EP4720610A2 - Systems and methods for sensing fluid flow - Google Patents

Abstract

A system uses a sensing membrane to determine a fluid flow of a working fluid through the membrane. The system detects an electrical current generated by a fluid flowing through the sensing membrane and correlates the current to bulk flow. The sensing membrane can also be used to induce fluid flow by applying a current to the membrane. In alternative embodiments, separate sensing membranes and actuating membranes can be used in the same enclosures to permit sensing and actuating simultaneously.

Description

TITLE

SYSTEMS AND METHODS FOR SENSING FLUID FLOW

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 63/469,105, filed on May 26, 2023, and U.S. Provisional Application Serial No. 65/023,588, filed on April 9, 2024, each of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH [0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] The present disclosure generally relates to flow sensors. More specifically, the disclosure relates to electrohydraulic sensing of a fluid flow in a thin membrane. While there are many methods of measuring fluid flow, most are large (>lmm thick) and designed to measure flow through open pipes or tubes. Electroosmotic pump actuator arrays, like the type disclosed in W02023023095A1, have the benefit of developing separated and individually controlled flows across a thin membrane through electrical control. Many separate flows can be generated in a small area, and thus there is a general need to sense the rate of these flows in a way that is similarly compact, thin, flexible, inexpensive, and compatible with manufacturing methods. This ensures ease of integration with these types of pumps. Therefore, it would be advantageous to develop systems and methods for detecting fluid flow in electroosmotic pump actuator arrays and similar types of systems.

BRIEF SUMMARY

[0004] According to embodiments of the present disclosure is a system and method for sensing fluid flow through a small, thin membrane with electrodes on either side of the membrane. Advantages of this approach are that a fluid flow sensor can be made extremely thin, lightweight, and inexpensively. Additionally, an elastomer membrane, or some other compliant or moving mechanism, can be hydraulically linked to the sensor, thus turning the device into a touch and pressure sensor for human computer interaction. Various other hydraulic linkages can be built to sense other, macroscopic parameters such as fluid displacement and pressure in cavities. Because the device can be made so small, it is also simple to create large arrays of sensors, and thus perform distributed pressure sensing, for example, at the end of a robotic manipulator.

[0005] Another advantage of this approach is that the same structure can be used to apply pressure to the system. If the sensing electrodes are instead attached to an electrical power source, the power source will drive the fluid through the membrane. This is known in the art as an electroosmotic pump. By integrating electroosmotic pump techniques in this new way, the same device can operate as both a sensor and actuator. This greatly increases the utility of the overall device. For instance, fluid pressure can be applied and then the resulting fluid flow can be sensed, leading to closed loop control of the system. This can help, for example, in detecting a block in the pump output, or in creating an interactable tactile button. In another embodiment, two pumping membranes and associated electrode pairs can be stacked in hydraulic series, with one serving as the pump, and the other serving as the sensor. This also allows simultaneous sensing and actuating. A stacked structure also has the advantage of reducing the voltage burden of the driver, allowing lower voltages to be used for the same output pressure and flows.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS [0006] Figs. 1 A-1B are diagrams showing main system sensing elements and sensing flow and current in response to sensing pressure.

[0007] Figs. 2A-2B depict an example embodiment of sensing and actuation system using a switching circuit.

[0008] Fig. 3 is an embodiment of simultaneous sensing and actuation of the system.

[0009] Fig. 4 shows an example of a closed loop sensing and actuation system using at least 2 membranes.

[0010] Fig. 5 is an embodiment of system using a single sensing membrane across multiple actuation membranes.

[0011] Fig. 6 is a system with a separate power source.

[0012] Fig. 7 shows an alternative embodiment with a separate fluid chamber.

[0013] Fig. 8 is an alternative embodiment using additional sensors.

DETAILED DESCRIPTION

[0014] According to embodiments of the disclosure is a system 200 for sensing fluid flow through a membrane 100, the membrane 100 having fluid permeability such that it introduces a resistance to fluid flow when under an external pressure gradient. The system 200 utilizes electro-osmosis, a pumping technique that induces fluid flow through the use of an electric field. In some embodiments, the pumping membrane 100 is separated by two electrodes, including a first electrode 104 and a second electrode 105. Common materials suitable for the membrane 100 include various polymers such as polyimide, polyamide, polypropylene, fibrous glass, polytetrafluoroethylene, etched silicon, ceramics such as aluminum oxide, silicon oxide, titanium oxide, or other materials. Thicknesses include the range of 5 microns to 3 millimeters, but sometimes 50 to 200 microns.

