A.T. Augousti

Construction and calibration of a new design of fiber optic respiratory plethysmograph (FORP)

The Fiber Optic Respiratory Plethysmograph (FORP) is a non-invasive instrument for respiratory and heart monitoring in humans, based on the design of the Respiratory Inductive Plethysmograph (RIP. The FORP uses two sensors at thoracic and abdominal levels that measure circumferences rather than the cross sectional areas measured by the RIP. Each sensor is made of a specifically looped optical fiber that responds to elongation with variation in light transmission, via the macrobending loss effect. The design and construction of the original version of the FORP has been reported previously 1. This paper presents the results of a new figure-of-eight construction for the fiber loops. The resulting system shows greater signal range, increased linearity and less hysteresis than former constructions. Results are presented detailing the calibration of the respiratory measurements against a spirometer using a range of calibration protocols, one based on isovolume breathing and others on a Least Mean Square (LMS) fit. Additional improvements to signal processing and the increased sensitivity of the new design now make it practicable to detect torso motion arising from cardiac activity. This paper also presents results showing the simultaneous monitoring of respiratory and cardiac signals, using only the FORP transducers.

Integral equations and the pressure at the liquid-solid interface

The relationship between the pressure in a fluid and the density-functional which controls the density profile of a fluid confined between two walls is examined. As a result, the conditions which must be fulfilled by an approximate density functional to yield a bulk pressure P, a normal pressure, P W at the interface between a hard wall and the fluid, and a fluid density, ρW, adjacent to the wall which satisfy the exact relations P W=P=k B T ρW, are established. The density-functional which yields the HNC closure for a hard-sphere fluid near a hard wall is modified so that the modified functional yields the Carnahan-Starling bulk pressure and hence fulfils the necessary conditions. The density profile to which this gives rise is compared with the results of computer simulation for various bulk densities when the fluid is bounded by two hard walls separated by a distance equal to 8 diameters of the hard sphere. The agreement is found to be very good even at a bulk reduced density of 0·91.

Bragg grating-based fiber-optic laser probe for temperature sensing

A novel Bragg grating-based fiber-optic laser probe for temperature sensing using erbium-doped fiber as the active gain medium is reported. The combination of a chirped grating and a normal grating was used to form the laser cavity to achieve temperature-tunable laser action over a wide measurement range. The laser probe used a metal sheath to enhance its mechanical strength and contain the normal grating at the sensing point. The temperature dependence of the wavelength of the laser probe gives a sensitivity of 12.01 pm//spl deg/C and a repeatability of /spl plusmn/1.7/spl deg/C from room temperature to 300/spl deg/C.

Improved fibre optic respiratory monitoring using a figure-of-eight coil

The macro-bending loss effect in optical fibres has been used to redevelop a sensor for the measurement of thoracic and abdominal circumferences in non-invasive respiratory monitoring. The new sensor uses a novel figure-of-eight loop configuration, which results in increased linearity of response, less mechanical resistance and hysteresis, as well as other benefits. The performance of the new sensor as applied to respiratory monitoring is examined, and indicates a higher resolution and sensitivity than the old. This enhanced performance enables measurement of respiratory and cardiac function using the same transducing fibre.

The capacitive drop tensiometer: a novel multianalysing technique for measuring the properties of liquids

A new instrumental method for measuring the physical properties of a liquid has been developed. The instrument, called a capacitive drop tensiometer (CDT), is based on the drop volume principle in combination with a capacitive transducer. A delivery head with a specialized wetting design was constructed for forming drops. The capacitive transducer uses the delivery head as one of its plates and a cylindrical ring plate, which surrounds the delivery head and the space occupied by the drop that is formed, as another. Excellent linearity is achieved by optimizing the design, with an accuracy of drop volume measurement of approximately . The system is suitable for measuring both drops in equilibrium and those in the process of growing. Its capability of real-time measurement makes it particularly useful for volatile liquids, in which instance the measurement of drop volume using a flowmeter or a pump is no longer reliable. The CDT can also be used to determine concentration. It was found that the concentration curve is linear for aqueous glycerol solutions although not so for aqueous ethanol solutions. The CDTs ability to measure surface tension was also explored and experimental results are presented here.

