Wave propagation and the frequency domain Green's functions in viscoelastic Biot/squirt (BISQ) media

In this paper, we examine the characteristics of elastic wave propagation in viscoelastic porous media, which contain simultaneously both the Biot-flow and the squirt-flow mechanisms (BISQ). The frequency-domain Green's functions for viscoelastic BISQ media are then derived based on the classic potential function methods. Our numerical results show that S-waves are only affected by viscoelasticity, but not by squirt-flows. However, the phase velocity and attenuation of fast P-waves are seriously influenced by both viscoelasticity and squirt-flows; and there exist two peaks in the attenuation-frequency variations of fast P-waves. In the low-frequency range, the squirt-flow characteristic length, not viscoelasticity, affects the phase velocity of slow P-waves, whereas it is opposite in the high-frequency range. As to the contribution of potential functions of two types of compressional waves to the Green's function, the squirt-flow length has a small effect, and the effects of viscoelastic parameter are mainly in the higher frequency range. Crown Copyright (C) 2006 Published by Elsevier Ltd. All rights reserved.

Word frequency cues word order in adults: cross-linguistic evidence

[EN] One universal feature of human languages is the division between grammatical functors and content words. From a learnability point of view, functors might provide entry points or anchors into the syntactic structure of utterances due to their high frequency. Despite its potentially universal scope, this hypothesis has not yet been tested on typologically different languages and on populations of different ages. Here we report a corpus study and an artificial grammar learning experiment testing the anchoring hypothesis in Basque, Japanese, French, and Italian adults. We show that adults are sensitive to the distribution of functors in their native language and use them when learning new linguistic material. However, compared to infants’ performance on a similar task, adults exhibit a slightly different behavior, matching the frequency distributions of their native language more closely than infants do. This finding bears on the issue of the continuity of language learning mechanism.

High bandwidth multimode fiber links using subcarrier multiplexing in vertical-cavity surface-emitting lasers

The usage of subcarrier multiplexing (SCM) techniques to allow link transmission in excess of the specified fiber bandwidth is described. A series of 200-Mbit/s channels with carrier frequencies of up to more than twenty times the 3-dB fiber bandwidth have been successfully used, the maximum being limited by the available electronics. To assess the transmission of the fiber, digitally modulated channels are placed on high frequency carrier signals and then used to modulate a vertical-cavity surface-emitting lasers (VCSEL).

Ultrafast sputtered ZnO thin films with high kT for acousticwave device applications

The fabrication of high frequency acoustic wave devices requires thedevelopment of thin films of piezoelectric materials with improved morphologicaland electro-acoustical properties. In particular, the crystalline orientationof the films, surface morphology, film stress and electrical resistivity are keyissues for the piezoelectric response. In the work reported here, ZnO thinfilms were deposited at high rates (>50 nm/min) using a novel process knownas the High Target Utilisation Sputtering (HiTUS). The films deposited possessexcellent crystallographic orientation, high resistivity (>109ωm), and exhibit surface roughness and film stress one order of magnitudelower than films grown with standard magnetron sputtering. The electromechanicalcoupling coefficient of the films, kT, was precisely calculated byimplementing the resonant spectrum method, and was found to be at least 6%higher than any previously reported kT of magnetron sputtered filmsto the Authors' knowledge. The low film stress of the film is deemed as one ofthe most important factors responsible for the high k T valueobtained. © 2010 IEEE.

Wide Area Passive UHF RFID System using Antenna Diversity Combined with Phase and Frequency Hopping

This paper presents a long range and effectively error-free ultra high frequency (UHF) radio frequency identification (RFID) interrogation system. The system is based on a novel technique whereby two or more spatially separated transmit and receive antennas are used to enable greatly enhanced tag detection performance over longer distances using antenna diversity combined with frequency and phase hopping. The novel technique is first theoretically modelled using a Rician fading channel. It is shown that conventional RFID systems suffer from multi-path fading resulting in nulls in radio environments. We, for the first time, demonstrate that the nulls can be moved around by varying the phase and frequency of the interrogation signals in a multi-antenna system. As a result, much enhanced coverage can be achieved. A proof of principle prototype RFID system is built based on an Impinj R2000 transceiver. The demonstrator system shows that the new approach improves the tag detection accuracy from <50% to 100% and the tag backscatter signal strength by 10dB over a 20 m x 9 m area, compared with a conventional switched multi-antenna RFID system.

