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Unlike input deadband, the sandwiched deadband between actuator and plant dynamics is very difficult to be explicitly compensated for due to the proceeding actuator dynamics whose effect may not be negligible. The paper presents a practical way to overcome the design conservativeness of existing methods in dealing with sandwiched deadband. Specifically a describing function based nonlinear analysis method is proposed to characterize the effect of the sandwiched deadband on the stability and performance of the overall closed-loop system. The analysis results can be used to determine the highest closed-loop bandwidth that can be achieved without inducing residual limit cycles and instability. Optimal controller parameters can then be found to maximize the achievable closed-loop control performance. The technique is applied to an electrohydraulic system controlled by closed-center valves and a nonlinear feedback controller. Simulation results showed severe oscillations as the feedback control gains are increased to the predicted threshold values. Comparative experimental results also showed the effectiveness of the proposed method in reducing the conservativeness of traditional design and the improved closed-loop control performance in implementation. [DOI: 10.1115/1.3089557] Keywords: deadband, describing function, electrohydraulics

The aim of this paper is the development of a theoretical model of medium-voltage (MV) cables in the frequency range of 25-200 kHz, which can be easily implemented in the Simulink enviroment. Two transmission-line configurations: 1) line-ground and 2) line-line were considered. The model requires the knowledge of the transmission channel parameters in the frequency domain. Thus, a characterization of MV cables in the two transmission-line configurations by means of experimental measurements was performed on commonly used MV cables, RG7H1R, of different sections, 95 [mm.sup.2] and 185 [mm.sup.2] with an aluminum core and copper shielded. To validate the model, a comparison between the attenuation constant [alpha] measured and the one simulated for both configurations under study was carried out. Index Terms--Attenuation constant, medium-voltage (MV) cables, power-line communication (PLC), transmission line.

Experiments using dose rates of 40 and 1270 rads/min from Co-60 and dual optical wavelengths, 850 and 1310 nm, are conducted to estimate fiber optic attenuation at other dose rates using low order kinetics models. The irradiation-induced attenuation is fit to power and saturating exponential models. The 1310 nm data exhibit a linearly increasing term with the saturating exponential whereas the 850 nm results do not. Representation of the long-term low-dose-rate induced attenuation is an impetus for developing a difference equation fitting routine that better characterizes the signal loss and has the capability of predicting the attenuation at saturation. Index Terms--Gamma-ray effects, optical fiber cables, optical fiber radiation effects, photon radiation effects.

Some basic rules and values to include the attenuation effect of terrain obstacles in the medium wave (MW) band are presented. The analysis applies to ground wave propagated signals and focuses on the new digital broadcasting systems (HD-RADIO/IBOC and DRM) that require accurate predictions for appropriate network planning. This study is based on field strength data from a measurement campaign and the results represent a complementary approach to numerical solutions for planning purposes. A simple but efficient classification of the terrain prominences is presented and attenuation curves are calculated. Index Terms--Channel characterization, digital radio, ground wave, irregular terrain, prediction methods.

Ultrasonic measurements of attenuation versus frequency were made on model systems comprising olive oil, sucrose and tripalmitin for representing the constituents of chocolate. Results suggest that the addition of sucrose crystals at high concentration leads to modification in the effect of ultrasonic scattering from tripalmitin crystals in olive oil.

An easy-to-manufacture setup for a displacement sensor based on plastic optical fiber (POF) is analyzed, showing computational and experimental results. If the displacement is the consequence of force or pressure applied to the device, this can be used as a force or pressure transducer. Its principle of operation consists of bending a POF section around a flexible cylinder and measuring light attenuation when the whole set is subjected to side pressure. Attenuations are obtained computationally as a function of side deformation for different design parameters. Experimental results with an actually built prototype are also provided. OCIS codes: 060.2370, 250.5460, 080.2720, 000.4430.

A large database of radiosoundings, brightness temperatures, and satellite beacon data was used to verify the ability of radiometers in estimating the attenuation in nonprecipitating conditions at millimeter wavelengths. The mass absorption models proposed by Liebe and Rosenkranz have been used coupled with the Helsinki University of Technology (TKK) cloud-detection model to derive coefficients for the calculation of the attenuation due to integrated water vapor and liquid water contents. Comparison of predicted and measured attenuation cumulative distribution functions in the 20-50-GHz band confirms radiometers as a unique tool for retrieving attenuation in nonrainy condition and shows the very good performance of the TKK model for propagation applications. Index Terms--Attenuation, radiometry.

