Patent Publication Number: US-2022229000-A1

Title: Bubble Detection Sensor

Description:
FIELD OF THE INVENTION 
     The present invention relates to a sensor and, more particularly, to a bubble detection sensor for detecting bubbles in a fluid. 
     BACKGROUND 
     Bubble detection sensors used to detect bubbles in a fluid have an emitter and a receiver on opposite sides of a tube carrying the fluid. A signal is transmitted from the emitter to the receiver through the fluid and is analyzed to determine the presence or absence of bubbles in the fluid. Detecting the presence of bubbles in a fluid is critical in many applications. In the medical field, for example, bubbles in a fluid transmitted to a patient for intravenous infusion or dialysis are detected to avoid potentially dangerous air embolisms. Current applications require increased sensitivity of the bubble detection sensor for more reliable detection of smaller bubbles. 
     U.S. Patent Application No. 2009/0293588 discloses a bubble detection sensor including an emitter and a receiver that are offset laterally from each other. The lateral offset of the emitter and the receiver increases the sensitivity of the bubble detection sensor to allow the detection of smaller bubbles. Due to the lateral offset, however, less of the signal emitted from the emitter is received by the receiver, decreasing an efficiency of the bubble detection sensor. Increasing the efficiency of such an arrangement requires expensive additional signal amplification or better signal processing. 
     In fluid detection sensors generally, as disclosed for example in  Fundamentals of Ultrasonic Flow Meters  (Conrad et al.), an emitter and a receiver may be rotated to account for refraction of the signal through the fluid medium. The angle of rotation of the emitter and receiver is selected only to optimize the efficiency of the signal; ensuring as much as possible of the signal emitted by the emitter is received by the receiver as a result of the refraction. The angle of rotation does not account for the sensitivity of the signal to scatterers such as bubbles. 
     SUMMARY 
     A bubble detection sensor includes an emitter having an emitting surface and a receiver positioned on a side of a fluid conduit opposite the emitter. The receiver has a receiving surface adapted to receive a signal emitted by the emitter through a fluid of the fluid conduit. A sensor axis extending normal to the emitting surface and the receiving surface is disposed at a rotation offset angle with respect to a plane extending normal to a longitudinal conduit axis of the fluid conduit. The rotation offset angle is set to optimize a ratio of a sensitivity of the signal received by the receiver to an efficiency of the signal received by the receiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying Figures, of which: 
         FIG. 1  is a front view of a bubble detection system according to an embodiment; 
         FIG. 2  is a rear view of the bubble detection system; 
         FIG. 3  is a perspective view of a bubble detection sensor of the bubble detection system; 
         FIG. 4  is a rear view of a bubble detection sensor according to another embodiment; 
         FIG. 5  is a rear view of a bubble detection sensor according to another embodiment; 
         FIG. 6  is a rear view of a bubble detection sensor according to another embodiment; 
         FIG. 7  is a graph of an output voltage of the bubble detection system in the presence and absence of a bubble; and 
         FIG. 8  is a graph of an efficiency, a sensitivity, and a figure of merit of the bubble detection system over a range of rotation offset angles. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments of the present disclosure will be described hereinafter in detail with reference to the attached drawings, wherein like reference numerals refer to like elements. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that the present disclosure will convey the concept of the disclosure to those skilled in the art. In addition, in the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. However, it is apparent that one or more embodiments may also be implemented without these specific details. 
     A bubble detection system  10  according to an embodiment, as shown in  FIGS. 1 and 2 , comprises a bubble detection sensor  100 , a controller  200  connected to the bubble detection sensor  100 , and a fluid conduit  300  disposed in the bubble detection sensor  100 . 
