Measurement Of Frequency Shift Research Articles

Photonic Measurement for Doppler Frequency Shift and Angle of Arrival Based on a Dual-Polarization Dual-Drive Mach–Zehnder Modulator

A novel photonic-assisted system for realizing the simultaneous measurement of Doppler frequency shift (DFS) and angle of arrival (AOA) is proposed. It is a simplified structure that is based on a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM). The DFS direction can be accurately determined by comparing the phase relationship between the upper and lower low-frequency signal waveforms. An amplitude comparison function (ACF), which constructs a one-to-one mapping between the power ratio and the phase difference of echo microwave signals, can reduce the AOA measurement errors. The simulation results show that the simulated ACFs agree well with the theoretical ACFs, and the measurement errors of AOA are less than ±2.8° in a range of 0° to 78°. Moreover, the DFS can be realized by analyzing the spectrum of the low-frequency electrical signal with a measurement error of less than ±0.05 Hz. The system structure is compact and cost-effective, which provides an alternative solution for modern radar and electronic warfare receivers.

Simultaneous Measurement of Microwave Doppler Frequency Shift and Angle of Arrival Based on a Silicon Integrated Chip

A system for simultaneous measurement of micro-wave Doppler frequency shift (DFS) and angle of arrival (AOA) is proposed based on a silicon integrated chip. In the chip, two dual-drive Mach–Zehnder modulators (DDMZMs) with a microring resonator (MRR) inserted between them are integrated. When an external laser is coupled into the chip, it is first modulated by two echo signals via the first DDMZM and then goes through the MRR to introduce an optical phase shift to one of the first-order sidebands that falls into the resonance of the MRR. After being remodulated by the transmitted signal at the other DDMZM, the lightwave is coupled out from the chip and separated into two channels by an optical coupler. In each channel, a bandpass filter (BPF) is employed to select the upper and lower sidebands. By measuring and comparing the powers, frequencies, and phases of the beat signals in the two channels, the DFS (without direction ambiguity) and AOA can be acquired. Based on the proposed method, DFS within ±100 kHz at 10, 15, and 20 GHz is successfully estimated with a maximum error of ±0.028 Hz, and AOA measurement from 0° to 75° with errors less than ±1.53° is also realized.

Measurements of Majorana transition frequency shift in caesium atomic fountain clocks

The caesium atomic fountain clock is a primary frequency standard. During its operation, a Majorana transition frequency shift will occur once a magnetic field at some special locations along the atomic trajectory is singular. In this study, by developing a physical model, we analyzed the magnetic field requirements for atomic adiabatic transition and calculated the influence of the Majorana atomic transition on the atomic state via a quantum method. Based on the simulation results for the magnetic field in the fountain clock, we applied the Monte Carlo method to simulate the relationship between the Majorana transition frequency shift and the magnetic field at the entrance of the magnetic shielding, as well as the initial atomic population. Measurement of the Majorana transition frequency shift was realized by state-selecting asymmetrically populated atoms. The relationship between the Majorana transition frequency shift and the axial magnetic field at the entrance of the magnetic shielding was obtained. The measured results were essentially consistent with the calculated results. Thus, the magnetic field at the entrance of the magnetic shielding was configured, and the Majorana transition frequency shift of the fountain clock was calculated to be 4.57 × 10−18.