Attenuation [[alpha].sub.n] versus viscosity [eta] of adjacent liquid is measured for each normal mode n generated in 30 different plates of commercially available, piezoelectric crystals with thickness-to-wavelength ratio in the range h/[lambda] = 0.6 - 2.5, and two modes with an optimal combination of sensitivity, insertion loss and stop-band rejection are found with h/[lambda] = 1.67. Both modes are found to be suited for viscosity measurements and other sensing tasks in viscous liquids.

The influence of scatter type on two existing attenuation estimation algorithms is analyzed and a novel technique for handling large statistical variations based on combined assumptions of monotonicity and smoothness is presented. Visible differences in attenuation estimates from each technique were revealed, which are supported by the theoretical analysis suggesting that the novel technique for reducing statistical variations is sufficient to allow some degree of correction of shadowing and enhancement.

An analysis of the error generation mechanisms that affect the accuracy of measurements of ultrasonic wave attenuation coefficient and phase velocity as functions of frequency is presented. Errors can originate from digital processing of acoustic signals however an appropriate sampling frequency, effective anti-aliasing filters, and the use of floating point computations of adequate precision for time-to-time frequency transformation render such errors negligible.

A two-port ring resonator is used to characterize the microwave properties of a microstrip line printed on Ferro A6-S low-temperature co-fired ceramic. The ring and its coupling gaps are simulated using a simple lumped-element model. The coupling gaps are modeled as capacitors, the values of which are extracted using a commercial two-and-one-half-dimensional electromagnetic simulator. The validity of the lumped-element model is assessed by comparing the simulated and experimental resonant frequencies and, for the first time, the simulated magnitudes of both the reflection and transmission coefficients are also compared with those obtained experimentally. A correction for the frequency pushing due to the capacitive loading of the coupling gaps is also presented. The resulting model is then shown to predict the resonant frequencies to within 0.11% from 5 to 40 GHz. The simulated and experimental reflection magnitudes are within 0.5 dB across the band, whereas the transmission magnitudes are within 3.5 dB up to 22 GHz. Experimental results indicate that the loss of the microstrip ranges from approximately 0.11 to 0.42 dB/cm across the band and that the relative permittivity of the substrate is nearly constant versus frequency with an average value of 6.17. Index Terms--Attenuation and permittivity measurements, equivalent lumped elements, resonant frequency, ring resonator.

This paper describes and rigorously validates single- and multiple-layer models of microstrip conductor loss appropriate for high-accuracy application in electromagnetic analysis software. The models are validated by comparison with measurement and by comparison with converged results. It is shown that in some cases an extremely small cell size is needed in order to achieve convergence. Several effects that make a significant contribution to loss and are not modeled by the classic square root of frequency loss model are investigated including dispersion and current on the side of transmission lines. Finally, the counterintuitive result that there is an optimum metal thickness for minimum planar conductor loss is explored. Index Terms--Conductivity, dispersion, electromagnetic, high frequency, loss, microstrip, microwave, resistance, skin effect, stripline, surface impedance.

We have recently derived an analytic method of image reconstruction for the rotating slant-hole (RSH) SPECT scanner for cardiac imaging. The method assumes that the emission activity lies in a region of constant attenuation. It operates by rebinning the three-dimensional (3-D) measured projections into the geometry of a stack of two-dimensional (2-D) slices and performing 2-D reconstruction in a second step. An important consequence of this method is a mathematical proof that opposing projections are not necessary for full tomographic reconstruction in the presence of attenuation. We have now tested our algorithm in the presence of noisy projection data and with projections which violates the constant attenuation assumption. We present results from simulated and real phantom data demonstrating effective attenuation correction in the presence of a uniform low-level of background in the torso, with truncated liver activity, and without opposing views. Our conclusions are that attenuation correction can be performed for RSH SPECT without measuring opposing views, and that the effect of background activity (which violates the assumptions required for exponential data) and truncated activity of a nearby liver are small and easily dominated by typical noise levels in SPECT imaging. Index Terms--Attenuation correction, emission tomography, exact rebinning.

