Xiaoxi Zhong

Structural, magnetic and electrical properties in Al-substitued NiZnCo ferrite prepared via the sol–gel auto-combustion method for LTCC technology

Al-substituted NiZnCo ferrite, Ni0.4Zn0.5Co0.1AlxFe2−xO4 (0 ≤ x ≤ 0.20), were synthesized by the sol–gel auto-combustion method. The effects of Al substitution on the structural, magnetic and electrical properties have been investigated. The X-ray diffraction patterns show that the lattice parameter decreases with the increase of Al substitution. The SEM images show that the grain size decreases with the increase of Al substitution. The initial magnetic permeability reaches the maximum value when Al substitution is 0.05. The resonance frequency is inversely proportional to initial magnetic permeability which obeys Snoeks law. The temperature coefficient reaches the maximum value when Al substitution is 0.05, and it has the minimum value when Al substitution is 0.20. The Curie temperature decreases with the increase of Al temperature due to the number of nonmagnetic Al3+ ions increase results in the decrease of superexchange interaction. The saturation magnetization and coercivity of the ferrite decrease linearly with the increase of Al substitution. The real dielectric constant of Ni0.4Zn0.5Co0.1AlxFe2−xO4 ferrite decreases exponentially as frequency increases, and the dielectric constants decrease with the increase of Al substitution. The direct-current resistivity decreases and follows an exponential decay with the increase of temperature, and it increases with Al substitution.

Diagnosis of Coupled Resonator Bandpass Filters Using VF and Optimization Method

This paper presents a hybrid method combining a vector fitting (VF) and a global optimization for diagnosing coupled resonator bandpass filters. The method can extract coupling matrix from the measured or electromagnetically simulated admittance parameters (Y -parameters) of a narrow band coupled resonator bandpass filter with losses. The optimization method is used to remove the phase shift effects of the measured or the EM simulated Y -parameters caused by the loaded transmission lines at the input/output ports of a filter. VF is applied to determine the complex poles and residues of the Y -parameters without phase shift. The coupling matrix can be extracted (also called the filter diagnosis) by these complex poles and residues. The method can be used to computer-aided tuning (CAT) of a filter in the stage of this filter design and/or product process to accelerate its physical design. Three application examples illustrate the validity of the proposed method.