Frequency Ramp Research Articles

Effective collinear optical pumping for nuclear spin polarization

By numerically solving the density matrix equations, we show that the laser frequency ramping method by means of position-dependent Zeeman splitting can efficiently polarize nuclear spin of atoms/ions in an accelerator beamline. This minimizes a quantum phenomenon, coherent population trapping, which limits the optical pumping efficiency in the polarized beamline for radioactive nuclear spin polarization. We consider the Li8 atomic system interacting with two circularly polarized laser beams in the presence of time-dependent magnetic field. From numerical results, we find that optimum frequency ramping allows efficient optical pumping for a short interaction time, e.g., 2 μs.

77 GHz Radar Transmitter With PLL Based on a Sub-Harmonic Gilbert Frequency Doubler

This contribution highlights the usage of a high-quality voltage controlled oscillator (VCO) at 19.25 GHz fundamental frequency with a succeeding times four frequency multiplication scheme facilitating a 77 GHz output frequency. Signal tapping at the VCO's common emitter node allows obtaining the second-order harmonic tone that drives a single Gilbert frequency doubler. Beneficial to the PLL implementation is a reduced overall prescaler ratio allowing faster frequency ramps.

High-resolution frequency-modulated continuous-wave laser ranging for precision distance metrology applications

Frequency-modulated continuous wave (FMCW) laser ranging is one of the most interesting techniques for precision distance metrology. In order to ensure the theoretical measurement range and precision, a narrow linewidth external cavity tunable laser with large tuning range is chosen. In practical situations, the tuning nonlinearity of the laser reduces the measurement precision, hence an auxiliary interferometer is used to measure the laser tuning rate and linearize the frequency ramp. Then, fast Fourier transform algorithm is applied to the resampled signal of the main interferometer, and the full-width at half maximum of the frequency spectrum is narrowed. In the end, the experiments are carried out using the FMCW laser ranging system and demonstrate 50-<italic<μ</italic<m range resolution at 8.7 m.

A 160-GHz system in package for short-range mm-wave applications

This paper proposes a fully integrated 160-GHz transmitter and receiver in package for millimeter-wave applications. The monolithic integrated circuits were designed with a harmonic approach and were fabricated using a SiGe:C HBT production technology with an fTand fmaxof 170 and 250 GHz, respectively. The manufactured 2006 × 1865 µm2bare dies were integrated in 6 × 6 mm2embedded wafer level ball grid array packages, where they were interconnected with highly directional antennas built on the redistribution layer of the packages. With a total frequency multiplication factor of 36 and an active balun at the first stage, the transmitter allows the use of a 4.5-GHz input signal driven from a single-ended signal source [1] and distributed on a standard low-cost printed circuit board. The receiver comprises a Gilbert-cell-based subharmonic mixer with a simulated 1-dB input compression point of −4 dBm, and a minimum double-sideband noise figure of 16.5 dB. The functionality of the proposed system was successfully demonstrated in a quasi-monostatic FMCW radar measurement with a 1-ms up-chirp frequency sweep from 157 to 160 GHz and in a forward-scatter imaging experiment with an 8-GHz frequency ramp from 157 to 165 GHz.

Incidence and risk factors of renal hematoma: a prospective study of 1,300 SWL treatments

Shock wave lithotripsy (SWL) is the gold standard for the treatment of upper urinary tract stones. Despite being relatively non-invasive, SWL can cause renal hematoma (RHT). The aim of this study was to determine incidence and risk factors for RHT following SWL. 857 patients were included in a prospectively maintained database. The observation period spans from 2007 to 2012. 1,324 procedures were performed due to kidney stones. Treatment protocol included power ramping and shock wave frequency of 60-90 per minute as well as an ultrasound check within 3 days of SWL for all patients. Patients with RHT were analyzed, and treatment characteristics were compared with the complete population in a non-statistical manner due to the low event count. RHTs after SWL, sized between 2.6 × 0.6 cm and 17 × 15 cm, were verified in seven patients (0.53%). In four patients, the RHT was asymptomatic. Three patients developed pain after SWL treatment due to a RHT. In one patient surgical intervention was necessary due to a symptomatic RHT, the kidney was preserved. The risk of RHT following SWL treatment of kidney stones is about 0.5%. Clinically relevant or symptomatic RHTs occur in 0.23%, RHTs requiring surgical intervention are extremely rare. Older age and vascular comorbidities appear to be risk factors for the development of RHT. The technical characteristics of SWL treatment and intake of low-dose acetylsalicylic acid due to an imperative cardiologic indication do not appear to influence the risk. Prospective studies are warranted.

