This paper presents a novel technique for efficient evaluation of magnetic resonance imaging (MRI)-induced electric fields or induced voltages in the vicinity of implanted metallic leads. The technique is based on the reciprocity theorem in conjunction with the Huygens Principle. This approach allows one to decouple the micro-scale metallic lead simulation/measurement from the macro-level phantom human simulations within the MRI scanners. Consequently, the estimation of MRI-induced heating on an implanted lead, and the induced voltage on the pacemaker device can be greatly simplified. In addition, this method clearly explains the induced lead heating mechanism during MRI procedures. Several numerical examples, as well as measurement results are given to demonstrate the efficiency and accuracy of this method.

[1] An efficient finite difference time domain (FDTD) algorithm with a simple periodic boundary condition (PBC) is developed to analyze reflection and transmission properties of general periodic structures with arbitrary incident angles. In this new approach, the FDTD simulation is performed by setting a constant horizontal wave number instead of a specific incident angle. The principle of the FDTD/PBC algorithm is discussed and two important implementation issues are addressed, namely, the excitation of plane wave and the suppression of horizontal resonance. The validity of the approach is demonstrated through several numerical examples on dielectric slabs and frequency selective surfaces.Citation: Yang, F., J. Chen, R. Qiang, and A. Elsherbeni (2007), A simple and efficient FDTD/PBC algorithm for scattering analysis of periodic structures, Radio Sci., 42, RS4004,

We show that the enhanced directivity phenomenon for light passing through a subwavelength aperture in a silver film with corrugations on the exit face, is due to a leaky wave that decays exponentially from the aperture. We show quantitatively that the field along the interface of the silver film is dominated by the leaky wave, and that the radiation of the leaky wave, supported by the periodic structure, yields the directive beam. The leaky wave propagation and attenuation constants parameterize the physical radiation mechanism, and provide important design information for optimizing the structure. Maximum directivity occurs when the phase and attenuation constants are approximately equal.

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In order to further suppress the 2 nd and 3 rd harmonics simultaneously, the two types of rectangular loops as EBG structures are combined alternatively on the middle layer. The simulated performances of the parallel-coupled BPF without and with two types of EBG structure are shown in Figure 4. It is interesting to note that the simulated performances of the parallel-coupled BPF with two types of rectangular loops on the middle layer has spurious suppression at Ϫ32 and Ϫ42 dB for the 2 nd and 3 rd harmonics, respectively, as clearly shown in Figure 4. The designed filter is then fabricated on two FR4 GD substrates with relative permittivity r ϭ 4.4, loss tangent ␦ ϭ 0.02, and 0.8-mm thickness. The performances of the proposed BPF are characterized using an Agilent 8753E network analyzer. For practical measurements, the 2 nd and 3 rd harmonics are all below the level of Ϫ30 dB; in particular, the 3 rd harmonic is suppressed below Ϫ60 dB, which is extremely beneficial for the output of the active devices. In addition, the parallel-coupled BPF with EBG structure has a central frequency of 2.02 GHz and insertion loss S 21 ϭ Ϫ2.79 dB. The low insertion loss verifies that the conductor loss does not increase, as the EBG cells are constructed in the middle plane. The slight difference of the measured center frequency may result from the two FR4 boards not being pressed together closely, thus causing the to permeate the two FR4 boards; hence, the effective dielectric constant drops and the center frequency rises. According to the above results, the spurious characteristic of the parallel-coupled BPF with our designed EBG structure is superior to that without the EBG structure. In particular, it is noted the designed EBG structure may be cause the error of shifting the center frequency in the measured results. For example,in [3], the center frequency of the filter added to the PBG structure shifted to a lower frequency of about 15%, corresponding to the original designed center frequency of the filter without the EBG structure. However, the center frequency of our filter with EBG loops added shifted 1% higher, corresponding to the originally designed center frequency. It was found that our EBG periodic cells on the middle layer that depart from the microstrip have no significant effect on the original frequency response, as compared to the results in [3]. CONCLUSIONA novel microstrip parallel-coupled BPF using two types of rectangular EBG loops has been proposed. Two types of rectangular EBG loops on the middle layer have been designed to avoid the package problem and to achieve multiple suppressions. We have shown that this proposed PBG BPF has the superior characteristic of Ϫ30-dB spurious suppression for the same dimensions as those of conventional parallel-coupled BPFs. The EBG periodic cells on the middle layer that depart from the microstrip line have no significant effect on the original passband response and insertion loss.