Sensitivity Transfer Function Research Articles

Monte Carlo modeling of storage phosphor plate readouts

Storage phosphor based imaging detectors are widely used in various fields of X-ray radiography. In this work, a numerical procedure based on the Monte Carlo algorithm is presented to simulate the image readout of storage phosphor plates (SPPs). Several experimentally measurable model parameters, including the optical anisotropy coefficient, the optical absorption coefficient and the mean scattering length, are used to deal with multiple light-scattering processes during the image readout. The density distribution profile of the readout laser and escape probability of the luminescence photons are simulated. Such image metrics as line spread function, photostimulated luminescence (PSL) sensitivity and modulation transfer function (MTF) can be calculated. The simulated MTFs and PSL sensitivities are in good agreement with experimental data at different SPP thickness within 5%.

Visual acuity, contrast sensitivity, and phase transfer function depend on the Stiles Crawford peak location

Visual acuity, contrast sensitivity, and phase transfer function depend on the Stiles Crawford peak location

Ability of transfer function method to diagnose axial displacement of transformer windings

AbstractTransient currents can cause the mechanical displacement of transformer windings. The transfer function method is presented as a tool to detect this displacement. In order to be able to evaluate the measurements, the correlation between the characteristics of transfer functions and possible damages must be known. Axial displacement of transformer windings has been studied in this research. As test object a transformer with a primary winding of 31 double inverted disk (approx. 1.3 MVA, 10 kV) and a secondary winding with four layer concentric winding was used. A detailed mathematical model was developed for the test object and a comparison was carried out between measured and calculated results. To compare the sensitivity of transfer functions, five different transfer functions with different terminal conditions are simulated. It is shown that the detailed model can present the behaviour of the transformer winding in case of sound and displaced windings.

Digital correlation microwave polarimetry: analysis and demonstration

The design, analysis, and demonstration of a digital-correlation microwave polarimeter for use in Earth remote sensing is presented. The authors begin with an analysis of a three-level digital correlator and develop the correlator transfer function and radiometric sensitivity. A fifth-order polynomial regression is derived for inverting the digital correlation coefficient into the analog statistic. In addition, the effects of quantizer threshold asymmetry and hysteresis are discussed. A two-look unpolarized calibration scheme is developed for identifying correlation offsets. The developed theory and calibration method are verified using a 10.7 GHz and a 37.0 GHz polarimeter. The polarimeters are based upon 1-GS/s three-level digital correlators and measure the first three Stokes parameters. Through experiment, the radiometric sensitivity is shown to approach the theoretical as derived earlier in the paper and the two-look unpolarized calibration method is successfully compared with results using a polarimetric scheme. Finally, sample data from an aircraft experiment demonstrates that the polarimeter is highly useful for ocean wind-vector measurement.

Identification of contributors to HDD servo errors by measuring PES only

In this paper, disturbances, the source of TMR being the barrier to high track density of HDD are analyzed quantitatively using PES only without extra sensors. Disturbances are separated into RRO and NRRO, then, NRRO is separated into input torque disturbance, output disturbance, and noise. The effect of each disturbance on PES is compared. It is shown that PES NRRO measured in open-loop and in closed-loop can be used to calculate sensitivity transfer function. Using separated disturbances, PSD of PES RRO and NRRO are predicted for various gain levels in track following servo, and they are compared with PSD of PES measured in experiments. We propose that this can be used to predict servo performance accurately. Also addressed are some discussions on the differences between this work and the former contributing work.

The effect of thermal noise on the operation of DC SQUIDs at 77 K-a fundamental analytical approach

A rigorous analytical analysis of DC SQUIDs having reduced inductance smaller than 1//spl pi/ and operating in the presence of thermal fluctuations has been developed. On the basis of the Fokker-Planck equation the expressions for the output voltage across the Josephson junctions and the circulating current in the SQUID loop were found. This reduces the problem of finding all important SQUID characteristics (current-voltage curves, dynamic resistance, transfer function, and energy sensitivity) and their optimization to a simple exercise of elementary mathematics. As expected, the present analytical approach gives unique insights and significantly contributes to understand the physics related to the effects of large thermal fluctuations on system's operation.

