Low-frequency Sensor Research Articles

Acoustic emission energy b -value for local damage evaluation in reinforced concrete structures subjected to seismic loadings

Abstract A modification of the original b-value (Gutenberg-Richter parameter) is proposed to evaluate local damage of reinforced concrete structures subjected to dynamical loads via the acoustic emission (AE) method. The modification, shortly called energy b-value, is based on the use of the true energy of the AE signals instead of its peak amplitude, traditionally used for the calculation of b-value. The proposal is physically supported by the strong correlation between the plastic strain energy dissipated by the specimen and the true energy of the AE signals released during its deformation and cracking process, previously demonstrated by the authors in several publications. AE data analysis consisted in the use of guard sensors and the Continuous Wavelet Transform in order to separate primary and secondary emissions as much as possible according to particular frequency bands. The approach has been experimentally applied to the AE signals coming from a scaled reinforced concrete frame structure, which was subjected to sequential seismic loads of incremental acceleration peak by means of a 3 × 3 m2 shaking table. For this specimen two beam-column connections—one exterior and one interior—were instrumented with wide band low frequency sensors properly attached on the structure. Evolution of the energy b-value along the loading process accompanies the evolution of the severe damage at the critical regions of the structure (beam-column connections), thus making promising its use for structural health monitoring purposes.

Development of a hybrid ECT sensor for JSFR SG double-wall tubes

ABSTRACTA new design has been adopted for the steam generator (SG) tubes of the Japan Sodium-cooled Fast Reactor (JSFR) using double-wall tubes. This paper estimates and assesses the effectiveness of detecting defects in SG double-wall tubes of the JSFR by using combined high-frequency eddy current testing (ECT) and low-frequency remote field eddy current sensors. We confirm that the proposed hybrid ECT sensor is highly sensitive to small defects, fatigue cracks, and other defects even when located under support plates of tubes. The parameters of the hybrid ECT sensor are designed and optimized to detect small defects using accurate numerical simulations based on the finite element method, using an in-house developed code. The sensitivity and high performance of the hybrid ECT sensor was validated with experimental measurements.

Near Real-Time Appliance Recognition Using Low Frequency Monitoring and Active Learning Methods

Electricity load monitoring in residential buildings has become an important task allowing for energy consumption understanding, indirect human activity recognition and occupancy modelling. In this context, Non Intrusive Load Monitoring (NILM) is an approach based on the analysis of the global electricity consumption signal of the habitation. Current NILM solutions are reaching good precision for the identification of electrical devices but at the cost of difficult setups with expensive equipments typically working at high frequency. In this work we propose to use a low-cost and easy to install low frequency sensor for which we improve the performances with an active machine learning strategy. At setup, the system is able to identify some appliances with typical signatures such as a fridge. During usage, the system detects unknown signatures and provides a user-friendly procedure to include new appliances and to improve the identification precision over time.

A digitally adjustable sensor signal conditioning circuit for low frequency operation

A fully digitally adjustable sensor signal conditioning circuit (SCC) is proposed herein. The SCC is meant to properly adjust the input signal delivered either by active sensors or by passive sensors (e.g. thermocouples, piezoelectric and/or pyroelectric sensors, etc.). The circuit is meant to be resistively connected to the sensor that delivers a signal containing low frequency components, ranging from direct current (DC) to 2×103Hz. The signal conditioning circuit is mainly based on one or two inverting stages, each provided with the possibility to digitally control both the gain coefficient (GC) and the direct current (DC) offset. The GC of each stage can be adjusted in a range spanning from sub-unitary to supra-unitary values, therefore the signal conditioning circuit can be used to preserve the dynamic range of an analog to digital converter (ADC) in an optimum domain, while avoiding saturation, also when the input signal is within the dynamic range of the SCC’s input but out of the dynamic range necessary at output. The circuit is designed to detain a low-pass characteristic, thus eliminating high frequency components; therefore it provides a basic bandwidth control. A digital to analog conversion stage is employed to adjust the DC offset and to run self-calibration and self- test procedures. The proposed circuit is meant as a basic building block, employed to interface a wide range of sensor signals in order to provide optimal levels for the ADC stage, or to be inserted in an analog signal chain, where signal level conversion may be achieved (for example signal expansion or compression from 0–5V voltage levels to 0–3.3V levels). Alternatively, the proposed SCC could be inserted into more specialized data acquisition systems providing a digital system with the ability to self-condition the input signal before acquiring it. The developed SCC prototype has been employed for separating efficiently small temperature and magnetic field’s intensity (very low frequency) sensor signals from the continuous components and for best fitting the dynamic range of an ADC. An automatic parameters adjustment algorithm, with no loss of the output signal has been implemented.

