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Dive into the research topics where Robert Rehammar is active.

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Featured researches published by Robert Rehammar.


Nano Letters | 2013

Electromechanically Tunable Carbon Nanofiber Photonic Crystal

Robert Rehammar; Farzan Alavian Ghavanini; Roger Magnusson; Jari M. Kinaret; Peter Enoksson; Hans Arwin; Eleanor E. B. Campbell

We demonstrate an electrically tunable 2D photonic crystal array constructed from vertically aligned carbon nanofibers. The nanofibers are actuated by applying a voltage between adjacent carbon nanofiber pairs grown directly on metal electrodes, thus dynamically changing the form factor of the photonic crystal lattice. The change in optical properties is characterized using optical diffraction and ellipsometry. The experimental results are shown to be in agreement with theoretical predictions and provide a proof-of-principle for rapidly switchable photonic crystals operating in the visible that can be fabricated using standard nanolithography techniques combined with plasma CVD growth of the nanofibers.


Nanotechnology | 2010

Optical properties of carbon nanofiber photonic crystals

Robert Rehammar; Roger Magnusson; A.I. Fernandez-Dominguez; Hans Arwin; Jari M. Kinaret; Stefan A. Maier; Eleanor E. B. Campbell

Carbon nanofibers (CNFs) are used as components of planar photonic crystals. Square and rectangular lattices and random patterns of vertically aligned CNFs were fabricated and their properties studied using ellipsometry. We show that detailed information such as symmetry directions and the band structure of these novel materials can be extracted from considerations of the polarization state in the specular beam. The refractive index of the individual nanofibers was found to be n(CNF) = 4.1.


Optics Express | 2008

Nanowire-based tunable photonic crystals

Robert Rehammar; Jari M. Kinaret

Photonic crystals, materials with periodically varying refractive indices, show exciting optical properties that enable many technological applications. Conventional photonic crystals have optical properties that are determined at the time of fabrication and the ability to tune them is quite limited, particularly at visible frequencies. We investigate theoretically the possibility to use nanowires or nanotubes as the building block for tunable two-dimensional photonic crystals. Tunability is achieved by fabricating flexible nanowires in a periodic pattern and actuating them electrostatically. This changes the lattice basis, which in turn modifies the optical properties of the photonic crystal. We use a finite-difference time-domain method to model photonic crystals with changeable bases. We show that the optical transmission through a two-dimensional photonic crystal with only a few rows of nanowires in the light propagating direction can be electrostatically tuned from over 90% transmission to less than 10%. We demonstrate that tunability is maintained in realistic three-dimensional experimental geometries. Finally, we analyse the performance of the photonic crystals in terms of actuation voltages and tuning speeds, and conclude that the response time of a tunable carbon-nanofibre-based photonic crystal lies in the microsecond range.


Optics Letters | 2012

Diffraction from carbon nanofiber arrays

Robert Rehammar; Y. Francescato; Antonio I. Fernández-Domínguez; Stefan A. Maier; Jari M. Kinaret; Eleanor E. B. Campbell

A square planar photonic crystal composed of carbon nanofibers was fabricated using e-beam lithography and chemical vapor deposition. The diffraction properties of the system were characterized experimentally and compared with theory and numerical simulations. The intensities of the (-1,0) and (-1,-1) diffraction beams were measured as functions of the angles of incidence for both s and p-polarization. The obtained radiation patterns can be explained using a simple ray interference model, but finite-difference time-domain (FDTD) calculations are necessary to reproduce the observed dependence of the scattered radiation intensity on incident laser polarization. We explain this in terms of the aspect ratio of the nanofibers and the excitation of surface plasmon polaritons at the substrate interface.


european conference on antennas and propagation | 2013

On the use of reverberation chambers for assessment of MIMO OTA performance of wireless devices

Christian Lötbäck Patané; Anton Skårbratt; Robert Rehammar; Charlie Orlenius


european conference on antennas and propagation | 2013

A practical method to measure total radiated power of a mobile device handled by a live person

John Kvarnstrand; Robert Rehammar; Anton Skårbratt; Christian Lötbäck Patané


european conference on antennas and propagation | 2015

802.11p measurements in reverberation chamber

Anton Skårbratt; Robert Rehammar


international symposium on electromagnetic compatibility | 2014

OTA device sensitivity in the presence of interference measured in a reverberation chamber

Patrik Svedjenäs; Weiming Dong; Klas Arvidsson; Robert Rehammar; Charlie Orlenius


international symposium on antennas and propagation | 2015

Antenna measurements in reverberation chambers and their relation to Monte Carlo integration methods

Robert Rehammar; Anton Skårbratt; Christian Lotback-Patane


european conference on antennas and propagation | 2013

Measuring 4x4 MIMO capability in a reverberation chamber

Robert Rehammar; Anton Skårbratt; Charlie Orlenius

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Jari M. Kinaret

Chalmers University of Technology

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Charlie Orlenius

Chalmers University of Technology

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Farzan Alavian Ghavanini

Chalmers University of Technology

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Peter Enoksson

Chalmers University of Technology

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Weiming Dong

Chalmers University of Technology

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