     The bubble detection sensor  100 , as shown in  FIGS. 1-3 , includes a housing  110 , an emitter  130  disposed in the housing  110 , and a receiver  150  disposed in the housing  110 . 
     The housing  110 , as shown in  FIGS. 1-3 , has an exterior surface  112  and an interior surface  114  opposite the exterior surface  112 . The housing  110  forms a first receiving section  115  and a second receiving section  117 . The first receiving section  115  and the second receiving section  117  each protrude in a transverse direction T on the exterior surface  112 , the first receiving section  115  forming a first receiving space  116  on the interior surface  114  and the second receiving section  117  forming a second receiving space  118  on the interior surface  114 . 
     On the exterior surface  112 , as shown in  FIGS. 1 and 3 , the first receiving section  115  and the second receiving section  117  are positioned parallel to one another along a longitudinal conduit axis L perpendicular to the transverse direction T. The first receiving section  115  and the second receiving section  117  are spaced apart and separated from one another on the exterior surface  112  in a depth direction D perpendicular to the transverse direction T and the longitudinal conduit axis L, defining a channel  119  formed by the exterior surface  112  between the first receiving section  115  and the second receiving section  117 . 
     In the embodiment shown in  FIGS. 1-3 , the housing  110  is integrally formed in a single piece with the first receiving section  115 , the second receiving section  117 , and the channel  119 . In other embodiments, the components of the housing  110  could be formed separately and assembled together to form the housing  10  as shown and described herein. 
     The emitter  130 , in the embodiment shown in  FIGS. 2 and 3 , is a piezoelectric crystal that is capable of being electrically excited at its resonant frequency with an input voltage to produce ultrasonic sound waves. The emitter  130  is held in the first receiving space  116  of the first receiving section  115  with an emitting surface  132  of the emitter  130  facing the channel  119 . The emitter  130  is held in the first receiving section  115  at a rotation offset angle A shown in  FIG. 2  and described in greater detail below. 
     The receiver  150 , in the embodiment shown in  FIGS. 2 and 3 , is a piezoelectric crystal that receives the ultrasonic sound waves from the emitter  130  and produces an output voltage based on the ultrasonic sound waves. The receiver  150  is held in the second receiving space  118  of the second receiving section  117  with a receiving surface  152  of the receiver  150  facing the channel  119 . The receiver  150  is held in the second receiving section  117  at the rotation offset angle A shown in  FIG. 2  and described in greater detail below. 
     As shown in  FIG. 2 , the emitter  130  has an emitter cross-sectional area  136  and the receiver  150  has a receiver cross-sectional area  156 . In the shown embodiment, the emitter  130  and the receiver  150  each have a rectangular prism shape. In other embodiments, the emitter  130  and the receiver  150  may each have a cylindrical shape or any other type of shape capable of emitting and receiving the ultrasonic waves as described herein. In the embodiment shown in  FIGS. 2 and 3 , the emitter cross-sectional area  136  is equal to the receiver cross-sectional area  156 . In other embodiments, as shown in  FIG. 5 , the emitter cross-sectional area  136  may be different from the receiver cross-sectional area  156 . 
     The controller  200 , shown in  FIGS. 1 and 2 , includes a processor  210  and a memory  220  connected to the processor  210 . The memory  220  is a non-transitory computer readable medium capable of storing program instructions thereon that are executable by the processor  210 . The processor  210  executes programs stored on the memory  220  to perform the functions of the controller  200  described herein. The controller  200  has an emitter connection line  230  connecting the controller  200  to the emitter  130  along which the controller  200 , by execution of the processor  210 , can transmit an input voltage  232  to the emitter  130 . The controller  200  has a receiver connection line  240  connecting the controller  200  to the receiver  150  along which the controller  200 , by execution of the processor  210 , can receive an output voltage  242  from the receiver  150 . 
