Fiber Optic Transducer Research Articles

Optical pressure measurement

The supersonic combustor of a hypersonic engine is a harsh environment in which to apply close-coupled sensors. While fiber optic sensors have some inherent advantages over conventional electronic sensors, the first challenge was to design a fiber optic connector that could support the application of fiber optic sensors. We have designed a high-temperature fiber optic connector that will allow the placement of a fiber optic sensor into the wall of a high-temperature pressure vessel such as the DCR combustor. This connector has proven versatile enough to support monitoring of the ignition status of the combustor via looking at the spectral content of the flame. Additional information about the combustion process can be obtained by using multiple fibers and multiple detectors with different wavelength sensitivities or by connecting the fiber to a spectrometer. We have also shown that two different fiber optic transducer manufacturers, using two different fiber optic sensing technologies, can produce fiber optic pressure transducers that can be installed inside of the high-temperature fiber optic connector. These pressure transducers were closely coupled to the combustor and have successfully monitored the combustor pressure during short ground tests. The transducers used for these tests were modifications of standard designs by Fiso Technologies and Optrand Inc. The small size of the fiber optic pressure transducers and their high-temperature capability allowed them to be applied in locations where the application of conventional strain gauge transducers is not possible. Such close coupling of the transducers allowed observation of phenomena not seen with prior existing instrumentation. Both of the transducers furnished useful data; however, optimization of the transducers was not possible under the scope of this program. It should be noted that the hypersonic DCR tests are short ground tests using heat sink model hardware. The optical sensors have not yet been proven in a flight environment, where the run times will be longer and the combustor temperatures will be higher. We must perform additional work to make them ready for flight tests.

Dynamic loading of the plantar aponeurosis in walking.

The plantar aponeurosis is known to be a major contributor to arch support, but its role in transferring Achilles tendon loads to the forefoot remains poorly understood. The goal of this study was to increase our understanding of the function of the plantar aponeurosis during gait. We specifically examined the plantar aponeurosis force pattern and its relationship to Achilles tendon forces during simulations of the stance phase of gait in a cadaver model. Walking simulations were performed with seven cadaver feet. The movements of the foot and the ground reaction forces during the stance phase were reproduced by prescribing the kinematics of the proximal part of the tibia and applying forces to the tendons of extrinsic foot muscles. A fiberoptic cable was passed through the plantar aponeurosis perpendicular to its loading axis, and raw fiberoptic transducer output, tendon forces applied by the experimental setup, and ground reaction forces were simultaneously recorded during each simulation. A post-experiment calibration related fiberoptic output to plantar aponeurosis force, and linear regression analysis was used to characterize the relationship between Achilles tendon force and plantar aponeurosis tension. Plantar aponeurosis forces gradually increased during stance and peaked in late stance. Maximum tension averaged 96% +/- 36% of body weight. There was a good correlation between plantar aponeurosis tension and Achilles tendon force (r = 0.76). The plantar aponeurosis transmits large forces between the hindfoot and forefoot during the stance phase of gait. The varying pattern of plantar aponeurosis force and its relationship to Achilles tendon force demonstrates the importance of analyzing the function of the plantar aponeurosis throughout the stance phase of the gait cycle rather than in a static standing position. The plantar aponeurosis plays an important role in transmitting Achilles tendon forces to the forefoot in the latter part of the stance phase of walking. Surgical procedures that require the release of this structure may disturb this mechanism and thus compromise efficient propulsion.

A Novel Fiber-Optic Pressure Sensor Operated at 1300-nm Wavelength

In this paper, we discuss a particular topology of a fiber-optic pressure transducer, developed recently at the Laboratory of the Photonics Research Center, University of Quebec en Outaouais. The sensor, which is an extension of our previous polarimetric configuration, was designed to operate using typical telecommunications components at the wavelength of 1300 nm. The pressure sensor is temperature compensated in an innovative way and has no polarizer between the LD and the sensor. The absolute accuracy of this sensor can be less than 1% in a wide range of temperatures, and including all types of metrological errors such as hysteresis and unrepeatability.

