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A compact integrated microstrip bandstop filter(BSF) with low cost magnetic nanoparticle thin film loaded in the air substrate has been designed, fabricated and characterized. First, an optimized microstrip BSF patterned on a thin Liquid Crystal Polymer (LCP) was mounted on a partially 3D printed air substrate through a lego-like process to have the rejection of 41 dB at 8.5 GHz. To achieve the compactness, various magnetic nanoparticles were deposited within the air substrate to have the magnetic film thickness of 30 µm and 100 µm, which gave the self-resonances of the BSFs from 7.6 GHz to 8.3 GHz. The filter can also operate at higher a center frequency with a rejection over 30 dB by applying an external DC magnetic bias of 2500 Oe that is normal to the filter. Detailed comparison of the filter performance in terms of types of magnetic materials, film thicknesses and magnetic bias strength is provided. This work demonstrates a low cost and compact BSF utilizing the magnetic nanoparticle film which could find many applications in RF and microwave circuits and devices.

A new stripline fabricated using MnFe 2 O 4 nanoparticle thick films is demonstrated to have multiband frequency selectivity and high attenuation range. Using the Solution Cast method, thick MnFe 2 O 4 nanoparticles films were fabricated on the $45\ \text{mm}\times \mathbf{14\ mm}$ Liquid Crystal Polymer (LCP) substrate to have an average film thickness of about $\mathbf{30}\ \mu \mathrm{m}$ , which was inserted into the trench area of the stripline. The stripline was measured over the frequency range of 0 – 18 GHz at four different RF input power levels spanning from −22 dBm to −7 dBm with a 5 dB steps. The Ferromagnetic Resonance (FMR) effects are observed when the DC magnetic field bias is applied to the stripline under all four power levels. In particular, the FMR effects appear successively within five frequency bands, namely 4 – 8 GHz, 5 – 10 GHz, 8 – 13 GHz, 12 – 16 GHz and 15 – 18 GHz, as the magnetic field strength increases. The exact FMR frequencies under specific magnetic bias strength can be located by calculating the absolute power absorption rate of the MnFe 2 O 4 nanoparticles. In addition, more attenuation is observed under stronger bias and the absolute power absorption increases as the RF input power gets larger. This work presents for the first time the characterization of thick MnFe 2 O 4 nanoparticle film in terms of the FMR effect using the 3D printed stripline structure, which can be used to fabricate the Frequency Selective Limiter (FSL) in a wide range of power-sensitive, broadband RF and microwave applications.

In this paper, cobalt ferrite (CoFe 2 O 4 ) magnetic nanoparticles were deposited as 5 μm thick films on soda lime glass substrates based on a new fabrication method. Coplanar Waveguide (CPW) transmission lines with a characteristic impedance close to 70 Ω were fabricated on samples with and without the magnetic thin films. Measurements show an increase in the group delay for the magnetic films samples commensurate with their thickness as compared to lines with no magnetic film. We simulate the CPW lines with the magnetic nanofilms, and estimate the relative permeability of the magnetic films by matching the simulation results with the measurements.

In this paper, the propagation characteristics of an enhanced-thickness magnetic nanoparticle thin film are investigated on high resistivity silicon substrate (10,000 ohm-cm) for the first time up to 60 GHz. Contrary to other thin films, this nanoparticle thin film can achieve a thickness up to several hundred nanometers, even to micron. The enhanced thickness of this thin film is achieved by repeated coating of CoFe 2 O 4 and poly, thus providing the thin film with the high permeability capable of potential practical wireless applications. Finite Ground Coplanar (FGC) waveguides are fabricated and characterized on silicon with the novel thin film. The measured attenuation and effective dielectric/magnetic constant are reported. Results show that the FGC waveguides with the thin film feature a lower attenuation compared to those on silicon for frequencies higher than 18 GHz. The extracted relative permeability has a value of 68 by matching of the effective dielectric/magnetic constant between simulation and measurement.

Spinel magnetic nanoparticle thin films were fabricated on high resistivity silicon substrates. TRL (through-reflect-line) calibration standards for CPW lines were fabricated on samples of high resistivity silicon with and without the magnetic thin film. Measurements show an increase of approximately 0.3 in the effective combined dielectric/magnetic constant for a film thickness of 100 nm. Capacitors are fabricated to determine the relative permittivity of the thin film. The relative permeability is determined using comparisons of the measured effective dielectric/magnetic constant with simulated data.