Single-frequency Test Research Articles

Design of a Compact Analog Complex Correlator for Millimeter-Wave Radiation Temperature Measurement System.

Human body temperature is a fundamental physiological sign that reflects the state of physical health. It is important to achieve high-accuracy detection for non-contact human body temperature measurement. In this article, a Ka band (32 to 36 GHz) analog complex correlator using the integrated six-port chip is proposed, and a millimeter-wave thermometer system based on the designed correlator is completed for human body temperature measurement. The designed correlator utilizes the six-port technique to achieve large bandwidth and high sensitivity, and miniaturization of the correlator is achieved through an integrated six-port chip. By performing the single-frequency test and the broadband noise measurement on the correlator, we can determine that the dynamic range of input power of the correlator is -70 dBm to -35 dBm, and the correlation efficiency and equivalent bandwidth are 92.5% and 3.42 GHz, respectively. Moreover, the output of the correlator varies linearly with the input noise power, which reveals that the designed correlator is suitable for the field of human body temperature measurement. Then, a handheld thermometer system, with a size of 140 mm × 47 mm × 20 mm, is proposed using the designed correlator, and the measurement results show that the temperature sensitivity of the thermometer is less than 0.2 K.

Thermo-Viscoelastic Characterization of 3D Printing Polymers

Polymer materials used in 3D printing exhibit degradation of material mechanical properties when exposed to thermal environments and thermal expansions can induce residual stresses in products or molds, which may result in dimensional instability and subsequent structural failures. In this study, based on linear thermo-viscoelastic principles, material degradation master curves, shift functions, and glass transition temperatures for four different polymers used for 3D printing techniques such as MultiJet Printing and Digital Lighting Process were measured by using a dynamic mechanical analyzer. Based on the single frequency test, the glass transition temperature was measured. In addition, dynamic measurements were carried out over a frequency range at isothermal condition and storage modulus vs. frequency curves were obtained. Then, the storage moduli curves measured at different temperatures were superposed into master curves using the frequency–temperature superposition principle and shift factors were calculated as a function of temperature. Subsequently, the complex moduli curves that were measured in the frequency were curve-fitted onto generalized Maxwell models by using the least squares method and the master curves of relaxation moduli at reference temperature were obtained. The effects of temperature, frequency, and time on dynamic moduli and relaxation behaviors of four polymers used for 3D printing were evaluated. Experimental results showed that Polymers C and D could be suitable to use at the service temperature above 100 °C and Polymer C was highly crosslinked and showed low modulus reduction after about a year. The master relaxation curves obtained through this process can be utilized to predict the long-term performance of polymer molds made by 3D printing at a given environmental condition.

Frequency-band down-sampled stereo-DIC: Beyond the limitation of single frequency excitation

A low-speed stereo-camera DIC setup was used in this paper to measure the down-sampled bandpass vibration signal of a plate in a given frequency range, which is much higher than the available frame rate. Down-sampled vibration measurements are well known in the literature. However, they are always subject to the strong hypothesis of having a single frequency component in the excitation source (e.g., pure sinusoidal excitation). In this scenario, several approaches can be found in the literature to reconstruct the actual response from the down-sampled data. In this paper, a data postprocessing algorithm is newly introduced to properly reconstruct the target response in the case of a frequency band excitation, thus relaxing the single frequency excitation constraint and allowing to explore a given frequency range with a single measurement. Additionally, a custom excitation signal is presented in this paper to achieve a constant intensity in the studied frequency range. The proposed approach is presented and experimentally validated by measuring a cantilever plate vibration in the kHz range using a 100 fps acquisition. A single acquisition of 98 frames allowed to describe the deformed shapes at 49 different frequency values in the range 1110–1160 Hz, highlighting two resonance peaks. The comparison with the results of multiple conventional single-frequency tests and LDV measurements confirmed the effectiveness of the proposed approach.

Optimizing Clinical Interpretation of Distortion Product Otoacoustic Emissions in Infants.

