Interconnection challenges on integrated terahertz photonic systems

In order to improve the sensitivity and reliability of the arc sensor, it is necessary to know how its characteristics change with the welding circuit conditions and the welding process variables and so on, because the sensor simply uses the electric signals — the weling current and/or the welding voltage as it's outputs. The present work has theoretically analyzed these relationships based on the nonlinear and the linearized models of the arc sensor. The analyses were made in time-domain and in frequency-domain. The results have revealed that the welding loop inductance Lw shows a little effects on the characteristics of the arc sensor if the variation frequency (f) of the torch height is lower than about 6 Hz, but its effect becomes greater in higher frequency range and increases with increasing f. The equivalent output resistance Ks (the slope of U-I (voltage-current) characteristic) of welding power supply exhibits greater effect on the characteristics of the arc sensor in full frequency range. The change in compositions of electrode wire or in welding conditions also effects the characteristics of the arc sensor but these effects are small in extent compared with Lw and Ks.Finally, the real-time behaviour of the arc sensor during the welding for a V-type joint groove was simulated, and the results were discussed by combination of the frequency-characteristics of the arc sensor and real welding conditions. Based on these results, it may be a better selection to use the welding current rather than the voltage as a detected signal in lower frequency range, but it does not necessarily remain good way in high frequency range for current wave-form generally exihibits greater asymetry with respect to the center of groove and current response also normolly declines with increasing f for a conventional welding system.

Microwave frequency downconversion is optically implemented by using two cascaded polarization modulators (PolMs), characterized by full-frequency-range coverage and high conversion efficiency. In this proposed approach, the incident radio-frequency signal (RF) and the local oscillator signal (LO) are applied to the first PolM at the transmitter and the second one at the receiver, respectively. Effective optical carrier suppression can be achieved using the cascaded PolMs, whereas the optical sidebands induced by the RF and the LO signals remain unchanged. Since no additional optical filter is needed, the lower operation frequency limit in other approaches with an optical filter is eliminated, such that a full-frequency-range coverage is ensured in this approach. Meanwhile, the use of optical carrier suppression (OCS) enables high conversion efficiency for microwave downconversion. In the proof-of-concept experiments, the conversion efficiency is improved by over 20 dB within the frequency range from 2 to 15 GHz, as compared to those of cascaded modulators without OCS. Both the upper and the lower limits of such a frequency range can be greatly extended when test instruments with full frequency range are used.

This paper describes frequency scanning slot arrays operating from 130 to 180 GHz. The arrays are micro-fabricated using the PolyStrata sequential copper deposition process. Measured reflection coefficient and radiation patterns agree with HFSS full-wave simulations. The voltage standing wave ratio is less than 1.75:1 over the entire frequency range, and the measured scanning is 1.04 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ }/$</tex> </formula> GHz from 130 to 150 GHz and 32.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ }$</tex></formula> over the full frequency range. The measured gain is 15.5 dBi for a 10-element array at 150 GHz and 18.9 dBi for a 20-element array at 150 GHz with about 3 dB of variation over the scan range.

The paper deals with the robust control of a vibrating linear structure under seismic motion described by the Kanai-Tajimi model. The roust control is performed using two tuned mass dampers (TMD) mounted in parallel configuration and designed using a new displacement reliability-based optimization (RBO) approach. Assuming a failure mode characterized by the displacement exceedance, of the hosting structure, of a specified threshold level during a time interval, the optimal TMD parameters are obtained by minimizing the corresponding failure probability. By making use of the Poisson assumptions and the Rice’s formula, the statistics required for the evaluation of the failure probability have been estimated by integrating the displacement power spectral density (PSD) over a limited frequency range in contrast with the classical RBO approach which considers the full frequency range. Assuming bounded uncertainties, the failure probabilities corresponding to the nominal and the perturbed structural parameter, are considered as two objective functions, to be minimized, and the TMD parameters are obtained using a multi-objective optimization. The comparison of the obtained results, in both deterministic and uncertain contexts, with others from the literature, showed good performances of the proposed approach.KeywordsRobust control of vibrationsReliability-based optimization of parallel TMDsUncertain bounded parametersSeismic motionKanai-Tajimi model

This paper deals with the analysis of a single degree of freedom vibration isolation system with dry friction damper. Based on the analysis of classical vibration isolation transmission ratio, the conditions of free resonance are found. Regard to the character of vibration isolation system on critical frequency of vibration isolation and resonance, the transmission ratio formula of vibration isolation with friction force under full frequency range is educed which provided the rounded theory principle for free resonance vibration isolation. The vibration isolation system is designed which can realize the non-amplification in low frequency range and better vibration isolation effect in high frequency. Lately, the correctness of the principle is verified by the actual experiment.

