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Telecommunications through an electrically conductive medium require the use of carrier bands with very-low and ultralow frequencies to establish radiofrequency links in harsh environments. Recent advances in atomic magnetometers operating at very-low frequencies have facilitated the reception of digitally modulated signals. We demonstrate the transmission and reception of quadrature phase-shift keying (QPSK) signals using a multi-resonant loop antenna and atomic magnetometer, respectively. We report the measured error vector magnitude according to the symbol rate for QPSK modulation and analyze the bandwidth of a receiver based on the atomic magnetometer. The multi-resonant loop antenna noticeably enhances the bandwidth by over 70% compared with a single-loop antenna. QPSK modulation for a carrier frequency of 20 kHz and symbol rate of 150 symbols per second verifies the feasibility of demodulation, and the measured error vector magnitude and signal-to-noise ratio are 7.29% and 30.9 dB, respectively.

This letter presents the topology of a novel approach to magnetic communication using a giant magnetoimpedance (GMI)-based receiver with a GMI sensor in underwater media such as freshwater. In addition, practical channel test results for the magnetic communication link of a GMI receiver in freshwater are first presented. For this test, a magnetic communication system using a GMI-based receiver, including triangularly arranged transmission coil antennas, was proposed. Wireless digital communication using quadrature phase shift keying (QPSK), which is less sensitive to noise and has a high data rate, was used to evaluate the proposed GMI receiver. Several performance metrics, such as constellation, data rate, and error vector magnitude, were measured at 20 kHz. The test results were meaningful, indicating that the proposed magnetic communication system using a GMI-based receiver can be a promising solution for wireless communication in extreme environments, such as underwater media.

This paper presents the topology of a novel approach to magnetic communication using a differential magnetic induction (MI)-based receiver and a differential MI receiving sensor. In this paper, a differential MI sensor based on two ferromagnetic cores is proposed as a receiving sensor, unlike the air coil-type MI sensor in the conventional search coil sensor concept. This differential MI sensor has the advantages of ultra-high sensitivity characteristics of the pT/ $\surd $ Hz level, which can detect weak magnetic fields in magnetic communication; moreover, the sensor is smaller than a conventional air coil MI sensor. The proposed differential MI sensor contributes to improving sensor performance by increasing its signal-to-noise ratio. The design and fabrication of the proposed MI sensor were based on a printed circuit board (PCB). The pickup coil of the PCB-based MI sensor directly wound the pickup coil onto a ferromagnetic core composed of Ni-Zn ferrite material. To analyze the key factors that affected the performance of the receiver, the magnetic field-to-voltage conversion ratio (MVCR) and equivalent magnetic spectral density measurements of the proposed PCB-based MI sensor were performed. Wireless digital communication using quadrature phase shift keying (QPSK), which is less sensitive to noise and has a high data rate, was used to evaluate the proposed MI-based receiver. The transmitted and received waveforms were compared to confirm that the transmitted digital data were accurately received as a result of the final demodulation of the receiver. Additionally, several performance metrics, such as constellation and error vector magnitude, were measured. The results of the comprehensive analysis confirmed the applicability of the proposed differential MI-based receiver to a magnetic field.

In this paper, a deformed radiating element is proposed to design a comb-line array antenna for low sidelobe levels in the millimeter-wave band. To design the comb-line array antenna with a low sidelobe level, the use of the wide radiating elements for a relatively large radiation conductance is required. However, the conventional rectangular radiating element has transverse current flows on it, resulting in undesirable transverse radiation conductance for cross-polarization. On the contrary, in the proposed radiating element, which is implemented by cutting obliquely the connection part to the feeding line from a rectangular element, the radiations from the transverse currents cancel each other, and low radiation conductance for cross-polarization and dominant radiation conductance for co-polarization are achieved. A 17-element linear comb-line array antenna with the sidelobe below −20 dB is designed and measured at 79 GHz. Using the proposed radiating elements, we obtained the sidelobe level of −21.9 dB in the array, but the array using the conventional radiating elements shows the sidelobe level of −16.9 dB. This letter demonstrates the availability of the proposed element for the easy and accurate design of the comb-line array antenna with the low sidelobe level.

