System for detecting injuries suffered by passengers in a vehicle after an accident or a strenuous situation

Abstract

System for detecting injuries suffered by passengers in a vehicle after an accident or a strenuous situation, the system comprising: one or more FBG sensors (1) arranged on a safety belt (2; 10) of a vehicle seat (6); an FBG interrogator (7) configured to obtain strain measurements from the one or more FBG sensors (1); and a detection unit (8) configured to compute a load distribution map (9) using the strain measurements.

Description

[0001] SYSTEM FOR DETECTING INJURIES SUFFERED BY PASSENGERS IN A VEHICLE AFTER AN ACCIDENT OR A STRENUOUS SITUATION

[0002] DESCRIPTION

[0003] FIELD

[0004] The present invention is comprised within the field of sensors and systems used to measure the force and pressure exerted over the human body of the vehicle passengers after an accident or after a strenuous activity, such as the forces suffered by a professional racing driver during a race.

[0005] BACKGROUND

[0006] In the field of systems for evaluating passenger trauma, patent document US11610684- B2 discloses an automated system for evaluation and report of passenger pain and trauma in a vehicular crash. This system includes a set of in-vehicle sensors in contact or near a passenger for direct measurement of external forces on organs of the passenger during an accident. In particular, pressure sensors are allocated on the back of the steering wheel, on the headrest, on the seat, on the inflated airbag zones of the vehicle, in the top or bottom parts, or at the buckle, of the seatbelt of the vehicle. The system further comprises a heartbeat and respiration sensor, also located on the belt. The sensors allow creating a picture of the movements and impacts of passengers in order to assess the severity of the injuries suffered by the passengers.

[0007] However, the system disclosed in US11610684-B2 requires a lot of number of pressure sensors arranged within the vehicle to estimate the extent of the injuries suffered by passengers and, even so, the system is not able to locate the injuries in the body with high precision.

[0008] The present invention provides a much simpler solution that allows detecting and locating the forces (and, possibly, injuries) suffered by the passengers with precision.

[0009] SUMMARY

[0010] The present invention refers to a system for detecting injuries suffered by passengers in a vehicle after an accident or a strenuous situation. The system comprises one or more FBG sensors arranged on a safety belt of a vehicle seat, an FBG interrogator configured to obtain strain measurements from the one or more FBG sensors, and a detection unit configured to compute a load distribution map using the strain measurements.

[0011] The plurality of optical fibers with fiber Bragg gratings (FBG sensors) are arranged on the belts of a safety belt of a vehicle. In an embodiment, the safety belt is a race safety harness, normally implemented as a 6-point safety belt with 6 belts and six anchorage points. However, the safety belt may have a different number of belts and anchorage points, such as a 3-point seatbelt.

[0012] Unlike the prior art that use pressure sensors arranged on the belt, the present invention employs a strain sensor on each belt that provides a direct measurement of the belt’s tension. Strain sensors measure the force applied to the belt as a whole, which is a direct measurement of the restraining load exerted on the passenger's body. This is especially useful for assessing passenger restraint without requiring physical pressure on a specific area, as is the case with pressure sensors.

[0013] Harness strain represents the total force supported and allows for a more holistic assessment of the harness's effectiveness in its restraint function. Pressure sensors, on the other hand, focus on specific points where pressure is measured against the body, which may not represent the strain distributed across the harness. With strain sensors more accurate data on how the load is distributed along the harness can be obtained, optimizing the design to avoid excessive pressure points and improve comfort and safety.

[0014] Strain sensors can also anticipate harness overload situations before structural failure or passenger harm occurs. By detecting increased strain in real time, the system can automatically adjust the restraint force or even alert other safety systems, something that is more difficult to achieve using pressure sensors focused on a specific area.

[0015] Strain sensors also improve sensitivity to motion. In a high-motion environment, such as traffic or racing, pressure sensors can be susceptible to false positives from body displacement. Strain sensors, however, filter out these effects because they measure the total load on the harness, providing a more stable signal that is less subject to interference from minor movements. In summary, strain sensors provide a comprehensive, dynamic assessment of passenger safety by directly measuring force across the harness, whereas pressure sensors are limited to specific points and do not capture load distribution.

