Wrocław University of Technology

About: Wrocław University of Technology is a education organization based out in Wrocław, Poland. It is known for research contribution in the topics: Laser & Fuzzy logic. The organization has 13115 authors who have published 31279 publications receiving 338694 citations.

Broadband 4 $\times$ 4 Butler Matrices as a Connection of Symmetrical Multisection Coupled-Line 3-dB Directional Couplers and Phase Correction Networks

Abstract: An innovative approach for realization of broadband 4 times 4 Butler matrices, in which broadband symmetrical multisection 3-dB/90deg directional couplers are used as basic elements, has been presented. A new technique for realization of center crossover together with 45deg phase shifters is proposed where phase correction networks, consisting of a number of coupled-line sections, are applied. The use of the proposed phase correction networks allows to achieve equal-ripple 45deg differential phase characteristics in a wide frequency range. Numerical results for the design of broadband 4 times 4 Butler matrices consisting of multisection symmetrical 3-dB/90deg directional couplers having three, five, seven, and nine coupled-line sections in conjunction with phase correction networks having an appropriate number of coupled-line sections are given in a tabular form. A method of performance improvement for broadband Butler matrices by the combinatory use of directional couplers consisting of different number of coupled-line sections is also proposed. To verify the presented analysis a broadband 4 times 4 Butler matrix consisting of six 3-dB/90deg three-section symmetrical coupled-line directional couplers and two single-section coupled-line phase correction networks has been designed, manufactured, and measured. Results of measurements of the designed Butler matrix fully confirm the validity of the proposed technique of broadband 4 times 4 Butler matrix realization.

Estimates of the Green Function for the Fractional Laplacian Perturbed by Gradient

Abstract: The Green function of the fractional Laplacian of the differential order bigger than one and the Green function of its gradient perturbations are comparable for bounded smooth multidimensional open sets if the drift function is in an appropriate Kato class.

DASH7 alliance protocol 1.0: Low-power, mid-range sensor and actuator communication

Abstract: This paper presents the DASH7 Alliance Protocol 1.0. It is an industry alliance standard for wireless sensor and actuator communication using the unlicensed sub-1 GHz bands. The paper explains its historic relation to active RFID standards ISO 18000-7 for 433 MHz communication, the basic concepts and communication paradigms of the protocol. Since the protocol is a full OSI stack specification, the paper discusses the implementation of every OSI layer.

Selective excitation of Eu3+ in the core of small β-NaGdF4 nanocrystals

Abstract: The influence of the nanocrystal matrix on the optical properties of lanthanide dopants is investigated with europium ions used as local crystal field probes. The analysis is performed on small NaYF4 and NaGdF4 nanocrystals obtained by the thermolysis of the corresponding metal trifluoroacetates. An important role in the synthesis is played by trioctylphosphine oxide which induces the crystallization of nanocrystals with small diameters (∼5 to 6 nm). In such small particles, the energy transfer from gadolinium to europium ions is studied with photoluminescence, photoluminescence excitation and time-resolved experiments. We demonstrate that excited gadolinium ions efficiently transfer their energy to europium, and their photoluminescence spectra depend on the nanocrystal size. This is contrary to the direct excitation of Eu3+ ions, which produces size-dependent emission corresponding to the surface to volume ratio of europium sites. Finally, we propose that Gd3+ ions transfer their energy mainly to the Eu3+ in the core of the nanocrystals. These observations provide a base for the optically controlled emission from only the core of the nanocrystals.