Power Ratio Measurements Research Articles

Improving the Accuracy of the Effective Atomic Number (EAN) and Relative Electron Density (RED) with Stoichiometric Calibration on PCD-CT Images

The photon counting detector (PCD) in computed tomography (CT) can count the number of incoming photons in order to obtain energy information for photons corresponding to user-defined thresholds. Research on the extraction of effective atomic number (EAN) and relative electron density (RED) using dual-energy CT (DECT) is currently underway. This study proposes a method for improving EAN and RED accuracy of tissue-equivalent materials by using PCD-CT-based stoichiometric calibration. After obtaining DECT images in energy bin (EB) and full spectrum (FS) modes for eight tissue-equivalent materials, the EAN was calculated with stoichiometric calibration. Using the EAN image, the RED image was acquired to evaluate the accuracy. The errors of both EAN and RED obtained with EB were within 4%. In particular, the accuracy of RED was higher than that of the FS method. Study results indicate that PCD-CT contributes to improving EAN and RED accuracy. Further studies will be aimed at reducing ring artifacts by pixel-correcting PCD images and improving stopping power ratio (SPR) measurements for dose calculation in particle therapy.

Systematic study of the iodinated rectal hydrogel spacer material discrepancy on accuracy of proton dosimetry.

PurposeIodination of rectal hydrogel spacer increases the computed tomography (CT) visibility. The effect of iodinated hydrogel spacer material on the accuracy of proton dosimetry has not been fully studied yet. We presented a systematic study to determine the effect of iodination on proton dosimetry accuracy during proton therapy (PT).MethodsPT plans were designed for 20 prostate cancer patients with rectal hydrogel spacer. Three variations of hydrogel density were considered. First, as the ground truth, the true elemental composition of hydrogel true material (TM), verified by our measurement of spacer stopping power ratio, was used for plan optimization and Monte Carlo dose calculation. The dose distribution was recalculated with (1) no material (NM) override based on the CT intensity of the iodinated spacer, and (2) the water material (WM) override, where spacer material was replaced by water. The plans were compared with the ground truth using the metrics of gamma index (GI) and dosimetric indices.ResultsThe iodination of hydrogel spacer affected the proton dose distribution with the NM scenario showing the most deviation from the ground truth. The iodination of spacer resulted in a notable increase in CT intensity and led to the treatment planning systems mistreating the iodinated spacer as a high‐density material. Among the structures adjacent to the target, neurovascular bundles showed the largest dose difference, up to 350 cGy or about 5% of the prescribed dose with NM. Compared to the WM scenario, dose distribution similarity and GI passing ratios were lower in the NM scenario.ConclusionThe inaccurate CT intensity‐based material for iodinated spacer resulted in errors in PT dose calculation. We found that the error was negligible if the iodinated spacer was replaced with water. Water density can be used as a clinically accessible and convenient alternative material override to true spacer material.

Characterization, Measurement and Specification of Device Imperfections in Optical Coherent Transceivers

Transceiver imperfections become the primary source of impairment as baud rate and modulation order grow in advanced optical coherent communications. Thus, transceiver imperfections, both linear and nonlinear, need to be appropriately characterized, measured, and specified. Treatments for linear imperfections are relatively mature. This study reviews the transceiver's linear imperfection modeling, characterization, and measurement technologies. In practical applications, in-field measurement using the transceiver and a few low speed additional devices is preferred. In the case of nonlinear imperfections, the situation is complex. One important task is to estimate the nonlinear system performance from the nonlinear characteristics of the devices. In this study, we attempt to establish a connection between them by examining different technologies. Although the orthogonal component has a good correlation with nonlinear system performance, its measurement is prohibitively complex. In the nonlinear noise to power ratio measurement, a certain frequency component of the input signal is notched, and the re-growth component at the notch frequency is measured at the nonlinear device output. The ratio between the re-growth component power and the output signal power is the noise to power ratio. While this method is easy to carry out, it does not correctly estimate nonlinear impairment in general. The reason for this is that the signal incurs different nonlinear responses in two conditions, i.e., with or without a notch. This method accurately estimates the nonlinear impairment in some special but useful cases, such as Gaussian input signals and nonlinear systems whose dominant nonlinear term is the even order term.