[0016] The invention also relates to an intelligent seatbelt system incorporating one or more Fiber Bragg Grating (FBG) optical sensors directly integrated into the belt textile to measure elongation, tension and load in real time during vehicle operation. The system comprises at least one strain-sensitive FBG and at least one temperature-compensation FBG arranged along the seatbelt, an optical interrogator, and a controller configured to perform temperature-compensated strain calculations, detect improper belt tension, identify slack events, monitor belt dynamics during driving or racing, and / or record maximum loads during impacts.

[0017] Another aspect of the present invention refers to a method of manufacturing an instrumented seatbelt, comprising the following steps:

[0018] Placing (102) a seatbelt segment under controlled pre-tension;

[0019] Positioning (104) at least one FBG strain sensor (25) along a longitudinal axis of the seatbelt;

[0020] Bonding (106) the FBG strain sensor (25) to the textile of the seatbelt using discrete adhesive regions located outside the grating region of the FBG strain sensor (25);

[0021] - Adding (108) at least one temperature-sensing FBG sensor (26) in proximity to the FBG strain sensor (25);

[0022] - Applying (110) protective layers over the bonded fiber.

[0023] Performing (112) a calibration procedure comprising a baseline wavelength measurement and a post-cure thermal validation,

[0024] The seatbelt system may be used for different applications, such as monitoring belt tension in motorsport racing for ensuring correct restraint load during dynamic driving, crash reconstruction and biomechanical injury analysis, and professional driver simulators to reproduce realistic belt tensioning patterns. Crash reconstruction employs the full-time history of measured belt strain to derive load profiles during the crash. These load profiles are aligned with vehicle deceleration data to compute occupant loading. The resulting load curves are compared to established injury criteria to determine likely injury mechanisms (e.g., excessive chest compression, high load rates, or abnormal load distribution).

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] A series of drawings which aid in better understanding the invention and which are expressly related with an embodiment of said invention, presented as a non-limiting example thereof, are very briefly described below.

[0027] Figure 1 shows an embodiment of a system for detecting injuries suffered by the occupants of a vehicle after an accident or a strenuous situation.

[0028] Figures 2 and 3 show a FBG sensor used as a strain sensor.

[0029] Figure 4 depicts a race safety harness with FBG sensors.

[0030] Figure 5 depicts an injury detection made by the detection unit using the load distribution map.

[0031] Figure 6 shows a signal output by the detection unit warning about a wrong adjustment of the safety belt.

[0032] Figure 7 represents an embodiment of a seatbelt system that generates an alert whenever abnormal strain values are detected.

[0033] Figure 8 shows a multiplexing layout of FBG sensors on an optical fiber.

[0034] Figure 9 shows an exemplary strain measurement over time and the associated derivate at a certain time instant.

[0035] Figure 10 depicts a flow diagram of a manufacturing process of an instrumented seatbelt according to an embodiment.

[0036] DETAILED DESCRIPTION Figure 1 represents a system for detecting injuries suffered by the occupants of a vehicle after an accident or a strenuous situation. The system can also be used with crash test dummies, to analyze the types of injuries that can occur in an accident.

[0037] The system comprises a plurality of FBG sensors 1 (i.e. optical fibers with fiber Bragg gratings, FBGs) arranged on the belts of a safety belt of a vehicle seat 6, for example a 3-point seatbelt 2 including a lap belt 3 and a diagonal belt 4 together in one piece and connected at three points (5a, 5b, 5c). The system further comprises an FBG interrogator 7 and a detection unit 8 that receives and analyzes the signals acquired by the FBG sensors 1.

