168 research outputs found
Coupling of the lattice and superlattice deformations and hysteresis in thermal expansion for the quasi one-dimensional conductor TaS
An original interferometer-based setup for measurements of length of
needle-like samples is developed, and thermal expansion of o-TaS crystals
is studied. Below the Peierls transition the temperature hysteresis of length
is observed, the width of the hysteresis loop being up to . The behavior of the loop is anomalous: the length changes so
that it is in front of its equilibrium value. The hysteresis loop couples with
that of conductivity. The sign and the value of the length hysteresis are
consistent with the strain dependence of the charge-density waves (CDW) wave
vector. With lowering temperature down to 100 K the CDW elastic modulus grows
achieving a value comparable with the lattice Young modulus. Our results could
be helpful in consideration of different systems with intrinsic
superstructures.Comment: 4 pages, 3 figures. Phys. Rev. Lett., accepted for publicatio
A millimeter-wave inflatable frequency-agile elastomeric antenna
This letter reports a millimeter-wave frequency agile microstrip antenna printed on an ultrasoft elastomeric PDMS substrate. The microstrip patch antenna is supported by a PDMS membrane suspended over an air cavity. The distance H between the patch and the ground plane, and thus the resonant frequency of the antenna, are tuned using pneumatic actuation, taking advantage of the extreme softness of the PDMS membrane. A continuous frequency shift varying from 55.35 to 51 GHz ( ≈8%) has been obtained for a tuning range of H between 200µm and 575µm. In all configurations, the antenna remains matched and its radiation characteristics are very satisfactory
A millimeter-wave microstrip antenna array on ultra-flexible micromachined polydimethylsiloxane (PDMS) polymer
The use of Polydimethylsiloxane (PDMS), an ultra flexible polymer, as a substrate for the realization of reconfigurable microwave devices in the 60-GHz band is presented. As bulk PDMS is demonstrated to be lossy at millimeter waves, membrane-supported devices are considered. A new reliable and robust technological process has been developped to micromachine membrane-supported transmission lines and microstrip antenna arrays. It is shown that transmission lines printed on 20-µm thick membranes exhibit similar performances as bulk substrates commonly used at millimeter-wave frequencies. A microstrip antenna array has been also designed and fabricated to demonstrate the feasibility of directive antennas supported by large membranes. Promising applications for mechanical beam-steering, beam forming and frequency tunable antennas are expected
THE DECISION OF FORM FOR DIFFRACTIVE STRUCTURES IN THE PROBLEM OF SCATTERING OF RADIO WAVES.
В работе рассматривается задача рассеяния электромагнитных волн на различных дифракционных структурах. Решение задачи рассеяния осуществляется на основе метода интегральных уравнений. По диаграммам обратного рассеяния при разных частотах падающей волны принимается решение о форме исследуемого объекта.This paper considers the problem of scattering of electromagnetic waves in different diffraction structures. The solution of the scattering problem is based on the method of integral equations. On diagrams of backscattering at various frequencies of the incident wave, the decision about the form of the object is carried out
THE OPTIMIZATION OF ELECTRODYNAMIC CONFIGURATION OBJECT WITH THE DESIRED CHARACTERISTICS OF SCATTERING.
В работе рассматривается задача оптимизация характеристик рассеяния электромагнитных волн на периодической электродинамической структуре. Решение задачи рассеяния осуществляется на основе метода интегральных уравнений, оптимизация характеристик проводится на основе генетического алгоритма. Даны рекомендации по параметрам периодической структуры при заданных углах наблюдения.This paper considers the problem of optimization of the characteristics of scattering of electromagnetic waves on periodic electrodynamic structure. The solution of the scattering problem is based on the method of integral equations, the optimization of the characteristics is based on the genetic algorithm. Recommendations on the parameters of the periodic structure under given angles are given
THE SIMULATION OF SCATTERING OF ELECTROMAGNETIC WAVES ON ANGULAR STRUCTURES.