A DLL-Supported, Low Phase Noise Fractional-N PLL With a Wideband VCO and a Highly Linear Frequency Ramp Generator for FMCW Radars

This paper describes a frequency synthesizer for frequency-modulated continuous wave (FMCW) radars, operating in combination with a frequency multiplier, at 77 GHz. The fractional-N phase-locked loop (PLL)-based synthesizer is equipped with a wideband voltage-controlled oscillator, which is realized with CMOS transistors in a current-reuse technique, and a delay-locked loop (DLL). Utilized as a frequency multiplier for the reference signal, the DLL improves both the phase noise performance of the PLL and the linearity of the frequency sweep generated by the PLL. Two types of voltage-controlled delay lines used in the DLL are also introduced and compared in this paper. Both show a good performance in terms of phase noise and can be easily realized in a standard CMOS technology. The false-lock issue of the DLL is also discussed and a solution is proposed. Furthermore, a frequency multiplier is used to multiply the output frequency of the PLL by a multiplication factor of 18. This architecture enables an increase in the target resolution and an improvement in the accuracy of the measurements of FMCW radars.

P and M Class Phasor Measurement Unit Algorithms Using Adaptive Cascaded Filters

The new standard C37.118.1 lays down strict performance limits for phasor measurement units (PMUs) under steady-state and dynamic conditions. Reference algorithms are also presented for the performance (P) and measurement (M) class PMUs. In this paper, the performance of these algorithms is analyzed during some key signal scenarios, particularly those of offnominal frequency, frequency ramps, and harmonic contamination. While it is found that total vector error (TVE) accuracy is relatively easy to achieve, the reference algorithm is not able to achieve a useful rate of change of frequency (ROCOF) accuracy. Instead, this paper presents alternative algorithms for P and M class PMUs, which use adaptive filtering techniques in real time up to 10-kHz sample rates, allowing consistent accuracy to be maintained across a ±33% frequency range. ROCOF errors can be reduced by factors of > 40 for P class and > 100 for M class devices.

Auditory evoked responses to a frequency glide following a static pure tone

In this study, we look at the auditory evoked response to a frequency glide following a static pure tone. A frequency glide is a frequency ramp with specific frequency change range (Δf) and duration (Δt). Frequency change rate (Δf/ Δt) and direction (increasing or decreasing frequency) of a glide are important cues for speech perception. P1-N1-P2 acoustic change complex (ACC) responses to increasing or decreasing frequency glides were observed in the recordings of normal hearing subjects. Subjects were also asked to behaviorally discriminate similar stimuli with a fixed Δt at 50 ms or 200 ms and a varying Δt in a separate experiment. Similar findings were obtained with glides at both 500 and 1 kHz base frequency. In these preliminary data, we observed larger N1-P2 responses with the glides of fixed Δt 50 ms at both 500 Hz and 1000 Hz base frequency. However, larger N1-P2 responses for increasing glides than for decreasing glides were only observed with glides at 500 Hz base frequency. Larger N1-P2 respons...

Phase Noise Modeling for Integrated PLLs in FMCW Radar

The effect of frequency modulation (FM) on the phase noise spectrum of a charge pump phase-locked loop (PLL) for frequency-modulated continuous-wave (FMCW) radar is investigated. The static phase error is calculated as a function of frequency ramp slope and basic PLL design parameters. The phase noise spectrum under FM is deduced from the spectrum in the steady state. Design guidelines for integrated PLLs to be used in FMCW radar are derived from theoretical considerations and experimental results from the literature.

