The coplanar resonator technique for determining the surfaceimpedance of YBa2Cu3O7-δ thinfilms

We describe how coplanar microwave resonators fabricated from patterned thin films of YBa₂Cu₃O₇(-δ) (YBCO) can he used to measure the ab-plane microwave surface impedance Z_s=R_s+jX_s of the films, in particular the absolute value and temperature dependence of the magnetic penetration depth λ. The current distribution of the resonator is calculated by modelling the resonator as a network of coupled transmission lines of rectangular cross-sections; this is then used to estimate the ab-plane λ(T) from the measurements of resonators of different geometries patterned onto the same film. We obtain values of λ(0) in the range 150-220 nm. The unloaded quality factors of the linear resonators at 7.95 GHz are around 45000 at 15 K and around 6500 at 77 K. We estimate the corresponding values of the intrinsic R_s at 7.95 GHz to be 23 μΩ and 110 μΩ at 15 K and 77 K, respectively. These values are comparable with those of other high quality unpatterned YBCO films reported in the literature. Z_s for the best optimised films appears to be insensitive to the effects of patterning     

Comparison of radio-frequency and microwave superconductingproperties of YBaCuO dedicated to magnetic resonance imaging

Properties of YBaCuO thin films are evaluated in two distinct frequency ranges using different patterns made during the same process on LaAlO₃ substrate. Microwave superconducting properties in the range 1-45 GHz are determined by S-parameters measurement of a superconducting coplanar waveguide in the range 53-95 K. We obtain a surface resistance of 0.4 mΩ at 10.8 GHz and 77 K. Radio-frequency properties are obtained by measuring the Q-factor of a superconducting resonator (YBCO multiturn transmission lines separated by a sapphire sheet) dedicated to surface magnetic resonance imaging. At 52 MHz and 77 K we measure a Q-factor of 33180. The extraction of the radio-frequency surface resistance from Q-factor measurements in the 64-95 K range takes into account external loss mechanisms and nonuniform normal current distribution and leads to a 0.0093-μΩ surface resistance at 52 MHz and 77 K, in good agreement with the value extrapolated from microwave measurements assuming an ω² frequency dependence. The evaluation of λ₀ is carried out by using several models for X_L(t). Least squares fits to data in the microwave and radio-frequency domain are performed using the Gorter-Casimir expression for X_L(t) and give the same λ₀ value for both devices     

Toward prediction of physiological state signals in sleep apnea

A recurrent connectionist model is described to predict dynamic respiratory state in the apneic sleeping patient. The time-domain model of nonlinear time-lagged interactions between heart rate, respiration, and oxygen saturation was developed to implicitly embed the dynamics of the respiration and cardiovascular control systems. Multiple future time scales were enforced on the network during training to explore the limits of the prediction horizon and produce a global representation of dynamic state trajectory. Predicted apneic respiration state results are presented in terms of invariant geometric statistics (largest Lyapunov exponent λ_L and correlation dimension D_c). The λ_L prediction error was 13%, while D_c error was within 9% of the true time series value. The magnitude of these errors may fall within experimental noise levels. This methodology may eventually be useful in dynamic control of continuous positive airway pressure (CPAP) therapy devices, and may lead to increased patient compliance with this therapy     

Field response of ultra-thin type II superconducting transmissionlines

This work describes the effect of a tangential magnetic field on the superconducting penetration depth, λ, as modeled by the theory of Ginzburg and Landau. In particular, an increasing magnetic field decreases the magnitude of the order parameter Ψ. Consequently, the London equations have been modified to include field dependent values of the penetration depth, λ(T,H) and complex conductivity, σ(T,H). The analysis assumes that the superconducting films are free of vortices. For Type II films, this criteria can only be met when the thickness of the conductors is less than 1.8ξ_GL. The G-L theory is used to find closed form solutions that describe the electromagnetic characteristics of a kinetic inductance transmission line including phase velocity, impedance, and energy loss, as functions of power, temperature and magnetic fields. Limitations of power are also discussed. To validate these concepts, experiments verifying the effects of temperature and bias field were implemented using niobium superconductors 500 Å thick separated by 1000 Å of Al₂O₃. Potential device applications include variable phase-shifters, tunable filters, and extremely sensitive bolometers     

