This study quantifies the detuning and impedance mismatch of antennas implanted inside the human body. Maximum frequency shifts caused by variations in the electrical properties of body tissues and different anatomical distributions were derived. The results are relevant to the design of implantable antennas. They indicate the bandwidth enhancement and initial tuning necessary for correct functioning. The study was carried out using electromagnetic modeling based on the finite-difference time-domain method and high-resolution anatomical models. Four anatomical computer models of two adults and two children were used. The implanted antennas operated in the Medical Implant Communication Service band. The most important detuning and impedance mismatch was found for subcutaneous locations and in areas where a layer of fat tissue was present. The maximum frequency shift towards higher frequencies was 70 MHz. The frequency shift did not occur symmetrically around 403 MHz, but was shifted towards higher frequencies.

An improved designable composite right/left-handed transmission line (CRLH-TL) is presented in this paper, whose operating frequency-band and transmission characteristics can be tuned, respectively, by three structure variables. The equivalent characteristic impedance is studied carefully, and CRLH-TLs with arbitrary characteristic impedances are obtained. Some useful empirical formulae are derived for engineering application. Then, a sample of 50-Ω CRLH-TL, which can be used directly as a wide-band filter, is fabricated with the center frequency of 2.8 GHz. The measured results show that a relative 3-dB bandwidth of 74.6% is achieved, in good agreement with the simulated results. Moreover, the phase-frequency responses of our proposed CRLH-TLs are discussed in detail. A novel hybrid ring is then proposed, where 70-Ω CRLH-TL is used. At the center frequency of 5.8 GHz, equal power dividing is achieved with return loss and isolation more than 20 dB and 30 dB, respectively. The sample is finally fabricated and good agreements among theoretical analysis, simulated results, and measured results are obtained.

Terahertz (THz) spectroscopy can potentially be used to probe and characterize inhomogeneous materials. However, identification of spectral features from diffuse scattering by inhomogeneous materials has not received much attention until now. In this paper, THz diffuse scattering from granular media is modeled by applying radiative transfer (RT) theory for the first time in THz sensing. The diffuse scattered field from compressed polyethylene (PE) pellets containing steel spheres was measured in both transmission and reflection modes using a THz time domain spectroscopy (THz-TDS) system. The RT model was validated by successfully reproducing qualitative features observed in experimental results. Diffuse intensity from granular media containing lactose was then simulated using RT theory. In the results, spectral features of lactose were observed in the diffuse intensity spectra from the granular media.

Impact of electromagnetic interference on front-end receiver behaviour is theoretically and experimentally studied outside the bandwidth of the antennas. Microwave chaotic generation is observed. Under certain conditions, reflected waves combined to the non linearity of the front-end receiver leads to a chaotic signal generation between the antenna and the front-end receiver. Different antennas, such as patch, loop, monopole and horn, are tested. Theoretical and experimental results are presented for each antenna.

Recently, we proposed a wireless ambulatory gait analysis system that provides a high ranging accuracy using ultra-wideband (UWB) transceivers. In this paper, we further investigate the performance of our proposed system including ranging using suboptimal templates, power consumption, and sensor-fusion. We show that the proposed system is capable of providing a 1.1 mm ranging accuracy (1.17 cm for current systems) at a signal-to-noise-ratio (SNR) of 20 dB using suboptimal-based receivers in industry accepted body-area-network UWB channels. For the angular-displacement, our system provides an accuracy that is less than 1^o for the knee-flexion angle. This accuracy is superior to the accuracy reported in the literature for current technologies (less than 4^o). Finally, we propose the integration of UWB sensors with force sensors. The system performance and design parameters are investigated using simulations and actual measurements. Ultimately, the proposed system is suitable for taking accurate measurements, and for tele-rehabilitation.

This paper presents a novel modified composite right/left-handed (CRLH) unit cell to achieve sharp rejection at 5.8 GHz. Design formulas are theoretically derived and numerically verified. Based on this unit cell, ultra-wideband (UWB) bandpass filters with two and three cells are designed, fabricated, and on-wafer measured. The measurement results show that the CRLH bandpass filter has a rejection of >60 dB at 5.8 GHz, a minimum insertion loss of 1.1 dB, and 3-dB bandwidths of 3.09-4.79 GHz and 3.22-4.61 GHz for the two and three unit cells, respectively.

This paper deals with several aspects relative to the Multiple-Input Multiple-Output (MIMO) propagation channel. Measurement campaigns, made in a real gold mine at 2.4 GHz under line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios, have been analyzed to obtain the relevant statistical parameters of the channel. It was shown that the MIMO exploit the multipath propagation in rich scattering environment to increase the capacity. Hence, the channel is characterized in terms of K-factor, path loss, shadowing, and capacity. Results show a propagation behavior that is specific for these underground environments with rough surfaces.

