Imaging of dipole sources and transfer of modulated signals using phase conjugating lens techniques

The authors discuss the imaging properties and transfer of amplitude and phase-modulated signals through a phase conjugating lens (PCL). The authors outline the mechanisms of the near-field and far-field subwavelength imaging of Hertzian dipole sources using PCL, particularly the authors show that one-dimensional subwavelength resolution of multiple sources is possible in the far-field using a PCL augmented with specially designed scatterers located in both the adjacent vicinity of the sources and in the mirror symmetric positions in the image plane. These scatterers enable evanescent-to-propagating spectrum and its dual, propagating-to-evanescent, field conversion. Thus, the subwavelength information encoded into propagating waves on the source side can be extracted on the image side. Next, for the first time the transfer of amplitude and phase modulated signals through a PCL augmented with evanescent-to-propagating spectrum conversion is discussed and it has been demonstrated that multiple amplitude or phase modulated dipole sources can be distinguished in the far-field with subwavelength resolution without the necessity for numerical post-processing of the received data. From the study conducted here, it is concluded that a system of transmitters/receivers augmented with a PCL and appropriate scatterers operates without the need for any numerical processing of the receive data in order to separate channel information from very close proximity stations.

Reflection amplifier phase conjugation properties

The potential of employing a millimetre-wave MMIC reflection amplifier as a building block for a retrodirective reflectarray is investigated. With this in mind the phase conjugating behaviour of the device is experimentally quantified at 21 GHz.

USE OF RETRODIRECTIVE ARRAY PHASE CONJUGATION CIRCUITRY FOR NEAR- AND FAR-FIELD POSITION ANGLE OF ARRIVAL DETECTION

In this article, we present position indication functionality as obtained by using a retrodirective array, thereby allowing location information extraction of the position of the remote transmitter with which the retrodirective array is cooperating. This is carried out using straightforward circuitry with no requirement for complex angle of arrival algorithms, thereby giving a result in real time enabling tracking of fast moving transmitters. We show using a 10 x element retrodirective array, operating at 2.4 GHz that accuracies of far-field angle of arrival of within +/- 1 degrees over the arrays +/- 30 degrees azimuth field of view are possible. While in the near-field for angles of arrival of +/- 10 degrees it is possible to extract the position of a dipole source down to a resolution of 032 lambda. (C) 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1031-1034, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25097

Active Phase Conjugating Lens With Sub-Wavelength Resolution Capability

Experimental results are presented for the focusing capability of an active phase conjugating lens for a single and a dipole source pair and these are compared with predictions. In addition for a single source we illustrate the ability of the lens to project a null at the lens focus instead of a peak. A scheme is also presented such that when a source or pair of sources is imaged through an identical pair of passive scatterers located symmetrically about the lens that imaging with sub-wavelength resolution is possible. The rationale for the operation of the lens and aberrations observed due to its finite array size is discussed and is supported throughout by means of numerical simulation.

Amplitude and Phase Controlled Reflectarray Element Based on an Impedance Transformation Unit

An architecture to simultaneously affect both amplitude and phase control from a reflectarray element using an impedance transformation unit is demonstrated. It is shown that a wide range of control is possible from a single element, removing the conventional necessity for variable sized elements across an array in order to form a desired reflectarray far-field pattern. Parallel plate waveguide measurements for a 2.2 GHz prototype element validate the phase and amplitude variation available from the element. It is demonstrated that there is sufficient control of the element's reflection response to allow Dolph-Tschebyscheff weighting coefficients for major-lobe to side-lobe ratios of up to 36 dB to be implemented.

A Phase Grating Approach to Modeling Surface Diffusion in FDTD Room Acoustics Simulations

In this paper, a method for modeling diffusive boundaries in finite difference time domain (FDTD) room acoustics simulations with the use of impedance filters is presented. The proposed technique is based on the concept of phase grating diffusers, and realized by designing boundary impedance filters from normal-incidence reflection filters with added delay. These added delays, that correspond to the diffuser well depths, are varied across the boundary surface, and implemented using Thiran allpass filters. The proposed method for simulating sound scattering is suitable for modeling high frequency diffusion caused by small variations in surface roughness and, more generally, diffusers characterized by narrow wells with infinitely thin separators. This concept is also applicable to other wave-based modeling techniques. The approach is validated by comparing numerical results for Schroeder diffusers to measured data. In addition, it is proposed that irregular surfaces are modeled by shaping them with Brownian noise, giving good control over the sound scattering properties of the simulated boundary through two parameters, namely the spectral density exponent and the maximum well depth.

Fast, copper-free click chemistry: a convenient solid-phase approach to oligonucleotide conjugation

Solid-phase oligonucleotide conjugation by nitrile oxide-alkyne click cycloaddition chemistry has been successfully demonstrated; the reaction, compatible with all nucleobases, requires no metal catalyst and proceeds under physiological conditions.

