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 method of detecting a physiological parameter, the method comprising:
 positioning a sensor under a body, the sensor comprising:
 a multi-mode optical fiber comprising an inner core, a cladding layer, and an outer coating, wherein a core diameter is greater than 50% of a cladding diameter; 
 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; and 
 a deformer structure consisting of a single mesh layer formed of mesh having openings disposed therein, the openings having a surface area between 30% and 60% of a total surface area of the mesh layer;
 wherein the optical fiber is arranged in a plane in contact with a surface of the deformer structure, and the deformer structure is configured with an amount of microbending sufficient to detect the physiological parameter; 
 
   detecting, by the receiver, a change in an intensity of light traveling through the optical fiber, wherein the change in light intensity corresponds to fiber deformation caused by a movement of the body; and   determining a physiological parameter from the change in light intensity.   
     
     
         2 . The method of  claim 1 , wherein determining the physiological parameter comprises determining a ballistocardiography (BCG) waveform of the body. 
     
     
         3 . The method of  claim 1 , wherein determining the physiological parameter further comprises:
 determining an EEG waveform of the body; and   calculating a time between an R peak of the EEG waveform and a J peak of the BCG waveform to determine beat-to-beat blood pressure changes.   
     
     
         4 . The method of  claim 1 , wherein determining the physiological parameter comprises:
 recording the signal detected at the receiver;   converting the signal to a digital waveform;   filtering out breathing and body movement waveforms from the digital waveform to extract a heartbeat waveform;   identifying heartbeat peak values from the heartbeat waveform by separating the heartbeat waveform into a first channel for time domain analysis and into a second domain for frequency domain analysis; and   applying a Fast Fourier Transform in the frequency domain to obtain the heartbeat rate value.   
     
     
         5 . The method of  claim 1 , 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. 
     
     
         6 . The method of  claim 5 , wherein 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. 
     
     
         7 . The method of  claim 1 , wherein 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 d1 is a diameter or width of each mesh fiber in the x direction, w is a width of a mesh opening wide, Ey is Young's modulus, and D fiber  is a diameter of the optical fiber. 
     
     
         8 . The method of  claim 1 , wherein detecting by the receiver further comprising steps of:
 generating input light from the LED light source and transmitting to optical multimode fiber;   detecting raw data of the intensity of light and converting the raw data into an analog electrical signal by the receiver;   amplifying the analog electrical signal by an electrical amplifier;   converting the analog electrical signal into a digital signal by an analog-to-digital converter; and   transmitting the raw data of the intensity of light in a form of digital signal after the analog-to-digital converter to a processor.   
     
     
         9 . The method of  claim 8 , wherein determining a physiological parameter comprises:
 computing applied forces from change in an intensity of light via the processor; and/or,   computing one or more vital signs of a user from the data on the applied forces via the processor; and/or   extracting a heartbeat waveform, respiration waveform, or movement waveform from the raw signal via the processor; and/or   identifying a movement frequency and amplitude from the signal via the processor.   
     
     
         10 . The method of  claim 8 , wherein the detected intensity of light is at the highest level when there is no user on the sensors; the detected intensity of light drops significantly in a very short period at a moment when a user sits, stands, or lays on the sensor; the detected intensity of light keeps within a relatively narrow range when the user is sitting or lying on the sensor without moving; the detected intensity of light recovers to the original level when the user leaves the sensor. 
     
     
         11 . The method of  claim 8 , after receiving the raw data from the analog-to-digital converter, further comprising:
 checking an optical intensity absolute value by the processor; and   comparing the received signal to the optical intensity absolute value to determine whether a user is on the sensor.   
     
     
         12 . The method of  claim 11 , if a user is not on the sensor, further comprising:
 operating in sleep mode to save battery power.   
     
     
         13 . The method of  claim 11 , if there is a significant light loss and a resultant decline in the intensity of light, further comprising:
 determining whether the user is moving by the processor.   
     
     
         14 . The method of  claim 13 , if a repeated or continual relatively large light loss change is detected, further comprising:
 defining this moment as a moving moment and outputs a movement waveform.   
     
     
         15 . The method of  claim 13 , if the intensity of light remains relatively constant with little changes, further comprising:
 splitting the raw digital data signal into two channels.   
     
     
         16 . The method of  claim 15 , wherein the signal in one channel undergoes multiple stages of filtering, which further comprises:
 combining different stage high pass and low pass filters to remove noise from the signal, and isolating heartbeat waveform;   splitting the heartbeat waveform into two channels including one channel for time domain analysis while another channel for frequency domain analysis.   
     
     
         17 . The method of  claim 16 , wherein multiple stages of filtering further comprising:
 performing a normalization process in time domain analysis to make data consistent for ease of analysis, and keeping data in one fixed window by zooming in and zooming out; and   squaring the data in frequency domain, and performing a Fast Fourier Transformation to get heartbeat rate value;   matching heartbeat rate value from time and frequency domain to reduce error rate; and   outputting heartbeat rate value by the processor.   
     
     
         18 . The method of  claim 15 , wherein another channel of the raw digital signal is further processed, which comprises:
 averaging the signal and applying a low pass filter; and   outputting a breathing waveform.   
     
     
         19 . The method of  claim 18 , further comprising:
 saving a time window of multiple data points;   finding a peak value a the time domain;   identifying the peak value of a respiration waveform; and   obtaining the respiration rate.   
     
     
         20 . The method of  claim 19 , further comprising:
 matching an average respiration rate to the latest respiration rate; and   outputting the breathing rate by the processor.