Measurements In Noisy Environments Research Articles

Correlation Technologies for Emerging Wireless Applications

In this article, we introduce correlation technologies both at RF/mmWave and baseband frequencies. At RF and mmWave frequencies, power-spectra and energy-spectra metrics are introduced for measuring the power-density of mobile devices and systems. New ASIC-embedded smart connectors are developed for bringing correlation-based signal processing close to antenna modules. At baseband frequencies, DSP-based convolutional accelerators are proposed for fast and accurate measurement of EVM (error vector magnitude) using correlation technologies. Porting of the DSP-based convolutional accelerators into advanced fully depleted silicon-on-insulator (FDSOI)-based ASIC platforms for co-integration with adaptive RF/mmWave front-end modules will enable real-time extraction of auto-correlation and cross-correlation functions of stochastic signals. Perspectives for optically synchronized interferometric-correlation technologies are drawn for accurate measurements in noisy environments of stochastic EM fields using power-spectra and energy-spectra metrics. Adoption of correlation technologies will foster new paradigms relative to interactions of humans with smart devices and systems in randomly fluctuating environments. The resulting new paradigms will open new possibilities in communication theory for properly combining and reconciling information signal theory (Shannon information-based entropy) and physical information theory (statistical-physics-based entropy) into a unified framework.

Steady‐State Surface NMR for Mapping of Groundwater

AbstractGroundwater is a critical freshwater source for billions of people (Klee, 2013), but resources are increasingly stressed by climate change, pollution, and overexploitation (Frappart & Ramillien, 2018, https://doi.org/10.3390/rs10060829). Locating groundwater sources and monitoring their sustainable use is a difficult task. One method that shows great promise is surface nuclear magnetic resonance (NMR), as it is the only technique capable of non‐invasive direct measurements of subsurface water content and pore‐space properties. Unfortunately, surface NMR often suffers from low‐amplitude signals that limit mapping speeds and may prohibit measurements in noisy environments. We demonstrate a steady‐state scheme for surface NMR, enabled by recent breakthroughs in transmitter capabilities and numerical modeling that delivers orders of magnitude signal enhancements. The new technique is a highly efficient measurement that is both narrowband and utilizes the full measurement interval in contrast to traditional approaches. Our results demonstrate that high‐fidelity groundwater measurements are now possible in hitherto inaccessible areas.

Automatic partial discharge recognition using the cross wavelet transform in high voltage cable joint measuring systems using two opposite polarity sensors

This paper presents a new wavelet analysis approach in partial discharges cable joint measurements in noisy environments. The proposed technique uses the Cross Wavelet Transform (XWT) to separate PD signals from noise and external disturbances in partial discharges measurements in cable joints using two opposite polarity sensors. The partial discharge measurements were performed during impulse and superimposed voltages, leading to a huge amount of noise and pulse shaped external disturbances. The XWT foundations, the experimental setup and the XWT methodology proposed are presented together with the results of the recognition of PD originated in the cable joint. In the experiments, 51,898 signals were acquired, in which 733 were PD signals from the joint and 51,165 corresponded to noise or external disturbances. The XWT performance was studied, finding that 97% of the PD signals were correctly separated by the technique proposed. The results demonstrate the effectivity of the XWT in separating PD signals from noise and external disturbances in this particular measuring system configuration.

Damage identification for large span structure based on multiscale inputs to artificial neural networks.

In structural health monitoring system, little research on the damage identification from different types of sensors applied to large span structure has been done in the field. In fact, it is significant to estimate the whole structural safety if the multitype sensors or multiscale measurements are used in application of structural health monitoring and the damage identification for large span structure. A methodology to combine the local and global measurements in noisy environments based on artificial neural network is proposed in this paper. For a real large span structure, the capacity of the methodology is validated, including the decision on damage placement, the discussions on the number of the sensors, and the optimal parameters for artificial neural networks. Furthermore, the noisy environments in different levels are simulated to demonstrate the robustness and effectiveness of the proposed approach.

First-order high- Tc SQUID gradiometer

SQUID gradiometers are attractive for magnetic field measurements in noisy environments. A first-order planar gradiometer has been designed and fabricated. The layout of the planar gradiometer used to have two symmetric pickup coils; however, our design adopted one compensation loop with the same size as the SQUID loop at the symmetric position to reduce the imbalance caused by the SQUID. The gradient field resolution is up to 2.2 pT cm −1 Hz −1/2 (white noise) and 30 pT cm −1 Hz −1/2 at 1 Hz.

Thin-Film Planar Gradiometer with Long Baseline

Gradiometers are attractive for magnetic field measurements in noisy environments. Thin-film planar gradiometers are in particular attractive for measurements of the off-diagonal components of the magnetic field gradient tensor, and they can be fabricated with high intrinsic balance owing to the precision photolithographic techniques used to fabricate these devices. We have developed a low-Tc first-order planar gradiometer with a long baseline of 4 cm. The pickup loops are series configured and connected to the input circuit of a dual washer gradiometric dc SQUID. The white rms flux noise measured in a shielded environment is 1.6 µΦ0/Hz½. The magnetic field sensitivity referred to one pickup loop is 2 nT/Φ0, resulting in an rms magnetic field noise referred to one pickup loop of 3.2 fT/Hz½ and an rms gradient noise of 0.8 fT/cm-Hz½. Based on the lithographic methods used to fabricate the gradiometers, the expected balance level is 1 part in 24, 000 or 0.004%. The gradiometer is operable without shielding in typical laboratory environments without losing lock, with an rms white noise at 10 kHz of 3.5 µΦ0/Hz½.