The purpose of this study was to analyze distortion product otoacoustic emission (DPOAE) level and signal to noise ratio in a group of infants from birth to 4 months of age to optimize prediction of hearing status. DPOAEs from infants with normal hearing (NH) and hearing loss (HL) were used to predict the presence of conductive HL (CHL), sensorineural HL (SNHL), and mixed HL (MHL). Wideband ambient absorbance was also measured and compared among the HL types. This is a prospective, longitudinal study of 279 infants with verified NH and HL, including conductive, sensorineural, and mixed types that were enrolled from a well-baby nursery and two neonatal intensive care units in Cincinnati, Ohio. At approximately 1 month of age, DPOAEs (1-8 kHz), wideband absorbance (0.25-8 kHz), and air and bone conduction diagnostic tone burst auditory brainstem response (0.5-4 kHz) thresholds were measured. Hearing status was verified at approximately 9 months of age with visual reinforcement audiometry (0.5-4 kHz). Auditory brainstem response air conduction thresholds were used to assign infants to an NH or HL group, and the efficacy of DPOAE data to classify ears as NH or HL was analyzed using receiver operating characteristic (ROC) curves. Two summary statistics of the ROC curve were calculated: the area under the ROC curve and the point of symmetry on the curve at which the sensitivity and specificity were equal. DPOAE level and signal to noise ratio cutoff values were defined at each frequency as the symmetry point on their respective ROC curve, and DPOAE results were combined across frequency in a multifrequency analysis to predict the presence of HL. Single-frequency test performance of DPOAEs was best at mid to high frequencies (3-8 kHz) with intermediate performance at 1.5 and 2 kHz and chance performance at 1 kHz. Infants with a conductive component to their HL (CHL and MHL combined) displayed significantly lower ambient absorbance values than the NH group. No differences in ambient absorbance were found between the NH and SNHL groups. Multifrequency analysis resulted in the best prediction of HL for the SNHL/MHL group with poorer sensitivity values when infants with CHL were included. Clinical interpretation of DPOAEs in infants can be improved by using age-appropriate normative ranges and optimized cutoff values. DPOAE interpretation is most predictive at higher F2 test frequencies in young infants (2-8 kHz) due to poor test performance at 1 to 1.5 kHz. Multifrequency rules can be used to improve sensitivity while balancing specificity. Last, a sensitive middle ear measure such as wideband absorbance should be included in the test battery to assess possibility of a conductive component to the HL.

Multi-instrument view on solar eruptive events observed with the Siberian Radioheliograph: From detection of small jets up to development of a shock wave and CME

The first 48-antenna stage of the Siberian Radioheliograph (SRH) started single-frequency test observations early in 2016, and since August 2016 it routinely observes the Sun at several frequencies in the 4–8 GHz range with an angular resolution of 1–2 arc minutes and an imaging interval of about 12 s. With limited opportunities of the incomplete antenna configuration, a high sensitivity of about 100 Jy allows the SRH to contribute to the studies of eruptive phenomena along three lines. First, some eruptions are directly visible in SRH images. Second, some small eruptions are detectable even without a detailed imaging information from microwave depressions caused by screening the background emission by cool erupted plasma. Third, SRH observations reveal new aspects of some events to be studied with different instruments. We focus on an eruptive C2.2 flare on 16 March 2016 around 06:40, one of the first flares observed by the SRH. Proceeding from SRH observations, we analyze this event using extreme-ultraviolet, hard X-ray, white-light, and metric radio data. An eruptive prominence expanded, brightened, and twisted, which indicates a time-extended process of the flux-rope formation together with the development of a large coronal mass ejection (CME). The observations rule out a passive role of the prominence in the CME formation. The abrupt prominence eruption impulsively excited a blast-wave-like shock, which appeared during the microwave burst and was manifested in an “EUV wave” and Type II radio burst. The shock wave decayed and did not transform into a bow shock because of the low speed of the CME. Nevertheless, this event produced a clear proton enhancement near Earth. Comparison with our previous studies of several events confirms that the impulsive-piston shock-excitation scenario is typical of various events.

