Fiber Optic Transducer Research Articles

Neural-network-based method of calibration and measurand reconstruction for a high-pressure measuring system

The problem of applying the neural networks for static calibration of measuring systems and for measurand reconstruction is addressed. A multilayered neural network based method for the static calibration of this system is proposed. The functioning of the calibrated measuring system is based on three fiber-optic transducers whose static characteristics are nonmonotonic and significantly influenced by temperature. The applicability of the proposed calibration method is demonstrated in the case under consideration using synthetic and real data. The neural network is designed and implemented in a general purpose microcontroller. In comparison with the spline-based method of calibration, for the same reference data, the proposed method allows obtention of a better quality of calibration and, most important, when calibrated, the multilayered neural network does not require the measurement of temperature for pressure reconstruction.

Dynamic pressure sensing with a fiber-optic polarimetric pressure transducer with two-wavelength passive quadrature readout

We describe the combination of a polarimetric pressure sensor with a two-wavelength passive quadrature demodulation system allowing for dynamic pressure sensing in the 10-MPa range with unambiguous fringe counting. Furthermore, continuous phase measurement with the arctan method applied to the quadrature interference signals after automatic offset subtraction is demonstrated for the first time, to our knowledge. A single low-coherent superluminescent diode is used as a light source, and a polarizing beam splitter in combination with two adjustable interference filters of slightly different central wavelengths serves for the creation of the quadrature signals. Results of initial experiments with 60-ms pressure relaxation-time constants with the fringe-counting technique demonstrate the performance that was predicted theoretically. The measured pressure sensitivity exhibits excellent agreement with the previous research of Bock and Urbanczyk [IEEE Trans. Instrum. Meas. 44, 694-697 (1995)] using a polarimetric readout. The fringe-contrast variation and the measurement range obtained experimentally show the fiber dispersion to influence dephasing (deviation from quadrature) and visibility decrease significantly with increasing pressure.

Comparison of Surface Texture Measurement by Stylus and Fiber Optic Transducers

Abstract Signals obtained from a fiber optic transducer with an optical extender used to scan surfaces of varying texture been examined through analysis of their statistical functions, and compared with the signals obtained from a conventional contact profilometer. The amplitude/time and autocorrelation functions, probability density, and power spectra analyzed to assess the potential of technology where contact methods are impossible, such as the in-process monitoring of grinding wheel wear.

Limitations on Threshold Sensitivity and Measurement Errors in Pulsed Optical Fiber Accelerometers

Estimation of the ultimate metrological performance of precision digital accelerometers with pulsed optical fiber transducer carried out in [1] was based on an idealized model in which the authors deliberately neglected a number of factors that restrict performance. In this paper, we consider the effect of the natural limitations of threshold sensitivity and of the minimally attainable acceleration measurement errors that are due to the effect of temperature on the modulator sensitive element of the optical fiber transducer and also to the instability of the period of revolution of the modulator which is a real self-oscillating system with finite quality factor. In thermal equilibrium, the atoms of the modulator are in chaotic oscillatory motion. Assuming that the modulator is an ensemble of atoms described by statistical laws, one can consider its average thermal energy whose fluctuations are added to the total mechanical energy. Starting from the equipartition law [2], we assume that the number of degrees of freedom is i = 2 (kinetic and potential energy). According to [2], the uncertainty of the total energy of the sensitive element of the modulator is taken to be kΘ (where k is the Boltzmann constant and Θ is absolute temperature); this will be seen to determine the corresponding degree of instability of the oscillations. Let us estimate it.

A clinical evaluation of the Codman MicroSensor for intracranial pressure monitoring

The strain-gauge Codman MicroSensor intracranial pressure (ICP) transducer has shown consistently good laboratory performance. To assess the practical performance of the system in patients following acute brain injury, 10 patients were fitted with a MicroSensor and a second ICP monitor. In five cases this was a fibre-optic transducer and in five cases an intraventricular fluid-filled device. Paired ICP values were recorded every 5 min. ICP values ranged from 0 to 31 mmHg. Altman-Bland plots showed that individual readings could differ by as much as 9 mmHg. Further analysis showed that much of this disagreement could be explained by a constant offset on each occasion. Comparison traces of ICP in individual patients show high agreement in timing and size of changes. The unexplained constant offset leads to uncertainty about the true ICP. Treatment decisions are often based upon absolute levels of ICP and patient care may therefore differ depending upon the monitor used.

