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1. EMI Mitigation, Material Characterization, Transformer Equivalent Circuit Modeling

   Vahdani, Reza (May 2025, Missouri S&T Library)

   Modern high-frequency electronic systems demand precise characterization and modeling techniques to ensure signal integrity and electromagnetic compatibility. This thesis presents three core studies focused on real-world challenges in high-speed and power electronics: EMI mitigation using 3D printed absorbers, wideband liquid dielectric charac- terization, and accurate transformer modeling. The first study demonstrates a targeted approach to mitigating electromagnetic in- terference (EMI) in a commercial router. By using holography imaging to identify radiation hotspots, custom absorber structures were designed with commercially available materials, fabricated via 3D printing, and applied directly to emission sources. Radiated emission tests in a reverberation chamber showed up to 9 dB reduction in EMI, validating the method’s effectiveness for practical applications. The second study proposes a wideband method (up to 30 GHz) to characterize liquid dielectrics using a differential microstrip line and the Djordjevic-Sarkar model. Dielectric constant (DK) and dissipation factor (Df) were extracted by comparing S-parameters of air and liquid-immersed conditions between measurement and simulation results. Experi- mental validation with PAO4 and DC-15 liquids showed strong agreement with traditional cavity resonance methods, with DK deviations under 1.5%. The third study addresses transformer modeling across 100 kHz to 30 MHz by developing an equivalent circuit model that accurately captures winding effects, parasitic capacitance, and leakage inductance. The approach incorporates an optimized coupling coefficient based on physical parameters. Validation with air-core inductors demonstrated high model accuracy, with an average relative error of 2.2%. 

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2. Mode-Dependent Effective Dielectric Constants of Inhomogeneous Dielectric Layers for PCB Applications

   https://doi.org/10.1109/TSIPI.2025.3558202  

   Li, Chaofeng; Mousavi, Mehdi; Mousavi, Seyed Mostafa; Asadi, Reza; Ye, Xiaoning; Kim, DongHyun (January 2025, IEEE Transactions on Signal and Power Integrity)

   The dielectric substrate of printed circuit boards (PCBs) generally consists of epoxy or polyurethane resin and fiberglass, which can be modeled as inhomogeneous dielectric layers (IDLs). IDLs are not homogeneous in the perpendicular direction of the layers’ interface, which means that they constitute an anisotropic material. Thus, the effective dielectric constant (Dk) for IDLs is direction dependent, i.e., mode dependent. In this study, the effective Dk values of IDLs are extracted for different modes using three commonly used full-wave simulation models: the transverse electric (TE), transverse magnetic (TM), and equivalent parallel-plate capacitor models. The results for the TE and TM modes showed a 10% discrepancy. The effective Dk of IDLs was efficiently estimated by the parallel-plate capacitor model based on the layers’ dielectric properties and thicknesses. Moreover, the analytical formulas of resonance frequency for a cylindrical cavity resonator filled with IDLs were derived to extract the effective Dk of the IDLs at different resonance modes, which could be used as a guideline of resonator methods for PCB material characterization. These results correlated with the results from the equivalent parallel capacitor model. Finally, the impact of IDL anisotropy on transmission line loss and time-domain reflectometry impedance was analyzed based on full-wave simulation. 

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3. Selective passive tuning of cavity resonance by mode index engineering of the partial length of a cavity

   https://doi.org/10.1364/OE.543323  

   Khurana, Mohit; Delfan, Sahar; Yi, Zhenhuan (January 2025, Optics Express)

   Cavities in large-scale photonic integrated circuits (PICs) often suffer from a wider distribution of resonance frequencies due to fabrication errors. It is crucial to adjust the resonances of cavities using post-processing methods to minimize the frequency distribution. We have developed a concept of passive tuning by manipulating the mode index of a portion of a microring cavity, which we named mode index engineering (MIE). Through analytical studies and numerical experiments, we have found that depositing a thin film of dielectric material on top of the cavity or etching the material enables us to fine-tune the resonances and minimize the frequency distribution. This versatile method allows for the selective tuning of each cavity’s resonance in a large set of cavities in a post-fabrication step, providing robust passive tuning in large-scale PICs. We show that the proposed method achieves a tuning resolution below 1/Q and a range of up to 10³/Q for visible to near-infrared wavelengths. Furthermore, this method can be applied and explored in various integrated photonic cavities and material configurations. 

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4. Temperature-dependent dielectric behavior of A 6 B 2O17 ( A  = Zr, Hf; B  = Nb, Ta) phases

   https://doi.org/10.1063/5.0219964  

   Spurling, R Jackson; Marakovits, Michael T; Hossain, Arafat; Almishal, Saeed_S I; Perini, Steven E; Lanagan, Michael T; Maria, Jon-Paul (August 2024, Applied Physics Letters)

   We report on temperature-dependent dielectric behavior of disordered ternary A6B2O17 (A = Zr, Hf; B = Nb, Ta)-form oxides in the GHz frequency range. The microwave dielectric properties including relative permittivity, dielectric loss, and temperature-dependent relative permittivity were characterized using cylindrical dielectric resonators using a resonant post measurement technique. Dielectric measurements through the resonant post method approach generally agree with dielectric measurements of A6B2O17 bulk ceramics measured through standard resonant post techniques. Coefficients describing the temperature-dependent relative permittivity for ternary A6B2O17 phases are strongly positive, suggesting contributions to polarizability arising from long-range mechanisms potentially associated with structural disorder. These observations support the working hypothesis that material functionality can be engineered by the chemical diversity and structural disorder possible in high configurational entropy A6B2O17 phases. 

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5. Extraction of DK glass and DK resin for PCB Striplines and Analysis of Far-End Crosstalk

   https://doi.org/10.1109/TSIPI.2025.3583657  

   Park, Junyong; Guo, Yuandong; Ye, Xiaoning; Kim, DongHyun (January 2025, IEEE Transactions on Signal and Power Integrity)

   Far-end crosstalk (FEXT) in typical high-speed printed circuit board striplines is primarily attributed to dielectric inhomogeneity. In this article, the inhomogeneity problem is comprehensively addressed by a novel algorithm that characterizes the dielectric constants (DKs) of glass fibers and epoxy resin. In contrast to other methods, the proposed approach enables one to assess the impact of geometrical parameters on stripline FEXT and to estimate DK core and DK prepreg based on DK glass and DK resin values extracted through analytical expressions. Full-wave simulations and real-board measurements are conducted to verify the proposed approach. 

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