An implantable magneto-electric antenna (IMEA) aiming for operation at ultra-wideband (UWB: 3.1-10.6 GHz) frequency spectrum is presented for biotelemetry usages for the first time. The IMEA is composed of a horizontal planar bowtie radiator, from whose middle the antenna is excited, and a vertically inclined rectangular radiator. The two radiators are complementary and correspond to electric and magnetic dipoles, respectively. The radiators are built over a square dielectric material (εr = 6, σ =0.0005) with a cavity for embedding suitable accompanying circuitry system. The IMEA with its biocompatible insulator (PEEK: εr = 3.2, tan δ = 0.01) measures 1456 mm3 in volume. HFSS software was used to carry out numerical optimization of the IMEA with a simple multilayered model of body tissue (Skin, Fat and Muscle) as the host environment. The simulated result of the proposed IMEA shows over 90% impedance bandwidth (S11<-10 dB) and records a remarkable high gain of 2 dBi within 70% bandwidth. The radiation efficiency is around 50%, and a unidirectional radiation pattern with little back lobe is observed.
In this paper, we present a compact tri-band bandpass filter (BPF) using two stub-loaded dual mode resonators (SLDMRs) combined with intra-coupled internal resonators. The designed filter operates at 1.575, 2.4, and 3.45 GHz, corresponding to the GNSS, WLAN, and WiMAX applications, respectively. The passbands of the filter are determined by odd- and even-mode frequencies created by the SLDMR and the internal open loop resonator inside of it. The corresponding even-mode frequency can be adequately tuned by adjusting the length of the stub while the odd-mode frequency is fixed. Two transmission zeros (TZs) are introduced on each side of the passband to improve the selectivity of the implemented filter. Five TZs around the edges of three passbands make the passbands highly isolated, and these transmission zeros can be placed according to the desired choice. The proposed tri-band BPF was designed, fabricated and measured, and the simulated and measured results corresponded very well.
The uniformity of the incident electromagnetic radiofrequency fields (RF) is an important factor that can influence the results in biological in vivo and/or in vitro exposure experiments using animals and humans or their cells. The International Electrotechnical Commission (IEC) has published IEC 61000-4-20 standard which defined field uniformity criteria for emission and immunity testing in a defined region in transverse electromagnetic (TEM) waveguides. In this paper, we present a numerical analysis method to determine aperture field uniformity in biological experiments according to IEC 61000-4-20:2010 standard. With the numerical analysis method, the uniformity of electromagnetic field can be analyzed in Cartesian coordinates system by aperture-field method (AFM). Then, with the simultaneous application of AFM and the field uniformity criteria defined by IEC 61000-4-20:2010, the two functions can be programmed to evaluate the field uniformity in region of interest (ROI) which can then be meshed into the given observation points where biological examples are exposed to RF. At the specified position of ROI along z far from the aperture of the WR-430 rectangular open-ended waveguide, the field and the minimum uniform distances vs. frequencies can be calculated by AFM. Thus, the results of the numerical analysis method can be applied to design the exposure setups for biological experiments with the field uniformity required in ROI.
The efficacy of applying magnetic hyperthermia (MHT) and capacitive hyperthermia (CHT) to treat hepatocellular carcinoma (HCC) is studied. Magnetoquasistatic (MQS) and electroquasistatic (EQS) formulations are develpoed to compute the magnetic field and electric field dirtributions, respectively, which are numerically solved by using finite element method. The heat transport equation is applied to compute the temperature distribution in the treated area. Simulation results of temperature distribution are used to compare the efficacy of MHT and CHT.