A Gray-code-based fiber optic liquid level transducer

A level transducer based on a six-fiber sensing element is proposed. A 1 m full-scale, 4 mm resolution prototype was realized and tested. The adopted hardware and software strategies ensure high static and dynamic performance, and good reliability, as confirmed by the experimental tests carried out on fuel liquids. The possibility of remote control and low cost suggests suitability for many applications.

MANAGEMENT OF INCREASED INTRACRANIAL PRESSURE

BACKGROUND- Increased intracranial pressure (ICP) is a pathological state common to a variety of serious neurological illnesses, all of which are characterized by the addition of volume to the intracranial vault. Hence, all ICP therapies (e.g., ventricular drainage, hyperventilation, mannitol) are directed toward reducing intracranial volume. REVIEW SUMMARY- Elevated ICP can lead to brain damage or death by two principle mechanisms: 1) global hypoxic-ischemic injury, which results from reduction of cerebral perfusion pressure (CPP) and cerebral blood flow; and 2) mechanical distortion, compression, and herniation of brain tissue, which results from mass effect associated with compartmentalized ICP gradients. In unmonitored patients with acute neurologic deterioration, head elevation, hyperventilation, and mannitol (1 g/kg) can lower ICP within minutes. Fluid-coupled ventricular catheters and intraparenchymal fiberoptic transducers (i.e., Camino system) are the most accurate and reliable devices for measuring ICP. In a monitored patient, treatment of critical ICP elevation (>20 mm Hg) should proceed in the following steps: 1) consideration of repeat CT scanning to assess the need for a definitive neurosurgical procedure; 2) intravenous sedation to attain a quiet, motionless state; 3) reduction of blood pressure if CPP is >120 mm Hg or pressor infusion if CPP is <70 mm Hg; 4) administration of mannitol; 5) moderate hyperventilation (PCO2 26 to 30 mm Hg); and 6) high-dose pentobarbital therapy. Applied moderate hypothermia (32 to 33°C) shows promise as a newer method for treating refractory ICP. CONCLUSIONS- Placement of an ICP monitor is the critical first step in effectively treating intracranial hypertension. ICP elevation is best managed using a stepwise protocol, with careful attention to sedation and CPP control before mannitol and hyperventilation are administered.

Prospective Study of Zero Drift in Fiberoptic Pressure Monitors Used in Clinical Practice

✓ One hundred and one fiberoptic pressure transducers (59 subdural and 42 ventricular) were studied in 86 patients (some in whom more than one device had been inserted). Only four complications occurred: two transient cerebrospinal fluid leaks after removal and two clinically insignificant intracerebral hematomas. No intracranial infections could be attributed to the devices. Technical problems occurred 23 times, with 11 devices ceasing to function before removal, seven becoming displaced, and five microventricular catheters failing to enter the ventricles. Zero-drift readings were obtained for 83 devices at the time of removal (median 66 hours after insertion, range 2 hours–13 days). There was a clear negative bias in the readings (median −3), with a wide range of values (−12 to +14 mm Hg; interquartile range −6 to −1) that was apparent even in the first 3 days of use. There was no important relationship between zero drift and any recorded variable. It is concluded that zero drift of fiberoptic pressure ...

P-2-143 - Evaluation of the Camino fiberoptic ICP transducer

P-2-143 - Evaluation of the Camino fiberoptic ICP transducer

Self-excited oscillations in a fiber-optic laser-collimator-microresonator system

This paper proposes and studies experimentally a design for a fiber-optic self-excited oscillator, characterized by high stability of the operating point. The design appears promising for developing fiber-optic transducers of physical quantities with a frequency output.

An automatic optical fibre feedback potometer for transpiration studies

A new automatic feedback potometer for physiological studies of water uptake by root systems is described. A dual-optical-fibre amplitude-modulating displacement transducer of improved sensitivity is employed to detect the changes in liquid level. The merits of optimal double-cut fibres, which make full use of the critical angle and improve coupling between the emitter and the receiver, have resulted in a sensor that is 64 times more responsive than the simple emitter - detector probe. Positioning the optical fibre transducer in a narrow capillary and using feedback to control the liquid level allows continuous measurement of volumes in the nanolitre range. The optical sensor used does not need re-calibration for the different salt solutions used in such studies.

The design of an optical fiber pressure transducer for use in the upper airways.

