1.1 本指南主要用于教程目的。它概述了用于超声检测的电磁声换能器（EMAT）的操作和使用的一般原则。 1.2 本指南描述了一种通过使用电磁场将超声波能量耦合到导电或铁磁性材料或两者的非接触技术。本指南描述了操作理论和基本设计考虑以及该技术的优点和局限性。 1.3 本指南旨在作为一般参考，以帮助确定EMAT对给定应用的有用性，并提供有关其设计和操作的基本信息。本指南为使用EMAT生成纵向、剪切、瑞利和兰姆波模式提供了指导。 1.4 本指南不包含在任何特定应用中使用EMAT的详细程序； 它也不提倡在未进行彻底测试的情况下使用EMAT进行检查。第节概述了EMAT已成功应用的一些应用 9 . 1.5 单位- 以英寸-磅为单位的数值应视为标准值。括号中给出的SI值仅供参考。 1.6 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.7 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 4.1 概述- 超声波检测是一种广泛使用的无损检测方法。大多数超声波检查是使用换能器进行的，换能器通过使用压电晶体将电能直接转换为声能。本指南描述了一种替代技术，其中电磁能用于在导电或铁磁性材料内产生声能。与传统的压电超声搜索装置相比，电磁超声具有独特的特性，使其成为一些超声检测应用的重要工具。 4.2 原则- 电磁声换能器（EMAT）产生和接收超声波，而无需接触声波传播的材料。EMAT的使用要求被检查的材料具有导电性或铁磁性，或两者兼有。 EMAT系统有两个基本组件，一个磁铁和一个线圈。磁铁可以是电磁铁或永磁体，用于在被测材料中产生磁场。线圈以所需的超声波频率使用交流电驱动。线圈和交流电流也会在被测材料中产生表面磁场。在静态磁场存在的情况下，表面电流经历洛伦兹力，产生所需的超声波。当接收到超声波时，导体表面在磁场中振荡，从而在线圈中产生电压。传导过程发生在电磁趋肤深度内。EMAT是产生和检测超声波的可再生非接触系统的基础。 4.3 具体优势- 由于EMAT技术不必与受检材料接触，因此不需要流体耦合剂。 其重要后果包括应用于远程或危险位置的移动物体、高温物体或粗糙表面物体。EMAT技术是环境安全的，因为它不使用潜在的污染或危险化学品。该技术有助于快速扫描具有复杂几何形状的部件。由于声波的产生方式，EMAT信号具有高度的可再现性。EMAT还可以在不进行模式转换的情况下产生水平极化剪切波，并且可以在使用SH波的同时适应扫描。（注意，为了通过传统超声波技术产生这种波模式，需要环氧树脂或高粘性耦合剂。因此，当使用SH波模式时，传统超声波技术不容易扫描。）此外，EMAT允许用户以电子方式控制剪切波。 4.4 具体限制- 与传统超声方法相比，电磁超声技术的效率非常低，插入损耗为40 dB或更高。EMAT技术只能用于电导体或铁磁性材料。高度腐蚀的表面，尤其是内表面，如果表面干扰洛伦兹力的产生，可能导致EMAT不适合使用。EMAT探头的设计通常比类似的压电搜索单元更复杂，并且通常尺寸相对较大。由于其效率较低，EMAT通常需要更专业的仪器来产生和检测超声波信号。高发射电流、低噪声接收器和仔细的电气匹配在系统设计中至关重要。一般来说，EMAT探头与压电换能器一样，都是特定于应用的。

1.1 This guide is intended primarily for tutorial purposes. It provides an overview of the general principles governing the operation and use of electromagnetic acoustic transducers (EMATs) for ultrasonic examination. 1.2 This guide describes a non-contact technique for coupling ultrasonic energy into an electrically conductive or ferromagnetic material, or both, through the use of electromagnetic fields. This guide describes the theory of operation and basic design considerations as well as the advantages and limitations of the technique. 1.3 This guide is intended to serve as a general reference to assist in determining the usefulness of EMATs for a given application as well as provide fundamental information regarding their design and operation. This guide provides guidance for the generation of longitudinal, shear, Rayleigh, and Lamb wave modes using EMATs. 1.4 This guide does not contain detailed procedures for the use of EMATs in any specific applications; nor does it promote the use of EMATs without thorough testing prior to their use for examination purposes. Some applications in which EMATs have been applied successfully are outlined in Section 9 . 1.5 Units— The values stated in inch-pound units are to be regarded as the standard. The SI values given in parentheses are for information only. 1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 4.1 General— Ultrasonic testing is a widely used nondestructive method for the examination of a material. The majority of ultrasonic examinations are performed using transducers that directly convert electrical energy into acoustic energy through the use of piezoelectric crystals. This guide describes an alternate technique in which electromagnetic energy is used to produce acoustic energy inside an electrically conductive or ferromagnetic material. EMATs have unique characteristics when compared to conventional piezoelectric ultrasonic search units, making them a significant tool for some ultrasonic examination applications. 4.2 Principle— An electromagnetic acoustic transducer (EMAT) generates and receives ultrasonic waves without the need to contact the material in which the acoustic waves are traveling. The use of an EMAT requires that the material to be examined be electrically conductive or ferromagnetic, or both. There are two basic components of an EMAT system, a magnet and a coil. The magnet may be an electromagnet or a permanent magnet, which is used to produce a magnetic field in the material under test. The coil is driven using alternating current at the desired ultrasonic frequency. The coil and AC current also induce a surface magnetic field in the material under test. In the presence of the static magnetic field, the surface current experiences Lorentz forces that produce the desired ultrasonic waves. Upon reception of an ultrasonic wave, the surface of the conductor oscillates in the presence of a magnetic field, thus inducing a voltage in the coil. The transduction process occurs within an electromagnetic skin depth. The EMAT forms the basis for a very reproducible noncontact system for generating and detecting ultrasonic waves. 4.3 Specific Advantages— Since an EMAT technique does not have to be in contact with the material under examination, no fluid couplant is required. Important consequences of this include applications to moving objects, in remote or hazardous locations, to objects at elevated temperatures, or to objects with rough surfaces. The EMAT technique is environmentally safe since it does not use potentially polluting or hazardous chemicals. The technique facilitates the rapid scanning of components having complex geometries. EMAT signals are highly reproducible as a consequence of the manner in which the acoustic waves are generated. EMATs can also produce horizontally polarized shear (SH) waves without mode conversion and can accommodate scanning while using SH waves. (Note that in order to produce this wave mode by conventional ultrasonic techniques, either an epoxy or a highly viscous couplant is required. Thus, conventional ultrasonic techniques do not lend themselves easily to scanning when using SH wave modes.) Additionally, EMATs can allow the user to electronically steer shear waves. 4.4 Specific Limitations— EMATs have very low efficiency as compared with conventional ultrasonic methods, with insertion losses of 40 dB or more. The EMAT technique can be used only on materials that are electrical conductors or are ferromagnetic. Highly corroded surfaces, especially inner surfaces, may render EMAT unsuitable for use if the surface disturbs the generation of the Lorentz forces. The design of EMAT probes is usually more complex than comparable piezoelectric search units, and are usually relatively large in size. Due to their low efficiency, EMATs usually require more specialized instrumentation for the generation and detection of ultrasonic signals. High transmitting currents, low-noise receivers, and careful electrical matching are imperative in system design. In general, EMAT probes are application-specific, in the same way as are piezoelectric transducers.