Optimized Parameter Estimation for the LPM Local Positioning System

The LPM local positioning system is based on a bi-static frequency-modulated continuous-wave radar where the frequency ramps are generated by two different units of circuitry: one of higher quality in the base station (BS) and one optimized for low power consumption in the transponder (TP). This difference in circuitry causes a small chirp rate difference (CRD) between the ramp incline of the BS and that of the TP, which has previously been considered negligible. We show that it is imperative to take account of this CRD in the intermediate frequency signal. We derived a method based on a nonlinear least squares (NLS) estimation principle to estimate its value. The NLS method can further be used for fault detection and to mitigate the effect of multipath signals, which we validate with both simulated and measured data.

Multiphysics modelling of the separation of suspended particles via frequency ramping of ultrasonic standing waves

A model was developed to determine the local changes of concentration of particles and the formations of bands induced by a standing acoustic wave field subjected to a sawtooth frequency ramping pattern. The mass transport equation was modified to incorporate the effect of acoustic forces on the concentration of particles. This was achieved by balancing the forces acting on particles. The frequency ramping was implemented as a parametric sweep for the time harmonic frequency response in time steps of 0.1s. The physics phenomena of piezoelectricity, acoustic fields and diffusion of particles were coupled and solved in COMSOL Multiphysics™ (COMSOL AB, Stockholm, Sweden) following a three step approach. The first step solves the governing partial differential equations describing the acoustic field by assuming that the pressure field achieves a pseudo steady state. In the second step, the acoustic radiation force is calculated from the pressure field. The final step allows calculating the locally changing concentration of particles as a function of time by solving the modified equation of particle transport. The diffusivity was calculated as function of concentration following the Garg and Ruthven [1] equation which describes the steep increase of diffusivity when the concentration approaches saturation. However, it was found that this steep increase creates numerical instabilities at high voltages (in the piezoelectricity equations) and high initial particle concentration. The model was simplified to a pseudo one-dimensional case due to computation power limitations. The predicted particle distribution calculated with the model is in good agreement with the experimental data as it follows accurately the movement of the bands in the centre of the chamber.

Muscle velocity recovery cycles: Effects of repetitive stimulation on two muscles

We sought to characterize the excitability properties of tibialis anterior (TA) and brachioradialis (BR) muscles at rest and during electrically induced muscle activation in normal subjects. Two centers recruited 10 subjects each. Multi-fiber velocity recovery cycles (VRCs) were recorded from TA (both centers) and BR (one center). VRCs were assessed at rest and during repetitive stimulation (intermittent 20 Hz for 6 min). Changes in latency and peak amplitude of the muscle action potential induced by a frequency ramp to 30 Hz were also characterized. Excitability properties recorded from TA were very similar between centers. Repetitive stimulation generated marked excitability changes, which were similar between TA and BR. Standardized tests of muscle VRCs and responses to repetitive stimulation can provide consistent measures of membrane function and may encourage their wider use in clinical neurophysiology to investigate the pathophysiology of neuromuscular disorders.

Battery Energy Storage for Enabling Integration of Distributed Solar Power Generation

As solar photovoltaic power generation becomes more commonplace, the inherent intermittency of the solar resource poses one of the great challenges to those who would design and implement the next generation smart grid. Specifically, grid-tied solar power generation is a distributed resource whose output can change extremely rapidly, resulting in many issues for the distribution system operator with a large quantity of installed photovoltaic devices. Battery energy storage systems are increasingly being used to help integrate solar power into the grid. These systems are capable of absorbing and delivering both real and reactive power with sub-second response times. With these capabilities, battery energy storage systems can mitigate such issues with solar power generation as ramp rate, frequency, and voltage issues. Beyond these applications focusing on system stability, energy storage control systems can also be integrated with energy markets to make the solar resource more economical. Providing a high-level introduction to this application area, this paper presents an overview of the challenges of integrating solar power to the electricity distribution system, a technical overview of battery energy storage systems, and illustrates a variety of modes of operation for battery energy storage systems in grid-tied solar applications. The real-time control modes discussed include ramp rate control, frequency droop response, power factor correction, solar time-shifting, and output leveling.

