WO2013109191A1 - A device and a method for determining a flow rate of fluid in a fluid line - Google Patents

Abstract

According to embodiments of the present invention, a method for determining a flow rate of fluid in a fluid line is provided. The method includes flowing a fluid through a fluid line, generating at least one bubble configured to flow in the fluid by means of a transducer, determining a first time at which a first capacitance at a first location on the fluid line changes, corresponding to a flow of the bubble through the first location, determining a second time at which a second capacitance at a second location on the fluid line changes, corresponding to the flow of the bubble through the second location, wherein the second location is spaced apart from the first location by a predetermined distance, and determining a flow rate of the fluid as a function of the predetermined distance and a difference between the first time and the second time.

Description

A DEVICE AND A METHOD FOR DETERMINING A FLOW RATE OF FLUID IN A

FLUID LINE

Cross-Reference To Related Application

[0001] This application claims the benefit of priority of Singapore patent application No. 201200401-6, filed 18 January 2012, the content of it being hereby incorporated by reference in its entirety for all purposes. Technical Field

[0002] Various embodiments relate to a device and a method for determining a flow rate of fluid in a fluid line, a method for determining whether a leak is present in a fluid line, and a sensing device for a fluid line.

Background

[0003] Insulin delivery systems are available in the market to be used by diabetics to receive their insulin, as schematically shown in FIG. 1. The insulin delivery system 100 includes a pump system (or pump unit) 102, an infusion set 104, and a tubing 106 connecting the pump system 102 and the infusion set 104. The infusion set 104 includes a cannula 108 for insertion into the skin 110, at an infusion site, of a diabetic user or patient. The system 100 delivers insulin in a manner more similar to a pancreas than periodic injections, by supplying a constant low level insulin injection and then gives a bolus of insulin as needed. The user inputs data into the pump system 102 periodically to let the insulin delivery system 100 know their calorie intake and the pump system 100 will calculate the insulin injection based on that data.

[0004] The insulin pump system 102 and the infusion set 104 occasionally have leaks, causing leakages in the insulin delivery system 100. For example, there may be insulin leaks due tube breakage, misplacement of cannula 108 or reservoir 103 of the pump system 102, leaky o-rings, choke or blockage, for example an insulin reservoir/O-ring leak at the pump system 102, a tubing leak in the tubing 106, for example due to breakage, and insertion leak at the infusion site, as illustrated in FIG. 1.

[0005] If there is a leak of the insulin solution, it is almost impossible for the patient to detect because the volumes are minuscule. The typical insulin flow rates and tube parameters for the insulin delivery system 100 are shown in Table 1.

Table 1

[0006] A second issue of the insulin delivery system 100 or the pump system 102 is related to the chemistry used in the insulin solution which over time outgasses. The gaseous material forms into small bubbles and at times combine into a larger bubble whose volume is >10μ1. If the large bubbles get into the tubing 106 and disrupt the flow of insulin, this would be a problem for the patient. As a result, an incorrect insulin dose may be given to the user, which can lead to health problems, including death if not handled quickly. Also, these bubbles will impact the flow measurement. Furthermore, such bubbles may be injected into the user. Currently, there is no method to deal with the bubbles in the insulin delivery system 100 except that the user is to inspect the insulin reservoir of the pump system 102 periodically.

[0007] Existing flow rate detection technologies typically cannot detect the very low flow rates of the insulin delivery system 100 or other systems providing such low flow rates. The lowest flow rate of the system 100 is 7 x lO^"5 μΐ/s. It is very difficult or impossible to detect those flow rates with conventional methods such as inertial flow sensors, ultrasound Doppler sensors, etc.

[0008] Laser particle imaging has been used to investigate the flow rate of insulin at higher flow rates. While this could measure most flow rates of interest, it is not a practical method for measurement because it adds particles to the stream, and the equipment for measuring the flow is cost prohibitive for mass production. Another method for measuring low flow rates is to use a silicon micro channel that would produce bubbles. Another method is to fabricate a microelectromechanical systems (MEMS) heater and monitor the temperature change as the fluid is flowing. The problem with both of these latter methods is that they require a change in the tubing material that is in contact with the insulin. However, for existing system available in the market, for example the insulin delivery system 100, all the work and procedures to obtain FDA approval have been completed to use the tubing 106 already in use. If the tubing material is to be changed, the process to obtain Food and Drug Administration (FDA) approval would need to be repeated and this would represent an undue cost and delay.

[0009] One method for detecting flow rates in fluids that don't have any ultrasound contrast agents has been developed where cavitation bubbles are used as contrast agents in fluid flows. However, such a method would not work, for example for the insulin delivery system 100, because the bubbles Would be moving too slow for ultrasound Doppler detection to be used.

Summary

[0010] According to an embodiment, a method for determining a flow rate of fluid in a fluid line is provided. The method may include flowing a fluid through a fluid line, generating at least one bubble configured to flow in the fluid by means of a transducer, determining a first time at which a first capacitance at a first location on the fluid line changes, corresponding to a flow of the bubble through the first location, determining a second time at which a second capacitance at a second location on the fluid line changes, corresponding to the flow of the bubble through the second location, wherein the second location is spaced apart from the first location by a predetermined distance, and determining a flow rate of the fluid as a function of the predetermined distance and a difference between the first time and the second time.

[0011] According to an embodiment, a device for determining a flow rate of fluid in a fluid line is provided. The device may include an ultrasound transducer configured to generate at least one bubble configured to flow in a fluid flowing through the fluid line, a first capacitor comprising a first pair of electrodes adapted to be arranged on opposing sides of the fluid line, the first capacitor being configured to sense a first capacitance of the fluid line between the first pair of electrodes, a second capacitor comprising a second pair of electrodes adapted to be arranged on opposing sides of the fluid line, the second capacitor being configured to sense a second capacitance of the fluid line between the second pair of electrodes, wherein the second capacitor is spaced apart from the first capacitor by a predetermined distance, a circuit in communication with the first capacitor and the second capacitor, the circuit being configured to determine a first time at which the first capacitance changes, corresponding to a flow of the bubble through the first capacitor, and a second time at which the second capacitance changes, corresponding to the flow of the bubble through the second capacitor, and wherein the circuit is further configured to determine a flow rate of the fluid as a function of the predetermined distance and a difference between the first time and the second time.

[0012] According to an embodiment, a method for determining whether a leak is present in a fluid line is provided. The method may include flowing a fluid through a fluid line, generating at least one first bubble configured to flow in the fluid by means of at least one transducer, determining a first flow rate of the fluid flowing through a first portion of the fluid line based on a flow of the first bubble through the first portion, generating at least one second bubble configured to flow in the fluid by means of the at least one transducer, determining a second flow rate of the fluid flowing through a second portion of the fluid line based on a flow of the second bubble through the second portion, and determining whether a leak is present in the fluid line between the first portion and the second portion based on the first flow rate and the second flow rate.