基于奇偶模分析法的四模谐振器结构的双通带带通滤波器设计

提出了一款基于四模谐振器的新型双通带带通滤波器.设计的四模谐振器基于微带线结构,由四个开路枝节和一个短路枝节组成.两次采用奇偶模分析法对该四模谐振器结构进行分析.该四模谐振器的每个模式能够实现独立调节,同时每两个模式形成一个通带.采用源与负载耦合的馈电方式,提高滤波器的带外抑制性.该滤波器具有四个传输零点和四个传输极点.测试结果表明,该双模双通带滤波器工作于2.08GHz和6.07GHz,3dB带宽分别为11.06%和7.74%.设计的滤波器具有紧凑的结构,只有0.28λ_g×0.11λ_g大小.     

On the automorphism group of various Goppa codes

We determine the automorphism group of various Goppa codes 𝒞 _L(D,G) associated with certain function fields F/F _q of genus g>0. It is well known that, for deg D=n>2g+2, the automorphism group {Aut_D,G(F/F_q) can be embedded into Aut(𝒞_L(D,G)) as a subgroup. We show that, under certain conditions on the divisors D and G Aut_D,G(F/F_q ) is actually isomorphic to Aut(𝒞_L(D,G))     

Geometrical structures and fundamental characteristics of microwavestepped-impedance resonators

λ_g/4-,λ_g/2-, and λ_g-type transmission-line stepped-impedance resonators (SIRs) have been proposed and various practical applications have been reported on the basis of the analysis related to each resonator. This paper standardizes these three types of SIRs and systematically summarizes their fundamental characteristics, such as resonance conditions, resonator length, spurious (higher order) responses, and equivalent circuits. Practical applications which employ features of three types of SIRs are investigated with demonstrations of specific structures. Original design formulas with respect to λ_g-type dual-mode resonators are analytically derived. Advanced SIR's using composite material and multisteps are also introduced and their availability is discussed     

Ti:Er:LiNbO3 waveguide laser of optimized efficiency

The development of a Fabry-Perot-type Ti,Er:LiNbO₃ waveguide laser of optimized CW output power up to 63 mW (λ_s =1561 nm) at a pump power level of 210 mW (λ_p=1480 nm) and a slope efficiency of up to 37% is reported. The theoretical model for the waveguide laser is presented and applied to determine the optimum resonator configuration using waveguide parameters obtained from a detailed characterization of the laser sample. With pulsed pumping, waveguide laser pulses of up to 6.2 W peak power were observed. Apart from residual relaxation oscillations, the laser emission proved to be shot-noise limited     

CW Nd:MgO:LiNbO3 self-frequency-doubling laser at roomtemperature

A CW Nd:MgO:LiNbO₃ self-frequency-doubling laser has been demonstrated at room temperature for the first time. The second-harmonic output at λ=547 nm up to 18 mW was achieved in a simple resonator     

Mode coupling in superconducting parallel plate resonator in acavity with outer conductive enclosure

We have carefully studied the mode coupling effect from analysis of the measured microwave scattering parameters of superconducting films using a parallel-plate-resonator technique. Due to its high resolution and simplicity, this technique has been widely employed to identify the quality of high-T_c superconducting films by measuring the resonance bandwidth, from which the microwave surface resistance is directly derived. To minimize the radiation loss, the resonator is usually housed in a conductive cavity. Using this method, we observe that a number of strong “cavity” modes due to the test enclosure fall around the lowest TM mode of the superconducting resonator and that a strong interaction between these two types of resonant modes occurs when their eigenfrequencies are close, causing a significant distortion or a strong antiresonance for the resonator mode. To describe this effect, a coupled harmonic-oscillator model is proposed. We suggest that the interaction arises from a phase interference or a linear coupling among the individual oscillators. Our model fits very well the observed Fano-type asymmetric or antiresonant features, and thus can be used to extract the intrinsic Q of the superconducting resonator     

Dependence of Ti-diffused Er:LiNbO3 laser efficiency onwaveguide fabrication parameters and pump wavelength

