电磁屏蔽基本原理介绍

pwm · 发表于 2007-10-1 22:01:12

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在电子设备及电子产品中，电磁干扰（Electromagnetic Interference）能量通过传导性耦合和辐射性耦合来进行传输。为满足电磁兼容性要求，对传导性耦合需采用滤波技术，即采用EMI滤波器件加以抑制；对辐射性耦合则需采用屏蔽技术加以抑制。在当前电磁频谱日趋密集、单位体积内电磁功率密度急剧增加、高低电平器件或设备大量混合使用等因素而导致设备及系统电磁环境日益恶化的情况下，其重要性就显得更为突出。 屏蔽是通过由金属制成的壳、盒、板等屏蔽体，将电磁波局限于某一区域内的一种方法。由于辐射源分为近区的电场源、磁场源和远区的平面波，因此屏蔽体的屏蔽性能依据辐射源的不同，在材料选择、结构形状和对孔缝泄漏控制等方面都有所不同。在设计中要达到所需的屏蔽性能，则需首先确定辐射源，明确频率范围，再根据各个频段的典型泄漏结构，确定控制要素，进而选择恰当的屏蔽材料，设计屏蔽壳体。 <img height="26" src="http://www.emckairong.com/images/dianci1.jpg" width="100" v:shapes="_x0000_s1026" /> <div style="mso-element: dropcap-dropped; mso-element-frame-height: 33.05pt; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2"><table height="44" cellspacing="0" cellpadding="0" align="left" hspace="0" vspace="0"><tbody><tr><td style="

ADDING-RIGHT: 0cm; PADDING-LEFT: 0cm; PADDING-BOTTOM: 0cm; PADDING-TOP: 0cm" valign="top" align="left" height="44"> <p class="MsoNormal" style="VERTICAL-ALIGN: baseline; LAYOUT-GRID-MODE: char; LINE-HEIGHT: 33.05pt; mso-element: dropcap-dropped; mso-element-frame-height: 33.05pt; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2; mso-line-height-rule: exactly">屏  </td></tr></tbody></table></div>蔽体对辐射干扰的抑制能力用屏蔽效能SE（Shielding Effectiveness）来衡量，屏蔽效能的定义:没有屏蔽体时，从<a href="http://www.emchome.net/">辐射干扰源</a>传输到空间某一点(P)的场强<shape id="_x0000_i1025" style="WIDTH: 12pt; HEIGHT: 14.25pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image003.wmz" /></shape /><img height="19" src="http://www.emckairong.com/images/dianci2.gif" width="16" v:shapes="_x0000_i1025" /> 1（<shape id="_x0000_i1026" style="WIDTH: 14.25pt; HEIGHT: 15pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image005.wmz" /></shape /><img height="20" src="http://www.emckairong.com/images/dianci3.gif" width="19" v:shapes="_x0000_i1026" /> 1）和加入屏蔽体后，辐射干扰源传输到空间同一点(P)的场强<shape id="_x0000_i1027" style="WIDTH: 12pt; HEIGHT: 15pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image007.wmz" /></shape /><img height="20" src="http://www.emckairong.com/images/dianci4.gif" width="16" v:shapes="_x0000_i1027" /> 2（<shape id="_x0000_i1028" style="WIDTH: 14.25pt; HEIGHT: 15pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image005.wmz" /></shape /><img height="20" src="http://www.emckairong.com/images/dianci5.gif" width="19" v:shapes="_x0000_i1028" /> 2）之比，用dB（分贝）表示。