A systematic and quantitative comparison of electrical detection systems in scanning microwave microscopy is reported. Scanning microwave microscopy (SMM) is capable of investigating nanoscale electrical properties with high accuracy over a broad frequency range of 1-20 GHz. However, due to the passive matching network only discrete frequencies can be used every 1 GHz with varying signal-to-noise ratio (SNR). Here we study in detail the impedance matching mechanism using an interferometric network where a two-port measurement is implemented with a reduction of the trace noise due to signal subtraction. The interferometer setup shows superior performance resulting in a 2-8 fold increased SNR with respect to the standard shunt solution, in addition to stable broadband performance over the full frequency range. We perform a comparison of the electrical sensitivity obtained using a direct connection from the network analyser to probe, the typically implemented shunt-resonator impedance matching network, and the proposed interferometer setup. The interferometer SMM allows us also for calibrated impedance measurements, which we demonstrate on Tobacco mosaic viruses with 18-nm diameter, with a capacitance resolution of 0.67 attoFarads at 10 ms acquisition time per pixel.

The linewidth of the electron-spin resonance in aluminum has been studied experimentally in many laboratories over the frequency range 1.3-80 GHz and at temperatures from 4 to 100 K. At low temperatures the width is thought to be due to motionally narrowed $g$ anisotropy, and at high temperatures spin-flip scattering by phonons is assumed to dominate. Models are developed in this paper, based on previous calculations of the $g$ anisotropy by Beuneu, which give a good semiquantitative account of the linewidth variation over the full range of frequency and temperature.

The multiple light scattering in a turbid medium degrades imaging through the medium. The degradation can be quantitatively described by the modulation transfer function (MTF). Knowledge of the MTF of a turbid medium is important for imaging system design, imaging processing, and related areas The MTF of a turbid medium is equivalent to the transmitted radiance distribution from the medium under isotropic diffuse illumination with unit intensity. By solving the radiative transfer problem we could obtain the MTF in full spatial frequency range and investigate effects of any kind of scattering parameters on the MTF. The radiative transfer problem in a typical turbid medium could only be solved numerically, and an explicit analytical expression of the MTF is impossible to be given in a general manner. A convenient analytical MTF expression is useful and necessary for application. The widely used MTF expression is obtained from the small-angle-approximation (SAA) analysis The SAA approximation is valid only for a rather narrow frequency range. Though the MTF is affected by the whole scattering properties of the turbid medium the SAA MTF expression depends only on the scattering and absorption optical thickness. An analytical MTF expression for a turbid medium is obtained as a function of some main scattering parameters. It is found that the analytical expression of MTF is with high accuracy at practical frequencies for a typical optical thickness.

The ever-increasing application of sensor networks in many different fields is causing a growing demand of low-cost passive sensors for monitoring physical variables such as temperature, pressure or ambient humidity. These sensors need a conditioning circuit that allows an easy interface to a microcontroller, taking advantage of the full range of the sensor and reducing the microcontroller requirements. This paper presents a conditioning system designed to transform the output of low-cost resistive sensors to a digital value. The system consists of a voltage to frequency converter circuit and the implementation of a frequency to code algorithm programmed on a low-power microcontroller. The conversion circuit was designed to use the full frequency range available, providing a good resolution while the resulting quasi-digital signals are compatible to the logic levels of a standard low-power microcontroller. The algorithm provides a suitable accuracy at low requirements in microcontroller resources.

While many vibrational Raman spectroscopy studies of liquid water have investigated the temperature dependence of the high-frequency O-H stretching region, few have analyzed the changes in the Raman spectrum as a function of temperature over the entire spectral range. Here, we obtain the Raman spectra of water from its melting to boiling point, both experimentally and from simulations using an ab initio-trained machine learning potential. We use these to assign the Raman bands and show that the entire spectrum can be well described as a combination of two temperature-independent spectra. We then assess which spectral regions exhibit strong dependence on the local tetrahedral order in the liquid. Further, this work demonstrates that changes in this structural parameter can be used to elucidate the temperature dependence of the Raman spectrum of liquid water and provides a guide to the Raman features that signal water ordering in more complex aqueous systems.

