Small target flow meter

Abstract

A flow measurement device is provided, the flow measurement device comprising: a rigid housing defining a fluid flow path having a flow path input and a flow path output, the fluid flow path being configured to allow a fluid medium to flow from the flow path input to the flow path output; a moving member hingedly mounted within the fluid flow path and extending transverse to a direction of flow of the fluid medium, the moving member including a moving member magnet, the moving member operatively moving upon exposure to a drag force resulting from fluid passing through the fluid flow path, the moving member being formed from a flexible support structure forming a living hinge, the moving member magnet being coupled to the flexible support structure; and a fixed magnet disposed at least proximate a sidewall of the fluid flow path, the fixed magnet having the same polarity as the moving member magnet and arranged to operatively exert a repulsive force on the moving member magnet thereby limiting its displacement in proportion to a magnitude of the drag force exerted by the fluid flow, linearizing the relationship between flow rate of the fluid medium and displacement of the moving member. and a sensing element disposed relative to the moving member and configured to provide an output indicative of the movement of the moving member within the fluid flow path.

Description

[Technical field]

[0001] The present invention relates to a miniaturized flow sensing method for fluid media. The present invention relates to a sensing technique that allows for accurate and stable measurement in real time of the volume of a fluid, gas or liquid passing through a flow path, and provides a wide dynamic sensing range, especially when used with flow paths having cross-sectional areas on the order of square millimeters. [Background technology]

[0002] Many methods have been employed for flow sensing in limited form factors, primarily thermal methods, such as velocimetry, calorimetry, and time-of-flight, to name a few. These methods are well suited for low flow rates, but suffer from saturation at high flow rates, especially in media with high thermal conductivity such as water. Another drawback is that the sensor configuration and flow channel geometry are critical, and it is difficult to avoid sensitivity to flow direction and conditions (turbulent / laminar).

[0003] A simple alternative to the thermal approach is the target flow meter (also called vane or paddle flow meter), where a physical target partially occludes the flow passage, and the displacement or distortion due to the flow force on this target is converted into a flow measurement. Although conceptually simple, this type of flow meter has several limitations. The first of these arises from the fact that the flow force increases as an order of magnitude with respect to the flow rate. This inherently limits the turndown ratio (dynamic range), since a 10-fold increase in flow means that the force on the target will increase by a factor of 100.

[0004] A further complication is that, especially in the context of flow measurement in confined spaces, the target needs to be connected in a hinged manner in order to record the deflection. Conventional mechanical hinges will have variable frictional resistance, which can suppress the deflection force at low flow rates. Living hinges (sometimes called integral hinges, which are thin flexible hinges made from the same material as the two rigid parts they connect) can circumvent this problem, but only if the hinge material is perfectly elastic. Viscoelastic materials such as plastics present a similar friction effect, albeit internal to the material. Considering elastic materials, the most common among them are metals, which are also characterized by a higher modulus of elasticity. This means that even in very thin sheets, they are too stiff to deflect against small flow forces. This is especially true when the flow channel diameter is on the order of millimeters.

[0005] With a view to overcoming these limitations, relevant examples of target flow meters equipped with magnets are referred to in the following prior art documents:

[0006] US Patent No. 5,399,633 to Howe-Gould Robert is an early example of a target flow meter. It discloses a flow meter in which a fluid flow moves a vane inside the fluid flow passage, the vane being connected to a spindle that traverses the fluid flow passage. The movable spindle is connected to a first magnet and is combined with a second spindle that moves in an outer chamber and is connected to a second magnet of opposite polarity. The second spindle terminates in a pointer to which the movement of the vane is transmitted through the magnet to provide a reading of the fluid velocity on a graduated scale.

[0007] US Patent No. 5,399,933 to Grant Needham discloses a flow meter including a target in a fluid flow conduit and a beam attached to the target. The beam is coupled to a sensor that moves with the beam upon passage of fluid through the flow path. Displacement of the movable sensor produces a signal. The signal is detected by an electrostatic sensor and represents the flow rate of the fluid. The movable sensor may include an inductive sensor, and each fixed sensor plate includes a printed circuit board having at least one primary coil and at least one secondary coil.

[0008] US Patent No. 5,393,333 to Drew S. Weaver discloses a method and apparatus for testing flow meters in which a displacer moving inside a flow tube carries a magnetic target whose movement is detected by an inductive transducer along the flow tube, and the signal generated by the transducer indicates the velocity of the displacer from which the fluid velocity can be inferred.

[0009] US Pat. No. 5,399,363 to Richard DeVerse discloses a mass flow meter consisting of a flap structure arranged transverse to the fluid flow in a flow channel, allowing the fluid to flow in only one direction. The flap is mounted to rotate about a shaft whose axis is perpendicular to the direction of flow and is counterbalanced by a spring. A stiffer spring will limit the flow range to higher flow rates, while a weaker spring will result in a less sensitive flow range. Although this invention addresses the problem of counteracting the force exerted by the fluid on a hinged element in the flow channel, it only allows the selection of a high or low flow range due to the limitations of the mechanical properties of the spring. Furthermore, the nature of the mechanical components in this sensing unit makes its use cumbersome when the size of the flow channel cross section is reduced to the millimeter range.

[0010] US Patent No. 5,399,363 to Paul K. Edwards discloses a switch operated by fluid flow. The switch is formed from an assembly having a paddle at a first end, an actuation magnet at a second end, and a pivot shaft between the first and second ends. A bias magnet is located on the outer housing of the sensor unit and is intended to repel the magnet on the paddle assembly and hold it in a stable, inactive position under zero flow conditions. An actuation sensor interacts with the magnet on the paddle to signal the presence of flow. The invention relates to paddles with magnets that are located outside the fluid flow path and serve primarily to hold the paddle in a stable, vertical position under no flow conditions.

[0011] US Patent No. 5,399,933 to Stanley E. Hawkins discloses an in-line flow meter for drip irrigation systems. The system provides visual flow indications of both higher and lower flow rates relative to a field adjustable normal flow rate. The flow meter consists of a paddle in the fluid flow path to which a permanent magnet is attached. The paddle is suspended downward in the flow and rotates up and down depending on whether the flow is increasing or decreasing. An indicator lever outside the fluid flow path is attached to a second magnet that interacts with the magnet on the paddle, the rotation of which mimics the angular orientation of the paddle in the fluid flow path through the interaction of the two magnets of opposite magnetism. The invention describes flow measurement through the interaction of the paddle and magnetic forces, which are intended to indicate flow rate relative to a field adjusted null position that corresponds to a predetermined value of flow rate.

[0012] US Patent No. 5,399,633 to Murray F. Feller discloses an apparatus for measuring flow rate, in which a target within a fluid flow path moves an amount dependent on the flow rate and an external force applied to the target by an electromagnetic mechanical transducer that senses the amount of target movement and converts it into a reading of the flow rate. The target can be either a shaft with rigid vanes attached to it, the shaft being rotated by an electric motor (the transducer), or a vane attached to a post, the transducer including at least one electrical winding connected to the post and cooperating with a permanent magnet attached to the vane.

[0013] No. 6,399,633 discloses a rotating plate type flow measurement device with magnetic linearization. The flowmeter includes a rigid housing, a moving member including a rotating plate with a moving member magnet I0, a fixed magnet, and a sensing member. At low flow rates, the magnets provide a low repulsive force, and as the flow rate increases and the magnets approach each other, the repulsive force increases, providing linearization.