<img height="142" src="http://www.emckairong.com/images/dianci7.gif" width="216" v:shapes="_x0000_s1028 _x0000_s1029 _x0000_s1030 _x0000_s1031 _x0000_s1032 _x0000_s1033 _x0000_s1034 _x0000_s1035 _x0000_s1036 _x0000_s1037 _x0000_s1038" />   <img height="144" src="http://www.emckairong.com/images/dianci6.gif" width="357" v:shapes="_x0000_s1039 _x0000_s1040 _x0000_s1041 _x0000_s1042 _x0000_s1043 _x0000_s1044 _x0000_s1045 _x0000_s1046 _x0000_s1047 _x0000_s1048 _x0000_s1049 _x0000_s1050 _x0000_s1051 _x0000_s1052 _x0000_s1053 _x0000_s1054 _x0000_s1055" /> 图1  屏蔽效能定义示意图 屏蔽效能表达式为 <img height="56" src="http://www.emckairong.com/images/dianci8.gif" width="119" v:shapes="_x0000_i1029" />  (dB)   或   <shape id="_x0000_i1030" style="WIDTH: 90.75pt; HEIGHT: 42pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image016.wmz" /></shape /><img height="56" src="http://www.emckairong.com/images/dianci9.gif" width="121" v:shapes="_x0000_i1030" /> （dB） <shape id="_x0000_s1027" style="MARGIN-TOP: 8.2pt; Z-INDEX: 2; LEFT: 0px; MARGIN-LEFT: 188.45pt; WIDTH: 82.5pt; POSITION: absolute; HEIGHT: 19.85pt; TEXT-ALIGN: left; mso-wrap-edited: f" type="#_x0000_t75" wrapcoords="-196 0 -196 20769 21600 20769 21600 0 -196 0" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image018.png" croptop="-941f" cropbottom="5957f" /><wrap type="tight" /></shape /><img height="26" hspace="12" src="http://www.emckairong.com/images/dianci10.jpg" width="110" v:shapes="_x0000_s1027" />   工程中，实际的辐射干扰源大致分为两类：类似于对称振子天线的非闭合载流导线辐射源和类似于变压器绕组的闭合载流导线辐射源。由于电偶极子和磁偶极子是上述两类源的最基本形式，实际的 辐射源在空间某点产生的场，均可由若干个基本源的场叠加而成(图2)。因此通过对<a href="http://www.emchome.net/">电偶极子</a>和<a href="http://www.emchome.net/">磁偶极子</a>所产生的场进行分析，就可得出实际辐射源的<a href="http://www.emchome.net/">远近场</a>及<a href="http://www.emchome.net/">波阻抗</a>和远、<a href="http://www.emchome.net/">近场</a>的场特性，从而为屏蔽 分类提供良好的理论依据。      <img height="171" src="http://www.emckairong.com/images/dianci11.gif" width="404" v:shapes="_x0000_s1026 _x0000_s1027 _x0000_s1028 _x0000_s1029 _x0000_s1030 _x0000_s1031 _x0000_s1032 _x0000_s1033 _x0000_s1034 _x0000_s1035 _x0000_s1036 _x0000_s1037 _x0000_s1038 _x0000_s1039 _x0000_s1040 _x0000_s1041 _x0000_s1042 _x0000_s1043 _x0000_s1044 _x0000_s1045 _x0000_s1046 _x0000_s1047 _x0000_s1048 _x0000_s1049 _x0000_s1050 _x0000_s1051 _x0000_s1052 _x0000_s1053 _x0000_s1054 _x0000_s1055 _x0000_s1056 _x0000_s1057 _x0000_s1058 _x0000_s1059 _x0000_s1060 _x0000_s1061 _x0000_s1062 _x0000_s1063 _x0000_s1064 _x0000_s1065 _x0000_s1066 _x0000_s1067 _x0000_s1068 _x0000_s1069 _x0000_s1070 _x0000_s1071 _x0000_s1072 _x0000_s1073 _x0000_s1074 _x0000_s1075 _x0000_s1076 _x0000_s1077 _x0000_s1078 _x0000_s1079 _x0000_s1080 _x0000_s1081 _x0000_s1082" />     图2  两类基本源在空间所产生的叠加场 <div style="mso-element: dropcap-dropped; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2"><table cellspacing="0" cellpadding="0" align="left" hspace="0" vspace="0"><tbody><tr><td style="