On-Chip Pseudorandom MEMS Testing

This paper presents a Built-In-Self-Test (BIST) implementation of pseudo-random testing for MEMS. The technique is based on Impulse Response (IR) evaluation using pseudo-random Maximum--Length Sequences (MLS). The MLS approach is capable of providing vastly superior dynamic range in comparison to the straightforward technique using an impulse excitation and is thus an optimal solution for measurements in noisy environments and for low-power test signals. The use of a pseudo-random sequence makes the practical on-chip implementation very efficient in terms of the extra hardware required for on-chip testing. We will demonstrate the use of this technique for an on-chip fast and accurate broadband determination of MEMS behaviour, in particular for the characterisation of cantilever MEMS structures, determining their mechanical and thermal behaviour using just electrical tests.

Improved common-path fast-scanning heterodyne interferometer system as potential dense-plasma diagnostics

An improved common-path fast-scanning heterodyne interferometer system has been developed. The mechanical vibration is one of the most critical error sources in typical interferometry system. These errors can be mostly eliminated in a common-path interferometry using a full common-mode rejection scheme. Taking advantage of it, the common-path interferometry is suitable for the measurements in noisy environments and can be applied even to the scanning interferometry. A prototype common-path interferometer system with He–Ne laser has been constructed with the capability of fast scanning by adding a rotating polygon mirror. A test of this system has been completed successfully by measuring the thickness profile of the scratched glass. In this study, the interferometer system is proposed and discussed as a potential density profile diagnostics for dense plasmas. By using a CO2 laser instead of a He–Ne laser, it may also be applied to get the time evolution of steep density profiles of plasma transport barriers in tokamak plasmas.

On-Chip Testing of Linear Time Invariant Systems Using Maximum-Length Sequences

With the rapid development of system-on-chip (SoC) applications, containing digital and analogue parts, the need for fast and reliable on-chip testing methods has become obvious. We present a method for a fast and accurate broadband determination of the behaviour of analogue and mixed-signal circuits. This technique is based on impulse response (IR) evaluation using pseudo-random Maximum-Length Sequences (MLS). This approach provides a large dynamic range and is thus an optimal solution for measurements in noisy environments and for low-power test signals. We will show the algorithms of the MLS generation and of the impulse response calculation which can be easily implemented on-chip.

Teleseismic shear wave splitting measurements in noisyenvironments

SUMMARY High noise levels hamper teleseismic shear wave splitting measurements, which bandpass filtering does not always help. To investigate how robust splitting measurements are to noise, we analysed a set of synthetic records with known splitting parameters and added fixed levels of noise. In the presence of weak anisotropy, single-waveform splitting measurements are unreliable when operating with noisy data sets. A practical rule in terms of S/N ratio and splitting delay time parameters is that splitting is confidently detectable at S/N>8, regardless of the wave’s original polarization orientation. However, for the evidence of weak anisotropy to be detectable and measurable at an S/N value of 4, the backazimuth separation of the phases from the fast polarization direction needs to be higher than 20°. Stacks of individual measurements consistently yield reliable results down to S/N values of 4. Applying stacking to data from DSB (Dublin, Ireland), the fast polarization direction w and lag time dt are 58° and 0.95 s. This orientation reflects surface trends of deformation in the area, as found elsewhere in the UK. Our result thus reinforces the proposed model that the detected anisotropy in the British Isles originates from lithospheric coherent deformation preserved from the last main tectonic episode.

Ensemble average requirement for acoustical measurements in noisy environment using the m‐sequence correlation technique

This paper describes an experiment that provides additional evidence to demonstrate the possibility of making acoustical measurements in noisy environments by using an m‐sequence correlation technique. A criterion for choosing the proper number of synchronous averages is established and a demonstration of making noise reduction measurement between two rooms is also given.

Integrated-impulse method measuring sound decay without using impulses

A method of measuring linear-system responses (such as room responses) is described using ’’maximum-length’’ pseudorandom noise as the test signal. In this manner, high signal-to-noise ratios can be achieved, even for measurements in noisy environments and for low-power test signals. Pseudorandom noise has also been used successfully as the test signal in the ’’integrated-impulse’’ method of measuring sound decay and reverberation time. Thus, the need to radiate a short pulse of high peak energy for impulse type measurements is completely avoided. Improvements in signal-to-noise ratios are equal to the period length of the pseudorandom noise, typically 40 dB in room acoustical applications. The necessary digital processing to realize these gains in signal-to-noise ratio and accuracy of response can be performed on available minicomputers. Apart from maximum-length sequences, another type of periodic binary sequency, called the ’’Legendre sequence,’’ can be used as a test signal. Like maximum-length sequences, Legendre sequences have flat power spectra, but their discrete Fourier components have only two phase angles (?±90°), thus simplifying their digital representation (for storage and transmission). In fact, the discrete Fourier transform of a Legendre sequence is equal (within a constant factor) to the sequence itself! Legendre sequences exist for all period lengths equal to a prime number of the form 4k−1, where k is an integer. Thus, there are many more period lengths to choose from than for maximum-length sequences.