The finite element implement of the generalized Lorenz gauged A formulation has been proposed for low-frequency modeling. However, the inverse of mass matrix of intermediate scalar in the finite element implement leads to additional computation cost and dense coefficient matrix. In this paper we propose to adopt a diagonal lumping mass matrix in the finite element discretization of the generalized Lorenz gauged double-curl operator in charge-free electromagnetic problems. Consequently, a sparser discrete system with improved condition number is thus obtained which is more favourable for low-frequency modeling in frequency-domain analysis. Furthermore, we apply the diagonal lumping formulation in time-domain analysis, showing that it can remedy spurious linear growth problem. Numerical examples are used to demonstrate the validity.
In this paper, an efficient Transmission Line Matrix (TLM) algorithm for modeling chiral media is presented. The formulation is based on auxiliary differential equations (ADE) of electric and magnetic current densities. Permittivity and permeability are assumed to follow the Lorentz model while chirality is assumed to follow the Condon model. The proposed method models the dispersive nature of permittivity, permeability, and chirality by adding both voltage and current sources in supplementary stubs to the conventional symmetrical condensed node (SCN) of the TLM method. The electromagnetic coupling appears explicitly in the update equations of the voltage and current sources. The algorithm is developed to simulate electromagnetic wave propagation in a chiral medium. The co-polarized and cross-polarized transmitted and reflected waves from a chiral slab due to a normal incident plane wave are calculated. Validation is performed by comparing the results obtained from the proposed method with those obtained analytically.
A higher-order accurate solution to electromagnetic scattering problems is obtained at reduced computational cost in a p-variable finite volume time domain method in a scattered field formulation. Spatial operators of lower order, including first-order accuracy, are employed locally in substantial parts of the computational domain during the solution process. The use of computationally cheaper and lower order spatial operators does not affect the overall higher-order accuracy of the solution. The order of the spatial operator at a candidate cell during numerical simulation can vary in space and time and is dynamically chosen based on an order of magnitude comparison of scattered and incident fields at the cell centre. Numerical results are presented for electromagnetic scattering from perfectly conducting two-dimensional scatterers subject to transverse magnetic and transverse electric illumination.
A dual-function radar-communication system is a technology equipped with a joint platform that enables performing a radar function (primary function) and a communication function (secondary function) simultaneously. This duality has become increasingly necessary, since it alleviates congestion and ease competition over frequency spectrum. In this paper, we put forward a technique for information embedding, specifically to multiple-input multiple-output (MIMO) radar employing frequency-hopping chirp (FHC) waveforms. We use FHC codes to implement the primary function (i.e., MIMO radar operation), while embedding communication symbol, for example, phase shift keying (PSK), in each FHC code for secondary function (i.e., communication operation). We show that the communication operation does not interfere with the MIMO radar function. In addition, standard ratio testing is used at the communication receiver to detect the embedded PSK symbols. Furthermore, the waveform designed has the superiorities of high range resolution, constant time domain and almost constant frequency-domain modulus, large time-bandwidth product, and low time-delay and frequency-shift correlation peaks. Numerical results show that: 1) data rates can be accurately detected, and thus, several Mbps are achieved in the system; 2) the SER performance characteristics are significantly improved; 3) the orthogonal frequency-hopping chirp waveforms achieve better range and Doppler resolution with reduced sidelobes levels compared to that of conventional frequency hopping waveforms.
This paper presents a novel breast model system based on a UWB antenna for locating a tumor cancer. The antenna with overall size of 35 mm×20 mm×1.6 mm is characterized with an ultra-wideband of 120% and frequency range of 3 GHz-12 GHz for the FCC band. The proposed antenna exhibits good impedance matching, high gain and omnidirectional radiation patterns. The measurment results are presented to illustrate the performances of the proposed antenna. This antenna has been implemented in a designed system model with dielectric properties of a human breast capable to detect strange objects. The size and localization coordinates of the tumor are studied in detail for better tumor detection. The coordinates of the corresponding maximum value of SAR are identified in order to accurately detect different locations of tumor inside the breast. The results show that the localization of the tumor can be detected with high precision which demonstrates the performance of the proposed antenna and the entire system. The proposed breast model system was developed using the commercial CST Microwave studio simulator.