ADDING-RIGHT: 0cm; PADDING-LEFT: 0cm; PADDING-BOTTOM: 0cm; PADDING-TOP: 0cm" valign="top" align="left"><p class="MsoNormal" style="VERTICAL-ALIGN: baseline; LAYOUT-GRID-MODE: char; LINE-HEIGHT: 150%; mso-element: dropcap-dropped; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2">远  </td></tr></tbody></table></div>近场的划分是根据两类基本源的场随1/r（场点至源点的距离）的变化而确定的，<shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f" /> <stroke joinstyle="miter" /><formulas /><f eqn="if lineDrawn pixelLineWidth 0" /><f eqn="sum @0 1 0" /><f eqn="sum 0 0 @1" /><f eqn="prod @2 1 2" /><f eqn="prod @3 21600 pixelWidth" /><f eqn="prod @3 21600 pixelHeight" /><f eqn="sum @0 0 1" /><f eqn="prod @6 1 2" /><f eqn="prod @7 21600 pixelWidth" /><f eqn="sum @8 21600 0" /><f eqn="prod @7 21600 pixelHeight" /><f eqn="sum @10 21600 0" /></formulas /><path o:extrusionok="f" gradientshapeok="t" o:connecttype="rect" /><lock v:ext="edit" aspectratio="t" /></shapetype /><shape id="_x0000_i1025" style="WIDTH: 39.75pt; HEIGHT: 18pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image001.wmz" /></shape /><img height="24" src="http://www.emckairong.com/images/ianci1.gif" width="53" v:shapes="_x0000_i1025" /> 为远近场的分界点，两类源在远近场的场特征及传播特性均有所不同。 表1  两类源的场与传播特性 <div align="center"><table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellspacing="0" cellpadding="0" width="546" border="1"><tbody><tr style="HEIGHT: 19.9pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 19.9pt" width="132" rowspan="2">场源类型  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 19.9pt; mso-border-left-alt: solid windowtext .5pt" width="179" colspan="2">近场（<shape id="_x0000_i1026" style="WIDTH: 36pt; HEIGHT: 15.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image003.wmz" /></shape /><img height="21" src="http://www.emckairong.com/images/ianci2.gif" width="48" v:shapes="_x0000_i1026" /> ）  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 19.9pt; mso-border-left-alt: solid windowtext .5pt" width="187" colspan="2">远场(<shape id="_x0000_i1027" style="WIDTH: 36pt; HEIGHT: 15.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image005.wmz" /></shape /><img height="21" src="http://www.emckairong.com/images/ianci3.gif" width="48" v:shapes="_x0000_i1027" /> )  </td></tr><tr style="HEIGHT: 17.2pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 17.2pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="73">场特性  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 17.2pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="91">传播特性  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 17.2pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="76">场特性  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 17.2pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="96">传播特性  </td></tr><tr style="HEIGHT: 30.7pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 30.7pt; mso-border-top-alt: solid windowtext .5pt" width="132"><a href="http://www.emchome.net/">电偶极子</a>  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 30.7pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="73"><a href="http://www.emchome.net/">非平面波</a>  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 30.7pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="91">以<shape id="_x0000_i1028" style="WIDTH: 17.25pt; HEIGHT: 30.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image007.wmz" /></shape /><img height="41" src="http://www.emckairong.com/images/ianci4.gif" width="23" v:shapes="_x0000_i1028" /> 衰减  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 30.7pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="76"><a>平面波</a>  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 30.7pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="96">以<shape id="_x0000_i1029" style="WIDTH: 11.25pt; HEIGHT: 30.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image009.wmz" /></shape /><img height="41" src="http://www.emckairong.com/images/ianci5.gif" width="15" v:shapes="_x0000_i1029" /> 衰减  </td></tr><tr><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; mso-border-top-alt: solid windowtext .5pt" width="132"><a href="http://www.emchome.net/">磁偶极子</a>  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="73"><a>非平面波</a>  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="91">以<shape id="_x0000_i1030" style="WIDTH: 17.25pt; HEIGHT: 30.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image007.wmz" /></shape /><img height="41" src="http://www.emckairong.com/images/ianci6.gif" width="23" v:shapes="_x0000_i1030" /> 衰减  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="76"><a href="http://www.emchome.net/">平面波</a>  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="96">以<shape id="_x0000_i1031" style="WIDTH: 11.25pt; HEIGHT: 30.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image009.wmz" /></shape /><img height="41" src="http://www.emckairong.com/images/ianci5.gif" width="15" v:shapes="_x0000_i1029" />衰减  </td></tr></tbody></table></div><div style="mso-element: dropcap-dropped; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2"><table cellspacing="0" cellpadding="0" align="left" hspace="0" vspace="0"><tbody><tr><td style="