A novel compact bandpass filter (BPF) with wide upper-stopband has been proposed in this paper. The structure is based on spiral-shaped resonators. Cross coupling is used to generate two transmission zeros at the lower and upper stopbands. Therefore, the out-of-band performance is improved. In addition, two spur-lines are adopted in the feed lines to reject the spurious response. The central frequency f₀ of this filter is at 2.45 GHz with a minimum insertion loss of less than 1 dB and a 3 dB bandwidth of 12.5%. Four transmission zeros are located at 2 GHz, 3 GHz, 5.5 GHz, and 8 GHz. The attenuation is greater than 20dB in a wide upper stopband up to 9.8 GHz.

A new image reconstruction algorithm for early breast cancer detection using ultra-wideband microwave signals is proposed. In this algorithm, the backscattered electric and magnetic fields are measured and combined in a novel way; the direction of power flow with respect to a given focal point is used to localize tumors. Significant improvement in signal-to-mean raito (SMR) and signal-to-clutter ratio (SCR) are achieved when driving signals consist of waves with multiple polarizations. Numerical results demonstrate nearly 5.5 dB improvement of SMR and SCR over the traditional Confocal Microwave Imaging method when a single 8 mm breast tumor is present. Breast Cancer Facts Figures 2011-2012

We report on experimental and numerical studies on the coupling effect of a single split ring resonator (SRR) and its mirror image inside an X-band hollow waveguide. It is shown that, for single SRR with gap bearing side perpendicular to $E$ field, the magnetic resonance exhibits red/blue shift as SRR moves to the gap facing/backing waveguide edge, due to the capacitance and magnetic dipoles coupling effect between original SRR and its mirror image, respectively. Furthermore, electric dipole interplay dominates the coupling effect between SRR and its image when SRR has the gap bearing side parallel to the E field, although SRR is excited by E and H field simultaneously.

A standalone, printed monopole antenna with a two-branch shorting strip and a grounding wire to achieve a small size and yet multi-band operation for penta-band wireless wide area network (WWAN) operation (824-960/1710-2170 MHz) is presented. The antenna was formed on a low-cost, single-layered dielectric substrate with the dimensions 10 mm×50 mm. By applying the proposed grounding wire and the dual-shorting strip, two resonant modes in close proximity in the antenna's lower band were obtained to cover the GSM850/900 operation. Further, the proposed shorting strip led to two additional, higher-order resonance excitation at about 1700 and 1800 MHz to assist in the formation of a wide upper band to cover the GSM1800/1900/UMTS operation. The proposed antenna also showed good radiation properties. Details of the design are described and discussed in the article.

A new class of miniaturized dual-mode substrate integrated waveguide (SIW) band-pass filters is proposed, which are loaded by double/single T-shaped structures. By introducing a double T-shaped structure in original dual-mode SIW band-pass filter, the resonant frequency is lowered from 9.46 GHz to 8.91 GHz due to the longer effective length. The introduced single T-shaped structure performs an even lower resonant frequency of 6.88 GHz for the same reason. Compared with dual-mode band-pass filters in references, the proposed dual-mode SIW band-pass filters with double/single T-shaped structures have the advantages such as compact size (like microstrip dual-mode filters) and high Q factors (like SIW dual-mode filters). The proposed filters are fabricated and measured, and the experimental results are in good agreement with simulated ones.

The cosine window function with the parameters optimized by Genetic Algorithm (GA) is applied in bistatic planar near-field scattering measurements so as to effectively improve the measurement precision. With the infinitely long ideal conductor cylinder as the target under test, the bistatic planar near-field scattering measurement technique is studied by the method of computer simulation and some useful results and basic laws are obtained. The calculation results show that the truncation errors caused by finite scan plane in the far-field Radar Cross Section (RCS) of the target under test obtained by near-field to far-field transformation can be reduced greatly by the weighting process of the measured scattered near-field data by means of the cosine window function with the parameters optimized by GA.

Lorentz Reciprocity principle is often used to describe electrical networks and reception/radiation properties of antennas residing in a linear, time-invariant, and symmetric medium. In its reaction integral form, it is usually conceived as a mathematical tool to prove electromagnetic relations. However, reciprocity, more than a mathematical tool, can be used as a powerful alternative to convert a penetration problem into a radiation one for numerical computations and measurements. We review the reciprocity formulation and show simple steps on how to apply reciprocity to penetration problems. Numerical calculations for a wire probe (antenna) inside missile-like structure are carried out for both radiation and its reciprocity formulated penetration problems, and it is shown numerically that results from both methods are identical. One of the advantages of this indirect formulation is that the radiation properties of the structure can be easily measured contrary to the direct measurement of the penetrated signal inside the structure.