Probe temperature effect on the curling probe and its correction technique

This article introduces the effect of the probe temperature existing in a curling probe, which enables one to measure the electron density in plasma and the thickness of deposited film on the probe surface. We have recognized the effect appearing on the resonant frequency in previous reports, but we made measurement conditions where no temperature affected the frequency shift. The practical use of curling probes does not always allow one to have such an ideal condition, so it is necessary to have a good understanding of the probe temperature effect. Toward the understanding, we firstly measured the resonant frequency shift for five different operating powers with a curling probe having a heater and thermocouple attached to the probe surface. The frequency shift measurement showed consistent trends with plasma off and on. With some careful analyses, we found that the correction factor, which is necessary to compensate for the electron density measurement due to geometry reasons, etc for curling probe, had a regularity as a function of probe temperature; the inversed square of the correction factor was proportional to the degree of resonant frequency shift. Furthermore, the proportionality depended on the probe temperature with the regularity, so we finally were able to include the probe temperature effect on the correction factor, which realized the correction of the electron density even when the probe has a temperature variation. The electron density measurement with this correction technique worked well and followed the density measured with the Langmuir probe well. In particular, this research revealed that the correct technique is effective when probing temperature increases.

Surface charge dependent structure of ionic liquid/alkali halide interfaces investigated by atomic force microscopy

Ionic liquid (IL)/solid interfaces are relevant to a broad range of physicochemical phenomena and technological processes such as catalysis, corrosion, electrochemistry, and lubrication. Hence, understanding the effect of substrate surface nature on the interfacial properties has a significant impact on improving technological processes in which interfacial properties are dominant. In this work, we investigated interfacial structures between 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) IL and KBr crystal surfaces by frequency modulation atomic force microscopy utilizing a quartz tuning fork sensor. KBr(100) and (111) surfaces were used as the substrates, where the (100) surface is electrically neutral, and the (111) surface is highly charged. We investigated the influence of surface charge on their surface structures and interfacial solvation structures by atomic-scale topographic imaging and frequency shift versus distance curve measurement. The behavior of IL at these two interfaces was found to be significantly different due to these different surface properties.

Simplified Doppler Frequency Shift Measurement Enabled by Serrodyne Optical Frequency Translation

A simplified Doppler frequency shift (DFS) measurement approach based on Serrodyne optical frequency translation is reported. A sawtooth wave with high amplitude is sent to one phase modulation arm of a Mach–Zehnder modulator in conjunction with the transmitted signal to implement the Serrodyne optical frequency translation, as well as the optical phase modulation of the transmitted signal on the frequency-shifted optical carrier. The echo signal is applied to the other arm of the modulator. The lower first-order optical sidebands from the modulator are selected by an optical bandpass filter and detected in a photodetector. By measuring the frequency of the output low-frequency signal, the value and direction of the DFS can be determined. DFS from −100 to 100 kHz is measured for 6- to 17-GHz microwave signals with a measurement error of ±0.03 Hz and a measurement stability of ±0.015 Hz in 30 min when a 500-kHz sawtooth wave is used.

A Brillouin scattering-based fast temperature measurement method for ADSS of distribution IoT in electricity

In order to decrease time of temperature measurement for optical fiber in ADSS (all-dielectric self-supporting cable) of distribution IoT (Internet of Things) in electricity, the slope-assisted method is applied to its temperature demodulation. According to the introduction of the Brillouin scattering-based optical fiber temperature measurement method, the basic principle of Brillouin frequency shift measurement method based on the spectra fitting algorithm and the slope-assisted method is analyzed. Based on simulated Brillouin spectra with different signal-to-noise ratios (SNRs), the measurement time and accuracy of the spectra fitting algorithm and the slope-assisted method are compared. The results indicate that when if the SNR of Brillouin spectra is not less than 35 dB, the mean error of temperature measurement by the slope-assisted method is less than 0.5°C, which is slightly larger than the error of the spectra fitting algorithm, but the spectra measurement time is only 1/17 of that of the latter.

Overcoming acoustic crosstalk in the BOTDA sensor with a bidirectional frequency-modulated probe.

Conventional Brillouin optical time-domain analyzer (BOTDA) with a frequency-modulated probe (FMP) could avoid non-local effects, while still suffering from the acoustic crosstalk between different frequencies. The induced Brillouin frequency shift (BFS) measurement errors over the whole sensing fiber link reduce system certainty subsequently. A BOTDA scheme with a bidirectional frequency-modulated probe (BFMP) is proposed to overcome such an effect. It utilizes BFMP to generate the crosstalk of the same magnitude and opposite direction to compensate each other. Experimental results indicate that the pulse interval of the coded sequence could be reduced to ∼500 ns to improve the measurement efficiency and BFS estimation errors (∼2.2 MHz) over 117.46-km sensor link are eliminated simultaneously.

