Real-time micro-vibration measurement in sinusoidal phase-modulating interferometry

As there exist some problems with the previous laser diode (LD) real-time microvibration measurement interferometers, such as low accuracy, correction before every use, etc., in this paper, we propose a new technique to realize the real-time microvibration measurement by using the LD sinusoidal phase-modulating interferometer, analyze the measurement theory and error, and simulate the measurement accuracy. This interferometer utilizes a circuit to process the interference signal in order to obtain the vibration frequency and amplitude of the detective signal, and a computer is not necessary in it. The influence of the varying light intensity and light path difference on the measurement result can be eliminated. This technique is real-time, convenient, fast, and can enhance the measurement accuracy too. Experiments show that the repeatable measurement accuracy is less than 3.37 nm, and this interferometer can be applied to real-time microvibration measurement of the MEMS. (C) 2007 Elsevier GmbH. All rights reserved.

Near infrared for non-destructive testing of articular cartilage

The concept of non-destructive testing (NDT) of materials and structures is of immense importance in engineering and medicine. Several NDT methods including electromagnetic (EM)-based e.g. X-ray and Infrared; ultrasound; and S-waves have been proposed for medical applications. This paper evaluates the viability of near infrared (NIR) spectroscopy, an EM method for rapid non-destructive evaluation of articular cartilage. Specifically, we tested the hypothesis that there is a correlation between the NIR spectrum and the physical and mechanical characteristics of articular cartilage such as thickness, stress and stiffness. Intact, visually normal cartilage-on-bone plugs from 2-3yr old bovine patellae were exposed to NIR light from a diffuse reflectance fibre-optic probe and tested mechanically to obtain their thickness, stress, and stiffness. Multivariate statistical analysis-based predictive models relating articular cartilage NIR spectra to these characterising parameters were developed. Our results show that there is a varying degree of correlation between the different parameters and the NIR spectra of the samples with R2 varying between 65 and 93%. We therefore conclude that NIR can be used to determine, nondestructively, the physical and functional characteristics of articular cartilage.

Development and Longer Term In Situ Evaluation of Fiber-Optic Sensors for Monitoring of Structural Concrete

In this paper, new solutions to the problem of making measurements, of carbonation and chloride ingress, in particular, in concrete structures are considered. The approach has focused on the design, development, and use of fiber-optic sensors (FOSs), recognizing the need in that conventional devices are often either inaccurate, expensive, or unsuitable for encapsulation in the material. The sensors have been designed to monitor, in situ and nondestructively, relevant physical, and chemical changes in cementitious materials. Three different types of FOS were constructed, tested, and evaluated specifically for this application, these being a temperature sensor (based on the fluorescence decay) and pH and chloride sensors, based on sol-gel (solidified gel) technology with appropriate impregnated indicators. The sensors were all designed to be inserted into the structures and evaluated under the harshest conditions, i.e., being mounted when the mortar is poured and thus tested in situ, with the temperature and pH sensors successfully embedded in mortar. The outcomes of these tests have shown that both the temperature sensor and the pH sensor were able to function correctly for the duration of the work - for over 18 months after placement. The laboratory tests on the chloride sensor showed it was able to make measurements but was not reversible, limiting its potential utility for in situ environments. Research is ongoing to refine the sensor performance and extend the testing.

Preliminary Development and Evaluation of Fiber-Optic Chemical Sensors

This paper could be consider seminal in the Civil Engineering field as it describes the first application of these sensors to a complex durability and management issue. For this reason it is potentially controversial as it requires Civil Engineers to re-evaluate the nature and scale of durability testing.

Study of reliability of fibre Bragg grating fibre optic strain sensors for field-test applications

In this paper, the reliability and thus the suitability of optical fibre strain sensors for surface strain measurement in concrete structures was investigated. Two different configurations of optical strain sensors were used each having different mountings making them suitable for different uses in various structures. Due to the very limited time available to install the sensors and take result, commercially packaged sensors were used. In the tests carried out each sensor was mounted onto a concrete beam which was then subjected to a range of known and calibrated loadings. The performance of the optical strain sensors thus evaluated was compared with the results of conventional techniques. This comparison allows for selecting the best performing combination of sensor/mounting, i.e. long-gauge sensor with mounts bolted to threaded rods glued into the concrete for use in future work in a field test where a limited time window was available for installation, testing and post-test demounting. © 2012 Elsevier B.V.

Next generation Bridge weigh-in-motion using fibre optic sensors

There have been over 3000 bridge weigh-in-motion (B-WIM) installations in 25 countries worldwide, this has led vast improvements in post processing of B-WIM systems since its introduction in the 1970’s. Existing systems are based on electrical resistance strain gauges which can be prohibitive in achieving data for long term monitoring of rural bridges due to power consumption. This paper introduces a new low-power B-WIM system using fibre optic sensors (FOS). The system consisted of a series of FOS which were attached to the soffit of an existing integral bridge with a single span of 19m. The site selection criteria and full installation process has been detailed in the paper. A method of calibration was adopted using live traffic at the bridge site and based on this calibration the accuracy of the system was determined. New methods of axle detection for B-WIM were investigated and verified in the field.

Bilateral posterior ischaemic optic neuropathy after severe diabetic ketoacidosis, cardiopulmonary resuscitation and respiratory failure

A 44-year-old male European with type I diabetes mellitus fell into diabetic ketoacidosis. In the emergency room, he developed an episode of asystole and respiratory failure requiring one cycle of cardiopulmonary resuscitation and extracorporeal membrane oxygenation (ECMO). Waking up 7 days later, he presented a bilateral complete loss of vision. Ophthalmological examination including funduscopy on days 1 and 10, after extubation, showed bilateral large round pupils non-reactive to light and a normal fundus. Neuroimaging studies, including MRI and MRA of the brain, were all within normal limits. A lumbar puncture and comprehensive serological testing excluded an infectious or rheumatic cause. An empirical high-dose intravenous steroid treatment administered for 5 days had no effect on his vision. His eye examination at 1.5 months follow-up showed a normal fundus except for progressive bilateral optic nerve disc pallor, which pointed towards the diagnosis of a posterior ischaemic optic neuropathy.

Field Testing and Development of Novel SHM systems at Queen’s University Belfast

Ageing and deterioration of infrastructure is a challenge facing transport authorities. In
particular, there is a need for increased bridge monitoring in order to provide adequate
maintenance and to guarantee acceptable levels of transport safety. The Intelligent
Infrastructure group at Queens University Belfast (QUB) are working on a number of aspects
of infrastructure monitoring and this paper presents summarised results from three distinct
monitoring projects carried out by this group. Firstly the findings from a project on next
generation Bridge Weight in Motion (B-WIM) are reported, this includes full scale field testing
using fibre optic strain sensors. Secondly, results from early phase testing of a computer
vision system for bridge deflection monitoring are reported on. This research seeks to exploit
recent advances in image processing technology with a view to developing contactless
bridge monitoring approaches. Considering the logistical difficulty of installing sensors on a
‘live’ bridge, contactless monitoring has some inherent advantages over conventional
contact based sensing systems. Finally the last section of the paper presents some recent
findings on drive by bridge monitoring. In practice a drive-by monitoring system will likely
require GPS to allow the response of a given bridge to be identified; this study looks at the
feasibility of using low-cost GPS sensors for this purpose, via field trials. The three topics
outlined above cover a spectrum of SHM approaches namely, wired monitoring, contactless
monitoring and drive by monitoring