The mode size, effective pump area, and coupling efficiency as function of initial Ti-stripe width W, diffusion temperature T, and initial Ti-stripe thickness H in c-cut Ti-diffused Er:LiNbO₃ waveguide laser have been studied theoretically, taking into account optical pumping λ_p=1.477 μm and 0.98 μm. The main features of the mode sizes in terms of these diffusion parameters were collected and, as compared with the experimental results, a qualitative agreement has been achieved. The effective pump areas exhibit both significant initial Ti-stripe width and diffusion temperature dependence, especially for W>9 μm and T>1050°C, whereas the initial Ti-stripe thickness can hardly give influence when pumping with λ_p=0.98 μm radiation. On the other hand, coupling efficiency is approximately unchanged with values 0.76-0.78 for λ_p=1.477 μm and 0.8-0.85 for λ _p=0.98 μm, indicating that there are no optimized values of these parameters to increase slope efficiency through coupling efficiency. Moreover, the 0.98 μm pumping reveal lower threshold and higher coupling efficiency than 1.477-μm pumping. Finally, the appropriate waveguide fabrication parameters were proposed for the fabrication of a more efficient laser     

Power dependence of HTS disk-resonator quality factor

The simple closed-form model of nonlinear response of a high-temperature superconducting disk resonator on microwave power is proposed. The model is based on superconducting film nonlinearity and describes the dependence of unloaded quality factor on the incident power. The specified normalizing power is used as the only fitting parameter. Good quantitative agreement of modeled and measured data has been obtained. The results observed exhibit the kinetic nature of the nonlinearity of the disk resonator on an LaAlO₃ substrate at T=60 K and more complicated, presumably thermal, heating nature of the nonlinearity at lower temperature     

Current distribution, resistance, and inductance forsuperconducting strip transmission lines

A method for the calculation of the current distribution, resistance, and inductance matrices for a system of coupled superconducting transmission lines having finite rectangular cross-section is presented. These calculations allow accurate characterization of both high-T_c and low-T _c superconducting strip transmission lines. For a single stripline geometry with finite ground planes, the current distribution, resistance, inductance, and kinetic inductance are calculated as functions of the penetration depth for various film thicknesses. These calculations are then used to determine the penetration depth for Nb, NbN, and YBa₂Cu₃O_7-x superconducting thin films from the measured temperature dependence of the resonant frequency of a stripline resonator. The calculations are also used to convert measured temperature dependence of the quality factor to the intrinsic surface resistance as a function of temperature for an Nb stripline resonator     

Sensitivity of Rs-measurement of HTS thin films by threeprime resonant techniques: cavity resonator, dielectric resonator, andmicrostrip resonator

The microwave surface resistance, R_s measurement of YBa ₂Cu₃0_{7 -δ} (YBCO) thin film deposited on 10 mm × 10 mm LaAlO₃ substrate using three prime resonating techniques, namely, cavity end plate substitution technique (20 GHz), dielectric resonator technique (18 GHz), and microstrip resonator technique (5 GHz), is reported. In addition, theoretical analysis for each technique has been performed to calculate the relative percentage error in the measured R_s -value of the YBCO thin film as a function of temperature. It has been found that the shielded dielectric resonator provides far better sensitivity for R.-measurement of the YBCO thin film with minimum relative percentage error (<4%) in the temperature range from 20 K to transition temperature of YBCO thin film compared to the other two techniques     

Wavelength selective detection using excitonic resonances inmultiquantum-well structures

The wavelength and voltage dependence of photocurrent near excitonic resonances are used to study the wavelength selectivity of p-i(multiple quantum well, or MQW)-n photodiode structures with a parallel sequence of optical bits, each with a different wavelength. The selectivity is considered good if the state of a λ_i wavelength bit can be detected regardless of λ_j(j ≠i) state of the bits. Photocurrent is found to have very good selectivity only if λ_j bits are all zero, i.e., the optical information is serial, but it is also found that differential photocurrent (ΔI_ph/ΔV ) provides a good selectivity for random states of λ_j bits (i.e., parallel input). Four channel selectivity is demonstrated at 200 K. Specifically designed quantum-well structures can greatly improve this selectivity     