A Compact Analog Complex Cross-Correlator for Passive Millimeter-Wave Imager

The design, analysis, implementation, and measurement of a compact analog complex cross-correlator for passive millimeter-wave imaging applications are presented in this paper. The correlator uses the “add and square” and “subtract and square” detection scheme by adopting the Schottky diodes and RF distribution network. Meanwhile, in order to realize the correlator with a compact size and low cost, commercially available surface mounting devices and multilayer PCB technique are employed. The relationship between the phase error of the correlator and the phase unbalance of the RF distribution network is also analyzed. Single-frequency test is applied to the correlator, and the results of the measurement reveal that the correlator operates well within the frequency range of 1.5–2.5 GHz. Moreover, a measurement system based on an actual imaging scenario is also developed to characterize the performance of the correlator when injected with correlated broadband noise signals, and the measurement results show that the correlator is well suited for imaging applications. The bandwidth of the current version correlator is around 1 GHz, but it could easily be changed by replacing distributed components.

Hydrodynamic response of a cage system under waves and currents using a Morison-force model

Accurate computation of forces and deformations on cages under wave and current loads is a key element when designing mooring systems for fish farms. In this study, an analysis of a cage under combinations of current and wave loading is carried out and the numerical results are compared with experimental data. The numerical tool used in this analysis is based on a Morison-force model. For the case of single frequency tests, drag and inertia coefficients for the surface collar are selected based on Re and KC numbers. For irregular wave conditions, coefficients in Morison equation are selected based on significant wave height and peak period. Net is represented by an equivalent array of cylinders, which considers the same wet mass, projected area, and axial stiffness as the prototype net. This approach allows discretizing the net using a small number of elements. The present model predicts the loads over the floating collar as well as the drag force over the net. Overall, the study shows that current load dominates for most of wave and current conditions analyzed; yet, for large and steep waves, its effect is of similar importance as the current load.

Accurate and cost‐effective technique for jitter and noise separation based on single‐frequency measurement

A simple and cost-effective technique is proposed for jitter and noise separation in ADC test. On the basis of the property that clock jitter is modulated by the slope of input signal, few simple mathematical manipulations are performed on a single data record of ADC output to separate jitter and noise. The proposed method requires only one high-frequency signal test and eliminates the need for a second low-frequency test in conventional dual-frequency jitter tests. Compared with existing single-frequency test, the new method is accurate and robust to non-harmonic distortion, without requiring any additional data acquisition time. Therefore, both hardware overhead and data acquisition time are saved significantly. Experimental results show that both jitter and signal-to-noise ratio are estimated accurately, and the accuracy of jitter estimation is comparable with that of conventional dual-frequency test.

Extracting random jitter and sinusoidal jitter in ADC output with a single frequency test

Extracting random jitter and sinusoidal jitter in ADC output with a single frequency test

Neonatal total liquid ventilation: is low-frequency forced oscillation technique suitable for respiratory mechanics assessment?

This study aimed to implement low-frequency forced oscillation technique (LFFOT) in neonatal total liquid ventilation (TLV) and to provide the first insight into respiratory impedance under this new modality of ventilation. Thirteen newborn lambs, weighing 2.5 + or - 0.4 kg (mean + or - SD), were premedicated, intubated, anesthetized, and then placed under TLV using a specially design liquid ventilator and a perfluorocarbon. The respiratory mechanics measurements protocol was started immediately after TLV initiation. Three blocks of measurements were first performed: one during initial respiratory system adaptation to TLV, followed by two other series during steady-state conditions. Lambs were then divided into two groups before undergoing another three blocks of measurements: the first group received a 10-min intravenous infusion of salbutamol (1.5 microg x kg(-1) x min(-1)) after continuous infusion of methacholine (9 microg x kg(-1) x min(-1)), while the second group of lambs was chest strapped. Respiratory impedance was measured using serial single-frequency tests at frequencies ranging between 0.05 and 2 Hz and then fitted with a constant-phase model. Harmonic test signals of 0.2 Hz were also launched every 10 min throughout the measurement protocol. Airway resistance and inertance were starkly increased in TLV compared with gas ventilation, with a resonant frequency < or = 1.2 Hz. Resistance of 0.2 Hz and reactance were sensitive to bronchoconstriction and dilation, as well as during compliance reduction. We report successful implementation of LFFOT to neonatal TLV and present the first insight into respiratory impedance under this new modality of ventilation. We show that LFFOT is an effective tool to track respiratory mechanics under TLV.

