Vital signs fiber optic sensor systems and methods

Abstract

An intensity-based, micro-bending optical fiber sensor is disclosed herein, which is configured to acquire clean, stable, and reliable vital sign signals. Related systems and methods for vital sign monitoring are also provided herein. The sensor of various embodiments includes a multi-mode optical fiber, an LED light source, an LED driver, a receiver, and a single layer deformer structure. In various embodiments, the optical fiber and single layer deformer structure of the sensor are selected to meet specific parameters necessary to achieve a level of reliability and sensitivity needed to successfully monitor vital signs. In some embodiments, a specific sizing relationship exists between the optical fiber and the single layer deformer structure. In some embodiments, the sensor is configured to acquire ballistocardiograph waveforms.

What is claimed is: 
     
         1 . A sensor for detecting a physiological parameter, the sensor comprising:
 a multi-mode optical fiber comprising an inner core, a cladding layer, and an outer coating;   an LED (light emitting diode) light source coupled to a first end of the optical fiber;   an LED driver electrically coupled to the LED light source and configured to regulate a power level of the LED light source;   a receiver coupled to a second end of the optical fiber, the receiver configured to sense changes in an intensity of light traveling through the optical fiber; and   a deformer structure consisting of a single mesh layer formed of mesh having openings disposed therein, wherein a surface area of the openings is between 30% and 60% of a total surface area of the single mesh layer;   the mesh layer is formed of interwoven fibers;   a flexible cover is configured to surround both the optical fiber and the deformer structure to form both an upper cover on the optical fiber and a back cover under the deformer structure such as to distribute uniformly any force applied on the sensor;   the optical fiber is arranged directly on the mesh layer, and is arranged in a plane in contact with a surface of the deformer structure;   the sensor has the multimode optical fiber and the single layer of mesh together held between the upper cover and the back cover to form a sensor sheet;   the sensor sheet is configured that a first portion of the optical fiber is capable of microbending into an opening of the single mesh layer and a second portion of the optical fiber is capable of flexing against the mesh under an applied outside force onto the sensor; and   an amount of microbending sufficient to detect vital signs can be achieved using the single deformer structure.   
     
     
         2 . The sensor of  claim 1 , wherein the sensor is configured to detect a ballistocardiogram of a patient; the outside force is caused by body weight, a heartbeat, respiration, or other physiological parameter; an amount the optical fiber will bend ΔX in response to the application of force per unit length ΔF on the sensor is as defined by Eq. (1): 
       
         
           
             
               
                 
                   
                     
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                           8 
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                                   d 
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                                 w 
                               
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                             4 
                           
                         
                         
                           
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                             y 
                           
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         where d 1  is a diameter or width of each mesh fiber in the x direction, w is a width of a mesh opening wide, E y  is Young's modulus, and D fiber  is a diameter of the optical fiber. 
       
     
     
         3 . The sensor of  claim 1 , wherein a total diameter of the optical fiber consists of a diameter across the inner core, the cladding layer, and the outer coating; each opening of the single mesh layer is 100% to 300% of the total diameter of the optical fiber; the diameter of the inner core is substantially greater than 50% of the diameter of the cladding layer. 
     
     
         4 . The sensor of  claim 3 , wherein a width of the mesh opening w is in a range of 200-750 μm, or the mesh opening is up to three times greater than the total optical fiber diameter; the inner core has a diameter of at least 62.5 μm. 
     
     
         5 . The sensor of  claim 3 , wherein a diameter of each interwoven fiber is less than 25% of the total diameter of the optical fiber; or a diameter of each interwoven fiber is 75% to 125% of the total diameter of the optical fiber; or each mesh fiber has a diameter greater than 70% and less than 100% of the total diameter of the optical fiber; or the optical fiber has a cladding layer diameter of 125 μm and a total diameter of 250 um, a diameter of each mesh fiber is selected to be in the range of 180 to 240 μm. 
     
