摘要
电磁层析成像技术(Electromagnetic Tomography，简称EMT)，是20世纪90年代随着计算机和检测技术的不断进步而出现并发展起来的一种过程层析成像技术(Progress Tomography，简称PT)，它以电磁感应为基本原理，通过获取反映被测物场空间电导率和磁导率分布信息的边界测量值，利用图像重建算法得到物场空间的分布特性。相对于其他电学层析成像技术，电磁层析成像技术能够获得的信息量更大，而且具有非接触、无侵害、多点测量实时成像以及无辐射等优点，因此受到了人们的广泛关注。
电磁成像技术虽然起步较晚，但发展迅速，国内的一些高校如天津大学等已经开发出了自己的系统样机。然而，目前大多数的EMT装置由于设计工作频率低，只能探测电导率较高的物质，大大限制了电磁层析成像技术的应用范围，因此开展宽频EMT技术的研究具有很大的实际意义。
鉴于以上问题，本文的主要工作体现在以下四个方面：
第一、针对高频信号易受干扰、传输困难的特点，设计了一种前端电路板，通过在靠近高频信号源的地方对有用信号进行预处理的方法，提高了信号的传输质量，保证了感应信号的正确采集。
第二、在高频信号前端板的基础上，又设计了一种高频信号采集板，旨在通过FPGA的控制实现对高频感应信号的传输，并最终完成感应信号的采样和处理，为图像重建提供原始数据。
第三、完成了USB通讯模块的设计，实现了FPGA和上位机之间数据的高速传输，保证了成像的正确性和实时性。
第四、在以上工作的基础上，针对不同电导率的物质设计了相关的实验，并对数据做了分析处理，为将来实现宽频EMT系统检测低电导率物质做了可行性的探索。
Electromagnetic Tomography(EMT), a modality of Progress Tomography(PT)based on the law of Electromagnetic induction, has been developed since1990s. It hasbeen used to obtain spatial distribution information through acquisition of theboundary measurements and suitable image reconstruction algorithms.
Compared to other electrical tomography techniques, EMT is capable ofobtaining greater amount of information, and it has advantage of being non-contact,harmlessness, multi-point measurement, real-time imaging and non-radiative. EMThas received wide attention.
Despite a late start, EMT has developed rapidly; some domestic universities suchas Tianjin University, have developed their prototype. However, due to the lowoperating frequency, most of the EMT equipments can only work on highconductivity materials, which have greatly limited its application. For this reason, it isof great practical significance to carry out the research of wideband EMT.
In view of the problem above, this paper works in the following four areas:
Firstly, a kind of front-end circuit board is designed for high frequency signal,which is susceptible to interference and difficult to transmit, by pre-processing theuseful signal at the place close to the signal source, the board can improve the signaltransmission quality and ensure the correct sensor signal acquisition.
Secondly, based on the front-end circuit board, a type of high-frequency signalacquisition board is designed, aiming at achieving high-frequency induction signalacquisition controlled by FPGA, and finally complete the signal's sampling andprocessing, providing raw data for the image reconstruction.
Thirdly, by designing the USB communication module, a high-speed datadelivery has been achieved, which ensure the imaging's validity and real-timing.
Finally, on the basis of the works above, some experiments have been done,intending to detect the objects of different conductivity. The data processing followedhas verified the possibility to detect the low conductivity objects with the widebandEMT system.
引文
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