PECan A Canadian Parabolic Equation Model for Underwater Sound Propagation

PECan is a Canadian N×2D/3D parabolic equation (PE) underwater sound propagation model that was developed for matched-field processing applications. It is based on standard square-root operator and/or propagator approximations that lead to an alternating direction solution of the 3-D problem. A 2-D split-step Pade approximation is employed for propagation in range. The 3-D azimuthal corrections are computed using either a split-step Fourier method or a Crank–Nicolson finite-difference approximation. It features a heterogeneous formulation of the differential operators on an offset vertical grid, energy conservation, a choice of initial field including self-starter, and both absorbing and nonlocal boundary conditions. Losses due to shear wave conversion in an elastic bottom are handled in the context of a complex density approximation. In this paper, PECan is described and validated against some standard benchmark solutions to underwater acoustics problems. Subsequently, PECan is applied to several single-frequency test cases that were offered for numerical consideration at the SWAM'99 Shallow Water Acoustic Modeling workshop.

PECAN: A CANADIAN PARABOLIC EQUATION MODEL FOR UNDERWATER SOUND PROPAGATION

PECan is a Canadian N× 2D/3D parabolic equation (PE) underwater sound propagation model that was developed for matched-field processing applications. It is based on standard square-root operator and/or propagator approximations that lead to an alternating direction solution of the 3-D problem. A 2-D split-step Padé approximation is employed for propagation in range. The 3-D azimuthal corrections are computed using either a split-step Fourier method or a Crank–Nicolson finite-difference approximation. It features a heterogeneous formulation of the differential operators on an offset vertical grid, energy conservation, a choice of initial field including self-starter, and both absorbing and nonlocal boundary conditions. Losses due to shear wave conversion in an elastic bottom are handled in the context of a complex density approximation. In this paper, PECan is described and validated against some standard benchmark solutions to underwater acoustics problems. Subsequently, PECan is applied to several single-frequency test cases that were offered for numerical consideration at the SWAM'99 Shallow Water Acoustic Modeling workshop.

Wind tunnel testing of a Mach-scaled rotor model with trailing-edgeflaps

This paper presents the wind tunnel testing of a four-bladedMach-scaled rotor model with piezoelectric bender actuated trailing-edgeflaps. Correctly phased, this flap motion can be used for the activesuppression of vibratory hub loads. First, the University of Maryland AdvancedRotorcraft Code was used to conduct a parametric study to determine theoptimal flap sizing and location as well as the required deflectionamplitudes. Next, a simplified rotor analysis which explicitly models theactuator dynamics was used to design a multi-layer actuator configuration thatis capable of achieving the required flap deflections. Based on the abovedesign studies, a matched set of four Mach-scaled rotor blades withpiezo-bender actuated trailing-edge flaps were fabricated in-house. This rotormodel was operated using a one-seventh scale Bell-412 Mach-scaled rotor hub.Finally, the rotor system was tested in forward flight in the Glenn L Martinwind tunnel. These tests consisted of open-loop single-frequency tests atdifferent rotor speeds and collective settings. Some preliminary closed-looptests using a neural network control algorithm were also conducted.Presented at the American Helicopter Society 56th AnnualForum, Virginia Beach, VA. Copyright 2000 by the AmericanHelicopter Society, Inc. All rights reserved.

Estimation of the time-varying phase (instantaneous frequency) in atmospheric sound propagation

Atmospheric turbulence affects both the amplitude and phase (instantaneous frequency) of transmitted sound. The effect is similar to that of random variations in sound propagation velocity. Two methods to estimate the time-varying phase are discussed, one based on an FFT with optimum data windows and the other based on the discrete Hilbert transform. Accuracy of the two methods is compared using synthesized single-frequency test signals. Comparisons are made between the methods applied to acoustic data obtained from sound propagating through a turbulent atmosphere. a)On leave from the University of Hawaii.

