Phase Stability under Thermal Drifts in Photodiode-Conditioning Transimpedance Amplifiers for Distance Metrology

Transimpedance amplifiers (TIA) are widely used for front-end signal conditioning in many optical distance measuring applications in which high accuracy is often required. Small effects due to the real characteristics of the components and the parasitic elements in the circuit board may cause the error to rise to unacceptable levels. In this work we study these effects on the TIA delay time error and deduce analytic expressions, taking into account the trade-off between the uncertainties caused by the delay time instability and by the signal-to-noise ratio. A specific continuous-wave phase-shift case study is shown to illustrate the analysis, and further compared with real measurements. General strategies and conclusions, useful for designers of this kind of system, are extracted too. The study and results show that the delay time thermal stability is a key determinant factor in the measured distance accuracy and, without an adequate design, moderate temperature variations of the TIA can cause extremely high measurement errors.

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High-speed high-resolution laser diode-based photoacoustic microscopy for in vivo microvasculature imaging

Visual Computing for Industry Biomedicine and Art ◽

10.1186/s42492-020-00067-5 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Xiufeng Li ◽

Victor T C Tsang ◽

Lei Kang ◽

Yan Zhang ◽

Terence T W Wong

Keyword(s):

High Resolution ◽

High Speed ◽

High Performance ◽

Continuous Wave ◽

Signal To Noise Ratio ◽

Cost Effective ◽

High Signal ◽

Photoacoustic Microscopy ◽

Mouse Ear

AbstractLaser diodes (LDs) have been considered as cost-effective and compact excitation sources to overcome the requirement of costly and bulky pulsed laser sources that are commonly used in photoacoustic microscopy (PAM). However, the spatial resolution and/or imaging speed of previously reported LD-based PAM systems have not been optimized simultaneously. In this paper, we developed a high-speed and high-resolution LD-based PAM system using a continuous wave LD, operating at a pulsed mode, with a repetition rate of 30 kHz, as an excitation source. A hybrid scanning mechanism that synchronizes a one-dimensional galvanometer mirror and a two-dimensional motorized stage is applied to achieve a fast imaging capability without signal averaging due to the high signal-to-noise ratio. By optimizing the optical system, a high lateral resolution of 4.8 μm has been achieved. In vivo microvasculature imaging of a mouse ear has been demonstrated to show the high performance of our LD-based PAM system.

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Signal-to-noise ratio of heterodyne beats between a comb and a continuous wave laser above the limit of a single mode

CLEO: 2013 ◽

10.1364/cleo_si.2013.ctu2i.6 ◽

2013 ◽

Author(s):

Jean-Daniel Deschênes ◽

Jérôme Genest

Keyword(s):

Continuous Wave ◽

Signal To Noise Ratio ◽

Single Mode ◽

Continuous Wave Laser ◽

Signal To Noise ◽

Wave Laser ◽

Noise Ratio

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An autofocusing method for imaging the targets for TWI radar systems with correction of thickness and dielectric constant of wall

International Journal of Microwave and Wireless Technologies ◽

10.1017/s1759078718001356 ◽

2018 ◽

Vol 11 (1) ◽

pp. 15-21 ◽

Cited By ~ 1

Author(s):

Sandeep Kaushal ◽

Bambam Kumar ◽

Dharmendra Singh

Keyword(s):

Genetic Algorithm ◽

Dielectric Constant ◽

Continuous Wave ◽

Signal To Noise Ratio ◽

Imaging Systems ◽

Signal To Noise ◽

Radar Systems ◽

Stepped Frequency ◽

Correct Image ◽

Wall Imaging

AbstractIn through the wall imaging systems, wall parameters like its thickness and dielectric constant play an important role in the true and correct image formation of an object behind the wall made of various materials like brick cement, wood, plastic, etc. Incorrect estimation of these parameters leads to dislocation of the object and smearing or blurriness of the image too. A new autofocusing technique for a stepped frequency continuous wave -based radar at the frequency of 1–3 Ghz has been developed that corrects the wall's parameters like its thickness and dielectric constant and provides a better focused image of the target. For this purpose, a peak signal to noise ratio -based autofocusing technique has been developed by using curve fitting and the genetic algorithm. It is observed that the proposed technique has capability to focus the image up to good extent.

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Repetition frequency locking of a terahertz quantum cascade laser emitting at 4.2 THz

Terahertz Science and Technology ◽

10.1051/tst/2020131032 ◽

2020 ◽

Vol 13 (1) ◽

pp. 32-40

Author(s):

Wen Guan ◽

Ziping Li ◽

Kang Zhou ◽

Wenjian Wan ◽

Xiaoyu Liao ◽

...