On the Distribution of Signal Phase in Body Area Networks

In this letter, we investigate the distribution of the phase component of the complex received signal observed in practical experiments using body area networks. Two phase distributions, the recently proposed kappa-mu and eta-mu probability densities, which together encompass the most widely used fading models, namely Semi-Gaussian, Rayleigh, Hoyt, Rice, and Nakagami-m, have been compared with measurement data. The kappa-mu distribution has been found to provide the best fit over a range of on-body links, while the user was mobile. The experiments were carried out in two dissimilar indoor environments at opposite ends of the multipath spectrum. It has also been found that the uniform phase distribution has not arisen in anyone of the experiments.

Attosecond phase locking of harmonics emitted from laser-produced plasmas

Laser-driven coherent extreme-ultraviolet (XUV) sources provide pulses lasting a few hundred attoseconds(1,2), enabling real-time access to dynamic changes of the electronic structure of matter(3,4), the fastest processes outside the atomic nucleus. These pulses, however, are typically rather weak. Exploiting the ultrahigh brilliance of accelerator-based XUV sources(5) and the unique time structure of their laser-based counterparts would open intriguing opportunities in ultrafast X-ray and high-field science, extending powerful nonlinear optical and pump-probe techniques towards X-ray frequencies, and paving the way towards unequalled radiation intensities. Relativistic laser-plasma interactions have been identified as a promising approach to achieve this goal(6-13). Recent experiments confirmed that relativistically driven overdense plasmas are able to convert infrared laser light into harmonic XUV radiation with unparalleled efficiency, and demonstrated the scalability of the generation technique towards hard X-rays(14-19). Here we show that the phases of the XUV harmonics emanating from the interaction processes are synchronized, and therefore enable attosecond temporal bunching. Along with the previous findings concerning energy conversion and recent advances in high-power laser technology, our experiment demonstrates the feasibility of confining unprecedented amounts of light energy to within less than one femtosecond.

Far field subwavelength source resolution using Phase Conjugating Lens Assisted With Evanescent-to-Propagating Spectrum Conversion

The imaging properties of a phase conjugating lens operating in the far field zone of the imaged source and augmented with scatterers positioned in the source near field region are theoretically studied in this paper. The phase conjugating lens consists of a double sided 2D assembly of straight wire elements, individually interconnected through phase conjugation operators. The scattering elements are straight wire segments which are loaded with lumped impedance loads at their centers. We analytically and numerically analyze all stages of the imaging process; i) evanescent-to-propagating spectrum conversion; ii) focusing properties of infinite or finite sized phase conjugating lens; iii) source reconstruction upon propagating-to-evanescent spectrum conversion. We show that the resolution that can be achieved depends critically on the separation distance between the imaged source and scattering arrangement, as well as on the topology of the scatterers used. Imaged focal widths of up to one-seventh wavelength are demonstrated. The results obtained indicate the possibility of such an arrangement as a potential practical means for realising using conventional materials devices for fine feature extraction by electromagnetic lensing at distances remotely located from the source objects under investigation

On the Capacity of Non-Uniform Phase MIMO Nakagami-m Fading Channels

This letter investigates the ergodic capacity of MIMO Nakagami-m fading channels with both uniformly and non-uniformly distributed phases. We first obtain a tight capacity upper bound for the channel and then derive exact expressions for the low signal-to-noise ratio (SNR) capacity metrics, based on which we examine the impact of fading parameter m on the capacity.

Shape-induced phase transition of domain patterns in ferroelectric platelets

Using a combination of experimental and computational techniques, changes in the domain structures seen infreestanding single-crystal platelets of BaTiO3 have been described in terms of a second-order phase transition.The transition is driven by the change in the length-to-width ratio of the platelet sidewalls and results in a symmetrybreaking of a complex, quadrant domain pattern. The phenomenon can be described by a Landau formalism inwhich (1) the order parameter is not the polarization but rather is the degree to which the domain pattern becomesoff-centered, and (2) the shape anisotropy of the platelet substitutes for temperature in the conventional Landauexpansion as the controlling thermodynamic variable. Bistability, in terms of the direction in which the domainpattern moves off center, coupled with the spontaneous macroscopic polarization and toroidal moment that resultfrom this off-centering, prompt the possibility of a new form of memory storage.

Evaluation of Pt and Re oxidation state in a pressurized reactor: difference in reduction between gas and liquid phase

Determination of metal oxidation state under relevant working conditions is crucial to understand catalytic behaviour. The reduction behaviour of Pt and Re was evaluated simultaneously as a function of support and solvent in a pressurized reactor (autoclave). The bimetallic catalysts are used in selective hydrogenation of carboxylic acids and amides. Gas phase reduction reduced the metals more efficiently, in particular Pt.