In this paper, an efficient lightweight double-layer absorber with impedance-matching structure at X-Ku bands was designed, optimized and implemented. First, genetic algorithm (GA) was considered to optimize the thicknesses and material properties for better absorption of the incident electromagnetic wave and reduction of radar cross section (RCS). Next, with the aid of the obtained dielectric and magnetic properties, the microwave absorber was fabricated from magnetodielectric composite materials besides a natural rubber. Finally, the analytical and numerical results were compared with the measurements to check the validity of the design. Experiments showed that the reflection coefficient for each layer backed with a metallic sheet was insufficient; however, for the double layer absorber, the reflectivity measurement values reached up to -28 dB in the case of normal incidence and -17 dB for oblique incidence.
In this paper, a novel broadband equalizer optimization technique is introduced for high-speed digital system designs. Through effectively compensating both conductor loss and dielectric loss, this technique provides a new solution to find optimal equalizer for high-speed signaling over printed circuit board (PCB) with continuous time linear equalizer (CTLE) as an application. The coefficients of CTLE are quickly identified through searching the minimum of the variation of total transfer functions over the low-mid frequency range. Channel simulations with different server interfaces of 12 Gbps and 25 Gbps are performed, respectively. Simulation results are presented to validate the technique.
In this paper, a new de-embedding technique with Look-Up Table (LUT) is proposed for accurate and efficient characterization of interconnects, particularly printed circuit board (PCB) transmission lines including microstrip and stripline. LUT is pre-created to cover various fixture effects including the reference structures inside and/or outside test printed circuit boards (PCBs). The pre-established LUT is introduced to eliminate the errors of ``probing and launching fixtures'' in characterization of transmission lines. It is applied to characterization of loss of microstrip and stripline. Simulations and measurements are performed to verify its accuracy and feasibility. Results show it is in good agreement with conventional Delta-L like methods but significantly reduces the cost of characterization. It provides an accurate but cost-effective solution for characterization of high speed interconnects, in particular for high volume manufacturing environments.
This paper investigates the source reconstruction problem in underwater mediums using a compressive Near-Field Electromagnetic Holography (NEH) approach. More specifically we investigate the use of ℓ1 regularization for the purpose of decomposing near-field magnetic and/or electric surface measurements into electric and magnetic dipole sources. Our study indicates that not only do ℓ1 decompositions enable much higher resolution of sources than traditional ℓ2 approaches, but important features of the dipoles are preserved in the reconstruction. Our hypothesis are supported by numerical experiments as well as underwater physical measurements obtained in an earth field simulator facility.
Dispersion characteristics of four types of superconducting nanowire single photon detectors, nano-cavity-array- (NCA-), nano-cavity-deflector-array- (NCDA-), nano-cavity-double-deflector-array- (NCDDA-) and nano-cavity-trench-array- (NCTA-) integrated (I-A-SNSPDs) devices was optimized in three periodicity intervals commensurate with half-, three-quarter- and one SPP wavelength. The optimal congurations capable of maximizing NbN absorptance correspond to periodicity-dependent tilting in S-orientation (90˚ azimuthal orientation). In NCAI-A-SNSPDs absorptance maxima are reached at the plasmonic Brewster angle (PBA) due to light tunneling. The absorptance maximum is attained in a wide plasmonic-pass-band in NCDAI1/2*λ-A, inside a flat-plasmonic-pass-band in NCDAI3/4*λ-A and inside a narrow plasmonic-band in NCDAIλ-A. In NCDDAI1/2*λ-A bands of strongly coupled cavity and plasmonic modes cross, in NCDDAI3/4*λ-A an inverted-plasmonic-band-gap develops, while in NCDDAIλ-A a narrow plasmonic-pass-band appears inside an inverted-minigap. The absorptance maximum is achieved in NCTAI1/2*λ-A inside a plasmonic-pass-band, in NCTAI3/4*λ-A at inverted-plasmonic-band-gap center, while in NCTAIλ-A inside an inverted-minigap. The highest 95.05% absorptance is attained at perpendicular incidence onto NCTAIλ-A. Quarter-wavelength type cavity modes contribute to the near-field enhancement around NbN segments except in NCDAIλ-A and NCDDAI3/4*λ-A. The polarization contrast is moderate in NCAIA-SNSPDs (~102). NCDAI- and NCDDAI-A-SNSPDs make possible to attain considerably large polarization contrast (~102-103 and ~103~104), while NCTAI-A-SNSPDs exhibit a weak polarization selectivity (~10-102).
