Digital Lock-in Algorithm for Biomedical Spectroscopy and Imaging Instruments with Multiple Modulated Sources

During the past two decades there has been a dramatic rise in the use of functional near-infrared spectroscopy (fNIRS) as a neuroimaging technique in cognitive neuroscience research. Diffuse optical tomography (DOT) and optical topography (OT) can be employed as the optical imaging techniques for brain activity investigation. However, most current imagers with analogue detection are limited by sensitivity and dynamic range. Although photon-counting detection can significantly improve detection sensitivity, the intrinsic nature of sequential excitations reduces temporal resolution. To improve temporal resolution, sensitivity and dynamic range, we develop a multi-channel continuous-wave (CW) system for brain functional imaging based on a novel lock-in photon-counting technique. The system consists of 60 Light-emitting device (LED) sources at three wavelengths of 660nm, 780nm and 830nm, which are modulated by current-stabilized square-wave signals at different frequencies, and 12 photomultiplier tubes (PMT) based on lock-in photon-counting technique. This design combines the ultra-high sensitivity of the photon-counting technique with the parallelism of the digital lock-in technique. We can therefore acquire the diffused light intensity for all the source-detector pairs (SD-pairs) in parallel. The performance assessments of the system are conducted using phantom experiments, and demonstrate its excellent measurement linearity, negligible inter-channel crosstalk, strong noise robustness and high temporal resolution.

The fast data acquisition system (FAS) has been developed for the motional Stark effect (MSE) diagnostic in many machines. The FAS digitizes the signals coming directly out of the photomultiplier tube. The software solution of digital lock-in technique to derive the MSE signals from the data of FAS is presented in this article. The calculated frequency and phase of the photoelastic modulators (PEMs) with this digital lock-in technique can reach so high precision that the first, second, and fourth harmonic frequency signals of PEMs can be perfectly recovered.

Cell-based sensor expressing odorant receptor with fluorescent imaging has a potential for realization of high performance odor sensing system. In this study, we developed digital lock-in detection system for 2-dimensional data such as an image. Since the system has many digital lock-in amplifiers on field programmable gate array and process the image stream from a commercially available image sensor, it has a capability of robust measurement against ambient light. In order to test the system, the fluorescent image of the sensor array including two kinds of olfactory receptor was analyzed by using principal component analysis. The result suggests that the system can discriminate between different odors.

A probing technique using ultrasonic waves and a digital lock-in detection scheme is developed to monitor changes within an elastic body. The scheme integrates products of the signal and reference rather than low pass filtering them. Two applications are illustrated: detecting acoustic emissions and monitoring slow dynamic nonlinear elasticity. The probe is capable of resolving the earliest times (<10-3 s) of the slow dynamic recovery and does not suffer distortion from the pump wave.

The wingbeat frequency of insect migrant is regarded potentially valuable for species identification and has long drawn widespread attention in radar entomology. Principally, the radar echo signal can be used to extract wingbeat information, because both the signal amplitude and phase could be modulated by wing-beating. With respect to existing entomological radars, signal amplitude modulation has been used for wingbeat frequency measurement of large insects for many years, but the wingbeat frequency measurement of small insects remains a challenge. In our research, W-band and S-band coherent radars are used to measure the insect wingbeat frequency. The results show that the wingbeat-induced amplitude modulation of W-band radar is more intense than that of the S-band radar and the W-band radar could measure the wingbeat frequency of smaller insects. In addition, it is validated for the first time that the signal phase could also be used to measure the insect wingbeat frequency based on micro-Doppler effect. However, whether the wingbeat frequency measurement is based on the amplitude or phase modulation, it is found that the W-band coherent radar has better performance on both the measurement precision and the measurable minimum size of the insect.

This article introduces the design and implementation of a hierarchical multi digital signal processor system aimed to perform parallel multichannel measurements and data processing of the type widely used in hard-field tomography. Details are presented of a complete tomography system with modular and expandable architecture, capable of accommodating a variety of data processing modalities, configured by software. The configuration of the acquisition and processing circuits and the management of the data flow allow a data frame rate of up to 250 kHz. Results of a case study, guided path tomography for temperature mapping, are shown as a direct demonstration of the system's capabilities. Digital lock-in detection is employed for data processing to extract the information from ac measurements of the temperature-induced resistance changes in an array of 32 noninteracting transducers, which is further exported for visualization.

A novel time-of-flight estimation method of acoustic signals for temperature and velocity measurement of gas medium

Periodic tidal ocean currents induce electric currents and, therefore, magnetic field signals that are observable using spaceborne and ground-based observation techniques. In theory, the signals can be used to monitor oceanic temperature and salinity variations. Tidal magnetic field amplitudes and phases have been extracted from magnetometer measurements in the past. However, due to uncertainties caused by a plentitude of influencing factors, the shape and temporal variation of these signals are only known to a limited extent. This study uses past extraction methods to characterize seasonal variations and long-term trends in the ten year magnetometer time series of three coastal island observatories. First, we assess data processing procedures used to prepare ground-based magnetometer observations for tidal ocean dynamo signal extraction to demonstrate that existing approaches, i.e., subtraction of core field models or first-order differencing, are unable to reliably remove low-frequency contributions. We hence propose low-frequency filtering using smoothing splines and demonstrate the advantages over the existing approaches. Second, we determine signal and side peak magnitudes of the M2 tide induced magnetic field signal by spectral analysis of the processed data. We find evidence for seasonal magnetic field signal variations of up to 25% from the annual mean. Third, to characterize the long-term behavior of tidal ocean dynamo signal amplitudes and phases, we apply different signal extraction techniques to identify tidal ocean-dynamo signal amplitudes and phases in sub-series of the ten-year time series with incrementally increasing lengths. The analyses support three main findings: (1) trends cause signal amplitude changes of up to approx 1~nT and phase changes are in the order of {mathcal {O}}(10^{circ }) within the observation period; (2) at least four years of data are needed to obtain reliable amplitude and phase values with the extraction methods used and (3) signal phases are a less dependent on the chosen extraction method than signal amplitudes.Graphical