Improving the Brillouin frequency shift measurement resolution in the Brillouin optical time domain reflectometry (BOTDR) fiber sensor by artificial neural network (ANN)

We propose to use an artificial neural network (ANN) model to improve the Brillouin frequency shift (BFS) resolution of the sub-meter spatial resolution differential cross-spectrum Brillouin optical time domain reflectometry (DCS-BOTDR) fiber sensor. ANN technique was chosen due its nonlinear mapping characteristic that makes it suitable to effectively extract the BFS distribution along the fiber optic. Importantly, the ANN model offers more flexibility in estimating the BFS because one does not need to set the initial parameters like the conventional polynomial function based on Lorentzian curve fitting (LCF) model. In our ANN model, we used the BFS distribution data measured by the pulse duration TL = 14 ns at 56,000 times averaging as the ground truth in the training phase, because they provided the highest BFS resolution compared to that of obtained by other pulse duration cases, as reported previously. After training the data, we tested them with the BFS distribution results for TL = 2, 4 and 60 ns cases, which they showed poor BFS resolution when processed by the conventional model. For TL = 2 and 4 ns cases, the deployment of ANN has significantly improved the BFS resolution at least two times higher than that by the conventional polynomial fitting. Surprisingly, for TL = 60 ns case, despite the reduced number of averaging from 56,000 to 7000 times (i.e., eight times faster measurement), the BFS resolution has improved about seven times from 21.13 MHz to 2.88 MHz. This indicates the significant contribution of the ANN model in reducing the measurement time in the DCS-BOTDR

An Invar Alloy SLM Printed Diplexer With High Thermal Stability

This paper presents a selective laser melting (SLM) 3-D printed Ku-band diplexer using dual-mode resonators with high thermal stability. The diplexer is designed using dual-mode dimpled ellipsoid resonators which enables the diplexer mechanically self-supported in fabrication. Hence, the design has higher compatibility with the SLM printing process and the design can be extended to multiplexers with more channels. The excellent thermal stability is benefited from both the 4J36 invar alloy material with a lower coefficient of thermal expansion (C.T.E) as well as the tailored SLM printing process. Electrical and thermal performances of the diplexer are measured, showing that the fabricated diplexer is with average insertion losses of 0.69dB/0.42dB, return losses of >14dB, and centre frequency shifts of 5.62MHz/3.75MHz (<0.04%) in the two channels after copper plating. The measured frequency shift is less than 0.5 MHz over 100∘ temperature change, which is equivalent to a C.T.E of 0.5 ppm.

Towards a quantum interface between spin waves and paramagnetic spin baths

Spin waves have risen as promising candidate information carriers for the next generation of information technologies. Recent experimental demonstrations of their detection using electron spins in diamond pave the way towards studying the back-action of a controllable paramagnetic spin bath on the spin waves. Here, we present a quantum theory describing the interaction between spin waves and paramagnetic spins. As a case study we consider an ensemble of nitrogen-vacancy spins in diamond in the vicinity of an Yttrium-Iron-Garnet thin film. We show how the back-action of the ensemble results in strong and tuneable modifications of the spin-wave spectrum and propagation properties. These modifications include the full suppression of spin-wave propagation and, in a different parameter regime, the enhancement of their propagation length by $\sim 50\%$. Furthermore, we show how the spin wave thermal fluctuations induce a measurable frequency shift of the paramagnetic spins in the bath. This shift results in a thermal dispersion force that can be measured optically and/or mechanically with a diamond mechanical resonator. In addition, we use our theory to compute the spin wave-mediated interaction between the spins in the bath. We show that all the above effects are measurable by state-of-the-art experiments. Our results provide the theoretical foundation for describing hybrid quantum systems of spin waves and spin baths, and establish the potential of quantum spins as active control, sensing, and interfacing tools for spintronics.