     The fluid conduit  300 , as shown in  FIGS. 1 and 2 , contains a fluid  310 . The fluid  310  passes along the fluid conduit  300  in the longitudinal conduit axis L. In the shown embodiment, the fluid conduit  300  is a cylindrical tube with a circular cross-section. In other embodiments, the fluid conduit  300  can be any shape or type of fluid conduit  300  capable of being used with the bubble detection sensor  100  as described in detail below. 
     As shown in  FIGS. 1 and 2 , the fluid conduit  300  is disposed in the channel  119  and extends along the longitudinal conduit axis L. In an embodiment, an outer diameter  302  of the fluid conduit  300  is larger than a height  120  of the channel  119  in the depth direction D, and the fluid conduit  300  is slightly compressed between the first receiving section  115  and the second receiving section  117  to removably hold the fluid conduit  300  in the channel  119  by an interference fit. In other embodiments, the fluid conduit  300  may be removably secured in the channel  119  other than by an interference fit, and the outer diameter  302  may be less than or equal to the height  120  of the channel  119 . 
     With the fluid conduit  300  disposed in the channel  119 , as shown in  FIG. 2 , the emitter  130  and the receiver  150  are positioned on opposite sides of the fluid conduit  300  in the depth direction D. The emitting surface  132  faces the fluid conduit  300  in the channel  119  and the receiving surface  152  faces the fluid conduit  300  in the channel  119 . 
     As shown in  FIG. 2 , the emitter  130  and the receiver  150  do not extend parallel to the fluid conduit  300  but rather are held in the respective receiving sections  115 ,  117  of the housing  110  at an angle with respect to the fluid conduit  300 . A sensor axis S extends through the emitter  130  and the receiver  150  normal to the emitting surface  132  and the receiving surface  152 . The sensor axis S is rotated with respect to a plane P extending, along the depth direction D and the transverse direction T, normal to the longitudinal conduit axis L of the fluid conduit  300  by the rotation offset angle A shown in  FIG. 2 . With the sensor axis S disposed at the rotation offset angle A, the emitting surface  132  is parallel to the receiving surface  152 . 
     In the embodiment shown in  FIG. 2 , in addition to having the sensor axis S disposed at the rotation offset angle A with respect to the plane P, the emitter  130  and the receiver  150  are each laterally offset from the sensor axis S in a direction extending perpendicular to the sensor axis S. Due to the degree of the lateral offset shown in the embodiment of  FIG. 2 , the emitting surface  132  does not overlap with the receiving surface  152  in a direction extending parallel to the sensor axis S. 
     In another embodiment, as shown in  FIGS. 4 and 5 , the sensor axis S is disposed at the rotation offset angle A with respect to the plane P, and the emitting surface  132  and the receiving surface  152  overlap with one another in a direction extending parallel to the sensor axis S. In the embodiment shown in  FIGS. 4 and 5 , the emitter  130  and the receiver  150  are each laterally offset from the sensor axis S in the direction extending perpendicular to the sensor axis S with an emitting overlapping portion  134  of the emitting surface  132  overlapping with a receiving overlapping portion  154  of the receiving surface  152  along a direction extending parallel to the sensor axis S. 
     In the embodiment shown in  FIG. 2 , the emitting surface  132  and the receiving surface  152  do not overlap in a direction parallel to the sensor axis S; the emitting overlapping portion  134  is 0% of the emitting surface  132  and the receiving overlapping portion  154  is 0% of the receiving surface  152 . In the embodiment shown in  FIGS. 4 and 5 , the emitting overlapping portion  134  is approximately 50% of the emitting surface  132  and the receiving overlapping portion  154  is approximately 50% of the receiving surface  152 . In other embodiments, the emitting overlapping portion  134  may be greater than 0% and less than 50% of the emitting surface  132  and the receiving overlapping portion  154  may be greater than 0% and less than 50% of the receiving surface  152 . 