Analysis of peak-to-average power ratio in filter bank multicarrier with offset quadrature amplitude modulation systems using partial transmit sequence with shuffled frog leap optimization technique

<p class="Abstract">Because of its low adjacent channel leakage ratio, the Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC-OQAM) has sparked the attention of many researchers in recent times. However, the problem of high Peak-to-Average Power Ratio (PAPR) measurement has a detrimental influence upon the FBMC system's energy measurement efficiency. We study PAPR reduction of FBMC-OQAM signals using the Partial Transmit Sequence (PTS) methods in this work. The PTS with shuffled frog leap phase optimization method is proposed in this paper to reduce the larger PAPR measurement, which is the major disadvantage of the filter bank multicarrier with offset quadrature amplitude modulation system. According to the simulation software findings, the suggested approach has a considerably superior PAPR, which may reduce the PAPR by about 2 dB at complementary cumulative distribution function 10<sup>-3</sup> when compared to the traditional PTS method, and it has a much lower computational complexity than the previous ways. The experimental parameters are measured, and results are evaluated using MATLAB tool.</p>

Electronic Mode Stirring for Improved Backscatter Communication Link Margin in a Reverberant Cavity Animal Cage Environment

Neuroscience research in nonhuman primates (NHPs) often requires multiday neural recordings from freely moving animals inside their home cages, making ultralow-power uplinks using wireless backscatter communication highly desirable. Previous work reveals that the channel transfer function (CTF) of a standard NHP home cage in the 915 MHz and 2.4 GHz industrial, scientific, and medical (ISM) bands resembles a resonant cavity exhibiting deep nulls throughout the cage volume, which are particularly acute for round-trip backscatter paths. In this work, we investigate a novel application of passive antenna mode stirring via switched parasitic antennas (SPAs) to reduce the magnitude and prevalence of deep nulls in the cage CTF. We present a system leveraging four cage-ceiling-mounted SPAs with two dynamically controlled impedance states each, yielding 16 total mode stirring configurations. We compare the frequency-domain power ratio measurements at 126 positions throughout the cage taken with and without passive antenna mode stirring. In the 915 MHz ISM band, the optimized SPA configuration improved the maximum two-way insertion loss in 68% of testing locations, reducing the worst case two-way insertion loss by 60.2 dB. In the 2.4 GHz ISM band, the maximum two-way insertion loss was improved in 53% of testing locations, reducing the worst case two-way insertion loss by 35.6 dB. This approach eliminates the deepest nulls in the cage volume and leads to significantly improved link margin for a backscatter-based wireless brain–computer interface (BCI).

Two-frequency amplification in a semiconductor tapered amplifier for cold atom experiments**Project supported by the National Natural Science Foundation of China (Grant No. 61473166).

Simultaneous two-frequency amplification is highly desirable in cold atom experiments. The nonlinear response would appear in the two-frequency amplification with a semiconductor tapered amplifier (TA) and has a direct influence on the experimental result. We investigated in detail the effects of frequency difference, total power, and power ratio of two seeding lasers on the output components based on a simplified theoretical model. The simulation results showed that the multiple sideband generation in the amplifier due to self-phase and amplitude modulation could be suppressed and the TA tended to linearly amplify the power ratio between two-frequency components, when the two seeding lasers had a large frequency difference. This was verified experimentally in the output power ratio measurement via a calibrated Fabry–Perot interferometer method with a good linearity and an uncertainty of 1%. We also discussed the consequences of power ratio responses in the amplification in light of cold atom experiments, especially in the ac Stark shift related phase error of Raman-type atom interferometers (AIs). It was shown that the fluctuation of intensity ratio of Raman beams may induce significant systematic errors for an AI gyroscope.

Centralized Rainfall Estimation Using Carrier to Noise of Satellite Communication Links

In this paper, we present a centralized method for real-time rainfall estimation using carrier-to-noise power ratio ( $C/N$ ) measurements from broadband satellite communication networks. The $C/N$ data of both forward link and return link are collected by the gateway station from the user terminals in the broadband satellite communication network and stored in a database. The $C/N$ for such Ka-band scenarios is impaired mainly by the rainfall. Using signal processing and machine learning techniques, we develop an algorithm for real-time rainfall estimation. Extracting relevant features from $C/N$ , we use artificial neural network in order to distinguish the rain events from dry events. We then determine the signal attenuation corresponding to the rain events and examine an empirical relationship between rainfall rate and signal attenuation. Experimental results are promising and prove the high potential of satellite communication links for real environment monitoring, particularly rainfall estimation.

Calibration of a Terahertz Attenuator by a DC Power Substitution Method

An attenuation calibration system is developed using an isothermal temperature control-type calorimeter for a terahertz (THz) attenuator. This system is based on a power ratio measurement by dc power substitution. A highly sensitive calorimeter achieves a simple and accurate attenuation calibration at room temperature. Calibration is performed for metalized-film attenuators at 1 THz using a photomixer as the THz source. The measurement uncertainties in the system are evaluated, and the expanded uncertainty is found to be 0.19–0.84 dB ( $k = 2$ ) for an attenuation measurement range up to 12 dB.