The development of an optical fiber transducer for use in biomedical applications has been presented. The design was targeted for use in the upper airways of patients with sleep disorders stemming from partial or total occlusion of the airway. The transducer's preliminary specification was suited for that of upper airway manometry: a resolution of 10 Pa over the range +/- 5 kPa, a single transducer being less than 0.94 mm in diameter. Amplitude modulated optical fiber sensors are susceptible to loss due to bending of the fiber core and cladding. The design of the transducer uses a series of three optical fibers, one emitting and two receiving, the combination of the two receiving optical fibers is used to reduce effects of light loss: a bend radius of 50 mm is typical for the insertion into the naso-pharynx. The transducer transduction element is a silicone gel coated with reflective titanium dioxide, the meniscus deforms under pressure and modulates the intensity of light reflected back into the receiving optical fibers. The main disadvantage of optical fiber pressure transducers is their susceptibility to temperature drift. Temperature in the airway rarely changes more than 17 degrees C. The frequency of breathing and the high thermal mass of the catheter means that temperature drift in this application is not significant, and will cause an insignificant error of 12 Pa. The transducer is inexpensive to produce, and may be deemed disposable: approximately $20 in material costs (using current manufacturing techniques this can be halved). The system has the added advantage of being electrically, magnetically, and chemically passive. The potential for miniaturization is limited only by the mechanical strength of the optical fibers as mechanical problems associated with fragile elastic membranes do not apply.

Sensing fatty acid binding protein with planar and fiber-optical surface plasmon resonance spectroscopy devices

The human heart-type fatty acid binding protein (H-FABP) can be used as an early heart infarction marker in clinical diagnostics because its concentration in blood plasma increases about 1.5 to 3 hours after the onset of an acute myocardial infarction. Hence, it is of main interest to determine an infarct with a fast immunosensor. Surface plasmon resonance spectroscopy (SPRS) is one of the most versatile and sensitive direct optical technologies used for biochemical sensors. The aim of this study is the development of a direct optical immunosensor for the detection of H-FABP. Two different SPRS devices have been constructed: the well-known planar configuration and a new promising fiber-optical transducer. Both transducers are compared under the same conditions with regard to the measurement of H-FABP. They show a similar response and an excellent correspondence of the calibration curves. The detection limit of H-FABP in a competitive assay is about 200 ng ml −1 in both cases.

Performance analysis of fiber-optic transducer for measuring low pressures

In this paper we present an analysis of the performance of an industrial prototype of a fiber-optic transducer for measuring low hydrostatic pressure. Panda 800 and novel elliptical-core side-hole fibers were used as highly birefringent sensing elements for two ranges of pressure: up to 2.1 MPa and up to 0.28 MPa, respectively. Metrological data presented here show that an overall accuracy of 1%, including stability, repeatability, and temperature error compensation, can be maintained over a significant range of temperatures. Leading input and output fibers using FC single-mode optical connectors allow convenient exchange of sensing heads and remote operation up to about 1 km. Using standard pressure fittings, the transducer can easily be connected to any kind of pressure chamber or vessel.

Fiber optic magnetostrictive transducers for magnetic field sensing

A number of fiber optic magnetostrictive transducers were fabricated using various metallic glass ribbons made of Co₇₀Fe₁₀B₂₀, Co₇₆Fe₄B₂₀, Co₈₀B₂₀, Ni, Fe₇₉B₁₆Si₅, and Fe₄₀Ni₃₈Mo₄B₁₈ and were characterized by a typical optical fiber Mach-Zehnder interferometer constructed by splicing the fiber transducers to the single-mode-fiber sensing arm. The ac magnetostrictive responses for the metallic glasses measured with the fiber optic sensing system show that the dc-bias field (<i>H_p</i>) for the maximum response with a Co₇₀Fe₁₀B₂₀ ribbon is ~ 0.97 Oe, that with a Ni ribbon is 23 Oe, and with a Fe₇₉B₁₆Si₅ ribbon is 5.7 Oe. A magnetostriction function describing the magnetostrictive response of the transducer was also empirically found. The measured effective magnetostrictive parameters and saturation magnetostrictions are 1.3 x 10^-7/Oe² to 7 x 10^-7/Oe² and -4.6 x 10^-6 to 5.7 x 10^-6, respectively. The optical fiber sensors exhibit minimum detectable fields <i>H</i>_min of the order of between 10^-5 Oe(rms)/√Hz and 10^-7 Oe(rms)/√Hz above 1 kHz at their respective dc-bias fields <i>H_p</i>. The <i>H</i>_min can be much further improved by reducing the level of noises that limit the phase resolution to ~ 10^-4 rad/√Hz in the interferometer.

