1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD AEROSPACE SERIES BS G 257
2、 : Part 1 : 1998 ICS 33.100; 49.060 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Design of electromagnetic hazard protection of civil aircraft Part 1. Guide to theory and threatsBS G 257 : Part 1 : 1998 This British Standard, having been prepared under the direction of the
3、Engineering Sector Board, was published under the authority of the Standards Board and comes into effect on 15 March 1998 BSI 1998 The following BSI references relate to the work on this standard: Committee reference ACE/66 Draft for comment 94/714808 DC ISBN 0 580 28984 2 Amendments issued since pu
4、blication Amd. No. Date Text affected Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee ACE/66, Aerospace electromagnetic compatibility of aircraft, upon which the following bodies were represented: ERA Technology Ltd. Fede
5、ration of the Electronics Industry Civil Aviation Authority (Airworthiness Division) Ministry of Defence Society of British Aerospace CompaniesBS G 257 : Part 1 : 1998 BSI 1998 i Contents Page Committees responsible Inside front cover Foreword iii 1 Scope 1 2 Informative references 1 3 Definition 1
6、4 Background 1 5 Basic principles of EMH protection design 2 6 EM hazards 28 Table 1 Current component 36 Figures 1 Magnetic field at a point distant from a current element 3 2 Interaction of magnetic field with conducting loop 3 3 The summation of magnetic field around a closed loop 4 4 Concept of
7、displacement current 5 5 A wave in space 6 6 A wave f (x, t) in time 6 7 A wave f (x, t) in space 7 8 A sinusoidally periodic wave 8 9 Exponential decay of signal with position 8 10 A standing wave 9 11 An EM wave propagating in the x-direction 10 12 The components of an elliptically polarized wave
8、10 13 A short dipole in cartesian co-ordinates 11 14 Antenna types 13 15 Wave propagation in three media 15 16 Plane wave incident on a cylinder 16 17 The current distribution on a cylindrical body 16 18 Current crowding at corners 17 19 Shielding effectiveness of spherical shells 18 20 Typical shie
9、ld imperfections 19 21 Penetration through an aperture 20 22 Penetration through a low conductivity panel 21 23 The mechanism of shielding reduction by a penetrating conductor 21 24 A short circuit observed down a transmission line 22 25 An open circuit observed down a transmission line 23 26 The de
10、velopment of a dipole from an open-circuit transmission line 23 27 Current and field distribution in coaxial cable 24 28 H-field coupling and common-mode interference 26 29 Long-tailed pair with common-mode current rejection 27 30 Filter installation 28 31 Typical high-frequency equivalent circuit o
11、f a motor 29 32 Transformation of pulse into the frequency domain 31 33 Possible intersystem coupling paths 32 34 Model of a severe negative lightning flash current waveform 33BS G 257 : Part 1 : 1998 ii BSI 1998 Page 35 Model of a moderate positive lighting flash current waveform 33 36 Intra- and i
12、nter-cloud, multiple burst current waveforms 34 37 Pre-strike electric field voltage waveforms 38 38 Current component A 39 39 Current component A h 40 40 Current component B 41 41 Current component C 42 42 Current component D 43 43 Multiple stroke 44 44 External idealized current component H 45 45
13、Double exponential current waveform 1 46 46 Double exponential derivative voltage waveform 2 46 47 Damped sinusoidal voltage/current waveform 3 47 48 Double exponential voltage waveform 4 47 49 Double exponential current waveform 5 48 List of references Inside back coverBS G 257 : Part 1 : 1998 BSI
14、1998 iii Foreword BS G 257 : Parts 1 to 3, which have been prepared by Technical Committee ACE/66, constitute a design guide providing information to engineers involved at all levels in the hardening of civil aircraft and their systems against electromagnetic hazards (EMHs). The design guide will be
15、 published in three Parts as follows: Part 1. Guide to electromagnetic theory and the electromagnetic threats posed to aircraft Part 2. Guide to protection Part 3. Guide to clearance and testing This Part of BS G 257 provides background material on electromagnetic (EM) theory and the threats posed b
16、y EMH to aircraft and their systems. A detailed account of EM theory is not given, but enough of an insight is provided in order to understand the threats posed to the aircraft system, resulting effects and avoidance techniques described. This material is covered in the form of a qualitative descrip
17、tion of electric, magnetic and EM fields, and the ways in which these interact with conducting bodies. In addition, the section contains discussion of the types and classification of signals which can occur, and the way in which they relate to each other. In particular, it discusses the concepts of
