Biomedical Pressure Sensing System

Abstract

A biomedical pressure sensing system comprising a contact lens; a flexible resonator embedded in the contact lens; and a measuring means for transmitting and receiving signals and measuring differences between the transmitted signal and the received signal. The purpose of this invention is to provide a sensor which is electrically passive, wireless and low cost to measure intraocular pressure.

What is claimed is: 
     
         1 . A biomedical pressure sensing system comprising:
 a contact lens;   a flexible resonator embedded in the contact lens; and   measuring means for transmitting and receiving signals and measuring differences between the transmitted signal and received signal.   
     
     
         2 . The biomedical pressure sensing system of  claim 1 , wherein the measuring means is an antenna pair, placed at proximity of the flexible resonator, the antenna pair including a transmitting antenna and a receiving antenna; wherein the transmitting antenna sends electromagnetic wave to the flexible resonator; the receiving antenna captures the electromagnetic wave from the flexible resonator, the captured electromagnetic wave is converted into a signal;
 wherein the system further includes a readout circuit, configured to process the signal from the receiving antenna.   
     
     
         3 . The biomedical pressure sensing system according to  claim 2 , wherein the flexible resonator is a split-ring which includes a gap and two extension portions at both ends of the gap; and the flexible substrate is made of cellulose acetate. 
     
     
         4 . The biomedical pressure sensing system according to  claim 3 , wherein an inductance of the split-ring is expressed the following equation: 
       
         
           
             
               L 
               = 
               
                 
                   μ 
                   0 
                 
                  
                 
                   
                     R 
                     m 
                   
                    
                   
                     ( 
                     
                       
                         log 
                          
                         
                           
                             8 
                              
                             
                               R 
                               m 
                             
                           
                           
                             h 
                             + 
                             w 
                           
                         
                       
                       - 
                       
                         1 
                         2 
                       
                     
                     ) 
                   
                 
               
             
           
         
         wherein μ 0  is free-space permeability, R m  is effective radius of the split-ring, w is a width of the split-ring, and h is a height of the split-ring. 
       
     
     
         5 . The biomedical pressure sensing system according to  claim 3 , wherein a capacitance of the gap is calculated as follows: 
       
         
           
             
               
                 C 
                 gap 
               
               = 
               
                 
                   
                     ɛ 
                     0 
                   
                    
                   
                     hw 
                     g 
                   
                 
                 + 
                 
                   C 
                   0 
                 
               
             
           
         
         wherein ε 0  is free-space permittivity, C0 is the capacitance caused by fringing fields and can be calculated as C 0 =ε 0 (h+w+g). 
       
     
     
         6 . The biomedical pressure sensing system according to  claim 3 , wherein the split-ring has a resonant frequency in S-band which is 2-4 GHz of an electromagnetic band. 
     
     
         7 . The biomedical pressure sensing system according to  claim 3 , wherein the split-ring is made of a silver conductive paint. 
     
     
         8 . The biomedical pressure sensing system according to  claim 3 , wherein a thickness of the split-ring is 500 μm. 
     
     
         9 . The biomedical pressure sensing system according to  claim 3 , wherein a width of the split-ring is 1.5 mm and a length of the extension portion is 3.5 mm. 
     
     
         10 . The biomedical pressure sensing system according to  claim 3 , wherein a width of the gap is 1 mm.