Flat capillary nonintrusive liquid pressure sensor

Abstract

A sensor and a method for nonintrusive liquid pressure sensing in microfluidic systems is provided. The pressure sensor comprises a flat capillary tube section with enclosing walls formed of flexible material(s), so that a change in pressure within tube section will cause the enclosing walls to expand or contract. A pair of separate, flexible, thin electrode pads positioned opposite each other on opposing outer wide sides of the tube section. A pressure sensing unit is electrically connected to the electrode pads to form an impedance measuring circuit with a signal generator configured to generate a voltage signal in the first impedance measuring circuit and a processor configured to measure electrical impedance in the impedance measuring circuit. The measured impedance is indicative of a pressure within the tube section, and a pressure can be calculated or determined based on correlation data. A typical application of the sensor is in a liquid delivery device for administering doses of medicine to a patient.

Description

[0001] FLAT CAPILLARY NONINTRUSIVE LIQUID PRESSURE SENSOR

[0002] FIELD OF THE INVENTION

[0003] The present disclosure pertains to the field of pressure and flow sensing, in particular for nonintrusive pressure sensing in microfluidic systems such as liquid delivery devices for medical purposes.

[0004] BACKGROUND

[0005] The term ‘microfluidic’ is used to designate systems, channels, and components for manipulating small volumes of fluid with a flow rate (Q) up to or in the microliter-per-minute range, such as Q e [1pL / min ; 1000pL / min]. Examples of microfluidic components include pumps, valves, sensors, detectors, and more.

[0006] Microfluidic components are especially interesting for use in wearable drug delivery systems, often referred to as “microfluidic patches” since they are intended to be attached to the skin of the user in a bandage or patch that can be peeled off. An exemplary microfluidic patch is an autonomous insulin delivery device for the treatment of diabetes. Prominent key performance parameters for components in a microfluidic patch include:

[0007] Size and wearability. Size and weight affect the user experience and, ultimately, the decision to adopt the treatment.

[0008] Drug delivery accuracy. A high accuracy ensures a high therapeutic efficacy, and a higher accuracy allows using more concentrated drugs which reduces liquid volumes and handling.

[0009] Power. Power consumption is important for the required battery capacity - and thus size and weight - as well as battery duration.

[0010] Such microfluidic components even hold the potential to be implanted in or under the skin, which would add further key performance parameters such as biocompatibility and nontoxicity.

[0011] In most microfluidic pumps, including those used in biomedical applications, precision and flow are controlled through pre-calibration tests where the pump is running with varying power while the resultant flow is observed. The collected data is then processed and extrapolated to predict flow and pressure under real-life conditions. Still, environmental factors, liquid variability (e.g. different solutes), and drift in pump performance can lead to dosing inaccuracies due to deviations from nominal calibrated performance.

[0012] In medical dosing applications precision is critical and unintended dose variations can have serious consequences, and accurate dosing could be ensured by directly monitoring the flowinto the subject. However, directly monitoring pressure and flow in microfluidic systems is a challenge due to the very small volumes, flow rates, and pressures involved, and adding a sensor increases the complexity and cost of the microfluidic delivery system.

[0013] One prior art liquid pressure sensor is a capacitive pressure sensor used to measure a pressure difference in chambers at different sides of a diaphragm, with one side fluidically connected to the liquid system. The diaphragm is also an electrode in a capacitive setup by which deflections of the diaphragm can be measured. It is a disadvantage of this liquid pressure sensor that it involves a diaphragm chamber which increases the size and the dead volume of the liquid system.

[0014] One prior art liquid pressure sensor uses a load cell sensor abutting a diaphragm in a liquid system. Pressure build-up in the chamber causes the diaphragm to deflect, and the deflection is measured by the load cell. EP2026862 describes such a liquid pressure sensor, where an external pressure sensor abuts an expandable portion of a tube instead of a diaphragm. It is a disadvantage of this liquid pressure sensorthat it combines a separate load cell or other pressure sensor with an elastic part of the liquid system, since this adds to the size and complexity of the combination.

[0015] For medical devices for delivering fluids to a patient, it often suffices to detect bubbles or occlusions in the system instead of measuring an actual pressure. Such a bubble or occlusion sensor is shown in e.g. EP1762263. It is a disadvantage of such bubble or occlusion sensors that they cannot measure the pressure of the liquid in the system.

[0016] SUMMARY

[0017] Accordingly, there is a need for a liquid pressure sensor and methods of using such, which may mitigate, alleviate, or address the shortcomings of existing liquid pressure sensors.

[0018] A nonintrusive liquid pressure sensor is disclosed, with the nonintrusive liquid pressure sensor comprising a flat capillary tube section having inner width (w), and inner height (h) where:

[0019] w e [0.5mm ; 10mm];

[0020] h e [0.05mm ; 1mm]; and

[0021] w> 5h.

[0022] Enclosing walls of the flat capillary tube section are formed of flexible material(s), so that a change in pressure within a liquid in the flat capillary tube section will cause the enclosing walls of the flat capillary tube section to expand or contract. The nonintrusive liquid pressure sensor comprises a first pair of electrode pads which are separate, flexible, and positioned opposite each other on opposing wide sides of a first segment of the flat capillary tube section, each electrode pad being formed on an outside, such as on an outside surface part,of the enclosing walls with thickness and material parameters selected for the electrode pads to conform to changes in shape of the enclosing walls of the wide sides of the flat capillary tube section, and being in continuous mechanical contact with the enclosing walls so that a volume defined between the first pair of electrode pads will change upon expansion and contraction of the first segment. The nonintrusive liquid pressure sensor comprises a pressure sensing unit electrically connected to the first pair of electrode pads to form a first impedance measuring circuit, the pressure sensing unit comprising a signal generator configured to generate a voltage signal in the first impedance measuring circuit and electronic processing circuitry configured to measure electrical impedance in the first impedance measuring circuit, which is indicative of a pressure within a liquid in the first segment.

[0023] A method for nonintrusive liquid pressure sensing is disclosed, with the method comprising providing a flat capillary tube section having an inner width (w), and an inner height (h) where:

[0024] w e [0.5mm ; 10mm];

[0025] h e [0.05mm ; 0.5mm]; and

[0026] w> 5h.

[0027] The enclosing walls of the flat capillary tube section are formed of flexible material(s), so that a change in pressure within a liquid in the flat capillary tube section will cause the enclosing walls of the flat capillary tube section to expand or contract. The method comprises providing a first pair of electrode pads, Piaand P , which are separate, flexible, and positioned opposite each other on opposing wide sides of a first segment of the flat capillary tube section, each electrode pad being formed on an outside, such as on an outside surface part, of the enclosing walls with thickness and material parameters selected for the electrode pads to conform to changes in shape of the enclosing walls of the wide sides of the flat capillary tube section, and being in continuous mechanical contact with the enclosing walls so that a volume defined between the first pair of electrode pads will change upon expansion and contraction of the first segment. The method comprises providing a pressure sensing unit electrically connected to the first pair of electrode pads to form a first impedance measuring circuit, the pressure sensing unit comprising a signal generator configured to generate a voltage signal in the first impedance measuring circuit and electronic processing circuitry configured to measure electrical impedance in the first impedance measuring circuit. The method comprises pumping a liquid through the flat capillary tube section. The method comprises measuring electrical impedance in the first impedance measuring circuit, the measured electrical impedance being indicative of a pressure within the liquid in the first segment the flat capillary tube section.The nonintrusive liquid pressure sensor is hereinafter also referred to simply as the ‘liquid pressure sensor’. The flat capillary tube section is hereinafter also referred to simply as the ‘tube section’.

