Measurement Bandwidth Research Articles

A Comprehensive Study on the Improved Radio-Frequency Magnetic Field Measurement for the Initial Upward Leader of a Negative Rocket-Triggered Lightning Flash

The spectrum analysis of the lightning current in the experiment campaign of 2019 reveals that the lightning current waveform contains rich medium-frequency (MF) radiation signals in the initial stage. However, there is a lack of resolution for MF signals by using conventional magnetic sensors. The bandwidth of radio-frequency magnetic field measurement is improved by extending to 20 kHz–1.2 MHz in the Guangdong Comprehensive Observation Experiment on Lightning Discharge (GCOELD). During the previously noticed “quiet period” that can only maintain the upward propagation with relatively small-scale breakdown, magnetic pulses of quiet period (MPQPs) are discerned more clearly than the previous experiment in GCOELD. Aided by the improvement of a magnetic sensor, this paper captures richer magnetic field signals radiated from the weak discharge of the precursory phage than previous experiments in GCOELD. The analysis shows that both aborted UPLs and UPLs are caused by weak discharge pulses called initial precursor pulses (IPPs), which are very similar to the amplitude of the streamer discharge obtained in the laboratory. In summary, the signals detected by an improved magnetic sensor will provide an important reference for exploring the pulse characteristics of the whole discharge process and formation mechanism of the UPL in the initial stage of triggered lightning.

Extraction of open-loop frequency response of power apparatus using transient data from multiple naturally occurring disturbances

Frequency response analysis (FRA) is a mature technique to characterize the behaviour of apparatus like transformers, and is commonly used for condition monitoring and diagnostics. FRA is also used for sub-synchronous resonance/control interaction analysis of rotating machines and power electronic converters. The frequency responses (transfer functions) can be experimentally obtained from tests at the apparatus terminals. These are generally done offline, i.e. when the equipment is out of service. Online testing is attractive as it can be done frequently and periodically, but it requires auxiliary equipment for injecting probing signals into an energized high voltage system. The alternative online approach uses high bandwidth measurements of “naturally” occurring external transients (due to faults, switching and other disturbances) to obtain the frequency response. The key challenge in online FRA of multi-port apparatus is in the extraction of the “open-loop” transfer function of the apparatus, while connected to the rest of the system, essentially in a “closed-loop” configuration. This paper proposes a technique to address this challenge by utilizing data from multiple independent events, and presents proof-of-concept simulations. The technique can be applied not only to passive components like transformers and transmission lines, but also to power electronic systems and rotating machines.

A miniaturized three‐dimensional log periodic Koch‐dipole array antenna using T‐shaped top loading

A log periodic dipole array antenna (LPDA) is miniaturized by using top loading. The Koch dipole further helps to shrink the antenna size. Different from the traditional LPDA that features a planar structure, the proposed log periodic Koch-dipole array (LPKDA) adopts two identical pairs of top-loaded Koch-dipoles that deploy orthogonally along the feed line. This results in a tree-like three-dimensional antenna geometry, which introduces one extra dimension of freedom for antenna designers. The influence of the top-loading on antenna's impedance bandwidth is studied under the Wheeler and Chu's limit. The characteristic of the Koch-dipole is analyzed. Taking the advantage of 3D printing technology to fabricate complex models, the proposed LPKDA is printed by selective laser melting using aluminum alloy. The simulated −10-dB bandwidth is 117.4% (0.91-3.54 GHz) The LPKDA has the average gain of 5.3 dBi over the 1 to 3.5 GHz impedance bandwidth in measurement. Radiation patterns agree well in simulation and measurement. Compared with conventional LPDA of the same impedance bandwidth, the proposed LPKDA features 42%-dimensional reduction. This letter proves the feasibility of antenna optimization by using both innovative design method and advanced fabrication process.

