Simple analytical formulas are introduced for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of ...metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied.
In the present study, we have aimed to characterize the intrinsic, extrinsic and ER-mediated apoptotic induction by hyperthermia in an in vitro model of human malignant melanoma and furthermore, to ...evaluate its therapeutic effectiveness in an adjuvant therapeutic setting characterized by combinational treatments with non-targeted (Dacarbazine & Temozolomide) and targeted (Dabrafenib & Vemurafenib) drugs. Overall, our data showed that both low (43 °C) and high (45 °C) hyperthermic exposures were capable of inducing cell death by activating all apoptotic pathways but in a rather distinct manner. More specifically, low hyperthermia induced extrinsic and intrinsic apoptotic pathways both of which activated caspase 6 only as opposed to high hyperthermia which was mediated by the combined effects of caspases 3, 7 and 6. Furthermore, significant involvement of the ER was evident (under both hyperthermic conditions) suggesting its role in regulating apoptosis via activation of CHOP. Our data revealed that while low hyperthermia activated IRE-1 and ATF6 only, high hyperthermia induced activation of PERK as well suggesting that ultimately these ER stress sensors can lead to the induction of CHOP via different pathways of transmitted signals. Finally, combinational treatment protocols revealed an effect of hyperthermia in potentiating the therapeutic effectiveness of non-targeted as well as targeted drugs utilized in the clinical setting. Overall, our findings support evidence into hyperthermia's therapeutic potential in treating human malignant melanoma by elucidating the underlying mechanisms of its complex apoptotic induction.
A retrodirective antenna (RDA) array for wireless power transmission (WPT) is presented. Applications include the wireless charging of mobile phones and other handheld devices. The reported RDA ...defines an active high-power transmitter module that retrodirects a received beacon tone back to a mobile unit by circularly polarized (CP) free-space radiation. In addition, this RDA architecture uses a network of four subarrays, defined by a total of 16 radiating patch elements, in an effort to boost the transmit gain while also reducing the supporting RF hardware requirements when compared to a more conventional RDA. Measurements and simulations in the reactive near-field of the system are in agreement in terms of the tracking capabilities of the high-power CP-RDA. Power levels in excess of 27 dBm were measured at 2.4 GHz at a receiver module, and when this RF power was rectified, more than 350 mW at dc was observed. To the best knowledge of the authors, this is the first demonstration of a WPT system using a mixer-based analog RDA. Previous low-power demonstrations were more complex computer-controlled systems that did not offer any real-time tracking ability. Other applications for the proposed RDA include target tracking, sensor charging, and other WPT systems.
The artificial magnetic conductor (AMC) and electromagnetic band gap (EBG) characteristics of planar periodic metallic arrays printed on grounded dielectric substrate are investigated. The currents ...induced on the arrays are presented for the first time and their study reveals two distinct resonance phenomena associated with these surfaces. A new technique is presented to tailor the spectral position of the AMC operation and the EBG. Square patch arrays with fixed element size and variable periodicities are employed as working examples to demonstrate the dependence of the spectral AMC and EBG characteristics on array parameters. It is revealed that as the array periodicity is increased, the AMC frequency is increased, while the EBG frequency is reduced. This is shown to occur due to the different nature of the resonance phenomena and the associated underlying physical mechanisms that produce the two effects. The effect of substrate thickness is also investigated. Full wave method of moments (MoM) has been employed for the derivation of the reflection characteristics, the currents and the dispersion relations. A uniplanar array with simultaneous AMC and EBG operation is demonstrated theoretically and experimentally.
Planar periodic metallic arrays behave as artificial magnetic conductor (AMC) surfaces when placed on a grounded dielectric substrate and they introduce a zero degrees reflection phase shift to ...incident waves. In this paper the AMC operation of single-layer arrays without vias is studied using a resonant cavity model and a new application to high-gain printed antennas is presented. A ray analysis is employed in order to give physical insight into the performance of AMCs and derive design guidelines. The bandwidth and center frequency of AMC surfaces are investigated using full-wave analysis and the qualitative predictions of the ray model are validated. Planar AMC surfaces are used for the first time as the ground plane in a high-gain microstrip patch antenna with a partially reflective surface as superstrate. A significant reduction of the antenna profile is achieved. A ray theory approach is employed in order to describe the functioning of the antenna and to predict the existence of quarter wavelength resonant cavities.