[0014] US Patent No. 5,399,633 describes a further rotating plate flow measurement device with a magnet attached to a moving member and a fixed magnet similar to that in US Patent No. 5,399,633. As the proximity of the magnets increases, the repulsive force increases. This repulsive force results in a strain that is measured by a strain gauge to provide the flow measurement.

[0015] Despite these known approaches, which fall within the broad category of "targeted flow meters" based on magnetic or inductive sensing technologies, there remains a need for systems and methods that would enable measurement of fluid volume over a wide dynamic range and linearization of sensor response, particularly for miniaturized applications. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] US Patent Publication No. 881586 [Patent Document 2] British Patent No. 2499995 [Patent Document 3] US Patent No. 8783088(B2) [Patent Document 4] U.S. Patent No. 8800473(B1) [Patent Document 5] European Patent Application Publication No. 1376635(A1) [Patent Document 6] International Publication No. 1999050621(A1) [Patent Document 7] U.S. Patent No. 6,681,645(B1) [Patent Document 8] China Patent Application Publication No. 111504395 [Patent Document 9] Japanese Patent Application Publication No. 2008089320 Summary of the Invention

[0017] These and other problems are addressed by a flow measurement device according to the teachings of the present invention. The device includes an arrangement of magnets, one in a hinged target and another downstream therefrom in a flow passage, that are positioned relative to one another such that their respective like poles face one another to generate a repulsive force between the opposing magnets. The force-distance relationship of the magnets is complex, but the function can be approximately represented by an nth order polynomial function, the order of which depends on the geometry of the magnets and their separation. The relative geometry and range of displacement are carefully selected to be dominated by the second order component, thereby canceling the secondary flow forces in the opposite direction and effectively linearizing the force-displacement relationship of the target over a wider range relative to other flow sensing technologies, thereby increasing the turndown ratio, or operating range, of the device. This arrangement provides reliable measurements with a wide dynamic range and fast response, particularly, but not limited to, in millimeter-sized flow passages.

[0018] A suitable arrangement of a flow measurement device or flow sensor as described herein comprises: a rigid housing defining a fluid flow path and dimensioned to allow a fluid medium to flow from a flow path input to a flow path output; a hinged target member mounted within the fluid flow path and oriented transverse to the direction of fluid flow, the target member including a permanent magnet against which the fluid flow exerts a resisting force; a fixed element formed of a permanent magnet of the same polarity embedded within a wall of the fluid flow path facing the target member, the fixed element configured to exert a counteracting magnetic force on the target member to limit its displacement proportional to the flow rate; a sensing element positioned external to the fluid flow path, the sensing element proximate to and oriented orthogonal to the target member, the sensing element configured to measure variations in a static magnetic field generated by the displacement of the target and proportional to the mass / volume flow of fluid in the flow path.

[0019] In another arrangement, the fixed permanent magnet of the flow sensor is positioned in the center of the fluid flow path, transverse to the direction of flow and parallel to the rest position of the hinged target, by using an adhesive or other fixing or fastening means.

[0020] In another arrangement, the sensing element operates according to capacitive principles and is formed from a pair of capacitive plates, one plate on a moving target transverse to the flow direction and the other plate fixed transverse to the flow direction adjacent either the flow channel input or the flow channel output. In this arrangement, the displacement of the hinged target caused by the fluid flow in the flow channel will induce a variation in the electric field between the electrode pair, with the fluid medium as a dielectric. The sensed capacitance variation can then be converted into a flow rate reading by connected electronic circuitry.

[0021] In another arrangement, the displacement of the hinged target is measured via optical sensing. One or more optical luminescent transducers can be positioned near the flow channel wall, and the displacement of the hinged target can be detected via optical time-of-flight, Doppler shift, or interferometric techniques applied to light reflected from the target and detected by a receiver on the optical transducer. The detected signal can be converted to a flow rate reading by associated electronic circuitry.

[0022] In another arrangement, the hinged target is an electromagnet, which may be, for example but not limited to, formed from a conductive track on a flexible substrate. In this arrangement, a current is applied to the conductor such that when the target is distorted by the fluid flow, the target experiences a repulsive magnetic force from a magnet on the opposite side of the flow path in proportion to the resistive force. The parameters of the current applied to the conductor can be adjusted depending on the desired range in the flow rate to be measured in a selected application.

[0023] In an alternative arrangement, the fixed magnets at the flow channel outputs can be replaced by electromagnets and the sensor unit can be formed from a combination of permanent and electromagnet groups depending on the selected application.

[0024] In another arrangement, where both magnets in the fluid flow path are electromagnets, the displacement of the hinged target is measured via inductive sensing. When a current is applied to both electromagnets, causing the target to be distorted by the fluid flow, the target experiences a repulsive magnetic force of the fixed electromagnet proportional to the repulsive force. At the same time, the mutual inductance on the electromagnets will vary proportional to the distance between the moving and fixed electromagnets, and this inductance variation is measured on the fixed electromagnet and converted to a flow rate reading by the connected electronic circuitry. The measuring electromagnet in this arrangement can also be placed at the flow path input, with the inductance variation measured between it and the electromagnet on the moving element, and a third electromagnet or permanent magnet providing the repulsive magnetic force.

[0025] In another low friction arrangement, instead of being connected to a living hinge, a moving target member within the fluid flow path is mounted transverse to the fluid flow and connected to a pin so that a permanent magnet on the moving member moves parallel to the direction of flow, towards a fixed magnet located downstream, in the center of the fluid flow path. Sensing means located near the fluid flow path detects the displacement of the moving member, the output of which is sent to a processing unit and converted into a reading of the flow rate.

[0026] In another arrangement, a moving target member within the fluid flow path is mounted transverse to the fluid flow and supported by a number of living hinges which keep the movement of the member perpendicular to the flow. In this arrangement, the moving member is pushed by the fluid medium transverse to the fluid flow towards a fixed magnet located downstream in the fluid flow path. Sensing means located near the fluid flow path detects the displacement of the moving member and the output is sent to a processing unit and converted into a flow rate reading.

[0027] To further understand the principles related to the present teachings, it is useful to describe the nature of the forces acting within a fluid flow path: 1) the magnetic force between two cylindrical magnets as the distance between the magnets varies, and 2) the drag force of a fluid with a non-zero velocity acting on a target transverse to the fluid flow.

[0028] 1) The force between two cylindrical magnets with their magnetic dipoles aligned on the z-axis is proportional to the quantity

[0029]

number

[0030] Here, M is the magnetization of the magnet group, L is the length of the magnet group, r is the radius of the magnet group, and z is the distance between the magnet groups. For small values of z, this approximation becomes invalid because the force increases for distances close to zero. When L << z, the point dipole approximation can be considered, and the force along the z direction decreases in proportion to 1 / z for large distances z according to the following formula. 4 It decreases in proportion to

[0031] [Number]

[0032] Here, μ 0 is the permeability of free space, m 1 , m 2 are two dipole moments, and z is the distance between the two dipoles. However, when the separation distance z is comparable to the size of the cylindrical magnet, the accuracy of the dipole approximation decreases. Therefore, the relationship between the magnetic force and the separation distance cannot be precisely modeled and needs to be measured experimentally for individual cases.

[0033] 2) The drag force exerted on the target by the fluid and perpendicular to the direction of the flow is proportional to the power of the fluid velocity according to the following formula.

[0034] [Number]

[0035] Here, c d is the drag coefficient, ρ is the fluid density, v is the fluid velocity, and A is the area of the target. It is clear how the drag force on the target increases on the order of the square as the flow rate increases.