In Situ Analysis of the Growth and Dielectric Properties of Organic Self-Assembled Monolayers: A Way To Tailor Organic Layers for Electronic Applications.

Organic nanoscale science and technology relies on the control of phenomena occurring at the molecular level. This is of particular importance for the self-assembly of molecular monolayers (SAM) that can be used in various applications ranging from organic electronics to bioelectronic applications. However, the understanding of the elementary nanoscopic processes in molecular film growth is still in its infancy. Here, we developed a novel in situ and extremely sensitive detection method for the analysis of the electronic properties of molecular layer during molecular layer deposition. This low-frequency sensor (1 kHz) is employed to analyze the standard vapor deposition process of SAMs of molecules and, subsequently, it is used to optimize the growth process itself. By combining this method with an ex situ determination of the effective thickness of the resulting layers via ellipsometry, we observe a large difference of the permittivity (1 kHz) of the examined aminosilanes in the liquid state (εliquid = 5.5-8.8) and in SAMs (εSAM = 22-52, electric field in the plane of the layer). We ascribe this difference to either the different orientation and order of the molecules, the different density of molecules, or a combination of both effects. Our novel in situ analyses not only allows monitoring and optimizing the deposition of organic layers but also demonstrates the high potential of organic SAMs as organic high-k layers in electronic devices.

Correlation of Plastic Strain Energy and Acoustic Emission Energy in Reinforced Concrete Structures

This paper presents a comparison of the acoustic emission (AE) energy and the plastic strain energy released by some reinforced concrete (RC) specimens subjected to cyclic or seismic loadings. AE energy is calculated, after proper filtering procedures, using the signals recorded by several AE low frequency sensors (25–100 kHz) attached on the specimens. Plastic strain energy is obtained by integrating the load displacement curves drawn from the measurements recorded during the test. Presented are the results obtained for: (i) two beams (with and without an artificial notch) and a beam-column connection subjected to several cycles of imposed flexural deformations; (ii) a reinforced concrete slab supported by four steel columns, and a reinforced concrete frame structure, both of the latter are subjected to seismic simulations with a uniaxial shaking table. The main contribution of this paper, which is a review of some papers previously published by the authors, is to highlight that, in all cases, a very good correlation is found between AE energy and plastic strain energy, until the onset of yielding in the reinforcing steel. After yielding, the AE energy is consistently lower than the plastic strain energy. The reason is that the plastic strain energy is the sum of the contribution of concrete and steel, while the AE energy acquired with thresholds higher than 35 dBAE captures only the contribution of the concrete cracking, not the steel plastic deformation. This good correlation between the two energies before the yielding point also lends credibility to the use of AE energy as a parameter for concrete damage evaluation in the context of structural health monitoring.

Localization of CO2 leakage from transportation pipelines through low frequency acoustic emission detection

Carbon Capture and Storage is a technology to reduce greenhouse gas emissions. CO2 leak from high pressure CO2 transportation pipelines can pose a significant threat to the safety and health of the people living in the vicinity of the pipelines. This paper presents a technique for the efficient localization of CO2 leakage in the transportation pipelines using acoustic emission method with low frequency and narrow band sensors. Experimental tests were carried out on a lab scale test rig releasing CO2 from a stainless steel pipe. Further, the characteristics of the acoustic emission signals are analyzed in both the time and the frequency domains. The impact of using the transverse wave speed and the longitudinal wave speed on the accuracy of the leak localization is investigated. Since the acoustic signals are expected to be attenuated and dispersed when propagating along the pipe, empirical mode decomposition, signal reconstruction and a data fusion method are employed in order to extract high quality data for accurate localization of the leak source. It is demonstrated that a localization error of approximately 5% is achievable with the proposed detecting system.

