Cardiovascular diseases are the main cause of death in the world and its occurrence is closely related to arterial stiffness. Arterial stiffness is commonly evaluated by analysing the arterial pulse waveform and velocity, with electromechanical pressure transducers, in superficial arteries such as carotid, radial and femoral. In order to ease the acquisition procedure and increase the patients comfort during the measurements, new optical fibre techniques have been explored to be used in the reliable detection of arterial pulse waves, due to their small size, high sensitivity, electrical isolation and immunity to electromagnetic interference. More specifically, fibre Bragg gratings (FBGs) are refractive index modulated structures engraved in the core of an optical fibre, which have a well-defined resonance wavelength that varies with the strain conditions of the medium, known as Bragg wavelength. In this work, FBGs were embedded in a commercial resin, producing films that were used to assess the arterial pulse in superficial locations such as carotid, radial and foot dorsum. The technique proved to be a promising, comfortable and trustworthy way to assess the arterial pulses, with all the optical fibre use advantages, in a non-intrusive biomedical sensing procedure. Examples of possible applications of the developed structures are smart skin structures to monitor arterial cardiovascular parameters, in a stable and reliable way, throughout daily activities or even during exams with high electromagnetic fields, such as magnetic resonance imaging.
This work consists on the design and implementation of a compact and accurate biaxial optical fiber sensor (OFS) based on two in-line fiber Bragg gratings (FBGs) for the simultaneous measurement of shear and vertical forces. The two FBGs were inscribed in the same optical fiber and placed individually in two adjacent cavities. In the calibration and performance tests, the response from the optical fiber cells was compared with the values given by a three-axial electronic force sensor. Sensitivity values obtained for the FBG1 are K1V= (14.15±0.10) pm/N (vertical force) and K1S= (-26.02±0.08) pm/N (shear force) and for the FBG2 are K2V= (7.35±0.02) pm/N and K2S= (-24.29±0.08) pm/N. The conversion of the Bragg wavelength shift, given by the optical fiber sensors, into the shear and vertical force values is also presented along with its comparison to the values retrieved by an electronic sensor, yielding to low RMSE values, which shows the high accuracy of the algorithm applied. This work stands out from the others with optical fiber by the simplicity of its structure. The proposed solution represents a compact and reliable device for simultaneous measurement of shear and vertical forces, useful in several areas, such as: incorporation into insoles for plantar pressure and shear force measurement; electronic skin technologies; smart rehabilitation robotic exoskeletons; or even biomimetic prosthesis.
Tilted fiber Bragg gratings (TFBGs) are one of the most attractive kind of optical fiber sensor technology due to their intrinsic properties. On the other hand, the acousto-optic effect is an important, fast and accurate mechanism that can be used to change and control several properties of fiber gratings in silica and polymer optical fiber. Several all-optical devices for optical communications and sensing have been successfully designed and constructed using this effect. In this work, we present the recent results regarding the production of optical sensors, through the acousto-optic effect in TFBGs. The cladding and core modes amplitude of a TFBG can be controlled by means of the power levels from acoustic wave source. Also, the cladding modes of a TFBG can be coupled back to the core mode by launching acoustic waves. Induced bands are created on the left side of the original Bragg wavelength due to phase matching to be satisfied. The refractive index (RI) is analyzed in detail when acoustic waves are turned on using saccharose solutions with different RI from 1.33 to 1.43.
In an era of unprecedented progress in technology and increase in population age, continuous and close monitoring of elder citizens and patients is becoming more of a necessity than a luxury. Contributing toward this field and enhancing the life quality of elder citizens and patients with disabilities, this work presents the design and implementation of a noninvasive platform and insole fiber Bragg grating sensors network to monitor the vertical ground reaction forces distribution induced in the foot plantar surface during gait and body center of mass displacements. The acquired measurements are a reliable indication of the accuracy and consistency of the proposed solution in monitoring and mapping the vertical forces active on the foot plantar sole, with a sensitivity up to 11.06 pm/N. The acquired measurements can be used to infer the foot structure and health condition, in addition to anomalies related to spine function and other pathologies (e.g., related to diabetes); also its application in rehabilitation robotics field can dramatically reduce the computational burden of exoskeletons’ control strategy. The proposed technology has the advantages of optical fiber sensing (robustness, noninvasiveness, accuracy, and electromagnetic insensitivity) to surpass all drawbacks verified in traditionally used sensing systems (fragility, instability, and inconsistent feedback).