A Noise Power Ratio Measurement Method for Accurate Estimation of the Error Vector Magnitude

Error vector magnitude (EVM) and noise power ratio (NPR) measurements are well-known approaches to quantify the inband performance of communication systems and their respective components. In contrast to NPR, EVM is an important design specification and is widely adopted by modern communication standards such as 802.11 (WLAN). However, EVM requires full demodulation, whereas NPR excels with simplicity requiring only power measurements in different frequency bands. Consequently, NPR measurements avoid bias due to insufficient synchronization and can be readily adapted to different standards and bandwidths. We argue that NPR-inspired measurements can replace EVM in many practically relevant cases. We show how to set up the signal generation and analysis for power-ratio-based estimation of EVM in orthogonal frequency-division multiplexing systems impaired by additive noise, power amplifier nonlinearity, phase noise, and in-phase-quadrature (IQ) imbalance. Our method samples frequency-dependent inband errors via a single measurement and can either include or exclude the effect of IQ mismatch using asymmetric or symmetric stopband locations, respectively. We present measurement results using an 802.11ac PA at different backoffs, corroborating the practicability and accuracy of our method. Using the same measurement chain, the mean absolute deviation from the EVM is less than 0.35 dB.

Measuring phased‐array antenna beampatterns with high dynamic range for the Murchison Widefield Array using 137 MHz ORBCOMM satellites

AbstractDetection of the fluctuations in a 21 cm line emission from neutral hydrogen during the Epoch of Reionization in thousand hour integrations poses stringent requirements on calibration and image quality, both of which necessitate accurate primary beam models. The Murchison Widefield Array (MWA) uses phased‐array antenna elements which maximize collecting area at the cost of complexity. To quantify their performance, we have developed a novel beam measurement system using the 137 MHz ORBCOMM satellite constellation and a reference dipole antenna. Using power ratio measurements, we measure the in situ beampattern of the MWA antenna tile relative to that of the reference antenna, canceling the variation of satellite flux or polarization with time. We employ angular averaging to mitigate multipath effects (ground scattering) and assess environmental systematics with a null experiment in which the MWA tile is replaced with a second‐reference dipole. We achieve beam measurements over 30 dB dynamic range in beam sensitivity over a large field of view (65% of the visible sky), far wider and deeper than drift scans through astronomical sources allow. We verify an analytic model of the MWA tile at this frequency within a few percent statistical scatter within the full width at half maximum. Toward the edges of the main lobe and in the sidelobes, we measure tens of percent systematic deviations. We compare these errors with those expected from known beamforming errors.

Electroencephalographic Upper/Low Alpha Frequency Power Ratio Relates to Cortex Thinning in Mild Cognitive Impairment

Objective: Temporoparietal cortex thinning is associated with mild cognitive impairment (MCI) due to Alzheimer disease (AD). The increase in EEG upper/low α frequency power ratio has been associated with AD converter MCI subjects. We investigated the association of the EEG upper/low α frequency power ratio with patterns of cortical thickness in MCI. Methods: 74 adult subjects with MCI underwent clinical and neuropsychological evaluation, electroencephalography (EEG) recording and high-resolution 3-dimensional magnetic resonance imaging (MRI). The EEG upper/low α frequency power ratio as well as cortical thickness were computed for each subject. Three MCI groups were detected according to increasing tertile values of EEG upper/low α frequency power ratios, and the difference of cortical thickness among the groups was estimated. Results: The EEG high upper/low α frequency power ratio group had a total cortical grey matter volume reduction of 471 mm², greater than that of the EEG low upper/low α frequency power ratio group (p < 0.001). The EEG high upper/low α frequency power ratio group showed a similar but less marked pattern (160 mm²) of cortical thinning when compared to the EEG middle upper/low α frequency power ratio group (p < 0.001). Moreover, the EEG high upper/low α frequency power ratio group had wider cortical thinning than other groups, mapped to the supramarginal gyrus and precuneus bilaterally. No significant regional cortical thickness differences were found between middle and low EEG upper/low α frequency power ratio groups. Conclusion: A high EEG upper/low α frequency power ratio was associated with temporoparietal cortical thinning in MCI subjects. The combination of upper/low α frequency power ratio and cortical thickness measurement could be useful for identifying individuals at risk for progression to AD dementia and may be of value in the clinical context.

