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Development of a conventional electromagnetic acoustic transducer with variable wavelengths and multi modes for Lamb waves

开发用于兰姆波的可变波长和多模式的传统电磁声换能器

基本信息

批准号：
13650108
负责人：
MURAYAMA Riichi
金额：
$ 2.56万
依托单位：
Fukuoka Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

Lamb waves are normally utilized for inspecting thin metal sheets. Wheel-type probes using piezoelectric oscillators have generally been used as the sensors for Lamb waves. Recently, an electromagnetic acoustic transducer (EMAT) has been developed and is beginning to be used as a Lamb wave detector. The EMAT offers the advantage of inspection without using a coupling medium. The EMAT generates Lamb waves with fixed wavelengths determined by the interval between the meander lines in the sensor coil that constitutes the EMAT.We have studied an EMAT consisting of a meander line coil with intervals from 1mm to 4mm and having a paired structure symmetrically embraced with a thin steel sheet on opposite sides. The resonance condition of the sensor coil was tuned to 0.5, 1.0 or 2.0 MHz by changing the condensers connected to the sensor coil. The generated Lamb wave mode, the optimum driving frequency and the wavelength were basically determined by the velocity dispersion curve for the drive f … More requency (sheet thickness) and the phase velocity was determined by the EMAT with the meander line sensor coil. Actually, the observed Lamb wave was influenced by various conditions of the measurement system and the EMAT, for example, the resonance condition or the width of the finger. That is, we could observe the Lamb wave with various modes and different wavelengths using the same EMAT by controlling the different drive conditions. When we used the EMAT with a wide interval between the fingers, the S_0-mode Lamb wave could be only generated, at that condition, and the intensity and the wavelength of the S_0-mode Lamb wave simply changed as the resonance condition changed. However, when we used the EMAT with a narrow finger interval, various Lamb waves could be generated ; the discrimination of their modes and wavelengths might be difficult. However, the Lamb wave must be used with various modes and wavelengths to do a precise inspection. It is then very important to clarify how a Lamb wave is generated under the drive conditions. We could confirm that the symmetrical and asymmetrical Lamb wave modes could be distinguished by using the drive method from both sides of the thin steel sheets Less

兰姆波通常用于检测薄金属片。采用压电振荡器的轮式探头通常被用作兰姆波的传感器。最近，一种电磁声换能器（EMAT）已经被开发出来，并开始用作兰姆波检测器。EMAT的优点是无需使用耦合介质即可进行检测。EMAT产生的兰姆波具有固定的波长，由构成EMAT的传感器线圈中弯曲线之间的间隔决定。我们研究了一种EMAT，该EMAT由一个间隔为1mm至4mm的曲线线圈组成，并在两侧对称地包裹着薄钢板。通过改变与传感器线圈相连的电容器，将传感器线圈的谐振条件调谐到0.5、1.0或2.0 MHz。产生的兰姆波模式、最佳驱动频率和波长基本由驱动的速度色散曲线决定，更大的频率（片厚）和相速度由带有弯曲线传感器线圈的EMAT确定。实际上，观测到的兰姆波受到测量系统和EMAT的各种条件的影响，例如共振条件或手指宽度。也就是说，通过控制不同的驱动条件，我们可以在同一EMAT上观测到不同模式和不同波长的Lamb波。当我们使用手指间距较宽的EMAT时，在该条件下只能产生s_0模式Lamb波，并且s_0模式Lamb波的强度和波长只是随着共振条件的变化而变化。然而，当我们使用窄指距的EMAT时，可以产生各种Lamb波；分辨它们的模式和波长可能很困难。然而，兰姆波必须与各种模式和波长一起使用，才能进行精确的检测。因此，阐明在驱动条件下如何产生兰姆波是非常重要的。在薄钢板的两侧采用驱动方法可以区分出对称和不对称的兰姆波模式