[0013] According to an embodiment, a method for determining whether a leak is present in a fluid line is provided. The method may include flowing a fluid through a fluid line, generating at least one bubble configured to flow in the fluid by means of at least one transducer, determining a first flow rate of the fluid flowing through a first portion of the fluid line based on a flow of the bubble through the first portion, determining a second flow rate of the fluid flowing through a second portion of the fluid line based on the flow of the bubble through the second portion, and determining whether a leak is present in the fluid line between the first portion and the second portion based on the first flow rate and the second flow rate. [0014] According to an embodiment, a sensing device for a fluid line is provided. The sensing device may include an ultrasound transducer configured to generate a bubble in a fluid flowing through the fluid line, and a capacitor comprising a pair of electrodes adapted to be arranged on opposing sides of the fluid line, the capacitor being configured to sense a capacitance between the pair of electrodes so as to determine a flow of the bubble through the fluid line.

Brief Description of the Drawings [0015] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:

[0016] FIG. 1 shows a schematic of an insulin delivery system.

[0017] FIG. 2A shows a flow chart illustrating a method for determining a flow rate of fluid in a fluid line, according to various embodiments.

[0018] FIG. 2B shows a schematic block diagram of a device for determining a flow rate of fluid in a fluid line, according to various embodiments.

[0019] FIG. 2C shows a flow chart illustrating a method for determining whether a leak is present in a fluid line, according to various embodiments.

[0020] FIG: 2D shows a flow chart illustrating a method for determining whether a leak is present in a fluid line, according to various embodiments.

[0021] FIG. 2E shows a schematic block diagram of a sensing device for a fluid line, according to various embodiments.

[0022] FIG. 3 shows a sensor system, according to various embodiments.

[0023] FIG. 4A shows a perspective view of a sensing device, according to various embodiments.

[0024] FIG. 4B shows a perspective view of a sensing device, according to various embodiments. [0025] FIG. 4C shows a cross-sectional view of a sensing device, according to various embodiments.

[0026] FIG. 4D shows a cross-sectional view of a sensing device, according to various embodiments.

[0027] FIG. 5 shows a cross-sectional view of a sensing device, according to various embodiments.

[0028] FIG. 6 shows a plot of the ultrasound pressure required for generation of bubbles at different operation frequencies, according to various embodiments.

[0029] FIG. 7 shows a plot of the capacitance change as a function of bubble movement along a tubing, according to various embodiments.

[0030] FIG. 8 shows a plot of the bubble lifetime as a function of the bubble size and the amount of dissolved gas in solution, according to various embodiments.

Detailed Description

[0031] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0032] Embodiments described in the context of one of the methods or devices are analogously valid for the other method or device. Similarly, embodiments described in the context of a method are analogously valid for a device, and vice versa.

[0033] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0034] In the context of various embodiments, the articles "a", "an" and "the" as used with regard to a feature or element includes a reference to one or more of the features or elements.

[0035] In the context of various embodiments, the phrase "at least substantially" may include "exactly" and a reasonable variance.

[0036] In the context of various embodiments, the term "about" or "approximately" as applied to a numeric value encompasses the exact value and a reasonable variance.

[0037] As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0038] As used herein, the phrase of the form of "at least one of A or B" may include A or B or both A and B. Correspondingly, the phrase of the form of "at least one of A or B or C", or including further listed items, may include any and all combinations of one or more of the associated listed items.

[0039] Various embodiments may relate to fields related to medical devices for diabetic infusion system, closed loop diabetic management, very low flow rates and addition of bubbles to fluid streams. Various embodiments may relate to biosensor.

[0040] Various embodiments may provide one or more of insulin infusion leak detection, bubble detection or flow rate sensors.

[0041] Various embodiments may provide an ultrasound and capacitive based low flow rate measurement device or system.

[0042] Various embodiments may provide ultrasound bubble generation and electrical detection (for example based on capacitance change). The electrical detection of bubbles may allow measurement of even lower flow rates. Capacitors may be placed along the flow path to detect the flow rate.

[0043] Various embodiments may be employed for the flow of a solution where bubble(s) may be generated and/or where bubble(s) already exist in the flow. Therefore, the use of the sensing device and sensor system of various embodiments are not dependent on bubbles already being in the solution. [0044] Various embodiments may provide one or more of the following : bubble creation or generation by ultrasound, bubble detection by capacitance change, bubble velocity detection by multiple electrodes, use of standing wave to hold a bubble in place, and detection of incoming bubbles by capacitance change.

[0045] Various embodiments may provide an approach that makes use of ultrasonically generated bubbles and electrostatic bubble detection to determine flow rate. While a time of flight ultrasonic approach may be used, there may be challenges as at a minimum flow rate of about 600 nm/s, the bubble may not survive long enough for 2 ultrasonic transducers to be placed far enough apart.

[0046] In various embodiments, an ultrasonically generated bubble is used along with a capacitive sensor to detect the movement of the bubble. The capacitive change between gas and liquid may be used as an indication of fluid flow. It has been observed that, when using an ultrasound mist maker, it sets up standing waves in certain configurations and that bubbles may become caught in the standing waves. This may be used to control the bubble position in one direction while allowing the flow to move the bubble. Furthermore, the approach for the sensor of various embodiments may allow detection of the entrance of large bubbles into a tubing or fluid line.

[0047] Various embodiments may provide a sensor or sensor system that may allow monitoring of the flow of fluid, e.g. insulin, at various points along the infusion system supplying the fluid to a user or patient. The sensor system may provide detection capability lower than most conventional sensors. In various embodiments, the minimum detection may be limited by the tube geometry and electrode geometry. The sensor system may be used for non-contact measurements, meaning that there is non-contact with the fluid (e.g. insulin) during the measurement. The sensor system may be employed for bubble detection due to out-gassing from a fluid (e.g. insulin) and other mishandling issues and bubble management. The sensor system may have a small foot print to be integrated with an infusion tubing system. The sensor system may be low cost and/or cost effective and/or may be disposable.

[0048] In order that the invention may be readily understood and put into practical effect, particular embodiments will now be described by way of examples and not limitations, and with reference to the figures. [0049] FIG. 2A shows a flow chart 200 illustrating a method for determining a flow rate of fluid in a fluid line, according to various embodiments.

[0050] At 202, a fluid is flowed through a fluid line.

[0051] At 204, at least one bubble configured to flow in the fluid is generated by means of a transducer. In the context of various embodiments, a bubble having a diameter of between about 20 μιη and about 300 μηι may be generated.

[0052] At 206, a first time at which a first capacitance at a first location on the fluid line changes is determined, corresponding to a flow of the bubble through the first location.

[0053] At 208, a second time at which a second capacitance at a second location on the fluid line changes is determined, corresponding to the flow of the bubble through the second location, wherein the second location is spaced apart from the first location by a predetermined distance.

[0054] At 210, a flow rate of the fluid is determined as a function of the predetermined distance and a difference between the first time and the second time.

[0055] In various embodiments, at 206, the method includes determining the first time at which the first capacitance is less than a first predefined value, and at 208, the method includes determining the second time at which the second capacitance is less than the first predefined value.

[0056] In various embodiments, at 206, the method includes determining the first time at which the first capacitance changes by a second predefined value, and at 208, the method includes determining the second time at which the second capacitance changes by the second predefined value.

[0057] In various embodiments, the method may further include applying energy to the bubble.

[0058] In the context of various embodiments, the method may further include operating an ultrasound transducer to generate the bubble.