[0015] In one embodiment, shown Fig. 1A, there is a fluid permeable sensing membrane 100 embedded in a fluid tight enclosure 101. The fluid tight enclosure or reservoir 101 has at least one, sometimes two, area(s) of compliance, which is able to bend under an applied pressure (as shown in Fig. IB). The sensing membrane 100 separates the enclosure 101 into at least two separate volumes 102 and 103, introducing a hydraulic resistance between them. Fluid 130 traveling between these two volumes 102/103, for example in Fig IB under the influence of an external pressure or, as will be seen later, as a result from an internally induced flow, travels, at least in part, through the sensing membrane 100. Disposed on either side of the sensing membrane 100 is a first electrode 104 and second electrode 105 which, taken together, form a differential electrode pair. These electrodes 104/105 are made of a conductive material and serve as the main electrical interface between the hydraulic and electrical systems. A working fluid 130 fills the volume of the enclosure 101, permeating the sensing membrane 100 and contacting the first electrode 104 and second 105 electrode.

[0016] The configuration of the differential electrode pair 104/105 and sensing membrane 100, including their location, geometry, fluid permeability, material, and surface coating, is adjusted such that when an external pressure is applied to the compliance of the sensing surface 140, shown Fig. IB, a bulk fluid flow flows between the two interior volumes, from volume 103 to volume 102 of the enclosure 101 (denoted by arrow in Fig. IB), generating an appreciable sensing current which can be detected by a sensing amplifier 106 and associated circuitry in electrical contact with the first electrode 104 and the second electrode 105. The sensing surface 140 is the flexible portion of the enclosure 101 that is able to deform under an applied load. When this portion of the enclosure 101 deforms, it causes a change in pressure in the second volume 103 of the enclosure 101.

[0017] This sensing current is a result of charged ions present in the working fluid 130, which have been weakly polarized due to an electrical double layer potential at the surface of the sensing membrane 100 and the working fluid 130. This sensing current is induced across the finite hydraulic resistance of the sensing membrane 100. This results in an associated sensed potential which is proportional, in part, to the bulk fluid flow across the sensing membrane 100. This coupling between the hydraulic and electrical system is because the bulk flow is viscously linked to charged ions in the fluid 130. Bulk fluid flow drags charged ions, which, as they flow, create an electrical potential difference in the fluid 130. This potential difference is transferred across the electrodes 104/105 and to the sensing amplifier 106 via an electrical sensing current (shown as an arrow in Fig. IB). Stated differently, the sensing current produced across the sensing membrane 100 is measured via the differential sensing electrodes 104/105 and amplifier 106.

[0018] In one embodiment, the electrodes 104/105 are connected to a high input impedance electrical differential amplifier 106 through a system routing network 135. The system routing network 135 may include the wires and electrical components used to connect the amplifier 106 to the electrodes 104/105. In some embodiments, the routing network 135 may also include the switching circuit 111, which is shown in Figs 2A-2B. Various methods of routing electrical signals are known in the art. One electrode 104 or 105 could also be connected to a system ground reference to reduce the number of connections needed. The high input impedance of the sensing amplifier 106 prevents large current flowing through the electrode/fluid interface, avoiding half-cell overpotential drops and redox reaction pathways at the electrode/fluid interface. Limiting the current through this interface ensures a minimized electrical double layer forms, and that chemical reactions (which are driven by applied voltage differences between the fluid and metal), are minimized. These polarization effects are inherent in all electrochemical interfaces, and dictate important aspects of the sensing signal. This means that the sensing electrodes 104/105 are able to take on nearly the same potential of the portion of fluid 130 they are immersed in. The high impedance differential amplifier 106 is then routed to an analog-to-digital 110 converter, and the digitization of the sensing potential across the membrane 100 is complete. In this manner, a sensitive and compact sensing pathway is established.