Extracting Brillouin frequency shift accurately based on particle swarm optimization and a cross-correlation method.

A fitting algorithm based on particle swarm optimization (PSO) and the cross-correlation method (XCM) was proposed to accurately extract features of the Brillouin scattering spectrum. Both the simulation and experiment were conducted to verify the validity of the proposed algorithm. The results show that the algorithm achieves high demodulation accuracy and is suitable for Brillouin scattering spectra with different signal-to-noise ratios, full width at half-maximums, frequency sweep intervals, and spectral symmetries. Compared with the Lorenz curve fitting and XCM algorithm, the extraction error of the PSO-XCM can be optimized up to 99.98% and 99.93%, and the fitting degree can be improved by 98%. Moreover, based on the proposed algorithm, the minimum temperature measurement error can reach 0.06°C and the Brillouin frequency shift measurement error is 0.07 MHz in 10 km sensing fiber for the Brillouin optical time domain analysis (BOTDA) sensing system.

Contactless Monitoring of Breathing Pattern and Thoracoabdominal Asynchronies in Preterm Infants Using Depth Cameras: A Feasibility Study

Objective: Monitoring infants’ breathing activity is crucial in research and clinical applications but remains a challenge. This study aims to develop a contactless method to monitor breathing patterns and thoracoabdominal asynchronies in infants inside the incubator, using depth cameras. Methods: We proposed an algorithm to extract the 3D displacements of the ribcage and abdomen from the analysis of depth images. We evaluated the accuracy of the system in-vitro vs. a reference motion capture analyzer. We also conducted a feasibility study on 12 patients receiving non-invasive respiratory support to estimate the mean and the variability of the chest wall displacements in preterm infants and evaluate the suitability of the proposed system in the clinical setting. Results: In-vitro, the mean (95% CI) error in the measurement of amplitude, frequency and phase shift between compartmental displacements was −0.14 (−0.57, 0.28) mm, 0.02 (−0.99, 1.03) bpm, and −0.40 (−1.76, 0.95)°, respectively. In-vivo, the mean (95% CI) amplitude of the ribcage and abdomen displacements were 0.99 (0.34, 2.67) mm and 1.20 (0.40, 2.15) mm, respectively. Conclusions: The developed system proved accurate in-vitro and was suitable for the clinical environment. Clinical Impact: The proposed method has value for evaluating infants’ breathing patterns in research applications and, after further development, may represent a simple monitoring tool for infants’ respiratory activity inside the incubator.

Wave-Equation-Based Q Tomography With Local Peak Frequency Shift Measurements

Wave-Equation-Based Q Tomography With Local Peak Frequency Shift Measurements

Simple Doppler Frequency Shift Measurement Scheme Based on Microwave Photonics

Based on the theory of microwave photonics, we propose a new scheme to measure the Doppler frequency shift (DFS) in a radar system. This scheme is a single-channel system based on dual-parallel Mach–Zehnder modulator (DPMZM). And the frequencies of the transmitted signal and the reference signal are added together to form a combined signal. Then we add the combined signal and the echo signal to the two sub-modulators (sub-MZMs) of DPMZM, respectively. By measuring the beat signal output by the photoelectric modulator (PD), the DFS can be measured, whose error is maintained at −0.8Hz to 0.8Hz. The DFS’s direction is determined by comparing the frequencies of the obtained signal and the reference signal. The system has the advantages of wide operating frequency range, simple structure, low cost, and easy integration.