[0059] FIG. 2B shows a schematic block diagram of a device 220 for determining a flow rate of fluid in a fluid line, according to various embodiments. The device 220 includes an ultrasound transducer 222 configured to generate at least one bubble configured to flow in a fluid flowing through the fluid line, a first capacitor 224 including a first pair of electrodes 226 adapted to be arranged on opposing sides of the fluid line, the first capacitor 224 being configured to sense a first capacitance of the fluid line between the first pair of electrodes 226, a second capacitor 228 including a second pair of electrodes 230 adapted to be arranged on opposing sides of the fluid line, the second capacitor 228 being configured to sense a second capacitance of the fluid line between the second pair of electrodes 230, wherein the second capacitor 228 is spaced apart from the first capacitor 224 by a predetermined distance, and a circuit 232 in communication with the first capacitor 224 and the second capacitor 228, the circuit 232 being configured to determine a first time at which the first capacitance changes, corresponding to a flow of the bubble through the first capacitor 224, and a second time at which the second capacitance changes, corresponding to the flow of the bubble through the second capacitor 228, and wherein the circuit 232 is further configured to determine a flow rate of the fluid as a function of the predetermined distance and a difference between the first time and the second time. In FIG. 2B, the line represented as 234 is illustrated to show the relationship between the ultrasound transducer 222, the first capacitor 224, the first pair of electrodes 226, the second capacitor 228, the second pair of electrodes 230 and the circuit 232, which may include electrical coupling and/or mechanical coupling.

[0060] In various embodiments, the circuit 232 may be configured to determine the first time when the first capacitance is less than a first predefined value, and to determine the second time when the second capacitance is less than the first predefined value.

[0061] In various embodiments, the circuit 232 may be configured to determine the first time when the first capacitance changes by a second predefined value, and to determine the second time when the second capacitance changes by the second predefined value.

[0062] In various embodiments, the device 220 may further include the fluid line, the fluid line having a cross section adapted to match a cross section of the first pair of electrodes 226 and a cross section of the second pair of electrodes 230.

[0063] Each of the first pair of electrodes 226 and the second pair of electrodes 230 may form or may have an at least substantially circular cross section. In such embodiments, the fluid line may have a circular cross section.

[0064] Each of the first pair of electrodes 226 and the second pair of electrodes 230 may form or may have an at least substantially oval (or ellipse) cross section. In such embodiments, the fluid line may have an oval cross section. The first pair of electrodes 226 may be adapted to be arranged on either side of a major axis of the oval cross section of the first pair of electrodes 226. The second pair of electrodes 230 may be adapted to be arranged on either side of a major axis of the oval cross section of the second pair of electrodes 230. The ultrasound transducer 222 may be adapted to be arranged at one end of a major axis of the oval cross section of the fluid line.

[0065] In various embodiments, the ultrasound transducer 222 may be configured to generate the bubble having a diameter of between about 20 μηι and about 300 μηι.

[0066] In the context of various embodiments, the ultrasound transducer 222 may be a piezoelectric transducer or a capacitive transducer or a magnetostrictive transducer.

[0067] FIG. 2C shows a flow chart 240 illustrating a method for determining whether a leak is present in a fluid line, according to various embodiments.

[0068] At 242, a fluid is flowed through a fluid line.

[0069] At 244, at least one first bubble configured to flow in the fluid is generated by means of at least one transducer. In the context of various embodiments, the first bubble may have a diameter of between about 20 μπι and about 300 μηι.

[0070] At 246, a first flow rate of the fluid flowing through a first portion of the fluid line is determined based on a flow of the first bubble through the first portion.

[0071] At 248, at least one second bubble configured to flow in the fluid is generated by means of the at least one transducer. In the context of various embodiments, the second bubble may have a diameter of between about 20 μιη and about 300 μηι.

[0072] At 250, a second flow rate of the fluid flowing through a second portion of the fluid line is determined based on a flow of the second bubble through the second portion.

[0073] At 252, whether a leak is present in the fluid line between the first portion and the second portion is determined based on the first flow rate and the second flow rate.

[0074] In various embodiments, at 252, the method includes comparing the first flow rate with the second flow rate to determine whether a leak is present in the fluid line.

[0075] In various embodiments, the method may further include providing an indication that the leak is present if the first flow rate and the second flow rate are different. The indication may be provided if the difference between the first flow rate and the second flow rate is more than a predefined value. [0076] In various embodiments, at 246, the method may include determining a first time at which a first capacitance at a first location within the first portion of the fluid line changes, corresponding to the flow of the first bubble through the first location, determining a second time at which a second capacitance at a second location within the first portion of the fluid line changes, corresponding to the flow of the second bubble through the second location, wherein the second location is spaced apart from the first location by a first predetermined distance, and determining the first flow rate of the fluid through the first portion as a function of the first predetermined distance and a difference between the first time and the second time.

[0077] In various embodiments, at 250, the method may include determining a third time at which a third capacitance at a third location within the second portion of the fluid line changes, corresponding to the flow of the second bubble through the third location, determining a fourth time at which a fourth capacitance at a fourth location within the second portion of the fluid line changes, corresponding to the flow of the second bubble through the fourth location, wherein the fourth location is spaced apart from the third location by a second predetermined distance, and determining the flow rate of the fluid through the second portion as a function of the second predetermined distance and a difference between the third time and the fourth time.

[0078] FIG. 2D shows a flow chart 260 illustrating a method for determining whether a leak is present in a fluid line, according to various embodiments.

[0079] At 262, a fluid is flowed through a fluid line.

[0080] At 264, at least one bubble configured to flow in the fluid is generated by means of at least one transducer. In the context of various embodiments, the bubble may have a diameter of between about 20 μηι and about 300 μηι.

[0081] At 266, a first flow rate of the fluid flowing through a first portion of the fluid line is determined based on a flow of the bubble through the first portion.

[0082] At 268, a second flow rate of the fluid flowing through a second portion of the fluid line is determined based on the flow of the bubble through the second portion.

[0083] At 270, whether a leak is present in the fluid line between the first portion and the second portion is determined based on the first flow rate and the second flow rate. [0084] FIG. 2E shows a schematic block diagram of a sensing device 280 for a fluid line, according to various embodiments. The sensing device 280 includes an ultrasound transducer 282 configured to generate a bubble in a fluid flowing through the fluid line, and a capacitor 284 including a pair of electrodes 286 adapted to be arranged on opposing sides of the fluid line, the capacitor 284 being configured to sense a capacitance between the pair of electrodes 286 so as to determine a flow of the bubble through the fluid line. In FIG. 2E, the line represented as 288 is illustrated to show the relationship between the ultrasound transducer 282, the capacitor 284 and the pair of electrodes 286, which may include electrical coupling and/or mechanical coupling.

[0085] In the context of various embodiments, a bubble having a diameter of between about 20 μπι and about 300 μιη may be generated.

[0086] The pair of electrodes 286 may form or may have an at least substantially circular cross section. In such embodiments, the fluid line may have a circular cross section.

[0087] The pair of electrodes 286 may form or may have an at least substantially oval (or ellipse) cross section. In such embodiments, the fluid line may have an oval cross section. The pair of electrodes 286 may be adapted to be arranged on either side of a major axis of the oval cross section. The ultrasound transducer 282 may be adapted to be arranged at one end of the major axis of the oval cross section.

[0088] In various embodiments, the sensing device 280 may further include a non- variable capacitor coupled to the capacitor in a parallel connection.