[0019] Once digitized, various sensing algorithms known in the art can be applied in software to the signal to compensate for any non-idealities, for instance, changes due to heat, time, or fluid properties. These compensations help estimate the total fluid 130 passing through the sensing membrane 100. This information can be a proxy for system pressure in one or more of the enclosed volumes 102/103, or, in the case of a flexible enclosure 101, this can be a proxy for a change in system volume or bending configuration. Signal baselining, differentiating, thresholding, and similar techniques can also be applied. It should be appreciated that many of these software techniques could also be applied in hardware, firmware, logical controllers, and many hardware techniques can be applied in software, as is common in the art.

[0020] System flow, pressure, and enclosed volume are parameters that can affect performance when the system 200 is used as a touch and pressure sensor, as in the case of an interaction surface. In this example embodiment, one of the enclosed volumes 102/103 is hydraulically linked to a sensing surface 140, or some other compliant surface or structure, such that applied surface forces and deformations can be sensed. By severely restricting the flow through the sensing membrane 100, a nearly pure pressure can also be recorded. This is because the amount of fluid 130 that actually flows in this case is very small, and it takes a long time for the system to relax to its original state. Therefore, any current that flows is due to large pressure spikes in the system 200. Various other hydraulic elements and materials can be linked to the sensing membrane 100 to transduce other system parameters indirectly. The thin and flat nature of this sensor 200 allows this integration in a novel way that would not be practical elsewise. Total system thickness can be on the order of 0.2mm or less, down to 10-20pm, in practical settings. [0021] The general structure of the sensor 200 is such that it can also be used as an actuator, if the sensing electrodes 104/105 are driven with an electrical power source 132 using a driving amplifier 112 instead of being only applied to a sensing amplifier 106, as shown in Fig 2A. This requires a different set of driving electronics and, in some cases, a circuit 111 for switching between the driving 112 and sensing electronics 106. In this configuration, the working fluid 130 can now be both actuated and sensed by the same set of electrodes 104/105. In another embodiment, the electrical voltage and current is monitored, via a high-side or low-side electrical monitoring circuit 113 during actuation. An example low-side monitoring circuit 113 using a series sensing electrical resistor is shown in Fig 3.

[0022] For a given applied voltage by the actuation amplifier 112, a portion of the resulting current through the system is proportional to the bulk fluid flow through the device 200. This means that that portion of the current changes if the actual fluid flow changes. This can be sensed by the high-side or low-side electrical monitoring circuit 113 and digitized by the analog to digital converter 110 for further processing. Changes in the resulting current then reflect changes in the flow that is occurring through the sensing membrane 100. This is because the resulting current is a combination of electroconvective flow (proportional to bulk flow) and non-flow producing phenomenon, such as dielectric polarization current and bidirectional ionic flow (which produces no net electroconvective flow). These effects are calibrated out during a characterization stage and can be continuously monitored and adjusted for by baselining and other on-line processing steps. Some of examples of these processing steps include: a dynamic thresholding algorithm, which looks for signal fluctuations above or below a specific value, and then adjusts that value over time based on periodic measurements taken over longer time scales (minutes, days, weeks), a leaky system integrator, which continuously sums the value of the incoming signal over a short time window and gradually subtracts from the signal over a longer time window, or a peak detection algorithm, which looks at the peak value of a signal over a short time period resulting from a sudden applied voltage.

[0023] In another embodiment, time domain multiplexing may be used between sensing and actuating. Here a short voltage pulse is applied to the system 200 using the actuation amplifier 112, which induces a transient flow, and a resulting current is then read by rapidly switched using the sensing electronics 111 and the electronics are hooked up to the sensing electrodes 104/105 to a sense circuit or amplifier 106. The resulting sensing current can be the inertial residue of the original electrical source driven flow, or it can be a backflow (of opposite direction), coming from compliance of the compliant membrane 140 pushing fluid back to an equilibrium state. This switching circuit 111 can be implemented using solid state, multiplexing switches, so it is very rapid, and does not significantly reduce actuator output power if done in rapid succession.

[0024] In another embodiment, the sensing amplifier 106 can have circuit protection built in so it is not affected by remaining applied voltage from the driving amplifier 112. Various other actuation and sensing switching schemes for the switching circuit 111 are also possible, such as row-column matrix addressing in combination with time or frequency domain multiplexing. Switching circuits 111 may also be placed on either sensing electrode 104/105, or both. In this manner, an entire array of membranes 100, with their own separate or shared sensing electrodes 104/105 could be rapidly actuated and sensed.