Because the effects of physical factors such as photon attenuation and spatial resolution are distance-dependent in single-photon emission computed tomography (SPECT), it is generally considered that accurate image reconstruction requires knowledge of the data function over 2[pi]. In SPECT with only uniform attenuation, Noo and Wagner recently showed that an accurate image can be reconstructed from knowledge of the data function over the interval [0, [pi]). In this work, we consider image reconstruction in [pi]-scheme SPECT with nonuniform attenuation. In its most general form, [pi]-scheme SPECT entails data acquisition over disjoint angular intervals without conjugate views, totaling to [pi] radians. We develop an heuristic perspective for observing that the data function in full-scan SPECT contains redundant information and that the data function in [pi]-scheme SPECT contains complete information necessary for accurate image reconstruction. We conduct simulation studies in which the expectation maximization algorithm is used for image reconstruction from the data acquired in [pi]-scheme SPECT with nonuniform attenuation. The results in these simulation studies seem to corroborate hypothesis that accurate images can be reconstructed from [pi]-scheme data. [pi]-scheme SPECT allows data acquisition over different combinations of disjoint angular intervals, thereby providing a flexibility in choosing projection views at which the emitted gamma-rays may undergo the least attenuation and blurring. It should be stressed, however, that the proposed perspective on redundant information is intended only to heuristically reveal the data redundancy in SPECT with nonuniform attenuation and that it has not been demonstrated mathematically to guarantee the stability and exactness of image reconstruction from the [pi]-scheme data. Index Terms--Attenuation correction, consistency conditions, short-scan, SPECT.

The work reported herein empirically derived the coefficients of the power-law relation between the specific attenuation Y and each of two other quantities: the radar reflectivity factor Z and the rainfall rate R. The derivation was accomplished using raindrop size distributions (DSDs) measured in Montreal and Toronto using the precipitation occurrence sensor system (POSS) and a Joss-Waldvogel disdrometer (JWD). The specific attenuation was calculated for both spherical and oblate spheroidal raindrops. Prior to doing so, the effects of inaccuracies in small drop detection by the two systems on the resulting Y-Z and Y-R relations were examined. In computing the relations, the influence of grouping the DSDs according to the corresponding values of Z was assessed. The results from the two sites were then combined in a regression analysis to determine the coefficients of the power-law expressions. The final expressions were used to calculate the probability distribution of rain attenuation over several path lengths at 30 GHz. Conclusions that can be drawn from this work include that i) the uncertainties in the measurements of small drops do not appear to be critical to the derived relations for some frequencies considered in this work, ii) in computing rain attenuation estimates from radar reflectivity factors, different criteria for grouping the reflectivity factor measurements can be adopted without changing the statistics of the corresponding attenuation estimates, iii) differences, which are the smallest for frequencies around 20-30 GHz, are observed in the coefficients derived from the measured DSDs compared with those recommended by the ITU-R, and iv) the attenuation statistics at 30 GHz computed by applying the Y-Z power-law expression are resistant to spatial averaging. Index Terms--Radio propagation meterological factors, rain.

It was previously shown that the number of array elements must exceed the number of sources for subspace-based directional-of-arrival (DOA) estimation. This is clearly not practical for a direct-sequence code-division multiple access (DS-CDMA) wireless system since the number of mobile users is very large. To overcome the restriction, a DOA's estimator employing the code-matched filters and parallel MUSIC algorithms is proposed. In the asynchronous DS-CDMA system, we show that the multiple access interference (MAI) throughout the code-matched filter tends toward the real Gaussian distribution with zero mean. In addition, based on the singular value decomposition (SVD) of a finite amount of data, we achieve a theoretical expression for the mean-squared error (MSE) of the DOA's estimation. With the advantage of code-matched filter inherent in the DS-CDMA system, we prove that the proposed technique can obtain an unbiased DOA estimation with low MSE, even in the environment where the number of mobile users far exceeds the number of array elements. Simulation results verify the theoretical derivation. Index Terms--Direction of arrival estimation, multiaccess communication, singular value decomposition.