[0089] In various embodiments, the sensing device 280 may further include a plurality of capacitors adapted to be arranged along the fluid line, each capacitor including a respective pair of electrodes adapted to be arranged on opposing sides of the fluid line. A respective capacitor may be coupled to a subsequent third capacitor in a parallel connection.

[0090] In the context of various embodiments, the ultrasound transducer 282 and the capacitor 284 may be integrated.

[0091] In the context of various embodiments, the ultrasound transducer 282 may be a piezoelectric transducer or a capacitive transducer or a magnetostrictive transducer.

[0092] In the context of various embodiments relating to any pair of electrodes, the pair of electrodes may include a first electrode and a second electrode spaced apart from each other. Each of the first electrode and the second electrode may have a width, w, of between about 1 μηι and about 100 μιη, e.g. between about 1 μπι and about 50 μηι, between about 1 μιη and about 10 μιη, between about 10 μηα and about 100 μηι or between about 30 μιη and about 50 μιη, for example depending on at least one of the capacitor (pair of electrodes) specification, the bubble speed resolution or the size of the bubble generated. The first electrode and the second electrode may be spaced apart from each other by a spacing, d, at a minimum value of approximately 1.5. times the desired bubble diameter, but not so large a spacing that there may be no change in the capacitance due to the bubble passing through. As a non-limiting example, for a bubble diameter of approximately 30 μιή, a spacing of between about 45 μηι and 150 μηι may be provided, e.g. between about 45 μιη and 100 μηι, between about 45 μπι and 60 μηι or between about 80 μηι and 150 μηι. Each of the first electrode and the second electrode may have an area determined by the static capacitance needed in the sensor or sensing device. The electrodes or series of electrodes may cover approximately 90 percent (90%) of the perimeter of the tubing or fluid line.

[0093] In the context of various embodiments where two pairs of electrodes are positioned spaced apart from each other and adjacent to each other, the two adjacent pairs of electrodes may be spaced apart from each other by a spacing, s, having a minimum value that may be determined by fabrication tolerances. The maximum value should not be more than one-half (½) of the bubble diameter so that the position of the bubble may be monitored. As a non-limiting example, for a 30 μηι diameter bubble, a minimum spacing may be about 1 μιη and a maximum spacing may be about 15 μιη, e;g. between about 1 μπι and 15 μιη, between about 1 μιη and 10 μηι, between about 1 μπι and 5 μιη or between about 5 μηι and 15 μηι.

[0094] Various embodiments may provide an approach to integrate multiple flow rate meters or sensing devices along a tubing or tube, for example for performing at least one of a flow rate detection, leak detection or bubble detection.

[0095] FIG. 3 shows a sensor system 300, according to various embodiments. The sensor 300 may include a reservoir 302, a coil 304 for inductive coupling, a tubing or fluid line 306, and two flow meters or sensors or sensing devices, in the form of a first sensing device 308a and a second sensing device 308b. The first sensing device 308a and the second sensing device 308b are coupled to or over the tubing 306. The first sensing device 308a and the second sensing device 308b may be arranged spaced apart from each other along the length of the tubing 306. The first sensing device 308a may be arranged towards one end of the tubing 306 that may be connected to the reservoir 302, while the second sensing device 308b may be arranged towards an opposite end of the tubing 306, distal to the reservoir 302, such that a fluid may flow in a direction from the reservoir 302 towards the first sensing device 308 a and then onward towards the second sensing device 308b. It should be appreciated that any number of the flow meter or sensing device (e.g. 308a, 308b) may be provided along the length of the tubing 306, for example-, one, two, three, four or any higher number, and/or the sensing device(s) (e.g. 308a, 308b) may be arranged at any position(s) along the length of the tubing 306.

[0096] Each of the first sensing device (or sensor) 308a and the second sensing device (or sensor) 308b includes an ultrasonic transducer 320 and a capacitive detector (e.g. capacitive bubble detector) 322. The capacitive detector 322 may perform detection or sensing by a capacitive effect, meaning by means of a change in the capacitance. The capacitive detector 322 may include one or more capacitors, each capacitor being defined by a pair of electrodes, as will be described later. The capacitive detector 322 may be arranged adjacent to and in proximity with the ultrasonic transducer 320. The ultrasonic transducer 320 may be coupled to or over a portion of the capacitive detector 322.

[0097] The ultrasonic transducer 320 may be used to create one or more bubbles 330 with a diameter of approximately 30 μηι, which would have a volume of approximately 1.41 x 10^-5 μΐ. The bubbles 330 may be created as the low pressure areas from the ultrasound waves generated by the ultrasonic transducer 320 go below the vapor pressure of the gas dissolved in the fluid (e.g. insulin solution) that may flow through the tubing 306.

[0098] As these bubbles 330 move through the electrode pairs of the capacitors of the capacitive detector 322, the bubbles 330 may change the capacitance, which may be detected by the capacitive detector 322. This phenomenon or effect may be used to detect the velocity of the fluid passing through the tubing 306 and therefore, the flow rate of the fluid may be calculated or determined. [0099] The sensor system 300 may be employed for an infusion set, e.g. the infusion set 104 of FIG. 1. The reservoir 302 may be coupled or connected into the pump system 102 (FIG. 1). The pump system 102 may have a matching coil for inductive coupling between the pump system 102 and the sensor 300, for example for transmission of data between the pump system 102 with the first sensing device 308a and the second sensing device 308b, and/or transmission of power to the first sensing device 308a and the second sensing device 308b, via the coil 304 of the sensor 300. The end of the tubing 306 distal to the reservoir 302 may be coupled or connected to the infusion set 104 (FIG. 1). As described above, two sensing devices, in the form of the first sensing device 308a and the second sensing device 308b, may be placed along the long tubing 306. The first sensing device (or flow sensor) 308a may be positioned close to the exit of the reservoir 302 and may be used to detect bubbles leaving the reservoir 302. The second flow rate measurement location, where the second sensing device 308b may be positioned, may be close to the cannula (e.g. 108, FIG. 1) where the insulin is injected into a patient. The two flow rate sensors (first sensing device 308a and the second sensing device 308b) may allow for the monitoring of the flow across the tubing 306 as well as any changes in the flow.

[0100] The first sensing device 308a and the second sensing device 308b may be employed to detect the flow rate of liquid flowing through the tubing 306, and/or any changes in the flow rate, for example due to leaks. Furthermore, the first sensing device 308a and the second sensing device 308b may be employed to detect the presence of bubbles in the fluid flowing through the tubing 306. As the first sensing device 308 a and the second sensing device 308b would not contact the insulin during operation of the sensor 300, there is no need for FDA approval because the materials in contact with the insulin would not have changed (in other words, the use of the first sensing device 308 a and the second sensing device 308b does not require a change in the material of the insulin flow path), for example no re-certification of the tubing material is needed, as compared to conventional flow rate sensors which require contact with the fluid (e.g. insulin) to perform the measurement, and thus the use of such conventional flow rate sensors may require additional FDA approval. [0101] Therefore, the first sensing device 308a and the second sensing device 308b and the sensor 300 may be employed for medical devices or systems available in the market.