Analytical Theory of DC SQUIDS Operating in the Presence of Thermal Fluctuations

A comprehensive analytical theory of symmetric DC SQUIDs is presented taking into account the effects of thermal fluctuations. The SQUID has a reduced inductance β < 1/π where β = 2LIc/Φ0, L is the loop inductance, Φ0 is the flux quantum, and Ic is the critical current of the identical Josephson junctions which are assumed to be overdamped. The analysis, based on the two dimensional Fokker–Planck equation, has been successfully performed in first order approximation with β considered a small parameter. All important SQUID characteristics (circulating current, current-voltage curves, transfer function, and energy sensitivity) are obtained. In the limit βΓ ≪ 1( Γ = 2πkBT/IcΦ0 is the noise parameter, kB is the Boltzmann constant, and T is the absolute temperature) the theory reproduces the results of numerical simulations performed for the case of small thermal fluctuations. It was found that for Γ < 1 the SQUID energy sensitivity is optimum when β is higher than 1/π, i.e., outside the range for which the present analysis is valid. However, for Γ ≥ 1 the energy sensitivity has a minimum at L = LF , where LF = (Φ 0 /2π) 2/kB , and therefore, in this case, the optimal reduced DC SQUID inductance is β opt = 1/πΓ, i.e., within the range for which the present analysis is valid. In contrast to the case of an RF SQUID, for a DC SQUID the transfer function decreases not only with increasing L/LF but also with increasing Γ (as 1/Γ). As a consequence, the energy sensitivity of a DC SQUID with β < 1/π degrades more rapidly (as Γ 4 ) with the increase of Γ than that of an RF SQUID does (as Γ 2 ).

High Tc SQUIDs with two or three junctions for application in disturbed environment

Abstract Different dc SQUIDs for galvanometer type high T c SQUID sensors are investigated. The aim is to achieve a high flux-to-voltage transfer function and good sensitivity to the current originated in a directly coupled pickup loop. Furthermore, the stability against external fields is investigated. For these purposes 2 and 3 junction SQUIDs with various layouts are compared. The 3 junction SQUID showed no advantage for the application in a galvanometer type SQUID sensor. For the layout slim and long SQUID loops give best results in all respects.

Interactive control system design by a mixed H/sup ∞/-parameter space method

This paper presents an interactive graphical method to determine sets of stabilizing controllers satisfying any combination of constraints on the sensitivity, complementary sensitivity, and input sensitivity transfer functions. The method is limited to single-input/single-output systems but offers significant advantages over current H/sup /spl infin// methods. It can handle pure time delays in an exact manner. The weighting functions need not be rational. By virtue of producing the required parameter space region for the frequency response criteria, subsequent direct time-domain optimization is possible. The controllers obtained are of lower order for comparable performance than those produced by current H/sup /spl infin// techniques. The method is particularly well suited to robust control problems, where frequency domain constraints emerge from the analysis of uncertainties in the system, and also to suboptimal problems, where the frequency-domain loop shaping is used to achieve time-domain specifications.

Tectonic process monitoring by variations of the geomagnetic field absolute intensity

We propose a novel technique for tectonic process monitoring. The technique includes: measurements of absolute intensity variations, at network sites, synchronously with measurements of horizontal geomagnetic field variations at a reference site; spectral analysis of measured time series and construction non-conventional transfer functions and interpretation of the transfer functions constructed in order to detect or/and to forecast the tectonic processes. Using numerical modelling we show the sensitivity of transfer functions obtained with respect to the temporal changes in the Earth's resistivity associated with tectonic processes. We also demonstrate that the components of the geomagnetic field are reconstructed in terms of spatial distribution of absolute intensity variations.