18、broadband and narrowband signals, balanced and unbalanced transmission, common- and differential-mode signal configuration, and the basic concepts of bandwidth and amplitude limitation. The following Parts focus on the description of protection techniques and clearance and testing. Finally, this Par
19、t discusses all the threats and their interactions with the aircraft including continuous wave radio frequency (RF) fields, lightning and static electricity. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front
20、 cover, an inside front cover, pages i to iv, pages 1 to 48, an inside back cover and a back cover.iv blank BSI 1998 1 BS G 257 : Part 1 : 1998 1 Scope This Part of BS G 257 has been written to assist engineers working at all levels within companies involved in the aircraft industry. The guide does
21、not contain mandatory requirements, but rather advice to assist in the solution of design problems. In order to meet the EMH protection needs of the customers specification, it is strongly recommended that engineers consider the features discussed and use the suggestions made or provide an alternati
22、ve solution for any problem. This guide does not discuss the following: a) the protection of the airframe against the structurally damaging, direct effects of lightning; b) the design of communication systems in order to produce interference-free operation, since these aspects of RF systems design a
23、re covered in adequate detail in other documents; however, the problems of interaction between radio receivers and transmitters remain an important class of electromagnetic compatibility (EMC) problem. 2 Informative references This Part of BS G 257 refers to other publications that provide informati
24、on or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions. 3 Definition For the purposes of this Part of BS G 257, the following definition applies. electromagnetic compatibili
25、ty (EMC) Situation in which an assembly of equipments or systems co-exist without mutual interference or damage and/or upset by the EM environment in which they are immersed. 4 Background 4.1 The design of EMH protection for an electronic system should aim to ensure that the EM environment in which
26、the system is immersed does not affect the normal operation of the system. In addition, the design should reduce the emissions of conducted or radiated EM energy from the system to a level which will not upset or damage the normal operation of other systems. Thus, the overall target of EMH protectio
27、n should be to achieve EMC. 4.2 It was not until the early 1970s that aircraft made extensive use of electronic systems and thus EMH protection became a concern. In particular, systems affecting flight safety had become dependent on the reliable operation of an electronic system (e.g. fly-by-wire sy
28、stems). Such widespread use of electronics necessitated the deliberate design of systems for EMC because the probability of interference had increased enormously, and the difficulty and expense of curing the likely problems was prohibitive. In addition, electronic technology had developed towards ve
29、ry compact, low-power, solid-state components utilizing low-level signalling and thus the susceptibility to electromagnetic interference (EMI) was increased. 4.3 From the early 1980s onwards, the extensive use of carbon fibre composite (CFC) in the airframe has significantly decreased the protection
30、 provided by the airframe to the electronic system from external EM threats of frequency content below 100 MHz. This has produced further design needs: the electrical design of the airframe should be considered in order to provide the system with sufficient protection against the external EM environ
31、ment and there should be minimum intersystem EM coupling. 4.4 Ensuring sufficient protection against EMHs for the complete aircraft has become a deliberate and complex design activity which should include the electrical design of the airframe, the system installation and the design of the electronic
32、 equipment. A balanced protection strategy should ensure that the overall EMH protection needs of the aircraft are met within weight, volume and cost targets. 4.5 Achieving the EMC of aircraft systems is fraught with a number of problems, which include the high levels of EM threats, particularly the
33、 induced effects of lightning in the airframe, the proximity of the onboard transmitters (particularly the high-frequency (HF) transmitter) and the high cross-coupling between systems as a result of the unavoidable proximity of systems. These EM threats have to be countered within the usual aerospac
34、e constraints of weight and volume. In addition, due regard should be taken of the extreme climatic and vibrational environment. 4.6 It is essential that designing for protection against EMHs should be considered from the very earliest stages of the airframe and system installation design. In order