[0038] FBSs are made by laterally exposing the core of a single-mode fiber to a periodic pattern of intense laser light. The exposure produces a permanent increase in the refractive index of the fiber’s core, creating a fixed index modulation according to the exposure pattern. This fixed index modulation is called a grating. At each periodic refraction change a small amount of light is reflected. All the reflected light signals combine coherently to one large reflection at a particular wavelength when the grating period is approximately half the input light’s wavelength. This is referred to as the Bragg condition, and the wavelength at which this reflection occurs is called the Bragg wavelength. Light signals at wavelengths other than the Bragg wavelength, which are not phase matched, are essentially transparent. This principle is shown in Figure 2.

[0039] Therefore, light propagates through the grating with negligible attenuation or signal variation. Only those wavelengths that satisfy the Bragg condition are affected and strongly back-reflected. The ability to accurately preset and maintain the grating wavelength is a fundamental feature and advantage of fiber Bragg gratings. The central wavelength of the reflected component satisfies the Bragg relation:Bragg = 2nA, with n the index of refraction and A the period of the index of refraction variation of the FBG. Due to the temperature and strain dependence of the parameters n and A, the wavelength of the reflected component will also change as function of temperature and / or strain. Figure 3 shows the FBG response as function of strain. This dependency is well known what allows determining the temperature or strain from the reflected FBG wavelength. The FBG sensors 1 advantageously provide absolute referenced measurements and are immune to electro-magnetic and radio frequency interferences. In addition, they have reduced cable requirements due to their intrinsic multiplexing capability, and they may be separated by long distances from the FBG interrogator 7.

[0040] Unlike the pressure sensors used in prior art solutions (e.g., US11610684-B2) that provide data regarding the pression exerted directly on the sensor, the FBG sensors 1 are used as a strain sensor and provide data relating to the strain suffered by the belt. Pressure is the force applied per unit area, but in a safety belt what really matters is the force or load that the belt exerts on the pilot's body, not so much how this force is distributed over a specific area. Strain, instead, better describes the internal stress along a linear material, such as a belt or fiber.

[0041] In this case, the FBG sensors 1 arranged on the seatbelts (e.g. glued or sewn to the belts 3 and 4) detect changes in the wavelength reflected from an optical fiber which are directly related to the mechanical stress experienced by the fiber, thus directly measuring the changes in length or deformation caused by the applied load, which is directly related to strain.

[0042] Using a FGB sensor 1 arranged on a belt of the seatbelt, and used as a strain sensor, provide several advantages over pressure sensors arranged on the belt. First, measuring strain provides direct data on the force to which the seatbelt is subjected, since strain allows for direct calculation of the load supported by the seatbelt without the need to estimate contact areas along the belt, which is more complex and can be less accurate. Secondly, strain data can be better integrated into monitoring or simulation systems that evaluate seatbelt or harness performance during racing conditions. Thirdly, with only one FBG sensor all kind of forces can be detected along the belt, since all these forces cause belt strain; however, multiple pressure sensors arranged at different locations of the belt would be required to detect the forces exerted by a passenger’s body in contact with the belt, since the contact point along the belt may vary.

[0043] Back to Figure 1 , the detection unit 8 receives the strain measurements (straini, strain2) acquired by the FBG interrogator 7 using the response of the FBG sensors 1 (reflected signal in Figures 2 and 3). By analyzing the strain measurements, the detection unit 8 computes a load distribution map 9 for the FBG sensors 1 in the safety belt, showing how the forces and / or strains are distributed in the belts in real time.

[0044] Figure 4 depicts another type of safety belt on which the present invention may be applied to, in this case a race safety harness 10 having six belts and anchorage points (a 6-point seatbelt). In this embodiment, the FBG sensors 1 are arranged on four of the six belts of the race safety harness 10. In particular, the FBG sensors 1 are arranged on the chest belts 11 (the straps that pass over each shoulder) serving as chest sensors to detect the strain in these areas during accelerations, decelerations, pilot movements and impacts. The FBG sensors 1 are also arranged on the hip belts 12, located where the straps hold the pelvis, serving as hip sensors that measure the load generated by braking forces, side impacts or pilot movements.