Lightning Observation in 3D Using a Multiple LF Sensor Network and Comparison with Radar Reflectivity

SUMMARYA three‐dimensional (3D) lightning mapper consisting of multiple low‐frequency (LF) sensors has been developed to monitor thunderstorms and to estimate their charge structure. We have been conducting an observation campaign using the 3D lightning mapper in Kansai, Japan, since October 2012. In this study, we determine 3D source locations of intracloud and cloud‐to‐ground flashes and compare them with the radar reflectivity estimated by phased‐array radar (PAR) with high temporal and spatial resolution. Most LF sources are located in high radar reflectivity regions, confirming that the 3D LF lightning mapper monitors thunderstorms. A lightning flash with heavy branches is clearly imaged. Based on the bidirectional leader theory that negative and positive ends of a lightning leader develop simultaneously, we estimate the positive and negative charge regions in a thundercloud from the LF source locations. The radar reflectivity estimated by PAR supports the charge structure estimated by LF source locations.

Watts linkage based large band low frequency sensors for scientific applications

The UNISA Folded Pendulum class of horizontal and vertical sensors, based on an innovative configuration of the classical Watt׳s linkage mechanical architecture, allows the design and implementation of very large band monolithic sensors (10−7Hzto102Hz), whose sensitivities for the most common applications are defined by the noise introduced by their readouts (e.g. <10−12m/Hz with classical LVDT readouts). These unique features, coupled other relevant properties like scalability, compactness, lightness, high directivity, frequency tunability (typical resonance frequencies in the band 10−1Hzto102Hz), very high immunity to environmental noises and low cost make this class of sensors very effective for the implementation of uniaxial (horizontal and/or vertical) and triaxial seismometers and accelerometers for ground, space and underwater applications, including UHV and cryogenics ones.

Noise Behavior of High Sensitive GMI-Based Magnetometer Relative to Conditioning Parameters

The lowest measurable magnetic field of a high sensitive magnetometer based on giant magnetoimpedance (GMI) effect will be determined by its noise level. Numerous previous works have showed that the equivalent magnetic noise level of GMI magnetometer presents a 1/f behavior at low frequencies and a white noise. Currently, performances of the magnetometer are still limited by the electronic conditioning as well as the intrinsic equivalent magnetic noise of the GMI sensor. To improve sensor performances, particularly at low frequency, we have investigated two focuses on research: 1) reduce the electronic noise of the conditioning electronic by increasing the voltage sensitivity, in units of V/T and 2) reduce the intrinsic equivalent low frequency sensor noise. As previously reported, the equivalent magnetic noise at 1 Hz can be reduced by increasing the excitation current in addition to a dc bias current. By working on these bias conditions, on the given samples, we almost 1 pT/√Hz in white noise region and 15 pT/√Hz at 1 Hz.

Multi-Source Information Fusion Based on Kalman Filtering

Thehigh-frequency angular micro-vibration on satellite platform results in theoptical axis pointing decreasing accuracy. The Kalman filtering based on attitudeinformation fusion method is presented to solve this case and improve the pointing accuracy of attitude determination. Thesimulation results indicate that the estimated accuracy of Kalman filteringattitude information fusion method is better than the result only fromconventional low frequency sensor. Accordingly, the attitude information fusionmethod is verified and accuracy.