[0028] In the context of the nonintrusive liquid pressure sensor or sensing, “nonintrusive” means that there is no physical contact, nor any requirement or possibility of physical contact, between a liquid held in the flat capillary tube section and any of the electrode pads, pressure sensing unit, impedance measuring circuit, signal generator, electronic processing circuitry, or other parts outside the enclosing walls of the tube section. In other words, a liquid held in the tube section is strictly confined by its enclosing walls. In other words, all parts of the liquid pressure sensor are located outside the inner surface of the enclosing walls of the tube section. In this sense, the nonintrusive nature of the liquid pressure sensor and sensing method is advantageous, as it prevents contamination of the liquid within the tube section caused by the sensing process or the sensor itself.

[0029] In the context of the flat capillary tube section, the term “flat” means that an inner crosssection of the tube section has an aspect ratio (width / height) equal to or larger than 5 such as equal to or larger than 8, such as equal to or larger than 10.

[0030] Because the electrode pads are very thin compared to the dimensions of the tube section, each electrode pad can be considered as a surface, which may be either flat or curved. Since a pair of electrode pads are positioned opposite each other on the wide sides of the tube section, the phrase "a volume defined between a pair of electrode pads" refers to the space enclosed between the two surfaces of the electrode pads, with its boundaries determined by the shortest connections between the edges of these surfaces.

[0031] An microfluidic occlusion sensor is disclosed, with the microfluidic occlusion sensor being provided by the disclosed liquid pressure sensor, in which the electronic processing circuitry of the pressure sensing unit is configured to indicate an occlusion and / or generate an alarm when a measured impedance and / or a pressure determined based thereon and / or a volumetric liquid flow rate determined based thereon falls outside a predetermined range.

[0032] A microfluidic pumping system is disclosed, with the microfluidic pumping system comprising the disclosed liquid pressure sensor, wherein the flat capillary tube section is serially connected to a micropump configured to pump a liquid through the flat capillary tube section, and wherein the pressure sensing unit is configured to provide a measured impedance and / or a pressure determined based thereon and / or a volumetric liquid flow rate determined based thereon to a control unit of the micropump.A microfluidic liquid delivery patch is disclosed, with the microfluidic liquid delivery patch configured to be attached onto an epidermis of a subject and comprises the disclosed liquid pressure sensor, a first liquid interface configured to provide liquid communication between the flat capillary tube section and a receptacle holding a liquid to be delivered to the subject, and a second liquid interface configured to provide liquid communication between the flat capillary tube section and an infusion cannula. The microfluidic liquid delivery patch is hereinafter also referred to simply as the ‘liquid delivery patch’.

[0033] A use of the disclosed nonintrusive liquid pressure sensor in a microfluidic liquid delivery patch configured to be attached onto an epidermis of a subject is disclosed.

[0034] An implantable microfluidic liquid delivery device is disclosed, with the implantable microfluidic liquid delivery device configured to be implanted in or under an epidermis of a subject and comprises the disclosed liquid pressure sensor, a first liquid interface configured to provide liquid communication between the flat capillary tube section and a receptacle holding a liquid to be delivered to the subject, and a second liquid interface configured to provide liquid communication between the flat capillary tube section and an implantable infusion cannula. The implantable microfluidic liquid delivery device is hereinafter also referred to simply as the ‘liquid delivery device’.

[0035] A use of the disclosed nonintrusive liquid pressure sensor in an implantable microfluidic liquid delivery device configured to be implanted in or under the epidermis of a subject is disclosed.

[0036] The liquid delivery patch and the liquid delivery device may comprise a micropump for applying a pressure to the liquid upstream of the liquid pressure sensor and may be configured to deliver the liquid via the flat capillary tube section.

[0037] Liquids to be delivered can be or contain one or more of drugs, medicines, nutrients, vitamins, contrast agents, tracer substances, electrolytes, hormones, biologies, antibodies, enzymes, vaccines, suspensions, emulsions, saline or buffer solutions, etc.

[0038] A method for liquid delivery is disclosed, the method comprising:

[0039] providing the disclosed microfluidic liquid delivery patch or the disclosed implantable microfluidic liquid delivery device;

[0040] connecting a receptacle holding a liquid to the first interface;

[0041] connecting an infusion cannula to the second interface;

[0042] applying pressure to the liquid to deliver liquid from the receptacle to the infusion cannula via the flat capillary tube section of the disclosed liquid pressure sensor; andmonitoring, using the pressure sensing unit of the disclosed liquid pressure sensor, a measured impedance and / or a pressure determined based thereon and / or a volumetric liquid flow rate determined based thereon.

[0043] Liquid delivery may comprise liquid micro-dosing or liquid nano-dosing, such as the delivery of a liquid with a flow rate (Q) in the microliter-per-minute range or nanolitres-per-minute range. Alternatively, or additionally, liquid micro-dosing or liquid nano-dosing may refer to the delivery of a given dose of liquid, with a volume (V) in the microliter range or nanolitres range.

[0044] It is an advantage of the present disclosure that it provides a microfluidic liquid pressure sensor capable of non-intrusively detecting pressure and / or flow variations without compromising the sterility of the liquid.

[0045] It is an advantage of the present disclosure that it provides a microfluidic liquid pressure sensor with a lower form factor and thus increased compactness and wearability in comparison to prior art liquid pressure sensors. This form factor is crucial as size and weight affect the user experience and, ultimately, the decision to adopt the treatment. This effect is achieved in part because no diaphragm chamber, valves, or other additional microfluidic circuitry are needed.

[0046] It is an advantage of the present disclosure that it utilizes a microcapillary geometry with almost no "dead volume". This is achieved since the capillary tube section of the microfluidic liquid pressure sensor can be connected directly in-line with a microfluidic system. Thereby, no microfluidic circuit besides the capillary tube section holding the electrode pads is required.

[0047] It is an advantage of the present disclosure that it provides a microfluidic liquid pressure sensor that can be connected directly in-line with a microfluidic channel, and where a separate diaphragm chamber is not necessary. The absence of such a separate chamber simplifies the design and reduces the size and the dead volume.

[0048] BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The above and other features and advantages of the present disclosure will become readily apparent to those skilled in the art by the following detailed description of examples thereof with reference to the attached drawings, in which:

[0050] Figs. 1 A and B illustrate cross-sectional views of an exemplary flat capillary tube section of a microfluidic liquid pressure sensor according to the disclosure,

[0051] Figs. 2A and B illustrate perspective views of an exemplary flat capillary tube section of a microfluidic liquid pressure sensor according to the disclosure,Fig. 3 illustrates a perspective view of an exemplary flat capillary tube section of a microfluidic liquid pressure sensor according to the disclosure,

[0052] Fig. 4 illustrates an exemplary first impedance measuring circuit of a microfluidic liquid pressure sensor according to the disclosure,

[0053] Fig. 5 illustrates an exemplary microfluidic liquid pressure sensor according to the disclosure,

[0054] Fig. 6 illustrates an exemplary microfluidic liquid delivery patch comprising a microfluidic liquid pressure sensor according to the disclosure,

[0055] Fig. 7 illustrates an exemplary method for nonintrusive liquid pressure sensing according to the disclosure,

[0056] Figs. 8A-B - 11 A-B are impedance magnitude and phase graphs depicting performance of a proof-of-concept prototype of an exemplary microfluidic liquid pressure sensor according to the disclosure.