A comparison of single frequency and wide frequency range impedance tests for painted metals

The single frequency (1 kHz) and wide frequency range impedance methods have been compared for painted Zn-55Al alloy coated steel immersed in a range of chloride ion solutions at 50°C in order to be able to interpret trends with sample immersion time in the resistive, αflk, and capacitive, cflk, components of impedance for the single frequency test. The paint film resistance, Rpf, decreases with time after an initial steady period, whereas paint film capacitance, Cpf, is relatively constant. This is shown to cause αflk to rise to a maximum and then decrease rapidly and cflk to rise rapidly, both after initial steady values. Stray cell capacitance can also cause aflk to have initial steady values even when Rpf is decreasing with time. These explanations assist in promoting further use of the single frequency test which has advantages of simplicity in terms of instrumentation, experimentation and analysis of results over the wide frequency range test.

Influence of angular velocity and movement frequency on development of fatigue in repeated isokinetic knee extensions.

Six sedentary students, six orienteers, and six soccer players were each subjected to 15 tests, comprising 120 s of repeated, maximal isokinetic knee extensions. The tests differed with respect to movement velocity (30 degrees.s-1, 120 degrees.s-1, and 300 degrees.s-1), and movement frequency (5 at each velocity). At a certain velocity, a rectilinear relationship was found between muscular performance intensity (expressed either as average power output or as exercise time ratio) and development of fatigue (expressed either as an absolute or as a fractional decline in work output). Significant inter-velocity differences existed between the slopes of these lines at some combinations of performance and fatigue expressions. Only tendencies towards a difference in x-intercept values were found. This x-intercept value can be taken as a measure of the greatest attainable intensity level of performance without the development of fatigue. This suggestion is valuable both in basic physiological research, and as a possible criterion for optimization of muscular performance. At a given exercise time ratio, increasing movement velocity produced increasing fatigue. However, at a given muscular power output--above 15 W approximately--fatigue developed to a greater extent at the low velocity than at the two higher ones, which did not differ significantly. Substantial individual variation was seen in the positions of the low-, medium-, and high-velocity lines. These variations did not depend on the training background. This implies that the validity of using single-velocity, single-frequency tests in determining isokinetic endurance is doubtful.

Relationships governing fatigue crack propagation in structural steels in dual-frequency loading

1. In comparison with single-frequency loading, the magnitude of increase of the rate of FCG in dualfrequency loading of the 15Kh2MFA (I) and 15Kh2MFA (II) steels increases with an increase of the amplitude and frequency ratios. 2. The effect of dual-frequency loading on the rate of FCG starts to operate when the specific value of the summary SIF (Konset) is exceeded; this value decreases with an increase of the amplitude and frequency ratios. The start of operation of the effect of the high-frequency cycles on the rate of FCG in dual-frequency loading can be predicted using the dependence of the threshold ranges of SIF on the cycle asymmetry coefficient determined in single-frequency loading. 3. The effect of dual-frequency loading with the triangular form of the low-frequency cycle on FCG in 15Kh2MFA (I) steel is more damaging than that of dual-frequency loading with the trapezoidal form of the lowfrequency cycle in the amplitude ratio variation range from 0.05 to 0.2. This is expressed not only in a reduction of the level of Konset but also in an increase of the rate of FCG with other conditions being equal. 4. Application of the LDS hypothesis for predicting the rate of FCG in dual-frequency loading is justified in the conditions which do not lead to any changes in the failure mechanisms operating in single-frequency loadloading, and also in cases in which the range of SIF in the high-frequency cycles exceeds the threshold ranges of SIF which correspond to these cycles and were determined on the basis of the results of single-frequency tests. If these conditions are not fulfilled, the LDS hypothesis yields too low values of the rate of FCG in structural materials.

Hysteresis effects with varying superposed magnetizing forces

THE hysteresis effects discussed in this paper occur when magnetic fields are produced in iron by electrical circuits carrying simultaneously currents of different frequencies. Investigations have shown that when two currents of different frequencies are so superposed, the losses in the iron corresponding to each frequency may differ greatly from those obtained when each frequency is acting alone in the circuit. These effects are, therefore, particularly important in the electrical communication field because of the practise of transmitting over one circuit currents of different frequencies. Predictions of the behavior of iron-cored inductance coils and transformers in such a circuit may be erroneous if based on measurements of the iron losses which have been made in the usual way with single-frequency test currents.