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Relative Humidity (RH) sensors based on Fiber Bragg Grating (FBG) technology have been fabricated by polymer functionalization, using hygroscopic material, namely agar. The sensor is specifically intended to monitor moisture in stones of cultural heritage buildings and monuments, in particular to be positioned under hydrophobic coatings used for protecting stones from absorption of water and dissolved chemicals, thus providing early warning of coating deterioration by RH monitoring. The performance of the prototype was first tested exposing the sensors in controlled environment and then assessed for the application simulating “in field” operating conditions, with sensors installed on marble and travertine tiles. Results show that the proposed sensor is able to monitor the presence of moisture inside the stones. © 2018 Elsevier Ltd

Hyperthermal techniques are spreading as an alternative to conventional surgery for cancer removal. A real-time temperature feedback can be used to adjust the treatment settings, in order to improve the clinical outcomes. In this paper, we experimentally assessed the feasibility for distributed temperature monitoring of a custom probe, which consists of a needle embedding six fiber Bragg gratings (FBGs). Since FBGs are also sensitive to strain, we focused on the analysis of the measurement error (artifact) caused by respiratory movements. We assessed the artifact both on ex vivo pig liver and lung (by mimicking the movement of these organs caused by respiration) and on in vivo trial on pig liver. Lastly, we proposed an algorithm to detect and minimize the artifact during ex vivo liver laser ablation. During both ex vivo and in vivo trials, the probe insertion within the organ was easy and safe. The artifact was significant (up to 3 °C), but the correction algorithm allows minimizing the error. The main advantages of the proposed probe are: 1) spatially resolved temperature monitoring (in six points of the tissue by inserting a single needle) and 2) the needle is magnetic resonance (MR)-compatible, hence can be used during MR-guided procedure. Even if the model is close to humans, further trials are required to investigate the feasibility of the probe for clinical applications.

Continuous respiratory monitoring is important to assess adequate ventilation. We present a fiber optic-based smart textile for respiratory monitoring able to work during Magnetic Resonance (MR) examinations. The system is based on the conversion of chest wall movements into strain of two fiber Bragg grating (FBG) sensors, placed on the upper thorax (UT). FBGs are glued on the textile by an adhesive silicon rubber. To increase the system sensitivity, the FBGs positioning was led by preliminary experiments performed using an optoelectronic system: FBGs placed on the chest surface experienced the largest strain during breathing. System performances, in terms of respiratory period (TR), duration of inspiratory (TI) and expiratory (TE) phases, as well as left and right UT volumes, were assessed on four healthy volunteers. The comparison of results obtained by the proposed system and an optoelectronic plethysmography highlights the high accuracy in the estimation of TR, TI, and TE: Bland-Altman analysis shows mean of difference values lower than 0.045 s, 0.33 s, and 0.35 s for TR, TI, and TE, respectively. The mean difference of UT volumes between the two systems is about 8.3%. The promising results foster further development of the system to allow routine use during MR examinations.Continuous respiratory monitoring is important to assess adequate ventilation. We present a fiber optic-based smart textile for respiratory monitoring able to work during Magnetic Resonance (MR) examinations. The system is based on the conversion of chest wall movements into strain of two fiber Bragg grating (FBG) sensors, placed on the upper thorax (UT). FBGs are glued on the textile by an adhesive silicon rubber. To increase the system sensitivity, the FBGs positioning was led by preliminary experiments performed using an optoelectronic system: FBGs placed on the chest surface experienced the largest strain during breathing. System performances, in terms of respiratory period (TR), duration of inspiratory (TI) and expiratory (TE) phases, as well as left and right UT volumes, were assessed on four healthy volunteers. The comparison of results obtained by the proposed system and an optoelectronic plethysmography highlights the high accuracy in the estimation of TR, TI, and TE: Bland-Altman analysis shows mean of difference values lower than 0.045 s, 0.33 s, and 0.35 s for TR, TI, and TE, respectively. The mean difference of UT volumes between the two systems is about 8.3%. The promising results foster further development of the system to allow routine use during MR examinations.