[0102] FIG. 4A shows a perspective view of a sensing device 400, according to various embodiments. The sensing device 400 may be coupled to or on a tubing or fluid line 482. The sensing device 400 has a sensor structure including an ultrasonic (US) transducer 484 which may be used to create or generate one or more bubbles 486. A series of electrodes may be placed near the ultrasonic transducer 484 to detect the bubble 486 as it moves in the stream within the tubing 482. The series of electrodes includes a number of pairs of electrodes for detecting the movement of the bubble 486. As a non-limiting example, FIG. 4A shows a sensing device 400 having four pairs of electrodes, including a first pair of electrodes 410, a second pair of electrodes 420, a third pair of electrodes 430 and a fourth pair of electrodes 440. It should be appreciated that any number of pairs of electrodes may be provided for the sensing device 400, for example one, two, three, four, five or any higher number of pairs of electrodes.

[0103] Each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes 430 and fourth pair of electrodes 440 includes two electrodes arranged on opposite sides of the tubing 402. Using the first pair of electrodes 410 as a non-limiting example, the first pair of electrodes 410 includes a first electrode 411 and a second electrode 412 arranged on opposite sides of the tubing 482. An electrode (e.g. first electrode 411) of each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes 430 and fourth pair of electrodes 440 may be arranged at least substantially aligned with each other on one side of the tubing 482, while the other electrode (e.g. second electrode 412) of each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes 430 and fourth pair of electrodes 440 may be arranged at least substantially aligned with each other on the opposite side of the tubing 482. Each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes 430 and fourth pair of electrodes 440 defines a capacitor.

[0104] The sensing device 400 has a circular cross section, as illustrated in FIG. 4A. Each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes 430 and fourth pair of electrodes 440 has or form an at least substantially circular cross section. The tubing 482 may have a circular cross-section. Each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes 430 and fourth pair of electrodes 440 may be arranged at least substantially around the circumference of the tubing 482. The transducer 484 may be arranged over the tubing 482.

[0105] FIG. 4B shows a perspective view of a sensing device 404, according to various embodiments. The sensing device 404 may be coupled to or on a tubing or fluid line 482. The sensing device 404 has a sensor structure including an ultrasonic (US) transducer 484 which may be used to create or generate one or more bubbles 486. A series of electrodes may be placed near the ultrasonic transducer 484 to detect the bubble 486 as it moves in the stream within the tubing 482. The series of electrodes includes a number of pairs of electrodes. As a non-limiting example, FIG. 4B shows a sensing device 404 having seven pairs of electrodes, including a first pair of electrodes 410, a second pair of electrodes 420, up to and including a sixth pair of electrodes 460 and a seventh pair of electrodes 470. It should be appreciated that any number of pairs of electrodes may be provided for the sensing device 404, for example one, two, three, four, five or any higher number of pairs of electrodes.

[0106] Each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470 includes two electrodes arranged on opposite sides of the tubing 482. Using the first pair of electrodes 410 and the second pair of electrodes 420 as a non-limiting example, the first pair of electrodes 410 includes a first electrode 411 and a second electrode 412 arranged on opposite sides of the tubing 482, while the second pair of electrodes 420 includes a first electrode 421 and a second electrode 422 arranged on opposite sides of the tubing 482. Each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470 defines a capacitor.

[0107] An electrode (e.g. first electrodes 411, 421) of each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470 may be arranged at least substantially aligned with each other on one side of the tubing 482, while the other electrode (e.g. second electrodes 412, 422) of each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470 may be arranged at least substantially aligned with each other on the opposite side of the tubing 482.

[0108] The sensing device 404 has an oval (or ellipse) cross section, as illustrated in FIG. 4B. Each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470 has or form an at least substantially oval cross section, having a major axis (longer axis) 488 and a minor axis (shorter axis) 489 being perpendicular to the major axis 488. Accordingly, the tubing 482 may have an oval cross-section. The transducer 484 may be arranged over the tubing 482.

[0109] As illustrated in FIG. 4B, each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470, may be arranged on either side of the major axis 488 of the oval cross section. This means that an electrode (e.g. first electrodes 411, 421) of each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470 may be arranged on one side of the major axis 488 of the oval cross section of the series of electrodes and the tubing 482, while the other electrode (e.g. second electrodes 412, 422) of each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470 may be arranged on the opposite side of the major axis 488 of the oval cross section of the series of electrodes and the tubing 482.

[0110] Therefore, the respective electric field corresponding to each of the first pair of electrodes 410, second pair of electrodes 420, third pair of electrodes, fourth pair of electrodes, fifth pair of electrodes, sixth pair of electrodes 460 and seventh pair of electrodes 470 may cross or flow in a direction across the minor axis 489. The ultrasound transducer 484 may be arranged at one end of the major axis 488 of the oval cross section, across the major axis 488. Such a configuration of the sensing device 404 may allow for lower frequency standing waves to be used and higher sensitivities to bubbles moving through the flow.

[0111] In various embodiments, therefore, the tubing 482 may have a cross section adapted to match a cross section of the series of electrodes of the sensing devices 400, 404 and/or the series of electrodes of the sensing devices 400, 404 may have a cross section adapted to match a cross section of the tubing 482.

[0112] As a non- limiting example, when the sensing device 400 or 404 is used in the sensor 300 (FIG. 3), together with the pump system or unit 102 (FIG. 1) and the infusion set 104 (FIG. 1), data from the sensing device 400 or 404, may be transmitted to the pump system 102 via wires that may run along the tubing 482 to the coil 304 (FIG. 3) that may be wrapped around the insulin reservoir 302. The pump system 102 (FIG. 1) may have another coil internally for inductive coupling with the coil 304 that may allow for the transmission of data and of power to the sensing device 400 or 404.

[0113] FIG. 4C shows a cross sectional view of a sensing device 406 having six pairs of electrodes, including a first pair of electrodes 410, a second pair of electrodes 420, a third pair of electrodes 430, a fourth pair of electrodes 440, a fifth pair of electrodes 450 and a sixth pair of electrodes 460. It should be appreciated that any number of pairs of electrodes may be provided for the sensing device 406, for example one, two, three, four, five or any higher number of pairs of electrodes.

[0114] The first pair of electrodes 410 includes a first electrode 411 and a second electrode 412, the second pair of electrodes 420 includes a first electrode 421 and a second electrode 422, the third pair of electrodes 430 includes a first electrode 431 and a second electrode 432, the fourth pair of electrodes 440 includes a first electrode 441 and a second electrode 442, the fifth pair of electrodes 450 includes a first electrode 451 and a second electrode 452 and the sixth pair of electrodes 410 includes a first electrode 411 and a second electrode 412.

[0115] The first electrodes 411, 421, 431, 441, 451, 461 are arranged on one side of the tubing 482 and the second electrodes 412, 422, 432, 442, 452, 462 are arranged on the opposite side of the tubing 482. Each of the second electrodes 412, 422, 432, 442, 452, 462 may be connected to ground. Each of the first electrodes 411, 431, 451 may be connected together to which a voltage, Vi, may be applied, and each of the first electrodes 421, 441, 461 may be connected together to which a voltage, V₂, may be applied. V may or may not be the same as V₂.

[0116] Each of the first electrodes 411, 421, 431, 441, 451, 461, and second electrodes 412, 422, 432, 442, 452, 462 may have a width, w. Adjacent pairs of electrodes (e.g. between the fifth pair of electrodes 450 and the sixth pair of electrodes 460) may be spaced apart by a spacing, s. Each of the first electrodes 41 1, 421, 431, 441, 451, 461, may be separated or spaced apart from its corresponding second electrodes 412, 422, 432, 442, 452, 462, respectively, by a spacing, d. As a non-limiting example, w may be about 30 μηι, ί may be about 1 μιη and d may be about 100 μιη.