[0045] The detection unit 8 generates a load distribution map 9 showing the forces and / or strains suffered by the passenger’s body in different sections of the safety belt. The FBG sensors 1 allow the measurement of mechanical strain along the straps of the safety belt, which is transformed into different visual representations depending on the desired analysis.

[0046] In an embodiment, the load distribution map 9 is a strain map that represents the amount of strain experienced in each section of the safety belt in real time. The map is preferably color coded (e.g., green for low strain, red for high strain) showing which areas of the belts are carrying the most load to identify critical zones during a race or an impact.

[0047] In another embodiment, the load distribution map 9 is a distributed force map that estimates the total force exerted on the pilot's body (or passenger’s) based on the strain measured by the FBG sensors 1 . This map may be a 2D or 3D graph that combines the strain readings from the sensors to show how the forces are distributed on the human’s body (e.g. across the chest and hip in the example of Figure 4). This map may be used to validate that the racing harness distributes forces evenly, minimizing injury.

[0048] Using historical data, the detection unit 8 may obtain a risk map that highlights areas where there is a higher risk of harness overload or failure. The map may include a visual representation based on critical strain thresholds, used for preventive safety and design improvements. The graphical representation of the load distribution map 9 may include the positions of the sensors on the straps in 2 axes (2D map) or 3 axes (3D map), the displayed data including strain magnitudes, converted to force units (in Newtons) if necessary. The conversion of strain into force can be performed using a previous calibration process. The load distribution map 9 can be a heatmap, vector diagrams (showing direction and magnitude of strain), or 3D graphics modeling the pilot’s body with applied forces.

[0049] Regarding the process to build a load distribution map 9 from the FBG sensor signals, each FBG sensor 1 is glued on a belt (3,4; 11 ,12) of the seatbelt (2; 10) in a known physical position, and when the belt is loaded each FBG sensor 1 changes wavelength according to the local strain. This wavelength shift is converted into strain by the detection unit 8 (a data processing unit such as a processor), and then into local belt tension using the stiffness of the belt material. Each tension value is assigned to the physical position of the corresponding FBG sensor 1 on the belt. The_detection unit 8 may generate a continuous load distribution map 9 by interpolating between points. Therefore, since every FBG sensor 1 outputs how much force is passing through that specific point on the belt, a full tension profile may be reconstructed.

[0050] In an embodiment shown in Figure 5, the detection unit 8 uses the load distribution map 9 to detect and locate possible injuries (injury detection 13) suffered by the passenger after an accident or after a strenuous situation (e.g. during a professional race). The detection and localization of the injury may be performed, for instance, by using a strain or force threshold, so that those points in the load distribution map 9 surpassing the threshold will be considered as areas of injury.

[0051] Since different belt areas (e.g. chest belts 11 or hip belts 12 in the example of Figure 4) correspond to different parts of the body, the load distribution map 9 contains information on where the body experienced the highest forces. The detection unit 8 may look for patterns known to be associated with injury risk, such as very high local peaks, strong left / right asymmetry, acceleration forces and sustained high loading. By checking where these patterns occur along the belt, the detection unit 8 can estimate which part of the body was most exposed, for example, clavicle area or lower ribs. This forms the injurylikelihood indication (injury detection 13).

[0052] The injury detection 13 may also be wirelessly reported to an emergency service, so that the ambulance attending the accident is warned in advanced about the type (and magnitude) of injury suffered by the passengers.

[0053] The load distribution map 9 also provides real-time monitoring of harness performance and information that can be used for dynamic adjustment of the safety belt (e.g. to correct a wrong adjustment of the safety belt that may cause an injury). The detection unit 8 may output a warning signal (warning message 14 shown in Figure 6), e.g. to a display or speaker, so that the passenger is warned about a wrong safety belt adjustment and can correct it accordingly. Alternatively, the detection unit 8 may automatically adjust the restraint force of the belts, provided an automatic restrain system is installed in the vehicle.