An Additively Manufactured Four-Sensor Fast Response Aerodynamic Probe

Abstract This study describes the design, development, and testing of a miniature fast response aerodynamic probe (FRAP) with four sensors (4S), which are able to perform measurements in the unsteady three-dimensional flow field. Moreover, the calibration and first results with the newly developed probe are provided. The miniature FRAP-4S demonstrates a 3 mm tip diameter, offering a 25% reduction in diameter size, in comparison to a first-generation FRAP-4S, without any loss in terms of measurement bandwidth. The 3 mm outer casing of the probe is additively manufactured with a high-precision binder jetting technique. In terms of aerodynamic performance, the probe demonstrates high angular sensitivity up to ± 18 deg incidence angle in both directions. To evaluate the measurement accuracy of the newly developed FRAP-4S, measurements are performed at the Laboratory for Energy Conversion (LEC) in both a round axisymmetric jet and an one-and-a-half stage, unshrouded and highly loaded axial turbine configuration. Turbulence measurements performed with the miniature FRAP-4S are compared against hot-wire studies in round free-jets found in the literature. Good agreement in both trends but also absolute values is demonstrated. Moreover, the performance of the probe is compared against traditional instrumentation developed at LEC, namely, miniature pneumatic and FRAP-2S probes. The results indicate that the FRAP-4S, despite its larger size in comparison to the other probes tested, can resolve the main flow patterns, with the highest deviations occuring in the presence of highly skewed and sheared flow. Furthermore, the additively manufactured probe was proven to be robust after more than 50 hours of testing in the representative turbine environment configuration. Finally, it should be highlighted that the newly developed FRAP reduces measurement time by a factor of three in comparison to FRAP-2S, which directly translates to reduced development time and thus cost during the turbomachinery development phase.

Effects of bandwidth limitations on low-boom perceived level

Estimating sonic boom noise levels during community noise testing of low-boom supersonic aircraft such as the NASA X-59 can be challenging because of bandwidth limitations caused by ambient noise contamination of boom recordings. This paper describes the effect of spectral bandwidth limitations on a candidate sonic boom metric for community response: the perceived level (PLdB). This metric was calculated using spectral data of measured sonic booms from NASA’s Quiet Supersonic Flights 2018 (QSF18) test campaign. Spectral data were obtained using a 650 ms time window for both the boom and the ambient recordings, with the ambient recording immediately preceding the detected boom, and the measurement bandwidth estimated using the signal-to-noise ratio (SNR) at each frequency. Analysis of several booms at four different measurement stations, each with several measurement configurations, shows that not accounting for limited bandwidth can add several decibels to the sonic boom metrics. The effects of measurement location and instrumentation are discussed. Future work may include developing methods for how to account for limited bandwidth, including potential filtering and spectral extrapolation methods. [Work supported by NASA Langley Research Center through the National Institute of Aerospace.]

Generation of −10.7 dB unbiased entangled states of light

In a continuous variable quantum key distribution (CV-QKD) system, strong Einstein–Podolsky–Rosen entangled states can significantly boost the robustness and distance for secure communication. However, an inevitable bias of two entanglement quadratures may degrade the secret key rate and distance during random quadrature base switching. The bias originates from several interdependent factors in the generation, propagation, and detection of entangled states, which faces a challenge to be completely eliminated. Here, we analyze in detail the origin of the bias effect and report on a scheme of generating unbiased entangled states, whereby a −10.7 ± 0.1 dB quadrature noise unbiased entanglement is first generated experimentally with two single-mode squeezed states. The unbiased quadrature correlations within the measurement bandwidth are expected to immensely enhance the key rate and secure distance for CV-QKD.

Modulation frequency selection and efficient look-up table inversion for frequency domain diffuse optical spectroscopy.

