Effects of sensor locations on air-coupled surface wave transmission measurements across a surface-breaking crack

Previous studies show that the surface wave transmission (SWT) method is effective to determine the depth of a surface-breaking crack in solid materials. However, nearfield wave scattering caused by the crack affects the reliability and consistency of surface wave transmission measurements. Prior studies on near-field scattering have focused on the case where crack depth h is greater than wavelength λ of surface waves (i.e., h/λ > 1). Near-field scattering of surface waves remains not completely understood in the range of h/λ for the SWT method (i.e., 0 ≤ h/λ ≤ 1/3), where the transmission coefficient is sensitive to crack depth change and monotonically decreases with increasing h/λ. In this study, the authors thoroughly investigated the near-field scattering of surface waves caused by a surface-breaking crack using experimental tests and numerical simulations for 0 ≤ h/λ ≤ 1/3. First, the effects of sensor locations on surface wave transmission coefficients across a surface-breaking crack are studied experimentally. Data are collected from Plexiglas and concrete specimens using air-coupled sensors. As a result, the variation of transmission coefficients is expressed in terms of the normalized crack depth (h/λ) as well as the normalized sensor location (x/λ). The validity of finite element models is also verified by comparing experimental results with numerical simulations (finite element method). Second, a series of parametric studies is performed using the verified finite element model to obtain more complete understanding of near-field scattering of surface waves propagating in various solid materials with different mechanical properties and geometric conditions. Finally, a guideline for selecting appropriate sensor arrangements to reliably obtain the crack depth using the SWT method is suggested.     

A photonic crystal fiber sensor for pressure measurements

The pressure sensitivity of two photonic crystal fibers (PCFs) was measured. A PCF pressure sensor was then successfully developed with PCF PM-1550-01. The measurement results of the pressure sensor at three different temperatures are presented, and in the working region the maximum deviation is within 1% of the dynamic range of the sensor.     

A double-laser diode onboard sensor for velocity measurements

In this paper, we validate the feasibility of an onboard velocity sensor using the self-mixing effect. Roughness of the target surface, wet target surface, noncontrolled changes of incident angle, and speed vector vertical components have been considered during this development. A first prototype has been designed with an automotive application so to illustrate this feasibility. This low-cost and low-clutter prototype presents an interesting basic performance (/spl sigma//spl ap/0.22%). In order to improve the accuracy as well as the robustness of the system, a double-laser diode sensor has then been tested successfully (/spl sigma//spl ap/0.038%) by removing the influence of the pitching and the pumping effects.     

A digital optical sensor for the remote monitoring of temperature

A method for the continuous monitoring of the change in temperature of remote physical objects based on waveguide ring microwave resonators, and also its diagramatic representation, is proposed. The results of calculations, which enable the range of accuracy of temperature measurements to be optimized using a digital optical sensor, are presented. The short response time and the small dimensions and mass of the proposed sensor enable continuous remote monitoring of the temperature to be achieved in locations that are difficult to access. __________ Translated from Izmeritel’naya Tekhnika, No. 3, pp. 54–57, March, 2007.     

Magnetooptic sensor for remote evaluation of surfaces

A new magnetooptic (MO) detection method utilizing changes in the optical path through a transparent MO thin film has been developed and studied for evaluation of surface deformation created by subsurface or internal defects in materials. Investigation of defects cannot be performed on nonconducting and nonmagnetic materials using conventional electromagnetic techniques such as eddy-current or magnetic flux leakage. The new method utilizes the controlled periodic displacement of a domain wall in the MO thin film and can be used to measure remotely mechanical deformation of a surface of any type of material by measuring the changes of width of the shoulder in the intensity versus time waveform.     

A piezoelectric sensor for pressure measurements behind a shock front

The construction and measuring circuit of a pressure pickup designed for measurements in ionized gases behind a shock front are described. Calibration results are given, along with oscillograms of the pressure up to the arrival of the rarefaction wave.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 21, No. 1, pp. 168–171, July, 1971.     

Noncontacting electrical conductivity sensor for remote, hostileenvironments

A device for measuring the electrical conductivity at the surface of a large or semi-infinite body at centimeter scale has been developed. The right frequency contacting measurement uses single turn transmitter and receiver loops to generate and detect eddy currents in the material to be probed. Response is linear in conductivity over the four decades of interest in geophysical investigations. The mechanical design of the sensor makes it insensitive to temperature and pressure changes, and to accelerations, impact, and abrasion. Therefore, it is operable in remote, hostile environments such as deep boreholes     

A novel sensor array for field based ocular ultraviolet radiation measurements

The intensification of terrestrial solar ultraviolet radiation (UVR) due to the diminution of the ozone layer has promoted a variety of research into establishing the impact of this elevated potential dose of UVR on biological tissues. Certain anterior ocular tissues have been found to be susceptible to damage by incident UVR and potentially blinding diseases such as pterygium are thought to be a direct result of absorbed UVR at the nasal limbus. There is a need for more accurate quantification and localisation of incident UVR at the anterior ocular surface. A novel solar blind photodiode sensor array system has been designed, constructed and tested for this purpose. Initial measurements to quantify the irradiance across the anterior ocular surface within the latitudes known as the 'pterygium belt' provide us with a set of core data for different head orientations and tilt angles and indicate the accuracy and stability of the system.     

