Highly-directive cross-polarized backscatterers integrated with a ground plane

Cross-polarized backscatterers integrated with a ground plane are a key element of different applications, including chipless RFIDs, sensing, ambient backscattering communications, and data storage. The use of a cross-polarized signal removes the difficulties arising from the strong copolar signal reflected by the ground plane. Concurrently, the cross-polarized signal is typically very weak, hindering the effectiveness of crosspolarized backscatterers in noisy and uncontrolled environments. Herein, the generalized optical theorem is used to derive upper bounds on the cross-polarized backscattering cross section of systems integrated with a ground plane and identify viable strategies to design them based on highly directive scattering systems. Popular antenna configurations, including elementary electric and magnetic dipoles and their combinations, such as Huygens sources and endfire arrays, are examined to ascertain which ones can be used to realize highly directive cross-polarized backscattering performance when they are integrated with a ground plane. Realistic single-antenna elements that attain the upper-bound performance are identified. A two-element endfire array based on crossed electric dipole elements also achieves the upper bound performance, further confirming the efficacy of the derived cross-polarized backscattering bounds

Melaleuca armillaris Essential Oil as an Antibacterial Agent: The Use of Mesoporous Bioactive Glass Nanoparticles as Drug Carrier

Bioactive glasses have been proposed for bone tissue engineering due to their excellent biocompatibility and osteo-inductive behaviour. The generation of mesoporous bioactive glass (nano) particles adds a high surface area for the dissolution and release of bioactive ions, and the possibility to load them with different drugs for antibacterial purposes. Essential oils (EO) are an interesting resource for alternative medical therapy, providing antimicrobial compounds that come from organic/natural resources like aromatic plants. Also, a biological polymer, such as chitosan, could be used to control the release of active agents from mesoporous bioactive glass (MBG) loaded particles. This work presents MBG particles with nominal composition (in mol) 60% SiO2, 30% CaO and 10% P2O5, loaded with essential oil of Melaleuca armillaris, which contains 1,8-cineol as the main active component, with an inhibitory in vitro activity against several bacterial species. Also, co-loading with a broad-spectrum antibiotic, namely gentamicin, was investigated. The MBG particles were found to be of around 300nm in diameter and to exhibit highly porous open structure. The release of EO from the particles reached 72% of the initial content after the first 24 h, and 80% at 48 h of immersion in phosphate buffered solution. Also, the MBG particles with EO and EO-gentamicin loading presented in vitro apatite formation after 7 days of immersion in simulated body fluid. The antibacterial tests indicated that the main effect, after 24 h of contact with the bacteria, was reached either for the MBG EO or MBG EO-gentamicin particles against E. coli, while the effect against S. aureus was less marked. The results indicate that MBG particles are highly bioactive with the tested composition and loaded with EO of Melaleuca armillaris. The EO, also combined with gentamicin, acts as an antibacterial agent but with different efficacy depending on the bacteria type