Paulo Roriz

Review of fiber-optic pressure sensors for biomedical and biomechanical applications

Abstract. As optical fibers revolutionize the way data is carried in telecommunications, the same is happening in the world of sensing. Fiber-optic sensors (FOS) rely on the principle of changing the properties of light that propagate in the fiber due to the effect of a specific physical or chemical parameter. We demonstrate the potentialities of this sensing concept to assess pressure in biomedical and biomechanical applications. FOSs are introduced after an overview of conventional sensors that are being used in the field. Pointing out their limitations, particularly as minimally invasive sensors, is also the starting point to argue FOSs are an alternative or a substitution technology. Even so, this technology will be more or less effective depending on the efforts to present more affordable turnkey solutions and peer-reviewed papers reporting in vivo experiments and clinical trials.

From conventional sensors to fibre optic sensors for strain and force measurements in biomechanics applications: A review

In vivo measurement, not only in animals but also in humans, is a demanding task and is the ultimate goal in experimental biomechanics. For that purpose, measurements in vivo must be performed, under physiological conditions, to obtain a database and contribute for the development of analytical models, used to describe human biomechanics. The knowledge and control of the mechanisms involved in biomechanics will allow the optimization of the performance in different topics like in clinical procedures and rehabilitation, medical devices and sports, among others. Strain gages were first applied to bone in a live animal in 40s and in 80s for the first time were applied fibre optic sensors to perform in vivo measurements of Achilles tendon forces in man. Fibre optic sensors proven to have advantages compare to conventional sensors and a great potential for biomechanical and biomedical applications. Compared to them, they are smaller, easier to implement, minimally invasive, with lower risk of infection, highly accurate, well correlated, inexpensive and multiplexable. The aim of this review article is to give an overview about the evolution of the experimental techniques applied in biomechanics, from conventional to fibre optic sensors. In the next sections the most relevant contributions of these sensors, for strain and force in biomechanical applications, will be presented. Emphasis was given to report of in vivo experiments and clinical applications.

Fabry-Perot cavity based on silica tube for strain sensing at high temperatures

In this work, a Fabry-Perot cavity based on a new silica tube design is proposed. The tube presents a cladding with a thickness of ~14 μm and a hollow core. The presence of four small rods, of ~20 μm diameter each, placed in diametrically opposite positions ensure the mechanical stability of the tube. The cavity, formed by splicing a section of the silica tube between two sections of single mode fiber, is characterized in strain and temperature (from room temperature to 900 °C). When the sensor is exposed to high temperatures, there is a change in the response to strain. The influence of the thermal annealing is investigated in order to improve the sensing head performance.

In vivo measurement of the pressure signal in the intervertebral disc of an anesthetized sheep.

Abstract. The purpose of the present study was to measure the intradiscal pressure signal of an anesthetized sheep under spontaneous breathing. An ultra-miniature fiber optic high-pressure sensor was implanted into the nucleus pulposus of the fifth lumbar intervertebral using a dorsolateral transforaminal approach. Results suggested the periodicity of the intradiscal pressure signal was similar to the mean respiratory rate of the animal. The average resting intradiscal pressure was also calculated and compared to available data.

Evaluation of the performance of orthodontic devices using FBG sensors

Cross-bite, as a malocclusion effect, is defined as a transversal changing of the upper dental arch, in relation to the lower arch, and may be classified as skeletal, dental or functional. As a consequence, the expansion of maxilla is an effective clinical treatment used to correct transversal maxillary discrepancy. The maxillary expansion is an ancient method used in orthodontics, for the correction of the maxillary athresia with posterior crossbite, through the opening of the midpalatal suture (disjunction), using orthodontic- orthopaedic devices. Same controversial discussion arises among the clinicians, about the effects of each orthodontic devices as also about the technique to be employed. The objective of this study was to compare the strain field induced by two different orthodontic devices, named disjunctor with and without a connecting bar, in an acrylic model jaw, using fiber Bragg grating sensors to measure the strain patterns. The orthodontic device disjunctor with the bar, in general, transmits higher forces and strain to teeth and maxillae, than with the disjunctor without bar. It was verified that the strain patterns were not symmetric between the left and the right sides as also between the posterior and anterior regions of the maxillae. For the two devices is also found that in addition a displacement in the horizontal plane, particularly in posterior teeth, also occurs a rotation corresponding to a vestibularization of the posterior teeth and their alveolar processes.