[0057] The figures are schematic and simplified for clarity, and they merely show details that aid in understanding the disclosure, while other details have been left out. Throughout, the same reference numerals are used for identical or corresponding parts.

[0058] DETAILED DESCRIPTION

[0059] Various examples and details are described hereinafter, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the examples. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated example does not show all the aspects or advantages. An aspect or an advantage described in conjunction with a particular example is not necessarily limited to that example and can be practiced in any other examples, even if not so illustrated, or if not so explicitly described.

[0060] The disclosure relates to a nonintrusive liquid pressure sensor comprising a flat capillary tube section formed of flexible material(s) so that pressure changes within a liquid therein cause the flat capillary tube section to expand or contract. The liquid pressure sensor also comprises a pair of thin, flexible electrode pads positioned opposite each other on opposing wide sides of the flat capillary tube section so that a volume defined between the pair of electrode pads will change upon expansion and contraction of the flat capillary tube section. The liquid pressure sensor also comprises a pressure sensing unit being connected to the pair of electrode pads to form an impedance measuring circuit and being configured to measure electrical impedance in the impedance measuring circuit. The measured impedance is indicative of a pressure within a liquid in the flat capillary tube section.The concept of measuring an impedance between electrode pads deposited on the outside of a tube means that the liquid remains completely encapsulated by the capillary tube throughout the measurement process. This allows measuring the pressure without contacting or exposing the liquid in the tube so that the pressure sensing is nonintrusive.

[0061] Impedance is a well-known parameter used to characterize electronic circuits, components, and the materials used in the components. Impedance (Z) is generally defined as the total opposition a device or circuit offers to the flow of an alternating voltage (AC) at frequency (f). Impedance ( / ) is represented as a complex quantity or vector with a real part being the resistance (R) and an imaginary part being the capacitive reactance ( ). The pair of electrode pads 8a and 8b effectively form a capacitor holding part of the flat capillary tube section 2 and any liquid held therein, combined referred to as the dielectric. The capacitance (C) of the pair of electrode pads 8a and 8b is characteristic of the geometry of the pads and the dielectric, and is related to the capacitive reactance (X) of the complex impedance by:

[0062] X = ^ 2n—fC (v1) ' For the ideal case of a pair of flat, parallel electrodes, the capacitance depends on the following parameters:

[0063] C

[0064]

[0065] = (2) Where A is the electrodes’ area, srand e0are the relative and vacuum permittivity, and h is the distance between the electrodes.

[0066] Measuring the capacitance, C(f), and thus the capacitive reactance, X(f), as a function of frequency, f, provides a fingerprint of the capacitor and the dielectric comprising the part of the flat capillary tube section 2 and a liquid held therein. Measuring the impedance of the impedance measuring circuit may therefore also be used to characterize the liquid.

[0067] For the disclosed liquid pressure sensor, the flat capillary tube is formed in flexible material(s) that expands / contracts when the liquid pressure therein changes. Expansion or contraction of the flat capillary tube will typically also involve a deformation of the electrode pads, and the presumption of flat, parallel electrodes in Equation (2) is not valid. However, while Equation (2) is for an ideal case, more complex geometries still have the same proportionalities.

[0068] For the disclosed liquid pressure sensor, it follows that an increase in liquid pressure in the flat capillary tube section causes a volume between the pads (and thus their mean distance) to increase. Such expansion and change in distance h -> h’ is illustrated in Figs. 1A-B and 2A-B, resulting in a decrease in the capacitance of the capacitor formed by the pair of electrode pads 8a and 8b. Conversely, a decrease in liquid pressure would cause thevolume between the pads (and thus their mean distance) to decrease, resulting in an increase in the capacitance of the capacitor formed by the pair of electrode pads 8a and 8b. The pressure sensing unit of the liquid pressure sensor may be configured to determine a pressure within a liquid in the tube section based on the electrical impedance measured for the electrode pads. The determination of a liquid pressure may comprise calculating a pressure based on known parameters of the liquid pressure sensor, such as geometry, dimensions, and material parameters of the enclosing walls and the electrode pads. The determination of a liquid pressure may comprise using correlation data comprising measured electrical impedances and corresponding pressures applied to a liquid within the flat capillary tube section.

[0069] Figs. 1 A and B illustrates cross sectional views of an exemplary flat capillary tube section 2 of a microfluidic liquid pressure sensor according to the disclosure. The flat geometry of the flat capillary tube section 2 serves to increase the sensitivity of the pressure sensor, since a given change in volume (or area, if we look at cross-section) requires less stretching or deformation of its enclosing walls 4 compared to a round or square geometry. Hence, it is easier for a given pressure to cause the given change in volume and thus the corresponding change in measured impedance between electrode pads 8a and 8b. This can be understood intuitively by imagining a circular cross-section. A circle is the 2D geometry with largest area for a given circumference. For a given change in area, a circular geometry with a flexible enclosing wall would therefore cause the maximum change in circumference, and therefore the maximum stretching of the enclosing wall and thus the maximum resistance against the change in area. The flatter the geometry, the smaller the area for a given circumference. For a flat geometry with a flexible enclosing wall, a given change in area would therefore cause a much smaller change in circumference, and therefore less stretching of the enclosing wall, and thus smaller resistance against the change in area. A technical effect of the flat geometry is therefore to increase the sensitivity of the impedance measurement to changes in volume or cross-sectional area of the capillary tube section 2.

[0070] As shown in Figs. 1 A and B, the flat capillary tube section 2 has inner width, w, and inner height, h. In one or more embodiments, the flat geometry of the capillary tube section 2 is characterized by w > 10h, i.e. an aspect ratio w / h > 10. If the aspect ratio is very small, the inner cross-sectional area of the tube is very small, and only a very small volume of liquid can flow through the tube. On the other hand, as shown above, if the aspect ratio is large, the sensitivity of the sensor decreases. The preferred minimum aspect ratio of 10 corresponds to a balance between flow rate and sensitivity.

[0071] Liquid conduits with capillary dimensions (see below for capillary) can generally be divided into self-supporting tubes that can be moved and manipulated and channels formed on and bound to a substrate. Self-supporting tubes will typically have round geometries, sincecorners in for example rectangular geometries will typically be high-stress and therefore weak features subject to breaking. On the other hand, channels on substrates will typically be formed by layer depositions and have rectangular geometries since rounded geometries are more difficult to fabricate. In one or more preferred embodiments, the flat capillary tube section is self-supporting, meaning that it can be lifted from a supporting surface without breaking. In one or more preferred embodiments, the flat capillary tube section has a rounded cross-sectional shape, such as an elliptical, oval, or pill shape, a rounded rectangle, or a shape with no corners or a shape with any corners having an internal angle larger than 90 degrees, such as larger than 120 degrees. Rounded shapes with flat geometries also have well-defined widths, heights, and aspect ratios. For example, the aspect ratio of an ellipse is defined as b / a, where a is the major axis and width w and b is the minor axis and height h.

