Array Of Point Sensors Research Articles

Hydrogen wide area monitoring of LH2 releases

The characterization of liquid hydrogen (LH2) releases has been identified as an international research priority to expand the safe use of hydrogen as an energy carrier. The elucidation of LH2 release behavior will require the development of dispersion and other models, guided and validated by empirical field measurements such as those afforded by Hydrogen Wide Area Monitoring (HyWAM). HyWAM can be defined as the quantitative spatial and temporal three-dimensional monitoring of planned or unintentional hydrogen releases. With support provided through the FCH JU Prenormative Research for the Safe Use of Liquid Hydrogen (PRESLHY) program, HSE performed a series of LH2 releases to characterize the dispersion and pooling behavior of cold hydrogen releases. The NREL Sensor Laboratory developed a HyWAM system based upon a distributed array of point sensors that is amenable for profiling cold hydrogen plumes. The NREL Sensor Laboratory and HSE formally committed to collaborate on profiling the LH2 releases. This collaboration included the integration of the NREL HyWAM into the HSE LH2 release hardware. This was achieved through a deployment plan jointly developed by the NREL and HSE personnel. Under this plan, the NREL Sensor Laboratory provided multiple HyWAM modules that accommodated 32 sampling points for near-field hydrogen profiling during the HSE PRESLHY LH2 releases. The NREL HyWAM would be utilized throughout the LH2 release study performed under PRESLHY by HSE, including Work Package 3 (WP3—Release and Mixing--Rainout) and subsequent work packages (WP4—Ignition and WP5—Combustion). Under the auspices of the PRESLHY WP6 (Implementation), data and findings from the HSE LH2 Releases are to be made available to stakeholders in the hydrogen community. Comprehensive data analysis and dissemination is ongoing, but the integration of the NREL HyWAM into the HSE LH2 Release Apparatus and its performance as well as some key outcomes of the LH2 releases in WP3 are presented.

Acoustic Emission Sensing for Crack Monitoring in Prefabricated and Prestressed Reinforced Concrete Bridge Girders

Prefabricated and prestressed beams are integral to accelerated bridge construction (ABC) and other construction projects, but concerns exist regarding the development of cracks during curing, form removal, detensioning, transport, installation, and operation. Acoustic emission (AE) sensing techniques have the potential for detecting and locating cracking in prefabricated, prestressed concrete girders used as prefabricated bridge elements and systems (PBES) in ABC as part of a quality assurance/quality control (QA/QC) program. AE measures the elastic waves produced by crack nucleation and growth with an array of point sensors. The AE instrument system is relatively portable, which can allow for it to be an option for off-site fabrication QA/QC and on-site field QA/QC. This paper presents AE measurements and analysis on relatively small laboratory reinforced concrete beam specimens under pullout and three-point bending to demonstrate the efficacy of AE in detecting cracks. It then presents application of AE during detensioning and lifting of full-scale Northeast Extreme Tee (NEXT) beams and Bulb Tee. The results indicate that AE sensing is a practical QA/QC process for PBES elements.

Ultra-short distributed feedback fiber laser with sub-kilohertz linewidth for sensing applications

A low-noise, ultra-short linear-cavity distributed feedback fiber laser (DFB-FL) with extremely narrow linewidth is presented. The FL has a total length of 17 mm, which is, to our knowledge, the shortest DFB-FL being reported. It has a measured linewidth of merely 250 Hz without active stabilization. It has a polarization beat frequency of 101 MHz, which is several times lower than that of most FLs. The relaxation oscillation frequency and relative peak are 110 kHz and −76.5 dB/Hz, respectively. The FL exhibited low-noise characteristics, with an intensity noise of −107 dB/Hz at 1 MHz. Due to low dopant concentration of the EDF and low splice loss with ordinary single-mode fibers, the net insertion loss amounts to only 0.45 dB. Such low pump power loss greatly enhances the capability of multiplexing a large number of FL sensors. Thus, these ultra-short DFB-FLs open up new opportunities for the development of compact-sized point sensor array systems for large-scale high sensitivity sensing applications.

Vibration reduction of curved panels by active modal control

Active vibration control using modal controllers has been successfully implemented on simple structures such as beams and plates. Since the dynamic behavior of a variety of mechanical structures can be expressed in terms of modal parameters, the application of modal control concepts can be extended to structures with more complex geometries. For such structures, the evaluation of modal parameters from numerical calculations of local modes is complicated because the results strongly depend on proper boundary conditions of the truncated structure. Therefore, the modal data is identified using experimental modal analysis. The transformation of the experimentally measured mode shapes into closed-form analytical formulations and the extraction of modal input and output factors for sensors and actuators are used to connect experimental modal analysis with modal control theory. The implementation of the input and output factors in a modal state space formulation results in a modal filter for the point sensor array and a retransformation filter for the segmented actuator patches. In this study, PVDF film is used for sensors and actuators. The modal controller is implemented on a digital controller board, and experimental tests with the floor panel and center panel of a car body are carried out to validate the proposed concept.