Overall optimization of high-speed semiconductor laser modules

Based on the high frequency techniques such as frequency response measurement, equivalent circuit modeling and packaging parasitics compensation, a comprehensive optimization method for packaging high-speed semiconductor laser module is presented in this paper. The experiments show that the small-signal magnitude frequency response of the TO packaged laser module is superior to that of laser diode in frequencies, and the in-band flatness and the phase-frequency linearity are also improved significantly.

Frequency dependence of junction capacitance of GaN p-i-n UV detectors

In this paper frequency dependence of small-signal capacitance of p-i-n UV detectors, which were fabricated on GaN grown on sapphire substrate by metalorganic chemical vapor deposition, has been studied. The Schibli-Milnes model was used to analyze the capacitance-frequency characteristics. According to high frequency C-V measurements, the deep level mean concentration is about 2.98 x 10(20) cm(-3). The deep level is caused by the un-ionised Mg dopant. The calculated Mg activation energy is 260 meV and the hole thermal capture cross section of the deep level is about 2.73 x 10(-22) cm(2). The applicability of the Schibli-Milnes model is also discussed when the concentration of deep levels exceeds that of the heavily doped n-side. It is concluded that the analytic expression of the Schibli-Milnes model can still be used to describe the capacitance-frequency characteristics of GaN p-i-n UV detectors in good agreement with experiment. (c) 2005 Elsevier Ltd. All rights reserved.

High-power electroabsorption modulator for radio over fibre system

An electroabsorption modulator using an intra-step quantum well (IQW) active region is fabricated for a radio over fibre system. The strain-compensated InGaAsP/InGaAsP IQW shows good material quality and improved modulation properties, high extinction ratio efficiency (10 dB V-1) and low capacitance (< 0.42 pF), with which high frequency (> 15 GHz) can be obtained. High-speed measurement under high-power excitation shows no power saturation up to an excitation power of 21 dBm. To our knowledge, the input optical power is the highest reported for a multi-quantum well EAM without a heat sink.

High-power electroabsorption modulator using intrastep quantum well

An electroabsorption modulator using the intrastep quantum well (IQW) active region is fabricated for optical network systems. The strain-compensated InGaAsP/InGaAsP IQW shows good material quality and improved modulation properties, high extinction ratio elliciency 10 dB/V and low capacitance (< 0.42 pF), with which an ultra high frequency (> 15 GHz) can be obtained. High-speed measurement under high-power excitation shows no power saturation up to excitation power of 21 dBm. To our knowledge, the input optical power is the highest reported for multi-quantum well EAMs without heat sinks.

Characterization of parasitics in TO-packaged high-speed laser modules

An elaborate analysis of the parasitic network of high-speed through-hole packaging (TO)-type laser modules is presented using a small-signal equivalent circuit model. The intrinsic laser diode is obtained using the optical modulation technique, and is embedded into the model as a separate component. Three step-by-step measurements are made for determining the packaging parasitic network, including the test fixture, TO header, submount, bonding wire, and parasitics of the laser chip. A good agreement between simulated and measured results confirms the validation and accuracy of the characterization procedures. Furthermore, several key parasitic elements are found based on the simulation of the high-frequency responses of the packaged devices. It is expected that the 3-dB bandwidth of 12 GHz or more of the low-cost TO packaged laser module may be achieved using the proposed optimization method.

Potential frequency bandwidth estimation of TO packaging techniques for photodiode modules

Scattering parameters of photodiode chip, TO header and TO packaged module are measured, and the effects of TO packaging network on the high-frequency response of photodiode are investigated. Based on the analysis, the potential bandwidth of TO packaging techniques is estimated from the scattering parameters of the TO packaging network. Another method for estimating the potential bandwidth from the equivalent circuit for the TO packaged photodiode model is also presented. The results obtained using both methods show that the TO packaging techniques used in the experiments can potentially achieve a frequency bandwidth of 22 GHz.