[0036] It will be appreciated that this makes it difficult to tailor the dimensions and select appropriate materials for the hinged target in contact with the fluid, especially in those applications where the dynamic range of flow rates spans many orders of magnitude: indeed, low flow rates result in small deflections, while high flow rates can lead to irreversible bending of the target's flexible members.

[0037] This interplay between the forces described above is exploited within the sensing techniques described in this application: the increase in repulsive magnetic force as a magnet on a target approaches a fixed magnet on the other side of the flow path is advantageously used to counteract the effect of the drag force that the fluid flow exerts on the target.

[0038] The linearization effect and range of measurable flow rates can be matched to the drag force vs. target displacement relationship by appropriate selection of the magnet group properties and their separation within the fluid flow path, as well as the geometry of the fluid flow path, which is another advantage of the sensing method deployed according to the present teachings.

[0039] These and other advantages of the present invention will be further understood upon consideration of the following detailed description of the embodiments and drawings. [Brief description of the drawings]

[0040] The accompanying drawings provide further understanding of the sensing arrangement described in the present invention, but are not intended to limit the scope of the appended claims.

[0041] [Figure 1A] 1 is a schematic diagram illustrating a cross section of a device according to the present teachings in a zero flow configuration, where the sensing element is a Hall effect sensor. [Figure 1B] 1B is a schematic diagram illustrating a cross-section of the device of FIG. 1A in an exemplary state of maximum opening corresponding to a maximum detectable flow rate, where the sensing element is a Hall effect sensor. [Figure 1C]FIG. 1B is a schematic diagram of the rear section of the device of FIG. 1A showing the geometry of the flow path sections and transfer members. [Figure 2A] FIG. 2 is a simplified representation of the voltage response of a Hall effect linear sensor when a magnetic field is applied along the length of the sensor. [Figure 2B] FIG. 2 is a diagram illustrating how the strength of the magnetic field generated by a permanent magnet decays over distance from the magnet. [Diagram 3] 1B is a schematic diagram illustrating a cross-section of an alternative arrangement of the device of FIG. 1A, where the moving member is formed from a flexible structure and the permanent magnet is attached to the moving member by adhesive or other clamping means. [Figure 4] FIG. 1B is a schematic diagram illustrating a cross-section of an alternative arrangement of the device of FIG. 1A, where a fixed magnet is positioned in the center of the flow channel, transverse to the fluid flow and parallel to the stationary position of the moving member. [Figure 5A] FIG. 1B is a schematic diagram illustrating a cross-section of an alternative arrangement of the device of FIG. 1A, where the moving member includes an electromagnet. [Figure 5B] 5B is a schematic diagram showing a cross-section of the arrangement of FIG. 5A, where the moving member includes an electromagnet, and where either a fixed magnet or a second electromagnet is positioned in the center of the flow channel, transverse to the fluid flow and parallel to the resting position of the moving member, and where the displacement of the moving member can be measured by an external sensing unit or inductive sensing techniques. [Figure 6A] 1B is a schematic diagram showing a cross-section of the arrangement of FIG. 1A, illustrating the forces acting on the moving member in the expected operating state of the flow sensor when the central axis of the flow channel is parallel to the horizontal. [Figure 6B] FIG. 1B is a schematic diagram showing a cross section of the arrangement of FIG. 1A. This shows the central axis of the flow channel at an angle "

[0042]

number

[0043] " describes the force acting on the moving member. [Figure 7A] 1 is a schematic diagram depicting a cross-section of a flow channel in an alternative arrangement of a device of the present teachings, where displacement of the moving member is measured via capacitive sensing techniques with a pair of capacitive plates, one on the moving member and the other fixed adjacent the flow channel input, transverse to the flow direction with the fluid medium as a dielectric. [Figure 7B] 1 is a schematic diagram depicting a cross-section of a flow channel in an alternative arrangement of a device of the present teachings, where displacement of the moving member is measured via capacitive sensing techniques with a pair of capacitive plates, one on the moving member and the other fixed adjacent the flow channel output, transverse to the flow direction with the fluid medium as a dielectric. [Figure 8A] 1 is a schematic diagram illustrating a cross-section of a flow channel in an alternative configuration of a device of the present teachings, where displacement of a moving member is measured via optical sensing techniques with one or more optical transducers disposed on the walls of the flow channel and inside the flow channel. [Figure 8B] 1 is a schematic diagram illustrating a cross-section of a flow channel in an alternative configuration of a device of the present teachings, where displacement of a moving member is measured via optical sensing techniques with one or more optical transducers disposed on the walls of the flow channel and outside the flow channel. [Figure 9A] 1A-1C are schematic diagrams of the side and front of a flow channel in an alternative arrangement of a device of the present teachings at zero flow, where the moving member in the flow channel is a permanent magnet whose displacement is parallel to the flow direction, and a fixed magnet is positioned parallel to the moving member, downstream of the flow channel, in the center of the flow channel. [Figure 9B] 1A-1C are schematic diagrams of the side and front of a flow channel in an alternative arrangement of a device of the present teachings at zero flow, where the moving member in the flow channel is a permanent magnet whose displacement is parallel to the flow direction, and a fixed magnet is positioned parallel to the moving member, downstream of the flow channel, in the center of the flow channel. [Figure 10A]1A-1C are schematic diagrams depicting the side and front, respectively, of an alternative arrangement of a device of the present teachings in a zero flow condition, where a moving member within a flow channel is supported by multiple living hinges such that the motion of the member remains perpendicular to the flow. [Figure 10B] 1A-1C are schematic diagrams depicting the side and front, respectively, of an alternative arrangement of a device of the present teachings in a zero flow condition, where a moving member within a flow channel is supported by multiple living hinges such that the motion of the member remains perpendicular to the flow. [Figure 11] This is a diagram showing the relationship between the magnetic force acting on two cylindrical magnets with radius r equal to length L and the distance between them. [Figure 12] FIG. 13 depicts a calibration function for a flow sensor of the present teachings illustrating the relationship between sensor output and flow rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] 1A and 1B, a schematic representation in cross section of a preferred arrangement of a flow sensor provided in accordance with the present teachings is provided, and FIG. 1C, a schematic representation of the rear of the flow sensor is provided.

[0045] The sensor comprises a rigid housing (101) defining a fluid flow path therein, the fluid flow path having an input port (102) and an output port (103). In operation, the fluid will flow in a directional flow from the input port to the output port. A moving member (104) is mounted within the fluid flow path transverse to the direction of fluid flow and adjacent the input port (102) of the flow path. The moving member (104) acts as a target and can be operatively moved in a hinged manner under the influence of fluid flowing within the fluid flow path. The moving member has a first rest position shown in FIG. 1A and a second rest position shown in FIG. 1B. Here, the moving member is moving toward the output port (103) under the influence of fluid moving within the fluid flow path. This movement is facilitated by the use of a living hinge that includes a flexible structure (105) and a permanent moving member magnet (106) against which the fluid flow exerts a drag force. A fixed member (107), formed of a permanent magnet of the same polarity as the moving member magnet (106) on the moving member (104), is mounted on or embedded within the wall of the fluid flow path, facing the moving member and adjacent the flow path output port (103). The fixed member (107) is oriented relative to the moving member magnet and is adapted to exert a counteracting magnetic force on the moving member magnet. When the moving member magnet is disposed on a moveable target member, this counteracting force serves to limit the displacement of the target member in proportion to the magnitude of the resistive force exerted by the fluid flow.