This paper presents a miniaturized ultra wideband (UWB) antenna with metamaterial for WLAN and WiMax applications. For miniaturization of UWB antenna resonating 3.1-10.6 is designed Ghz using fractalization of the radiating edge and slotted ground structure approach. A miniaturization of active patch area and antenna volume is achieved up to 63.48% and 42.24% respectively, with respect to the conventional monopole UWB antenna. This antenna achieves a 143% impedance bandwidth covering the frequency band from 2.54 GHz to 15.36 GHz under simulation and 132% (2.95-14.28 GHz) in measurement. The electrical dimension of this antenna is 0.32 × 0.32 (38mm × 38mm) at lower frequency of 2.54 GHz. As per IEEE 802.11a/b/g and IEEE 802.16e standards, WLAN (2.4 -2.5 GHz, 5.150 -5.250 GHz, 5.725 -5.825 GHz), WiMAX (3.3-3.8 GHz) bands are achieved by using slotted ground structure and metamaterial rectangular split ring resonator. The proposed antenna is fabricated on FR4 substrate of thickness 1.6 mm and a dielectric constant 4.3 and tested. The proposed antenna yields a −10 dB impedance bandwidth of about 11.1% (2.39-2.67 GHz), 59.1% (2.87-5.28 GHz) and 7.4% (5.58-6.01 GHz) under simulation and 4.5% (2.41-2.52 GHz), 51.1% (3.12-5.26 GHz) and 3.8% (5.69-5.91 GHz) in measurement for 2.4, 3.5 & 5 and 5.8 GHz bands respectively. Stable radiation patterns with low cross polarization, high average antenna gain of 3.02 dBi under simulation and 2.14 dBi in measurement and measured peak average radiation efficiency of 76.6% are observed for the operating bands. Experimental results seem in good agreement with the simulated ones of the proposed antenna.
Magnetic induction tomography (MIT) is a non-invasive medical imaging technique with promising applications such as brain imaging and cryosurgery monitoring. Despite its potential, the realisation of medical MIT application is challenging. The computational complexity of both the forward and inverse problems, and specific MIT hardware design are the major limitations for the development of MIT research in medical imaging. The MIT forward modeling and linear system equations for large scale matrices are computationally expensive. This paper presents the implementation of GPU (graphics processing unit) for both forward and inverse problems in MIT research. For a given MIT mesh geometry composed of 167,488 tetrahedral elements, the GPU accelerated Biot-Savart Law for solving the free space magnetic field and magnetic vector potential is proved to be over 200 times faster compared to the time consumption of a CPU (central processing unit). The linear system equation arising from the forward and inverse problem, can also be accelerated using GPU. Both simulations and experimental results are presented based on a new GPU implementation. Laboratory experimental results are shown for a phantom study representing potential cryosurgery monitoring using an MIT system.
The aim of angular super-resolution is to surpass the real-beam resolution. In this paper, a method for forward-looking scanning radar angular super-resolution imaging through a deconvolution method is proposed, which incorporates the prior information of the target's scattering characteristics. We first mathematically formulate the angular super-resolution problem of forward-looking scanning radar as a maximum a posteriori (MAP) estimation task based on the forward model, and convert it to an equivalent unconstrained optimization problem by applying the log-transforms to the posterior probability, which guarantees the solution converges to a global optimum of an associated MAP problem and it is easy to implement. We then implement the unconstrained optimization task in convex optimization framework using an iterative shrinkage method, and the computational complexity of the proposed algorithm is also discussed. Since the anti log-likelihood of the noise distribution and the prior knowledge of the scene are utilized, the proposed method is able to achieve angular super-resolution imaging in forward-looking scanning radar effectively. Numerical simulations and experimental results based on real data are presented to verify that the proposed deconvolution algorithm has better performance in preserving angular super-resolution accuracy and suppressing the noise amplification.
Doppler weather radar is an effective tool for monitoring mesoscale and small scale weather systems, quantitatively estimating precipitation and guarding against severe convective weather. The quality of the data obtained by Doppler weather radar will be seriously affected by the anomalous propagation of electromagnetic wave in tropospheric ducts. A novel method is introduced in this paper to retrieve the surface ducts, and it is based on the Principal Component Analysis (PCA) method for modeling M profile and Parabolic Equation (PE) propagation model which is a well-established technique for efficiently solving the equations for beam propagation in an inhomogeneous atmosphere. The inversion echo powers and equivalent reflectivity factor are in accordance with the measured data, which indicates that the surface ducts can be effectively retrieved by this method.
The optical theorem is a fundamental result that describes the energy budget of wave scattering phenomena. Most past formulations have been derived in the frequency domain and thus apply only to linear time-invariant (LTI) scatterers and background media. In this paper we develop a new theory of the electromagnetic form of the optical theorem directly in the time domain. The derived formulation covers not only the ordinary optical theorem but also the most general form of this result, known as the generalized optical theorem. The developed formulation provides a very general description of the optical theorem for arbitrary probing fields and general scatterers that can be electromagnetically nonlinear, time-varying, and lossy. In the derived formalism, both the scatterer and the background medium can be nonhomogeneous and anisotropic, but the background is assumed to be LTI and lossless. The derived results are illustrated with a computer simulation study of scattering in the presence of a corner reflector which acts as the background. Connections to prior work on the time-domain optical theorem under plane wave excitation in free space are also discussed.