[0025] In another embodiment, shown in Fig. 4, there are totally separate membranes for sensing (sensing membrane 100) and actuating (actuating membrane 114), which can be placed in a hydraulic communication, meaning there is a hydraulic pressure or flow which links the two systems together. This configuration implies that the driving electronics 112 can be actuating one pumping membrane 114, while the sensing electronics 106 are monitoring a second membrane 100. This is another way of simultaneously sensing and actuating a fluid 130. In this embodiment, there are two pairs of electrodes, meaning a third electrode 115 and fourth electrode 116 are introduced beyond the first example. In some cases, one of the electrodes 115/116 can be shared between sensing and actuating, resulting in only three electrodes being needed. [0026] This dual membrane 100/114 configuration has many practical advantages, for example, each membrane 100/114 and set of electrodes 104/105 or 115/116 can be optimized for either sensing or actuating, depending on its core function. This optimization can be that different materials and coatings are used (for the electrodes and membrane 100/114) or different geometries are used (gross geometries, or fine geometries). For instance, it may be desirable to introduce little hydraulic resistance in the sensing membrane 100, but a lot of resistance in the actuating membrane 114, leading to larger pores and a thinner membrane for the sensing membrane 100. Since the membranes 100/114 are also decoupled, many actuating membranes 114 can all be placed in series with a single sensing membrane 100, allowing one set of sensing electronics 106 to be used for many actuators. This allows a type of hydraulic multiplexing to occur, where a single sensing membrane 100 and set of electrodes 104/105 is linked to a plurality of actuation membranes 114 and 122 and their associated electrodes 115/116 and 121/123 (respectively), as shown in Fig. 5. In this embodiment, the sensing current contains information from both hydraulic actuation flows. In this case, membranes 114/122 are placed in series, or directly stacked.

[0027] Another advantage of the stacked configuration, exemplified in Fig. 4, is that any given membrane 100/114 can be switched from a sensing membrane 100 to an actuating membrane 114 (or vice versa) by making use of a switching circuit 111. Multiple membranes can all be used for sensing, or all be used for actuating, or in any combination therein. This gives the advantage of boosting the sensing signal (raising the sensing current) for the case of sensing and increasing the actuation pressure (boosting the available backpressure for a given potential) in the case of actuating. This allows system designers tremendous flexibility, as different voltage levels of drive electronics 112 and sensing electronics 106 can be used and optimized for. This advantage is particularly large in the case of many stacked membranes being used for actuating, as similar hydraulic pressures can be achieved for less applied voltage when compared to a single membrane approach (e.g. the same output pressure of 50kPa could be achieved at half the voltage if using two membranes). This is useful since known techniques in the art require large voltages (200-300V) for appreciable pressure, and this can cause undue burden on system designers to find the right types of driving electronics and to shield system routing from a user’s touch, as voltages above approximately 50V are known to present a potential shock hazard.

[0028] In the sensing case, many stacked membranes 100 may be used to increase the sensing current such that sufficient signal is attained by the sensing amplifier 106 in the presence of system noise. It can also be used to keep electrode 104/105 voltage potentials below electrochemical limits, leading to a more stable electrode fluid interface and more stable measurements. In the many membrane configurations, there are a plurality of electrodes going to a plurality of membranes 100. The membranes 100 may be of the same material, or different materials, in order to optimize the magnitude and polarity of the zeta potential. The effect this has is to alter the direction and amplitude of fluid flow a membrane 100 will create for a given polarity of applied voltage.

[0029] In addition to the membrane 100/114 being used for sensing or actuating, in another embodiment it can be attached to a power harvesting circuit 131, such as a super capacitor, separate electrochemical battery, traditional capacitors, and appropriate dc/dc boost/buck converters to transform voltage levels. Fig. 6 shows a device 200 with a power harvesting circuit 131 in electrical communication with the switching circuit 111. These types of circuit and storage elements are commonly known in the art. This allows a third function of the membrane 100, power harvesting, to be integrated into the device 200 in a nearly seamless manner by taking advantage of a switching circuit 111. This configuration is similar to the sensing configuration, shown in Fig. 1, but the impedance of the electrical circuit 131 is much lower than that of the fluid/el ectrode cell, meaning significant energy is allowed to flow via hydraulic to electrical transduction. The energy captured can be used to power functions of the device 200 during other operational states. Critically, this could eliminate the need of a self- contained device 200 to require an external power source, a highly desirable capability for applications such as wearable human computer interfaces, tetherless robotics, or implanted medical devices.