[0072] This also means that rounded shapes with flat geometries have well-defined sides 6a and 6b, and short sides 7, even when these are not separated by corners, this is illustrated in Fig. 1A.

[0073] For tubes with rounded shapes, the flat geometry means that the wide sides 6a and 6b will be at least approximately planar, and more planar than less flat geometries. This has the technical effect that the capacitor formed by the electrode pads 8a and 8b will have a geometry similar or close to the planar geometry of an ideal capacitor described by Equation (2). So, for capillary tubes with rounded shapes, the flat geometry provides the technical effect that the capacitance of the electrode pads being easier to model and simulate in comparison to more complex geometries. A further technical effect of the flattened geometry in relation to rounded shapes is that it is easier to form the electrode pads 8a and 8b with uniform thickness and continuous mechanical contact with the enclosing walls 4. For less flat rounded shapes, such as an ellipse with eccentricity 0, the curvature of the flat sides makes it more difficult to deposit electrode pads 8a and 8b with uniform thickness.

[0074] A capillary tube is considered capillary when an internal dimension, such as diameter or area, is small enough to restrain a liquid by capillary action, where the largest possible internal diameter depends on the surface tension and viscosity of the liquid and the wettability (contact angle) of the materials of the enclosing walls. The capillary action is dependent on the surface tension and viscosity of the liquid and the adhesion between the liquid and the tube. While the main parameter deciding capillarity is the cross-sectional size, the capillarity also depends on the liquid and the tube materials. For most fluids and materials (i.e., ignoring superfluids and highly hydrophilic / hydrophobic materials), a tube is capillary when its inner cross-sectional area is 10mm2or less, where the exact threshold depends on the liquid’s properties (surface tension and viscosity) and the tube’s materials and surface texture. In one or more embodiments, the inner cross-sectional dimensions ofthe capillary tube section are w e [0.5mm ; 10mm] and h e [0.05mm ; 1 mm]. For the flat capillary tube section, the aspect ratio w / h > 10 is to be used as a constraint when selection the inner cross-sectional dimensions. The provided aspect ratio and the inner cross-sectional dimensions are to be measured with the flat capillary tube section in a relaxed state, i.e. , where the pressure inside the tube section is identical to the pressure outside the tube section.

[0075] The use of a capillary in this sensor is intended to enhance device precision, particularly at low flow rates (less than 1 mL / min). Due to its limited internal volume and elongated, thin profile, even small flow variations (=pL / min) can generate a measurable sensing signal. Furthermore, the capillary shape improves the signal-to-noise ratio, as the measured capacitive signal is inversely proportional to the pad distance, as described in Eq. (2).

[0076] Figs. 2A and B illustrate perspective views of an exemplary flat capillary tube section 2 having length L. In order for the tube section to conduct a liquid flow from one place to another and to exclude mere ‘tubular bands’ with little or no longitudinal extension, it is preferred that L > 3w.

[0077] At least parts of the enclosing walls 4 of the flat capillary tube section 2 are formed of flexible material(s), so that a change in pressure within a liquid in the flat capillary tube section 2 will cause the enclosing walls 4 to expand or contract. In one or more embodiments, the capillary tube section, i.e. the enclosing walls 4, is formed in flexible materials. As illustrated in Fig. 1 A, the enclosing walls 4 of the flat capillary tube section 2 has a thickness t.

[0078] It should be understood that the plural ‘walls’ is used for the enclosing walls 4 throughout the disclosure, and this is meant to include all flat geometries regardless of any nominal distinction between embodiments with only one enclosing wall (which could be said of an oval geometry) and embodiments with a plurality of enclosing walls (a rectangular geometry could be said to have four walls). Similarly, the material composition of the enclosing walls is also referred to in the plural “materials” without excluding that only a single material composition is used. Embodiments where different parts of the enclosing walls are formed in different materials or material compositions can be imagined and are intended to fall within the scope of the present disclosure. Also, the thickness, t, means the mean or predominant thickness of the enclosing walls. Firstly, the thickness will typically decrease when the tube section expands, thus it is not constant. Secondly, designs with varying thickness can be imagined and are intended to fall within the scope of the present disclosure.

[0079] The flexible materials comprise one or more materials that can be elastically and reversibly deformed by stresses at room and body temperature. In an exemplary embodiment, the flexible material forming the enclosing walls of the flat capillary tube section has a Young's modulus below 10GPa, such as below 5GPa, such as below 1GPa.If the wall-thickness t becomes too large relative to the height and width of the capillary tube, it becomes difficult for the strain exerted by the pressure of the confined liquid to expand the flat capillary tube section and thus increase the distance between the electrode pads. This will lead to a lower sensitivity of the pressure sensor. In general, the thinner and more flexible the enclosing walls are, the larger the change in volume between the electrode pads for a given pressure, and the larger the change in impedance and thus the larger sensitivity. Therefore, in one or more embodiments, the thickness t of the enclosing walls 4 is t < 3h, or preferably t < 2h. In exemplary embodiments, a thickness t of the enclosing walls of the capillary tube has a wall thickness t in the range t e [10 pm; 300 pm], preferably in the range t < 150 pm.

[0080] In one or more embodiments, the enclosing walls 4 of the flat capillary tube section 2 comprises one or more of, polymeric materials, polymers, polyimide, polytetrafluoroethylene, polyethene, polypropylene, polymethyl methacrylate, polyvinyl chloride, polyamide, acrylonitrile butadiene styrene (ABS), polycarbonate and other medical safe plastics.

[0081] In one embodiment, enclosing walls are formed in polyimide (PI), a polymer that can be easily flexed even by relatively low pressure. PI is especially suited for depositing electrically conductive pads on the surfaces of the wide sides using polymer thin-film coupling technology.

[0082] As illustrated in Figs. 1 A-B and 2A-B, the liquid pressure sensor also comprises a first pair of thin, flexible electrode pads 8a, 8b positioned opposite each other on opposing wide sides 6a and 6b of the flat capillary tube section 2, so that a volume defined between the first pair of electrode pads 8a and 8b will change upon expansion and contraction of the flat capillary tube section. Such expansion caused by an increase in liquid pressure and the resulting change of volume between pads is illustrated in Figs. 1A-B and Figs. 2A-B. In one or more embodiments, the first pair of electrode pads 8a, 8b are separate, flexible, and positioned opposite each other on opposing wide sides 6a, 6b of a first segment 12 (see Fig. 2B) of the flat capillary tube section 2. In one or more embodiments, each electrode pad 8a, 8b is a thin film formed on the outside of the enclosing walls 4. In one or more embodiments, each electrode pad 8a, 8b is in continuous mechanical contact with the enclosing walls 4 so that a volume defined between the first pair of electrode pads 8a, 8b will change upon expansion and contraction of the first segment 12. If there is no continuous mechanical contact between the electrode pad and the enclosing walls 4, the electrode pads may not expand or contract at the same rate as the flat capillary tube section. This may lead to unpredictable and / or non-proportional changes in the impedance that cannot be directly correlated to the expansion and thus to the change in pressure.In one or more embodiments, each electrode pad has thickness and material parameters selected for the electrode pads to conform to changes in shape of the enclosing walls of the wide sides of the flat capillary tube section. In one or more embodiments, each electrode pad has a thickness of less than 1 micron.