An auxiliary LQG/LTR robust controller design for cogeneration plants

A robust controller is designed to reduce the sensitivity of the frequency and the extraction steam pressure to the disturbance imposed on a cogeneration plant by using the LQG/LTR (linear quadratic Gaussian/loop transfer recovery) methodology. The natural frequency of the generator swing is analyzed to determine the frequency band of the disturbance due to the variation in load and utilized as a design specification for the LQG/LTR controller. The singular-value Bode diagram of the sensitivity transfer function matrix is shaped to reduce disturbance effects on the power system frequency and steam pressure according to the design specification. The high order LQG/LTR controller is reduced to a low order controller and implemented in a nonlinear cogeneration plant model. Simulation shows the performance of the LQG/LTR controller in disturbance rejection.

LQG/LTR Robust Controller Design for Disturbance Rejection in a Cogeneration Plant

A robust controller is designed to reduce the sensitivity of the frequency and the extraction steam pressure to the disturbance imposed on a cogeneration plant by using the LQG/LTR methodology. Natural frequency of generator swing is analyzed to determine the frequency band of the disturbance due to the variation in load and utilized as a design specification for the LQG/LTR controller. The singular-value Bode diagram of the sensitivity transfer function matrix is shaped to reduce disturbance effects on the power system frequency and steam pressure according to the design specification. The high order LQG/LTR controller is reduced to a low order controller and implemented in a nonlinear cogeneration plant model. Simulation shows the performance of the LQG/LTR controller in disturbance rejection.

LQG/LTR robust controller of cogeneration plant for disturbance rejection in electric frequency and steam pressure

A robust controller design is considered for reducing the sensitiveness of electric frequency and extraction steam pressure to the disturbances imposed on a cogeneration plant by applying LQG/LTR methodology. A sample cogeneration plant that includes the dynamics of the extraction condensing turbine and generator, actuators and valves, governor, and PID controllers is modelled as the 15th-order differential equation for controller design. As one of the important steps in the LQGILTR application, the analysis of the natural frequency of the generator swing is introduced to estimate the frequency band of the disturbances due to the variation in loads, and to set up the design specification of the LQG/LTR controller. In the robust MIMO controller design procedure, the singular value Bode diagram of the sensitivity transfer function matrix is shaped to reduce disturbance effects on the power system frequency and steam pressure, according to the design specification. Case studies are carried out by adding a reduced 11th-order controller to the nonlinear model of the cogeneration plant. Simulation results demonstrate the preferable performance of the LQG/LTR controller in disturbance rejection.

Auto- and cross-spectral analysis of cardiovascular fluctuations during pentobarbital anesthesia in the rat.

We applied auto- and cross-spectral analysis of systemic arterial pressure (SAP) and heart rate (HR) signals to quantify the effects of pentobarbital sodium on short-term cardiovascular fluctuations in adult, male Sprague-Dawley rats. Intravenous administration of pentobarbital, delivered as a bolus injection (5, 10, or 20 mg/kg) or continuous infusion (10, 20, or 40 mg.kg-1.h-1), elicited only mild hypotension and tachycardia. This was accompanied by a dose-related depression of the very low (0-0.25 Hz) and low (0.25-0.8 Hz)-frequency components of both SAP and HR signals and high (0.8-2.4 Hz)-frequency component of HR signals. Cross-spectral analysis of SAP and HR signals during intravenous infusion of pentobarbital revealed a maintained coherence in the high-frequency range, together with a gradual and dose-related decrease in magnitude of transfer function and baro-receptor reflex sensitivity. Stable plasma concentration and all hemodynamic parameters were observed during 120 min of infusion at 20 mg.kg-1.h-1. Under this dosing condition, autonomic blockade by phentolamine, propranolol, or atropine still evoked discernible but differential reductions in the SAP and HR spectral components. Our data suggest that continuous intravenous administration of pentobarbital at 20 mg.kg-1.h-1 offers maintained anesthesia while preserving the capacity of cardiovascular regulation.

