共查询到20条相似文献,搜索用时 31 毫秒
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《IEEE transactions on medical imaging》2008,27(12):1723-1727
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《IEEE transactions on medical imaging》2010,29(1):169-178
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《IEEE transactions on medical imaging》2010,29(1):179-184
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The advent of fast rise-time pulse techniques and their increasing importance brought on by high-speed microminiature circuits and the computer industry has resulted in an increased demand for pulse transformers of various types. The basic idea of constructing transmission line type transformers has been known and used for a number of years. However, such devices have not gained widespread usage, partly because their existence is not well known, but largely because of a lack of basic understanding of their operating principles in terms of elementary fundamentals as well as their capabilities and limitations. The purpose of this paper is twofold. One aim is to develop in step-by-step fashion the basic ideas of transmission line transformers from ordinary transmission line theory. The subject will be approached from the point of view of pulse response rather than ac excitation as is usually the case. Both impedance transformers and balanced-to-unbalanced (balun) transformers, including inverters, will be considered with physical insights into their operation. Several fundamental concepts will be developed and explored in detail (without mathematics), since they have a strong bearing on practical applications. The second purpose is to present new information and pulse measurements which will be useful in the design and applications of such devices, showing their capabilities and hitherto unexplored limitations, as derived from the fundamental concepts. Thus, this paper is partly supplementary to other published work and partly new work with the goal of providing a convenient fundamental understanding of these devices and their inherent potential and shortcomings. Although the intention is not to give a detailed design procedure, some approximate calculations and discussion of significant design criteria are included. 相似文献
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Lindsey D.P. McKee E.L. Hull M.L. Howell S.M. 《IEEE transactions on bio-medical engineering》1998,45(5):614-619
To reduce space requirements for implant electronics in in vivo telemetry applications, the purpose of this project was to develop and test a new data transmission method that utilizes the ionic properties of bodily fluids as the transmission medium. Motivated by an interest in using the new method to transmit information from a sensor which measures tension in anterior cruciate ligament (ACL) grafts, a sine wave was injected into a cadaver leg using platinum electrodes implanted into the lateral femoral epicondyle. The signal was detected by electromyogram (EMG) surface electrodes. The effect of transmission frequency, the current injected, interelectrode separation, distance of the electrodes from the joint line, and the surface of electrode placement on the signal attenuation was studied. The logarithmic relation between attenuation and frequency was constant from 2 kHz until 10 kHz. For frequencies above 10 kHz, the attenuation increased linearly at the rate of 1 dB/octave. Attenuation was inversely sensitive to both current and interelectrode separation with larger separations and currents giving less attenuation. Attenuation was significantly less for the lateral thigh surface than for the anterior surface and increased with increasing distance from the joint line for both surfaces. For the application of interest here, suitable values of transmission variables to avoid the possible negative consequences of injecting current into living tissue are a current of 3 mA injected at a frequency of 37 kHz. The values of reception variables for minimum attenuation are wide interelectrode separation (5 cm) with the electrodes placed 5 cm proximal of the joint line on the lateral surface of the thigh. With the exception of the surface which is application dependent, these values of the reception variables should also be appropriate for other applications 相似文献
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Shirasaki Y. Asakawa K. Kojima J. Iwamoto Y. Ohkubo M. 《Lightwave Technology, Journal of》1984,2(6):856-862
A new type of tether cable with high quality signal transmission characteristics was developed by adopting optical fibers. As the tether cable is subject to frequent and various mechanical and thermal loads under the severe operating conditions in the offshore environment, the greatest care should be paid to the design of its structure to preserve the optical fibers from those loads. This paper describes the design requirements and the characteristics of the optical fiber/power line composite tether cable under the loads such as tensile loading, bending, twisting, water pressure, and cable heating. The termination of the tether cable is also discussed. This tether cable has been in practical use for remotely operated submersible MARCAS whose mission is inspection and location of the submarine telecommunication cables. 相似文献
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This is a review paper concisely tracing the development of miniature superconductive coaxial transmission lines from the original invention as a vertical channel signal delay line for fractional nanosecond pulse oscillography to present-day work towards highly compact, broad-band, and low-loss telecommunication cables. The present state of development yields a 1.6-mm coaxial line operating at 4.2K and having Pb conductors, polyethylene dielectric, Z0 = 50 ± 0.3 Ω and a 1-GHz attenuation of the order of 1 dB/km. The attenuation up to 1 GHz is mainly due to dielectric losses. 相似文献
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Electric currents are applied to body in numerous applications in medicine such as electrical impedance tomography, cardiac defibrillation, electrocautery, and physiotherapy. If the magnetic field within a region is measured, the currents generating these fields can be calculated using the curl operator. In this study, magnetic fields generated within a phantom by currents passing through an external wire is measured using a magnetic resonance imaging (MRI) system. A pulse sequence that is originally designed for mapping static magnetic field inhomogeneity is adapted. AC current in the form of a burst sine wave is applied synchronously with the pulse sequence. The frequency of the applied current is in the audio range with an amplitude of 175-mA rms. It is shown that each voxel value of sequential images obtained by the proposed pulse sequence is modulated similar to a single-tone broadband frequency modulated (FM) waveform with the AC magnetic field strength determining the modulation index. An algorithm is developed to calculate the AC magnetic field intensity at each voxel using the frequency spectrum of the voxel signal. Experimental results show that the proposed algorithm can be used to calculate AC magnetic field distribution within a conducting sample that is placed in an MRI system 相似文献