Polarization maintaining optical fiber multi-intruder sensor

In this paper, an optical fiber multi-intruder sensor based on polarization maintaining optical fiber (PMF), without any interferometric fiber loop, is introduced. To map the local coordinates of intruders on the beating spectrum of the output modes, radiation from a ramp frequency modulated laser is injected at the input of PMF optical fiber sensor. It is shown that the local coordinates and some characteristics of intruders can be obtained by the measurement of the frequencies and amplitudes of the output mode beating spectrum. Generally the number of beating frequencies is more than the number of intruders. Among the beating frequencies, a group with maximum signal to noise ratio is chosen. The short Fourier denoising method is employed to increase the sensor resolution. Because the output signal is the superposition of finite numbers of discrete frequencies this method is a powerful tool for denoising even for negative signal to noise ratio.

Transcutaneous neuromuscular electrical stimulation: influence of electrode positioning and stimulus amplitude settings on muscle response

The aim of the study was to investigate the influence of two different transcutaneous neuromuscular electrical stimulation procedures on evoked muscle torque and local tissue oxygenation. In the first one (MP mode), the cathode was facing the muscle main motor point and stimulus amplitude was set to the level eliciting the maximal myoelectrical activation according to the amplitude of the evoked electromyogram (EMG); in the second one (RC mode), the electrodes were positioned following common reference charts for electrode placement while stimulus amplitude was set according to subject tolerance. Tibialis Anterior (TA) and Vastus Lateralis (VL) muscles of 10 subjects (28.4±8.2years) were tested in specific dynamometers to measure the evoked isometric torque. The EMG and near-infrared spectroscopy probes were placed on muscle belly to detect the electrical activity and local metabolic modifications of the stimulated muscle, respectively. The stimulation protocol consisted of a gradually increasing frequency ramp from 2 to 50Hz in 7.5s. Compared to RC mode, in MP mode the contractile parameters (peak twitch, tetanic torque, area under the torque build-up) and the metabolic solicitation (oxygen consumption and hyperemia due to metabolites accumulation) resulted significantly higher for both TA and VL muscles. MP mode resulted also to be more comfortable for the subjects. Based on the assumption that proper mechanical and metabolic stimuli are necessary to induce muscle strengthening, our results witness the importance of an optimized, i.e., comfortable and effective, stimulation to promote the aforementioned muscle adaptive modifications.

Optical detection of brain function: simultaneous imaging of cerebral vascular response, tissue metabolism, and cellular activity in vivo

It is known that a remaining challenge for functional brain imaging is to distinguish the coupling and decoupling effects among neuronal activity, cerebral metabolism, and vascular hemodynamics, which highlights the need for new tools to enable simultaneous measures of these three properties in vivo. Here, we review current neuroimaging techniques and their prospects and potential limitations for tackling this challenge. We then report a novel dual-wavelength laser speckle imaging (DW-LSI) tool developed in our labs that enables simultaneous imaging of cerebral blood flow (CBF), cerebral blood volume, and tissue hemoglobin oxygenation, which allows us to monitor neurovascular and tissue metabolic activities at high spatiotemporal resolutions over a relatively large field of view. Moreover, we report digital frequency ramping Doppler optical coherence tomography (DFR-OCT) that allows for quantitative 3D imaging of the CBF network in vivo. In parallel, we review calcium imaging techniques to track neuronal activity, including intracellular calcium approach using Rhod2 fluorescence technique that we develop to detect neuronal activity in vivo. We report a new multimodality imaging platform that combines DW-LSI, DFR-OCT, and calcium fluorescence imaging for simultaneous detection of cortical hemodynamics, cerebral metabolism, and neuronal activities of the animal brain in vivo, as well as its integration with microprobes for imaging neuronal function in deep brain regions in vivo. Promising results of in vivo animal brain functional studies suggest the potential of this multimodality approach for future awake animal and behavioral studies.