[0054] Figure 7 depicts an embodiment of the system; in particular, a smart seatbelt system 20 that constantly monitors belt tension and warns the driver if the belt becomes too loose or too tight during use. The seatbelt system 20 comprises a vehicle seatbelt 21 formed by one or more textile belts. In the example, the seatbelt 21 comprises a chest belt 22 and a hip belt 23, but it may include fewer or more textile belts, such as in Figure 4. The seatbelt 21 shown in the figure has three anchorage points 24, but it may include fewer or more anchorage points.

[0055] The seatbelt system 20 further comprises at least one FBG strain sensor 25 bonded directly to the seatbelt 21 and configured to measure belt elongation during use. In an embodiment, such as the one depicted in Figure 7, the seatbelt system 20 comprises a FBG strain sensor 25 bonded to each textile belt of the seatbelt 21. In other embodiments not every textile belt includes a FBG strain sensor 25.

[0056] The seatbelt system 20 also comprises at least one temperature-sensing FBG sensor 26 arranged adjacent to each FBG strain sensor 25. The FBG strain sensor 25 and the temperature-sensing FBG sensor 26 are both FBG sensors, which may be identical but with a different installation. The FBG strain sensor 25 is physically bonded to the textile belt and therefore responds to both strain and temperature. The temperature-sensing FBG sensor 26 is mechanically isolated to the textile belt, placed in a loose tube or adhesive-free pocket, so that it only responds to temperature and not to belt tension, providing the reference needed for thermal compensation of strain readings. The temperature-sensing FBG sensor 26 is placed nearby the FBG strain sensor 25 to reduce thermal gradients.

[0057] An optical interrogator 27, which is part of the seatbelt system 20, is configured to detect wavelength shifts of the FBG sensors (25,26) at a sampling rate sufficient to capture dynamic belt tension. A minimum sampling rate of 10 Hz is required to capture the tension variations in motorsport belts. Higher rates (up to 1 kHz) can be used depending on the interrogator capability.

[0058] The system further includes a controller unit 28 or data processing unit (such as a processor), configured to compute temperature-compensated strain or tension values of the seatbelt 21 based on the detected wavelength shifts, detect deviations from a predetermined safe tension range, and generate an alert 29 (e.g. a visual and / or acoustic signal using a vehicle screen or speaker) during vehicle operation based on the detected deviations.

[0059] When using several FBG strain sensors 25, each FBG strain sensor 25 is evaluated independently. For every sensor, the controller unit 28 compares its calculated tension with its individual safe range. A deviation in any sensor produces a localized alert and contributes to the global system state. The alert 29 may be generated when one or more deviations are detected, or when certain conditions are met (e.g. a predetermined number of deviations are detected).

[0060] The smart seatbelt system 20 with integrated Fiber Bragg Grating (FBG) sensors performs real-time strain, tension and load monitoring, which in turn allows detecting improper belt tension, identify slack events, monitor belt dynamics during driving or racing, and record maximum loads during impacts, among other applications.

[0061] Improper belt tension can be detected by converting each FBG sensor’s Bragg wavelength shift into microstrain through its calibration curve. Microstrain is then mapped to belt tension using the webbing’s mechanical stiffness. The controller unit 28 continuously checks whether the measured tension value falls outside a predefined safe range obtained from laboratory tensile tests. Any measurement outside this range is flagged as improper tension, and an alert 29 is generated and emitted to warn the user. In an embodiment, the FBG strain sensors 25 are mechanically bonded to the seatbelt 21 in controlled pre-tension using discrete adhesive points, isolation layers and strainrelief features to preserve linearity and minimize drift.