The prediction of wall losses is a fundamental aspect in the planning of cellular systems. The broad variety of building materials and construction codes makes accurate attenuation prediction very difficult without the support of specific construction data or measurements. In this paper, the attenuation and equivalent electric parameters [epsilon] and [sigma] of brick and doubly reinforced concrete walls are estimated for the 900-MHz band by fitting simple ray tracing models to empirical transmission data. The measurement setup is described, and extensive experimental results justifying the quasioptical modeling are presented. Index Terms--Materials parameters, measurements, modeling and simulation, RF propagation, RF system engineering.

A revised worldwide method has been recommended by the Radiocommunications Sector of the International Telecommunication Union (ITU-R) in Recommendation ITU-R 530-8 for predicting the deep-fading distribution due to multipath propagation in the average worst month on VHF-EHF terrestrial line-of-sight links. This paper presents detailed testing results for the revised method on a 239-link data base from 22 countries around the world in comparison with results for the leading regional methods still frequently used by some link designers for worldwide applications (viz., the Barnett-Vigants method of the United States and the Morita method of Japan). An evaluation of the form of the prediction equation is given for the revised and previous ITU-R methods and several regional methods. The revised ITU-R method is shown to perform significantly better than the other methods for both overland and coastal/overwater links. Index Terms--Fading channels, microwave radio propagation, multipath channels, prediction methods, radio repeaters.

Observations by the airborne X-band Doppler radar (known as EDOP) and the NCAR S-band polarimetric (S-Pol) radar from two field experiments are used to evaluate the surface reference technique (SRT) for measuring the path-integrated attenuation (PIA) and to study attenuation in deep convective storms. The EDOP, flying at an altitude of 20 km, uses a nadir beam and a forward-pointing beam. It is found that over land the surface scattering cross section is highly variable at nadir incidence but is relatively stable at forward incidence. It is concluded that measurement by the forward beam provides a viable technique for measuring PIA using the SRT. Vertical profiles of peak attenuation coefficient are derived in two deep convective storms by the dual-wavelength method. Using the measured Doppler velocity, the reflectivities at the two wavelengths, the differential reflectivity, and the estimated attenuation coefficients, it is shown that supercooled drops and (dry) ice particles probably coexisted above the melting level in regions of updraft and that water-coated partially melted ice particles probably contributed to high attenuation below the melting level.

The microwave tomographic inversion technique (MTIT) proposed in 1991 for reconstruction of rainfall fields at ground through microwave attenuation measurements is reconsidered here. A new algorithm for data inversion is presented [referred to as stochastic reconstruction technique (SRT)] that generally performs better than the one originally adopted [referred to as arithmetic reconstruction technique (ART)]. Improvement is achieved in spatial definition and general reliability of rainfall field reconstruction. The new model adopted to represent the reconstructed rainfall fields leads to a completely different strategy for the inversion problem, and this strategy is based on a global optimization stochastic technique (GOST). Results obtained through the SRT-MTIT are presented in the paper and compared to those obtained by employing the ARTMTIT. It also is shown that, based on the SRT-MTIT approach, fast and reliable time tracking of rainfall events is made possible by exploiting previous reconstructions and by the improved longterm physical consistency of the model adopted for rainfall field decomposition. Index Terms: Attenuation measurements, rainfall, tomography, tracking.

We report on the first clinical evaluation of the 137Cs single photon transmission measurement that has been implemented on the Siemens/CTI ECAT ART. Thorax phantom studies are performed to verify the accuracy of the transmission measurement. Pre-injection (with patient repositioning) and post-injection transmission scans and attenuation corrected emission images of 25 patients are compared with respect to estimated linear attenuation coefficients and specific activities in organs, and standardized uptake values in lesions. We find that both pre- and post-injection transmission provide accurate estimates of attenuation correction factors. Post-injection estimates for mean attenuation coefficients and specific activities in larger regions of interest (ROIs) are nearly the same as pre-injection values, but exhibit 17-18% greater pixel standard deviation. Estimates of standardized uptake in smaller lesion ROIs are 13% higher with post-injection correction, but there is little difference in the ROI pixel variances.

The ITALSAT propagation experiment, started in early 1991 and still on-going, allows an extensive program of measurements at 18.7, 39.6, and 49.5 GHz. This paper reports the results obtained so far from copolar signal measurements carried out at the Earth station of Spino d'Adda from 1993 to 1995. Statistics of rain and total attenuation and frequency scaling of total attenuation are presented and commented in the light of the ITU-R predictions.