.Significance: Frequency domain diffuse optical spectroscopy (FD-DOS) uses intensity modulated light to measure the absorption and reduced scattering coefficients of turbid media such as biological tissue. Some FD-DOS instruments utilize a single modulation frequency, whereas others use hundreds of frequencies. The effect of modulation frequency choice and measurement bandwidth on optical property (OP) extraction accuracy has not yet been fully characterized.Aim: We aim to assess the effect of modulation frequency selection on OP extraction error and develop a high-speed look-up table (LUT) approach for OP estimation.Approach: We first used noise-free simulations of light transport in homogeneous media to determine optimized iterative inversion model parameters and developed a new multi-frequency LUT method to increase the speed of inversion. We then used experimentally derived noise models for two FD-DOS instruments to generate realistic simulated data for a broad range of OPs and modulation frequencies to test OP extraction accuracy.Results: We found that repeated measurements at a single low-frequency (110 MHz) yielded essentially identical OP errors as a broadband frequency sweep (35 evenly spaced frequencies between 50 and 253 MHz) for these noise models. The inclusion of modulation frequencies diminished overall performance for one of the instruments. Additionally, we developed a LUT inversion algorithm capable of increasing inversion speeds by up to , with and error when a single modulation frequency was used.Conclusion: These results suggest that simpler single-frequency systems are likely sufficient for many applications and pave the way for a new generation of simpler digital FD-DOS systems capable of rapid, large-volume measurements with real-time feedback.

A Highly Linear Dual-Stage Amplifier With Beyond 1.75-THz Gain–Bandwidth Product

This work reports a multipurpose highly linear ultrawideband amplifier with a gain-bandwidth product (GBP) of 1.75 THz, the highest reported in any monolithic microwave integrated circuit (MMIC) process. A transimpedance amplifier is cascaded with a distributed amplifier, emulating a receiver subsystem. Using a diamond heat spreader, to dissipate heat from transistors, the cascaded amplification subsystem can achieve very high output third-order-intercept point (OIP3) from 20 to 24 dBm when measured between 5 and 65 GHz. A small-signal average gain of 24 dB is observed over a frequency range exceeding the maximum measurable bandwidth from dc to 110 GHz. Compared with other ultrawideband MMIC amplifiers beyond 110-GHz bandwidth, the circuit offers a unique combination of high linearity (OIP3) and high gain. As a result, the cascaded amplifier is suitable for applications in optical-electrical converters, spectroscopy, and ultrawideband measurement systems in the subterahertz frequency range.

Design, Analysis and Application of Single-Wheel Test Bench for All-Electric Antilock Braking System in Electric Vehicles

An antilock braking system (ABS) is one of the most important components in a road vehicle, which provides active protection during braking, to prevent the wheels from locking-up and achieve handling stability and steerability. The all-electric ABS without any hydraulic components is a potential candidate for electric vehicles. To demonstrate and examine the all-electric ABS algorithms, this article proposes a single-wheel all-electric ABS test bench, which mainly includes the vehicle wheel, the roller, the flywheels, and the electromechanical brake. To simulate dynamic operation of a real vehicle’s wheel, the kinetic energy of the total rotary components in the bench is designed to match the quarter of the one of a commercial car. The vertical force to the wheel is adjustable. The tire-roller contact simulates the real tire-road contact. The roller’s circumferential velocity represents the longitudinal vehicle velocity. The design and analysis of the proposed bench are described in detail. For the developed prototype, the rated clamping force of the electromechanical brake is 11 kN, the maximum vertical force to the wheel reaches 300 kg, and the maximum roller (vehicle) velocity reaches 100 km/h. The measurable bandwidth of the wheel speed is 4 Hz–2 kHz and the motor speed is 2.5 Hz–50 kHz. The measured results including the roller (vehicle) velocity, the wheel velocity, and the wheel slip are satisfactory. This article offers the effective tools to verify all-electric ABS algorithms in a laboratory, hence saving time and cost for the subsequent test on a real road.