Improved LDI digital filters derived from analog LC ladder filters

Lossless discrete integrator (LDI) digital filters derived from analog LC ladder filters are known to possess low sensitivities of the passband gain with respect to quantizations of the multiplier coefficients. However, previously reported LDI digital filter structures do not generally retain the desired one-to-one correspondence between the LDI digital ladder filter and the original LC analog ladder filter after quantizations of the multiplier coefficients are taken into account. This leads to increased transfer function sensitivities of the LDI digital filter, relative to that of the original LC analog filter. In this paper, it is shown that classical equivalent transformations of the LC ladder network can be used to obtain new LDI ladder structures that do retain (even after coefficient quantizations) the one-to-one correspondence with the LC ladder filter, leading to LDI digital filters having improved performance under coefficient quantizations. These equivalent network transformations also facilitate the design of different types of LDI ladder filters. The obtained LDI filters are suitable for VLSI implementation on a single chip FPGA using one multiplier.

Dynamics and control of instrumented harmonic drives.

Since torque in harmonic drives is transmitted by a pure couple, harmonic drives do not generate radial forces and therefore can be instrumented with torque sensors without interference from radial forces. The installation of torque sensors on the stationary component of harmonic drives (the Flexipline cup in this research work) produce backdrivability needed for robotic and telerobotic compliant maneuvers. Backdrivability of a harmonic drive, when used as torque increaser, means that the output shaft can be rotated via finite amount of torque. A high ratio harmonic drive is non-backdrivable because its output shaft cannot be turned by applying a torque on it. This article first develops the dynamic behavior of a harmonic drive, in particular the non-backdrivability, in terms of a sensitivity transfer function. The instrumentation of the harmonic drive with torque sensor is then described. This leads to a description of the control architecture which allows modulation of the sensitivity transfer function within the limits established by the closed-loop stability. A set of experiments on an active hand controller, powered by a DC motor coupled to an instrumented harmonic drive, is given to exhibit this method's limitations.

Elimination of phase noise of pulsed laser diodes in electrooptic sampling systems

The multimode operation of pulsed laser diode sources is converted into excess noise in electrooptic probing systems for electrical waveforms and prevents measurements with shot-noise-limited sensitivity. The transfer function of the sampling system is determined and analyzed in terms of the wavelength and electric field dependence. It is shown that by proper orientation of the polarizing components within the optical beam path, points of operation can by found which have both a vanishing wavelength dependence of the transfer function and maximum sensitivity to the electric fields to be measured. Excess noise sources due to wavelength fluctuations of the laser are thus eliminated, and shot-noise-limited voltage resolution is obtained. The system has been optimized to yield a voltage sensitivity of 2.3 mV/ square root Hz for a longitudinal LiNbO/sub 3/ probe crystal. >

Representations of controllers that achieve robust performance for systems with real parameter uncertainty

Consider a family of single input single output plants described by transfer functions that involve real parameter uncertainty. Parameter values are known to lie in a hypercube. Assume that a class of available controllers has been prescribed, along with a bound for the sensitivity transfer function to ensure tracking. It is of interest to determine whether a controller from the given class exists that guarantees robust stability and robust asymptotic tracking. In this paper we present a problem formulation and then provide a solution based on it. Not only do we address the existence question but also give representation of controllers from the class that meet the robustness requirements.

Unified approach to the synthesis of active compensated op.-amp. circuits

A general method is proposed for the generation of RC-active circuits, both inverting and non-inverting. The generated systems are compensated for zero transfer function sensitivity with respect to the op.-amp.'s time constant. The topologies of the systems are easily obtained from the classical uncompensated structures with a single op.-amp.

Systematic generation of active compensated inverting systems

A general system for the active compensation of the inverting blocks with a single op. amp. is given. The proposed system presents zero transfer function sensitivity with respect to the op. amp.'s time constant. Examples are given to illustrate the performance of the generated circuits.