验方法）。
该试验方法町适用于所冇试验频率。
3. 13
人身携带设备 human hody-mounted equipment
用于人身附属或近距离携带的设备。
包括人们携带的正在运行中的手持式设备（例如袖珍设备）和电子辅助装置以及植入式装置。
3. 14
独立窗口法 independent windows method
当EUT的被测试面不能完全被UFA所覆盖时所采用的试验方法（使用0. 5 mXO. 5 m的UFA）。 该试验方法可适用于1 GHz以上的试验频率。
3. 15
感应场 induced field
电场和/或磁场的主要能量存在于距离J