Wireless Transmission of Friedlander‐Type Signals for the Dynamic Measurement of Blast Pressure

AbstractDuring explosive detonation or air blast experiments, long cables are commonly used for transmitting signals delivered by pressure sensors to the safe place of the acquisition unit. While constant efforts are undertaken for enlarging the bandwidth of sensors in order to improve the measurement precision of the peak pressure, the limitations of the wired transmission of blast pressure signals delivered by these sensors are not addressed. We discuss here such limitations and propose a wireless new solution for the dynamic measurement of Friedlander‐type signals delivered by ultra‐wideband sensors (> ). Contrary to the wired solution, the distance between the sensor and the acquisition unit does not limit the measurement bandwidth of the wireless setup. Experimental results are reported for validation purposes and pave the way of the dynamic measurement of blast pressure variations occurring at the heart of the fireball generated during explosions.

Time-Domain Characterization and Linearization of a Dual-Input Power Amplifier Using a Vector Network Analyzer as the Receiver

A newly calibrated testbed based on a commercial vector network analyzer (VNA) is proposed for the fast in-band vector signal characterization and linearization of nonlinear multiport devices. The testbed can acquire both CW and wideband modulated periodic signals without breaking contact with the DUT, in up to five channels. The time-domain measurements are made possible by calibrating all the receivers in the frequency domain. This calibration provides a phase and amplitude correction for the modulation tones of all the incident and reflected waves in the acquisition bandwidth. The measurement bandwidth is determined at calibration by the bandwidth of the periodic OFDM signals used as a phase standard. It is independent of the VNA receivers' bandwidth. A 500-MHz 100 000-tones 64-QAM OFDM constellation is recovered with 0.48% error vector magnitude (EVM). As an application, a dual-input hybrid Doherty-outphasing power amplifier (HD-OPA) is characterized at 2.08 GHz. A CW signal is used to determine the outphasing angle and input power levels, which provides the best drain and power-added efficiencies for each output power. The dynamic response of the dual-input HD-OPA is acquired on five channels by using the same testbed. Various periodic OFDM signals, with 24 000 tones, are measured before and after predistortion linearization in a fraction of a second.

Estimation of the bandwidth parameter in Nadaraya-Watson kernel non-parametric regression based on universal threshold level

This paper proposes a new improvement of the Nadaraya-Watson kernel non-parametric regression estimator and the bandwidth of this new improvement is obtained depending on universal threshold level with wavelet of kernel function instead of using fixed bandwidth and variable bandwidth for geometric, arithmetic mean, range and median measurements. A simulation study is presented, including comparisons between the proposed method and five others Nadaraya-Watson kernel estimators (classical methods), as well as using real data depending on a program written in MATLAB language which was designed for this purpose. It was concluded that the proposed method is more accurate than all classical methods for all simulations and real data based on MSE criterion.

A Simple but Efficient Concept of Blended Teaching of Mathematics for Engineering Students during the COVID-19 Pandemic

In this article we present a case study concerning a simple but efficient technical and logistic concept for the realization of blended teaching of mathematics and its applications in theoretical mechanics that was conceived, tested and implemented at the Department of Civil, Environmental and Mechanical Engineering (DICAM) of the University of Trento, Italy, during the COVID-19 pandemic. The concept foresees traditional blackboard lectures with a reduced number of students physically present in the lecture hall, while the same lectures are simultaneously made available to the remaining students, who cannot be present, via high-quality low-bandwidth online streaming. The case study presented in this paper was implemented in a single University Department and was carried out with a total of n=1011 students and n=68 professors participating in the study. Based on our first key assumption that traditional blackboard lectures, including the gestures and the facial expressions of the professor, are even nowadays still a very efficient and highly appreciated means of teaching mathematics at the university, this paper deliberately does not want to propose a novel pedagogical concept of how to teach mathematics at the undergraduate level, but rather presents a technical concept of how to preserve the quality of traditional blackboard lectures even during the COVID-19 pandemic and how to make them available to the students at home via online streaming with adequate audio and video quality even at low internet bandwidth. The second key assumption of this paper is that the teaching of mathematics is a dynamic creative process that requires the physical presence of students in the lecture hall as audience so that the professor can instantaneously fine-tune the evolution of the lecture according to his/her perception of the level of attention and the facial expressions of the students. The third key assumption of this paper is that students need to have the possibility to interact with each other personally, especially in the first years at the university. We report on the necessary hardware, software and logistics, as well as on the perception of the proposed blended lectures by undergraduate students from civil and environmental engineering at the University of Trento, Italy, compared to traditional lectures and also compared to the pure online lectures that were needed as emergency measure at the beginning of the COVID-19 pandemic. The evaluation of the concept was carried out with the aid of quantitative internet bandwidth measurements, direct comparison of transmitted video signals and a careful analysis of ex ante and ex post online questionnaires sent to students and professors.