A low‐loss Ka‐band transition from waveguide to substrate integrated waveguide (SIW) is presented based on ridge waveguide stepped‐impedance transformer. This novel transition can operate across a ...full Ka‐band (26.5 to 40 GHz) with an insertion loss lower than 0.59 dB and return loss over 14.2 dB. Furthermore, compared to existing transitions the introduction of ridges reduces the metal usage, resulting in weight reduction and offering an encouraging application for weight‐sensitive satellite communications (SatComs).
A technique is proposed for the design of engineered reflectors consisting of doubly periodic arrays printed on thin grounded dielectric substrates that reflect an incoming wave from a given incoming ...direction to a predetermined outgoing direction. The proposed technique is based on a combination of Floquet theory for propagation in periodic structures and reflect-array principles. A flat surface designed to reflect a TE polarized wave incident at 45 ° back in the direction of the impinging signal at 14.7 GHz is employed as an example. By means of full-wave simulations, it is demonstrated that the monostatic RCS of a finite reflector is comparable with the specular RCS of a metallic mirror of the same dimensions. It is further shown that comparably high monostatic RCS values are obtained for angles of incidence in the 30 ° -60 ° range, which are frequency dependent and thus open opportunities for target localization. A prototype array is fabricated and experimentally tested for validation. The proposed solution can be used to modify the radar cross section of a target. Other potential applications are also discussed.
An electronically tunable reflection polarizer which exploits the dielectric anisotropy of nematic liquid crystals (LC) has been designed, fabricated and measured in a frequency band centered at 130 ...GHz. The phase agile polarizing mirror converts an incident slant 45° signal upon reflection to right hand circular (RHCP), orthogonal linear (-45 °) or left hand circular (LHCP) polarization depending on the value of the voltage biasing the LC mixture. In the experimental set-up this is achieved by applying a low frequency bias voltage of 0 V, 40 V and 89 V respectively, across the cavity containing the LC material.
Summary
Since May of 2014, NASA's Glenn Research Center has operated measurement campaigns for the Alphasat Aldo Paraboni Propagation Experiment alongside the European community of propagation ...experimenters. Presently, three NASA stations have been deployed to distinct climatological regions across Europe. NASA's participation in the campaign began in 2014 through a collaborative effort with the Politecnico di Milano (POLIMI) to jointly operate a 20/40 GHz ground terminal at the POLIMI campus in Milan, Italy. Subsequently, a single‐channel 40 GHz terminal was deployed to Edinburgh, Scotland in March 2016 in collaboration with Heriot‐Watt University (HWU). A third terminal was deployed to NASA's Madrid Deep Space Communications Complex (MDSCC) in March 2017 with NASA'S Jet Propulsion Laboratory (JPL), also observing the 40 GHz beacon. In addition, a fourth station is planned for deployment to Andøya, Norway by early 2019 in collaboration with the Norwegian Defence Research Establishment (FFI). This paper will detail the design and results of the two most established terminals, Milan and Edinburgh, which together comprise 11 station years of propagation measurements.
Since 2014, NASA's Glenn Research Center has operated measurement campaigns for the Alphasat propagation experiment. Presently, three NASA stations have been deployed to distinct climatological regions across Europe: at the Politecnico di Milano campus in Milan, Italy (May 2014), at Heriot‐Watt University in Edinburgh, Scotland (March 2016), and at NASA's Madrid Deep Space Communications Complex (MDSCC) in Robledo de Chavela, Spain (March 2017).This paper details the two most established terminals, Milan and Edinburgh, together comprising 11 station years of measurements.
A new inline coupling topology for narrowband helical resonator filters is proposed that allows to introduce selectively located transmission zeros (TZs) in the stopband. We show that a pair of ...helical resonators arranged in an interdigital configuration can realize a large range of in-band coupling coefficient values and also selectively position a TZ in the stopband. The proposed technique dispenses the need for auxiliary elements, so that the size, complexity, power handling and insertion loss of the filter are not compromised. A second order prototype filter with dimensions of the order of 0.05λ, power handling capability up to 90 W, measured insertion loss of 0.18 dB and improved selectivity is presented.
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