[0117] When voltages (e.g. Vi, V₂) are applied to the pairs of electrodes, respective electric fields, as represented by the lines, e.g. denoted by 492 for two such lines, are generated between its respective first electrodes 411, 421, 431, 441, 451, 461, and second electrodes 412, 422, 432, 442, 452, 462. The tubing 482 may carry a fluid 495 that flows within it. Where a bubble 486 is present in the fluid 495, the bubble 486 may interfere with the electric fields generated across the tubing 482, as illustrated in FIG. 4C for the electric field lines 492 corresponding to the third pair of electrodes 430 and the fourth pair of electrodes 440, which may lead to a change in the capacitance measured. As the bubble 486 flows through the tubing 482, the bubble 486 may affect or interfere with the electric fields corresponding to different pairs of electrodes.

[0118] The embodiment of FIG. 4C may be applied for the embodiments of FIGS. 4A and 4B.

[0119] In various embodiments, the pairs of electrodes, defining capacitors, of a sensing device, may be connected such that every third pair of electrodes or capacitor is connected in parallel, as illustrated in FIG. 4D. This may allow for the direction of the travel of the bubble 486 to be determined. The electrodes may also serve as the detectors for large bubbles. This is because the dielectric permittivity of water is 80 times larger than air, and may result in a capacitance change of 1/80 of normal operating conditions.

[0120] As illustrated in FIG. 4D, the sensing device 408 includes twelve pairs of electrodes. However, it should be appreciated that any number of pairs of electrodes may be provided for the sensing device 408, for example one, two, three, four, five or any higher number of pairs of electrodes. Each pair of electrodes may include a corresponding first electrode and a corresponding second electrode, which may be as described in the context of FIG. 4C. The dimensions of the pairs of electrodes may be as described in the context of FIG. 4C. In addition, the arrangements of the pairs of electrodes relative to the tubing 482 may be as described in the context of FIG. 4C.

[0121] As shown in FIG. 4D, the first pair of electrodes 410, the fourth pair of electrodes 440, the seventh pair of electrodes 470 and the tenth pair of electrodes 4100 may be connected together in parallel to which a voltage, Vi, may be applied. The second pair of electrodes 420, the fifth pair of electrodes 450, the eight pair of electrodes 480 and the eleventh pair of electrodes 4110 may be connected together in parallel to which a voltage, V₂, may be applied. The third pair of electrodes 430, the sixth pair of electrodes 460, the ninth pair of electrodes 490 and the twelfth pair of electrodes 4120 may be connected together in parallel to which a voltage, V₃, may be applied. Vi, V₂ and V₃ may be of the same voltage or of different voltages.

[0122] When voltages (e.g. Vi, V₂, V₃) are applied to the pairs of electrodes, respective electric fields, as represented by the lines, e.g. denoted by 492 for two such lines, are generated across each pair of electrodes. The tubing 482 may carry a fluid 495 that flows within it. Where a bubble 486, of a diameter, b, is present in the fluid 495, the bubble 486 may interfere with the electric fields generated across the tubing 482, as illustrated in FIG. 4D for the electric field lines 492 corresponding to the sixth pair of electrodes 460 and the seventh pair of electrodes 470, which may lead to a change in the capacitance measured. As the bubble 486 flows through the tubing 482 in a direction, as represented by the block arrow 499, from the first pair of electrodes 410 towards the twelfth pair of electrodes 4120, the bubble 486 may affect or interfere with the electric fields corresponding to different pairs of electrodes.

[0123] The embodiment of FIG. 4D may be applied for the embodiments of FIGS. 4A and 4B.

[0124] In various embodiments, the sensing device and the sensor system may be set up where, instead of using a long series of capacitors or pairs of electrodes (e.g. of the embodiments of FIGS. 4C and 4D), one respective static (or non-variable) capacitance may be connected in parallel with a respective variable capacitor on the tubing, as illustrated in FIG. 5 for a sensing device 500. The sensing device 500 employs an electrode setup that uses external static capacitances to measure a change in capacitance. Such an approach may reduce the overall size of the sensing device 500 and the sensor system including the sensing device 500, where for example, the tubing length may be reduced. However, there may be challenges in that a shorter length of the tubing may be sensitive to changes due to bubble formations or passing by the sensor.

[0125] The sensing device 500 includes three pairs of electrodes, including a first pair of electrodes 510, a second pair of electrodes 520, and a third pair of electrodes 530. It should be appreciated that any number of pairs of electrodes may be provided for the sensing device 500, for example one, two, three, four, five or any higher number of pairs of electrodes.

[0126] The first pair of electrodes 510 includes a first electrode 511 and a second electrode 512, the second pair of electrodes 520 includes a first electrode 521 and a second electrode 522, and the third pair of electrodes 530 includes a first electrode 531 and a second electrode 532.

[0127] The first electrodes 511, 521, 531, are arranged on one side of the tubing 550 and the second electrodes 512, 522, 532, are arranged on the opposite side of the tubing 550. Each of the second electrodes 512, 522, 532, may be connected to ground. The first first pair of electrodes (or first variable capacitor) 510 may be connected in parallel with a first static or non- variable capacitor 515, where the first static capacitor 515 may be coupled to the first electrode 51 1 of the first pair of electrodes 510, and to ground. Correspondingly, a second static capacitor 525 may be connected in parallel with the second pair of electrodes (or second variable capacitor) 520, and a third static capacitor 535 may be connected in parallel with the third pair of electrodes (or third variable capacitor) 530. Each of the first static capacitor 515, second static capacitor 525 and third static capacitor 535 may have the same capacitance, C₀. A voltage, Vi, may be applied to the first pair of electrodes 510, a voltage, V₂, may be applied to the second pair of electrodes 520, and a voltage, V₃, may be applied to the third pair of electrodes 530. Each of Vi, V₂ and V may be the same or different voltages.

[0128] When voltages (e.g. V_1? V₂, V₃) are applied to the pairs of electrodes, respective electric fields, as represented by the lines, e.g. denoted by 552 for two such lines, are generated between its respective first electrodes 511, 521, 531, and second electrodes 512, 522, 532. The tubing 550 may carry a fluid 554 that flows within it. Where a bubble 556 is present in the fluid 554, the bubble 556 may interfere with the electric fields generated across the tubing 550, as illustrated in FIG. 5 for the electric field lines 492 corresponding to the second pair of electrodes 520 and the third pair of electrodes 530, which may lead to a change in the capacitance measured. As the bubble 556 flows through the tubing 550, the bubble 556 may affect or interfere with the electric fields corresponding to different pairs of electrodes.

[0129] Sensor simulations will now be described by way of the following non-limiting examples. Simulations for the bubble formation and for the bubble detection may be performed. The bubble formation may be based on theoretical calculations, while the bubble detection may be based on finite element analysis (FEA) simulations.

[0130] With regard to the ultrasound transducer, the ultrasonic transducer (e.g. 484, FIGS. 4A and 4B) may be operated at certain frequencies close to or at least substantially similar to the natural frequency of a bubble so that a stable bubble size may be formed. The relationship between the required pressure to form a bubble, the operating frequency of the ultrasonic transducer and the size of the bubble formed, based on calculations, may be as shown in FIG. 6.