Match-running performance of young soccer players in different game formats

ABSTRACT Present study aimed to analyse the effect of game format, age-group, and playing position on match-running variables of soccer players (age ranging from 6.94 ± 0.7 to 13.46 ± 0.5 years; height ranging from 125.36 ± 6.04 to 159.16 ± 7.78 cm; weight ranging from 27.16 ± 5.75 to 49.89 ± 8.89 kgf). Match-running variables were assessed using global positioning system technology. Results suggest that game formats, which include more players have a significant effect on match-running variables than those having fewer players (p < 0.001). Moreover, oldest age-groups covered significantly higher distances in all categories than younger groups, total distance (TD): η2 = 0.32, p < 0.001; low-intensity running (LIR): η2 = 0.09, p < 0.001; high-intensity running (HIR): η2 = 0.25, p < 0.001; very high-intensity running (VHIR): η2 = 0.34, p < 0.001; very high-intensity activity (VHIA): η2 = 0.42, p < 0.001; and sprinting (SP): η2 = 0.41, p < 0.001). Match-running variables also differ among playing positions. Defenders covered lowest TD and HIR in all age-groups; midfielders covered highest TD and LIR in all age-groups (p < 0.001); forwards covered highest VHIR, VHIA, and SP in U14 age-group. Defenders covered lowest TD, LIR, HIR, and VHIR; midfielders covered highest TD and HIR regardless game format (p < 0.001); forwards covered highest VHIR, VHIA, and SP in 11v11 format (p < 0.001). These findings can provide an opportunity for coaches to maximise the efficiency of their training sessions.

Effects of pitch surface and playing position on external load activity profiles and technical demands of young soccer players in match play

Abstract This study aims to analyse the effect of different pitch surface, i.e. artificial turf (AT), natural turf (NT) and dirt field (DF) on running activity and technical demands of young soccer players (age:13.4 ± 0.5yrs; height: 161.82 ± 7.52cm; body mass; 50.79 ± 7.22kg; and playing experience: 3.5 ± 1.4 yrs). Running activity data were collected using GPS units which allowed the calculation time–motion variables. Technical performance data were registered filming soccer matches. Analysis of variance (ANOVA) with repeated measures was employed to assess differences among variables. Total distance covered; distance for low-intensity running and very high-intensity running were higher on AT than NT (TD: η2 = .09, p = .007); (LIR: η2 = .062, p ≤ .05); and (VHIR: η2 = .05, p ≤ .05), respectively. Significant differences were identified between pitch surfaces on successful passing (η2 = .052, p = .051); unsuccessful passing (η2 = .155, p < .001); and interceptions (η2 = .1087, p < .001). Results suggest that pitch surface influences running activity and technical actions of young players. This information contributes to understand the different demands imposed in each pitch surface and, provides to the coaches the opportunity to implement strategies that could optimise players’ performance.

Centre of mass determination based on an optical weighing machine using fiber Bragg gratings

The purpose of the present work was to construct a weighing machine based on fiber Bragg gratings (FBGs) for the location of the 2D coordinates of the center of gravity (COG) of objects with complex geometry and density distribution. The apparatus consisted of a rigid equilateral triangular platform mounted on three supports at its vertices, two of them having cantilevers instrumented with FBGs. As an example, two femur bone models, one with and one without a hip stem prosthesis, are used to discuss the changing of the COM caused by the implementation of the prosthesis.

A fiber optic buckle transducer for measurement of in vitro tendon strain

The purpose of the present study is to present a prototype of a fiber optic based buckle transducer suitable for measuring strain caused by stretching of a tendon. The device has an E-shape and its central arm is instrumented with a fiber Bragg grating (FBG) sensor. The tendon adjusts to the E-form in a fashion that when it is stretched the central arm bends causing a shift of the Bragg’s wavelength (λB) that is proportional to the amount of strain. This prototype is presented as an alternative to conventional strain gauge (SG) buckle transducers.

Measuring strain at extreme temperatures with a Fabry-Perot optical fiber sensor

In this work, a Fabry-Perot optical fiber sensor for the measurement of strain at extreme temperatures is proposed. The cavity is formed by splicing a short section of a silica tube between two sections of single mode fiber. The tube, with a cladding ~14 μm thick and a hollow core, presents four small rods, of ~20 μm in diameter each, positioned in in diametrically opposite positions. This design ensures higher mechanical stability of the tube. Strain measurements are performed over a wide range of temperatures, until 900 °C. Some of the annealing effects are addressed in this study.