[0046] The fixed member (107) may be embedded or otherwise positioned in or on the channel wall by adhesive or other fastening means such that its bipolar axis forms an angle "θ" with the channel central axis (108). The sensing means or sensing element (109) is positioned outside the fluid flow path, perpendicular to the moving member (104) in this configuration. The sensing means is sufficiently close to the moving member such that the displacement of the moving member can be measured. The sensing means is configured to provide an output indicative of the sensed displacement. These output signals may be transmitted via a flexible cable (110) to a processing unit and converted into a measurement of flow rate.

[0047] In a preferred arrangement, the sensing means includes a Hall effect sensor. It will be appreciated that Hall effect sensors monitor magnetic fields with high accuracy, consistency, and reliability, and are also a cost-effective way to monitor the displacement of an object. A Hall effect sensor includes a Hall element, which is typically formed from a thin metal strip through which a current is applied. When a static magnetic field is applied perpendicular to the direction of the current, the charge carriers experience a Lorentz force and undergo a distortion. This effect creates a potential difference (Hall voltage) between the two sides of the strip, which is proportional to the strength of the applied magnetic field. The ability of the Hall effect sensor to respond to a static magnetic field is an important difference from an inductive sensor, which is only sensitive to a variable magnetic field. The output voltage of the Hall element is usually small (in the microvolt range), which makes it important to provide the Hall element with appropriate processing circuitry, such as amplification and noise suppression. The Hall element is typically integrated into the Hall sensor chip, which includes the signal processing and digitization circuitry, thus simplifying the interfacing process.

[0048] Hall effect sensors are widely found in industrial and consumer applications and are primarily used for proximity sensing, positioning, speed detection, and current sensing. They can be used as switches characterized by a binary response when combined with threshold detection, or they can be used as linear sensors where the output voltage varies in proportion to the magnetic field the Hall effect sensor is sensing.

[0049] 1A depicts the fluid flow path at zero flow conditions, with the hinged target member (104) shown in its rest position at an angle "α" = 90° to the central axis of the flow path. To maximize the resolution of the Hall effect sensor, it is important that the sensing element (109) is correctly positioned with respect to the magnet (106) on the hinged target (104) that generates the magnetic field to be measured. That is, the minimum and maximum distances of the sensing element should be located within the region where the maximum change in the magnetic field occurs.

[0050] To address this, in a preferred arrangement, when "α" = 90°, the sensing element is configured such that its edge at the flow path input side (111) corresponds to the edge of the permanent magnet (106) on the target.

[0051] To further understand this concept, in FIG. 2A a simplified illustration is provided of a typical voltage response of a Hall effect linear sensor to a magnetic field applied along the length l of the sensor, and in FIG. 2B how the magnetic field (B) generated by a permanent magnet decays over distance (d) from the magnet.

[0052] In the absence of a magnetic field, the sensor output is 0 As the applied magnetic field increases, the output voltage decreases with increasing supply voltage value (V MAX ) or towards the ground (V MIN) when the saturation point is reached, ideally the voltage output will not change any more when a stronger magnetic field is applied. In reality, as saturation is approached, the sensor response exhibits an inflection point that marks the end of the linear region, and the response is no longer distinguishable from the response of the sensor's active region.

[0053] To maximize the sensing resolution, it is important that the minimum to maximum distance values ​​of the Hall effect sensing element are located within the linear region marked with the dashed horizontal line in FIG. 2B, where the maximum change in the magnetic field occurs.

[0054] In a preferred arrangement, to enhance discrimination of low flow rates, the flexible member (105) of the target is advantageously fastened near the flow path input (102) so that, under zero flow conditions, the magnet (106) on the target is repelled by the downstream fixed magnet (107) and completely seals against the flow path input (102). This means that instead of drag being the dominant contribution to the target displacement, the pressure difference across the flow path forces the target to distort and open, even at very low flow rates. In this way, the target also constitutes a one-way valve that limits the presence of backflow affecting the measurement.

[0055] In a preferred arrangement, the housing of the sensing unit is advantageously manufactured using a hard material, so that the housing is shielded from external forces and the geometry of the flow path is protected during measurement. The selected material must have low magnetic permeability so as not to interfere with the magnetic field generated by the movement of the target. That is, examples include metals such as austenitic stainless steel, or engineering plastics such as PEEK or Delrin®. Delrin will be understood as an example of polyoxymethylene (POM), a high-performance acetal resin. PEEK (polyetheretherketone) is a high-performance semi-crystalline engineering thermoplastic.

[0056] To ensure correct operation of the sensing unit and to avoid any fluid leakage that may affect the sensor elements, the fluid flow path must be completely sealed and the fluid medium within the flow path must be isolated from the external environment. To achieve a complete seal around all components of the fluid flow path, the flexible member (105) is advantageously fixed within the sensor body using a suitable adhesive or mechanical fastening means.

[0057] 1B depicts the fluid flow path in an exemplary fully open condition corresponding to the maximum detectable flow rate, where the hinged target (104) forms an angle "α" < 90° with respect to the central axis of the flow path.

[0058] To maximize the sensing range of the Hall effect sensor, "α" should correspond to the maximum deflection of the target where the edge of the permanent magnet (106) on the target crosses the edge (112) of the sensing element at the flow path output. Once the target passes that edge (112), in fact, the signal from the Hall effect sensor is characterized by an inflection point and can no longer be distinguished from the active area of ​​the sensor.

[0059] To maximize the linearization of the relationship between drag and target deflection, the magnetic repulsion should be maximized when the deflection angle of the target is equal to "α". This means that the preferred orientation with respect to the fixed magnet (107) should be "θ" = "α", which means that the faces of the permanent magnet (106) on the target and the fixed magnet (107) with the same pole are parallel and their centers are ideally aligned. However, in the preferred arrangement where "α" = "θ" = 45°, the value of "α" that maximizes the flow rate should be calculated according to the desired measurement range and flow path parameters for the selected application.

[0060] Another important aspect for the design of the sensing unit is the selection of the parameters of the permanent magnet (106) integrated in or provided on the moving member (104). The magnetic strength of the magnet (106) must be adequate so that the Hall effect sensor can operate in its linear range without saturating, but the thickness of the magnet (106) must allow it to move within the sensing range of the Hall effect sensor to obtain the finest possible resolution. The cross-sectional area of ​​the magnet (106) must instead be selected according to two main design constraints: the ratio between the cross-section of the flow passage and the cross-section of the moving element (104) must maximize the drag force that the fluid exerts on the moving element; and the surface area of ​​the magnet (106) must be such that at the position of maximum opening of the flow passage, the face of the magnet (106) and the face of the fixed magnet (107) with the same polarity will be aligned, minimizing any fringing effects due to magnetic field lines emerging from the sides of the magnet. In effect, fringing causes the moving element (104) to deviate from its trajectory and flip away from the central axis of the magnet, thus exposing the opposite magnetic pole to the fixed magnet (107). Once the correct geometry for the magnet (106) on the moving element (104) is defined, the dynamic range of the measurement can be further adjusted by choosing the correct thickness for the fixed magnet (107) and strength for both magnetic elements (106, 107) and their separation in the flow path. Another advantage of the present teachings is that the dynamic range can be adjusted by either replacing the magnetic element with another magnetic element with a different magnetic strength suitable for the Hall effect sensor to continue operating within its linear range, or by using multiple magnetic elements, adding or removing magnets until the desired magnetic repulsion force is obtained, while keeping all geometric parameters unchanged.