Radiofrequency ablation (RFA) is a minimally invasive procedure used to treat tumors by means of hyperthermia, mostly through percutaneous approach. The tissue temperature plays a pivotal role in the achievement of the target volume heating, while sparing the surrounding healthy tissue from thermal damage. Several techniques for thermometry during RFA are investigated, most of them based on the use of single-point measurement system (e.g., thermocouples). The measurement of temperature map is crucial for the real-time control and fine adjustment of the treatment settings, to optimize the shape and size of the ablated volume. The recent interest about fiber optic sensors and, among them, fiber Bragg gratings (FBGs) for the monitoring of thermal effects motivated further investigation. In particular, the feature of FBGs to form an array of several elements, thus to be inscribed within the same fiber, allows the use of a single probe for the multi-points monitoring of the tissue temperature during RFA. Hence, the aim of this study is the development and characterization of a needle-like probe embedding an array of three FBGs, which was tested on pig liver during in vivo trials. The needle allows a safe and easy insertion of the fiber optic within the liver. It was inserted by ultrasound guidance into the liver, and monitored the change of tissue temperature during RFA controlled by the roll-off technique. Also the measurement error induced by breathing movements of the liver was assessed (less than 3 °C). Results encourage the use of the probe in clinical settings, as well as the improvement of some features, e.g., a higher number of FBGs for performing quasi-distributed measurement. © 2016 IEEE.

Comfortable and easy to wear smart textiles have gained popularity for continuous respiratory monitoring. Among different emerging technologies, smart textiles based on fiber optic sensors (FOSs) have several advantages, like Magnetic Resonance (MR)-compatibility and good metrological properties. In this paper we report on the development and assessment of an MR-compatible smart textiles based on FOSs for respiratory monitoring. The system consists of six fiber Bragg grating (FBG) sensors glued on the textile to monitor six compartments of the chest wall (i.e., right and left upper thorax, right and left abdominal rib cage, and right and left abdomen). This solution allows monitoring both global respiratory parameters and each compartment volume change. The system converts thoracic movements into strain measured by the FBGs. The positioning of the FBGs was optimized by experiments performed using an optoelectronic system. The feasibility of the smart textile was assessed on 6 healthy volunteers. Experimental data were compared to the ones estimated by an optoelectronic plethysmography used as reference. Promising results were obtained on both breathing period (maximum percentage error is 1.14%), inspiratory and expiratory period, as well as on total volume change (mean percentage difference between the two systems was ∼14%). The Bland-Altman analysis shows a satisfactory accuracy for the parameters under investigation. The proposed system is safe and non-invasive, MR-compatible, and allows monitoring compartmental volumes. © 2016 IEEE.

The paper aims to discuss the basic issues related to the analysis and design of magnetic sensors based on the employment of magneto-active materials. In particular, the basic idea is based on the integration of a Galfenol magnetostrictive alloy to a Fiber Bragg Grating (FBG) embedded into an optic fiber, able to sense the deformation of the material induced by magnetic field. The structure of the alloy and the characteristics of the fiber, make the device suitable to work also in harsh envi- ronments. One of the basic goals is to provide a sensor as simple as possible, with high field range detection and, at the same time, low reconstruction error. It has been observed that the increase of the field range could be achieved by exploiting the effects of the demagnetizing field, without exploit- ing the well-known magnetic hardening induced by the applied stress. In fact, the latter requires a clamping system, resulting in the increase of the sensor size. The demagnetizing field, conversely, provides a shielding of the external field, turning away the undesired approach to saturation. Finally, the employment of a material characterized by weak hysteresis phenomena avoids the use of complex compensation algorithm without losing accuracy. Some result of its characteristics and performances are provided.

