Time filter

Source Type

Reparaz J.S.,CSIC - Institute of Materials Science | Reparaz J.S.,TU Berlin | Muniz L.R.,CSIC - Institute of Materials Science | Goni A.R.,CSIC - Institute of Materials Science | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics

We have studied the electronic subband structure of a piezoelectric [311] Ga0.85In0.15 As/AlAs superlattice by means of high-hydrostatic pressure and excitation-power-dependent photoluminescence at 78 K. In particular, we unraveled the origin of two optical transitions at around 1.96 and 2 eV at ambient pressure, which were recently found to give rise to an unexpectedly strong resonant enhancement of the acoustic-phonon Raman scattering for such samples with permanent built-in piezoelectric fields. Here we demonstrate that these transitions are doubly indirect, in real and reciprocal space, corresponding to radiative recombination processes between electrons at the X valleys of the AlAs barriers and heavy holes at the Γ point of the Brillouin zone but confined to the GaInAs quantum wells. In addition, the partial screening of the piezoelectric field induced by carrier photoexcitation under illumination becomes largely suppressed for pressures above 1.1 GPa due to conduction-band Γ-X crossover effects. © 2010 The American Physical Society. Source

Hatamoto H.,Oki Electric Industry Co. | Ano S.,ATR Wave Engineering Laboratories | Kikuchi N.,Oki Electric Industry Co. | Shimizu S.,Oki Electric Industry Co.
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC

In this paper, transmission performance for wireless harness systems is evaluated using propagation models which include pathloss and power delay profile in an automobile engine compartment. In the wireless harness system in vehicles, it is assumed that an electronic control unit has a wireless access point (AP) and each sensor has a wireless station terminal (ST). First, pathloss and power delay profile models are analyzed using measured propagation data of the scattering parameter in the Toyota Prius's engine room which size is 0.9 × 1.2 × 0.6 m on condition that the vehicle's engine is turned off. Second, performance results of channel capacity and throughput, where on-off keying based signals are transmitted between the AP and each ST, are evaluated using analyzed propagation models. Simulation results confirm that high channel capacity and throughput performance are satisfied when transmit power is less than 0 dBm in 2-3 GHz on condition that positions of AP's antennas are fixed, positions of STs are uniformly set in the engine space, and wireless channels are quasi-static. © 2013 IEEE. Source

Ohira M.,ATR Wave Engineering Laboratories | Miura A.,Japan National Institute of Information and Communications Technology | Ueba M.,ATR Wave Engineering Laboratories
IEEE Transactions on Antennas and Propagation

A new wideband waveguide slot array is proposed for covering a wide elevation-angle range with a planar sector antenna of a multigigabit wireless LAN in the 60-GHz band. The requirement of millimeter-wave sector antennas is to realize both wide bandwidth of 11.2% and wide elevation-angle coverage with a required gain of over 10 dBi. To satisfy both the required gain and bandwidth, the important structural features of the proposed antenna are that multiple slot elements are successively arranged at an interval of the length less than one quarter guide wavelengths and that the slot length increases from the shorted waveguide end to the feed end. The operational principle of the slot array is based on multisection quarter-wavelength reflection cancellation, so the slot array can achieve the required bandwidth. Furthermore, this antenna produces a unidirectional radiation pattern by using the radiators and the reflectors, resulting in the required gain over a wide elevation-angle range. In the design, the structural parameters of the slot array are selected to meet the requirements for 60-GHz-band sector antenna. The developed substrate-integrated- waveguide (SIW) slot array achieves both the 10 dB return-loss bandwidth of 15% and the specified gain in 8896% of the one-sector coverage range of 5966 GHz. The effectiveness of the proposed slot array for a sector antenna is verified by the good agreement between the simulated and measured results. © 2010 IEEE. Source

Hou Y.,ATR Wave Engineering Laboratories | Tsukamoto S.,ATR Wave Engineering Laboratories | Ariyoshi M.,ATR Wave Engineering Laboratories | Kobayashi K.,ATR Wave Engineering Laboratories | Okada M.,Nara Institute of Science and Technology
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC

Leaky coaxial cables (LCX) have been widely used as antennas to form linear service areas for radio communication systems. Such services of linear cells have been deployed inside tunnels, along railways, and so on. Usually, one LCX is utilized as one antenna. Therefore it requires more than one LCX to configure an multi-input multi-output (MIMO) system. In this paper, we propose a MIMO system using single LCX, which can be utilized as two antennas. When different RF transmit signals are fed to each end of the proposed cable, single LCX can work as two antennas. To confirm the feasibility of the proposed MIMO system, we conduct experiments to measure the characteristics of 2 × 2 MIMO channel using single LCX. The results confirm that our proposed 2×2 MIMO channel using single LCX can realize a good channel condition for MIMO transmission even within a highly correlated propagation condition. The proposed MIMO system using LCX will release the space requirement and reduce the cost of system for configuration of LCX MIMO system especially with large number of LCXs. It benefits the design and configuration of LCX-MIMO system for many scenarios of linear-cell. © 2014 IEEE. Source

Nakamoto N.,ATR Wave Engineering Laboratories | Ban H.,ATR Wave Engineering Laboratories | Kobayashi K.,ATR Wave Engineering Laboratories
IEEE Antennas and Propagation Society, AP-S International Symposium (Digest)

We have been developing a 2.4 GHz point-to-multipoint wireless communication system suitable for use inside mechatronics ICT (Information and Communication Technology) equipment to replace wire harnesses inside equipment with wireless communication as a useful technique of weight reduction and simplification of system assembling [1]. One of the critical problems of such applications is that antennas are installed close to metallic components or in a narrow gap between metallic housings and thus suffer degradation of antenna performance due to effects of the ambient environment. Therefore, in order to maintain desired antenna performance inside equipment, we need to understand the dependence of antenna characteristics on the ambient environment inside equipment and design antennas with a consideration of it. © 2012 IEICE. Source

Discover hidden collaborations