In this paper, the effects of magnetization patterns on the performance of series hybrid excitation synchronous machines (SHESMs) are investigated. SHESMs have three magnetic field sources: armature winding currents, permanent magnets and auxiliary winding current. To initiate the investigation, the magnetic field distributions produced by these three sources are obtained. Using the magnetic field distributions, the machine is analyzed under no-load and on-load conditions. Furthermore, the operational indices, such as inductance, torque, and unbalance magnetic force, are calculated. Various magnetization patterns are considered to investigate their influences on the performance of the machine.
Resonance frequency of a Circular Microstrip Antenna (CMSA) depends on its diameter. Hence when CMSA is truncated or sectored into smaller elements, keeping the diameter same, it resonates at almost the same frequency. An analysis of the new antenna arrays designed using these truncated non-identical CMSA elements, to realize an amplitude distribution over pedestals leading to a desired first side lobe level (FSLL) has been presented. Truncated elements are designed as non-identical elements based on their gain variation with respect to the standard normalized aperture distribution coefficients. Experimental verification to validate the proposed concept and simulated results has been carried out using an antenna array with eight non-identical elements. There is good agreement between simulated and measured results at 1.76 GHz.
Antenna miniaturization, which is a requirement of modern wireless communication systems, is usually concomitant with the reduction of impedance bandwidth. On the other hand, small antennas should also possess stable radiation patterns across a broad frequency band, such as in UWB systems. In this paper, we propose a UWB antenna structure with a novel feeding system composed of an open cavity resonator. It has a wide relative bandwidth (of about 120%) particularly at the lower frequency limits. The variation of radiation pattern across its operating bandwidth is also negligible. The proposed antenna with the novel feed system is smaller and has a wider frequency bandwidth than other available UWB antennas in the literature. Furthermore, another antenna is proposed, which has a feeding system composed of a surface integrated resonator cavity, fabricated on a two-layer microstrip structure. It has achieved better miniaturization and bandwidth, albeit somewhat lower gain. Three prototype models of the proposed antennas are fabricated and measured, of which the frequency response is in excellent agreement with computer simulation results.
Studies have been reported in the literature on High Frequency (HF) radio channels in mid-latitude areas more frequently than in low-latitude areas. Ionosphere as a reflector of HF radio waves in low-latitude areas might behave differently from that in mid-latitude. This paper reports a statistical model of sky wave HF channel complex impulse response and its parameters, such as channel gain, path gain, phase shift, and delay spread statistics, derived from both simulation and measurement of a 3044 km link in Indonesia. From the evaluations it can be concluded that the multipaths observed with respect to their propagation delays form multiple clusters corresponding to their propagation modes. The channel gain is found to follow Rayleigh distribution, whereas the rms and maximum delay spread exhibit Rayleigh and Gaussian distributions, respectively. This model can be used in performance evaluation of digital communication schemes in low-latitude HF channels.
In this study, the scattering map of the breast is reconstructed by applying the matching-pursuit algorithm (MPA) to the simulation data obtained by the monostatic inverse synthetic aperture radar (ISAR) principle, and the locations of the tumors are determined by considering the peaks on the scattering map. The MPA iteratively searches the true solution by assuming every discrete point in the solution space to be a scattering center by dividing the imaging region onto a discrete grid. In order to obtain images with better resolution, the fine granularity of the grid for accurate solutions is provided at the expense of increased processing times. First, our approach based on MPA is tested on simulated data generated by MATLAB for breast tumor detection and imaging. Perfect reconstruction for the locations of the hypothetical breast tumor points is attained. Then, a full-wave electromagnetic simulation software named CST Microwave Studio (CST MWS) is used to generate backscattered electric field data from a constructed scenario in which a tumor is located in a breast model. Next, we use the collected data from the defined scenarios as an input to our algorithm. Resultant images provide successful detection and imaging of the tumor region within the breast model. The accuracy of the MATLAB and the CST MWS simulation results demonstrate the availability of our MPA-based focusing algorithm to be used effectively in medical imaging.