High-frequency (HF) band wireless power transfer systems offer the promise of cutting the last cord, allowing users to seamlessly recharge mobile devices as easily as wireless communication. Yet there are still many technical issues that need to be overcome. Among them, one of the most difficult problems is maintaining impedance match over a short range, where the distance between a transmitter and receiver could vary. In this paper, the effect of impedance mismatch of a HF-band wireless power transfer system is carefully investigated and two compensation methods are suggested to overcome this within a short range, where frequent impedance mismatch can occur. Each method has pros and cons. In order to verify the feasibility of the proposed methods, HF-band wireless power transfer systems, with a pair of rectangular loop resonators, were designed. The efficiency and input impedance variation were simulated and measured. From these results, proposed methods show enhanced efficiency performance than a typical wireless power transfer system without any compensation circuits.

The detection and identification of metal items and, in particular weapons, of linear size ≥10 cm, concealed upon the human body, is demonstrated as being entirely feasible by using a phased array of suitably ultra wide band transceivers. The complex natural resonances and especially the fundamental resonance, are excited by ultra wide band, stepped frequency continuous wave illumination of the target, using a phased array of antennae to focus the radiation. Broadband illumination of the target with microwave radiation of suitable frequency range (Typically 0.3-3 GHz for handgun sized objects) excites low order complex natural resonances and the late time response of the concealed item can be spatially located using phased array imaging techniques. Further processing of the late time response enables classification of the concealed object, based on the complex natural resonant frequencies of the object, so that threat items such as handguns and knives can be differentiated from benign items such as mobile phone handsets and cameras.

A novel nonlinear model for MESFET/HEMT devices is presented. The model can be applied to low power (GaAs) and high power (GaN) devices with equal success. The model provides accurate simulation of the static (DC) and dynamic (Pulsed) I-V characteristics of the device over a wide bias and ambient temperature range (from -70ºC to +70ºC) without the need of an additional electro-thermal sub-circuit. This is an important issue in high power GaN HEMT devices where self-heating and current collapse due to traps is a more serious problem. The parameter extraction strategy of the new model is simple to implement. The robustness of the model when performing harmonic balance simulation makes it suitable for RF and microwave designers. Experimental results presented demonstrate the accuracy of the model when simulating both the small-signal and large-signal behavior of the device over a wide range of frequency, bias and ambient temperature operating points. The model described has been implemented in the Advanced Design System (ADS) simulator to validate the proposed approach without convergence problems.

The aim of the present paper is to obtain explicit asymptotic expressions for the "transfer (diffraction) coefficients" related to the diffraction of high frequency cylindrical waves from the discontinuity occurred in the material properties as well as in the thicknesses of a coated cylindrically curved metallic sheet characterized by the second order GIBCs. Relying on the locality of the high frequency diffraction phenomenon, the angular interval φ∈(-π;π) is extended to the abstract innite space φ∈(-∞;∞) wherein the diffracting structure is replaced by a two-part cylindrically curved second order impedance sheet ρ = a extending from φ = -∞ to φ = ∞. The resulting boundary value problem is formulated as a Hilbert equation which is solved asymptotically in the high frequency limit. Some graphical results showing the eects of various parameters on the transfer coecients are presented.

A tunable filtering antenna (filtenna) realized using rings fed with an ultra-wideband (UWB) planar, elliptical monopole antenna is proposed. An array of slotted rings with varactors is placed in close proximity of the planar monopole to obtain the low profile tunable filtenna. The array of rings can be viewed as a small tunable frequency selective surface. The design produces a tuning range of about 3.8-4.4 GHz over a varactor reverse bias voltage of 1-4 V.

In this paper, we propose a cylindrical rolled-up negative permeability metamaterial (MM) lens for magnetic resonance imaging (MRI), and some analyses are given. The proposed cylindrical MM lens is fabricated by rolling a MM slab (constituted with capacitive-loaded copper split rings) into a tube that resembles a hollow ring. It can focus the field of a magnetic line source, which can increase the penetration depth and improve the sensitivity of a surface coil. The proposed cylindrical MM lens can also improve the discrimination of the signals coming from two independent sources. A clinical experiment is carried out in a General Electric Signa 1.5 T MRI system in order to verify the focusing ability of the proposed device.