Ultra directive antenna via transformation optics

Spatial coordinate transformation is used as a reliable tool to control electromagnetic fields. In this paper, we derive the permeability and permittivity tensors of a metamaterial able to transform an isotropically radiating source into a compact ultradirective antenna in the microwave domain. We show that the directivity of this antenna is competitive with regard to conventional directive antennas horn and reflector antennas, besides its dimensions are smaller. Numerical simulations using finite element method are performed to illustrate these properties. A reduction in the electromagnetic material parameters is also proposed for an easy fabrication of this antenna from existing materials. Following that, the design of the proposed antenna using a layered metamaterial is presented. The different layers are all composed of homogeneous and uniaxial anisotropic metamaterials, which can be obtained from simple metal-dielectric structures. When the radiating source is embedded in the layered metamaterial, a highly directive beam is radiated from the antenn

Experimental demonstration of non-magnetic metamaterial cloak at microwave frequencies

Metamaterials have paved the way to unprecedented control of the electromagnetic field1,2. The conjunction with space coordinate transformation has led to a novel "relativity inspired" approach for the control of light propagation. "Invisibility cloak" is the most fascinating proposed devices3,4. However, the realized structures up to now used a graded "metamagnetic" so as to achieve the cloaking function11. Artificial magnetism is however still very challenging to obtain in optics despite the currently promising building blocks13-17, not suited for optical cloaking. We report here the first experimental demonstration of non-magnetic cloak at microwave frequencies by direct mapping of the magnetic field together with the first experimental characterization of a cloak in free space configuration. The diameter of the concealed region is as big as 4.4 in wavelength units, the biggest reported experimentally so far. The principle can be scaled down to optical domain while keeping the compatibility with current nanofabrication technologies.Comment: 6 pages, 3figure

Waveguide taper engineering using coordinate transformation technology

Spatial coordinate transformation is a suitable tool for the design of complex electromagnetic structures. In this paper, we define three spatial coordinate transformations which show the possibility of designing a taper between two different waveguides. A parametric study is presented for the three transformations and we propose achievable values of permittivity and permeability that can be obtained with existing metamaterials. The performances of such defined structures are demonstrated by finite element numerical simulations

2D Waveguided Bessel Beam Generated Using Integrated Metasurface-Based Plasmonic Axicon

International audienc

High Risk of Anal and Rectal Cancer in Patients With Anal and/or Perianal Crohn’s Disease

International audienceBackground & AimsLittle is known about the magnitude of the risk of anal and rectal cancer in patients with anal and/or perineal Crohn’s disease. We aimed to assess the risk of anal and rectal cancer in patients with Crohn’s perianal disease followed up in the Cancers Et Surrisque Associé aux Maladies Inflammatoires Intestinales En France (CESAME) cohort.MethodsWe collected data from 19,486 patients with inflammatory bowel disease (IBD) enrolled in the observational CESAME study in France, from May 2004 through June 2005; 14.9% of participants had past or current anal and/or perianal Crohn’s disease. Subjects were followed up for a median time of 35 months (interquartile range, 29–40 mo). To identify risk factors for anal cancer in the total CESAME population, we performed a case-control study in which participants were matched for age and sex.ResultsAmong the total IBD population, 8 patients developed anal cancer and 14 patients developed rectal cancer. In the subgroup of 2911 patients with past or current anal and/or perianal Crohn’s lesions at cohort entry, 2 developed anal squamous-cell carcinoma, 3 developed perianal fistula–related adenocarcinoma, and 6 developed rectal cancer. The corresponding incidence rates were 0.26 per 1000 patient-years for anal squamous-cell carcinoma, 0.38 per 1000 patient-years for perianal fistula–related adenocarcinoma, and 0.77 per 1000 patient-years for rectal cancer. Among the 16,575 patients with ulcerative colitis or Crohn’s disease without anal or perianal lesions, the incidence rate of anal cancer was 0.08 per 1000 patient-years and of rectal cancer was 0.21 per 1000 patient-years. Among factors tested by univariate conditional regression (IBD subtype, disease duration, exposure to immune-suppressive therapy, presence of past or current anal and/or perianal lesions), the presence of past or current anal and/or perianal lesions at cohort entry was the only factor significantly associated with development of anal cancer (odds ratio, 11.2; 95% CI, 1.18-551.51; P = .03).ConclusionsIn an analysis of data from the CESAME cohort in France, patients with anal and/or perianal Crohn’s disease have a high risk of anal cancer, including perianal fistula–related cancer, and a high risk of rectal cancer