Given the interest of researchers for wireless communications in electromagnetic (EM) shadow areas, a magnetic field communication has emerged to overcome RF challenges based on magnetic permeability characteristics. However, magnetic field communication has the demerit of a short communication range. Considering this limitation, we have proposed the GMI sensor-based field receiver to obtain immunity to low-frequency noise and high sensitivity for extension of communication range in previous studies. Further, this paper designs a magnetic field communication system with a GMI sensor-based receiver including a transmitter. Even though the basic concept of magnetic field communication is taken from previous studies, this study conducts the different realization of the system with transmitter system and communication link. Besides, this paper proposes the experiment of magnetic field communication using a GMI sensor-based system to verify its applicability in the practical environment for the first time. Bit error rate (BER), spurious-free dynamic range (SFDR), and random noise are measured with an on-off keying (OOK) communication link to analyze the stability and reliability of the system. The experimental verification and analysis entail the conditions of communication distance and channel medium to mimic practical communication in atmospheric, underwater, and underground environments. A comprehensive analysis of the system design and experimental verification for application in a practical environment show the possibility of the proposed system to realize improved wireless communications in EM shadow areas.

This paper presents three types of phantom tests for non-invasive local thermotherapy using a 925 MHz phased array applicator. The microwave energy is focused at a depth of approximately 35 mm of the phantom with 100 W for 10 min. As a result, in the two cases focusing on the muscle area, the heating width is 23–31 mm (0.5–0.6 °C/mm) at the 10 °C rise point. On the other hand, when focusing on tumor area inside the bone, the maximum temperature rise is slightly less than 10 °C (0.3 °C/mm), and the surrounding temperature increases relatively more due to microwave reflections caused by the dielectric contrast between bone and muscle.

This paper presents a practical low-power, low-frequency magnetic induction (MI) transceiver based on symmetrical gaped two-loop antennas with an empirical circuit model for wireless underground communication. Because of the quasi-two-dimensional loop antennas for the transmitter (Tx) and the receiver (Rx), the tailored hardware platform is not only simple, but can be readily extended to a mutually orthogonal 3-D scheme. Through a mixed model of actual measurement data and theoretical parameters, we developed the two-loop antenna with the space of the antenna radius optimized for energy efficiency. The Tx power almost doubles that of the single Tx one, which provides channel expansion as well as system stability in terms of the Tx current level. Accordingly, the Rx signal is considerably increased by 9.5 dB in contrast with a typical single-Tx single-Rx configuration. Moreover, we used empirical-based modeling for a reliable electrical model. The empirical mutual inductance, which was modeled in a 25 m corridor, resulted in a channel correction factor of 0.86, showing that the signal intensity was reduced by 14% in the underground corridor compared to the free space. A maximum range of 68 m under a SNR of 9.5 dB and a path loss of 100.7 dB on a load of $50~\Omega $ at 34.5 dBm were predicted from the model. In addition, this study confirmed the system feasibility by a SNR of 8.7 dB in a practical lossy environment between two floors, where its value was converted into a MI channel at a distance of 70 m in the underground corridor.

Radio reception relies on the medium which determines the propagation characteristics of the electromagnetic fields carrying the information. The permittivity varies greatly depending on the medium, but it remains nearly constant, except when magnetic materials are used. For this reason, magnetic fields, typically affected by permeability, can be utilized in microwave challenging environments. In this paper, a new approach based on the giant magnetoimpedance (GMI) effect is presented. The proposed GMI-based receiver has an effective double-superheterodyne topology, where “effective” means that the receiver actually has a single mixer but appears to have added a virtual mixer due to the GMI effect. The magnetic field-to-voltage conversion ratio (MVCR), the spurious free dynamic range (SFDR) and the receiver sensitivity are characterized, and from these results the optimal operating conditions of the fabricated receiver are obtained. Additionally, wireless digital communication using on-off keying (OOK) is demonstrated and transmitted and received waveforms are compared, with the final demodulation result of the receiver showing that the transmitted digital data are precisely extracted.

