“…(a) Bruggeman EMA correction (b) Maxwell-Garnett EMA correction (c) Simple Volume correction -permittivity and permeability divided by the relative volume of the MUT as compared to volume without an air-gap. (ii) A capacitive correction which uses each interface between the layers of material and air with the assumption that each layer behaves in a similar fashion to series capacitors (permittivity) [18] and/or inductors (permeability) [19].…”
Section: Air-gap Correction Methodsmentioning
confidence: 99%
“…where r out , r in , and * are the outer radius, inner radius, and complex permittivity of the homogenous line. Inner and outer air-gaps can be analyzed and modeled as series capacitance [19,21] as shown in Fig. 5, which gives the effective capacitance of a transmission line with an air-gap as…”
Measurements of the complex permittivity and permeability of solids at high electromagnetic field greater than 10 kV/m pose a significant challenge to RF connectors and input amplifiers of the measurement equipment. Specifically, difficulties arise in measuring materials with high imaginary permittivity or low impedance, which act as short circuits, either exceeding the measurement equipment damage threshold or that of the material under test, and/or inducing an unacceptable signalto-noise in the collected data. In this work, we report the development of a new measurement technique where we introduce an outer air-gap between the material under test and the conductor of a coax airline. The introduced air-gap reduces the effective conductivity of the sample, mitigating damage to the materials under test and allowing for high power measurement. This study compares the ability of air-gap correction methods to recover the complex permittivity and permeability to within 10% of the value measured without an air-gap introduced.
“…(a) Bruggeman EMA correction (b) Maxwell-Garnett EMA correction (c) Simple Volume correction -permittivity and permeability divided by the relative volume of the MUT as compared to volume without an air-gap. (ii) A capacitive correction which uses each interface between the layers of material and air with the assumption that each layer behaves in a similar fashion to series capacitors (permittivity) [18] and/or inductors (permeability) [19].…”
Section: Air-gap Correction Methodsmentioning
confidence: 99%
“…where r out , r in , and * are the outer radius, inner radius, and complex permittivity of the homogenous line. Inner and outer air-gaps can be analyzed and modeled as series capacitance [19,21] as shown in Fig. 5, which gives the effective capacitance of a transmission line with an air-gap as…”
Measurements of the complex permittivity and permeability of solids at high electromagnetic field greater than 10 kV/m pose a significant challenge to RF connectors and input amplifiers of the measurement equipment. Specifically, difficulties arise in measuring materials with high imaginary permittivity or low impedance, which act as short circuits, either exceeding the measurement equipment damage threshold or that of the material under test, and/or inducing an unacceptable signalto-noise in the collected data. In this work, we report the development of a new measurement technique where we introduce an outer air-gap between the material under test and the conductor of a coax airline. The introduced air-gap reduces the effective conductivity of the sample, mitigating damage to the materials under test and allowing for high power measurement. This study compares the ability of air-gap correction methods to recover the complex permittivity and permeability to within 10% of the value measured without an air-gap introduced.
“…To obtain measurements of ε and especially μ for films such as those shown in figure 3 b over a range of microwave frequencies can be difficult. However, an approach has been developed in which films can be tightly wound on a central spool to form a ring shape, which is then inserted snugly into a coaxial line measurement arrangement [ 26 ]. Winding is usually done by hand but results in entrapped air gaps between layers of dielectric that subsequent density measurements, for example by a water displacement method, suggest may occupy up to 20 vol%.…”
Section: Processing Techniquesmentioning
confidence: 99%
“…Although this coaxial arrangement is simple and allows ready measurement of reflection and transmission behaviour of the film across a broad band of frequencies, it is necessary to apply analysis or a model that accounts for these inevitable air gaps. Figure 4 shows data in the frequency range 30 MHz to 10 GHz from an elastomeric film containing magnetic Fe flakes similar to the film in figure 3 b but with a stronger magnetic response, and where the measured permeability has been adjusted using an analytical layered capacitor model that considers the arrangement as alternating concentric rings of dielectric composite and air, and accounts for the presence of 12 vol% air gaps [ 26 ]. Figure 4.…”
Spatial transformations (ST) provide a design framework to generate a required spatial distribution of electrical and magnetic properties of materials to effect manipulations of electromagnetic waves. To obtain the electromagnetic properties required by these designs, the most common materials approach has involved periodic arrays of metal-containing subwavelength elements. While aspects of ST theory have been confirmed using these structures, they are often disadvantaged by narrowband operation, high losses and difficulties in implementation. An all-dielectric approach involves weaker interactions with applied fields, but may offer more flexibility for practical implementation. This paper investigates manufacturing approaches to produce composite materials that may be conveniently arranged spatially, according to ST-based designs. A key aim is to highlight the limitations and possibilities of various manufacturing approaches, to constrain designs to those that may be achievable. The article focuses on polymer-based nano- and microcomposites in which interactions with microwaves are achieved by loading the polymers with high-permittivity and high-permeability particles, and manufacturing approaches based on spray deposition, extrusion, casting and additive manufacture.
“…In contrast, measurements with coaxial transmission lines allow broadband measurements with a single sample, typically up to 18 GHz [5]- [7], but the toroidal shape of the sample causes difficulty in fabrication. The toroidal shape also causes difficulty in ensuring that there are no air gaps in between the conducting core and the circular inner sample boundary; however, it is possible to compensate for such air gaps in coaxial measurements by considering a coaxial capacitor model [8]- [10]. By comparison, the planar stripline geometry may cover a wide frequency band with a single sample and a simple geometry.…”
We present a stripline design and calibration method allowing the extraction of relative permittivity of single dielectric samples in the 200-MHz-50-GHz range. The simultaneous extraction of relative permittivity and permeability is also illustrated by characterizing a set of samples comprising magnetic inclusions over the same frequency range. The calibration method involves the use of seven measurements of the stripline scattering parameters (S-parameters) with different length shorts inserted. From these measurements, it is possible to determine the reflections at the transition regions of the stripline to correct the measured S-parameters for characterization. By quantifying a range of samples with increasing percentage volume filling of barium titanate in polyurethane for the case of dielectric samples, and carbonyl iron powder for magnetic samples, this paper demonstrates a reliable method for the broadband characterization of composite materials.
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