Low-Latency Live Streaming Over HTTP in Bandwidth-Limited Networks

HTTP adaptive streaming (HAS) can achieve low latency for live streaming with the Common Media Application Format. However, the legacy mechanisms inaccurately measure the available bandwidth because the download time is affected by not only the network but also idle times between chunks at the live encoder side. These wrong measurements may condemn users to a low quality-of-experience (QoE). This letter presents a HAS client with a novel bandwidth measurement heuristic. Our experiments show that it provides a better QoE with fewer video freezes and higher video quality while achieving a live latency down to one second in bandwidth-limited networks.

Detection and evaluation of the fibers' deposition parameters during wet filament winding

AbstractWet filament winding technology has been extensively used for the manufacture of rotationally symmetric parts made of fiber‐reinforced plastics (FRP). As the design and modeling of FRP‐parts require numerous assumptions, deviations between calculated and achieved mechanical properties are expected. One aspect that contributes to this discrepancy is the assumption of a homogeneous rectangular cross‐section of the fiber‐band. In this work, the fiber‐band geometry in a wet‐winding process of carbon fiber cylinders is analyzed. An Infrared‐optical system for the detection of the fiber bandwidth and winding‐angle is implemented. The influence of the winding speed and the resin temperature is analyzed. An image processing algorithm for the automatic measurement of the fiber's bandwidth and winding‐angle is developed. Manual and adaptive gamma corrections are implemented to improve image quality. A parameter study for the suitable selection of image processing parameters is performed.

Fiber optic propagation problems and signal bandwidth measurements under high temperature and high dopant germanium ratios

Abstract This study presents fiber optic losses/dispersion and signals bandwidth measurements under high temperature and high dopant germanium ratios variations for ultra-long haul distances without amplification stage. The fiber losses, fiber dispersion, and total fiber data rates are estimated and compared with the previous results under room temperature and high germanium dopant ratios to silica glass fiber. Then the model is extended for ultra-fiber transmission distances up to 500 km under high-temperature variations without using any amplification stage. The fiber losses/dispersion coefficient is degraded, and the total fiber data rates are enhanced with the increment of high dopant ratios of germanium.

Broadband Printed Modified Dipole for Personal Communication Systems

In this paper a modified printed dipole is proposed for mobile terminals operating in the first band of Personal Communication System (PCS) that is ranging from 800 to 900 MHz. One of the most important features of this kind of antenna is its wide bandwidth as required in the mentioned band. The modified design of the proposed antenna allows the user to move in any direction as is usual in mobile communications. The results of this article include an analytical design, simulations that have been performed numerically using a Finite Element Method (FEM) computational tool, structure optimization in order to maximize the antenna bandwidth and experimental measurements with the aim of spatial evaluating of electromagnetic radiated fields.