Automatic identification of the communication signal modulation mode is a hot topic of research in the signal processing field in recent years. It is an important part of electronic countermeasures, and also a rapidly developed field of signal analysis. Communication signal modulation recognition is widely used in signal confirmation, interference identification, radio listening, signal monitoring, as well as software-defined radio, satellite communications and other fields. This paper proposed a digital modulation signal automatic recognition algorithm for satellite communication applications,. The algorithm uses the higher order cumulants of modulating signal, combined with constellation map features, to classify the signal. It has invariance in signal amplitude and phase deviation, and inhibits the additive Gaussian noise at the same time. Compared with other identification algorithms, it has the characteristics of stability and wide application. Computer simulations show that, under the given data length and moderate SNR conditions, a higher recognition rate (&gt; 95%) can be obtained.

The analyzed amplitude and phase variations in electromagnetic VLF and LF signals at 20–45 kHz, received in Moscow, Graz (Austria), and Sheffield (UK) during the total solar eclipse of March 20, 2015, are considered. The 22 analyzed paths have lengths of 200—6100 km, are differently oriented, and cross 40–100% occultation regions. Fifteen paths crossed the region where the occultation varied from 40 to 90%. Solar eclipse effects were found only on one of these paths in the signal phase (–50°). Four long paths crossed the 90–100% occultation region, and signal amplitude and phase anomalies were detected for all four paths. Negative phase anomalies varied from–75° to–90°, and the amplitude anomalies were both positive and negative and were not larger than 5 dB. It was shown that the effective height of the ionosphere varied from 6.5 to 11 km during the eclipse.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Sergey S. Kurennoy; Electromagnetic modeling of beam position and phase monitors for SNS linac. AIP Conf. Proc. 27 November 2000; 546 (1): 283–291. https://doi.org/10.1063/1.1342597 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

This chapter considers the nonlinear distortions of harmonic signal and Amplitude Modulated (AM) signal on the passage through single-ended and push-pull nonlinear power amplifiers with memory and without it. The amplifier characteristic is preset by the cubic polynomial. We consider two operating modes of amplifier for harmonic signal: cutoff mode and non-cutoff mode. Demodulation of AM signal is performed using a coherent quadrature amplitude detector. The distortion estimate based on Total Harmonic Distortion (THD). Dependence of THD versus cutoff angle for harmonic signal and THD versus amplitude sensitivity m for AM signal are calculated.

A novel linearisation technique for reduction in the first and second kind of the third-order intermodulation products was applied in this paper. The second harmonics and second-order intermodulation products are led from the output to the input of a power amplifier through a feedback loop. The power amplifier including the feedback loop components (bandpass filter, phase shifter and attenuator) was designed as a hybrid microwave integrated circuit by using program ADS (Advanced Design System). The phase and amplitude of the loop signals are the adjustable parameters. Therefore, a voltage that controls the phase shift of the phase shifter and the control current of a PIN diode in the attenuator circuit were optimised to obtain a reduction in the third-order intermodulation distortion. For three fundamental signals at the power amplifier input, the lowest improvement of 13 dB for the fist and 18 dB for the second kind of the third-order intermodulation product levels was achieved.

Real-time image processing is one of the fundamental elements in achieving IR 4.0. The rapid development of digital image processing techniques has enabled various applications in fields such as healthcare, transportation, and manufacturing. People are seeking higher-performance image processing as traditional image processing is no longer fulfilling the demands. FPGA-based digital image processing has become one of the choices for the public due to its parallel pipelining, which enables shorter processing time and better performance. Several digital image processing algorithms have been developed in this project, which are gray level transformation, brightness manipulation, contrast adjustment, thresholding, and inversion. They are the most popular algorithms used in digital image processing. Microsoft Paint is used to convert the format of the color input image to bitmap format, followed by MATLAB to convert it into a hexadecimal file to be read and written in FPGA. Platforms such as ModelSim Altera and Intel Quartus II are used to write Verilog HDL for digital image processing algorithms. As a result, five hexadecimal files are obtained from the simulation. The output hexadecimal files are further processed in MATLAB to generate respective images.

A photonic scheme generating ternary modulated signals, which include amplitude, phase, and frequency modulated signals, has been proposed and demonstrated. This scheme is based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), where the X-DPMZM is used to generate an optical frequency comb (OFC), and the Y-DPMZM is utilized to accomplish ternary modulation. The key feature of this scheme is that ternary modulated signals with eight wavebands can be obtained by using only the DP-DPMZM in situations of different input signals. In the simulation, a 2.5 Gbit/s amplitude shift keying (ASK), phase shift keying signal (PSK), or an 8 GHz bandwidth linearly frequency modulated (LFM) signal are obtained. The generated signals have eight wavebands with a large frequency range from 10 GHz to 80 GHz. Moreover, the recovery and pulse compression performances of the generated signals are evaluated.