ADDING-RIGHT: 0cm; PADDING-LEFT: 0cm; PADDING-BOTTOM: 0cm; PADDING-TOP: 0cm" valign="top" align="left"><p class="MsoNormal" style="VERTICAL-ALIGN: baseline; LAYOUT-GRID-MODE: char; LINE-HEIGHT: 150%; mso-element: dropcap-dropped; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2">波  </td></tr></tbody></table></div>阻抗<shape id="_x0000_i1032" style="WIDTH: 21.75pt; HEIGHT: 20.25pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image013.wmz" /></shape /><img height="27" src="http://www.emckairong.com/images/dianc8.gif" width="29" v:shapes="_x0000_i1032" /> 为空间某点<a>电场强度</a>与<a>磁场强度</a>之比，场源不同、远近场不同，则波阻抗也有所不同，表2与图3分别用图表给出了<shape id="_x0000_i1033" style="WIDTH: 21.75pt; HEIGHT: 20.25pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image013.wmz" /></shape /><img height="27" src="http://www.emckairong.com/images/dianc9.gif" width="29" v:shapes="_x0000_i1033" /> 的波阻抗特性。 <p class="MsoNormal" style="LAYOUT-GRID-MODE: char; TEXT-INDENT: 0.95pt; LINE-HEIGHT: 150%; TEXT-ALIGN: center; mso-char-indent-count: .09; mso-char-indent-size: 10.55pt; tab-stops: right 415.6pt" align="center">表2  两类源的<a>波阻抗</a> <div align="center"><table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellspacing="0" cellpadding="0" border="1"><tbody><tr style="HEIGHT: 19.15pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 99pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 19.15pt" width="132" rowspan="2">场源类型  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 225pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 19.15pt; mso-border-left-alt: solid windowtext .5pt" width="300" colspan="2"><a>波阻抗</a><shape id="_x0000_i1034" style="WIDTH: 21.75pt; HEIGHT: 20.25pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image013.wmz" /></shape /><img height="27" src="http://www.emckairong.com/images/dianci10.gif" width="29" v:shapes="_x0000_i1034" /> （Ω）  </td></tr><tr style="HEIGHT: 15pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 117pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="156"><a>近场</a>（<shape id="_x0000_i1035" style="WIDTH: 36pt; HEIGHT: 15.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image003.wmz" /></shape /><img height="21" src="http://www.emckairong.com/images/dianc11.gif" width="48" v:shapes="_x0000_i1035" /> ）  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 108pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="144"><a>远场</a>（<shape id="_x0000_i1036" style="WIDTH: 36pt; HEIGHT: 15.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image018.wmz" /></shape /><img height="21" src="http://www.emckairong.com/images/dianc12.gif" width="48" v:shapes="_x0000_i1036" /> ）  </td></tr><tr style="HEIGHT: 32pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 99pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 32pt; mso-border-top-alt: solid windowtext .5pt" width="132"><a>电偶极子</a>  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 117pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 32pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="156">120π<shape id="_x0000_i1037" style="WIDTH: 23.25pt; HEIGHT: 30.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image020.wmz" /></shape /><img height="41" src="http://www.emckairong.com/images/dianc13.gif" width="31" v:shapes="_x0000_i1037" /> </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 108pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 32pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="144">120π  </td></tr><tr style="HEIGHT: 27.25pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 99pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 27.25pt; mso-border-top-alt: solid windowtext .5pt" width="132"><a>磁偶极子</a>  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 117pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 27.25pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="156">120π<shape id="_x0000_i1038" style="WIDTH: 23.25pt; HEIGHT: 30.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image022.wmz" /></shape /><img height="41" src="http://www.emckairong.com/images/dianc14.gif" width="31" v:shapes="_x0000_i1038" /> </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 108pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 27.25pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="144">120π  </td></tr></tbody></table></div><img height="280" src="http://www.emckairong.com/images/dianc15.gif" width="438" v:shapes="_x0000_s1027 _x0000_s1028 _x0000_s1029 _x0000_s1030 _x0000_s1031 _x0000_s1032 _x0000_s1033 _x0000_s1034 _x0000_s1035 _x0000_s1036 _x0000_s1037 _x0000_s1038 _x0000_s1039 _x0000_s1040" />能量密度包括电场分量能量密度和磁场分量能量密度，通过对由同一场源所产生的电场、磁场分量的能量密度进行比较，可以确定场源在不同区域内何种分量占主要成份，以便确定具体的屏蔽分类。