[0062] The invention enables continuous monitoring of driver restraint forces, early detection of tension loss, safety warnings, post-incident load analysis, and integration with vehicle data systems. A loss of tension corresponds to a sudden drop in microstrain. If the rate of decrease exceeds a threshold, the system classifies the event as a tension-loss onset. Safety warnings may be emitted when at least one FBG strain sensor leaves the safe tension range, when a rapid negative strain indicates belt loosening, when tension exceeds maximum allowable crash loads, or when inconsistencies between sensors suggest abnormal load distribution. These conditions are defined numerically during calibration. After an impact or abrupt event, the system analyzes peak strain, and total energy absorbed (integral of strain over time). These parameters are compared with biomechanical injury thresholds and known crash envelopes, allowing an estimation of likely injury severity.

[0063] In an embodiment, the at least one FBG strain sensor 25 is installed under a defined pretension to achieve a reproducible reference Bragg wavelength. Pre-tension is applied using a small mechanical device such as a calibrated spring, tensioning weight, or roller fixture that applies a known force (typically 0.5-1 .0 N) to the fiber during bonding. This ensures reproducible initial strain and consistent baseline wavelength.

[0064] The FBG strain sensor may be bonded using an adhesive pattern comprising multiple discrete adhesive points placed at least 10 mm away from the grating region to minimize residual strain. In an embodiment, the bonded region comprises a multilayer stack including an adhesive layer, a damping layer, and a protective textile layer. The system may include a thermal equalization layer selected from cork, foam or compliant epoxy placed beneath the FBG region to reduce thermal gradients. The system is operable under cockpit temperatures between -20°C and +85°C. The FBG sensor alignment angle relative to the belt longitudinal axis is preferably within ±15°. The optical fiber of the FBG sensors may be routed through strain-relief loops. The optical interrogator 27 may be mounted inside a vibration-damped housing to reduce spectral noise. The controller unit 28 may generate a tension or strain profile using the strain measurements provided by the at least one strain-sensing FBG sensor positioned along the belt. A strain profile is the spatial distribution of strain along the belt, obtained from one or multiple FBG strain sensors 25 placed at different locations. For example, a first sensor arranged near the chest reads 1800 e while a second sensor near the pelvis might reads 1100 pe, showing how load is distributed across the driver’s body during driving or impact.

[0065] In an embodiment, the FBG sensors (25, 26) are multiplexed on a single optical fiber and interrogated simultaneously by the optical interrogator 27. Figure 8 schematically shows an optical fiber 30 with several pair of FBG sensors (FGB strain sensor 25 and temperature-sensing FBG sensor 26) in sequence, all connected to the optical interrogator.

[0066] The controller unit 28 may be configured to apply a polynomial temperaturecompensation model selected from linear, quadratic, or cubic temperature coefficients. The compensation model may be calibrated using at least two temperature plateaus during manufacturing, so that after gluing the belt is placed at two controlled temperatures (e.g., 20°C and 50°C) and the Bragg wavelength of both strain-sensing and temperature-sensing FBG sensors is recorded at each plateau. From these two points, the thermal sensitivity is calculated to create an accurate compensation model.

[0067] The controller unit 28 may be configured to filter the signals acquired from the FBG sensors (25, 26) using a low-pass filter with a cutoff frequency between 1 Hz and 10 Hz to suppress vehicle vibration noise.

[0068] In an embodiment, the controller unit 28 is configured to identify slack events by detecting a negative strain derivative exceeding a predetermined threshold. Figure 9 shows an exemplary strain measurement 32 over time (i.e. a strain-related Bragg wavelength). When the slope a of the strain-related Bragg wavelength over time, which corresponds to the strain derivate, becomes sufficiently negative, exceeding a preset threshold a-™, this indicates belt loosening or sudden unloading (e.g. the slope ai at time instant h exceeds the threshold a™). This way, the system may identify micro-adjustments or loosening events caused by driver motion during racing when the derivative of strain becomes negative, exceeding the defined drop-rate threshold a™. The controller unit (28) may be configured to trigger a visual, acoustic, or haptic warning when belt tension moves outside a predetermined safe tension window. Each FBG strain sensor 25 has its own calibrated safe range. The controller unit 28 checks each FBG sensor individually, comparing its real-time tension value with its allowed limits. Any out- of-range value constitutes a violation, and the generated alert 29 causes a device installed on the vehicle or on the seatbelt itself, such as a display or a vibration motor, to emit a visual, acoustic and / or haptic warning.