A submersible autonomous sensor for spectrophotometric pH measurements of natural waters

An autonomous sensor for long-term in situ measurements of the pH of natural waters is described. The system is based upon spectrophotometric measurements of a mixture of sample and sulfonephthalein indicator. A simple plumbing design, using a small, low-power solenoid pump and valve, avoids the need for quantitative addition of indicator. A approximately 50-microL slug of indicator is pulled into the sample stream by the pump, and subsequent pumping and mixing results in a section of indicator and sample where absorbance measurements can be made. The design also permits direct determination of the indicator pH perturbation. Absorbances are recorded at three wavelengths (439, 579, and 735 nm) using a custom-built 1.7-cm path length fiber-optic flow cell. Solution blanks are obtained by periodically flushing the cell with sample. Field tests were performed in a local river over an 8-day period. The in situ accuracy, based on comparison with laboratory spectrophotometric pH measurements, was -0.003 pH unit (n = 16), similar to the measurement precision. No drift was observed during the 8-day period. The absorbance ratio used to calculate pH, in combination with a simple and robust optical design, imparts an inherent stability not achievable with conventional potentiometric methods, making the design feasible for long-term autonomous pH measurements.     

A microwave interferometer with imaging capability for remote measurements of building displacements

In this paper the authors report some experimental activities carried out in Italy during the last few years, aimed at verifying the effectiveness of the use of coherent radar imaging to retrieve information on buildings deformations. Maps of differential phase obtained by means of a microwave interferometer with imaging capabilities are presented. Images were obtained by a synthetic-aperture interferometric radar making use of continuous-wave step-frequency waveform. The deformation maps and the measurement of some mechanical parameters—as the oscillating frequency and the amplitude of the vibrating modes of the observed structures—were performed remotely with sub-millimetre accuracy.

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Résumé Dans cet article, les auteurs rapportent l'analyse de quelques activités expérimentales effectuées en Italie au cours de ces dernières années, pour vérifier l'efficacité de l'utilisation d'images radar cohérentes pour mesurer les déformations de batiments. On va présenter des cartes de la phase différentielle obtenues à l'aide d'un interféromètre à micro-ondes avec des capacités d'imagerie. Des images sont obtenues à partir d'un radar interférométrique à ouverture synthétique et à onde continue (forme d'onde: step-frequency). La mesure des paramètres mécaniques comme fréquence d'oscillation et la phase des modes vibrants des structures observées ont été expérimentées à distance avec une exactitude supérieure au millimètre.

     

Standard samples in the quality system for measurements in analytical chemistry

Problems of providing measurement quality in analytical chemistry using reference materials attested under primary methods are considered in this paper. We describe a scheme of establishing the traceability of measurement results in a substance’s chemical composition to SI units, exemplifying it by standard samples attested at FGUP URIM under a primary method—coulonometric titration technique.     

Miniaturized magneto-optic sensor for pulsed magnetic field measurements

The design and performance of a miniaturized magneto-optic probe using a terbium doped paramagnetic glass are described. The compactness and simplicity of the device are achieved by using the polarizer sheets obtained from a commonly available liquid crystal display. Plastic optical fibers are used to transport the light. A pulsed magnetic field up to 48 T has been generated and measured using high-voltage capacitor discharge in single-turn coils. A rise time and magnetic field-dependent anomalous behavior is observed in the terbium glass characteristics at room temperature.     

Differential absorption sensor applied for liquid oxygen measurements

Differential laser absorption was investigated for its merit in liquid oxygen (LOX) sensing. Whereas previous researchers have used differential absorption to detect trace concentrations of a substance, we use differential absorption to monitor small changes in large amounts of a substance. Two lasers of different wavelengths were intensity modulated 180 deg out of phase from each other and multiplexed into a single beam. After probing the LOX, the total transmitted signal was demodulated by a lock-in amplifier. Our experiment simulated rapid changes in LOX number density by varying the length of an approximately 73 mm path through pure LOX. In this experiment, we demonstrated the ability to monitor LOX number density with an uncertainty of approximately 1% with a time constant of 3 micros. The uncertainty could be halved by doubling the path length, and this improvement could be repeated as long as the relative intensity noise of the lasers is the dominating factor. We discuss the benefits of differential absorption for problems requiring an extended dynamic range.     

Interferometer using a laser pointer for remote microdisplacement measurements

A portable Michelson interferometer for remote optical sensing with imaging capability is developed based on a laser pointer and experimentally studied. The setup has an open sensing arm with a mirror that can be attached to any object for the measurement of responses such as microdisplacement, strain, stress, and temperature. A mirror in the reference arm is mounted on an encoded stepper motor, which can operate under remote control via Web/Internet for reset and calibration. Remote microdisplacement measurements precise to within 5 μm have been performed.