     
         6 . The sensor of  claim 1 , wherein the flexible cover is bonded to the optical fiber and deformer structure; the flexible cover is formed of silicone; the interwoven fibers comprise a polymeric fabric. 
     
     
         7 . The sensor of  claim 1 , wherein the optical fiber is arranged in the plane with a configuration in which a bending diameter of the optical fiber is greater than 1.5 cm;
 the optical fiber is at least 10 meters long; the optical fiber has a numerical aperture less than or equal to 0.29.   
     
     
         8 . The sensor of  claim 1 , wherein the LED light source is a low power LED with a 850 nm or 1310 nm central wavelength and 165 nm Full width at half maximum (FWHM); the receiver is comprised of a photo detector, the photo detector has a detection range from 1100 nm to 1650 nm and 0.4 A/W responsivity. 
     
     
         9 . The sensor of  claim 1 , wherein the optical fiber is coupled to the LED light source and the receiver via direct optical fiber connectors without the need for a separate lead fiber; and the light source supplies optical radiation to the multimode fiber embedded within the sensor sheet. 
     
     
         10 . The sensor of  claim 1 , wherein an amplifier is coupled to the receiver to amplify optical signal from the receiver, an analog-to-digital converter is coupled to the amplifier for processing the optical signal amplified; the light source, the LED driver , the receiver, the amplifier, and the analog-to-digital converter are connected to a control and processing module; input light is generated from the light source and transmitted to the optical multimode fiber; and changes in the amount of light intensity are processed and determined by the control and processing module. 
     
     
         11 . The sensor of  claim 10 , wherein the processing module comprises a processor and a memory; the processor executes instructions stored in a memory; the receiver converts the optical intensity into an analog electrical signal, which is then amplified by an electrical amplifier; the analog-to-digital converter converts the analog electrical signal into a digital signal that is transmitted to and processed by the processor. 
     
     
         12 . The sensor of  claim 11 , wherein optical fiber sensor is configured to microbend a sufficient amount and monitors BCG waveforms, EEG waveform of the body, heart rate, breathing rate, beat-to-beat blood pressure changes, heart rate variability, stress level or other physiological parameters; the outer force is generated by body weight, heartbeat, respiration, or other physiological parameter, is uniformly distributed on the optical multimode fiber and the single mesh layer; these forces microbend the multimode fiber. 
     
     
         13 . The sensor of  claim 12 , wherein the processor combines different stage high pass and low pass filters to remove noise; the BCG waveform acquired has clear H, I, J, K, L, and M peaks; the processor calculates heart rate by gathering all the time differences and transferring them into a frequency in time domain; the processor calculates heart rate variability by calculating the average time difference between adjacent peaks over a predetermined time period; the processor determines the stress level from heart rate variability; EEG waveform is received by the processor from an EEG sensor; the EEG sensor is external to the optical fiber sensor; a time between an R peak of the EEG waveform and a J peak of the BCG waveform is indicative of the beat-to-beat pressure change. 
     
     
         14 . A vital signs fiber optic sensor system, comprising:
 a sensor;   a user interface; and   a remote system;   wherein the user interface is provided and used by a user to control some or all of the system's functionality; raw or processed digital signal is transmitted to the remote system to display, store and/or further process the signal;   the sensor comprises:   a multi-mode optical fiber comprising an inner core, a cladding layer, and an outer coating;   an LED (light emitting diode) light source coupled to a first end of the optical fiber;   an LED driver electrically coupled to the LED light source and configured to regulate a power level of the LED light source;   a receiver coupled to a second end of the optical fiber, the receiver configured to sense changes in an intensity of light traveling through the optical fiber; and   a deformer structure consisting of a single mesh layer formed of mesh having openings disposed therein; wherein   the mesh layer is formed of interwoven fibers;   a flexible cover is configured to surround both the optical fiber and the deformer structure to form both an upper cover on the optical fiber and a back cover under the deformer structure such as to distribute uniformly any force applied on the sensor;   the optical fiber is arranged directly on the mesh layer, and is arranged in a plane in contact with a surface of the deformer structure;   the sensor has the multimode optical fiber and the single layer of mesh together held between the upper cover and the back cover to form a sensor sheet;   the sensor sheet is configured that a first portion of the optical fiber is capable of microbending into an opening of the single mesh layer and a second portion of the optical fiber is capable of flexing against the mesh under an applied outside force onto the sensor; and   an amount of microbending sufficient to detect vital signs can be achieved using the single deformer structure.   
     