Acoustic cluster control of noise radiated from a planar structure

Acoustic cluster control is proposed for the purpose of achieving global sound attenuation of a planar structure. First, acoustic cluster filtering using a point sensor array is presented, which enables the grouping of sound radiated from a target object into a set of clusters, such that each cluster possesses the same common characteristics. This allows the possibility of extracting the cluster of interest without causing observation spillover. Based on the principle of reciprocity, cluster actuation using a point source array is then presented. Driving the source array in accordance with a proposed control law, the excitation of the designated cluster is performed without causing control spillover. Moreover, by combining both acoustic cluster filtering and acoustic cluster actuation, acoustic cluster control may be performed. In implementing acoustic cluster control, the necessary and sufficient condition for the acoustic cluster control is illustrated. It is also shown that the sound radiated from a planar structure may be captured in appropriate acoustic cluster filtering so that acoustic cluster control may be implemented. Experiment was conducted demonstrating the capability as well as the validity of the acoustic cluster filtering, actuation, and control for suppressing the noise radiated from a rectangular panel.

ACTIVE VIBRATION CONTROL OF A CAR BODY BASED ON EXPERIMENTALLY EVALUATED MODAL PARAMETERS

Active vibration control has been successfully tested for structures with simple geometry, such as beams and plates, by using modal controllers. Since the dynamical behaviour of a variety of mechanical structures can be expressed in terms of modal parameters, the application of modal control concepts can be extended to structures with more complex geometries. For such structures the evaluation of modal parameters from numerical calculations of local modes is complicated because the results strongly depend on proper boundary conditions of the truncated structure. Therefore, the modal data are identified by an experimental modal analysis. The transformation of the experimentally evaluated mode shapes into a closed analytical formulation and the extraction of modal input and output factors for sensors and actuators connect experimental modal analysis and modal control theory. The implementation of the input and output factors into a modal state-space formulation results in a modal filter for the point sensor array and a retransformation filter for the segmented actuator patches. In this study, PVDF foil is used for sensors and actuators. The modal controller is implemented on a digital controller board and experimental tests with the floor panel and centre panel of a car body are carried out to validate the proposed concept.

PH Microscopy Applications

Abstract A scanning chemical microscope utilizing a flat pH sensor has proven effective for analyzing a number of biological specimens including human teeth surfaces, plant leafs, and rice. The key to this microscope, the “pH imaging sensor”, is an electrochemical semiconductor that can be made to function as an array of point sensors when scanned by backside laser illumination. Measured pH values at each measurement point can be processed into a pH image. So far a resolution of 5 μm with a 0.01 pH sensitivity has been attained by this imaging technology, although most images are made using 100 μm resolution. The time to acquire an image is, of course, dependent on the size of the measured area. For example, a 6.4 mm x 6.4 mm image with a resolution of 100 urn can be acquired in 25 s. Linear pH profiles can also be obtained at a speed of 1 cm/s.

Inspecting the Back of Woven Carpets for Pattern Distortion

Any distortion seen in the pattern repeat of woven Axminster carpets causes considerable problems for both manufacturer and end-user. Instrumental measurement of the straightness of the weft threads on the back of a woven carpet can be used to provide a direct indication of the nature and severity of any pattern distortion, on-line and in real time. This paper discusses two alternative methods for performing the measurement. The first, using a CCD line-scan camera and conventional digital-image-processing techniques, has been investigated fairly thoroughly and shown to be effective but is rather expensive. Evaluation of the other remains to he completed; it uses a well-spaced array of point sensors and promises to be equally effective hut much less expensive. The paper also considers how the results of the instrumental measurements should be presented to the end-user.

Comparison of two structural sensing approaches for active structural acoustic control

A numerical study comparing the use of two structural sensing approaches for sound radiation control is performed on a baffled rectangular plate. The first sensing approach implements an array of accelerometers whose outputs are filtered to construct an estimate of the sound pressure radiated at given angles in the far field. The second method uses the same array of point sensors to estimate the net volume acceleration of the plate. Results show the improved performances of the sensor observing far-field sound radiation over a volume acceleration based on sensor.

Sensor for the measurement of the level and volume of conductive liquids

A sensor for the measurement of the level and volume of liquids is described. The device employs an array of point sensors, each of which is sensitive to the large changes in impedance between a conductive liquid and the gas above it. The device, in principle, will function in any liquid medium that can conduct an electric current without significantly perturbing that medium. It has in fact been successfully tested in aqueous solutions with conductivity ranging from 9.0×10−7 Ω−1 cm−1 to 0.38 Ω−1 cm−1. The sensor is activated with either AC or DC applied voltage and used with electronic circuits having linear outputs. The sensor’s output is solution independent and a function of the number of conducting electrodes. The precision of the sensor is controlled by the spacing of its electrode array. The linear output of the sensor has been correlated linearly to solution volume regardless of the shape of the solution tank by the use of unequal spacing between the array electrodes. Several designs of sensors with fixed and adjustable precision are described.