In this paper, a multi-carrier nonlinear frequency modulation system based on pseudo-random frequency offset is designed. The reduction of the main lobe 3\,dB width and the side-lobe peaks cannot be realized simultaneously in conventional beamforming schemes, especially when the number of array elements remains unchanged. The proposed system can reduce the main-lobe 3 dB width and suppressing the side-lobe peaks simultaneously. This is done by adjusting the number of sub-signals, frequency offset coefficient and the inter-element spacing. Then, through time slot processing, signal power is focused on different targets. Numerical simulation experiments are implemented to validate the theoretical analysis of the proposed methodology, and comparisons with other techniques are made.
Vehicle-to-Vehicle (V2V) communications are characterized by dynamic environments due to the movement of the transceiver and scatterers. This characteristic makes V2V channel modeling particularly challenging. In this paper, a three-dimensional (3-D) geometrical propagation model and a generalized 3-D reference model that include line-of-sight (LoS) and single bounced (SB) rays are proposed for multiple-input-multiple-output (MIMO) V2V multipath fading in different roadway scenarios (e.g., flat roads, intersections and arcuate overpasses). In the models, the transceiver can move with nonlinearly varying velocities in nonlinearly varying directions, and each scatterer can move with a random velocity in a random direction. The corresponding space-time correlation functions (ST-CFs) are analytically investigated and numerically simulated in different roadway scenarios. Finally, the modeled Doppler power spectral density (D-PSD) is compared with the available measured data. The close agreements between the modeled and measured D-PSD curves confirm the utility of the proposed model.
A novel method is proposed and demonstrated to generate ultrahigh speed, ultrashort flat-top picosecond electrical pulses by combining laser pulse shaping with ultrafast electro-optics sampling technique. Starting with high repetition rate laser pulses, a sequence of birefringent crystals is employed to produce optical pulses with flat-top temporal profile and tunable duration. Subsequent measurement of optical waveforms by an ultrafast photodetector yields high-speed, ultrashort flat-top picosecond electrical pulses. By using two sets of YVO4 crystals for laser pulse shaping, we report on the generation of 704 MHz, 48 picoseconds and 704 MHz, 88 picoseconds flat-top electrical pulses with 16-30 picoseconds rise or fall time. To the best of our knowledge, these results are better than or comparable with the best performance using step recovery diodes and the direct electro-optics sampling technique.
A simple single feed circularly polarized microstrip antenna with Koch curve as boundary is presented. The two pairs of rectangular microstrip antenna edges are replaced by a Koch curve of 1st stage and 2nd stage with different indentation angles to get circular polarization. The proposed method is simple and easy to obtain circular polarization with reasonable 3 dB axial ratio bandwidth and 10 dB impedance bandwidth. The dependency of aspect ratio and fractal dimension of the boundary on the performance of the circularly polarized antenna is discussed.
The well-known ``Sommerfeld radiation problem" of a small -Hertzian- vertical dipole above flat lossy ground is reconsidered. The problem is examined in the spectral domain, through which it is proved to yield relatively simple integral expressions for the received Electromagnetic (EM) field. Then, using the Saddle Point method, novel analytical expressions for the scattered EM field are obtained, including sliding observation angles. As a result, a closed form solution for the subject matter is provided. Also, the necessary conditions for the emergence of the so-called Surface Wave are discussed as well. A complete mathematical formulation is presented, with detailed derivations where necessary.
The Meissner effect is explored based on the acceleration-dependent component of the Weber force. According to the Maxwell theory, a steady circulating current does not produce any dynamics on external resting charges; however, according to the Weber theory, the charges of the circulating current exhibit a centripetal acceleration, which affects the external charges at rest. It is demonstrated that the current generated in this manner can explain the Meissner effect in classical physics.