     In another embodiment shown in  FIG. 6 , the bubble detection sensor  100  has the emitter  130 , the receiver  150 , another emitter  170 , and another receiver  180  disposed in the housing  110 . The emitter  130  and the another emitter  170  are held in the first receiving space  116  of the first receiving section  115  and the receiver  150  and the another receiver  180  are held in the second receiving space  118  of the second receiving section  117 . The emitter  130  and the receiver  150  are positioned with respect to each other along the sensor axis S as described in the embodiments above. The another emitter  170  is identical to the emitter  130  and the another receiver  180  is identical to the receiver  150 . The another emitter  170  and the another receiver  180  are positioned along the sensor axis S at the rotation offset angle A and are positioned with respect to each other identically to the emitter  130  and the receiver  180 . The emitter  130  emits ultrasonic waves received by the receiver  150  and the another emitter  170  emits ultrasonic waves received by the another receiver  180 . In the embodiment shown in  FIG. 6 , the another emitter and the another receiver  180  provide redundancy to the transmitted signals in the bubble detection sensor  100  described herein. 
     The function of the bubble detection system  10  will now be described in greater detail primarily with reference to  FIGS. 1, 2, 7, and 8 . 
     As shown in  FIG. 2 , in use, the fluid  310  flows in the fluid conduit  300  along the longitudinal conduit axis L while the fluid conduit  300  is held in the channel  119  between the emitter  130  and the receiver  150 . A number of bubbles  312 ,  314  can be present in the fluid  310 , including, for example, a large bubble  312  and a small bubble  314 . In the exemplary embodiment, the large bubble  312  is approximately 70% of an inner diameter  304  of the fluid conduit  300  and the small bubble  314  is approximately 30% of the inner diameter  304 . 
     The bubble detection system  10  is used to detect the bubbles  312 ,  314  in the fluid  310 . To detect the bubbles  312 ,  314 , as shown in  FIG. 2 , the controller  200  outputs the input voltage  232  to the emitter  130  along the emitter connection line  230 . The emitter  130  produces ultrasonic sound waves in accordance with the input voltage  232 , which are emitted out from the emitting surface  132  toward the channel  119  and into the fluid  310  in the fluid conduit  300 . The ultrasonic sound waves may also be referred to as a “signal” herein. 
     The signal is received by the receiver  150  at the receiving surface  152  after it passes through the fluid  310 , and the receiver  150  outputs the output voltage  242  depending on the signal along the receiver connection line  240  back to the controller  200 . The signal received by the receiver  150  is impacted by refraction through the medium of the fluid  310  and by the presence of bubbles  312 ,  314  in the fluid  310 . The output voltage  242  is representative of the signal received by the receiver  150 . 
     The controller  200  analyzes the output voltage  242  to determine a presence or an absence of bubbles  312 ,  314  in the fluid  310 . The controller  200  monitors the output voltage  242  and, when a drop  244  in the output voltage  242  occurs as shown in the example embodiment of  FIG. 7 , the controller  200  determines that a bubble  312 ,  314  is present in the fluid  310 . The example embodiment of  FIG. 7  shows the drop  244  in the output voltage  242  for a small bubble  314 , but the concept of the output voltage  242  dropping to indicate a bubble  312 ,  314  applies equally to the small bubble  314  or any bubble  312 ,  314  larger than the small bubble  314 . 
     A comparison of the output voltage  242  to the input voltage  232  by the controller  200  indicates both an efficiency of the ultrasonic wave signal received by the receiver  150  in the absence of bubbles  312 ,  314  in the fluid  310 , and a sensitivity of the signal to the presence of a bubble  312 ,  314  in the fluid  310 . 
     An efficiency of the signal is calculated by the controller  200  according to the following equation: 
     