A Dynamic Synchrophasor Estimation Algorithm for Online Application

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A new algorithm for synchrophasor estimation is proposed to improve estimation accuracy under dynamic conditions. The real component of a constantly rotating vector and a low-frequency band-limited vector, which is linearized by Taylor series, is employed to model supplied signals in power systems. And dynamic characteristics of power systems are described in form of Taylor series' derivatives, which are calculated through consecutive phasors. The accuracy of phasor estimation was dramatically improved by the reassignment of estimation of short-time Fourier transform (STFT) with knowledge of these derivatives. Simulation results allow us to make the conclusion that the proposed algorithm improves the accuracy of phasor estimations under dynamic conditions dramatically, such as frequency ramping, low frequency oscillation, etc., at the cost of the calculation burden is a minimal increase whilst still meeting the requirements of the application for power systems. </para>

Compressive Receiver Using a CRLH-Based Dispersive Delay Line for Analog Signal Processing

A compressive receiver (CR) is presented utilizing a composite right/left-handed (CRLH) dispersive delay line (DDL) for analog signal processing applications. The CRLH DDL offers advantages such as arbitrary frequency of operation and wide bandwidth, filling a gap with competing DDL technologies. The presented CR system utilizes an impulse-driven CRLH DDL and mixer inversion for chirp generation required for real-time signal processing. At high frequencies, this eliminates frequency ramp generators. The CR is employed as a frequency discriminator and a tunable delay line with dispersion compensation. The simulation and experimental results fully validate the presented systems as proof-of-concept for high-frequency applications such as real-time Fourier transformers and signal analyzers.

Dynamic responsiveness of lumbar paraspinal muscle spindles during vertebral movement in the cat.

Muscle spindles provide essential information for appropriate motor control. In appendicular muscles, much is known about their position and movement sensitivities, but little is known about the axial muscles of the low back. We investigated the dynamic responsiveness of lumbar paraspinal muscle spindle afferents from L(6) dorsal root filaments during constant velocity movement of the L(6) vertebra (the feline has seven lumbar vertebrae) in Nembutal-anesthetized cats. Actuations of 1 mm applied at the L(6) spinous process were delivered at 0.5, 1.0 and 2.0 mm/s. The slow velocity component was measured as the slope of the relationship between displacement during the constant velocity ramp and instantaneous discharge frequency. The quick velocity component was the slope's intercept at zero displacement. The peak component was determined as the highest discharge rates occurring near the end of the ramp compared with control. The slow velocity component over the three increasing velocities was 23.9 (9.9), 21.6 (9.6) and 20.5 (9.5) imp/(s mm) [mean (SD)], respectively. The quick velocity component was 28.4 (8.6), 31.4 (9.8) and 35.8 (10.6) imp/s, respectively. These measures of dynamic responsiveness were at least 5-10 times higher compared with values reported for appendicular muscle spindles. The peak component's velocity sensitivity was 2.9 (imp/s)/(mm/s) [0.2, 5.5, lower, upper 95% confidence interval] similar to that for cervical paraspinal muscles as well as appendicular muscles. Increased dynamic responsiveness of lumbar paraspinal muscle spindles may insure central driving to insure control of intervertebral motion during changes in spinal orientation. It may also contribute to large, rapid and potentially injurious increases in paraspinal muscle activity during sudden and unexpected muscle stretch.

A digital frequency ramping method for enhancing doppler flow imaging in Fourier-domain optical coherence tomography

A digital frequency ramping method (DFRM) is proposed to improve the signal-to-noise ratio (SNR) of Doppler flow imaging in Fourier-domain optical coherence tomography (FDOCT). To examine the efficacy of DFRM for enhancing flow detection, computer simulation and tissue phantom study were conducted for phase noise reduction and flow quantification. In addition, the utility of this technique was validated in our in vivo clinical bladder imaging with endoscopic FDOCT. The Doppler flow images reconstructed by DFRM were compared with the counterparts by traditional Doppler FDOCT. The results demonstrate that DFRM enables real-time Doppler FDOCT imaging at significantly enhanced sensitivity without hardware modification, thus rendering it uniquely suitable for endoscopic subsurface blood flow imaging and diagnosis.