A low-frequency sensor for determination of honey electrical properties in varying temperature conditions

The aim of the research was to test a prototype sensor used to determine the electrical properties of acacia honey. The sensor, placed inside a measurement cell, was connected to a precise LCR meter, which collected the impedance readings in the frequency range from 20Hz to 2MHz. The measurement results were analyzed using the electrical equivalent circuit (EEC) approach. The values of parameters describing impedances of four EEC elements, which were a capacitor, a constant phase element and two resistors, obtained at various temperatures from −10°C to 35°C during honey heating and cooling processes, were presented, as well as dielectric permittivity spectra of honey. The paper discusses the temperature dependence of the EEC electrical parameters and the functionality of the sensor.

Resonant gravimetric immunosensing based on capacitive micromachined ultrasound transducers

High-frequency (40 MHz) and low-frequency (7 MHz) capacitive micromachined ultrasound transducers (CMUT) were fabricated and tested for use in gravimetric detection of biomolecules. The low-frequency CMUT sensors have a gold-coated surface, while the high-frequency sensors have a silicon nitride surface. Both surfaces were functionalized with bovine leukemia virus antigen gp51 acting as the antigen. On addition of an a specific antibody labeled with horseradish peroxidase (HRP), the antigen/antibody complex is formed on the surface and quantified by HRP-catalyzed oxidation of tetramethylbenzidine. It has been found that a considerably smaller quantity of immuno complex is formed on the high frequency sensor surface. In parallel, the loading of the surface of the CMUT was determined via resonance frequency and electromechanical resistance readings. Following the formation of the immuno complexes, the resonance frequencies of the low-frequency and high-frequency sensors decrease by up to 420 and 440 kHz, respectively. Finite element analysis reveals that the loading of the (gold-coated) low frequency sensors is several times larger than that on high frequency sensors. The formation of the protein film with pronounced elasticity and stress on the gold surface case is discussed. We also discuss the adoption of this method for the detection of DNA using a hybridization assay following polymerase chain reaction.

高感度低周波圧力センサを利用した乳牛の反芻自動計測装置の開発

高感度低周波圧力センサを利用した乳牛の反芻自動計測装置の開発

Study of the Ultrasonic Characteristics of Typical Partial Discharge on GIS

This Paper studied the typical PD in GIS by ultrasonic method. A GIS PD simulating and testing system is established, including a PD simulating system, an ultrasonic detecting system and a conventional pulse current method measurement system. The thesis focuses on four typical kinds of PD signals in GIS, including metal particles, bad contacts on high and grounding potential conductor, the protrusion on the high potential conductor. The statistics characteristics are obtained which include N-Φ spectrogram (relationship between discharge frequency and discharge phase Spectrogram) and Umax-Φ spectrogram (relationship between discharge amplitude and discharge phase Spectrogram). Experimental results show that low-frequency ultrasonic sensors can detect this four PD signals， signal spectra analysis shows that ultrasonic signals of different statistical model are with different characteristics. The results provide test data for the pattern recognition of Partial Discharge in GIS.

Evaluation of Standard Calibration Functions for Eight Electromagnetic Soil Moisture Sensors

An increasing number of electromagnetic (EM) sensors are deployed to measure volumetric soil water content (θ) for agricultural, ecological, and geotechnical applications. While impedance and capacitance sensors generally operate at frequencies between 20–300 MHz, time domain‐reflectometry (TDR) and‐transmissometry (TDT) function in the GHz range. In general, lower frequency sensors are less expensive but more sensitive to confounding effects of salinity, temperature, and soil textural variations. To simplify sensor application, factory‐supplied calibrations are often provided for different porous media types such as mineral, organic, and saline soils, or soilless‐substrates. The objective of the presented study was to evaluate the performance of eight commercially available EM moisture sensing systems (TDR 100, CS616, Theta Probe, Hydra Probe, SM300, Wet2, 5TE, 10HS) in seven well‐characterized and texturally varying soils using a standardized approach. The validity of factory supplied‐calibration relationships was evaluated and the influence of soil properties on the EM responses for θ measurements was observed. Results indicate that the factory‐supplied calibration relationships for groups of mineral and organic soils in general performed well, but some inconsistences were identified and suggestions for improvement are discussed. Soil‐specific calibrations from this study yielded accuracies of around 0.015 m3m−3 for 10HS, SM300, and Theta Probe, while lower accuracies of about 0.025 m3 m−3 were found for TDR100, CS616, Wet2, 5TE, and the Hydra Probe. These results are based on mineral soils having a large variation in texture, electrical conductivities below 2 dS m−1, organic matter below 10%, and specific surface areas of less than 50 m2 g−1.