能量密度的表达式由下列公式给出: 电场分量能量密度   <shape id="_x0000_i1025" style="WIDTH: 111pt; HEIGHT: 30.75pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image006.wmz" /></shape /><img height="41" src="http://www.emckairong.com/images/dianc16.gif" width="148" v:shapes="_x0000_i1025" /> 磁场分量能量密度   <shape id="_x0000_i1026" style="WIDTH: 117pt; HEIGHT: 30.75pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image008.wmz" /></shape /><img height="41" src="http://www.emckairong.com/images/dianc17.gif" width="156" v:shapes="_x0000_i1026" /> 场源总能量密度     <shape id="_x0000_i1027" style="WIDTH: 69.75pt; HEIGHT: 17.25pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image010.wmz" /></shape /><img height="23" src="http://www.emckairong.com/images/dianc18.gif" width="93" v:shapes="_x0000_i1027" /> 表3  两类源的能量密度 <div align="center"><table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; MARGIN-LEFT: 59.4pt; BORDER-LEFT: medium none; WIDTH: 333pt; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellspacing="0" cellpadding="0" width="444" border="1"><tbody><tr style="HEIGHT: 22.35pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 63pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.35pt" width="84" rowspan="2">场源类型  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 270pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.35pt; mso-border-left-alt: solid windowtext .5pt" width="360" colspan="2">能量密度比较  </td></tr><tr style="HEIGHT: 15pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 135pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="180">近场（<shape id="_x0000_i1028" style="WIDTH: 36pt; HEIGHT: 15.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image012.wmz" /></shape /><img height="21" src="http://www.emckairong.com/images/dianc19.gif" width="48" v:shapes="_x0000_i1028" /> ）  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 135pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="180">远场（<shape id="_x0000_i1029" style="WIDTH: 36pt; HEIGHT: 15.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image014.wmz" /></shape /><img height="21" src="http://www.emckairong.com/images/dianc20.gif" width="48" v:shapes="_x0000_i1029" /> ）  </td></tr><tr style="HEIGHT: 21.75pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 63pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 21.75pt; mso-border-top-alt: solid windowtext .5pt" width="84">电偶极子  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 135pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 21.75pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="180"><shape id="_x0000_i1030" style="WIDTH: 54pt; HEIGHT: 17.25pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image016.wmz" /></shape /><img height="23" src="http://www.emckairong.com/images/dianc21.gif" width="72" v:shapes="_x0000_i1030" /> </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 135pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 21.75pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="180"><shape id="_x0000_i1031" style="WIDTH: 48pt; HEIGHT: 17.25pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image018.wmz" /></shape /><img height="23" src="http://www.emckairong.com/images/dianc22.gif" width="64" v:shapes="_x0000_i1031" /> </td></tr><tr style="HEIGHT: 21.75pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 63pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 21.75pt; mso-border-top-alt: solid windowtext .5pt" width="84">磁偶极子  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 135pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 21.75pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="180"><shape id="_x0000_i1032" style="WIDTH: 54pt; HEIGHT: 17.25pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image020.wmz" /></shape /><img height="23" src="http://www.emckairong.com/images/dianc23.gif" width="72" v:shapes="_x0000_i1032" /> </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 135pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 21.75pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="180"><shape id="_x0000_i1033" style="WIDTH: 48pt; HEIGHT: 17.25pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image022.wmz" /></shape /><img height="23" src="http://www.emckairong.com/images/dianc24.gif" width="64" v:shapes="_x0000_i1033" /> </td></tr></tbody></table></div>表3给出了两种场源在远、近场的能量密度。从表中可以看出，两类源的近场有很大的区别，电偶极子的近场能量主要为电场分量，可忽略磁场分量；磁偶极子的近场能量主要为磁场分量，可忽略电场分量；两类源在远场时，电场、磁场分量均必须同时考虑。 屏蔽类型依据上述分析可以进行以下分类： 表4  屏蔽分类 <div align="center"><table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellspacing="0" cellpadding="0" width="618" border="1"><tbody><tr style="HEIGHT: 24.2pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 24.2pt" width="232">场源类型  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 24.2pt; mso-border-left-alt: solid windowtext .5pt" width="239">近场（<shape id="_x0000_i1034" style="WIDTH: 36pt; HEIGHT: 15.