An integrated on-line oil analysis method for condition monitoring

An on-line oil monitoring system offers a suitable solution to the practical problemsencountered in monitoring the conditions of machinery equipment. The objective ofthis paper is to present a systematic method for analysing wear particles in thelubricant used in a diesel engine, in a laboratory setting. An integrated on-line oilmonitoring system, which combines an inductive transducer with a fibre optictransducer, was developed to primitive design stage and some experiments havebeen done. The inductance transducer, whose operation is based on an inductivemeasurement technique, can detect large ferrous and non-ferrous wear debris. Aparticle’s material properties reflect its origin, and the frequency can be usedfor estimating wear particle size. The fibre optic transducer can detect smallparticles and is used for inspection of oil contamination levels. The integrated systemcombines the virtues of two measurement methods, extends the detection range andmeaningfully improves the reliability of oil monitoring. So it has great promise and thereare prospects for application as soon as the solutions to certain problems arefound.

Linear and steplike characteristics in an optical fiber refractometric transducer with hemispherical detection element

We present the results of a theoretical numerical analysis of transmission characteristics of a fiber optic refractometric transducer with a hemispherical glass detection element. In this transducer, the internal reflection of light from the element's spherical surface depends on the refractive index of the surrounding medium. We examine the effects of the transducer's geometrical and optical parameters and its refractive index on the transmission function, its nonlinearity, and the transducer's sensitivity to the refractive index of the surrounding medium. We show that through a proper choice of the transducer's material and geometrical parameters, it is possible to obtain a transmission function of any necessary span over a wide interval of the refractive index of the surrounding medium (from n = 1.0 to 1.7), and to modify the form of the transmission function from a linear one to a steplike one in virtually the same device. This permits us to use the proposed transducer for two contrasting applications: assessing the refractive index, and discriminating between two liquids or between air and a liquid, as in the detection of liquids, level measurement, etc. In addition, it is possible to adjust the transducer input range to the refractive index of a particular fluid (or fluids) of interest.

Correlation between active and passive isometric force and intramuscular pressure in the isolated rabbit tibialis anterior muscle

The purpose of this study was to quantify the relationship between intramuscular pressure (IMP) and muscle force during isometric muscle contraction of the rabbit tibialis anterior (TA) absent the effect of either bone or fascia. To quantify this relationship, length–tension experiments were performed on the isolated TA of the New Zealand White rabbit (mass=2.5±0.5 kg, n=12). The knee was fixed in a custom jig, the distal tendon of the TA was attached to a servomotor, and a 360 μm fiber optic pressure transducer was inserted into the TA. The peroneal nerve was stimulated to define optimal length ( L 0). The length–tension curve was created using 40 Hz isometric contractions with 2-min rest intervals between each contraction. Measurements began at L 0−50% L f and progressed to L 0+50% L f, changing the length–tension in 5% L f increments after each contraction. Qualitatively, the length–tension curve for isometric contractions was mimicked by the length–pressure curve for both active and passive conditions. Linear regression was performed individually for each animal for the ascending and descending limb of the length–tension curve and for active and passive conditions. Pressure–force coefficients of determination ranged from 0.138–0.963 for the active ascending limb and 0.343–0.947 for the active descending limb. Passive pressure coefficients of determination ranged from 0.045–0.842 for the ascending limb and 0.672–0.982 for the descending limb. These data indicate that IMP measurement provide a fairly accurate index of relative muscle force, especially at muscle lengths longer than optimal.

Fiberoptic measurement of tendon forces is influenced by skin movement artifact

Fiberoptic cables have previously been used for tendon force measurements in vivo. To measure forces in the Achilles tendon, a cable is passed mediolaterally through the skin and tendon, transverse to the loading axis. As the tendon is loaded, its fibers compress the cable and modulate the intensity of transmitted light, which can be related to tendon force by an in situ calibration. The relative movement between skin and tendon at the cable entry and exit sites may cause error by bending the cable and thus altering transducer output. Cadaver simulations of walking were conducted to compare fiberoptic measurements of Achilles tendon forces to known loads applied to the tendon by actuators attached in series. Force measurement errors, which were high when the skin was intact (RMS errors 24–81% peak forces), decreased considerably after skin removal (RMS errors 10–33% peak forces). The fiberoptic transducer is a useful tool for measurement of tendon forces in situ under natural loading conditions when skin can be removed, but caution should be exercised during in vivo use of this technique or under circumstances where skin is in contact with the fiberoptic cable at the insertion and exit sites.