Merged Sagnac-Michelson interferometer for distributed disturbancedetection

An interferometric technique is described to detect and locate perturbations along an optical fiber. This distributed sensor has a position dependent response to time-varying disturbances such as strain or temperature. These disturbances cause a phase shift which is detected and converted to spatial information, The sensor consists of a Sagnac interferometer merged with a Michelson interferometer. This is achieved by a frequency selective mirror in the center of the Sagnac-loop. The sensor is illuminated by two light sources with wavelengths λ₁ and λ₂, respectively. The mirror reflects λ₁ and transmits λ₂, causing the interferometer to operate as a Michelson at wavelength λ₁ and as a Sagnac at wavelength λ₂. Any time-varying perturbation on, the fiber will, result in a signal at λ₂ proportional to the product of the rate of phase change caused by the perturbation and the distance of the perturbation relative to the position of the mirror. The output of the Michelson interferometer at wavelength λ₁ is proportional to the phase change caused by the unknown perturbation. By dividing the output of the Sagnac interferometer by the time rate of change of the Michelson interferometer signal, the position of the disturbance relative to the mirror is located. Results obtained with a 200 m-distributed fiber sensor are discussed     

Steered coupled-cavity-backed Hertzian dipole array

This paper presents the operating characteristics of a coupled-cavity-backed Hertzian dipole resonator array excited with mutually injection-locked voltage-controlled oscillators (VCOs). It is demonstrated that microwave spatial power-combined inter-injection locking through mutual coupling of individual antenna oscillators can be obtained with an auxiliary coupling network formed by a cavity iris configuration introduced within a reduced-height waveguide arrangement. As a result, strong mutual-coupling control can be realized and exploited in conjunction with self-injection-locked oscillators in order to achieve direct phase modulation of the locked oscillators. Beam scanning up to 10° off the broadside through locked VCO phase modification has been demonstrated in a three-element array occupying a space of only 0.6 λ₀×0.027 λ_o at 998 MHz     

New converses in the theory of identification via channels

New converses for identification via arbitrary single-user and multiple-access channels, with finite first- and second-type probabilities of error, are developed. For the arbitrary single-user channel, it is shown that (λ₁, λ₂)-identification capacity is upper-bounded by λ-capacity, and optimistic (λ₁,λ₂ )-identification capacity is upper-bounded by optimistic λ-capacity, for any λ>λ₁+λ₂. The bounds become tight at the limit of the vanishing probabilities of error, thus generalizing previous results by Han and Verdu (1992), who showed that the identification capacity is equal to transmission capacity for channels satisfying the strong converse of the channel coding theorem. A by-product of the new identification converses is a general formula for optimistic λ-capacity. An outer bound on the (λ₁, λ₂)-identification capacity region of an arbitrary multiple-access channel is developed. A consequence of this bound is that the identification capacity region is equal to the transmission capacity region for any stationary, finite-memory multiple-access channel. The key tool in proving these bounds is the partial resolvability of a channel, a new notion in resolvability theory, which deals with approximation of the output statistics on a suitably chosen part of the output alphabet. This notion of approximation enables us to get sharp bounds on identification for arbitrary channels, and to extend these bounds to the multiple-access channel     

A three-terminal band-trap-band tunneling model for drainengineering and substrate bias effect on GIDL in MOSFET

A new three-terminal partial band-trap-band tunneling (BTB) model is proposed to predict the drain engineering effect and substrate bias effect on gate-induced-drain-leakage (GIDL) characteristics for virgin devices free from electric stress. The lateral field ϵ_L and the ratio of lateral field w.r.t. total field ϵ(ϵ_L /ϵ) are two key factors responsible for the tunneling barrier lowering and the enhancement of GIDL. The principle to suppress GIDL are two-fold: the first one is to eliminate process induced intrinsic interface states and the second one is to minimize ϵ_L and ϵ_L/ϵ by using drain engineering or changing bias conditions such as applying forward substrate biases     

Small eletric monopole mode dielectric resonator antenna

A novel dielectric resonator (DR) antenna is reported. The lowest order mode of the proposed antenna radiates like an electric monopole. The dimensions of the antenna are much smaller than a previously reported structure radiating in a similar mode, e.g. for an antenna fabricated out of ε_r=20 material, the diameter and height of the DR are ~0.08 λ₀ each