Ultra-broadband chip-to-chip interconnects at high frequencies are demonstrated. These interconnects, based on the Quilt Packaging (QP) approach, appear to be promising for applications in millimeter-wave circuits due to their extremely wide bandwidth and ease of assembly. The performance of chip-to-chip interconnects in a 50 Ω coplanar waveguide environment on high-resistivity silicon substrates has been measured to 220 GHz using a vector network analyzer, and is compared with projections obtained from 3D electromagnetic modeling. Single-mode, resonance-free operation is demonstrated through 220 GHz, with insertion loss below 1.5 dB over the full frequency range. Although the resistance of the conductive epoxy (used for the prototypes reported here) limits the performance of the QP nodules, simulations indicate that better joining methods such as soldering promise to yield insertion loss of much less than 1 dB at 220 GHz.

This paper describes the high-frequency characterizations of a vertical electro-absorption modulator (EAM) to ensure its monolithic integration onto a VCSEL for data communications. Splitting the emitting and the modulating parts is an attractive approach compared to directly current-modulated VCSEL since it releases the intrinsic limitations due to carriers dynamics that occurs in such VCSEL device. It is, in this aim, utmost to thoroughly characterize and understand the properties and performances of the vertically integrated EAM under high frequency operation, as it will be decisive for the application of EAM-VCSEL to very high data-rate communications. EAM measurements, presented up to 40 GHz, require a precise control of the optical fiber coupling and a precise evaluation of the injection losses over the full frequency range.

We report a computational study on vibronic effects in the spectroscopy, photoinduced processes and decay back to the ground state of aza[7]helicene, a helicene with an unusually high fluorescence quantum yield (QY = 0.39). In a first step, we compute and assign the absorption and electronic circular dichroism (ECD) spectra in its full frequency range from 2.7 to 5.0 eV, accounting for nonadiabatic effects. Then we compute the quantum dynamics of the cascade of ultrafast internal conversions of the highly-excited singlet states to the lowest-energy one S1. Finally we adopt Fermi golden rule rates to compute the QY of the dye, taking into account the competition between the radiative decay and the nonradiative decays to the ground state and to the energy-accessible triplet states. We use time-dependent density functional theory (TD-DFT), including solvent (dichloromethane) effects within the polarizable continuum model, to parameterize a linear vibronic coupling (LVC) model involving the first lowest 12 singlet states and all the normal coordinates. Nonadiabatic spectra and internal conversions dynamics are then computed through wavepacket propagations with the Multilayer (ML) extension of the Multiconfigurational Time Dependent Hartree method (ML-MCTDH). We highlight the molecular vibrations playing a major role in determining the shape of the spectra and analyse the effect of inter-state couplings. At the same time we report a breakdown of perturbative Herzberg-Teller approach. The computed QY is in perfect agreement with experiment and allows us to ascertain that intersystem crossings are the processes limiting the fluorescence from S1. They involve the three lowest triplet states and are made effective by spin-orbit coupling and vibronic effects.

A balanced amplifier utilizing 0.8 μm MESFET common-gate (CG) transistors was demonstrated to provide 6 dB of gain at 30 GHz and a 3 dB bandwidth of 3.5 GHz. The power at 1 dB gain compression was 9.67 dBm for the amplifier. The amplifier also demonstrated unconditional stability over the full frequency range. To our knowledge, this is the highest frequency amplifier with gain ever demonstrated with a process of this kind.

This paper analyzes the fault sensitivity of data feedback control which is synthesized with H∞/H_ optimization technique. With I/O data, a closed-loop output predictor is parameterized by stochastically uncertain Markov parameters which are estimated by least squares. The estimation error due to bias and noise are rejected over infinite horizon and guarantees mean square stability in the sense of worst case. The measured I/O data is setup as state which makes the stability analysis and data feedback control synthesis possible. In order to improve fault sensitivity, the H_ index method is applied. Then, the controller design problem based on multiobjective optimization approach is solved in a numerically efficient way such as Linear Matrix Inequality (LMI). The fault sensitivity is analyzed in the full frequency range and its effect on the pre-defined performance is described with a simulation example.