Mahmut Obol

Nano Ferrites Microwave Complex Permeability and Permittivity Measurements by T/R Technique in Waveguide

There is a huge demand to accurately determine the magnetoelectrical properties of particles in the nano-sized regime due to the modern IC technology revolution and biomedical applications. In this paper, we present a microwave waveguide measurement technique for measuring complex permeability and permittivity of expensive nano-sized magnetic powder materials. We used a vector network analyzer to provide a standard TRL calibration for free space inside waveguide measurements. In order to maintain the recommended insertion phase range, a very thin prepared sample was loaded inside the calibrated waveguide. The loaded materials magnetic and dielectric effects were also considered in the cutoff wavelength calculation of the propagation constant of the TE10 wave from the geometrical dimensions of the waveguides. These provisions make the permeability and permittivity measurements more reliable than those found by commonly used techniques. We used six different compounds of nano-sized ferrite powders (Fe3O4, CuFe2O4, CuFe2O4Zn, F12NiO3Zn, BaFe12O19, and SrFe12O19), in which the average diameter of nano particles is less than 40 nm, for measurement purposes. We measured the complex permeability and permittivity from 3.95 to 5.85 GHz. The results show that the dielectric permittivity of these materials is quite different from that of solid-state materials.

High Frequency Dielectric Characteristics of Tumorous and Non-tumorous Breast Tissues

The broadband dielectric properties of tumorous and non-tumorous tissues were analyzed at the microwave, millimeter wave, and terahertz ranges. In-vitro measurements were obtained using the coaxial probe and dispersive Fourier transform spectroscopy. Both techniques were modified to yield the complex real and imaginary permittivity, absorption coefficient, and refractive index. The results reveal the characteristic signatures of breast tissues and display a significant difference in the electromagnetic response of tumorous and non-tumorous tissues.

Using Coaxial Probe for Broadband Microwave Characterization of Biological Tissues

A key advantage of using coaxial probe for microwave characterization of biological media is the non-invasive nature of the technique. It is being used extensively for the complex permittivity measurements of materials in the microwave region. Usually, coaxial probe measurements require electromagnetic full-wave analysis or a calibrated reflection coefficient, S11, of the material under test. In this paper, we present a new coaxial probe technique for the microwave characterization of biological tissues based on the calibrated reflection coefficient S11 of a know dielectric constant. This technique only needs the well known distilled water as a reference material for the broadband microwave characterization of biological tissues. The complex permittivities of normal tissues from animals and both normal and cancerous tissues from human bodies were measured over a broadband microwave region with this technique. The biological tissue measurements showed that the complex permittivities measured by this technique are in good agreement with other investigations. This is a cost effective, non invasive and easy to use technique which makes it very suitable for diagnostic and therapeutic applications of microwaves in biomedicine.

Microwave permittivity and permeability properties and microwave reflections of micro/nano ferrite powders

The application of magnetic powders are becoming attractive in electromagnetic shielding interferences in wireless systems. Magnetic powders such as Fe₃O₄ are also very important in magnetic resonance imaging as well as drug delivery applications in biomedical researches. Also, some of the special catalyst nano magnetic particles are increasingly useful in the fuel cell applications. Hence, a good understanding of the electromagnetic wave response such as permittivity and permeability of magnetic powders may be important in modern microwave technological applications. In this paper we present broad-band measurements on the real and imaginary parts of permeability and permittivity of micron sized commercial nickel ferrites of Ni_1-x-yCo_xCu_yFe_2-z-dMn_zO₄ (TT2) and Ni_1-xZn_xFe_2-yMn_yO₄ (TT86) in the frequency range from 4 to 40 GHz. We also present broadband permeability and permittivity of some other commercially available nano and micron sized ferrite powders, so that this is a paper that explores microwave properties of nine different nano and micron sized magnetic powders in terms of permittivity and permeability aspects.