Keyword(s):

Quantum Cascade Laser ◽

Continuous Wave ◽

Frequency Comb ◽

Signal To Noise Ratio ◽

Phase Lock Loop ◽

Wave Mode ◽

Repetition Frequency ◽

Frequency Locking ◽

Frequency Combs ◽

Quantum Cascade

The electrically-pumped terahertz quantum cascade laser (QCL) is characterized by high power emission, compact, broad frequency coverage, and so on, which shows abilities for frequency comb operations. Although free-running QCLs can work as frequency combs by designing the laser structure with small group velocity dispersions and/or inserting mirrors to compensate laser intrinsic dispersions, the ideal comb operation can only be obtained by firmly locking the repetition frequency and carrier frequency of a laser. In this work, we have reported a repetition frequency locking of a terahertz QCL emitting around 4.2 THz. When the 6-mm-long laser is operated in continuous wave mode without any locking techniques, the repetition frequency is measured to be ~6.15 GHz with a linewidth of hundred kilohertz. Once a phase lock loop (PLL) is applied to dynamically control the drive current of the QCL, we have demonstrated a successful repetition frequency locking of the laser with a signal to noise ratio of 80 dB. This technique can be employed for the frequency comb and dual-comb operations of terahertz QCLs for high-resolution applications.

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Error Considerations for Turbine-Generator Torsional Vibration Monitoring

Volume 5: Controls, Diagnostics, and Instrumentation; Cycle Innovations; Cycle Innovations: Energy Storage ◽

10.1115/gt2020-15454 ◽

2020 ◽

Author(s):

Jindrich Liska ◽

Jan Jakl ◽

Sven Kunkel

Keyword(s):

Power Systems ◽

Torsional Vibration ◽

Gas Turbines ◽

Measurement Errors ◽

Power Plants ◽

Signal To Noise Ratio ◽

Vibration Monitoring ◽

Turbine Generator ◽

Turbine Generators ◽

Incremental Encoder

Abstract Turbine-generator torsional vibration is linked to electrical events in the power grid by the generator air-gap torque. Modern power systems are subject to gradual transformation by increasing flexibility demands and incorporation of renewable resources. As a result, electrical transient events are getting more frequent and thus torsional vibration is getting more and more attention. Especially in the case of large steam and gas turbines torsional vibration can cause material fatigue and present a hazard for safe machine operation. This paper freely builds on previous work, where a method for torsional vibration evaluation using an incremental encoder measurement was presented, in that it supplements error considerations to this methodology. Measurement errors such as precision of the rotor encoder manufacturing, choice of the proper sensor, its signal to noise ratio and the error of instantaneous velocity computation algorithm are analyzed. The knowledge of these errors is essential for torsional vibration as there is an indirect and relatively complicated path from the measurement to the final torsional vibration results compared to other kinds of vibration. The characteristics of particular errors of the processing chain are validated both on experimental data from a test rig as well as field data measured on turbine-generators in power plants.

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A Grey Model and Mixture Gaussian Residual Analysis-Based Position Estimator in an Indoor Environment

Sensors ◽

10.3390/s20143941 ◽

2020 ◽

Vol 20 (14) ◽

pp. 3941

Author(s):

Yan Wang ◽

Wenjia Ren ◽

Long Cheng ◽

Jijun Zou

Keyword(s):