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image024.wmz" /></shape /><img height="21" src="http://www.emckairong.com/images/dianc25.gif" width="48" v:shapes="_x0000_i1034" /> ）  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 24.2pt; mso-border-left-alt: solid windowtext .5pt" width="146">远场（<shape id="_x0000_i1035" style="WIDTH: 36pt; HEIGHT: 15.75pt" type="#_x0000_t75" /> <imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image026.wmz" /></shape /><img height="21" src="http://www.emckairong.com/images/dianc26.gif" width="48" v:shapes="_x0000_i1035" /> ）  </td></tr><tr style="HEIGHT: 15.15pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 15.15pt; mso-border-top-alt: solid windowtext .5pt" width="232">电偶极子（非闭合载流导线）  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 15.15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="239"><p class="MsoNormal" style="MARGIN-LEFT: 52.5pt; LAYOUT-GRID-MODE: char; TEXT-INDENT: -52.5pt; LINE-HEIGHT: 150%; TEXT-ALIGN: center; mso-char-indent-count: -5.0; mso-char-indent-size: 10.5pt" align="center">电屏蔽（包括静电屏蔽）  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 15.15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="146">电磁屏蔽  </td></tr><tr style="HEIGHT: 12.95pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 12.95pt; mso-border-top-alt: solid windowtext .5pt" width="232">磁偶极子（闭合载流导线）  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 12.95pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="239">磁屏蔽（包括恒定磁场屏蔽）  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 12.95pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="146">电磁屏蔽  </td></tr></tbody></table></div><shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f" /><stroke joinstyle="miter" /><formulas /><f eqn="if lineDrawn pixelLineWidth 0" /><f eqn="sum @0 1 0" /><f eqn="sum 0 0 @1" /><f eqn="prod @2 1 2" /><f eqn="prod @3 21600 pixelWidth" /><f eqn="prod @3 21600 pixelHeight" /><f eqn="sum @0 0 1" /><f eqn="prod @6 1 2" /><f eqn="prod @7 21600 pixelWidth" /><f eqn="sum @8 21600 0" /><f eqn="prod @7 21600 pixelHeight" /><f eqn="sum @10 21600 0" /></formulas /><path o:extrusionok="f" gradientshapeok="t" o:connecttype="rect" /><lock v:ext="edit" aspectratio="t" /></shapetype /><shape id="_x0000_s1026" style="MARGIN-TOP: 2.35pt; Z-INDEX: 1; LEFT: 0px; MARGIN-LEFT: 192.3pt; WIDTH: 74.85pt; POSITION: absolute; HEIGHT: 19.75pt; TEXT-ALIGN: left; mso-wrap-edited: f" type="#_x0000_t75" wrapcoords="-216 831 -216 20769 21600 20769 21600 831 -216 831" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image001.png" croptop="-2281f" cropbottom="3259f" cropleft="771f" cropright="1028f" /><wrap type="tight" /></shape /><img height="26" hspace="12" src="http://www.emckairong.com/images/dianci37.gif" width="100" v:shapes="_x0000_s1026" />  <div style="mso-element: dropcap-dropped; mso-element-frame-height: 31.55pt; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2"><table height="42" cellspacing="0" cellpadding="0" align="left" hspace="0" vspace="0"><tbody><tr><td style="PADDING-RIGHT: 0cm; PADDING-LEFT: 0cm; PADDING-BOTTOM: 0cm; PADDING-TOP: 0cm" valign="top" align="left" height="42"><p class="MsoNormal" style="VERTICAL-ALIGN: baseline; LAYOUT-GRID-MODE: char; LINE-HEIGHT: 31.55pt; mso-element: dropcap-dropped; mso-element-frame-height: 31.55pt; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2; mso-line-height-rule: exactly">电  </td></tr></tbody></table></div>屏蔽的实质是减小两个设备（或两个电路、组件、元件）间电场感应的影响。电屏蔽的原理是在保证良好接地的条件下，将干扰源所产生的干扰终止于由良导体制成的屏蔽体。因此，接地良好及选择良导体做为屏蔽体是电屏蔽能否起作用的两个关键因素。 <div style="mso-element: dropcap-dropped; mso-element-frame-height: 33.05pt; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2"><table height="44" cellspacing="0" cellpadding="0" align="left" hspace="0" vspace="0"><tbody><tr><td style="PADDING-RIGHT: 0cm; PADDING-LEFT: 0cm; PADDING-BOTTOM: 0cm; PADDING-TOP: 0cm" valign="top" align="left" height="44"><p class="MsoNormal" style="VERTICAL-ALIGN: baseline; LAYOUT-GRID-MODE: char; LINE-HEIGHT: 140%; mso-element: dropcap-dropped; mso-element-frame-height: 33.05pt; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2">磁  </td></tr></tbody></table></div>屏蔽的原理是由屏蔽体对干扰磁场提供低磁阻的磁通路，从而对干扰磁场进行分流，因而选择钢、铁、坡莫合金等高磁导率的材料和设计盒、壳等封闭壳体成为磁屏蔽的两个关键因素。 <div style="mso-element: dropcap-dropped; mso-element-frame-height: 30.05pt; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2"><table height="40" cellspacing="0" cellpadding="0" align="left" hspace="0" vspace="0"><tbody><tr><td style="PADDING-RIGHT: 0cm; PADDING-LEFT: 0cm; PADDING-BOTTOM: 0cm; PADDING-TOP: 0cm" valign="top" align="left" height="40"><p class="MsoNormal" style="VERTICAL-ALIGN: baseline; LAYOUT-GRID-MODE: char; LINE-HEIGHT: 140%; mso-element: dropcap-dropped; mso-element-frame-height: 30.05pt; mso-element-wrap: around; mso-element-anchor-vertical: paragraph; mso-element-anchor-horizontal: column; mso-height-rule: exactly; mso-element-linespan: 2">电磁  </td></tr></tbody></table></div>屏蔽的原理是由金属屏蔽体通过对电磁波的反射和吸收来屏蔽辐射干扰源的远区场，即同时屏蔽场源所产生的电场和磁场分量。由于随着频率的增高，波长变得与屏蔽体上孔缝的尺寸相当，从而导致屏蔽体的<a>孔缝泄漏</a>成为<a>电磁屏蔽</a>最关键的控制要素。 <img height="29" hspace="12" src="http://www.emckairong.com/images/dianci38.jpg" width="259" v:shapes="_x0000_s1027" />   屏蔽体的泄漏耦合结构与所需抑制的<a href="http://www.emcgarden.net/">电磁波</a>频率密切相关，三类屏蔽所涉及的频率范围及控制要素如表5所示： 表5 泄漏耦合结构与控制要素 <div align="center"><table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; MARGIN-LEFT: 23.4pt; BORDER-LEFT: medium none; WIDTH: 408.95pt; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellspacing="0" cellpadding="0" width="545" border="1"><tbody><tr style="HEIGHT: 22.65pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 75.8pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.65pt" width="101">屏蔽类型  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 103.8pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.65pt; mso-border-left-alt: solid windowtext .5pt" width="138"><a href="http://www.emcgarden.net/">磁屏蔽</a>  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 126pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.65pt; mso-border-left-alt: solid windowtext .5pt" width="168"><a href="http://www.emcgarden.net/">电屏蔽</a>  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 103.35pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.65pt; mso-border-left-alt: solid windowtext .5pt" width="138"><a href="http://www.emcgarden.net/">电磁屏蔽</a>  </td></tr><tr style="HEIGHT: 22.95pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 75.8pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.95pt; mso-border-top-alt: solid windowtext .5pt" width="101">频率范围  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 103.8pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.95pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="138">10kHz~500kHz  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 126pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.95pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="168">1MHz~500MHz  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 103.35pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.95pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="138">500MHz~40GHz  </td></tr><tr style="HEIGHT: 22.55pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 75.8pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.55pt; mso-border-top-alt: solid windowtext .5pt" width="101">泄漏耦合结构  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 103.8pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.55pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="138">屏蔽体壳体  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 126pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.55pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="168">屏蔽体壳体及接地  </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 103.35pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 22.55pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="138">孔缝及接地  </td></tr><tr style="HEIGHT: 22.85pt"><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1.5pt solid; WIDTH: 75.8pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 22.85pt; mso-border-top-alt: solid windowtext .5pt" width="101">控制要素  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 103.8pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 22.85pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="138">合理选择壳体材料  </td><td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 126pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 22.85pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="168">合理选择壳体材料 良好接地   </td><td style="BORDER-RIGHT: windowtext 1.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 103.35pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1.5pt solid; HEIGHT: 22.85pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="138">  抑制孔缝泄漏 良好接地   </td></tr></tbody></table></div>  实际屏蔽体上同时存在多个泄漏耦合结构（n个），设机箱接缝、通风孔、屏蔽体壁板等各泄漏耦合结构的单独屏蔽效能（如只考虑接缝）为SEi（i=1,2,…，n），则屏蔽体总的屏蔽效能                         <shape id="_x0000_i1025" style="WIDTH: 126.75pt; HEIGHT: 36pt" type="#_x0000_t75" /><imagedata src="file:///C:/DOCUME~1/HGJ/LOCALS~1/Temp/msoclip1/01/clip_image005.wmz" /></shape /><img height="48" src="http://www.emckairong.com/images/dianci39.gif" width="169" v:shapes="_x0000_i1025" /> 由上式可以看出，屏蔽体的屏蔽效能是由各个泄漏耦合结构中产生最大泄漏耦合的结构所决定的，即由屏蔽最薄弱的环节所决定的。因此进行屏蔽设计时，明确不同频段的泄漏耦合结构，确定最大泄漏耦合要素是其首要的设计原则。<span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-hansi-font-family: Times New Roman; mso-ascii-font-family: Times New Roman; mso-bidi-font-family: Times New Roman; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">在三类屏蔽中，磁屏蔽和电磁屏蔽的难度较大。尤其是电磁屏蔽设计中的孔缝泄漏抑制最为关键，成为屏蔽设计中应重点考虑的首要因素。 <img height="27" src="http://www.emckairong.com/images/dianci40.jpg" width="185" v:shapes="_x0000_s1037" /><img height="259" src="http://www.emckairong.com/images/dianci42.gif" width="350" v:shapes="_x0000_s1026 _x0000_s1027 _x0000_s1028 _x0000_s1029 _x0000_s1030 _x0000_s1032 _x0000_s1033 _x0000_s1034 _x0000_s1035 _x0000_s1036" />图4  典型机柜结构示意图 根据孔耦合理论，决定孔缝泄漏量的因素主要有两个：孔缝面积和孔缝最大线度尺寸。两者皆大，则泄漏最为严重；面积小而最大线度尺寸大则电磁泄漏仍然较大。 图4所示为一典型机柜示意图，上面的孔缝主要分为四类： ●     机箱（机柜）接缝 该类缝虽然面积不大，但其最大线度尺寸即缝长却非常大，由于维修、开启等限制，致使该类缝成为电子设备中屏蔽难度最大的一类孔缝，采用导电衬垫等特殊屏蔽材料可以有效地抑制电磁泄漏。该类孔缝屏蔽设计的关键在于：合理地选择导电衬垫材料并进行适当的变形控制。●     通风孔该类孔面积和最大线度尺寸较大，通风孔设计的关键在于通风部件的选择与装配结构的设计。在满足通风性能的条件下，应尽可能选用屏效较高的屏蔽通风部件。●     观察孔与显示孔 该类型孔面积和最大线度尺寸较大，其设计的关键在于屏蔽透光材料的选择与装配结构的设计。 ●     连接器与机箱接缝 这类缝的面积与最大线度尺寸均不大，但由于在高频时导致连接器与机箱的接触阻抗急剧增大，从而使得<a href="http://www.emcgarden.net/">屏蔽电缆</a>的共模传导发射变大，往往导致整个设备的辐射发射出现超标，为此应采用导电橡胶等连接器导电衬垫。综上所述，孔缝抑制的设计要点归纳为： ● 合理选择屏蔽材料； ● 合理设计安装互连结构。

