Dielectric characterization of low-loss materials a comparison oftechniques

Measurements on low-loss materials using closed and open cavity resonators, and dielectric resonator methods are presented. Results indicate that consistent measurement results can be obtained with a number of well-characterized fixtures. Uncertainties associated with each method are addressed. Measurements also were performed on materials used in previous intercomparisons     

Multi-Agent Radio Resource Allocation

This paper presents a spatially distributed and dynamic billing, pricing and allocation mechanism for which a user terminal requires Cognitive Radio abilities. That is, the Cognitive Radio abilities will be applied to the economical environment. The radio resource goods are allocated to the users by a multi-unit sealed-bid auction. Intelligent entities like the bidding strategy have to represent operator’s and users’ behavior and to make decisions for them in order to fulfill the preferences and QoS. The main functionalities, used to execute the dynamic auction sequence and located in the MAC are described, assuming the entities possess Cognitive Radio abilities.

Ferroelectric Poling of Methylammonium Lead Iodide Thin Films

Seemingly contradictory reports on polar domains and their origin have surrounded the controversial discussion about the ferroelectricity of the methyl ammonium lead iodide (MAPbI₃) thin films that are commonly employed in perovskite solar cells. In this work, microscopic modulations of the polar domain patterns upon application of an electric poling field are correlated with macroscopic changes to the currents through the MAPbI₃ layer. Piezoresponse force microscopy is used to monitor the widening, narrowing, generation or extinction of polar domains, as well as shifts of the domain walls at room temperature under an in‐plane electric poling field that is applied between two laterally organized electrodes. This poling leads to a net polarization of individual grains and the thin film itself. Macroscopically, this net polarization results in a persistent shift of the diode characteristics that is measured across the channel between the electrodes. Both the modulation of the polar domains upon electric poling and the concurrent persistent shift of the electric currents through the device are the unambiguous hallmarks of ferroelectricity, which demonstrate that MAPbI₃ is a ferroelectric semiconductor.     

Tunable ferroelectric impedance matching networks and their impact on digital modulation system performance

In this paper the bit error rate performance and error vector magnitude of a tunable impedance matching network is analyzed assuming QPSK, 16-QAM and 64-QAM digital modulation schemes. The characterized tunable impedance matching network is based on barium–strontium–titanate ferroelectric thick-film varactors. Inherent dispersive behavior is subsumed into the forward transmission of the passive device. Due to this nonlinear phase response, in general to maximize the overall system performance, an agile tuning of the varactor values is demonstrated, taking into account the phase and group delay of s₂₁ parameter. Detailed signal simulation results based on measured data of a testbed are presented. The influence of varying matched impedances on the tuning behavior with different modulation bandwidths is discussed at a center frequency of 1.9 GHz.     

Electromagnetic scattering from nonspherical particles: a new polarisability model with application to agglomerating spheres

A new model for the static polarisability tensor elements of small particles is proposed and investigated. The static polarisability tensor for nearly agglomerated and agglomerated homogeneous dielectric spheres is investigated using a numerical procedure. Excellent agreement is obtained with a recent theoretical formulation for the slightly separated case.<>     

Carbon‐Based Anodes for Lithium Sulfur Full Cells with High Cycle Stability

The lithium sulfur battery system has been studied since the late 1970s and has seen renewed interest in recent years. However, even after three decades of intensive research, prolonged cycling can only be achieved when a large excess of electrolyte and lithium is used. Here, for the first time, a balanced and stable lithium sulfur full cell is demonstrated with silicon–carbon as well as all‐carbon anodes. More than 1000 cycles, a specific capacity up to 1470 mAh g^?1 _sulfur (720 mAh g^?1 _cathode), and a high coulombic efficiency of over 99% even with a low amount of electrolyte are achieved. The alternative anodes do not suffer from electrolyte depletion, which is found to be the main cause of cell failure when using metallic lithium anodes.     

Ultrathin Polydopamine Films with Phospholipid Nanodiscs Containing a Glycophorin A Domain

Cellular membranes have long served as an inspiration for nanomaterial research. The preparation of ultrathin polydopamine (PDA) films with integrated protein pores containing phospholipids and an embedded domain of a membrane protein glycophorin A as simplified cell membrane mimics is reported. Large area, ultrathin PDA films are obtained by electropolymerization on gold surfaces with 10–18 nm thickness and dimensions of up to 2.5 cm². The films are transferred from gold to various other substrates such as nylon mesh, silicon, or substrates containing holes in the micrometer range, and they remain intact even after transfer. The novel transfer technique gives access to freestanding PDA films that remain stable even at the air interfaces with elastic moduli of ≈6–12 GPa, which are higher than any other PDA films reported before. As the PDA film thickness is within the range of cellular membranes, monodisperse protein nanopores, so‐called “nanodiscs,” are integrated as functional entities. These nanodisc‐containing PDA films can serve as semi‐permeable films, in which the embedded pores control material transport. In the future, these simplified cell membrane mimics may offer structural investigations of the embedded membrane proteins to receive an improved understanding of protein‐mediated transport processes in cellular membranes.     

Energy Level Engineering in Organic Thin Films by Tailored Halogenation

In modern electronics, it is essential to adapt band structures by adjusting energy levels and band gaps. At first sight, this “band structure engineering” seems impossible in organic semiconductors, which usually exhibit localized electronic states instead of Bloch bands. However, the strong Coulomb interaction in organic semiconductors allows for a continuous shift of the ionization energy (IE) over a wide range by mixing molecules with halogenated derivatives that exhibit different quadrupole moments. Here, this effect of energy level engineering on blends of pentacene and two fluorinated derivatives, in which the position but not the number of fluorine atoms differ, is studied. Structural investigations confirm that pentacene forms intermixed phases in blends with the fluorinated species. The investigation of electronic properties and simulations reveals a much larger shift of the ionization energy (1.5 eV) than in previous studies, allowing to test this model in a range not investigated so far, and emphasizing the role of the position of the halogen atoms. The tuning effect is preserved in electronic devices such as field‐effect transistors and significantly influences device characteristics.