This paper investigates the new developments of a class of magnetic field sensors based on the integration of Iron-Gallium magnetostrictive alloys (Galfenol) and fiber Bragg gratings used to detect the magneto-induced mechanical strain. This kind of sensor has the advantage of being able to work also in harsh environments, but on the other hand cannot detect fields beyond 10 kA/m, because of the magnetic softness of the active material. A simple solution consists in the exploitation of the demagnetizing field experienced by the ferromagnetic alloy by effect of its magnetization, generated by the application of the external magnetic field. Since the demagnetizing field effect depends only on geometrical parameters, the use of samples with different aspect ratios allows us to check how the shape of the active material can be used as a control parameter of the sensor detection range. © 1965-2012 IEEE.

Gaseous detectors are commonly used in HEP (High Energy Physics) experiments to reconstruct the track of elementary particles. They are often made by a very large number of chambers with relatively small individual volume, arranged in thick layers placed approximately all around the vertex of the experiment in order to detect elementary particles produced in any direction. The large volume of gas inside the detector must be monitored for many parameters as they can affect both the efficiency and the working life of the detector. The temperature of the gas inside the individual chambers is a critical parameter to be monitored, as it can both affect the efficiency of the detector and point out on-board electronic circuitry overheating. In this paper we propose a novel gas temperature sensing system based on optical fibre technology. The adopted technology is well suited to make distributed sensing systems with large number of sensors, it is immune to electromagnetic disturbances and it has adequate radiation hardness. A prototype of the basic sensor of the proposed system was tested at the experimental facility for Resistive Plate Chamber characterization available at the INFN laboratories in Frascati. Results are presented and discussed.

During thermal procedures, the monitoring of tissue temperature is useful to improve therapy success. The aim of this study is the feasibility assessment of a Fiber Bragg Grating (FBG)-based probe, which contains six FBGs, to obtain distributed temperature measurement in tissue undergoing laser ablation (LA). Among different thermometric techniques, FBG sensors show valuable characteristics, even though their sensitivity to strain entails measurement error for patient respiratory movement. We performed: i) the static calibration of the FBG-based probe to estimate the thermal sensitivity of the six FBGs; ii) the estimation of the response time of the FBGs. All FBGs have a thermal sensitivity of 10 pm·°C-1 and a time constant in the order of < 250 ms. Additionally, we performed a preliminary estimation of the error due to the strain and caused by respiratory movements. Experiments were carried out by simulating a typical respiratory movement on ex vivo swine liver. The measurement error was

An Aluminum coated FBG was heated to 650 °C in order to study the regeneration process at low temperature. When compared to the standard regeneration process (at 800 °C -1000 °C) the regeneration occurred at longer times, the onset of the process took around 150 days to appear. The reflected signal after regeneration also is weaker than that obtained in the usual process, although it presents a good stability after the recovery phase - measured for a time span of 200 days. © 2015 SPIE.

Temperature distribution monitoring in tissue undergoing laser ablation (LA) could be beneficial for improving treatment outcomes. Among several thermometric techniques employed in LA, fiber Bragg grating (FBG) sensors show valuable characteristics, although their sensitivity to strain entails measurement error for patient respiratory movements. Our work describes a solution to overcome this issue by housing an FBG in a surgical needle. The metrological properties of the probes were assessed in terms of thermal sensitivity (0.027 nm °C−1 versus 0.010 nm °C−1 for epoxy liquid encapsulated probe and thermal paste one, respectively) and response time (about 100 ms) and compared with properties of nonencapsulated FBG (sensitivity of 0.010 nm °C−1, response time of 43 ms). The error due to the strain caused by liver movements, simulating a typical respiratory pattern, was assessed: the strain induces a probes output error less than 0.5 °C, which is negligible when compared to the response of nonencapsulated FBG (2.5 °C). The metallic needle entails a measurement error, called artifact, due to direct absorption of the laser radiation. The analysis of the artifact was performed by employing the probes for temperature monitoring on liver undergoing LA. Experiments were performed at two laser powers (i.e., 2 W and 4 W) and at nine distances between the probes and the laser applicator. The artifact decreases with the distance and increases with the power: it exceeds 10 °C at 4 W, when the encapsulated probes are placed at 3.6 mm and 0 deg from the applicator, and it is lower than 1 °C for distance higher than 5 mm and angle higher than 30 deg.

