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📄 低频磁场的屏蔽.htm

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tppabs="http://www.emcdoc.com.cn/ebook/no2/img/t1-1.gif" v:shapes="_x0000_i1025"><![endif]><o:p></o:p></span></p>

<p align=center style='text-align:center'>图<span lang=EN-US>1 高导磁率材料提供了磁旁路，起到屏蔽作用<o:p></o:p></span></p>

<p>　　从这个机理上看，显然屏蔽体分流的磁场分量越多，则屏蔽效能越高。根据这个原理，我们可以用电路的的计算方法来计算磁屏蔽效果。用两个并联的电阻分别表示屏蔽材料的磁阻和空间的磁阻，用电路分析的方法来计算磁场的分流，由此可以计算屏蔽效果。<span
lang=EN-US><o:p></o:p></span></p>

<table border=0 cellspacing=0 cellpadding=0 width="90%" style='width:90.0%;
 mso-cellspacing:0cm;mso-padding-alt:0cm 0cm 0cm 0cm'>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p>　　计算屏蔽效果<span lang=EN-US><o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><![if !supportEmptyParas]>&nbsp;<![endif]><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>　</span><span style='font-size:15.0pt'> <span lang=EN-US><o:p></o:p></span></span></p>
  <p align=center style='text-align:center'><span lang=EN-US>H <sub>i</sub> = H
  <sub>0</sub> Rs / （ Rs + R<sub>0</sub>）<o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>式中：</span><span lang=EN-US style='font-size:15.0pt'><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　</span><span
  lang=EN-US style='font-size:15.0pt'>H <sub>i</sub> = </span><span
  style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
  mso-hansi-font-family:"Times New Roman"'>屏蔽体内的磁场强度</span><span lang=EN-US
  style='font-size:15.0pt'><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　</span><span
  lang=EN-US style='font-size:15.0pt'>H <sub>0</sub> = </span><span
  style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
  mso-hansi-font-family:"Times New Roman"'>屏蔽体外的磁场强度</span><span lang=EN-US
  style='font-size:15.0pt'><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　</span><span
  lang=EN-US style='font-size:15.0pt'>Rs = </span><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>屏蔽体的磁阻</span><span lang=EN-US style='font-size:15.0pt'><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　</span><span
  lang=EN-US style='font-size:15.0pt'>R<sub>0</sub> = </span><span
  style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
  mso-hansi-font-family:"Times New Roman"'>空气的磁阻</span><span lang=EN-US
  style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
</table>

<p class=MsoNormal><span lang=EN-US style='font-size:15.0pt;display:none;
mso-hide:all'><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></span></p>

<table border=0 cellspacing=0 cellpadding=0 width="90%" style='width:90.0%;
 mso-cellspacing:0cm;mso-padding-alt:0cm 0cm 0cm 0cm'>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><![if !supportEmptyParas]>&nbsp;<![endif]><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><![if !supportEmptyParas]>&nbsp;<![endif]><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>　　磁阻的计算公式</span><span lang=EN-US style='font-size:15.0pt;
  font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><![if !supportEmptyParas]>&nbsp;<![endif]><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p align=center style='text-align:center'>磁阻<span lang=EN-US> = S / （m A）<o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>式中：</span><span lang=EN-US style='font-size:15.0pt'><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　</span><span
  lang=EN-US style='font-size:15.0pt'>S = </span><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>磁路长度</span><span lang=EN-US style='font-size:15.0pt'><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　</span><span
  lang=EN-US style='font-size:15.0pt'>m = m <sub>0 m r</sub><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　</span><span
  lang=EN-US style='font-size:15.0pt'>m <sub>r</sub> = </span><span
  style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
  mso-hansi-font-family:"Times New Roman"'>屏蔽材料的相对磁导率</span><span lang=EN-US
  style='font-size:15.0pt'><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　</span><span
  lang=EN-US style='font-size:15.0pt'>A = </span><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>磁通流过的面积</span><span lang=EN-US style='font-size:15.0pt;
  font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
</table>

<p class=MsoNormal><span lang=EN-US style='font-size:15.0pt;display:none;
mso-hide:all'><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></span></p>

<table border=0 cellspacing=0 cellpadding=0 width="90%" style='width:90.0%;
 mso-cellspacing:0cm;mso-padding-alt:0cm 0cm 0cm 0cm'>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p align=center style='text-align:center'>因此圆形管子的磁阻为<span lang=EN-US><o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>　</span><span lang=EN-US style='font-size:15.0pt'>Rs = p b
  /</span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>（</span><span
  lang=EN-US style='font-size:15.0pt'> m <sub>0 m r</sub> 2t L</span><span
  style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
  mso-hansi-font-family:"Times New Roman"'>）</span><span lang=EN-US
  style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
</table>