Transducers of physical fields based on two-channel coaxial optical fibres

An analysis is made of a general basic configuration and of the transfer function of a fibre-optic transducer based on controlled coupling in a multilayer two-channel coaxial optical fibre. The influence of the structure parameters and of external factors on the errors of a sensitive element in such a transducer is considered. The results are given of an investigation of the characteristics of a number of transducers constructed in accordance with the basic configuration.

Dynamic intramuscular pressure measurement during gait

Intramuscular pressure is useful for quantifying muscle function during dynamic activities. Currently, theintegrated electromyogram (EMG) is used to indicate the timing and intensity of muscle contraction in gait.However, the relationship between EMG and muscle tension is unclear. There is a need for a reliable measure of muscle tension under dynamic conditions. This need may be filled through the measurement of intramuscular pressure.Intramuscular pressure can be measured with either fluid-filled or fiber optic transducers. The fluid-filled transducers can be used only when the limb position does not change relative to the horizontal plane. This type of transducer is not suitable for gait studies. In contrast, fiber optic transducers are not sensitive to hydrostatic artifacts and can be used effectively during gait. Current fiber optic transducers for measurement of intramuscular pressure are large (1.35-mm diameter) and thus the procedure is not typically used for clinical applications. However, a microsensor is being designed that is small (0.18-mm diameter) and will have direct clinical applications. The intramuscular pressure during walking parallels the electromyographic activity, but also accounts for passive stretch of the muscle. Interpretation of the intramuscular pressure does not require integration, which is necessary for EMG. The information gained from the measurement of intramuscular pressure can be used to treat patients who suffer from neuromuscular disorders.

Effects of medetomidine administration on intracranial pressure and cardiovascular variables of isoflurane-anesthetized dogs

SUMMARY Intracranial pressure and cardiovascular variables after iv administration of medetomidine (0.03 mg/kg of body weight) were evaluated in 6 healthy, mixed-breed dogs anesthetized with 1.3% end-tidal isoflurane concentration and mechanically ventilated to normocapnia (PaCO2, 35 to 45 mm of Hg). Baseline values were determined for intracranial pressure, heart rate, arterial blood pressure, cardiac output, mean pulmonary artery pressure, pulmonary capillary wedge pressure, central venous pressure, end-tidal CO2 tension and isoflurane concentration, arterial pH and CO2 and O2 tensions, and core body temperature. Cerebral perfusion pressure, cardiac index, systemic and pulmonary vascular resistances, plasma HCO3- concentration, and base excess were calculated. Intracranial pressure was measured, using a calibrated, fiberoptic transducer placed within the brain parenchyma and secured to the calvarium by means of a subarachnoid bolt. Cardiac output was determined by thermodilution. End-tidal CO2 tension and isoflurane concentration were determined, using an infrared gas analyzer. Administration of medetomidine did not change intracranial pressure, but was associated with significant (P &lt; 0.05) decreases in values for heart rate, cardiac index, end-tidal CO2, and HCO3- and with significant increases in systolic, mean, and diastolic pressure; pulmonary artery pressure; systemic vascular resistance; central venous pressure; and pulmonary capillary wedge pressure.

Illi intracranial pressure monitoring and fixation device. A new fixation system for intracranial pressure monitoring in children and adolescents in paediatric neurotraumatology, hydrocephalus and craniofacial surgery.

Fixation and positioning of intracranial pressure (ICP) monitoring devices in small children with very thin skull bones pose serious problems. We present a new ICP fixation device with two movable components compressing the skull bone from in- and outside. This new fixation system, designed by PD Dr. O.E. Illi and licensed by White Spot AG, Surgical Tools and Research, Baar, Switzerland, guarantees far greater stability and reliability than conventional screws or bolts. It is fully compatible with a range of fiberoptic or pneumatic transducer systems. We have applied this new device successfully in 10 patients.

An optical fiber transducer for single myofibril force measurement.

A force transducer has been developed for use in force measurement of skeletal muscle myofibrils. The transducer is suitable for measurement of passive and contractile forces in a range up to 200 micrograms, with 1 microgram resolution. It is based upon the operating principle of the deflection of an optical fiber of known compliance, sensed by the differential illumination of two phototransistors. Attractive features include ease of operation and specimen mounting, high bandwidth, adaptability for different force ranges, and simple and inexpensive construction.