[0061] In another exemplary arrangement, the sensing member is a magnetoresistance element, where the change in electrical resistance of the sensor is proportional to the magnetic field applied to the sensor. The sensing member can be based on one of the magnetoresistance effects typically found in various materials, such as: geometric magnetoresistance, positive magnetoresistance, Shubnikov-de Haas oscillations, i.e., oscillations in the electrical conductivity of a material in the presence of a very strong magnetic field, typically found in bulk non-magnetic metals and semiconductors; negative or anisotropic magnetoresistance (AMR), typically found in magnetic metals; giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), colossal magnetoresistance (CMR), and extraordinary magnetoresistance (EMR), typically found in multi-component or multi-layer systems.

[0062] In this arrangement, changes in the sensor resistance due to movement of the target (104) are measured by electronic circuitry connected to the sensing element (109) through a flexible cable (110) and transmitted to a processing unit where the changes are converted into a measurement of flow rate.

[0063] One example of a permanent magnet that can be integrated into the sensing unit is a neodymium (NdFeB) magnet. The advantage of neodymium magnets is their high strength; that is, they have a high level of magnetism and are highly resistant to demagnetization when compared to other magnetic compounds such as ferrite and even samarium-cobalt. They also have the advantage of being relatively inexpensive and are manufactured in a wide range of sizes, allowing them to be used in miniaturized applications, even with diameters as small as 1 mm.

[0064] In the context of flow measurement, it is advantageous if the magnetic elements in contact with the fluid medium are protected from the ingress of moisture, which can cause corrosion that has a detrimental effect on the structural integrity and performance of the magnet, especially in such applications (medical, food industry, etc.) where it is of paramount importance to avoid any contamination of the fluid being measured.

[0065] To address this issue, the magnet assemblage may be encapsulated with an inert coating, such as, but not limited to, epoxy, or a polymeric material such as silicone rubber.

[0066] 1B and 1C, the hinge connection region (113) may advantageously comprise a recessed semicircular cross-sectional feature in the polymeric structure that provides the living hinge, which should extend across substantially the entire width of the living hinge (105), and the vertical configuration of the hinge connection region (113) should be sufficiently clear of the channel walls that the living hinge (105) will allow the flexible support to flex without interfering with the channel wall structure.

[0067] Another useful configuration for the hinge connection region (113) is that it should ideally be located on the side of the living hinge (105) that faces the flow path input (102) so that the edges of the hinge connection region (113) do not come into contact with each other as the moving member (104) is distorted by the flow. It will be appreciated that the ideal cross-sectional geometry and depth of the hinge connection region (113) will need to be determined depending on the application selected and the material selected for the living hinge (105).

[0068] The already mentioned problems with hinges present in known target flow meters are also addressed by the present invention in that it is no longer necessary for a living hinge to provide a repulsive force for the flow since the magnet assemblage now meets this requirement. In a preferred arrangement, the living hinge (105) supporting the magnet (106) on the moving member can be made from a non-magnetic polymeric material as long as the hinge connection area (113) is thin enough so that the internal friction forces become negligible compared to the magnetic repulsive forces. Polymeric materials such as silicone rubber of appropriate Shore hardness can offer several advantages in the manufacture of living hinges, including but not limited to: Polymeric materials are suitable both for the fabrication of the living hinge itself as well as for the fabrication of the entire support structure for the magnetic element, and are easily manufacturable via injection molding, whilst ensuring its complete encapsulation and isolation from the fluid medium. The living hinge (105) itself can be part of a more complex structure, such as a gasket (114) between the flow path structure and any fastening means (115), to conveniently seal the fluid flow path; and The ideal amount of compression of the gasket (114) can be achieved for each application with proper sizing of the rubber thickness and Shore hardness.

[0069] Another important aspect of the present invention, which can be understood with reference to the cross-sectional views in Figures 1B and 1C, is that the cross-section of the fluid flow path defined by the rigid housing (101) and the moving element (104) should preferably be circular in order to limit vorticity or turbulence in the fluid flow path and maximize the effect of the fluid drag on the moving element (104). In addition, the ratio of the cross-sectional area of ​​the fluid flow path to the cross-sectional area of ​​the moving element (104) should be optimized to achieve a pressure difference between the flow path input port (102) and the output port (103) suitable for the flow path opening even at low flow rates of 10 μl / s.

[0070] The ability to handle such low flow rates and extend the dynamic range of measurement to much larger volumes depending on the selected flow path geometry and sensor unit component parameters, as well as the ability to measure a variety of fluids including air, make the flow sensor of the present invention suitable for a wide range of applications. Additionally, the sensor structure and its fast response time make the flow sensor of the present invention particularly suitable for real-time measurements of pulsatile flows, which are common in biomedical applications.

[0071] Biomedical applications in which flow sensors of the present teachings may be particularly advantageous include, but are not limited to, the following: Blood flow monitoring, where blood flow rates depend heavily on the distance from the heart and the size of the vessel, and can range from 20 μl / s in small vessels to 16 ml / s as blood is pumped directly from the heart into the aorta. For example, respiratory monitoring for measurement of peak expiratory flow rates. Typical values ​​range from 130 L / min in pediatric subjects to 600 L / min in adult males. For example, human breast milk secretion during lactation. Typical ranges of breast milk flow rates range from 10 μl / s to at least 5 ml / s; and Urine excretion. Typical flow rates range from 10 ml / s to 21 ml / s in adults.

[0072] In another arrangement, such as the arrangement presented in FIG. 3, the magnets (306) on the target can be fixed by adhesive or other fastening means on a flexible support structure (1) that constitutes a living hinge (305). The structure should be manufactured using a thin and flexible polymer film, such as, but not limited to, PEEK or polyimide. As mentioned above, the geometry and thickness of the flexible structure are selected to obtain optimal mechanical properties for the range of flow rates to be measured and to minimize internal friction forces against magnetic repulsion. In addition, a moisture-resistant coating should be applied to the assembly of the flexible film and magnets to protect the integrity of the magnetic element (306) and the adhesive layer (2).

[0073] Figure 4 depicts an alternative configuration of the device of Figure 1A in cross-section. Here, a fixed magnet (407) is positioned between the input port (402) and the output port (403) in the fluid flow path, closer to the output port (403) and transverse to the fluid flow. The fixed magnet (407) can be conveniently positioned in a suspended position along the flow path central axis (408) by adhesive or other fastening means and aligned with the rest position of the hinged target (404). In this arrangement, the fixed magnet (407) will restrict the cross-sectional area of ​​the fluid flow path, and the fluid flow will pass between the fixed magnet and the flow path wall.

[0074] FIG. 5A depicts an exemplary alternative arrangement of an apparatus of the present teachings in a cross-sectional view, where the hinged target (504) is an electromagnet and a fixed magnet (507) is embedded in the fluid flow channel wall at an angle "θ" to the fluid flow channel central axis (508). The electromagnet can be conveniently constructed by a conductive track (1) on a flexible substrate (2), such as a flat flex cable (FFC) or flexible printed circuit board (FPC), or alternatively, using conventional methods such as flat windings of magnet wire. In this arrangement, when a current is applied to the conductor (1) such that the target is deflected by the fluid flow, the target experiences a repulsive magnetic force from the fixed magnet (507) on the opposite side of the flow channel, proportional to the drag force.