     
         15 . The sensor system of  claim 14 , wherein the remote system can be a smart phone, tablet, other mobile computing device, or other computer with appropriate communication capabilities; the user interface comprises a user input device and/or an output device; the user input device can be configured to receive user commands to power the sensor on and off. 
     
     
         16 . The sensor system of  claim 14 , wherein the change in light intensity corresponds to fiber deformation caused by a movement of the body; the movement of the body comprises a micro-movement or a macro-movement. 
     
     
         17 . The sensor system of  claim 16 , wherein optical fiber sensor is configured to microbend a sufficient amount and monitors BCG waveforms, EEG waveform of the body, heart rate, breathing rate, beat-to-beat blood pressure changes, heart rate variability, stress level or other physiological parameters; the outer force is generated by the movement of the body, is uniformly distributed on the optical multimode fiber and the single mesh layer; these forces microbend the multimode fiber; the micro-movement comprises breathing or a heartbeat; the macro-movement comprises a shift in body position. 
     
     
         18 . The sensor system of  claim 14 , wherein the sensor is configured to detect a ballistocardiogram of a patient; the outside force is caused by body weight, a heartbeat, respiration, or other physiological parameter; an amount the optical fiber will bend ΔX in response to the application of force per unit length ΔF on the sensor is as defined by Eq. (1): 
       
         
           
             
               
                 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       X 
                     
                     = 
                     
                       
                         ( 
                         
                           Δ 
                            
                           
                               
                           
                            
                           
                             F 
                             dist 
                           
                         
                         ) 
                       
                        
                       
                         
                           8 
                            
                           
                             
                               ( 
                               
                                 
                                   d 
                                   1 
                                 
                                 + 
                                 w 
                               
                               ) 
                             
                             4 
                           
                         
                         
                           
                             E 
                             y 
                           
                            
                           π 
                            
                           
                               
                           
                            
                           
                             D 
                             fiber 
                             4 
                           
                         
                       
                     
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         where d 1  is a diameter or width of each mesh fiber in the x direction, w is a width of a mesh opening wide, E y  is Young's modulus, and D fiber  is a diameter of the optical fiber. 
       
     
     
         19 . The sensor system of  claim 14 , wherein a total diameter of the optical fiber consists of a diameter across the inner core, the cladding layer, and the outer coating; a surface area of the openings is between 30% and 60% of a total surface area of the single mesh layer; each opening of the single mesh layer is 100% to 300% of the total diameter of the optical fiber; the diameter of the inner core is substantially greater than 50% of the diameter of the cladding layer; a diameter of each interwoven fiber is less than 25% of the total diameter of the optical fiber; or a diameter of each interwoven fiber is 75% to 125% of the total diameter of the optical fiber. 
     
     
         20 . The sensor system of  claim 14 , wherein an amplifier is coupled to the receiver to amplify optical signal from the receiver, an analog-to-digital converter is coupled to the amplifier for processing the optical signal amplified; the light source, the LED driver, the receiver, the amplifier, and the analog-to-digital converter are connected to a control and processing module; input light is generated from the light source and transmitted to the optical multimode fiber; and changes in the amount of light intensity are processed and determined by the control and processing module; the processing module comprises a processor and a memory; the processor executes instructions stored in a memory; the receiver converts the optical intensity into an analog electrical signal, which is then amplified by an electrical amplifier; the analog-to-digital converter converts the analog electrical signal into a digital signal that is transmitted to and processed by the processor.