High-field cyclotron resonance and electron-phonon interaction in modulation-doped multiple quantum well structures

A systematic study of electron cyclotron resonance (CR) in two sets of GaAs/Al0.3Ga0.7As modulation-doped quantum-well samples (well widths between 12 and 24 nm) has been carried out in magnetic fields up to 30 T. Polaron CR is the dominant transition in the region of GaAs optical phonons for the set of lightly doped samples, and the results are in good agreement with calculations that include the interaction with interface optical phonons. The results from the heavily doped set are markedly different. At low magnetic fields (below the GaAs reststrahlen region), all three samples exhibit almost identical CR which shows little effect of the polaron interaction due to screening and Pauli-principle effects. Above the GaAs LO-phonon region (B > similar to 23 T), the three samples behave very differently. For the most lightly doped sample (3 x 10(11) cm(-2)) only one transition minimum is observed, which can be explained as screened polaron CR. A sample of intermediate density (6 x 10(11) cm(-2)) shows two lines above 23 T; the higher frequency branch is indistinguishable from the positions of the single line of the low density sample. For the most heavily, doped sample (1.2 x 10(12) cm(-2)) there is no evidence of high frequency resonance, and the strong, single line observed is indistinguishable from the lower branch observed from sample with intermediate doping density. We suggest that the low frequency branch in our experiment is a magnetoplasmon resonance red-shifted by disorder, and the upper branch is single-particle-like screened polaron CR. (C) 1998 Elsevier Science B.V. All rights reserved.

Strained MQW electro-absorption modulators with high extinction ratio and low capacitance

We fabricate an electro-absorption modulator for optical network system using a new strategy, the improved modulation properties of the strained InGaAs/InAlAs MQW show it's polarization independent, high extinction ratio (> 40dB) and low capacitance (C <0.6pF) which can achieve an ultra-high frequency(> 10GHz). The device is be used in 10Gbps optical time division multiplex (OTDM) system as a signal generator.

High-field cyclotron resonance and electron-phonon interaction in modulation-doped multiple quantum well structures

A systematic study of electron cyclotron resonance (CR) in two sets of GaAs/Al0.3Ga0.7As modulation-doped quantum-well samples (well widths between 12 and 24 nm) has been carried out in magnetic fields up to 30 T. Polaron CR is the dominant transition in the region of GaAs optical phonons for the set of lightly doped samples, and the results are in good agreement with calculations that include the interaction with interface optical phonons. The results from the heavily doped set are markedly different. At low magnetic fields (below the GaAs reststrahlen region), all three samples exhibit almost identical CR which shows little effect of the polaron interaction due to screening and Pauli-principle effects. Above the GaAs LO-phonon region (B > similar to 23 T), the three samples behave very differently. For the most lightly doped sample (3 x 10(11) cm(-2)) only one transition minimum is observed, which can be explained as screened polaron CR. A sample of intermediate density (6 x 10(11) cm(-2)) shows two lines above 23 T; the higher frequency branch is indistinguishable from the positions of the single line of the low density sample. For the most heavily, doped sample (1.2 x 10(12) cm(-2)) there is no evidence of high frequency resonance, and the strong, single line observed is indistinguishable from the lower branch observed from sample with intermediate doping density. We suggest that the low frequency branch in our experiment is a magnetoplasmon resonance red-shifted by disorder, and the upper branch is single-particle-like screened polaron CR. (C) 1998 Elsevier Science B.V. All rights reserved.

Characteristics in frequency domain by inductively coupled plasma atomic emission spectrometry with charge injection detection

The charactesistics of two-dimension spectra obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) with charge injection detection (CID) in frequency domain were studied in the present paper. The measurement spectra were Fourier transformed and the frequency distribution of the spectra was obtained. Results showed that the spectra in frequency domain could he divided into two parts:high frequency and low frequency signals. The later stood for measurement spectra and the former for background and noises. However, the high frequecny signals could not be smoothed simply to reduce noises because the background was deteriorated even though the spectral signal did not change significantly.