Kalman Filter ◽

Measurement Errors ◽

Unscented Kalman Filter ◽

Grey Model ◽

Interacting Multiple Model ◽

Multiple Model ◽

Localization Accuracy ◽

Gaussian Fitting ◽

Degree Of Membership ◽

Measured Distance

As the progress of electronics and information processing technology continues, indoor localization has become a research hotspot in wireless sensor networks (WSN). The adverse non-line of sight (NLOS) propagation usually causes large measurement errors in complex indoor environments. It could decrease the localization accuracy seriously. A traditional grey model considers the motion characteristics but does not take the NLOS propagation into account. A robust interacting multiple model (R-IMM) could effectively mitigate NLOS errors but the clipping point is hard to choose. In order to easily cope with NLOS errors, we present a novel filter framework: mixture Gaussian fitting-based grey Kalman filter structure (MGF-GKFS). Firstly, grey Kalman filter (GKF) is proposed to pre-process the measured distance, which can mitigate the process noise and alleviate NLOS errors. Secondly, we calculate the residual which is the difference between the filtered distance of GKF and the measured distance. Thirdly, a soft decision method based on mixture Gaussian fitting (MGF) is proposed to identify the propagation condition through residual value and give the degree of membership. Fourthly, weak NLOS noise is further processed by unscented Kalman filter (UKF). The filtered results of GKF and UKF are weighted using the degree of membership. Finally, a maximum likelihood (ML) algorithm is applied to get the coordinate of the target. MGF-GKFS is not supported by any of the priori knowledge. Full-scale simulations and an experiment are conducted to compare the localization accuracy and robustness with the state-of-the-art algorithms, including robust interacting multiple model (R-IMM), unscented Kalman filter (UKF) and interacting multiple model (IMM). The results show that MGF-GKFS could achieve significant improvement compared to R-IMM, UKF and IMM algorithms.

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Coded continuous wave meteor radar

Atmospheric Measurement Techniques ◽

10.5194/amt-9-829-2016 ◽

2016 ◽

Vol 9 (2) ◽

pp. 829-839 ◽

Cited By ~ 9

Author(s):

Juha Vierinen ◽

Jorge L. Chau ◽

Nico Pfeffer ◽

Matthias Clahsen ◽

Gunter Stober

Keyword(s):

Frequency Band ◽

Peak Power ◽

Large Scale ◽

Pulse Compression ◽

Continuous Wave ◽

Signal To Noise Ratio ◽

Radar Data ◽

Meteor Radar ◽

To Receive ◽

Computation Speed

Abstract. The concept of a coded continuous wave specular meteor radar (SMR) is described. The radar uses a continuously transmitted pseudorandom phase-modulated waveform, which has several advantages compared to conventional pulsed SMRs. The coding avoids range and Doppler aliasing, which are in some cases problematic with pulsed radars. Continuous transmissions maximize pulse compression gain, allowing operation at lower peak power than a pulsed system. With continuous coding, the temporal and spectral resolution are not dependent on the transmit waveform and they can be fairly flexibly changed after performing a measurement. The low signal-to-noise ratio before pulse compression, combined with independent pseudorandom transmit waveforms, allows multiple geographically separated transmitters to be used in the same frequency band simultaneously without significantly interfering with each other. Because the same frequency band can be used by multiple transmitters, the same interferometric receiver antennas can be used to receive multiple transmitters at the same time. The principles of the signal processing are discussed, in addition to discussion of several practical ways to increase computation speed, and how to optimally detect meteor echoes. Measurements from a campaign performed with a coded continuous wave SMR are shown and compared with two standard pulsed SMR measurements. The type of meteor radar described in this paper would be suited for use in a large-scale multi-static network of meteor radar transmitters and receivers. Such a system would be useful for increasing the number of meteor detections to obtain improved meteor radar data products.

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An Integrated Front-end Circuit Board for Air-Coupled CMUT Burst-Echo Imaging

Sensors ◽

10.3390/s20216128 ◽

2020 ◽

Vol 20 (21) ◽

pp. 6128

Author(s):

Lei Ye ◽

Jian Li ◽

Hui Zhang ◽

Dongmei Liang ◽

Zhuochen Wang

Keyword(s):

Imaging System ◽

Signal To Noise Ratio ◽

Three Dimensional ◽

Ultrasonic Transducers ◽

Circuit Board ◽

Capacitive Micromachined Ultrasonic Transducers ◽

Front End ◽

Field Programmable ◽

Good Potential ◽

Dc Bias

To conduct burst-echo imaging with air-coupled capacitive micromachined ultrasonic transducers (CMUTs) using the same elements in transmission and reception, this work proposes a dedicated and integrated front-end circuit board design to build an imaging system. To the best of the authors’ knowledge, this is the first air-coupled CMUT burst-echo imaging using the same elements in transmission and reception. The reported front-end circuit board, controlled by field programmable gate array (FPGA), consisted of four parts: an on-board pulser, a bias-tee, a T/R switch and an amplifier. Working with our 217 kHz 16-element air-coupled CMUT array under 100 V DC bias, the front-end circuit board and imaging system could achieve 22.94 dB signal-to-noise ratio (SNR) in burst-echo imaging in air, which could represent the surface morphology and the three-dimensional form factor of the target. In addition, the burst-echo imaging range of our air-coupled CMUT imaging system, which could work between 52 and 273 mm, was discussed. This work suggests good potential for ultrasound imaging and gesture recognition applications.

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