[0069] The safety thresholds, such as the drop-rate threshold a-™ or the safe tension window, may be dynamically adjusted based on a driving mode. The available driving modes may include, for instance, street, track, qualifying or endurance.

[0070] The seatbelt system 20 may communicate real-time strain data via CAN, Ethernet, or UDP interface to an onboard vehicle logging unit. The controller unit 28 may record relevant strain data in non-volatile memory for post-incident forensic analysis. The recorded data may be, for instance, maximum strain values and time-stamped event markers associated with buckling, unbuckling, tension spikes, and belt slips. The stored strain data may be used to estimate injury likelihood by correlating belt loads with vehicle acceleration or crash pulse data. Injury estimation combines measured belt loads (peak strain, load rate, and duration) with vehicle acceleration or crash-pulse data. These belt loads are compared to biomechanical models such as HIC, chest deflection limits, or thoracic injury curves. Matching measured loads to these standards provides an injurylikelihood estimate.

[0071] Applications of the smart seatbelt system 20 include motorsport, automotive safety systems, crash forensics, simulators, and advanced driver monitoring. The seatbelt system 20 may be used for real-time detection of belt tension, slack, overload, or impact forces during motorsport, automotive operation, crash events, or driver simulation.

[0072] The present invention also relates to a method 100 of manufacturing an instrumented seatbelt. Figure 10 is a flow diagram showing the steps of the manufacturing process, which comprises placing 102 a seatbelt segment under controlled pre-tension; positioning 104 at least one FBG strain sensor 25 along a (preferably marked) longitudinal axis of the seatbelt; bonding 106 the FBG strain sensor 25 to the textile of the seatbelt using discrete adhesive regions located outside the grating region of the FBG strain sensor 25; adding 108 at least one temperature-sensing FBG sensor 26 in proximity to the FBG strain sensor 25; applying 110 protective layers over the bonded fiber; and performing 112 a calibration procedure comprising a baseline wavelength measurement and a post-cure thermal validation, whereby the installed sensors retain linear strain response and stable baseline wavelength. Regarding the calibration process, after bonding the sensors a baseline Bragg wavelength is recorded at ambient temperature. The belt is then subjected to a thermal post-cure cycle (e.g., 20°C — > 60°C — > 20°C) to stabilize the adhesive. The Bragg wavelengths are measured again at the end of the cycle to confirm that the strain-wavelength relationship remains stable and reproducible.

[0073] The method 100 may further comprise the step of marking the sensor placement zone using a stencil or jig ensuring positional repeatability within ±1 mm. Adhesive curing may be monitored by logging real-time wavelength changes until stabilization is reached.

[0074] In an embodiment, the method 100 comprises a post-gluing thermal cycle including at least two temperature plateaus with compensation validation. After gluing the FBG sensors, the belt undergoes a controlled heating cycle with at least two stable temperature points. At each plateau, both strain and temperature FBGs are measured. These data validate that the compensation FBG correctly tracks temperature and that the strain FBG remains stable after adhesive curing.

Claims

CLAIMS1. A system for detecting injuries suffered by passengers in a vehicle after an accident or a strenuous situation, the system comprising: one or more FBG sensors (1) arranged on a safety belt (2; 10) of a vehicle seat (6); an FBG interrogator (7) configured to obtain strain measurements from the one or more FBG sensors (1); and a detection unit (8) configured to compute a load distribution map (9) using the strain measurements.

2. The system of claim 1 , wherein the load distribution map (9) represents the strains and / or forces distributed on the safety belt.

3. The system of claim 1 , wherein the detection (8) unit is further configured to detect and locate an injury in points of the load distribution map (9) having a strain or force magnitude higher than a predetermined threshold.

4. The system of claim 3, wherein the detection unit (8) is further configured to wirelessly transmit information about the detection and location of the injury to an emergency service.