[0131] FIG. 6 shows a plot 600 of the relationship between the ultrasound pressure required for generation of bubbles and the corresponding bubble size at operation frequencies corresponding to about 25 kHz corresponding to results 602, about 28.8 kHz corresponding to results 604, about 200 kHz corresponding to results 606, about 500 kHz corresponding to results 608 and about 1000 kHz corresponding to results 608. For example, an ultrasonic transducer operating at a frequency of about 200 kHz may produce 28 μπι bubbles at low ultrasonic pressure levels.

[0132] As may be observed from calculations and the result shown in FIG. 6, for a given operating frequency, a small range of bubble sizes may be generated. In addition, it may be observed that the pressure required to produce the bubble decreases sharply around the natural frequency (corresponding to the respective sharp dips indicated by the respective dashed arrows) of the bubble size. This may be taken advantage of or exploited because the ultrasonic transducer may be operated at a lower power to generate a given bubble size. [0133] With regard to the bubble velocity simulation, the bubble velocity detection simulation may be carried out using a FEA software. The model used in the FEA software may be a column of water with 150 electrode pairs, for example based on the embodiment illustrated in FIG. 4D, where the electrodes of the electrode pairs may have a width, w, of about 30 μπι and spaced apart by a spacing, s, of about 1 μηι. The electrode pairs may be divided up such that every third electrode pair may be or may form part of the same capacitor, as illustrated in FIG. 4D for a series of twelve pairs of electrodes. For example, based on FIG. 4D, the first pair of electrodes 410, the fourth pair of electrodes 440, the seventh pair of electrodes 470 and the tenth pair of electrodes 4100 may form or define a first capacitor (Cap 1), the second pair of electrodes 420, the fifth pair of electrodes 450, the eight pair of electrodes 480 and the eleventh pair of electrodes 4110 may form or define a second capacitor (Cap 2), and the third pair of electrodes 430, the sixth pair of electrodes 460, the ninth pair of electrodes 490 and the twelfth pair of electrodes 4120 may form or define a third capacitor (Cap 3.) The distance, d, from the ground electrode to the active electrode may be about 94 μηι. These dimensions may be chosen because it would be feasible to make a capacitor that is about 10 pF. A bubble having a diameter, b, of about 30 μιη may be used in the model.

[0134] A change in one electrode pair due to a bubble moving through it may cause a large enough capacitance change to be detected by electronics or circuit that may be built or designed for the detection. The simulation results are as shown in FIG. 7 which shows a plot 700 of the capacitance change as a function of bubble movement along a tubing, as the bubble moves in the electric field. Plot 700 shows the capacitances measured across Vj (Cap 1), as represented by diamond-shaped data points with one such data point denoted as 702, V₂ (Cap 2), as represented by square-shaped data points with one such data point denoted as 704, and V₃ (Cap 3), as represented by triangle-shaped data points with one such data point denoted as 706. The results show that the bubble may produce a 1% change in the capacitance.

[0135] Calculations may also be performed for the lifetime of the cavitation bubble. The bubble lifetime may be determined by the amount of dissolved gas in the liquid and the bubble size. FIG. 8 shows a plot 800 of the bubble lifetime as a function of the bubble size and the amount of dissolved gas in solution, according to various embodiments. Plot 800 shows the relationship between the bubble lifetime and the amount of dissolved gas for a bubble diameter of about 20 μπι corresponding to results 802, about 30 μηι corresponding to results 804, about 100 μηι corresponding to results 806 and about 200 μηι corresponding to results 808.

[0136] As may be observed from FIG. 8, where a 30 μιη diameter bubble is used and that the gas concentration is about 90% of saturated, the gas bubble may remain in the solution for approximately 23 seconds. If the bubble is traveling at approximately 600 nm/s, this may result in the bubble traveling approximately 15 μηα before dissolving back into the solution (e.g. insulin solution). This is assuming that the ultrasound is not reactivated while the bubble is traveling. If the ultrasound energy is reapplied, the gas bubble may be able to maintain its size long enough to pass from one pair of electrodes to another, or from one sensing device to another sensing device positioned along the length of a tubing.

[0137] As described above, various embodiments may provide a method for detecting bubbles, leaks , and the flow rate of a solution, for example insulin, dispensed by an insulin pump using cavitation, based on capacitance changes. Simulations have been performed for the bubble formation using cavitation and bubble detection by capacitance changes between electrode pairs. The bubbles formed by cavitation may only remain in the solution for about 10 to 30 seconds. During that time, the bubble may be detected by multiple capacitors or pairs of electrodes. As the bubble moves under different capacitors, the speed and direction of the bubble may be determined and therefore the flow rate of the insulin may also be determined. When a large bubble enters the tubing from the reservoir, there may be a change in capacitance. The pump interface may inform the patient that a large bubble has entered the tube and to take one or more corrective actions. The detection system of various embodiments may lead to a more reliable insulin delivery system and may improve the likelihood that a fully automated system may measure blood glucose and control insulin delivery.

[0138] The leak detection and bubble detection device of various embodiments may provide further capabilities, for example to the pump and infusion system as illustrated in FIG. 1, by giving it more reliability. Therefore, various embodiments may add safety features to currently available systems. Currently, there is not a commercially available system that would be able to detect the flow rates in use by the pump illustrated in FIG. 1.

[0139] The leak detector, bubble detector and flow rate monitor or sensing device of various embodiments may have the capability to detect bubbles that are as small as 30 μιη in diameter and the movement of that bubble, based on capacitance changes. Along with detecting small bubbles, the system or sensing device may also be used to detect large bubbles moving through the system and may display a warning on the pump display.

[0140] Various embodiments may further provide a sensor system including electronics and packaging, and having the following specifications:

• Detection of fluid velocities of 600 nm/s.

• Minimum flow rate of 70 pl/s.

• Maximum flow rate of 4.5 μΐ/s.

• Accuracy of ± (300 nm/s + 3% fluid velocity).

• Resolution of ± (300 nm/s + 1% fluid velocity).

• Lifetime of 3 days for the sensor system.

Various embodiments may also employ effective methods to receive power and transmit data, for example using inductive coupling between the sensor system and the pump system.

[0141] Various embodiments may be employed in various applications, including but not limited to applications relating to ultra low flow rate monitoring, and medical applications including drug delivery (including but not limited to insulin).

[0142] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

1. A method for determining a flow rate of fluid in a fluid line, comprising:

flowing a fluid through a fluid line;

generating at least one bubble configured to flow in the fluid by means of a transducer;

determining a first time at which a first capacitance at a first location on the fluid line changes, corresponding to a flow of the bubble through the first location;

determining a- second time at which a second capacitance at a second location on the fluid line changes, corresponding to the flow of the bubble through the second location, wherein the second location is spaced apart from the first location by a predetermined distance; and

determining a flow rate of the fluid as a function of the predetermined distance and a difference between the first time and the second time.

2. The method of claim 1,

wherein determining the first time at which the first capacitance at the first location on the fluid line changes comprises determining the first time at which the first capacitance is less than a first predefined value, and

wherein determining the second time at which the second capacitance, at the second location on the fluid line changes comprises determining the second time at which the second capacitance is less than the first predefined value.