The employment of sensors in harsh environments [1] is a challenging engineering task, occurring more frequently than it might be expected. So, the availability of reliable and accurate sensors is a task in great demand. However, this imply an effort demanding and an expensive design. In this frame we can place the present contribution which aims to develop a simple, robust magnetic filed sensor to be exploited in harsh conditions, such as the the Tokamak vessel for nuclear fusion experiments [2] where the presence of standard sensors based on electronic circuits based and hall effect is almost impossible. © 2015 IEEE.

Fiber Bragg Grating (FBG) technology is very attractive to develop sensors for the measurement of thermal and mechanical parameters in biological applications, particularly in presence of electromagnetic interferences. This work presents the design, working principle and experimental characterization of a force sensor based on two FBGs, with the feature of being compatible with Magnetic Resonance. Two prototypes based on different designs are considered and characterized: 1) the fiber with the FBGs is encapsulated in a polydimethylsiloxane (PDMS) sheet; 2) the fiber with the FBGs is free without the employment of any polymeric layer. Results show that the prototype which adopts the polymeric sheet has a wider range of measurement (4200 mN vs 250 mN) and good linearity; although it has lower sensitivity (≈0.1 nm-N1 vs 7 nm-N1). The sensor without polymeric layer is also characterized by employing a differential configuration which allows neglecting the influence of temperature. This solution improves the linearity of the sensor, on the other hand the sensitivity decreases. The resulting good metrological properties of the prototypes here tested make them attractive for the intended application and in general for force measurement during biomedical applications in presence of electromagnetic interferences. © 2014 IEEE.

Monitoring of local temperature in tissue undergoing Laser Ablation (LA) could be particularly beneficial to optimize treatment outcomes. A number of both invasive and non-invasive thermometric techniques may be employed to perform this task. Among others, Fiber Bragg Grating (FBG) sensors show the following valuable characteristics for temperature monitoring during LA: good sensitivity and accuracy, and immunity from electromagnetic interferences. The main drawbacks are their intrinsic invasiveness and the sensitivity to strain, which can entail measurement error for respiratory and patient movements. © 2015 IEEE.

Temperature monitoring in tissue undergone Laser Ablation (LA) may be particularly beneficial to optimize treatment outcome. Among many techniques, fiber Bragg grating (FBG) sensors show valuable characteristics for temperature monitoring in this medical scenario: good sensitivity and accuracy, and immunity from electromagnetic interferences. Their main drawback is the sensitivity to strain, which can entail measurement error for respiratory and patient movements. The aims of this work are the design, the manufacturing and the characterization of a needle-like probe which houses 4 FBGs. Three FBGs have sensitive length of 1 mm and are used as temperature sensors; one FBG with length of 10 mm is used as reference and to sense eventual strain. The optical fiber housing the FBGs was encapsulated within a needle routinely used in clinical practice to perform MRI-guided biopsy. Two materials were used for the encapsulation: i) thermal paste for the 3 FBGs used for temperature monitoring, to maximize the thermal exchange with the needle; ii) epoxy resin for the reference FBG, to improve its sensitivity to strain. The static calibration of the needle-like probe was performed to estimate the thermal sensitivity of each FBG; the step response was investigated to estimate the response time. FBGs 1 mm long have thermal sensitivity of 0.01 nm·°C(-1), whereas the reference FBG presents 0.02 nm·°C(-1). For all FBGs, the response time was in the order of 100 ms. Lastly, experiments were performed on ex vivo swine liver undergoing LA to i) evaluate the possible presence of measurement artifact, due to the direct absorption of laser light by the needle and ii) assess the feasibility of the probe in a quasi clinical scenario.