123456 · 发表于 2007-11-8 11:45:48

[s:9] [s:9] [s:9] [s:9] [s:9] [s:11] [s:11] [s:11] [s:12] [s:12] [s:12] [s:12] [s:19] [s:19] [s:19] [s:27]

xiami909 · 发表于 2007-12-8 18:35:12

gracious

hslz3 · 发表于 2008-3-27 16:10:33

金属屏蔽效率
     可用屏蔽效率(SE)对屏蔽罩的适用性进行评估，其单位是分贝，计算公式为 SEdB=A+R+B
其中 A：吸收损耗(dB) R：反射损耗(dB) B：校正因子(dB)(适用于薄屏蔽罩内存在多个反射的情况)一个简单的屏蔽罩会使所产生的电磁场强度降至最初的十分之一，即SE等于20dB；而有些场合可能会要求将场强降至为最初的十万分之一，即SE要等于100dB。
吸收损耗是指电磁波穿过屏蔽罩时能量损耗的数量，吸收损耗计算式为
AdB=1.314(f×σ×μ)1/2×t
其中 f：频率(MHz) μ：铜的导磁率 σ：铜的导电率 t：屏蔽罩厚度
      反射损耗(近场)的大小取决于电磁波产生源的性质以及与波源的距离。对于杆状或直线形发射天线而言，离波源越近波阻越高，然后随着与波源距离的增加而下降，但平面波阻则无变化(恒为377)。
  相反，如果波源是一个小型线圈，则此时将以磁场为主，离波源越近波阻越低。波阻随着与波源距离的增加而增加，但当距离超过波长的六分之一时，波阻不再变化，恒定在377处。
     反射损耗随波阻与屏蔽阻抗的比率变化，因此它不仅取决于波的类型，而且取决于屏蔽罩与波源之间的距离。这种情况适用于小型带屏蔽的设备。
近场反射损耗可按下式计算
R(电)dB=321.8-(20×lg r)-(30×lg f)-[10×lg(μ/σ)] R(磁)dB=14.6+(20×lg r)+(10×lg f)+[10×lg(μ/σ)]
其中 r：波源与屏蔽之间的距离。
SE算式最后一项是校正因子B，其计算公式为B=20lg[-exp(-2t/σ)]
      此式仅适用于近磁场环境并且吸收损耗小于10dB的情况。由于屏蔽物吸收效率不高，其内部的再反射会使穿过屏蔽层另一面的能量增加，所以校正因子是个负数，表示屏蔽效率的下降情况。

hslz3 · 发表于 2008-3-27 16:11:01

EMI抑制策略
      只有如金属和铁之类导磁率高的材料才能在极低频率下达到较高屏蔽效率。这些材料的导磁率会随着频率增加而降低，另外如果初始磁场较强也会使导磁率降低，还有就是采用机械方法将屏蔽罩作成规定形状同样会降低导磁率。综上所述，选择用于屏蔽的高导磁性材料非常复杂，通常要向EMI屏蔽材料供应商以及有关咨询机构寻求解决方案。
在高频电场下，采用薄层金属作为外壳或内衬材料可达到良好的屏蔽效果，但条件是屏蔽必须连续，并将敏感部分完全遮盖住，没有缺口或缝隙(形成一个法拉第笼)。然而在实际中要制造一个无接缝及缺口的屏蔽罩是不可能的，由于屏蔽罩要分成多个部分进行制作，因此就会有缝隙需要接合，另外通常还得在屏蔽罩上打孔以便安装与插卡或装配组件的连线。
     设计屏蔽罩的困难在于制造过程中不可避免会产生孔隙，而且设备运行过程中还会需要用到这些孔隙。制造、面板连线、通风口、外部监测窗口以及面板安装组件等都需要在屏蔽罩上打孔，从而大大降低了屏蔽性能。尽管沟槽和缝隙不可避免，但在屏蔽设计中对与电路工作频率波长有关的沟槽长度作仔细考虑是很有好处的。
  任一频率电磁波的波长为: 波长(λ)=光速(C)/频率(Hz)
     当缝隙长度为波长(截止频率)的一半时，RF波开始以20dB/10倍频(1/10截止频率)或6dB/8倍频(1/2截止频率)的速率衰减。通常RF发射频率越高衰减越严重，因为它的波长越短。当涉及到最高频率时，必须要考虑可能会出现的任何谐波，不过实际上只需考虑一次及二次谐波即可。
      一旦知道了屏蔽罩内RF辐射的频率及强度，就可计算出屏蔽罩的最大允许缝隙和沟槽。例如如果需要对1GHz(波长为300mm)的辐射衰减26dB，则150mm的缝隙将会开始产生衰减，因此当存在小于150mm的缝隙时，1GHz辐射就会被衰减。所以对1GHz频率来讲，若需要衰减20dB，则缝隙应小于15 mm(150mm的1/10)，需要衰减26dB时，缝隙应小于7.5 mm(15mm的1/2以上)，需要衰减32dB时，缝隙应小于3.75 mm(7.5mm的1/2以上)。
     可采用合适的导电衬垫使缝隙大小限定在规定尺寸内，从而实现这种衰减效果。
定在规定尺寸内，从而实现这种衰减效果。

xiaoye2800 · 发表于 2008-7-2 09:55:27

没有杂波就是屏蔽好了,,.....也 [s:9] [s:9] [s:9] [s:9]

jianghua999 · 发表于 2008-7-15 16:59:36

强强总结一下学到的东西。电磁干扰包含传导和泄露   传到用到EMI 比如磁环   泄露就相对较多了如导电泡棉、屏蔽罩等等产品

luoyue · 发表于 2008-7-26 15:19:20

怎么又是没有图片的？

caiyb · 发表于 2008-8-16 06:19:08

电磁干扰(EMI)是个头疼的事． [s:9]

szsnyn · 发表于 2008-8-26 11:22:16

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