[0083] Fig. 3 illustrates a perspective view of an exemplary flat capillary tube section 2. Here, the flat capillary tube section 2 is part of a capillary tube section that is not flat, such as has a cross-section with a small aspect ratio close or equal to 1, such as a circular cross-section. This embodiment is advantageous since the flat capillary tube section 2 may be a subsection of a longer capillary tube section with enclosing walls being the same as the enclosing walls 4 of the flat section 2 and thus formed in the same material. The longer capillary tube section may be used to interconnect the liquid pressure sensor to other parts of a microfluidic system to provide a platform for other components of a microfluidic system, such as micropumps.

[0084] The disclosed liquid pressure sensor also comprises a pressure sensing unit connected to the first pair of electrode pads to form a first impedance measuring circuit and configured to measure electrical impedance in the first impedance measuring circuit. Fig. 4 illustrates an exemplary pressure sensing unit (20) electrically connected to the first pair of electrode pads 8a and 8b via wires 16 to form an exemplary first impedance measuring circuit 18. In one or more embodiments, the pressure sensing unit 20 comprises a signal generator 19 configured to generate a voltage signal in the first impedance measuring circuit 18 and electronic processing circuitry 22 configured to measure electrical impedance in the first impedance measuring circuit 18.

[0085] Impedance measuring comprises measuring the real and the imaginary parts of an impedance vector and may comprise converting them into other relevant parameters such as magnitude, phase angle, admittance, conductance, and susceptance. There are several methods for designing the impedance measuring circuit 18 for measuring impedance, well-known to the skilled person, such as the bridge method, the automatically balanced bridge method, the current-voltage method, and the radio frequency current-voltage method.

[0086] Fig. 5 illustrates an exemplary microfluidic liquid pressure sensor 1 according to the disclosure, comprising the components described above in relation to Figs. 1A-B, 2A-B, and 3.

[0087] In one or more embodiments illustrated in Figs. 2A-B and 4, the nonintrusive liquid pressure sensor 1 according to the disclosure can comprise a second pair of electrode pads 9a, 9b, which are separate, flexible, and positioned opposite each other on opposing wide sides of a second segment 13 of the flat capillary tube section. The second pair of electrode pads 9a,9b are equivalent to the first pair of electrode pads 8a, 8b described previously. Hence, in one or more embodiments, each electrode pad 9a, 9b is a thin film, preferably less than 1 micron thick, formed on the outside of the enclosing walls 4, and being in continuous mechanical contact with the enclosing walls 4 so that a volume defined between the second pair of electrode pads 9a, 9b will change upon expansion and contraction of the second segment 13. The first segment 12 and the second segment 13 are distinct lengthwise portions of the flat capillary tube section 2.

[0088] In embodiments of the liquid pressure sensor 1 comprising the second pair of electrode pads 9a, 9b on the second segment 13, the pressure sensing unit 20 is also electrically connected to the second pair of electrode pads 9a, 9b to form a second impedance measuring circuit (not shown). Further, the signal generator 19 is configured to also generate a voltage signal in the second impedance measuring circuit. Finally, the electronic processing circuitry 22 is configured to also measure electrical impedance in the second impedance measuring circuit.

[0089] In one or more embodiments of the liquid pressure sensor 1 comprising the second pair of electrode pads 9a, 9b on the second segment 13, the electronic processing circuitry 22 is configured to determine a pressure of a liquid in the flat capillary tube section 2 based on electrical impedances measured in the first and second impedance measuring circuits. The determination of a liquid pressure may comprise calculating a pressure based on known parameters of different parts of the liquid pressure sensor, such as geometry, dimensions and material parameters of the enclosing walls and the electrode pads. The determination of a liquid pressure may comprise using correlation data comprising measured electrical impedances and corresponding pressures applied to a liquid within the flat capillary tube section.

[0090] In one or more embodiments illustrated in Figs. 2A-B and 4, the nonintrusive liquid pressure sensor 1 according to the disclosure can comprise a third pair of electrode pads 10a, 10b positioned on a third segment 14, with the first, second, and third segments 12, 13, and 14 being distinct lengthwise portions of the flat capillary tube section 2. In such embodiments, the pressure sensing unit 20, the signal generator 19, and the electronic processing circuitry 22 are all configured to enable measuring electrical impedance in a third impedance measuring circuit (not shown) comprising the third pair of electrode pads 10a, 10b.

[0091] Although a liquid flow through the flat capillary tube section 2 cannot be measured directly, it may be detected, estimated, or determined by determining a change in pressure at different positions along the length of the flat capillary tube section 2. In one or more embodiments with two or more pairs of electrode pads positioned on distinct lengthwise portions of the flat capillary tube section 2, the disclosed liquid pressure sensor may be configured to detect, estimate, or determine a liquid flow, such as a liquid flow rate, through the flat capillary tubesection 2. In one or more embodiments, the electronic processing circuitry 22 is configured to determine a volumetric liquid flow rate in the flat capillary tube section 2 based on electrical impedances measured in the first and second impedance measuring circuits.

[0092] In one or more embodiments, a flow is estimated based on a classical Venturi flow meter where the flat capillary tube section 2 comprises an un-constricted segment and a constricted segment with a smaller cross-sectional area than the un-constricted segment. Knowing the geometrical factors and measuring the pressures in unconstricted and constricted segments, one can determine a flow rate using the equation:

[0093] Q (3)

[0094]

[0095] Here, Q is the volumetric flow rate, Ai and 42are the cross-section areas of the unconstricted and constricted segments, p the fluid density, and pi and p2the pressures within the unconstricted and constricted segments.

[0096] In one or more embodiments where the liquid pressure sensor comprises two or more pairs of electrode pads positioned on distinct lengthwise portions of the flat capillary tube section 2, the flat capillary tube section provides a classical Venturi tube in that:

[0097] the first segment of the flat capillary tube section has an initial inner cross-sectional area Ai;

[0098] the second segment of the flat capillary tube section has an initial inner cross-sectional area A2different from Ai.

[0099] The pressure sensing unit may be configured to determine a volumetric liquid flow rate through the flat capillary tube section based on electrical impedances measured in the first and second impedance measuring circuits. The determination of a volumetric liquid flow rate by the pressure sensing unit may involve using a version of Equation (3) adapted to the geometries of the flat capillary.

[0100] Fig. 5 illustrates an exemplary microfluidic liquid pressure sensor 1 according to the disclosure, comprising a pressure sensing unit 20, a signal generator 19, and electronic processing circuitry 22 in relation to the flat capillary tube section 2. The pressure sensing unit 20 may comprise a computer-readable memory circuitry 24, for example, removable and non-removable storage devices. The memory circuitry 24 may hold computer-executable instructions, such as program code, to be executed by the electronic processing circuitry 22 to control the signal generator 19 and other functions of the pressure sensing unit 20.The liquid pressure sensor may be configured to determine a pressure within a liquid in any segment 12, 13, or 14 of the flat capillary tube section 2 based on electrical impedance measured in an impedance measuring circuit of that segment. In one or more embodiments, the electronic processing circuitry 22 is configured to determine a pressure within a liquid in the first segment 12 based on electrical impedance measured in the first impedance measuring circuit and on correlation data for the first segment 12, the correlation data comprising measured electrical impedances for, and corresponding pressures applied to a liquid within, the flat capillary tube section 2. For this purpose, the pressure sensing unit 20 may comprise memory circuitry 24 holding the correlation data, or an interface (not shown) providing access to external memory circuitry holding the correlation data. Alternatively or additionally, in one or more embodiments, the electronic processing circuitry 22 is configured to determine a pressure within a liquid in the first segment 12 based on electrical impedance measured in the first impedance measuring circuit and a model or simulation of the liquid pressure sensor 1 , such as by simulation or calculation.