Laser ablation (LA) is a minimally invasive procedure used to remove cancer by inducing hyperthermia. It is based on the interaction between laser light and tissue: the absorbed light is converted into heat causing a tissue temperature increase. The amount of damaged volume depends on temperature and time exposure of the tissue to the hyperthermia. As a consequence, the monitoring of tissue temperature during LA could be particularly beneficial to optimize treatment outcomes. Thermocouples are one of the most employed transducer for temperature measurement. Their main drawback is related to the strong light absorption of the two metallic wires which constitute a thermocouple. The light absorption causes an overestimation of actual temperature, in literature known as artifact. This work aims at assessing this artifact on ex vivo swine pancreases undergoing LA. The artifacts have been estimated at the three laser powers (1.6 W, 2 W and 5 W) and at two distances from the optical applicator. In particular, the artifact decreases with the distance from the optical applicator and depends on P: at 1.6 W and 2 W it is negligible at 12 mm of distance, on the other hand at 5 W it is significant also at 15 mm (1.7 °C). Summing up: the artifact is strongly influenced by the distance between the thermocouple and the optical applicator, and by the laser power; also at high distance from the applicator it can cause error which are not acceptable for the application of interest (e.g., at 5 W and 10 mm the error is about 4 °C). Although the use of thermocouples entails the concern related to the artifact, it must be considered that proper model can be employed to correct the measurement error. © 2015 IEEE.

Temperature monitoring in tissue undergoing Laser Ablation (LA) is particularly beneficial to optimize therapy outcomes. During last decades several approaches have been proposed to perform thermometry during thermal ablation. Among others, Fiber Bragg Grating (FBG) sensors show valuable characteristics for such measurement, but their sensitivity to strain entails measurement error for patient respiratory movements. In this work two needle-like probes were developed using two different procedures to encapsulate an FBG into a surgical needle, aiming to allow safe insertion into the patient tissue and to neglect mechanical disturbance due to tissue movements occurring during breathing. The static calibration of the two probes has been carried out in a wide range of temperature (i.e., from 18 °C up to 100 °C), and their response time has been estimated. The calibration curves of the two probes show good linearity and a different sensitivity, and their response time is fast enough to meet the criteria set for temperature monitoring during LA. Since the metallic needle entails a measurement error, called artifact, due to the direct absorption of the laser radiation, the two abovementioned probes have been employed during LA on ex vivo liver. Then, their measurements have been compared to the measurement provided by an FBG without needle, which does not experience artifacts. The good results in terms of both static and dynamic properties of the two probes encourage to perform further analysis regarding the amplitude of the artifacts due to the direct absorption of the metallic needle and regarding the capability of the probes to neglect mechanical disturbance. © 2014 IEEE.

In this work we tested use of thin film aluminium coating to enhance the temperature sensing features of FBG sensors. Thin film coating was evaporated on the Bragg grating after removal of the original acrylate recoating, using a modified vacuum evaporation system that allows uniform radial deposition around the fibre. Results show that recoating thickness up to 0.5 μm do not produce appreciable effects, whereas thickness of 2.3 μm appreciably increases temperature sensitivity without increasing time response constant. © 2013 SPIE.

We propose to adopt Fiber Bragg Grating technology to develop an innovative sensor for monitoring relative humidity of the gas fluxed in Resistive Plate Counters. Use of Fiber Bragg Grating as sensing device makes the proposed sensor well suited to develop distributed real-time monitoring systems to be installed on large volume detectors operated in high electromagnetic fields. In fact Fiber Bragg Gratings are fully immune from electromagnetic disturbances and allow simplified wiring by in-series interconnection of tens of them along a single optical fiber. In this paper we present results intended to investigate the feasibility of our proposal. © 2013 IOP Publishing Ltd and Sissa Medialab srl.