[0030] The core functions of a combined sensing and actuating system 200 using electroosmotic actuation and associated current sensing are numerous. The sensor 200 can be used to monitor the characteristics of the fluid 130, such as its conductivity, humidity, presence of air bubbles, contamination, etc. The device 200 can self-test, so that it can be ensured to be fully functional and up to specification. It could test the amount of fluid 130 within the system, the state of the electrodes 104/105, membrane 100, and, in general, could be used to monitor online power consumption by each individual device. From a total system perspective, sensing information can be fed into a closed control loop, as shown in Fig. 4, allowing system parameters such as displacement, pressure, and temperature to be more precisely controlled. [0031] In this embodiment, commands from a digital controller 118, are output via a digital - to-analog converter 117, which controls an actuation amplifier 112. The actuation amplifier 112 causes a flow of fluid 130 through its actuation membrane 114 by way of the electrodes 115/116. This flow is in series with the sensing membrane 100, which conveys the bulk sensed flow to the sensing amplifier 106 by way of the sensing electrodes 104/105. The sensing amplifier 106 is digitized by the analog-to-digital converter 110, and fed back into the digital controller 118.

[0032] This digital controller 118 can perform any number of signal conditioning processing steps. One signal conditioning processing step includes a “leaky integrator” function, which integrates (adds up) the signal over a small time window, determined by an associated time constant. After a longer time constant, the signal is reduced, and hence “leaky”. This type of processing step is useful because the signal from the sensing membrane 100 is proportional to the fluid flow, however, it is useful to get an estimate of the fluid displacement, which is, by definition, the integral of fluid flow. Other interesting parameters to consider are output pressure, temperature, acceleration, to name a few. The digital controller 118 keeps an estimate of these variables and updates its output via the digital-to-analog controller 117 in a closed- loop way. In this manner, system variables can be actively controlled. Of note, this means that the actuation amplifier 112 should have a variable output, which is able to apply a proportional signal to the actuation membrane 114. This can be achieved in many ways, such as via a fully analog, linear amplifier 112. However, a digital modulation method, such as digital pulse width modulation, can be used. A carrier frequency much larger than the desired actuation frequencies is used, for example, greater than 1kHz, and often close to 10kHz, which is large enough to avoid electroconduction effects in the fluid 130.

[0033] This closed-loop configuration can be used to have the system act as a self-contained tactile “button” which is able to inflate the output membrane 140 by using the actuation amplifier 112 and membrane 114, and then it can detect if the system is being pushed on by measuring the sensing current via the sensing amplifier 106. Various levels of pressure can be detected and the digital controller 118 can change the resulting pressure in the output volume 103 to create a haptic effect, back to the user touching the surface. Visual effects, such as animations and visual deformations can also be induced to create feedback for a user.

[0034] In a similar manner, the system 200 can sense if the actuating membrane 114 is being blocked, for example, if a user is pressing hard on the coupling membrane 140 of a touch sensor. In this way, information from outside the device 200 can be inferred by actuating the system 200 to probe the environment, then sensing the response to that actuation. In another example, a system 200 could determine how far away a user's finger is by rapidly actuating until it hits the finger, at which point the sensing current would change, since the flow is now blocked from occurring. This could give a three-dimensional depth image of an object in partial or no contact with the surface of the device 200 (at least initially before actuating). In another instance, the device 200 could engage with a user’s skin, apply known pressures, and look for back pressures coming from the body. This information could be used in a medical application, for instance, to determine blood pressure of an individual, or to determine the location and mechanical makeup of the contacting part of the body (e.g. if it is bone or soft tissue). In this way, the device 200 now serves a type of mechanical camera function, similar to how ultrasound transmitters and receivers probe the body for changes in mechanical properties. This type of camera-like array could also be used as a robotic sensor, allowing roboticists to image gripped and touched objects similar to how humans naturally do it, by first pressing against an object, and then feeling the amount of force and compliance the object gives.