[0101] The liquid pressure sensor 1 may be configured to generate correlation data to be used to determine a pressure within a liquid in a segment of the flat capillary tube section 2. In one or more embodiments, the pressure sensing unit 20 is configured to perform a pressure sweep procedure to generate correlation data, the pressure sweep procedure comprising measuring electrical impedances for a plurality of known pressures applied to a first liquid within the flat capillary tube section 2. In one or more embodiments, the pressure sweep procedure comprises electrical impedance in an impedance measuring circuit of a given segment of the flat capillary tube section 2, and for a plurality of known pressures applied to a first liquid within the segment. During the pressure sweep procedure, impedance is preferably measured over a frequency range corresponding to the frequency range used when making pressure measurements. The pressure sweep procedure preferably comprises generation correlation data in the form of one or more look-up tables and / or graphs that can be used to correlate a given measured impedance, impedance-spectrum, or quantities derived from impedance measurements with a corresponding pressure in the segment applied during the pressure sweep procedure.

[0102] As previously discussed, the measured impedance represents a fingerprint of the collected dielectric between the pair of electrode pads, with dielectric components originating from the enclosing walls and the liquid. Pressure changes in the flat capillary tube section tend to be continuous and slow since pressure must build up over time, resulting in continuous and slow changes in the measured impedance. A sudden discontinuous or fast change in the impedance may therefore indicate a sudden change in the dielectric component originating from liquid, such as in the dielectric permittivity of the contents inside the flat capillary tube section. Such sudden changes will typically be caused by a bubble or a solid material in the conducting liquid either passing or being stuck in the segment of the flat capillary tubesection. In one or more embodiments, the electronic processing circuitry 19 is configured to detect or indicate a change in dielectric permittivity of content in the flat capillary tube section based on a rate of change in the measured electrical impedances. Since a detection of high a rate of change in measured electrical impedances is indicative of a foreign body such as a bubble or a piece of solid material in the conducted liquid, the pressure sensing unit 20 may be configured to indicate a foreign body in the liquid and / or generate an alarm. This is advantageous since bubbles and foreign bodies in the liquid are possible causes for, and early indications of, occlusion and malfunctions. Another advantage is that the sudden change in permittivity gives rise to a high, and possibly short, rate of change in measured impedances, which can be detected much faster than a gradual change resulting from a gradual build-up of pressure.

[0103] The microfluidic system, in particular, a pump in such a system, is typically operated in a well-defined and predetermined pressure range. Continuous and / or slow rise or fall in pressure are expected and intended during normal operation within the predetermined pressure range. A rise in pressure to values above an upper or lower threshold of the predetermined pressure range may indicate malfunction or occlusion of the microfluidic system. The disclosed liquid pressure sensor 1 can function as malfunction or occlusion sensor by monitoring that the measured impedance stays within a predetermined impedance range corresponding to the predetermined pressure range. This is particularly relevant for medical dosing applications, where malfunction (no pressure, no or reduced flow) and occlusion (high pressure, no or reduced flow) can be detrimental to the subject receiving the dose. In one or more embodiments, the electronic processing circuitry 19 of the pressure sensing unit 20 is configured to indicate an occlusion and / or generate an alarm when a measured impedance and / or a pressure determined based thereon and / or a volumetric liquid flow rate determined based thereon falls outside a predetermined range.

[0104] In one or more embodiments illustrated in Fig. 6, the flat capillary tube section 2 of the liquid pressure sensor 1 is serially connected to a micropump 32 configured to pump a liquid through the flat capillary tube section. In one or more of such embodiments, the pressure sensing unit 20 is configured to provide a measured impedance and / or a pressure determined based thereon and / or a volumetric liquid flow rate determined based thereon to a control unit (not shown) of the micropump 32. Such measured pressure feedback to the control unit of the micropump 32 provides the technical effect of enabling operation of the micropump 32 in response to a measured pressure, such as to adjust the performance of the micropump to provide a pressure within a predetermined pressure range.

[0105] The disclosed nonintrusive liquid pressure sensor can be used in a large range of applications where a liquid dose is to be administered to a subject, in particular, where small and / or very precise doses are to be administered. Typical medical applications could be formicrofluidic devices for administering medications that need to be administered in steady or frequent doses for maximal therapeutic effects. Such drugs include insulin, anti-seizure medications, antidepressants, beta-blockers, immunosuppressants, opioid medications, parkinson’s disease medications, and drugs for blood thinning, hypothyroidism, and others.

[0106] For such and other applications, a microfluidic liquid delivery device 30 comprising an embodiment of the disclosed nonintrusive liquid pressure sensor 1 is disclosed and illustrated in Fig. 6. In one or more embodiments, the liquid delivery device 30 comprises a first liquid interface 38 configured to provide liquid communication between the flat capillary tube section 2 and a receptacle 39 for holding a liquid to be administered to the subject. The receptacle 39 may be an interchangeable receptacle that can be attached to and detached from the first liquid interface 38. The receptacle 39 may be a refillable receptacle permanently attached to and thus comprised by the liquid delivery device 30. In one or more embodiments, the liquid delivery device 30 comprises a second liquid interface 40 configured to provide liquid communication between the flat capillary tube section 2 and an infusion cannula 41. The infusion cannula 41 may be an interchangeable infusion cannula that can be attached to and detached from the second liquid interface 40. The infusion cannula 41 may be permanently attached to and thus comprised by the liquid delivery device 30.

[0107] In one or more embodiments, the microfluidic liquid delivery device 30 comprises a power interface 36 configured to provide electrical power to the pressure sensing unit from a power source 37. The liquid pressure sensor 1 and the microfluidic liquid delivery device 30 may further comprise a communication interface 25 shown in Fig. 5, configured for a user to provide instructions and operation parameters to the pressure sensing unit 20 and read out data from the pressure sensing unit 20.

[0108] The microfluidic liquid delivery device 30 may be worn by the subject. Hence, a microfluidic liquid delivery patch 31 configured to be attached onto an epidermis of a subject is disclosed. The microfluidic liquid delivery patch 31 comprises one or more embodiments of the microfluidic liquid delivery device 30 described above. A use of the disclosed nonintrusive liquid pressure sensor 30 in a microfluidic liquid delivery patch 31 configured to be attached onto the epidermis of a subject is also disclosed.