В работе рассматриваются особенности рассеяния электромагнитных волн на угловых дифракционных структурах. Решение задачи проводится на основе метода интегральных уравнений. Проведен сравнительный анализ характеристик рассеяния структур с различной формой.The paper discusses the characteristics of scattering of electromagnetic waves on the angular diffraction structures. The solution of the problem is based on the method of integral equations. A comparative analysis of the scattering characteristics of structures with different shape is carried out
A Compact Solid State Detector for Small Angle Particle Tracking
MIDAS (MIcrostrip Detector Array System) is a compact silicon tracking
telescope for charged particles emitted at small angles in intermediate energy
photonuclear reactions. It was realized to increase the angular acceptance of
the DAPHNE detector and used in an experimental program to check the
Gerasimov-Drell-Hearn sum rule at the Mainz electron microtron, MAMI. MIDAS
provides a trigger for charged hadrons, p/pi identification and particle
tracking in the region 7 deg < theta < 16 deg. In this paper we present the
main characteristics of MIDAS and its measured performances.Comment: 13 pages (9 figures). Submitted to NIM
Elaboration of a Novel Design Pirani Pressure Sensor for High Dynamic Range Operation and Fast Response Time
AbstractWe report a novel design for realizing Pirani sensor with a working range from a 1kPa up to pressure over than atmospheric one. The sensor is specifically designed to achieve high sensitivity, fast response time and high robustness. The proof of concept is composed of four metallic resistors interconnected to form a Wheatstone bridge. Two of them act simultaneously as the heating and sensing elements and the two others are used as a temperature reference. The heating element consists of a metallic wire of platinum Pt (3μm width, 1mm length) maintained on each lateral side by periodic silicon oxide SiO2 micro-bridges. The sensor design, fabrication technologies, electrical characterizations and voltage-pressure responses are described and shown. A future perspective is given, which describe the extension of this concept to elastic wave transduction of pressure using a combination of heater element and thin plate elastic waveguide
ЗАВИСИМОСТЬ ДЕФОРМАЦИОННОГО СОСТОЯНИЯ ПЛЕНОК GaAs НА ВИЦИНАЛЬНЫХ ПОДЛОЖКАХ Si(001) ОТ СПОСОБА ФОРМИРОВАНИЯ ПЕРВЫХ МОНОСЛОЕВ ПРОСЛОЙКИ GaP
A significant dependence of the strain state of GaAs film lattice grown by molecular−beam epitaxy (MBE) on the nucleation method of early GaP buffer layers (50 nm) on the vicinal substrate Si(001) 4° around the <011> axis was discovered. GaP growth started layer−by−layer with a gallium or a phosphorus sublayer. If GaP nucleated with a gallium sublayer, the GaAs film has a significant lattice rotation around the <011> axis. If the buffer starts forming with a phosphorus layer the GaAs film evidently rotates around the <001> axis. The film relaxation degree ex- ceeds 100%, and the film is in a laterally strained state. Analysis was carried out using the triclinic distortion model. A reciprocal space scattering map was obtained using X−ray diffraction in a three−axis low resolution setup. The map clearly shows that the GaAs film lattice is rotated.Выявлена существенная зависимость деформационного состояния кристаллической решетки пленок GaAs, выращенных методом молекулярнолучевой эпитаксии от способа зарождения первых слоев прослойки GaP (50 нм) на вицинальной подложке Si(001) 4° вокруг оси <011>. Рост GaP начинался послойно с галлиевого или фосфорного подслоя. Установлено, что в случае зарождения GaP с галлия, пленка GaAs имеет значительный поворот кристаллической решетки вокруг направления <011>. При фор- мировании прослойки с фосфорного подслоя заметен поворот пленки GaAs вокруг <001>. Степень релаксации пленки составляет более 100 %, она находится в латерально растянутом состоянии. Анализ проведен с использованием модели триклинных искажений. Представлена карта рассеяния в обратном пространстве, полученная с помощью рентгеновской дифрактометрии в трехосевой схеме малого разрешения. На карте явно виден факт поворота кристаллической решетки пленки GaAs.
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