3. The method of claim 1 ,

wherein determining the first time at which the first capacitance at the first location on the fluid line changes comprises determining the first time at which the first capacitance changes by a second predefined value, and

wherein determining the second time at which the second capacitance at the second location on the fluid line changes comprises determining the second time at which the second capacitance changes by the second predefined value.

4. The method of any one of claims 1 to 3, further comprising applying energy to the bubble.

5. The method of any one of claims 1 to 4, wherein generating the bubble comprises generating the bubble having a diameter of between about 20 μπι and about 300 μπι.

6. The method of any one of claims 1 to 5, comprising operating an ultrasound transducer to generate the bubble.

7. A device for determining a flow rate of fluid in a fluid line, the device comprising:

an ultrasound transducer configured to generate at least one bubble configured to flow in a fluid flowing through the fluid line;

a first capacitor comprising a first pair of electrodes adapted to be arranged on opposing sides of the fluid line, the first capacitor being configured to sense a first capacitance of the fluid line between the first pair of electrodes;

a second capacitor comprising a second pair of electrodes adapted to be arranged on opposing sides of the fluid line, the second capacitor being configured to sense a second capacitance of the fluid line between the second pair of electrodes, wherein the second capacitor is spaced apart from the first capacitor by a predetermined distance; and a circuit in communication with the first capacitor and the second capacitor, the circuit being configured to determine a first time at which the first capacitance changes, corresponding to a flow of the bubble through the first capacitor, and a second time at which the second capacitance changes, corresponding to the flow of the bubble through the second capacitor, and wherein the circuit is further configured to determine a flow rate of the fluid as a function of the predetermined distance and a difference between the first time and the second time.

8. The device of claim 7, wherein the circuit is configured to determine the first time when the first capacitance is less than a first predefined value, and to determine the second time when the second capacitance is less than the first predefined value.

9. The device of claim 7, wherein the circuit is configured to determine the first time when the first capacitance changes by a second predefined value, and to determine the second time when the second capacitance changes by the second predefined value.

10. The device of any one of claims 7 to 9, further comprising the fluid line, the fluid line having a cross section adapted to match a cross section of the first pair of electrodes and a cross section of the second pair of electrodes.

1 1. The device of claim 10, wherein each of the first pair of electrodes and the second pair of electrodes form an at least substantially circular cross section.

12. The device of claim 10, wherein each of the first pair of electrodes and the second pair of electrodes form an at least substantially oval cross section.

13. The device of claim 12, wherein the first pair of electrodes are adapted to be arranged on either side of a major axis of the oval cross section of the first pair of electrodes.

14. The device of claim 13, wherein the second pair of electrodes are adapted to be arranged on either side of a major axis of the oval cross section of the second pair of electrodes.

15. The device of any one of claims 12 to 14, wherein the ultrasound transducer is adapted to be arranged at one end of a major axis of the oval cross section of the fluid line.

16. The device of any one of claims 7 to 15, wherein the ultrasound transducer is configured to generate the bubble having a diameter of between about 20 μπι and about 300 μιη.

17. The device of any one of claims 7 to 16, wherein the ultrasound transducer is selected from the group consisting of a piezoelectric transducer, a capacitive transducer, and a magnetostrictive transducer.

18. A method for determining whether a leak is present in a fluid line, the method comprising:

flowing a fluid through a fluid line;

generating at least one first bubble configured to flow in the fluid by means of at least one transducer;

determining a first flow rate of the fluid flowing through a first portion of the fluid line based on a flow of the first bubble through the first portion;

generating at least one second bubble configured to flow in the fluid by means of the at least one transducer;

determining a second flow rate of the fluid flowing through a second portion of the fluid line based on a flow of the second bubble through the second portion; and

determining whether a leak is present in the fluid line between the first portion and the second portion based on the first flow rate and the second flow rate.

19. The method of claim 18, wherein determining whether a leak is present in the fluid line comprises comparing the first flow rate with the second flow rate.

20. The method of claim 18 or 19, further comprising providing an indication that the leak is present if the first flow rate and the second flow rate are different.

21. The method of claim 20, wherein the indication is provided if the difference between the first flow rate and the second flow rate is more than a predefined value.

22. The method of any one of claims 18 to 21, wherein determining the first flow rate of the fluid through the first portion of the fluid line comprises: determining a first time at which a first capacitance at a first location within the first portion of the fluid line changes, corresponding to the flow of the first bubble through the first location;

determining a second time at which a second capacitance at a second location within the first portion of the fluid line changes, corresponding to the flow of the second bubble through the second location, wherein the second location is spaced apart from the first location by a first predetermined distance; and

determining the first flow rate of the fluid through the first portion as a function of the first predetermined distance and a difference between the first time and the second time.

23. The method of claim 22, wherein determining the second flow rate of the fluid through the second portion of the fluid line comprises:

determining a third time at which a third capacitance at a third location within the second portion of the fluid line changes, corresponding to the flow of the second bubble through the third location;

determining a fourth time at which a fourth capacitance at a fourth location within the second portion of the fluid line changes, corresponding to the flow of the second bubble through the fourth location, wherein the fourth location is spaced apart from the third location by a second predetermined distance; and

determining the flow rate of the fluid through the second portion as a function of the second predetermined distance and a difference between the third time and the fourth time.

24. A method for determining whether a leak is present in a fluid line, the method comprising:

flowing a fluid through a fluid line;

generating at least one bubble configured to flow in the fluid by means of at least one transducer;

determining a first flow rate of the fluid flowing through a first portion of the fluid line based on a flow of the bubble through the first portion; determining a second flow rate of the fluid flowing through a second portion of the fluid line based on the flow of the bubble through the second portion; and

determining whether a leak is present in the fluid line between the first portion and the second portion based on the first flow rate and the second flow rate.

25. A sensing device for a fluid line, the sensing device comprising:

an ultrasound transducer configured to generate a bubble in a fluid flowing through the fluid line; and

a capacitor comprising a pair of electrodes adapted to be arranged on opposing sides of the fluid line, the capacitor being configured to sense a capacitance between the pair of electrodes so as to determine a flow of the bubble through the fluid line.

26. The sensing device of claim 25, wherein the pair of electrodes form an at least substantially circular cross section.

27. The sensing device of claim 25, wherein the pair of electrodes form an at least substantially oval cross section.

28. The sensing device of claim 27, wherein the pair of electrodes are adapted to be arranged on either side of a major axis of the oval cross section.

29. The sensing device of claim 28, wherein the ultrasound transducer is adapted to be arranged at one end of the major axis of the oval cross section.

30. The sensing device of any one of claims 25 to 29, wherein the sensing device further comprises a non-variable capacitor coupled to the capacitor in a parallel connection.

31. The sensing device of any one of claims 25 to 29, wherein the sensing device comprises a plurality of capacitors adapted to be arranged along the fluid line, each capacitor comprising a respective pair of electrodes adapted to be arranged on opposing sides of the fluid line.

32. The sensing device of claim 31, wherein a respective capacitor is coupled to a subsequent third capacitor in a parallel connection.

33. The sensing device of any one of claims 25 to 32, wherein the ultrasound transducer and the capacitor are integrated.

34. The sensing device of any one of claims 25 to 33, wherein the ultrasound transducer is selected from the group consisting of a piezoelectric transducer, a capacitive transducer, and a magnetostrictive transducer.