Harmonic and intermodulation performance of the differential fiber-optic transducer

Analytical expressions are obtained for predicting the harmonic and intermodulation performance of the differential fiber-optic transducer excited by a multisinusoidal signal. These expressions are in terms of the ordinary Bessel functions with arguments dependent on the displacement of the transducer and its physical dimensions.

Novel optical fiber refractometric transducer employing hemispherical detection element

We present the results of a theoretical numerical analysis of a novel fiber optic refractometric transducer. It consists of a hemispherical glass detection element and a pair of the multimode optical fibers attached symmetrically to the element's flat equatorial plane. The internal reflection of light from the element's spherical surface is sensitive to the refractive index of the surrounding medium. We exploit several internal reflections in series and the focusing of the beam by the element's spherical surface to achieve enhanced sensitivity to the refractive index of the surrounding medium and reduced intrinsic optical loss in the transducer. We present the data on the effect of transducer's parameters on its transmission function. We show that the transducer can operate in a relatively wide range of the refractive index of the surrounding medium (we show this for the interval n = 1.0 to n = 1.45). We also present experimental data confirming our theoretical results.

Direct Measurement of Intratracheal Pressure in Pediatric Respiratory Monitoring

We describe a method based on a Fabry-Perot interferometer at the tip of an optic fiber with a diameter of 0.25 mm for direct measurement of tracheal pressure in pediatric respiratory monitoring. The response time of the pressure transducer and its influence on the resistance of pediatric endotracheal tubes (internal diameter, 2.5 to 5 mm) during constant and dynamic flow at different ventilator settings in a lung model were measured. The transducer was positioned at -1.5 (inside), 0, and +1.5 cm (outside) relative to the tip of the endotracheal tube and compared with a reference pressure inside the trachea. The clinical application of the transducer was tested in five pediatric patients. The response time of the transducer was 1.3 ms. The influence of the fiberoptic transducer on tube resistance was negligible during constant flow in inspiratory and expiratory directions for all endotracheal tubes tested. There was no difference in pressure measurements with the transducer positioned at or 1.5 cm below or above the tip of the endotracheal tube during dynamic measurements. During clinical circumstances insertion of the fiberoptic transducer was easy, recordings were stable, and the safety of the patient was not jeopardized. The fiberoptic transducer provided a reliable and promising way of monitoring tracheal pressure in intubated pediatric patients. The presence of the probe did not interfere with either pressure-flow relationship or patient care and safety. The technique is proposed for monitoring of respiratory mechanics and calculation of changes in tube resistance caused by kinking and secretions.

Intracranial pressure monitoring in two district general hospital ICUs

There is a growing consensus that, in selected patients, intracranial pressure (ICP) monitoring is an appropriate intervention in district general hospitals. It improves outcome in patients with traumatic brain injury [1] and is safe [2]. In the Southwest region two district general hospitals without on-site neurosurgical facilities have been inserting Camino- fibreoptic transducers in their ICUs since 1997. I conducted a retrospective case note audit of ICP monitored patients at the two centres. Fifty-one patients had monitors inserted between 6 October 1997 and 28 February 2001. Data were collected on: sex, age, initial Glasgow coma score (GCS), diagnosis, duration of ICP monitoring and incidence and nature of complications. Sixty-nine percent of patients were male, with a median age of 29 (range 1-71 years). Median GCS was 6 and 76% had an initial GCS of 8 or less. The most common indication for ICP monitoring was traumatic brain injury (72%). Other diagnoses were anoxic coma (12%), meningitis (8%), subarachnoid haemorrhage (4%), intracerebral bleed (2%) and encephalitis (2%). Median duration of monitoring was 3 days. Only two patients were monitored for more than 5 days; both these patients received two monitors. The complication rate was low. One (2%) patient had a minor scalp haemorrhage. One (2%) patient had a small intracerebral haemorrhage, detected as an incidental finding on CT scan; it had no clinical sequelae. One (2%) monitor developed a fault and had to be resited. No infectious complications were seen. The data from this audit adds to the weight of evidence that ICP monitoring in selected patient groups is safe in district general hospitals.

