超声波束的聚焦简介

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                    <section><section powered-by="gulangu"><section><section><p>超声波束的聚焦定义</p></section> <p><img src="image/20201019/2d6679eee67edf391cecc54a9b74e9fe_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><p><img src="image/20201019/a7a8e460aaa94e8c65568e89538b9ff0_2.gif" /></p></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; 在超声场内，将声束中的超声能量会聚成一点的方法称为聚焦。它有利于减小声束，提高横向分辨力，可分为几何（机械）聚焦和电子聚焦。<br  /></p><p>&nbsp; &nbsp; &nbsp; &nbsp; 超声聚焦使超声束在一定深度内会聚，改善分辨力和灵敏度，分为声学聚焦和电子聚焦。</p></section></section></section><section powered-by="gulangu"><section><section><p>声学聚焦</p></section> <p><img src="image/20201019/2d6679eee67edf391cecc54a9b74e9fe_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;声学聚焦又称几何聚焦、机械聚焦，主要分为声透镜聚焦、声反射镜聚焦、凹面振子聚焦。</p></section></section></section><section powered-by="gulangu"><section><p><img src="image/20201019/e1cdb647b7ae3511d415b58c305a056b_4.jpg" /></p></section></section><section powered-by="gulangu"><section><p><img src="image/20201019/70c7c8e09fdb1ce7956dbb0de47f1c62_5.jpg" /></p></section></section><section powered-by="gulangu"><section><p><img src="image/20201019/f3c56ba439d14786091cf6dea215ef70_6.jpg" /></p></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp;厚度：声透镜中心部位厚度取λ/2可有最大投射率。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; 匹配：为防止反射，一般需采用匹配层。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; 材料：通常为环氧树脂、丙稀树脂与其它成分复合。</p></section></section></section><section powered-by="gulangu"><section><p><img src="image/20201019/742516bdd65d4db6fb3585adb46c57ca_7.jpg" /></p></section></section><section powered-by="gulangu"><section><section><p>电子聚焦</p></section> <p><img src="image/20201019/2d6679eee67edf391cecc54a9b74e9fe_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 在光学中，要使平行的光聚焦的话要利用透镜使各点的光聚焦在一点上，同样超声脉冲波同时驱动各阵子的波面无法聚焦；但使用延迟来定时驱动各阵子，中心阵子延迟时间长，两边阵子延迟时间依次减少，最终超声波就会形成电子凹面的聚焦。但一次发射信号只能在一点上设定聚焦，这就是超声波的电子发射聚焦。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; 发射时，各振元的激励信号相位按二次曲线变化，使发射超声经空间叠加后，合成超声波束产生会聚。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; 接收时，各振元的接收信号相位按同样形式变化，使接收信号经电路叠加后，接收灵敏区域产生会聚。改变相位二次曲线变化曲率，可改变会聚焦距，而二次曲线常为圆弧线。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; 在无偏向无聚焦发射中，各阵元发射信号无相位差。叠加声波最强区域---同相位波面密集区域，不偏向， 不会聚。</p></section></section></section><section powered-by="gulangu"><section><p><img src="image/20201019/18980f7d7a0c4a3b469b2a70f786fcea_9.jpg" /></p></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;在无偏向有聚焦发射中，各阵元的激励信号相位按二次曲线变化，叠加超声最强区域---同相位波面密集区域，在焦距内逐渐会聚，在焦距外逐渐扩散，不偏向。</p></section></section></section><section powered-by="gulangu"><section><p><img src="image/20201019/a11367b44cb571225384f8324682bdd1_10.jpg" /></p></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;在无偏向有聚焦接收中，各阵元的接收信号经延迟线，相位按二次曲线变化，使焦点处回波达到同相位，叠加电路对之有最大输出。接收灵敏区域产生会聚。不偏向。</p></section></section></section><section powered-by="gulangu"><section><p><img src="image/20201019/d9541ecaa029c457beaa9ab3b3dc92b3_11.jpg" /></p></section></section><section powered-by="gulangu"><section><section><p>电子动态接收聚焦</p></section> <p><img src="image/20201019/2d6679eee67edf391cecc54a9b74e9fe_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;不同深度的信号接收，其聚焦也不同。各阵子接收的信号根据接收到的时间的不同（深度的不同）产生相应的延迟后进行累加，就会增加接收信号的聚焦性。这就是超声波的电子动态接收聚焦。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; 一般为三点或四点动态聚焦，取得的焦点越多，成像速度越慢。</p></section></section></section><section powered-by="gulangu"><section><section> <section powered-by="gulangu"><section><section><p>欢</p></section></section></section> </section><section> <section powered-by="gulangu"><section><section><p>迎</p></section></section></section> </section><section> <section powered-by="gulangu"><section><section><p>关</p></section></section></section> </section><section> <section powered-by="gulangu"><section><section><p>注</p></section></section></section> </section></section></section><section powered-by="gulangu"><section><section><p><br  /></p></section></section></section><section powered-by="gulangu"><section><section> <section powered-by="gulangu"><section><p><img src="image/20201019/fab8ebcd13dd09a7eba2486fa1ca4eb6_13.jpg" /></p></section></section> </section><section> <section powered-by="gulangu"><section><section> </section></section></section> </section><section> <section powered-by="gulangu"><section><section><p>关注我们</p><p>一起涨姿势！</p></section></section></section> </section></section></section></section>