Investigation of the Near-Carrier Noise for Strain-Driven ME Laminates by Using Cross-Correlation Techniques

The near-carrier noise around the longitudinal mechanical resonance of a magnetoelectric laminated composite has been investigated. By simultaneously applying a high-frequency electric field across the piezoelectric phase, the sensor response to low-frequency magnetic signals can be shifted around the “carrier” frequency as side band modulation signals. This magnetoelectric response can appear either as an electric charge via piezoelectric-to-piezoelectric (PP) modulation effects or as a magnetic signal via piezoelectric-to-magnetic (PM) modulation effects. These two signals are detected either with a charge preamplifier or with a coil surrounding the sample and the low-frequency sensor response to the applied magnetic field can be recovered by using two independent synchronous detectors. We have designed an experimental setup to observe the direct (passive) low-frequency noise and the noise corresponding to the two above modulations. Noise cross-correlating measurements were also carried out to investigate the origin of the near-carrier noise. No noise coherence was found between the direct low-frequency noise and the noise resulting from either the PP or the PM modulations. However, a noise coherence factor of more than 50% has been found between the signals recovered from the two modulation techniques. A simple model has been used to explain this effect. The magnetoelectric sensor is considered as a nonlinear forced vibration system. Noise sources passing through such a system can be amplified and distributed around the carriers as side band noise where it hampers the equivalent magnetic noise performance. Electronic–thermal noise caused by dielectric dissipations in the piezoelectric phase can be considered as a noise source with a negligible contribution to the total noise floor. Mechanical–thermal low-frequency excess noise is found to be the only intrinsic noise source which is filtered by the nonlinear ME system and is present as an output near-carrier noise which dominates the noise level after the demodulation processes.

Mechanism of Bio-Inspired Ultrasensitive Low Frequency Sensor with Mechanics Analysis

It is essential to develop ultrasensitive low frequency sensors for efficient structural health monitoring and early warning of natural disasters. Many fishes have been reported to have acute sensitivity to low frequency. Based on the mechanism of the infrasound sensitivity of fish, mechanism of bio-inspired ultrasensitive low frequency sensor is explored by a mechanical model with gating spring hypothesis for simulating the mechanical-electricity transduction of the hair cell in fish ear. Numerical analyses of the mechanical model subject to static and dynamic loading are conducted respectively by OpenSees. Under static loading, displacement response of gating model is more sensitive to weak loading due to the opening of gating spring. Under dynamic loading, the gating model is more acute sensitive to low frequency and weak loading due to the adaptive amplification of gating spring. This mechanical function can be used as the theoretical basis for the design of ultrasensitive bio-inspired low frequency sensors.

Pure low-frequency flexural mode of [011]c poled relaxor-PbTiO3 single crystals excited by k32 mode

Rhombohedral phase relaxor-PbTiO(3) solid solution single crystals poled along [011](c) exhibits superior lateral extensional piezoelectric response, which enables the excitation of a pure low frequency flexural mode with a bridge-type electrode configuration. For the ternary 0.24Pb(In(1/2)Nb(1/2)) O(3)-0.46Pb(Mg(1/3)Nb(2/3))O(3)-0.30PbTiO(3) single crystal poled along [011](c), the electromechanical coupling factor of the flexural mode reached as high as 0.66, and the resonance frequency of this mode can be easily made in kHz range, making it possible to fabricate very small size low frequency sensors and actuators. We have delineated theoretically the coupling between flexural mode and other modes and realized a strong pure flexure mode.

Radio array starts work

Giant low-frequency sensor system on track to probe the birth of the first stars.