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分别采用一种"多层快速多极子+多导体传输线理论"混合方法和实验方法,研究了多点接地技术对降低载荷舱内电缆电磁辐射的作用.首先,利用多导体传输线(multi-conductor transmission line,MTL)方法快速求解电缆区域泄漏电流;其次,将泄漏电流作为激励源,分谐振与非谐振两种状态,利用多层快速多极子方法准确、有效地对不同接地点数情况下载荷舱内电缆的电磁辐射进行仿真.实验结果和仿真结果证明了该混合方法的计算精度和高效性.最终得出结论:通过多点接地方式可以明显降低载荷舱内电缆非谐振状态下的电磁辐射,大大改善舱内复杂电磁环境,为航天电磁兼容工程设计提供理论指导. 相似文献
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The technical concept realized by the channel bank is optimum with respect to a variety of requirements. Considerations of size and fabrication technology recommend a frequency of 50 kHz for the mechanical filter. The general concept of the modulator suggests a filter design with tuned conventional transformers. Since subsequent adjustment of the assembled mechanical part of the filter is undesirable, the provision of finite attenuation poles has been abandoned at the expense of adding two extra resonantors. The design imposes only modest demands as to the reproducibility of the mechanical couplings. By tuning the transformers it is possible to correct minor production tolerances. A special design of the channel and associated signal filter results in a very low temperature dependence and permits to connect both filters directly in parallel. 相似文献
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Modeling of magnetic-field coupling with cable bundle harnesses 总被引:3,自引:0,他引:3
D'Amore M. Sarto M.S. Scarlatti A. 《Electromagnetic Compatibility, IEEE Transactions on》2003,45(3):520-530
A field-to-line coupling model is developed for cable bundle harnesses in terms of the scattering currents and total line voltages. The equivalent distributed sources representing the effects of electromagnetic coupling are expressed as a function of the incident magnetic-field components. Such a formulation is particularly suitable to be used for the analysis of multiconductor transmission lines excited by a transient field, when data for the incident electric field are either inaccurate or not available. This model allows the accurate calculation of the induced voltages and currents on complex cable bundles. The effects on the induced voltages and currents due to ground losses and to the presence of the dielectric sheath in shielded and unshielded cables is discussed, considering bundles excited by either slow or fast transient fields. Numerical applications demonstrate the validity of the proposed procedure. 相似文献
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A simple iterative design procedure is given for a traveling-wave array of dipole elements fed in a shunt configuration by a meandering transmission line. The design procedure is based on a quasi-periodic analysis of the loaded line, which assumes a Bloch wave propagation on the structure. A design procedure is formulated for the cases of constant attenuation and tapered attenuation on the line. A ten-element array of vertical monopoles fed by a meandering stripline is used to illustrate the design technique. Results show that the design procedure based on power into the dipoles gives good agreement with one based on actual dipole currents if a certain assumption is used. It is important, however, to account for mutual coupling in the design procedure in order to obtain accurate patterns, especially for low sidelobe designs 相似文献
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《Microwave Theory and Techniques》2009,57(11):2617-2626
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A comparison of the contributions of common-mode anddifferential-mode currents in radiated emissions
It is shown that radiated emissions due to common-mode currents on printed circuit board lands can greatly exceed those due to differential-mode currents. It is concluded that predictions of radiated emissions based solely on differential-mode (transmission line) currents can bear little, if any, resemblance to actual measured emissions. Therefore, radiated emission prediction models that use only differential-mode (transmission-line) currents and ignore common-mode (antenna) currents are not adequate for the prediction of radiated emissions from printed circuit boards (as well as cables) 相似文献
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As the higher and higher frequency bands of existing metallic cables in access networks are being continuously exploited by modern transmission technologies, such as the G.fast, the necessity of providing accurate and suitable modeling of their transmission characteristics is evident. Therefore, this paper is focused on modeling of a propagation constant of twisted pairs and metallic cables at high frequencies up to 250 MHz, and an innovative arsinh model is proposed and described. This new model is based on an idea of adopting inverse hyperbolic sine function for modeling of both secondary line coefficients, attenuation constant and phase constant, and its main motivation is to provide their accurate estimations for G.fast frequencies up to 250 MHz for various types of metallic cables while maintaining a low computational complexity. The proposed model was compared with numerous characteristics measured for various real metallic cables as well as with several existing models in order to illustrate its potential. The results, which are presented within this paper, clearly illustrate that the proposed arsinh model generally outperforms existing standard models based on the equal number of required parameters. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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《Optical Fiber Technology》2001,7(2):101-140
The most significant features of plastic optical fibers (POFs) are reviewed, including the main types of POFs, their manufacture, and their possible present and future applications. Among others, their properties regarding bandwidth, attenuation, and influence of external parameters are discussed. These fibers serve as a complement for glass fibers in short-haul communications links, because they are easy to handle, flexible, and economical. Because of these merits, varied applications with POFs have been developed and commercialized, from their use as a simple light transmission guide to their utilization as sensors and telecommunications cables. This paper is a comprehensive introduction to POFs. In addition, its great number of references facilitates further inquires about the subject. 相似文献