5. The system of claim 1 , wherein the detection unit (8) is further configured to: detect, based on the load distribution map (9), a wrong adjustment of the safety belt; and output a warning message (14).

6. The system of claim 1 , wherein the safety belt is a race safety harness (10).

7. The system of claim 1 , wherein the safety belt is a 3-point seatbelt (2).

8. A seatbelt system (20), comprising: a vehicle seatbelt (21); at least one FBG strain sensor (25) bonded directly to the seatbelt (21) and configured to measure belt elongation during vehicle operation;at least one temperature-sensing FBG sensor (26) arranged adjacent to the FBG strain sensor (25); an optical interrogator (27) configured to detect wavelength shifts of the FBG sensors (25, 26); and a controller unit (28) configured to: compute temperature-compensated strain or tension values of the belt based on the detected wavelength shifts, detect deviations from a predetermined safe tension range, and generate an alert (29) during vehicle operation based on the detected deviations.

9. The seatbelt system of claim 8, wherein the at least one FBG strain sensor (25) is installed under a defined pre-tension to achieve a reproducible reference Bragg wavelength.

10. The seatbelt system of any of claims 8 to 9, wherein the FBG strain sensor (25) is bonded using an adhesive pattern comprising multiple discrete adhesive points placed at least 10 mm away from the grating region to minimize residual strain.

11. The seatbelt system of any of claims 8 to 10, wherein the bonded region comprises a multilayer stack including an adhesive layer, a damping layer, and a protective textile layer.

12. The seatbelt system of any of claims 8 to 11 , further comprising a thermal equalization layer selected from cork, foam or compliant epoxy placed beneath the FBG region to reduce thermal gradients.

13. The seatbelt system of any of claims 8 to 12, wherein the FBG sensor alignment angle relative to the belt longitudinal axis is within ±15°.

14. The seatbelt system of any of claims 8 to 13, wherein the optical fiber of the FBG sensors (25, 26) is routed through strain-relief loops.1715. The seatbelt system of any of claims 8 to 14, wherein the FBG sensors (25, 26) are multiplexed on a single optical fiber (30) and interrogated simultaneously by the optical interrogator (27).

16. The seatbelt system of any of claims 8 to 15, wherein the controller unit (28) is configured to apply a polynomial temperature-compensation model selected from linear, quadratic, or cubic temperature coefficients.

17. The seatbelt system of claim 16, wherein the compensation model is calibrated using at least two temperature plateaus during manufacturing.

18. The seatbelt system of any of claims 8 to 17, wherein the controller unit (28) is configured to filter the signals acquired from the FBG sensors (25, 26) using a low-pass filter with a cutoff frequency between 1 Hz and 10 Hz to suppress vehicle vibration noise.

19. The seatbelt system of any of claims 8 to 18, wherein the controller unit (28) is configured to identify slack events by detecting a negative strain derivative exceeding a predetermined threshold (a-™).

20. The seatbelt system of any of claims 8 to 19, wherein the controller unit (28) is configured to trigger a visual, acoustic, or haptic warning when belt tension is outside a predetermined safe tension window.

21. The seatbelt system of any of claims 8 to 20, wherein the optical interrogator (27) is mounted inside a vibration-damped housing to reduce spectral noise.

22. A method of manufacturing an instrumented seatbelt, comprising: placing (102) a seatbelt segment under controlled pre-tension; positioning (104) at least one FBG strain sensor (25) along a longitudinal axis of the seatbelt; bonding (106) the FBG strain sensor (25) to the textile of the seatbelt using discrete adhesive regions located outside the grating region of the FBG strain sensor (25); adding (108) at least one temperature-sensing FBG sensor (26) in proximity to the FBG strain sensor (25);18 applying (110) protective layers over the bonded fiber; and performing (112) a calibration procedure comprising a baseline wavelength measurement and a post-cure thermal validation.

23. The method of claim 22, further comprising a post-gluing thermal cycle including at least two temperature plateaus with compensation validation.

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