Experimental Synthetic Aperture Radar with Dynamic Metasurfaces

We investigate the use of a dynamic metasurface as the transmitting antenna for a synthetic aperture radar (SAR) imaging system. The dynamic metasurface consists of a one-dimensional microstrip waveguide with complementary electric resonator (cELC) elements patterned into the upper conductor. Integrated into each of the cELCs are two diodes that can be used to shift each cELC resonance out of band with an applied voltage. The aperture is designed to operate at K band frequencies (17.5 to 20.3 GHz), with a bandwidth of 2.8 GHz. We experimentally demonstrate imaging with a fabricated metasurface aperture using existing SAR modalities, showing image quality comparable to traditional antennas. The agility of this aperture allows it to operate in spotlight and stripmap SAR modes, as well as in a third modality inspired by computational imaging strategies. We describe its operation in detail, demonstrate high-quality imaging in both 2D and 3D, and examine various trade-offs governing the integration of dynamic metasurfaces in future SAR imaging platforms

Control of the Scattering Properties of Complex Systems By Means of Tunable Metasurfaces

We demonstrate the ability to control the scattering properties of a two-dimensional wave-chaotic microwave billiard through the use of tunable metasurfaces located on the interior walls of the billiard. The complex reflection coefficient of the metasurfaces can be varied by applying a DC voltage bias to varactor diodes on mushroom-shaped resonant patches, and this proves to be very effective at perturbing the eigenmodes of the cavity. Placing multiple metasurfaces inside the cavity allows us to engineer desired scattering conditions, such as coherent perfect absorption (CPA), by actively manipulating the poles and zeros of the scattering matrix through the application of multiple voltage biases. We demonstrate the ability to create on-demand CPA conditions at a specific frequency, and document the near-null of output power as a function of four independent parameters tuned through the CPA point. A remarkably low output-to-input power ratio of $\frac{P_{out}}{P_{in}} = 3.71 \times 10^{-8}$ is achieved near the CPA point at 8.54 GHz

Sub-Wavelength Focusing in Inhomogeneous Media with a Metasurface Near Field Plate

Overcoming the diffraction limit, which enables focusing much less than the wavelength, requires tailoring the evanescent spectrum of an aperture’s field distribution. We model and simulate a corrugated near field plate, which can generate a sub-wavelength focus in inhomogeneous background media. All reactive coupling, between the metasurface near field plate and the focusing domain and among the corrugations in the metasurface, is taken into consideration with the finite element method, which we solve in combination with a constraint to generate a desired focus. Various geometries for the near field plate are considered and we demonstrate that the proposed method can effectively create a deeply sub-wavelength focus within a layered medium having properties resembling brain tissue. Such a device could find use as a detector of biological signals or for hyperthermic treatment near the skin surface

Protestant Christian attitudes to ART

Study Question: How do Christian religious beliefs affect attitudes to ART? Summary Answer: Attitudes to ART depend on the religiosity of the respondent, and although the majority of those that had successfully used ART were positive or moderately positive in their views, the acceptability of procedures fell when damage to the marriage relationship or the embryo was a potential outcome. What is known already: Religion can impact views on ART. Sanctity of marriage and sanctity of the embryo are major concerns for some Christians, but details are unclear. Methods: A cross-sectional online survey was used to collect data from 1587 participants over a 3-month period in 2013, of which 1334 were of the Christian faith and included in this study. Descriptive statistics were reported for individual ARTs, and a general score of all ART approval was calculated. A multivariable linear and logistic regression was conducted on general approval for ART to identify predictors of ART approval. Main results and the role of chance:Indicators of religiosity (religious meeting attendance and Bible reading frequency) showed that this was a highly religious sample. We found that in this cohort of English-speaking, well-educated, practising and mainly Protestant Christians 164 (12.3%) of those had personal experience of ART. Most participants that had successfully used ART were positive or moderately positive in their views. Throughout the cohort, procedures were less acceptable if there was a perception that the marriage relationship or the life of the embryo was threatened: including donated gametes (28.7–29.1% approval), surrogacy (22.7–33.1% approval), and PGD (1.0– 23.8% approval). A multivariable analysis of the ART approval score found that it was higher among those with Protestant compared with Catholic/Orthodox faith (P Limitations, reasons for caution: This sample includes an uneven geographical spread of respondents and restriction to English speaking participants. Different views may be expressed by a different religious cohort. Use of an online survey platform means that a bias towards those with computers (consistent with education levels of this cohort) could exist. Use of this platform also makes it impossible to know the response rate, and the veracity of responses cannot be verified. However, despite these limitations we believe this survey gives us insight into the reservations held among a certain population of Christians regarding the use of reproductive technology. Wider implications of the findings: Our findings highlight the need for ART clinicians to consider the influence of patient spiritual beliefs on therapeutic options and provide detailed information that will allow them to be accommodated. Practices such as widening the options for collecting semen and limiting the number of embryos created through IVF so as to reduce or eliminate excess embryos may be helpful for these patients. Study funding/Competing interests: This study was supported by a grant from The Center for Bioethics & Human Dignity in Deerfield, Illinois, USA. The authors have no conflicts of interest to declare. Trial Registration Number: N/

Single-frequency microwave imaging with dynamic metasurface apertures

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Single-frequency near-field MIMO imaging

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