Qualitative and Quantitative Measurement of the Singing Voice

Objective: The aim of the study was to clarify the mechanisms underlying the singing voice. Patients and Methods: Forty-eight professional opera singers underwent flexible and rigid endoscopy, spectrographic analysis and perceptual evaluation. Results: The data provided by voice analysis were not as clear and relevant to the aim of our study as those commonly obtained for speech evaluation. Laryngoscopy with rigid and flexible fiber optics and the singing power ratio (SPR) measurement provided more applicable data. Indeed, the former allowed us to assess laryngeal position, the glottic pattern and vocal tract modifications during the actual singing performance. The latter, already recommended by other authors as a reliable vocal emission index, also yielded more relevant information in comparison with the assessment of voice quality. Specifically, SPR provided data directly correlated to both the years of singing activity and the vocal category of each singer (the higher the singing pitch, the wider the vocal extension). More importantly, the data fully reflected the subjective assessment of each phoniatrician. Conclusions: We suggest that the SPR indices can be used as the electroacoustic equivalent of the subjective judgment of vocal focus.

Studying the properties of galaxy cluster morphology estimators

X-ray observations of galaxy clusters reveal a large range of morphologies with various degrees of disturbance, showing that the assumptions of hydrostatic equilibrium and spherical shape which are used to determine the cluster mass from X-ray data are not always satisfied. It is therefore important for the understanding of cluster properties as well as for cosmological applications to detect and quantify substructure in X-ray images of galaxy clusters. Two promising methods to do so are power ratios and center shifts. Since these estimators can be heavily affected by Poisson noise and X-ray background, we performed an extensive analysis of their statistical properties using a large sample of simulated X-ray observations of clusters from hydrodynamical simulations. We quantify the measurement bias and error in detail and give ranges where morphological analysis is feasible. A new, computationally fast method to correct for the Poisson bias and the X-ray background contribution in power ratio and center shift measurements is presented and tested for typical XMM-Newton observational data sets. We studied the morphology of 121 simulated cluster images and establish structure boundaries to divide samples into relaxed, mildly disturbed and disturbed clusters. In addition, we present a new morphology estimator - the peak of the 0.3-1 r500 P3/P0 profile to better identify merging clusters. The analysis methods were applied to a sample of 80 galaxy clusters observed with XMM-Newton. We give structure parameters (P3/P0 in r500, w and P3/P0_max) for all 80 observed clusters. Using our definition of the P3/P0 (w) substructure boundary, we find 41% (47%) of our observed clusters to be disturbed.

PMD-Insensitive CD Monitoring Based on RF Clock Power Ratio Measurement With Optical Notch Filter

We propose and experimentally demonstrate a chromatic-dispersion (CD) monitoring method based on radio-frequency (RF) clock power ratio measurement in 38-Gb/s nonreturn-to-zero differential quadrature phase-shift keying (NRZ-DQPSK) and 57-Gb/s NRZ differential 8-level phase-shift keying (D8PSK) systems. A narrowband fiber Bragg grating (FBG) notch filter is centered at the optical carrier wavelength, such that the RF clock power decreases with CD. On the other hand, RF clock power increases with CD in the absence of the notch filter. By using the RF power ratio of the filtered and nonfiltered signals, polarization-mode-dispersion (PMD) effects on RF power ratio can be eliminated and CD measurement sensitivity can be increased. The CD monitoring range is 0 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\sim$</tex></formula> 250 ps/nm in the systems with a symbol rate of 19-Gsym/s. Moreover, the proposed CD-monitoring method is not affected by received optical power.

Dosimetric evaluation of a novel polymer gel dosimeter for proton therapy

The aim of this study is to evaluate the dosimetric performance of a newly developed proton-sensitive polymer gel formulation for proton therapy dosimetry. Using passive scattered modulated and nonmodulated proton beams, the dose response of the gel was assessed. A next-generation optical CT scanner is used as the readout mechanism of the radiation-induced absorbance in the gel medium. Comparison of relative dose profiles in the gel to ion chamber profiles in water is performed. A simple and easily reproducible calibration protocol is established for routine gel batch calibrations. Relative stopping power ratio measurement of the gel medium was performed to ensure accurate water-equivalent depth dose scaling. Measured dose distributions in the gel were compared to treatment planning system for benchmark irradiations and quality of agreement is assessed using clinically relevant gamma index criteria. The dosimetric response of the gel was mapped up to 600 cGy using an electron-based calibration technique. Excellent dosimetric agreement is observed between ion chamber data and gel. The most notable result of this work is the fact that this gel has no observed dose quenching in the Bragg peak region. Quantitative dose distribution comparisons to treatment planning system calculations show that most (> 97%) of the gel dose maps pass the 3%/3 mm gamma criterion. This study shows that the new proton-sensitive gel dosimeter is capable of reproducing ion chamber dose data for modulated and nonmodulated Bragg peak beams with different clinical beam energies. The findings suggest that the gel dosimeter can be used as QA tool for millimeter range verification of proton beam deliveries in the dosimeter medium.