<p class=MsoNormal><span lang=EN-US style='font-size:15.0pt;display:none;
mso-hide:all'><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></span></p>

<table border=0 cellspacing=0 cellpadding=0 width="90%" style='width:90.0%;
 mso-cellspacing:0cm;mso-padding-alt:0cm 0cm 0cm 0cm'>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><![if !supportEmptyParas]>&nbsp;<![endif]><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><![if !supportEmptyParas]>&nbsp;<![endif]><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>　为了简单，设截面为正方形，</span><span lang=EN-US style='font-size:
  15.0pt'><br>
  </span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>　管子内空气的磁阻为：</span><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>屏蔽效能为：</span><span lang=EN-US style='font-size:15.0pt;
  font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p align=center style='text-align:center'><span lang=EN-US>R<sub>0</sub> = 2
  b /（ m <sub>0 </sub>2b L）<o:p></o:p></span></p>
  </td>
  <td width="50%" style='width:50.0%;padding:0cm 0cm 0cm 0cm'>
  <p align=center style='text-align:center'><span lang=EN-US>SE = H <sub>0</sub>
  / H <sub>i</sub> <o:p></o:p></span></p>
  </td>
 </tr>
</table>

<p class=MsoNormal><span lang=EN-US style='font-size:15.0pt;display:none;
mso-hide:all'><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></span></p>

<table border=0 cellspacing=0 cellpadding=0 width="90%" style='width:90.0%;
 mso-cellspacing:0cm;mso-padding-alt:0cm 0cm 0cm 0cm'>
 <tr>
  <td width="100%" style='width:100.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><![if !supportEmptyParas]>&nbsp;<![endif]><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="100%" style='width:100.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>对于高导磁率屏蔽材料，</span><span lang=EN-US style='font-size:15.0pt'>Rs
  &lt; &lt; R<sub>0</sub> </span><span style='font-size:15.0pt;font-family:
  宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>，因此，屏蔽效能为：</span><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="100%" style='width:100.0%;padding:0cm 0cm 0cm 0cm'>
  <p align=center style='text-align:center'><span lang=EN-US>SE = R<sub>0</sub>
  / Rs = 2<sub> m r</sub> t / p b <o:p></o:p></span></p>
  </td>
 </tr>
</table>

<p>　　从公式中可以看出，屏蔽材料的导磁率越高、越厚，则屏蔽效能越高。另外，<span lang=EN-US>b越小，屏蔽效能越高，这意味着，屏蔽体距离所保护的空间越近，则效果越好。<o:p></o:p></span></p>

<p><strong><span lang=EN-US>2.基本概念</span></strong><span lang=EN-US><o:p></o:p></span></p>

<table border=0 cellspacing=0 cellpadding=0 width="100%" style='width:100.0%;
 mso-cellspacing:0cm;mso-padding-alt:0cm 0cm 0cm 0cm'>
 <tr>
  <td width="21%" style='width:21.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>磁场强度</span><span lang=EN-US style='font-size:15.0pt'> ( H
  )</span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>：</span><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
  <td width="79%" style='width:79.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>单位是奥斯特，与磁场源的强度和距离有关</span><span lang=EN-US
  style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="21%" style='width:21.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>磁通密度</span><span lang=EN-US style='font-size:15.0pt'>&nbsp;
  ( B )</span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>：</span><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
  <td width="79%" style='width:79.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>单位是高斯，度量穿过每平方厘米的磁力线数量，与源的方向有关</span><span lang=EN-US
  style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="21%" style='width:21.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>磁导率　</span><span lang=EN-US style='font-size:15.0pt'> ( m
  )</span><span style='font-size:15.0pt;font-family:宋体;mso-ascii-font-family:
  "Times New Roman";mso-hansi-font-family:"Times New Roman"'>：</span><span
  lang=EN-US style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
  <td width="79%" style='width:79.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>表征材料为磁力线提供通路的能力，</span><sub><span lang=EN-US
  style='font-size:15.0pt'> m </span></sub><span lang=EN-US style='font-size:
  15.0pt'>= B / H</span><span lang=EN-US style='font-size:15.0pt;font-family:
  宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="21%" style='width:21.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>饱和强度　　：</span><span lang=EN-US style='font-size:15.0pt;
  font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
  <td width="79%" style='width:79.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
  "Times New Roman"'>在饱和强度下，材料不能再通过多余的磁力线</span><span lang=EN-US
  style='font-size:15.0pt;font-family:宋体;color:black'><o:p></o:p></span></p>
  </td>
 </tr>
 <tr>
  <td width="21%" style='width:21.0%;padding:0cm 0cm 0cm 0cm'>
  <p class=MsoNormal style='line-height:18.0pt'><span style='font-size:15.0pt;
  font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
1234

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