This article presents a new application field of a giant magneto-impedance (GMI) sensor. It shows valuable findings for the GMI sensor on the possibility of a new receiving element in magnetic field communication. The proposed GMI sensors serve as antennas and mixers in receiver systems. They have the advantage of being easily implemented and in terms of mass production and manufacturing processes due to the manufacture base on a printed circuit board (PCB). Their smaller size, lower cost, and higher sensitivity have more advantages than conventional magnetic sensors, such as the magneto-inductive, anisotropic magneto-resistive, and giant magneto-resistive sensors. Two types of PCB-based GMI sensors are proposed. The first type of GMI sensor is directly wound around the solenoid-shaped pickup coil onto an alumina insulation tube inserted with an amorphous microwire. The second type of GMI sensor has a patterned pickup coil that does not require the winding of the coil, similar to the patterned pickup coil of a micro electro-mechanical system-based GMI sensor. This GMI sensor provides a new geometry that can be easily manufactured with two PCB substrates. The proposed GMI sensors achieve the equivalent magnetic noise spectral density to the high-sensitivity characteristics of the pT/√Hz level. The equivalent magnetic noise spectral density of 1.5 pT/√Hz at 20.03 MHz is obtained for the first type of GMI sensor, and 3 pT/√Hz at 3.03 MHz is achieved the second type. The analyzed results of the bandwidth and the channel capacity for the two types of GMI sensors are acceptable. This first analysis confirms the possibility of the implementation of GMI sensors in magnetic field communication. The results of this experiment confirm the high performance of the proposed GMI sensors and their applicability in magnetic field communication. The detailed experimental results of the proposed GMI sensors are presented and discussed.

This work investigated three‐dimensional (3D) focused microwave thermotherapy (FMT) at 925 MHz for a human tissue mimicking phantom using the time reversal (TR) principle for musculoskeletal disorders. We verified the proposed TR algorithm by evaluating the possibility of 3D beam focusing through simulations and experiments. The simulation, along with the electromagnetic and thermal analyses of the human tissue mimicking phantom model, was conducted by employing the Sim4Life commercial tool. Experimental validation was conducted on the developed FMT system using a fabricated human tissue mimicking phantom. A truncated threshold method was proposed to reduce the unwanted hot spots in a normal tissue region, wherein a beam was appropriately focused on a target position. The validation results of the simulation and experiments obtained by utilizing the proposed TR algorithm were shown to be acceptable. Effective beam focusing at the desired position of the phantom could be achieved.

This study is a computational study on focused microwave thermotherapy for knee pathological treatment using the time reversal (TR) principle in musculoskeletal disorders. The authors presented a modified TR algorithm with amplitude compensation for an accurate beam focusing of the knee tumour location in a lossy medium. Furthermore, they proposed a new approach called the truncated threshold method, which could be used to apply an effective beam focusing on a tumour location in the knee while the unwanted hot spots are controlled in the normal tissue region. Compared to the other existing methods, this new approach has the advantages of being implemented simply in the unwanted hot spot control and having a similar performance to the beam focusing on the target location. The application of the proposed algorithm and the new hot spot control method to knee pathological tissue achieved acceptable electromagnetic (EM) and thermal results. The anatomical based two- dimensional (2D) knee model for the simulation analysis was implemented using a segmentation result of the Korean human body model obtained from magnetic resonance imaging. 2D finite-difference time-domain electromagnetic and thermal solvers were developed and applied to conduct the 915 MHz focused microwave thermotherapy for knee pathological treatment. [ABSTRACT FROM AUTHOR]

This paper presents an experimental measurement system for 3-6 GHz microwave tomography (MT) of the breast. The measurement system is constructed as a minimal test bed to verify key components such as the sensing antennas, radio frequency (RF) transceiver, sensing mechanism, and image reconstruction method for our advanced MT system detecting breast cancer at an early stage. The test bed has eight RF channels operating at 3 to 6 GHz for high spatial resolution and a two-axis scanning mechanism for three-dimensional measurement. The measurement results from the test bed are shown and discussed. [ABSTRACT FROM AUTHOR]

A sensing probe for medical imaging diagnostic systems is presented. The proposed probe consists of a double-ridged waveguide (DRWG) filled with dielectric ceramic and an aperture with a tapered ridge. The DRWG is used to suppress higher-order mode radiations in the rectangular waveguide. The proposed probe is designed for broadband sensing in an immersion liquid with a complex dielectric constant. The performance of the fabricated probe successfully covers the frequency band of 3-6 GHz. The probe suppresses higher-order modes and provides symmetric and similar radiation patterns within the operating frequency range. [ABSTRACT FROM AUTHOR]