Comparison of microtransducer and fiberoptic catheters for urodynamic studies

OBJECTIVE: To assess the validity and reproducibility of a fiberoptic transducer urodynamic catheter for urethral closure pressure profiles and leak point pressure determination, using a microtransducer catheter as the standard. METHODS: Ninety women without significant pelvic organ prolapse underwent urodynamic evaluations with both fiberoptic and microtransducer catheters. Maximal urethral closure pressures and “leak point pressures” were repeatedly measured by the two catheters and statistically compared. The order of catheter use was randomized. RESULTS: Significantly lower mean maximal urethral closure pressures were recorded by the fiberoptic system than by the microtransducer system (28.9 cmH 2O ± 17.3 versus 43.2 cmH 2O ± 24.9, P < .001). The fiberoptic catheter predicted microtransducer values for maximum urethral closure pressure only within a range of 27 cmH 2O. Mean “leak point pressure” recorded by the fiberoptic catheters (66.9 cmH 2O ± 2.9) was not significantly different than that recorded by the microtransducer catheters (66.4 cmH 2O ± 2.9, P = .97). CONCLUSION: There is a significant difference between maximum urethral closure pressure values recorded by the microtransducer and fiberoptic catheter systems. No significant difference was found between the two systems in measurement of Valsalva “leak point pressure.”

Optical fibre transducer

Server virtualisation offers the promise of delivering irresistible benefits, including the consolidation of several autonomous servers into a single virtualised environment, the ability to scale the performance of servers as the business grows, the flexibility to quickly adapt to changing business needs and the capability to deliver automation that will keep applications running at peak performance. However, virtualising the server infrastructure is only a small component of deploying an efficient and cost effective datacentre.Many organisations have adopted server virtualisation because of the business benefits it offers. However, key areas of the next-generation datacentre have been overlooked, specifically in the area of network security infrastructure.In order to realise the full potential of the virtualised server architecture, the supporting infrastructure must deliver the same consolidation, scale, adaptability and automation benefits. Transitioning to a virtualised security infrastructure in co-ordination with virtualised servers can properly align the supporting security, explains Brian Robertson of Crossbeam Systems.

Measuring Strain Using Optical Fibres

Abstract: Optical fibres have emerged as versatile strain transducers. They can function as direct but topologically simple replacements for a range of strain gauges or can implement new measurements in distributed and integrating formats. Like all strain measurement techniques the properties of the transducer dictate its suitability for specific applications. In the case of optical fibres some of these applications are entirely new and in particular facilitate the techniques of “smart structures” fabricated from new advanced materials. This paper presents an overview of the principal approaches to optical fibre strain measurement and endeavours to set these into an applications context. In particular we shall highlight some of the more novel applications which are enabled through the use of fibre optic strain transducers.

Optical fiber bioluminescent whole-cell microbial biosensors to genotoxicants

Conservation of water resources calls for ever stricter regulatory measures and better monitoring systems. Whole-cell bacterial sensors have been genetically engineered to react to target toxicants by the induction of a selected promoter and the subsequent production of bioluminescent light through a recombinant lux reporter. In order to create a one-step assay, we have designed a new, self-contained, disposable optical fiber sensor module and a customized photodetector system that integrates these microorganisms. A photon-counting photomultiplier tube-based instrument was constructed. Optical fiber tip cores were covered with adlayer films consisting of calcium alginate containing bioluminescent bacterial sensors of genotoxicants. Multiplying these steps thickened the adlayer in increments, increasing the number of bacterial reporters attached to the optical fiber transducer. These whole cell optrodes are responsive to external traces of DNA damaging agents such as mitomycin C. Light production was shown to be dose-dependent and proportional to the number of bacterial layers.

The Dominant Role of Increased Intrasellar Pressure in the Pathogenesis of Hypopituitarism, Hyperprolactinemia, and Headaches in Patients with Pituitary Adenomas*