[0075] Figure 5B depicts, in cross-section, an exemplary alternative arrangement of the device of Figure 5A, where a fixed magnet (507) is positioned between the input and output ports (502 and 503) of the fluid flow path, closer to the output port (503), transverse to the fluid flow, in a suspended position along the flow path central axis (508), and aligned with the rest position of the hinged target (504).

[0076] 5A and 5B can include an electromagnet instead of a fixed magnet at the flow channel output, which generates a magnetic force against the hinged target (504). It is understood that the sensor unit can be constructed with a combination of permanent magnets and electromagnets depending on the selected application.

[0077] If both magnets in the embodiment in FIG. 5B are electromagnets, the displacement of the moving member (504) can also be measured via inductive sensing techniques. In this arrangement, current is applied to both the conductor (1) on the moving member (504) and the conductor (507) fixed downstream in the flow channel, so that when the target is deflected by the fluid flow, it experiences a repulsive magnetic force from the fixed electromagnet (507) in proportion to the drag force. At the same time, the mutual inductance on the electromagnets will vary in proportion to the distance between the moving element (504) and the fixed electromagnet (507), which represents the displacement of the target and is measured on the fixed electromagnet (507). The inductance measurement can be performed by modulating an AC signal on the magnetizing current of one coil and measuring the amplitude variation of this AC-coupled signal in the other coil. To obtain sufficient sensing resolution, the frequency of the AC signal is typically at least one order of magnitude higher than the paddle displacement frequency.

[0078] In an alternative arrangement, the measuring electromagnet (3) can be placed at the flow path input to maximize the coupling between the two inductor circuits, and the variation in mutual inductance caused by the displacement of the moving element (504) can be measured between the electromagnet (3) at the flow path input and the electromagnet (1) on the moving element (504), while the electromagnet (507) downstream in the fluid flow path only provides a magnetic repulsion force. Advantageously, the gap between the electromagnet (1) on the moving element (504) and the measuring electromagnet (3) is minimized to enhance the response. It is understood that in this alternative arrangement, the fixed electromagnet (507) can be replaced by a permanent magnet.

[0079] In the arrangement described above, the change in inductance on the electromagnet is measured by an electronic circuit connected to the measuring electromagnet through a flexible cable (710) and transmitted to a processing unit where the change is converted into a measurement of the flow rate.

[0080] 6A and 6B, in normal sensor operation, the hinged target (604) is subjected to a variety of forces, primarily a drag force (1) from the fluid medium resulting from fluid flow through the fluid flow path, and a magnetic repulsion force (2) from a stationary magnet (607) downstream in the flow path. Additional forces experienced by the hinged target (604) during sensor operation are gravity (3) and the buoyancy response of the fluid (4), which depends on the target volume and the density of the fluid medium.

[0081] Figure 6A depicts a typical operating condition, where the rigid housing (601) of the flow sensing unit is oriented horizontally and the fluid flow is perpendicular to the direction of gravity (3) acting on the target (604). In this configuration, the component of gravity parallel to the flow direction (608) is zero, and the deflection of the target, and therefore the opening of the flow passage, depends only on the balance between the drag force (1) and the magnetic repulsion force (2).

[0082] FIG. 6B depicts an alternative operating state, where the fluid flow path housing (601) is at an angle "

[0083]

number

[0084] ". In this case, the component (5) of gravity (3) that is parallel to the flow direction (608) is no longer zero and its effect on the hinged target (604) will be added to the overall balance of forces (1, 2) resulting in target deflection and therefore measurement errors of the fluid flow, especially for very low flow rates where the effect of gravity may be comparable to the drag force. To improve the accuracy and reliability of the sensing unit in any orientation, it will be advantageous to implement buoyancy compensation for the hinged target in the fluid flow path to eliminate or reduce the effect of gravity. This buoyancy compensation can be implemented in a deliberate manner by manufacturing the moving target with appropriate materials / geometry, so that the equivalent density of the target assembly matches the density of the fluid under investigation. Alternatively or additionally, numerical compensation can be introduced and the output from a sensor, such as an accelerometer, gyroscope, or position sensor, can be continuously detected the orientation of the sensing unit and calibrated to digitally eliminate the effect of gravity during the measurement.

[0085] FIG. 7A presents a cross-section of a fluid flow path in one alternative arrangement of the sensing unit of the present teachings, where the displacement of a moving target (704) is measured via a capacitive sensing technique. In this arrangement, the moving element (704) is formed by a permanent magnet (706) and an element that constitutes one electrode plate (1) of a variable capacitor, the other electrode plate (2) being placed on the fluid flow path, transverse to the direction of flow, close to the flow path input (702). In non-zero flow conditions, the displacement of the target (704) causes a variation in the distance between the two capacitor plates (1, 2), with the fluid medium as a dielectric, and a variation in the capacitance reading. The capacitance is measured by sensing electronics (709) connected to the capacitor plates (1, 2) through a flexible cable (710) and transmitted to a processing unit where the capacitance is converted into a measurement of the flow rate. As an exemplary arrangement, the stationary capacitor plate (2) can be ring-shaped for easy attachment to the flow path wall, or it can have a circular cross section and be suspended in the flow path, so long as the capacitor plates have as large a common area as possible to maximize capacitance.

[0086] Figure 7B shows a cross-section of the fluid flow path in an alternative arrangement to that shown in Figure 7A, where the fixed plate (2) of the variable capacitor is a plate with a circular cross section and is positioned transverse to the direction of flow, adjacent the flow path output (703).

[0087] It is important that the capacitor plate (1) on the moving element (704) always faces the fixed electrode plate (2) in the fluid flow path, so this capacitor plate will be located to the left of the permanent magnet (706) on the moving target (704) in the exemplary arrangement of Figure 7A and to the right of the permanent magnet (706) on the moving target (704) in the exemplary arrangement of Figure 7B. The capacitor plates in Figures 7A and 7B can be advantageously covered with an insulating layer to avoid contact with the fluid and to prevent contamination and corrosion that could result in errors in the capacitance readings.

[0088] In either arrangement, the addition of static capacitor plates to the flow channel walls helps to resolve the baseline permittivity of the fluid dielectric, thereby acting as a reference value for the variable capacitance.

[0089] 8A and 8B present cross-sections of a fluid flow path in an alternative arrangement of the sensing unit of the present teachings, where the displacement of a hinged target (804) is detected via optical sensing techniques.

[0090] In the exemplary arrangement of FIG. 8A, one or more optical transducers (1, 2) are arranged on the inner channel wall (3) of the fluid channel, parallel to the flow direction and in contact with the fluid. Depending on the optical sensing method selected for each application, the light emitting member (1) sends a series of light pulses towards the moving member (804), which reflects the light pulses back to the light receiving member (2). In non-zero flow conditions, the displacement of the moving member (804) can be detected via optical time of flight, Doppler shift, or interferometry, depending on the properties of the light reflected by the moving member (804). The signal from the optical transducers (1, 2) is measured by electronics connected to the sensing unit through a flexible cable (810) and transmitted to a processing unit where the signal is converted into a measurement of the flow rate.

[0091] Figure 8B presents an alternative arrangement to that depicted in Figure 8A, where one or more optical transducers (1, 2) are positioned parallel to the direction of flow, external to the channel walls (3). This arrangement requires the fabrication of the fluid flow channels using an optically transparent material to allow light transmission between the optical transducers (1, 2) and the moving member (804) through the channel walls (3).

