公开(公告)号：US5608164A

公开(公告)日：1997-03-04

申请号：US508172

申请日：1995-07-27

申请人： Daniel T. MacLauchlan

发明人： Daniel T. MacLauchlan

IPC分类号： G01F23/284 ,  G01F23/296 ,  G01N29/024 ,  G01N29/032 ,  G01N29/24 ,  G01N29/20

CPC分类号： G01N29/024 ,  G01F23/284 ,  G01F23/2962 ,  G01N29/032 ,  G01N29/2412 ,  G01N2291/015 ,  G01N2291/02818 ,  G01N2291/02836 ,  G01N2291/0421 ,  G01N2291/0422

摘要： An ultrasonic inspection technique using a specially designed electromagnetic acoustic transducer (EMAT) launches and receives longitudinal ultrasonic waves into a thin metal wall or thin metal foil seal of a container, causing it to vibrate and launch ultrasonic compressional waves into liquid contained therein. The contents of plastic containers having a metal foil seal forming one wall are easily inspected. The EMAT establishes a magnetic field in the surface of the metal parallel to the surface. Radio frequency (RF) eddy currents are also induced by the EMAT in the surface of the metal. A Lorentz force is generated in the metal surface according the vector product of J, the current density, and H, the magnetic field, and the force generated by the interaction of the perpendicular components of the magnetic field H and the eddy currents J is directed normally to the surface of the metal. This normal force oscillates with the frequency of the induced eddy currents creating ultrasonic compressional waves which propagate normal to the surface of the metal. In such thin-walled metal containers or thin metal foil seals, where the thickness of the metal is much shorter than the ultrasonic wavelength in the metal, the generation and reception process is analogous to the operation of a loudspeaker in air. In this application, the thin metal wall or foil acts as a membrane, with the Lorentz forces generated in the wall or foil causing the metal membrane to vibrate, generating ultrasonic waves in the liquid. Because the thin wall or foil is much more compliant than a thick piece of metal, much larger displacements are generated at the metal-liquid interface than for the thick-wall case, resulting in much larger signal amplitudes than in the thick-wall case.

摘要翻译： 使用专门设计的电磁换能器（EMAT）的超声波检查技术将容器的薄金属壁或薄金属箔密封件的纵向超声波发射并接收，使其对包含在其中的液体振动并发射超声压缩波。 具有形成一个壁的金属箔密封件的塑料容器的内容物容易检查。 EMAT在平行于表面的金属表面建立磁场。 射频（RF）涡流也由金属表面的EMAT引起。 根据J的矢量积，电流密度H，磁场和由磁场H的垂直分量与涡流J的相互作用产生的力在金属表面中产生洛伦兹力 通常到金属表面。 该法向力随感应涡流的频率振荡，产生垂直于金属表面传播的超声压缩波。 在这种薄壁金属容器或薄金属箔密封件中，金属的厚度比金属中的超声波长度短得多，生成和接收过程类似于扬声器在空气中的操作。 在这种应用中，薄金属壁或薄膜用作膜，在壁或箔中产生的洛伦兹力导致金属膜振动，在液体中产生超声波。 由于薄壁或箔片比厚的金属片更柔顺，在金属 - 液体界面处产生比厚壁壳体更大的位移，导致比厚壁情况下更大的信号幅度。