Xiao-Chuan Wang

A Compact Dual-Band Filter with Close Passbands using Asymmetric λ/4 Resonator Pairs with Shared Via-Hole Ground

A novel asymmetric λ/4 resonator pairs with shared via-hole ground is proposed, which is composed of two different λ/4 resonators that share the same via. Compared with traditional λ/2 stepped impedance resonators (SIRs) and λ/4 SIRs, the asymmetric λ/4 resonator pairs can realize flexible passband allocation and size reduction when it is utilized to design multi-band filters, especially for the multi-band filters with close dual passbands. To verify the presented concept, one experiment example of filter with a dual-band Chebyshev response operating at 2.4, 3.6 GHz has been designed and fabricated. The measured results are in good agreement with the full-wave simulation results.

Novel ZnAl2O4-Based Microwave Dielectric Ceramics with Machinable Property and its Application for GPS Antenna

(1−x)(0.79ZnAl 2 O 4 -0.21Mg 2 TiO 4 )-xSrTiO 3 microwave dielectric ceramics with proper machinable properties were prepared by the solid-state process. The effects of SrTiO 3 on the microstructures and microwave dielectric properties of the 0.79ZnAl 2 O 4 -0.21Mg 2 TiO 4 ceramics were investigated. A typical machinable microwave dielectric ceramics was synthesized with ϵ r = 10.6, Q • f of 55000 GHz and τ f of +9.3 ppm/°C when x is about 0.05. The mechanical properties and thermal properties of these ceramics were also presented including flexural strength, compressive strength and thermal expansion coefficient. Afterwards, a microstrip antenna for GPS with several via holes was designed and measured. Experimental results showed that the antenna operated at 1.57 GHz with an impedance bandwidth of 3% (VSWR ≤ 2), and satisfied axial ratio was obtained.

Dielectric and ferroelectric behavior of an incipient ferroelectric Sr(1−3x/2)CexTiO3 novel solid solution

Phase formation, chemical structure, microwave (MW) dielectric properties, and relaxor-to-ferroelectric phase transition behavior of a novel solid solution with Ce-doped, A-site SrTiO3 (Sr(1−3x/2)CexTiO3) ceramic sintered in nitrogen have been investigated. X-ray diffraction (XRD) showed that the samples with x ≤ 0.3 appeared cubic but exhibited splitting and superstructure reflections consistent with tetragonal (0.4 ≤ x ≤ 0.45) and orthorhombic (0.5 ≤ x ≤ 0.6) structures. Chemical structure analysis revealed that the addition of small amounts of ceria (x ≤ 0.3) promoted Ti3+ cation and oxygen vacancy . By contrast, the addition of large amounts of ceria (x ≥ 0.4) inhibited this process. Sr(1−3x/2)CexTiO3 ceramics displayed frequency-dependent relaxor dielectric anomalies and frequency-independent normal ferroelectric behaviors. The relaxor/dielectric properties were strongly dependent on structure-chemical factors. The value of er decreased several times when Sr was subsequently substituted with Ce, and induced a relaxor-to-ferroelectric phase transition. A good combination of the following microwave dielectric properties was obtained for the Sr0.1Ce0.6TiO3 orthorhombic solid solution at an optimum temperature of 1300 °C for 3 h: er = 50, Q × f = 11 311 GHz, and τf = +3 ppm per °C.

Improved dielectric properties of Ag@TiO2/PVDF nanocomposites induced by interfacial polarization and modifiers with different carbon chain lengths

In this study, poly(vinylidene fluoride) (PVDF)-based nanocomposites filled with surface-functionalized Ag@TiO2 core-shell nanoparticles were fabricated in order to achieve high dielectric permittivities. Using two phosphonic acid surfactants with differing carbon chain lengths, octyl and octadecyl phosphonic acid, the filler surfaces were modified to improve the dispersion of the core-shell filler in PVDF. The experimental results showed that the dielectric constant of the composite with fillers modified using octyl phosphonic acid (148 at 1 kHz) was almost three times that of the material with fillers modified using octadecyl phosphonic acid (58 at 1 kHz) at the same filler loading. The mechanisms of interfacial polarization between the modified core-shell filler and the polymer matrix were analyzed by introducing a circuit model based on AC impedance spectroscopy.In this study, poly(vinylidene fluoride) (PVDF)-based nanocomposites filled with surface-functionalized Ag@TiO2 core-shell nanoparticles were fabricated in order to achieve high dielectric permittivities. Using two phosphonic acid surfactants with differing carbon chain lengths, octyl and octadecyl phosphonic acid, the filler surfaces were modified to improve the dispersion of the core-shell filler in PVDF. The experimental results showed that the dielectric constant of the composite with fillers modified using octyl phosphonic acid (148 at 1 kHz) was almost three times that of the material with fillers modified using octadecyl phosphonic acid (58 at 1 kHz) at the same filler loading. The mechanisms of interfacial polarization between the modified core-shell filler and the polymer matrix were analyzed by introducing a circuit model based on AC impedance spectroscopy.