Erratum: Self-calibrating measurement of polarization-dependent frequency shifts from Rb- He3 collisions [Phys. Rev. A 49 , 2766 (1994)

Erratum: Self-calibrating measurement of polarization-dependent frequency shifts from Rb- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>He</mml:mi><mml:mprescripts /><mml:none /><mml:mn>3</mml:mn></mml:mmultiscripts></mml:math> collisions [Phys. Rev. A <b>49</b> , 2766 (1994)

A Moving Single-Station Doppler Ranging Solution by Means of Direction Finding Method

The Doppler shift is an angle dependent function. Based on the relationship between frequency shift and angle, direction-finding method can be used directly to obtain the ranging solution based on frequency shift measurement. The Doppler ranging solution obtained by this method has excellent calculation accuracy and can keep the same accuracy as the ranging solution based on frequency shift difference processing.

All-Optical Pulsed Signal Doppler Frequency Shift Measurement System

A simple and all-optical Doppler frequency shift (DFS) measurement system is presented. It is based on a dual-drive Mach Zehnder modulator (DDMZM) driven by a transmitted signal and an echo signal received by an antenna. A low-frequency sawtooth wave is applied to the DDMZM DC port to frequency shift the carrier and sidebands generated by the transmitted signal. Beating of a frequency-shifted transmitted signal sideband and an echo signal sideband at the photodetector produces a low-frequency electrical signal. The DFS, and consequently the speed and moving direction of a target, can be obtained from the frequency of this low-frequency electrical signal. The DDMZM used in the proposed DFS measurement system does not need to be operated at a specific point in the transfer function and hence it has no bias drift problem. The proposed DFS measurement technique can be used in both CW and pulsed radar systems. Experimental results demonstrate the proposed DFS measurement system has a wide operating frequency range of 10 GHz to 19.95 GHz, small DFS measurement error of less than ±0.6 Hz and long-term stable performance. Results also demonstrate, for the first time, DFS measurement of a pulsed signal using a microwave photonic technique.

Nonlinear reverberation spectroscopy with phase-sensitive superheterodyne reception

A technique is presented for determining elastic nonlinearity of materials from resonant frequency shifts as a function of signal amplitude during free vibrational decay after tone-burst excitation. The technique differs from previous nonlinear reverberation spectroscopy (NRS) techniques in that it employs phase-sensitive superheterodyne reception. Time-dependent amplitudes of in-phase and out-of-phase components of signals, relative to a reference sinusoid at the excitation frequency, are provided through analog hardware processing in the absence of digitization of the signal from the vibrational sensor. The time-dependent phase and amplitude of the signal are determined through software analysis of these in-phase and out-of-phase components, and the instantaneous frequency during free decay is then determined from the time derivative of the phase. With this approach, superheterodyne reception and low-pass filtering of the phase-detector outputs lead to a great reduction in noise and computation effort, relative to direct digitization and software processing of the sensor signal, while retaining information on frequency shifts on a relevant time scale during ringdown. As with other NRS techniques, rapid acquisition of data on amplitude dependence of the resonant frequency during ringdown leads to minimization of systematic errors from temperature drift. The technique is demonstrated with noncontacting electromagnetic-acoustic transduction on custom alloyed Al (0.2 at.% Zn) and commercial Al 7075 cylinders with axial-shear resonant frequencies between 658 kHz and 659 kHz. The precision of measurements of relative frequency shifts is found to be on the order of 0.1 parts per million (ppm), exceeding by two orders of magnitude the best reported precision of nonlinear resonant ultrasound spectroscopy (NRUS).

Nanoobject mass measurement using the node displacement of the second mode of the nanomechanical resonator

This work suggests a new approach to weighting the nanoscale objects placed at the tip of cantilever vibrating inside the camera of scanning electron microscope. In contrast to traditional approach to mass determination, we suggest tracing the shift of the node of the second vibration mode as an alternative to frequency shift measurement. We demonstrate the applicability of our approach to carbon nanowhisker cantilevers grown on tungsten needles by focused electron beam induced deposition. We compare experimentally the performance of the suggested approach with the traditional frequency shift-based method.