[0109] The microfluidic liquid delivery device 30 may be implanted under the skin of the subject. Hence, an implantable microfluidic liquid delivery device 30 configured to be implanted in or under the epidermis of a subject is disclosed, being configured to provide liquid communication between the flat capillary tube section 2 and a receptacle 39 for holding a liquid to be administered to the subject and between the flat capillary tube section 2 and an implantable infusion cannula 41. A use of the disclosed nonintrusive liquid pressure sensorin an implantable microfluidic liquid delivery device 30 configured to be implanted in or under the epidermis of a subject is also disclosed.

[0110] A method 60 for nonintrusive liquid pressure sensing is disclosed and illustrated in Fig. 7. The method 60 can be performed by the liquid pressure sensor disclosed herein. The method 60 for nonintrusive liquid pressure sensing comprises providing S61 one of the embodiments of the liquid pressure sensor disclosed herein, pumping S67 a liquid through the flat capillary tube section, and measuring S68 electrical impedance in the first impedance measuring circuit.

[0111] The method 60 comprises connecting S62 to a receptacle holding a liquid in liquid communication with an input to the flat capillary tube section. In one or more embodiments, the method 60 also comprises connecting S63 to an infusion cannula in liquid communication with an output of the flat capillary tube section. The method 60 comprises applying S64 a back-pressure to the liquid to induce a flow of the liquid through the flat capillary tube section of the liquid pressure sensor. This may comprise delivering liquid from a receptacle holding a liquid to an infusion cannula via the flat capillary tube section.

[0112] The method 60 comprises measuring S65 electrical impedance in an impedance measuring circuit of the liquid pressure sensor. In one or more embodiments, the method 60 comprises determining S66 a pressure within the liquid in the first segment of the flat capillary tube section based on the measured impedance. In one or more embodiments, the method 60 comprises monitoring S67 a flow through the liquid pressure sensor, such as by monitoring overtime the measured electrical impedance and / or a pressure determined based thereon and / or a volumetric liquid flow rate determined based thereon.

[0113] In the following, a demonstration of proof of concept of the disclosed microfluidic nonintrusive liquid pressure sensor is presented.

[0114] A series of basic devices was produced to demonstrate the feasibility of creating a sensor using flat polymeric capillary tube sections, hereinafter referred to as capillaries. A capillary was connected to a syringe using a needle of a similar size. On the opposing wide surfaces of the capillaries, electrode pads made of titanium nitride (TiN) and aluminium (Al) were deposited by sputtering, creating the capacitor geometry. Four pairs of capacitive pads were deposited, completely covering the flat region of the capillary. The

[0115] capacitive sensing pads were connected to lateral poles using 25pm copper wires with silver / epoxy paste. The syringe connected to the sensor allows the flow of liquid and pressurization of the capillary.When empty, a very low capacitance is measured per pad, barely reaching 1pF. This is because the only polarized materials are the air and the polyimide (PI). Air and PI have relatively low dielectric constants (er) of around 1 and approximately 3-4, respectively. When the capillary is filled with water, the measured capacitance increases fourfold, reaching approximately 4 pF per pad. This increase is due to the water's high erof about 80. The significant difference between empty and full values makes this sensor highly sensitive to priming. Additionally, due to the water's high er, the presence of voids, such as bubbles, can be easily detected. The different stages were reproducible, and the sensor exhibited an instantaneous response. Cycling measurement was conducted with all pads interconnected, exchanging local probing for higher capacitance and improving the signal-to-noise ratio.

[0116] The hardware used to measure impedance is a custom PCB with an AD5933 impedance measurement integrated circuit. The circuitry includes an ATMega328P microcontroller to command the AD5933 and send the results to the computer by USB connection. The pressure inside the fluid circuitry is measured by a commercial pressure sensor also connected to the microcontroller. This way, the impedance and the pressure are measured simultaneously. A commercial precision pump pumps the liquid into the fluid

[0117] circuitry. The sensor was placed in a Faraday cage to be connected to the electronic hardware, but the door was kept open. Due to the frequency domain of this method, external interferences did not affect the result.

[0118] The system was calibrated with a 330 kQ ± 5% resistor, which is close to the impedance of a 15pF capacitor at 30-50 kHz. The system performed reliable measurements for a range of impedances 1 / 2 to 2 times the value of the calibration resistor. The measurements were taken with an excitation frequency between 10 and 100 kHz, in steps of 10 kHz. As a control, the sensor impedance is first measured empty (only air in the fluid circuitry) and filled with water at atmospheric pressure.

[0119] Figs. 8A-B shows control measurements of impedance (8A) and phase (8B) as a function of frequency while the sensor is filled with air or with distilled water. The control measurements show that there is a big difference between the impedance measured when the sensor is filled and when it is not.

[0120] As an example for generating correlation data, the measured impedance was related to the liquid pressure by performing pressure sweeps of known liquid pressure values using a precision pump and a reference pressure sensor. The steps taken are:

[0121] Fill the liquid circuit

[0122] Attach the commercial sensor to one end

[0123] Attach the pump to the other end

[0124] Start the pumpTake continuous measurements until pressure increases to 60-70 kPa Send each measurement to the computer and save them

[0125] Once the pressure reaches 60-70 kPa, stop the pump

[0126] Detach the commercial sensor (pressure goes back to atmospheric)

[0127] Start again

[0128] This way, an impedance and phase curve were obtained for each pressure in the range of interest. Fig. 9A-B show impedance (9A) and phase (9B) curves as a function of frequency for each measured pressure of the pressure sweep procedure.

[0129] A frequency can be selected to get a function of pressure against impedance. The one with a good impedance range (close to calibration resistance) and good sensitivity to pressure changes, both in impedance and phase, was 60 kHz. The measured ohmic impedance is in the correct range for the calibration, and the difference between atmospheric pressure and the highest pressure is in the range of the tenths of kiloohms (>10%), so the sensitivity to pressure is enough to calculate a pressure as a function of measured impedance.

[0130] Figs. 10A-B show impedance (10A) and phase (10B) as a function of pressure. The lines are linear regressions of impedance and phase at the selected frequency (60 kHz) measured for each applied pressure. The error curves indicated by dashed lines are appr. 3,7kPa in both cases. A table with the measured data point, the graphs in Fig. 10aand B, and the linear regression equations with the determined linear coefficients are embodiments of correlation data according to the disclosure.

[0131] As illustrated in the curve in Fig. 11 A, a slight difference in impedance when there is flow across the sensor in comparison to when the pump is stopped (stale liquid) can be detected. The difference is in the range of kilo-ohms (1%). The difference is seen more notably in the phase curve shown in Fig. 11 B. The sensitivity of the sensor to flow is not as high as in the case of pressure. However, the resolution of impedance measurements at a particular frequency range can be improved by changing the hardware operational frequency, so a better use of the sensor sensitivity can be achieved.

[0132] Certain features discussed above as separate implementations can also be implemented in combination as a single implementation. Conversely, features described as a single implementation can also be implemented in multiple implementations separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations, one or more features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as any subcombination or variation of any sub-combination.It is to be noted that the word "based on" may be seen as “as a function of’ and / or “derived from”. The terms “based on” and “as a function of” can be used interchangeably. For example, a parameter determined “based on” a data set can be seen as a parameter determined “as a function of” the data set. In other words, the parameter may be an output of one or more functions with the data set as an input.

[0133] Although features have been shown and described, it will be understood that they are not intended to limit the claimed disclosure, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the claimed disclosure. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.

