Nonlinear magnetoelectric effects in Al-substituted strontium hexaferrite

This report is on the observation and theory of electric field E induced non-linear magnetoelectric (NLME) effects in single crystal platelets of ferrimagnetic M-type strontium aluminum hexagonal ferrite. Using microwave measurement techniques, it was found that a DC electric field along the hexagonal c-axis results in significant changes in the saturation magnetization and uniaxial magneto-crystalline anisotropy field and these changes are proportional to the square of the applied static electric field. The NLME effects were present with or without an external bias magnetic field. The E-induced variation in magnetic order parameters is attributed to weakening of magnetic exchange and spin–orbit interactions since conduction electrons in the ferrite are effectively excluded from both interactions while being in transit from one Fe ion to another. We present a phenomenological theory which considers magneto-bielectric effects characterized by a quadratic term in electric field E in the free energy density. The coefficients for the NLME coupling terms have been calculated from experimental data and they do show variations with the Al substitution level and the largest rates of change of the saturation magnetization and anisotropy constant change with the applied power were observed for x = 0.4. It was also clear from the study that strength of the NLME effect does not depend on the amount Al substitution, but critically depends on the electrical conductivity of the sample with the highest NLME coefficients estimated for the sample with the highest conductivity. Results of this work are of importance for a new family of electric field tunable, miniature, high frequency ferrite devices.

Developments and Recent Progresses in Microwave Impedance Microscope

Microwave impedance microscope (MIM) is a near-field microwave technology which has low emission energy and can detect samples without any damages. It has numerous advantages, which can appreciably suppress the common-mode signal as the sensing probe separates from the excitation electrode, and it is an effective device to represent electrical properties with high spatial resolution. This article reviews the major theories of MIM in detail which involve basic principles and instrument configuration. Besides, this paper summarizes the improvement of MIM properties, and its cutting-edge applications in quantitative measurements of nanoscale permittivity and conductivity, capacitance variation, and electronic inhomogeneity. The relevant implementations in recent literature and prospects of MIM based on the current requirements are discussed. Limitations and advantages of MIM are also highlighted and surveyed to raise awareness for more research into the existing near-field microwave microscopy. This review on the ongoing progress and future perspectives of MIM technology aims to provide a reference for the electronic and microwave measurement community.

The Performance Comparison of a Dual-Ridge Horn Antenna and a Planar Monopole Antenna in the Microwave Breast Cancer Detection

Detection of the breast cancer tumors at an early stage is very crucial to be successful in the treatment. Microwave measurement systems have gained much attention for this aim over last decades. The main principle of these systems is based on the significant difference in the dielectric properties of the malignant tumor and normal breast tissue in the microwave frequencies. In this paper, firstly several breast cancer detection techniques are mentioned. Then the advantages of the using microwaves in the detection systems are given. After that, some simulation and experimental studies of the radar-based ultra-wideband microwave measurement system are presented to detect tumor. The main purposes of these measurements are comparing the performance of a previously designed planar monopole antenna (PMA) with a dual-ridge horn (DRH) antenna and demonstrating a simple microwave breast cancer detection system. In the system, a planar breast phantom which is consisted of low dielectric constant material to represent the healthy tissue and high dielectric constant material to represent the tumor is used. Firstly, the measurements are made without tumor in the phantom. Then, the tumor-mimicking object is located to the phantom. In the measurements, both the PMA and DRH antennas are used respectively. These antennas are ultra-wideband and directional. They have narrow beamwidth and stable directional pattern at the interval of 3-10 GHz. According to the return loss results, the reflected energy increases when the antenna gets close to the tumor. Therefore, it can be said that the scattering parameters give important information about the tumor. According to the obtained results in this study, it can be said that the performance of the compact-sized PMA is better than the DRH antenna having larger size.