Mild hyperprolactinemia frequently accompanies the hypopituitarism seen in patients with pituitary macroadenomas that do not secrete PRL. Recent data suggested that the hypopituitarism and mild hyperprolactinemia in this setting are largely due to compression of pituitary stalk and portal vessels. Headaches (HAs) are frequently seen in patients with large adenomas and at times in those with microadenomas. Because the walls of the sella turcica are relatively rigid, we postulate that tumor growth within the sella increases intrasellar pressure (ISP), which in turn impairs portal blood flow, resulting in mild hyperprolactinemia and hypopituitarism. We also postulate that increased mean ISP (MISP) contributes to the development of HAs. Normal MISP is not known but is unlikely to exceed normal intracranial pressure of less than 10-15 mm Hg. We determined MISP in 49 patients who had transsphenoidal surgery for pituitary adenomas. MISP was measured using a commonly available intracranial monitoring kit where a fiberoptic transducer was inserted through a 2-mm dural incision at the time of adenomectomy. Patients with deficient FSH, LH, ACTH, or TSH secretion were considered hypopituitary. Data on serum PRL levels were included for analysis only in patients whose adenomas had negative immunostaining for the hormone. MISP measurements ranged from 7-56 mm Hg, with a mean (+/-SD) of 28.8 +/- 13.5 and a median of 26 mm Hg. The pressure measurements were higher in patients with hypopituitarism than in those with normal pituitary function (P = 4.6013 x 10(-6)). Patients presenting with HAs had higher MISP than those who did not (P = 5.44 x 10(-7)), regardless of their pituitary function or tumor sizes. PRL levels correlated positively with MISP values (r = 0.715, P < 0.0001). Tumor size did not correlate with MISP or PRL levels. The findings of increased MISP in hypopituitary patients and the documented correlation with PRL levels, suggest that ISP is a major mechanism involved in the pathogenesis of hypopituitarism and hyperprolactinemia. Similarly, the increased MISP in patients with HAs, irrespective of tumor size or pituitary function, suggest that increased ISP is a major mechanism involved in the pathogenesis of this symptom. The data support the hypothesis that in patients with pituitary adenomas increased ISP is a major mechanism contributing to the development of hyperprolactinemia, hypopituitarism, and HAs. Increased ISP in these patients leads to compression of the portal vessels and the associated interruption of the delivery of hypothalamic hormones to the anterior pituitary. This would explain the reversibility of pituitary function observed in most patients after adenomectomy. However, increased ISP may also lead to decreased blood supply, resulting in ischemic necrosis in some regions of the pituitary. The latter could limit potential recovery of pituitary function after adenomectomy.

On-Line Monitoring of Tool Wear and Control of Dimensional Inaccuracy in Turning

The present work deals with on-line monitoring of tool wear and control of workpiece diameter so as to avoid the formation of taper in the machined job. A noncontact, displacement optical fiber transducer is developed to monitor the tool wear indirectly by constantly monitoring the change in the workpiece diameter due to the tool wear. The results show that the dimensional inaccuracy can be maintained below 0.03 mm using the developed system.

Aerobiological pathogen detection by evanescent wave fibre optic sensor

An evanescent field fibre optic sensor was employed for detecting and monitoring aerobiological pathogen contamination in hospital environment. Measurements of methicillin-resistant Staphylococcus aureus (MRSA) and Streptococcus pneumoniae colonies were detected in 6 and 13 h, respectively, faster than those obtained by means of conventional techniques. All of the bacteria growth phases were clearly time resolved by means of the optical sensor. The 0.33 cm2 sensitive surface area fibre optic transducer also exhibited reproducibility, was of easy construction and low cost, which greatly enhances its potential and usefulness.

Overnight shunt pressure monitoring in children.

We audited the value of overnight shunt pressure monitoring in 17 children with symptoms of possible shunt dysfunction but no other supportive evidence. The shunt was accessed by a 25G butterfly connected to a disposable arterial pressure monitor positioned on the ipsilateral shoulder whose output was recorded continuously, while noting posture, sleep state and symptoms. Initially traces were analysed only for the portion spent both asleep and supine or prone. Six showed pressure peaks while asleep: of these four underwent shunt revision with remission of their symptoms and two resolved spontaneously, one with a simultaneous resolution of a peritoneal CSF collection, but the other had a recurrence of symptoms after six months. Two more subsequently shown to have blocked shunts had normal traces while asleep but abnormal pressure peaks when awake and upright. Two showed pressure troughs: one responded to insertion of an antisyphon device and one resolved spontaneously. Five had normal traces while asleep and awake: symptoms resolved in three and persisted in two in whom later prolonged extradural monitoring with a fibre-optic transducer was also normal. Studies failed in two. We conclude that prolonged overnight shunt pressure monitoring with this technique is useful in diagnosing shunt dysfunction and that abnormalities detected while awake and upright are as significant as those detected asleep and supine or prone.

A differential fiber-optic transducer for hydrostatic pressure measurement

A fiber-optic linear displacement sensor is developed to measure radial deformations in a free active element bulk-modulus transducer under high hydrostatic pressure. The response of the sensor was found to be practically linear within the range of 1000 bar and a 1.5% accuracy has been confirmed.