Analysis of limitations on recovery of gravity field based on satellite gravity gradient data

Although satellite gravity gradient data plays a great role in determining short-wavelength part of static gravity field model, accuracy of the long-wavelength part of gravity field model recovered by them are poor, which leads to only a few applications in time-variable gravity investigation. The reason is that some factors limit the accuracy of the gravity field recovered using gradient data, including accuracy of the gravity gradient observations, measurement bandwidth (MBW) of gradiometer, satellite inclination, etc. This paper aims at analyzing the influence of these limitations on gravity field recovery and discusses the possibility of time-variable gravity field detection by using gravity gradient observations. Firstly, for arbitrary satellite orbit inclination, we give the frequency distributions of all the components of gravity gradients (i.e. Txx,Tyy,Tzz,Txy,TxzandTyz, ). The results show that the maximum frequency of each component of the gravity gradients is the same, i.e. l/Ts (l is degree of the gravity field model, Ts is the orbital periods), and it is not influenced by the inclination of the satellite orbits. Secondly, the paper gives a theory proof to explain why only the low orders of the coefficients are influenced by polar gaps. Big polar gaps are experimented by a numerical test with inclination of 45°. Finally, considering that the measurement bandwidth can be expanded and accuracy of gradient observations can be improved by superconducting gravity gradiometer (SGG) compared to gradiometer used in Gravity field and steady-state Ocean Circulation Explorer (GOCE), the possibility of detecting time-variable gravity using gravity gradient observations is discussed. The results show that the SGG creates errors in MBW with magnitude of 0.014 mE, which is smaller than the magnitude of the time-variable gravity gradient signals (i.e., 0.02 mE) derived from Gravity Recovery and Climate Experiment (GRACE) gravity field models. This indicates the potential of SGG in time-variable gravity detection.

Broadband Optoelectronic Frequency Response Measurement Utilizing Frequency Conversion

A broadband optoelectronic (O/E) frequency response measurement method utilizing photonics-based frequency conversion is proposed and experimentally demonstrated. It is characterized by a sub-kilohertz frequency resolution and a doubled measurement bandwidth compared with the RF frequency sweeping range and the working bandwidth. A carrier-frequency-shifted optical double-sideband (ODSB) signal is produced by employing a dual-drive Mach-Zehnder modulator (DD-MZM) and stimulated Brillouin scattering (SBS). Then, a photodetector (PD) under test receives and converts the optical signal into a photocurrent. By detecting the frequency up- and down-conversion components generated by the two first-order sidebands and the optical carrier, the O/E frequency responses in the low- and high-frequency regions are achieved. After stitching the two measured responses together, an O/E frequency response with a frequency range that is twice the bandwidth of the input microwave signal is obtained. In an experiment, the O/E frequency response of a commercial high-speed PD is precisely characterized with a frequency resolution up to 5.55 MHz. A frequency bandwidth of 66.8 GHz (0.1–66.9 GHz) is achieved by using a 25-GHz DD-MZM. The measured O/E frequency response is coincident with that measured by a commercial instrument.

UltraLow Noise, High Bandwidth, Low Latency, No Overload 6-Axis Optical Force Sensor

In this article, we present a novel six-axis optical sensor that employs pairs of light-emitting diodes (LEDs) and bicell photodetectors, and corresponding slits that modulate the projected LED light onto the photodetectors in response to external forces. The sensor can be clamped on and off a structure and relies upon the compliance of the structure for force estimation; it has no flexible components, and therefore, it is robust to overload. The mechatronic design features low noise, wide dynamic range opto-electronics, and signal conditioning, coupled with colocated digital electronics based on a FPGA that samples all sensing channels synchronously, enabling very low noise displacement sensing with resolution of 1.62 nm, low measurement signal latency of 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s, high measurement bandwidth of 500 Hz, and high data transfer rates in excess of 11.5 kHz for transmission of six axis transducer data to a host computer. The transducer's resolution is better than 0.0001% of the full-scale. A sensor model has been derived and can be used to explore design tradeoffs. A calibration approach based on an external reference sensor and an approach to temperature compensation are presented and validated. A video is attached.