35、to achieve some control of the EMH protection design strategy throughout the aircraft design, development and production, a management strategy should be laid down at the very beginning. The document describing this strategy is often called the EMC control plan. The control plan should highlight a v
36、isible design process for the design of the airframe and a complementary system installation design, which will result in only acceptable interference voltages and currents arriving at the equipment connectors. The procurement of equipment with the required protection against EMH should be part of t
37、his plan and should be controlled via suitable specifications.2 BSI 1998 BS G 257 : Part 1 : 1998 4.7 The safety of the aircraft is of paramount importance and those aspects of protection against EMH that could affect safety should rank equal with all the other design issues. The required performanc
38、e of the aircraft will inevitably take precedence over the EMH considerations, providing the EMH problem does not seriously affect that performance. It should be noted that consideration of the EMH protection design from the earliest concepts, and in conjunction with other aspects of design, is the
39、only way to achieve optimum solutions in terms of weight, volume and cost. 5 Basic principles of EMH protection design NOTE. In 5.1 to 5.8, consideration is given to some of the more pertinent points of basic electromagnetics prior to discussing the subjects of intentional and unintentional EM radia
40、tion and the interaction of EM waves with conducting bodies. 5.1 EM theory The behaviour of EM fields is predictable and in broad terms, Maxwells equations and the basic laws of force field and flow, which will be described later, encompass the complete description of their behaviour. 5.2 The electr
41、ic field 5.2.1 The mechanical force between two charges q 1 and q 2 is proportional to the product of the charges and inversely proportional to the square of the distance between them, and acts along a line joining them. The force between charges or charged bodies leads to the concept of an electric
42、 field. This field produces a force on charges placed in it. If the charges are of the same polarity then the force is one of repulsion. Conversely, if the polarity of the charges is different then attraction occurs. Forces of this nature are encountered in many situations, such as the deflection of
43、 the electron beam by the field between the electrode plates in a cathode-ray tube, or the initial movement of free charges in a conductor on application of an electric field. 5.2.2 The magnitude of the electric field intensity E (in V/m) at a distance r (in m) from a charge q (in C) is given by Cou
44、lombs law: E = (1) q 4pe o e r r 2 where e o is the permittivity of free space (8.853 10 212 F/m); e r is the relative permittivity of the medium in which the charges are placed (dimensionless). The product e o e r (in F/m) is known as the permittivity e of the medium. The electric field is thought
45、of as having a flow or electric flux density (sometimes called displacement) associated with it, in a similar way to voltage (potential difference) producing a flow of current. In this case, the electric field E (in V/m) and electric flux density D (in C/m 2 ) at a point are related by: D = eE (2) w
46、here e is the permittivity of the medium (in F/m); D is the displacement (in C/m 2 ); E is the field strength (in V/m). 5.3 The magnetic field 5.3.1 A magnetic field may be described in a similar way to an electric field (see 5.2). However, unlike point charges, magnetic poles are not thought to exi
47、st as single poles in isolation; they always occur in pairs called magnetic dipoles. The manifestation of a magnetic field is therefore the rotational force or moment experienced by a magnetic dipole (electric fields can be treated analogously with regard to electric dipoles). The source of magnetic
48、 fields is electric current (at an atomic level in permanent magnets), and the relationship between the flux density of magnetic field B (in Wb/m 2 or T) at a point p situated a distance r (in m) from a short, infinitely thin conductor of length dl (in m) carrying a current I (in A) (see figure 1) i
49、s given by the Biot-Savart law: B = (3) m o m r I dl sinu 4pr 2 where u is the vector angle (in degrees); m o is the permeability of free space (4p3 10 27 H/m); m r is the relative permeability of the medium (dimensionless). The product m o m r (in H/m) is known as the permeability m of the medium. In the case of this relationship, the field is given in terms of the flux density, i.e. flow per unit area. BSI 1998 3 BS G 257 : Part 1 : 1998 q p dl I r Figure 1. Magnetic field at a point distant from a current element Figure 2. Interaction of magnetic field with conducting loop 5.