Improving the Linearity of GaN HEMTs by Optimizing Epitaxial Structure

This paper presents an effective method of improving the linearity of GaN/AlGaN high-electron mobility transistors (HEMTs) by optimizing barrier (AlGaN Layer) thickness or implementing doped GaN cap or a combination of both. HEMT devices with different epitaxial structures were simulated, fabricated, and measured to demonstrate this. Third-order intermodulation distortion and adjacent channel power ratio measurements were performed in order to compare linearity experimentally. A significant improvement of linearity is observed for an optimized architecture.

A 5 GHz high-temperature superconducting reaction-type transmitting filter based uponsplit open-ring resonators

A new kind of high-temperature superconducting (HTS) transmitting filter based on areaction-type resonator is presented. The purpose of an HTS reaction-type filter(HTS-RTF) is to eliminate the intermodulation distortion noise generated by microwavepower amplifiers such as those employed in mobile base stations. An HTS-RTFenables both higher power handling capability and sharper cutoff characteristicscompared to existing planar-type HTS transmitting filters, since a reaction-typeresonator does not resonate with high power fundamental signals. To achieve steepskirt characteristics and high power handling capability simultaneously, a 5 GHzthree-pole HTS-RTF using a split open-ring resonator is designed. This splitopen-ring resonator offers low maximum current densities and a high-unloadedQ factor with low radiation. The designed prototype filter has Chebyshev characteristics with a centrefrequency of 4.95 GHz and a bandwidth of 1.5 MHz. The HTS-RTF is fabricated using a double-sidedYBa2C3O7−δ thin film deposited on a 0.5 mm thick MgO substrate. The measured filter shows aninsertion loss of less than 0.1 dB and a third intermodulation distortion value of−56.7 dBc for a 40 dBm passband signal. In addition, adjacent channel leakage power ratio(ACLR) measurements using an actual wideband CDMA signal confirm an ACLRimprovement of about 10 dB for a four-carrier signal with power up to 40 dBm.

Measurement of helium-3 and deuterium stopping power ratio for negative muons

The measurement method and results measuring of the stopping power ratio of helium-3 and deuterium atoms for muons slowed down in the D/3He mixture are presented. Measurements were performed at four values of pure 3He gas target densities, ϕHe = 0.0337, 0.0355, 0.0359, 0.0363 (normalized to the liquid hydrogen density) and at a density 0.0585 of the D/3He mixture. The experiment was carried out at PSI muon beam μE4 with the momentum Pμ= 34.0 MeV/c. The measured value of the mean stopping ratio S$_{3^He/D}$ is 1.66±0.04.

Uncertainty Evaluation of a Broadband Attenuation Standard

A standard step attenuator has been developed. It comprises a build-up chain of ten steps of power ratio measurement and operates in a frequency range of 10 MHz to 18 GHz. The overall system has a dynamic range of 90 dB and an expanded uncertainty of 0.006 dB (k=2). The system is used as an attenuation standard in a series radio-frequency substitution scheme. The uncertainty factors in the attenuation measurement of 40 dB at 5 GHz are fully described. For the calibration of a typical step attenuator, the expanded uncertainties are 0.011 dB for the attenuation range up to 80 dB, including the mismatch uncertainty.

Percolation Studies in Synthetic Ferrimagnetic Recording Media

We have studied the percolation limit of synthetic ferrimagnetic media (SFM) by the measurement of noise power and third harmonic ratio and by imaging with a high-resolution magnetic force microscope (MFM). The noise power spectrum, which helps to find the onset of percolation, is significantly different in SFM structures compared to the conventional recording media. Properties of the stabilization layers, such as switching field distribution (SFD), are highly influential in deciding the integrated noise power spectrum. With suitable selection of high moment stabilization layers, the noise at higher densities, within the percolation density limit, can be substantially reduced. Third harmonic ratio studies indicate that the partial erasure occurs above /spl sim/900 kfci. Using a high-resolution high-Q MFM, it is possible to obtain stable and nonpercolating high density patterns up to 1000 kfci on media with tBr=0.22 memu/cm/sup 2/ and Hc/spl sim/4500 Oe. This results in practical designs of media for recording densities >150 Gbits/in/sup 2/.