[0092] 9A and 9B present another low-friction arrangement of the present teachings in a zero flow state, where a moving member (904) is mounted in a rigid housing (901) forming a fluid flow path, transverse to the direction of fluid flow and adjacent to the flow path input port (902), and the moving member (904) is a target formed by a permanent magnet (906) and a support member (1) parallel to the flow direction, against which the fluid exerts a drag force. A fixed member (907), a permanent magnet, is positioned transverse to the fluid flow between the input port (902) and the output port (903) of the fluid flow path, closer to the output port (903). The two permanent magnets (906, 907) have their faces of the same polarity facing each other, whereby the fixed member (907) exerts a counteracting magnetic force on the moving member (904) and limits its displacement in proportion to the magnitude of the drag force. The fixing member (907) may advantageously be ring-shaped to provide a sliding constraint to the support member (1) of the target (906) and to minimise friction in the sliding movement.

[0093] As shown in the exemplary arrangement of FIG. 9B, the fixed member (907) can be suspended in the flow channel through one or more support structures (2, 3) so as not to block the flow channel output. In this exemplary arrangement, the displacement of the moving member in the flow channel is parallel to the fluid flow, and the permanent magnet (906) on the target no longer requires a living hinge. The sensing means (909) can be positioned outside the fluid flow channel, perpendicular to and proximate to the moving member (904), and the sensing means measures the displacement of the moving member (904). The signal received by the sensing means (909) is transmitted to a processing unit via a flexible cable (910) and converted into a measurement of the flow rate.

[0094] FIG. 10A presents an alternative configuration of the present teachings at zero flow, where a moving member (1004) is mounted in a rigid housing (1001) that defines a fluid flow path, transverse to the direction of fluid flow, adjacent to a flow path input port (1002), the moving member (1004) is a target formed from a permanent magnet (1006) and is supported by a number of living hinges (1, 2, 3) that keep the movement of the moving member (1004) transverse to the flow. As shown in FIG. 10B, the living hinges (1, 2, 3) allow the moving member (1004) to be suspended in the center of the fluid flow path, with the geometry and materials for the living hinges (1, 2, 3) defined according to the selected application.

[0095] The fixed member (1007) formed of a permanent magnet is arranged between the input port (1002) and the output port (1003) in the fluid flow path, closer to the output port (1003), transverse to the fluid flow, and the faces of the same polarity on the two permanent magnets (1006, 1007) facing each other generate a magnetic repulsion force. As shown in this exemplary arrangement, the fixed member (1007) has a circular cross section and can be suspended in the fluid flow path by adhesive or other fastening means, but the fixed member can also be ring-shaped and fastened to the wall of the fluid flow path so as not to restrict the cross-sectional area of ​​the fluid flow path, as shown in the exemplary arrangement of Figures 9A and 9B. The fixed member (1007) will exert a counteracting magnetic force on the magnet (1006) on the moving member (1004), limiting its displacement in proportion to the flow rate. In this exemplary arrangement, the sensing means (1009) may be positioned external to the fluid flow path, perpendicular to and proximate to the moving member (1004), and the sensing means measures the displacement of the moving member (1004). The signal received by the sensing means (1009) is transmitted via a flexible cable (1010) to a processing unit and converted into a measurement of the flow rate.

[0096] FIG. 11 depicts the relationship between the magnetic force between two cylindrical magnets with radius R and length L, where R=L, and the ratio of their separation z to their radii R. Here, the force is attractive when the poles of the two magnets with opposite polarity face each other, and repulsive when the poles of the magnets with the same polarity face each other. When the magnets are aligned along the axis of their magnetic dipoles, ideally according to the fourth order polynomial law, it is clear from the trend lines in this graph how the magnetic force between the two magnets becomes very high when the two magnets approach each other, and how instead the magnetic force between the two magnets decreases rapidly when the two magnets move apart, when the magnets are aligned along the axis of their magnetic dipoles.

[0097] FIG. 12 illustrates the calibration function for the flow sensor of the present teachings; in particular, FIG. 12 shows the relationship between the magnetic field reading (d) from the sensing unit, which is proportional to the displacement of the target, and the flow rate (U) of the fluid in the flow path.

[0098] At zero flow (U=0), the distance between the magnet on the target and the fixed magnet in the fluid flow path is at a maximum, the target is at its rest position relative to the flow path input, and the sensor output corresponds to the saturation point (a). When the pressure difference between the flow path input and output exceeds the magnetic repulsion force between the two magnets, the target is moved away from the flow path input and the flow path opens. As the flow rate increases, the target moves further away from the flow path input and the magnetic repulsion force counteracts the drag force of the fluid on the target, thus limiting its displacement. This results in a linear relationship between the sensor output (d), which represents the displacement of the target, and the flow rate (U), as shown in region (b) of the graph.

[0099] When the target reaches its position of maximum displacement, the magnetic repulsion is at a maximum and the magnetic field reading from the sensing unit reaches the opposite saturation point (c). The dynamic range of the sensor then corresponds to the linearized curve in region (b), which can be extended depending on the parameters of the selected magnets and their separation in the fluid flow path.

Claims

1. 1. A flow measurement device, comprising: a. a rigid housing defining a fluid flow path having a flow path input and a flow path output, the fluid flow path configured to allow a fluid medium to flow from the flow path input to the flow path output; b) a moving member hingedly mounted within the fluid flow passage and extending transversely to a direction of flow of the fluid medium, the moving member including a moving member magnet, the moving member operatively moving upon exposure to a drag force resulting from fluid passing within the fluid flow passage, the moving member being formed from a flexible support structure forming a living hinge; c) a fixed magnet disposed at least adjacent a sidewall of the fluid flow passage, the fixed magnet having the same polarity as the moving member magnet and arranged to operatively exert a repulsive force on the moving member magnet, thereby limiting its displacement in proportion to the magnitude of the resistive force exerted by the fluid flow, thereby linearizing the relationship between the flow rate of the fluid medium and the displacement of the moving member; d. a sensing element positioned relative to the moving member and configured to provide an output indicative of the movement of the moving member within the fluid flow path; Equipment comprising:

2. The device of claim 1 , wherein one or both of the magnets in the fluid flow path are permanent magnets or electromagnets.

3. 3. The device of claim 1 or 2, wherein the flow path has a flow path central axis, and the fixed magnet is embedded within the fluid flow path or in a side wall of the fluid flow path, with its magnetic poles disposed at an angle "θ" relative to the flow path central axis and the direction of flow, the angle "θ" coinciding with an angle "α" between the flow path central axis and a maximum displacement position of the moving member.

4. 4. The device of claim 1, wherein the fluid flow path and the moving member are dimensioned such that the geometric shape of the fluid flow path and the moving member and the ratio between the cross-sectional area of ​​the fluid flow path and the cross-sectional area of ​​the moving member are provided such that the drag of the fluid flow against the moving member is maximized and a pressure difference between the flow path input port and the flow path output port opens the flow path when the flow rate of the fluid medium is at least 10 μl / s.

5. 5. The device of claim 1, wherein the moving member includes a hinge region defining a cutout portion extending across a width of the hinge region, the cutout portion being provided in a surface of the hinge region facing the flow path input.

6. The device of claim 1 , wherein the stationary magnet is suspended within the flow path transverse to the fluid flow and parallel to the moving member in its rest position.

7. 7. The device of claim 1, wherein the housing is formed from a rigid material having low magnetic permeability, the rigid material being one of austenitic stainless steel, or an engineering plastic, the engineering plastic being preferably polyetheretherketone or polyoxymethylene.

8. 8. The device of claim 1, wherein the moving member is hingedly coupled via a plurality of hinges such that the movement of the moving member remains perpendicular to the flow.