Claims

CLAIMS1. A nonintrusive liquid pressure sensor (1 ) comprising:a flat capillary tube section (2) having inner width (w), and inner height (h) where:w e [0.5mm ; 10mm];h e [0.05mm ; 1mm]; and- w> 10h;wherein enclosing walls (4) of the flat capillary tube section are formed of a flexible material, so that a change in pressure within a liquid in the flat capillary tube section will cause the enclosing walls of the flat capillary tube section to expand or contract;a first pair of electrode pads (8a, 8b) which are separate, flexible, and positioned opposite each other on opposing wide sides (6a, 6b) of a first segment (12) of the flat capillary tube section, each electrode pad being formed on the outside of the enclosing walls with thickness and material parameters selected for the electrode pads to conform to changes in shape of the enclosing walls of the wide sides of the flat capillary tube section, and being in continuous mechanical contact with the enclosing walls so that a volume defined between the first pair of electrode pads will change upon expansion and contraction of the first segment;a pressure sensing unit (20) electrically connected to the first pair of electrode pads to form a first impedance measuring circuit (18), the pressure sensing unit comprising a signal generator (19) configured to generate a voltage signal in the first impedance measuring circuit and electronic processing circuitry (22) configured to measure electrical impedance in the first impedance measuring circuit, which is indicative of a pressure within a liquid in the first segment.

2. The nonintrusive liquid pressure sensor according to claim 1, wherein the electronic processing circuitry is configured to determine a pressure within a liquid in the first segment based on electrical impedance measured in the first impedance measuring circuit and on correlation data comprising measured electrical impedances and corresponding pressures applied to a liquid within the flat capillary tube section.

3. The nonintrusive liquid pressure sensor according to claim 2, wherein the pressure sensing unit comprises memory circuitry (24) holding the correlation data.

4. The nonintrusive liquid pressure sensor according to any of the preceding claims, comprising a second pair of electrode pads (9a, 9b) which are separate, flexible, and positioned opposite each other on opposing wide sides of a second segment (13) of the flatcapillary tube section, each electrode pad being formed on the outside of the enclosing walls with thickness and material parameters selected for the electrode pads to conform to changes in shape of the enclosing walls of the wide sides of the flat capillary tube section, and being in continuous mechanical contact with the enclosing walls so that a volume defined between the second pair of electrode pads will change upon expansion and contraction of the second segment;wherein the first and second segments are distinct lengthwise portions of the flat capillary tube section; andwherein:the pressure sensing unit is electrically connected to the second pair of electrode pads to form a second impedance measuring circuit;the signal generator is configured to generate a voltage signal in the second impedance measuring circuit; andthe electronic processing circuitry is configured to measure electrical impedance in the second impedance measuring circuit, which is indicative of a pressure within a liquid in the second segment.

5. The nonintrusive liquid pressure sensor according to claim 4, wherein the electronic processing circuitry is configured to determine a pressure within a liquid in the flat capillary tube section based on electrical impedances measured in the first and second impedance measuring circuits.

6. The nonintrusive liquid pressure sensor according to any of claims 4 - 5, wherein the electronic processing circuitry is configured to determine a volumetric liquid flow rate in the flat capillary tube section based on electrical impedances measured in the first and second impedance measuring circuits.

7. The nonintrusive liquid pressure sensor according to any of the preceding claims, wherein the enclosing walls of the flat capillary tube section comprise one or more of, polymeric materials, polymers, polyimide, polytetrafluoroethylene, polyethene, polypropylene, polymethyl methacrylate, polyvinyl chloride, polyamide, acrylonitrile butadiene styrene (ABS), polycarbonate, and other medical safe plastics.

8. The nonintrusive liquid pressure sensor according to any of the preceding claims, wherein the flexible material forming the enclosing walls of the flat capillary tube section has a Young's modulus below 10GPa, such as below 5GPa, such as below 1GPa.

9. The nonintrusive liquid pressure sensor according to any of the preceding claims, wherein each electrode pad has thickness and material parameters selected for the electrode pads to conform to changes in shape of the enclosing walls of the wide sides of the flat capillary tube section.

10. The non-intrusive liquid pressure sensor according to any of the preceding claims, wherein the pressure sensing unit is configured to perform a pressure sweep procedure to generate correlation data, the pressure sweep procedure comprising measuring electrical impedances for a plurality of known pressures applied to a first liquid within the flat capillary tube section.

11. The nonintrusive liquid pressure sensor according to any of the preceding claims, wherein the electronic processing circuitry is configured to indicate a change in a dielectric permittivity of content held in the flat capillary tube section based on a rate of change in measured electrical impedances.

12. The nonintrusive liquid pressure sensor according to any of the preceding claims, wherein the electronic processing circuitry of the pressure sensing unit is configured to indicate an occlusion and / or generate an alarm when a measured impedance and / or a pressure determined based thereon and / or a volumetric liquid flow rate determined based thereon falls outside a predetermined range.

13. The nonintrusive liquid pressure sensor according to any of the preceding claims, wherein the flat capillary tube section is serially connected to a micropump (32) configured to pump a liquid through the flat capillary tube section, and wherein the pressure sensing unit is configured to provide a measured impedance and / or a pressure determined based thereon and / or a volumetric liquid flow rate determined based thereon to a control unit of the micropump.

14. The nonintrusive liquid pressure sensor according to any of the preceding claims, wherein each electrode pad is provided by a thin film formed on the outside of the enclosing walls.

15. The nonintrusive liquid pressure sensor according to claim 14, wherein the thin film is less than 1 micron thick.

16. A microfluidic liquid delivery device (30) comprising a nonintrusive liquid pressure sensor according to any of claims 1 through 15, a first liquid interface (38) configured to provide liquid communication between the flat capillary tube section and a receptacle (39) for holding a liquid to be administered to the subject, and a second liquid interface (40) configured toprovide liquid communication between the flat capillary tube section and an infusion cannula (41).

17. A method for nonintrusive liquid pressure sensing, the method comprising providing:• a flat capillary tube section having inner width (w), and inner height (h) where:w e [0.5mm ; 10mm];h e [0.05mm ; 0.5mm]; and- w> 10h;wherein enclosing walls of the flat capillary tube section are formed of a flexible material, so that a change in pressure within a liquid in the flat capillary tube section will cause the enclosing walls of the flat capillary tube section to expand or contract;• a first pair of electrode pads which are separate, flexible, and positioned opposite each other on opposing wide sides of a first segment of the flat capillary tube section, each electrode pad being formed on the outside of the enclosing walls with thickness and material parameters selected for the electrode pads to conform to changes in shape of the enclosing walls of the wide sides of the flat capillary tube section, and being in continuous mechanical contact with the enclosing walls so that a volume defined between the first pair of electrode pads will change upon expansion and contraction of the first segment; and• a pressure sensing unit electrically connected to the first pair of electrode pads to form a first impedance measuring circuit, the pressure sensing unit comprising a signal generator configured to generate a voltage signal in the first impedance measuring circuit and electronic processing circuitry configured to measure electrical impedance in the first impedance measuring circuit;pumping a liquid through the flat capillary tube section; andmeasuring electrical impedance in the first impedance measuring circuit, the measured electrical impedance being indicative of a pressure within the liquid in the first segment of the flat capillary tube section.

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