A laser-pumped temperature sensor using the fluorescent decay time of alexandrite

In this work a simple intensity-independent fiber-optic temperature sensor using alexandrite crystal was constructed. The sensor uses the change in the characteristics of the fluorescence of the material to sense the parameter required and operates using light from an electrooptically modulated He-Ne laser at 633 nm. Microprocessor control and signal processing is used to achieve an accuracy of \sim \pm1\deg C with a 3-s response.

Quantitative drop spectroscopy using the drop analyser: theoretical and experimental approach for microvolume applications of non-turbid solutions

The drop analyser, also termed the tensiograph, is an optical fibre-based instrument system for monitoring liquids. A comprehensive assessment of the drop analyser used as a UV–visible spectrophotometer has been undertaken employing both experimental and theoretical studies. A model of the tensiograph signal (tensiotrace) has been developed using a ray-tracing approach to accurately predict the form of the tensiotrace as an aid to drop spectroscopy. An analytical equation is derived for quantitative drop spectroscopy and the form of the equation has been experimentally tested. The equation applies to both the case of a growing drop and the situation in which the drop volume is held stationary. Measurements on both stationary and moving drops are of practical value. Modelling has been used to compute the average path length of the coupled light in the drop to give a result that compares favourably with values obtained from experimental measurements. An optimized method has been identified for quantitative drop spectroscopy measurements. Results from UV–visible studies on both pollutants in water and pharmaceuticals demonstrate the utility of this approach. Two key matters relating to the practicalities of drop spectroscopy are then discussed. Some experimental studies have been made to ascertain the practical limit in analyte concentration above which variations in transmitted light from the drop shape variations result. Here, tabulated information on a representative range of liquid types has been provided as a guide to optimized spectroscopic drop analysis. Secondly, the handling of micro-volume samples is discussed. The paper concludes with a brief evaluation of the usefulness of this drop spectroscopy approach, but specifically points to the importance of drop spectroscopy for nanoscience applications.

A theoretical study of the robustness of the isovolume calibration method for a two-compartment model of breathing, based on an analysis of the connected cylinders model

The use of the isovolume manoeuvre method as a calibration technique for respiratory monitoring instrumentation that detects the movement of the ribcage and the abdominal wall is analysed based on a model of two connected cylinders whose radii and heights may vary, and evidence is presented which suggests that this calibration method is robust in most circumstances. Some possible functional forms relating the variations in cylinder radius and height are examined, and methods for obtaining calibration constants based on these functional forms, purely from measurements of variations in the cylinder radius, are presented.

Evaluation of cardiac monitoring using fiber optic plethysmography.

A fiber optic plethysmograph (FOP) has been redesigned and used to monitor cardiac activity in real time during apnoea. The device was tested using four healthy subjects aged between 23 and 31, and it is concluded that the device performs reliably. Advanced algorithms have been developed and implemented to perform the cardiac signal extraction. A strong correlation is noted between the signals derived using the FOP and the respiratory inductive plethysmograph (RIP) when the latter has also been applied to monitor cardiac activity. The approach developed for interpreting thoracocardiograms (TCGs) and abdominocardiograms (ACGs) derived from the RIP is therefore directly applicable to the interpretation of the corresponding FOP signals. The prospect of using the FOP system for real-time gating in a magnetic resonance (MR) scanner environment is discussed.

A wide temperature tunable fibre laser using a chirped grating and a type IIA fibre Bragg grating

A fibre laser sensor has been developed to operate over a wide temperature range from room temperature to 440 °C, where the laser cavity has been formed using a combination of a chirped grating and a type IIA fibre Bragg grating (FBG), enclosing a length of erbium doped fibre as the active gain medium. A FBG stabilized 1480 nm laser diode was employed as the pump source to achieve laser oscillation associated with the type IIA Bragg grating wavelength on the wavelength band around 1550 nm. The broadband-chirped grating was used as one of the cavity end reflectors to achieve temperature-tunable laser action for sensing applications over a wide range. The sensitivity of the sensor was found to be 13.94 pm °C−1 with a root mean square error of 8.85 °C. The primary advantage of this laser-based sensor over passive optical fibre sensors is the significant improvement in both the signal-to-noise ratio and the narrow linewidth of the laser signal, making it especially well suited to multiplexing situations.