Preparation of Ni/PZT core-shell nanoparticles and their electromagnetic properties

The Ni nanoparticles coated with Pb(Zr,Ti)O3 (PZT) were synthesized by a sol-gel method and in situ reaction. And their structure, oxidation resistance, and electromagnetic properties were investigated. The X-ray diffraction patterns (XRD) exhibited that a small amount of impure phase characterized to Ni(OH)2 was detected from the ammonia-treated Ni nanoparticles and the ammonia-treated Ni nanoparticles coated with PZT. After being pre-treated with aqueous ammonia, the PZT coating layer was more uniform and about 10 nm in thickness. The oxidation resistance of the ammonia-treated Ni nanoparticles coated with PZT, compared with that of the non-treated ones, was improved by about 66 °C. The PZT shell layer prepared by in-situ reaction can greatly reduce the dielectric constant and improve the natural resonance loss at high frequency, so as to obtain the optimal impedance matching performance of the electromagnetic wave transmission.

Folded Feedthrough Multilayer Ceramic Capacitor EMI Filter

A chip three-terminal multilayer ceramic capacitor (MLCC) electromagnetic interference (EMI) filter with a good stopband characteristic was designed. Parasitic effects on the internal signal electrode, including equivalent parallel capacitance and series inductance, were utilized to form a tunable transmission zero in stopband by folding the traditional chip three-terminal feedthrough MLCC. Based on a network theory, an equivalent circuit was constructed in ADS to explain the operating mechanism of the proposed structure. The ADS and HFSS were utilized to simulate the proposed structure, and the measured results corresponded to the simulation results. The structure of the proposed EMI filter presents a new method to improve the stopband characteristic of capacitor EMI filters.

High field dielectric property and piezoelectric response in PMS-PZT piezoelectric ceramics modified with BiFeO3

ABSTRACT The piezoelectric ceramic Pb0.98Sr0.02(Mn1/3Sb2/3)0.05Zr0.48Ti0.47O3+0.25 wt%CeO2 modified with BiFeO3 was synthesized by conventional ceramics technology and the high field dielectric property was investigated. The XRD patterns show that BiFeO3 can be commendably dissolved into the PMS-PZT solid solution. Bi3+ replacement for A-site Pb2+ and Fe3+ replacement for B-site Ti4+ or Zr4+ cause BiFeO3 to act as “soft” and “hard” dopant. Therefore, an appropriate amount of BiFeO3 enhances the piezoelectric properties and high field dielectric properties simultaneously. The ceramic modified with 0.2 mol% BiFeO3 exhibited the following optimal properties: d33 = 359pC/N, kp = 0.622, Qm = 1519, ϵr = 1760, tanδ = 0.46% (1 kHz, 1V/mm), and tanδ = 3.26% (1 kHz, 500V/mm).

High permittivity and near-zero τε dielectrics Ca0.36Sr0.64TiO3–Li0.5Nd0.5TiO3 for multilayer ceramic capacitors

The microstructure and dielectric properties of (1 − x)Ca0.36Sr0.64TiO3–xLi0.5Nd0.5TiO3 (0 ≤ x ≤ 1) [abbreviated as (1 − x)CST–xLNT] solid solutions were investigated in this study. X-ray diffraction results showed that the samples exhibited a single cubic phase with x ≤ 0.5, whereas increasing LNT content resulted in a structural change from cubic to tetragonal phase in when x > 0.5. The permittivity (er) decreased with increasing x, while the dielectric loss (tan δ) increased and then decreased at x = 1.0. The temperature dependence of er and tan δ at 1 MHz for the (1 − x)CST–xLNT ceramics was also investigated. The temperature coefficient of the permittivity (τe) increased from highly negative values to positive values with increasing x. A near-zero τe was achieved at x = 0.57. Optimised dielectric properties were estimated to be er = 227, tan δ = 0.043 and τe = 12 ppm/°C. Therefore, the 0.43CST–0.57LNT ceramic is proposed as a promising candidate material for multilayer ceramic capacitors with good temperature stability and high capacitance.

Nonuniform meander-line monopole antenna with back-coupled patch for WLAN applications

In this letter, we present a planar nonuniform meander-line monopole antenna (NUMMA) with a back-coupled patch (BCP) for WLAN applications in IEEE 802.11a/b/g systems. Effects of the BCP on the resonant and radiation characteristics of the NUMMA are analyzed. Measured and simulated values of return loss and radiation patterns have been obtained. Good impedance bandwidth and omni-directional radiation performance have been observed.

A microwave ceramic band-pass filter for mobile communications with new coupling structure

A surface mounted device (SMD) microwave ceramic band-pass filter for mobile communication with a new coupling structure is reported in this paper. In this filter, the external and internal coupling structures are fabricated on an alumina substrate and both resonators and coupling structures are placed into a metal house to cut off its radiation. The relationship between the coupling structures and the performance of filter is analyzed by high frequency structure software (HFSS) and the filter with the center frequency of 836.5 MHz, the bandwith of 40.0 MHz, the pass-band ripple of 0.1 dB and the insertion loss of 1.5 dB has been successfully designed and fabricated. The measured results show a good agreement with the simulation results.