Simultaneous Permittivity and Permeability Characteristics of Magnetically Biased Thin Ferrite Disk Using Rectangular Waveguide

In this paper, a novel rectangular waveguide-based technique to accurately characterize linear and resonant microwave materials is presented. The proposed method resolves major challenges associated with phase ambiguities and guess parameters that have appeared in waveguide techniques reported thus far and establishes new, accurate formulations for simultaneous calculations of complex permittivity and permeability of microwave materials and systems under tests. It is shown that the proposed method works very accurately by presenting results obtained for linear materials of reasonable thickness and resonant non-reciprocal microwave systems. In doing so, the permittivity fluctuation is observed by such first research due to the ferromagnetic resonance of ferrites; here it is attributed to an induced voltage from the uniform flow of angular momentum in excited ferrites and this phenomenon is deemed as a distinct source of voltage from excited ferrite at room temperature for technologies.

Broadband absorbing material design and optimization of cavity-backed, two-arm Archimedean spiral antennas

In recent years, considerable interest has been placed on developing cavity-backed broadband antennas that retain their bandwidth performance despite having frequency-dependent lossy materials added to their cavities. Spiral antennas, especially Archimedean spiral antennas operating in the 2–18 GHz spectrum, are one of the most popular of these antennas, as they are very well-suited to a wide range of commercial, military and private applications where bandwidths of as much as 100:1 are desired. In most cases, a unidirectional pattern is preferred to detect reflections from or transmit towards one direction only. Therefore, a metallic cavity is added to absorb the back wave completely. Hence it becomes necessary to insert absorbing materials in the cavity that can effectively absorb EM energy over a wide range of desired frequencies.

Determination of negative permeability and permittivity of metal strip coated ferrite disks using the transmission and reflection technique

In this paper, a full band microwave isolator constructed from an array of metal wire-coated ferrite samples is presented. Here, the magnetic permeability of the metamaterialized structure is controlled by a relatively weak external magnetic field. The tunable permeability of the ferrites in this experiment allows us to create unidirectional wave propagation through the structure over the entire X-band frequency spectrum. The analysis presented here takes into account potential surface plasmon modes generated between the gaps of metal wires when the external magnetic field is applied. Here, we present a modification of the traditional transmission-reflection measurement method by normalizing the transmission and reflection coefficients. This modification removes the occurrence of atypical phenomena for negative imaginary components of permeability and permittivity that arises in the measurement of metamaterials. Our modified method precisely determines the refractive index, impedance, permittivity, and pe...

Direct broadband microwave characterization of biological tissues using the coaxial probe technique

A key advantage of using coaxial probe for microwave characterization of biological media is the non-invasive nature of the technique. The complex permittivities of normal tissues from animals and both normal and cancerous tissues from human bodies were measured over a broadband microwave region with this technique. The biological tissue measurements showed that the complex permittivities measured by this technique are in good agreement with other investigations. This is a cost effective, non invasive and easy to use technique which makes it very suitable for diagnostic and therapeutic applications of microwaves in biomedicine.

The use of microwave, millimeter wave and terahertz spectroscopy for the detection, diagnostics and prognosis of breast cancer

We have analyzed the broadband dielectric properties of cancerous and non-cancerous tissues were analyzed at the microwave, millimeter wave, and terahertz frequencies. In-vitro measurements were obtained using the vector network analyzer-based coaxial probe (2 - 50 GHz), backward-wave oscillator-based free space quasi-optical spectroscopy (30-120 GHz), and dispersive Fourier transform spectroscopy methods (60 -1.5 THz). All three techniques were modified to yield the complex real and imaginary permittivity, absorption coefficient, refractive index, and transmission data over an extended frequency range from 2 GHz to 1,500 GHz. The results reveal the characteristic signatures of breast tissues and display a significant difference in the electromagnetic response of cancerous (malignant) and non-cancerous (benign) tissues. All three techniques provide prospects for extending in-vitro measurements to in-vivo breast cancer detection and diagnostics.

Wireless Sensor Using High Q Resonator of Single Walled Carbon Nanotube for Liquids

Carbon nanotubes are an interesting material, in which the single walled carbon nanotube (SWCNT) can have a high microwave dielectric permittivity and a high conductivity as well. The resonators of the SWCNT were reported as gas sensors in the past. In this paper, we present a wireless sensing property of SWCNT resonators for liquids such as water and alcohols. In the experiments, it was noted that the central resonances frequencies of those excited modes in the resonator of the SWCNT were slightly moved when seeing the water and alcohol, respectively.