A study was conducted to validate the scattering mechanism of ultrasound in the skeletal muscle tissue. The methods used were backscattering measurements, sound speed attenuation measurements and scanning electron microscopy. Results revealed that ultrasonic backscattering conforms with the hypothesis which states that endomysial collagen fibers are the dominant ultrasonic scatterers in skeletal muscle during passive stretching.

Leak surface acoustic wave (LSAW) velocity and attenuation can be measured through the use of an absolute accuracy of the line-focus-beam (LFB) acoustic microscopy system. The LFB acoustic microscopy system, which utilizes standard specimens, is enhanced by a calibration method. The calibration method is important in the measurement of absolute values such as those in the LSAW propagation features which are dependent on the system.

The ability of a synthetic aperture radar (SAR) to detect targets under foliage is in part determined by the attenuation suffered by radiation propagating through the foliage and the backscatter from the foliage. MIT Lincoln Laboratory made measurements of foliage attenuation and backscatter using the NASA/JPL UHF, L-, C-band fully-polarimetric SAR in July 1990. In this experiment, a 48 [km.sup.2] forested area near Portage, Maine was imaged. Twenty-seven 8 ft trihedral corner reflectors were arrayed throughout the imaged area in order to measure foliage attenuation. Ground truth was recorded at the time of the experiment in order to correlate the attenuation and backscatter results with foliage biophysical properties. The probability densities for foliage attenuation and for backscatter are determined as functions of frequency, polarization, and depression angle.

The effect attributable to the nonparallelism of the guiding layer of a planar waveguide on the reflection dip of the attenuated total reflection (ATR) spectrum is investigated. It is considered that the reflected light from a nonparallel waveguide is, indeed, the superposition of a series of beams propagating in different directions. The ATR spectra are numerically calculated with various inclination values. Compared with those of the corresponding parallel ones, with the inclination of waveguides exceeding 1 [micro]rad, the characteristics of the ATR spectra begin to differ considerably, and when the inclination reaches 10 [micro]rad, the sensitivity of sensors based on the waveguide is reduced by 62.7% and 67.3% for the free space coupling structure and the prism coupling structure, respectively. When the inclination becomes larger than 100 [micro]rad, the ATR phenomenon cannot be observed any longer. OCIS codes: 120.4640, 230.7390.

The impact of attenuation characteristics for specific groups of physically active females during running by measuring the impact shock was examined as to how it was attenuated throughout the body by the performer. Results suggested that lifespan phases appear to affect impact attenuation strategies and variability of impact during running for females.

A new technique to image the patient surface has been developed to assist in the segmented attenuation correction, currently finding favor in positron emission tomography (PET). The goals of this approach are to outline the body's contours quickly, with an inherent surface enhancement that would permit transmission scanning after the emission scan. To achieve this, an orbiting, thin-windowed source, mounted out of the detector plane, illuminates the patient's skin with a soft positron flux, while a static emission scan quickly delineates the patient outline. The ability to visualize internal structures is a welcome, if unexpected, windfall. The measurements of resolution and sensitivity cover a grid of three positron radionuclides and two source assemblies imaging several phantoms to challenge four commercial scanners. Currently mounted on a CTI 933/04, the positron floodlight is well suited to virtually any ring-array PET scanner, with the potential for adaptation to the dual-headed camera instruments emerging on the market today. Index Terms--Positron floodlight, segmented attenuation correction.

We address the issue of using deformable models to reconstruct an unknown attenuation map of the torso from a set of transmission scans. We assume the three--dimensional (3-D) distribution of attenuation coefficients to be piecewise uniform. We represent the unknown distribution by a set of closed surfaces defining regions having the same attenuating properties. The methods of reconstruction published so far tend to directly deform the surfaces, the parameters being the surface elements. Rather than deforming the surfaces, we explore the possibility of deforming the space in which the geometrical primitives are contained. We focus on the use of free-form deformations (FFD's) to describe the continuous transformation of space used to match a set of transmission measurements. We illustrate this approach by reconstructing realistically simulated transmission scans of the torso with various noise levels and compare the results to standard reconstruction methods. Index Terms--Attenuation measurement, geometric modeling, image reconstruction.