[0035] In another configuration, as shown in Fig. 7, the compliant and movable part of the hydraulic system is in contact with a second fluid 142 through a mechanical or hydraulic coupling 141 and the sensor 200 can then be used to sense displacement and pressure of the second fluid 142. This could be useful for the purposes of moving and sensing fluids that are not in electrical contact and can be kept separated to limit contamination.

[0036] Because it is so advantageous to have a complete sensing and actuating system, additional non-membrane based sensors 145 can also be integrated into the system 200, as shown in Fig. 8. These sensors 145 can allow for system calibration, and serve as reliable backups for the methods discussed here. They can also entirely replace some functionality if there is enough benefit to do so. Additional sensing types might include mutual and projected capacitance sensing, resistive sensing, radio-frequency sweep analysis, audio or ultrasonic range vibration techniques, optical sensors (including cameras, phototransistors, etc.), and temperature flow sensors to name a few. Additional actuating types might include piezoelectrics, shape-memory alloys, electroactive polymers, electrostatic actuators, other electrohydraulic methods etc. Use of these additional sensing and actuating types does not preclude the use of the system and method disclosed here, but can be used to enhance overall system performance.

[0037] When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps, or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. [0038] The invention may also broadly consist in the parts, elements, steps, examples and/or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and/or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein. [0039] Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure. Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

Claims

CLAIMS What is claimed is:

1. A device for sensing a flow of a working fluid across a membrane comprising: a sensing amplifier for detecting a current across the membrane and a differential electrode pair adjacent to the membrane when the working fluid traverses the membrane.

2. The device of claim 1, further comprising: an analog to digital converter for receiving the current detected by the sensing amplifier.

3. The device of claim 1, wherein the sensing amplifier has an input impedance sufficiently high to reduce electrode polarization effects.

4. The device of claim 1, further comprising: a reservoir holding the working fluid, wherein the reservoir is in fluid communication with the membrane.

5. The device of claim 4, wherein an external force imparted on the reservoir creates a bulk flow of the working fluid through the membrane.

6. The device of claim 5, further comprising: a hydraulic or mechanical coupling the external force to the reservoir.

7. The device of claim 1, wherein the sensing amplifier is a differential amplifier.

8. The device of claim 1, the sensing amplifier has a terminal connected to electrical ground.

9. The device of claim 1, wherein the membrane has a surface coating.

10. The device of claim 1, wherein the working fluid has free ions.

11. The device of claim 1, wherein the working fluid has a high dielectric constant.

12. The device of claim 1, further comprising: a power source connected to the differential electrode pair through a switching circuit.

13. The device of claim 12, wherein the power source is a bipolar power source.

14. The device of claim 12, further comprising: a switching circuit to isolate a sensing circuit and an actuation circuit.

15. The device of claim 12, further comprising: a high-side or a low-side circuit that detects a current applied by the power source.

16. The device of claim 12, further comprising: a separate actuation membrane.

17. The device of claim 1, further comprising: a power source integrated into the sensing amplifier.

18. The device of claim 16, wherein the membrane and the actuation membrane share at least one electrode.

19. The device of claim 16, wherein the membrane is less restrictive to fluid flow than the actuation membrane.

20. The device of claim 16, further comprising: a controller connected to the membrane and the actuation membrane through a switching circuit.

21. The device of claim 1, further comprising: at least one of a temperature, pressure, and voltage sensor.

22. A method a sensing a flow of a working fluid across a membrane comprising: detecting a current across the membrane and a differential electrode pair adjacent to the membrane when the working fluid traverses the membrane using a sensing amplifier; using a controller to adjust system parameters in a closed-loop control process.

23. The method of claim 22, wherein the controller compares the current to a threshold and identifying an event when the current exceeds the threshold.

24. The method of claim 21, further comprising: applying an actuation across the membrane; and using the detected current to determine if a blockage in the membrane is present.

25. The method of claim 22, further comprising: controlling a displacement of a reservoir in fluid communication with the membrane by applying an actuation across the membrane and monitoring an integrated current.

26. The method of claim 22, further comprising: calibrating a threshold by actuating the membrane and recording a response.

27. The method of claim 22 further comprising: causing an inflation or deflation of a reservoir in fluid communication with the membrane in response to an external force applied to the reservoir.

28. The method of claim 22, wherein the inflation or deflation cause certain portions of the reservoir to change shape.