       
         
           
             
               
                 
                   Efficiency 
                   = 
                   
                     20 
                     ⁢ 
                     
                       
                         log 
                         
                           1 
                           ⁢ 
                           0 
                         
                       
                       ⁡ 
                       
                         ( 
                         
                           
                             V 
                             
                               i 
                               ⁢ 
                               n 
                             
                           
                           
                             V 
                             NoBubble 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     where V in  is the input voltage  232  and V NoBubble  is the output voltage  242  independent of an influence of a bubble  312 ,  314  in the fluid  310 ; i.e. the output voltage  242  without the drop  244  shown in  FIG. 7 . The efficiency of the signal is calculated based on a ratio of the input voltage  232  to the output voltage  242  in the absence of a bubble  312 ,  314 ; the efficiency of the signal represents how much of the emitted signal is received by the receiver  150  through the fluid  310  in the absence of bubbles  312 ,  314 . 
     A sensitivity of the signal is calculated by the controller  200  according to the following equation: 
     
       
         
           
             
               
                 
                   Sensitivity 
                   = 
                   
                     20 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         log 
                         
                           1 
                           ⁢ 
                           0 
                         
                       
                       ⁡ 
                       
                         ( 
                         
                           
                             V 
                             Bubble 
                           
                           
                             V 
                             NoBubble 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     where V bubble  is the output voltage  242  with the drop  244  indicating the presence of a bubble  312 ,  314  and V NoBubble  is the output voltage  242  without the drop  244 . The sensitivity of the signal is calculated based on a difference in an amplitude of the signal received by the receiver  150  between the absence of a bubble  312 ,  314  in the fluid  310  and the presence of the bubble  312 ,  314  in the fluid  310 . The sensitivity indicates a change in the magnitude of the output voltage  242  in the presence of a bubble  312 ,  314 . 
     The rotation offset angle A of the sensor axis S, shown in  FIGS. 2 and 4-6 , is set to optimize a ratio of the sensitivity of the signal received by the receiver  150  to the efficiency of the signal received by the receiver  150 . The rotation offset angle A is selected to optimize a figure of merit according to the equation: 
     
       
         
           
             
               
                 
                   Figure 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   of 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   Merit 
                   ⁢ 
                   
                     = 
                     
                        
                       
                         
                           20 
                           ⁢ 
                           
                             
                               log 
                               
                                 1 
                                 ⁢ 
                                 0 
                               
                             
                             ⁡ 
                             
                               ( 
                               
                                 Vbubble 
                                 Vnobubble 
                               
                               ) 
                             
                           
                         
                         
                           20 
                           ⁢ 
                           
                             
                               log 
                               
                                 1 
                                 ⁢ 
                                 0 
                               
                             
                             ⁡ 
                             
                               ( 
                               
                                 Vin 
                                 Vnobubble 
                               
                               ) 
                             
                           
                         
                       
                        
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
     The figure of merit is shown plotted in  FIG. 8  separate from the efficiency and sensitivity over a range of rotation offset angles A. The rotation offset angle A on the x-axis of the graph is shown relative to the rotation offset angle A at maximum efficiency; i.e. as shown in  FIG. 8 , the x-axis value of the rotation offset angle A is 1 at maximum efficiency. 
     As shown in  FIG. 8 , selecting a rotation offset angle A of the sensor axis S according to the figure of merit, maximizing a ratio of sensitivity to efficiency, results in a rotation offset angle A that is greater than an angle set to optimize only the efficiency of the signal received by the receiver  150 . The rotation offset angle A selected according to the figure or merit is nearly twice the angle selected for maximum efficiency in the embodiment shown in  FIG. 8 . In other embodiments, the rotation offset angle A is 1.6-2.1 times the angle selected for maximum efficiency. 
     The particular angle selected for the rotation offset angle A maximizing a ratio of sensitivity to efficiency according to the present invention will vary in different applications according to the particular specifications and dimensions of the housing  110 , the emitter  130 , the receiver  150 , and the fluid conduit  130 , among other variables. In an embodiment, the rotation offset angle A is greater than or equal to 20° and less than or equal to 35°. In such an embodiment, an angle selected only for maximum efficiency is approximately 15°. In another embodiment, the rotation offset angle A is greater than or equal to 25° and less than or equal to 30°. 
     By setting the rotation offset angle A to maximize a ratio of sensitivity to efficiency, the bubble detection sensor  100  of the bubble detection system  10  has an increased sensitivity to small bubbles  314  with a minimal impact on efficiency. The rotation offset angle A allows the detection of small bubbles  314  and large bubbles  314 , such as in critical medical or other applications, without requiring more expensive signal processing or additional amplification.