9. 9. The device of claim 1, wherein the bending force on the flow of material of the hinge is small compared to the magnetic repulsion force between two of the magnets.

10. 10. The device of claim 1, wherein the flexible support structure is formed from a flexible polymeric film, the polymeric film being one of a polyetheretherketone film or a polyimide film.

11. The device of claim 10 , wherein the flexible film is encapsulated with a moisture resistant coating.

12. 12. The device of claim 1, wherein the moving member is formed from a permanent magnet encapsulated in a polymer matrix such as silicone rubber, the polymer matrix acting both as the living hinge and as an encapsulation layer for the permanent magnet.

13. 13. An instrument as claimed in any one of claims 1 to 12, wherein the geometry and strength of the magnets within the flow path, their separation, and the geometry of the flow path are calibrated for a particular measurement range.

14. 14. The device of claim 1 , configured to dynamically adjust the measurement range by varying parameters of the magnet or by adding or removing magnetic elements from the sensing element.

15. 15. The apparatus of claim 1, wherein the transfer member is formed from a material having a density that matches a density of the fluid medium.

16. 16. The device of claim 1, wherein the sensing element uses a sensing technology selected from one of the following principles: Hall effect, magnetoresistance, inductive, capacitive, optical.

17. 17. The apparatus of claim 16, wherein the sensing technology is a magnetoresistance technology, the magnetoresistance technology being selected from one of the following: geometric magnetoresistance, positive magnetoresistance, Shubnikov-de Haas oscillations, negative or anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), colossal magnetoresistance (CMR), or extraordinary magnetoresistance (EMR).

18. 17. The device of claim 16, wherein the sensing technique is an inductive technique, and the inductive sensing is caused by using a first electromagnet on the moving member together with a second electromagnet fixed downstream from the first electromagnet in the fluid flow path, transverse to the fluid flow and opposite the first electromagnet, the first electromagnet also providing the magnetic repulsion force on the moving member, and a change in mutual inductance between the two electromagnets caused by the displacement of the moving member is an indication of the flow rate.

19. 17. The device of claim 16, wherein the sensing technique is an inductive technique, and the inductive sensing is caused using a first electromagnet on the moving member, transverse to the fluid flow, together with a second electromagnet mounted opposite the first electromagnet on the moving member and near the input of the fluid flow path, the change in mutual inductance between the two electromagnets caused by the displacement of the moving member being an indication of the flow rate, and a third electromagnet or permanent magnet fixed downstream of the moving member provides the magnetic repulsion force on the moving member.

20. 20. The apparatus of claim 18 or 19, wherein the distance between the first electromagnet and the second electromagnet is minimized to maximize signal response.

21. 17. The device of claim 16, wherein the sensing technique is a capacitive technique, and the capacitive sensing is effected using a pair of capacitor plates mounted within the fluid flow path, facing a capacitor plate within the moving member, with the fluid medium as a dielectric, and displacement of the moving member causes a change in distance and capacitance between the plates in proportion to the flow rate.

22. 22. The apparatus of claim 21, wherein the capacitor plates have as large a common area as possible to maximize capacitance.

23. 22. The device of claim 21, wherein the fixed capacitor plate is mounted near the flow path input or the flow path output.

24. 17. The device of claim 16, wherein the capacitor plates are optical technology and the optical sensing is caused by at least one light emitting member and at least one light receiving member.

25. 25. The apparatus of claim 24, wherein the position of the moving member is detected by optical time-of-flight, Doppler shift, or interferometry in response to characteristics of light reflected by the moving member onto the at least one light receiving member.

26. 25. The apparatus of claim 24, wherein the housing of the sensor is manufactured using an optically transparent material.

27. 27. An apparatus as claimed in any one of claims 1 to 26, wherein the moving member is configured as a check valve to prevent flow in an undesired direction.

28. 1. A flow measurement device, comprising: a. a rigid housing defining a fluid flow path having a flow path input and a flow path output, the fluid flow path configured to allow a fluid medium to flow from the flow path input to the flow path output; b. a moving member hingedly mounted within the fluid flow passage and extending transversely to a direction of flow of the fluid medium, the moving member including a moving member magnet, the moving member operatively moving when exposed to a drag force resulting from fluid passing within the fluid flow passage; c) a fixed magnet disposed at least adjacent a sidewall of the fluid flow passage, the fixed magnet having the same polarity as the moving member magnet and arranged to operatively exert a repulsive force on the moving member magnet, thereby limiting its displacement in proportion to the magnitude of the resistive force exerted by the fluid flow, thereby linearizing the relationship between the flow rate of the fluid medium and the displacement of the moving member; d. a sensing element positioned relative to the moving member and configured to provide an output indicative of the movement of the moving member within the fluid flow path; Equipped with 1. An instrument, the displacement of which is parallel to the direction of flow of the fluid medium, connected to a support parallel to the direction of flow of the fluid medium, the fixed magnet being positioned transverse to the fluid flow downstream in the center of the fluid flow path.

29. 30. The device of claim 28, wherein the moving member is connected to a sliding pin coupled to the fluid flow passage via a sliding constraint such that friction during sliding motion is minimized.

30. 30. The device of claim 28, wherein the fixed magnet is ring-shaped to provide support for the moving member without obstructing a cross-section of the flow path.

31. 29. The apparatus of claim 28, wherein the position of the moving member is detected via a sensing technique as described in any of claims 17 to 19 or 21.

32. 32. The device of claim 1, wherein the sensing element is coupled to a connecting cable for communicating an output signal to a peripheral device, the device further comprising an amplifier configured to amplify the output signal before being transmitted through the connecting cable in the vicinity of the fluid flow path to avoid external interference that may be coupled into the cable.

33. 33. The apparatus of any one of claims 1 to 32, configured to provide active amplification of the output signal, the active amplification being provided by at least one amplifier configured to amplify the output signal to a level such that a zero flow signal reading is close to the maximum value of a subsequent analog-to-digital transducer (ADC) to maximize signal resolution.

34. 34. The apparatus of claim 1, further comprising a processing unit in communication with the sensing element, the processing unit configured to receive the output signal and convert the output signal into a flow measurement using a calibration function, the function using a parameterized model, a look-up table (LUT), an interpolated value, or any combination thereof.

35. 35. An apparatus according to any one of claims 1 to 34, comprising a memory element for storing calibration coefficients of the sensing elements.

36. 36. An apparatus according to any one of claims 1 to 35, comprising a memory element for storing sensor wear information and / or usage information of the sensor.

37. 37. An apparatus according to any one of claims 1 to 36, comprising a cable extending from the sensor unit and connected to a processing unit.

38. 38. An apparatus according to any one of the preceding claims, comprising a wireless transmitter for transmitting measured readings to an external device.

39. 39. The device of any one of claims 1 to 38, wherein the device is a biomedical device and configured for real-time linear or pulsatile flow detection in biomedical applications.

40. 40. An instrument according to any one of claims 1 to 39, configured to measure the flow of a fluid, the fluid being in the form of a gas or a liquid.

41. 41. A measurement system comprising a processing unit, a visual display, and an instrument as described in any one of claims 1 to 40, wherein the processing unit is configured to receive sensing element data from the instrument and to provide a visual representation of the measured flow rate on the visual display.

42. 42. The system of claim 41, wherein the processing unit is a smartphone, the visual display is a screen of the smartphone, and the smartphone has application software running thereon that receives and processes flow sensor data from the sensor and provides a visual representation of the measured flow rate on the visual display.

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