The central pressure monitoring is considered a new key factor in hypertension assessment and cardiovascular prevention. In this work, it is presented the central arterial systolic pressure assessment with an intensity based POF sensor. The device was tested in four subjects, and stable pulse waves were obtained, allowing the calculation of the central pressure for all the subjects. The results shown that the sensor performs reliably, being a simple and low-cost solution to the intended application.
Fiber Bragg grating sensors were attached to the surface of a rechargeable lithium battery in order to monitor its thermal and strain fluctuations through charge and different discharge C rates. During the discharge process above 1C, it were observed, a temperature and strain fluctuations of a 4.12 ± 0.67 °C and 24.64 ± 6.02 με, respectively. In the regular charge process, a temperature and strain variation of 1.03 ± 0.67 °C and 15.86 ± 6.02 με, were detected.
In this paper are presented three optical fiber sensors for carotid pulse wave acquisition. Two probes are based on silica fiber Bragg gratings and the other is intensity-based using plastic optical fibers. Starting with feasibility tests of such measurements with FBG sensors, the sensors evolution was towards a simple method with a lower cost sensor. The sensors were full characterized and some human tests were performed. The results showed a fair compromise between easiness of applicability and technician training, as well as good pressure wave acquisition performance.
Cardiovascular diseases are one of the primary causes of death in the world. Hemodynamics is the study of the blood propagation and the physics aspects concerned to it, relating pressure, flow and resistance. One of the most important topics on hemodynamics is the evaluation of arterial wave reflections. Recently this physical parameter of the pressure wave propagation through the arterial tree was considered as a novel strong risk factor for cardiovascular diseases. Arterial pressure reflections can be quantified by central pressure profile analysis. In this work we study in the trial of an optical fibre Bragg grating based sensor of assess the central pressure profile, with the goal of to achieve a superior sensitivity, with a better signal quality than electromechanical probes, measured directly in the carotid artery.
The present work addresses the need for new devices felt in the context of quality control, especially in the food industry. Due to the spectral dependence of the attenuation coefficient, a novel dual-parameter sensor for colour and refractive index was developed and tested. The sensor employs plastic optical fibres to measure the transmitted optical power in three measurement cells each with a different incident wavelength. The performance of the sensor was tested using several dyes at different concentrations and aqueous solutions of glycerine and ethanol. Results show that this technique allows the monitoring of refractive index and colour without cross-sensitivity.
The arterial stiffness evaluation is largely reported as an independent predictor of cardiovascular diseases. The central pulse waveform can provide important data about arterial health and has been studied in patients with several pathologies, such as diabetes mellitus, coronary artery disease and hypertension. The implementation and feasibility studies of a fiber Bragg grating probe for noninvasive monitoring of the carotid pulse are described based on fiber Bragg grating technology. Assessment tests were carried out in carotids of different volunteers and it was possible to detect the carotid pulse waveform in all subjects. In one of the subjects, the sensor was also tested in terms of repeatability. Although further tests will be required for clinical investigation, the first studies suggest that the developed sensor can be a valid alternative to electromechanical tonometers.
One of the early predictors of cardiovascular diseases, with growing interest, is the arterial stiffness which is typically
evaluated through the velocity and morphology of the arterial pressure wave.
In each cardiac cycle the heart generates a pressure wave which propagates through the arterial tree. Along its path, the
pressure wave interacts with the arterial walls and, consequently, the morphology of a local arterial pressure wave can be
assessed by the arterial distention movement. Due to its superficiality, proximity of the heart and high probability of
atherosclerosis development, the carotid artery has particular interest to be monitored.
In this work, the development of a non-invasive fibre Bragg grating (FBG) probe for the acquisition of the arterial
distention wave is presented. Comparing to traditional methods, optical FBG based sensors can offer many advantages,
namely, compactness, immunity to electromagnetic interference, high sensitivity, low noise and immunity to light source
intensity due to its codification in the wavelength domain.
The arterial movements induce strain on a uniform FBG, with the arterial distention pattern. The carotid pulse wave was
successful accessed in young human carotid artery, with an acquisition rate of 950 Hz, allowing a clear distinction of the
carotid pulse identification points.