Wearable thermal sensors, systems and methods

Abstract

Systems and methods for monitoring flow of cerebrospinal fluid in shunts and blood in blood vessels using non-invasive, wearable epidermal electronics are disclosed. An exemplary wireless, flexible thermal sensor mountable on a body may comprise a barrier film, an enclosure, a first region with a first width, a second region with a second width, a thermal actuator disposed within the first region, a temperature sensor disposed within the first region, a power source disposed within the second region, and a third region with a third width, wherein the third width is smaller than the first width and the second width, wherein the thermal actuator, the temperature sensor and the power source are disposed within a cavity formed by the combination of the barrier film and the enclosure.

Description

WEARABLE THERMAL SENSORS, SYSTEMS AND METHODSCROSS REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Provisional Application No. 63 / 511,113 filed June 29, 2023, the contents of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The description herein generally relates to the field of wireless thermal flow sensing, and more particularly to systems and methods of monitoring flow of cerebrospinal fluid in shunts and blood in blood vessels using non-invasive, wearable epidermal electronics.

[0003] This invention was made with government support under NSF Award 1938472 awarded by National Science Foundation (NSF). The government has certain rights in the invention.BACKGROUND

[0004] Thermal sensors are used to monitor the temperature of objects and, when utilizing a thermal sensor which has an electrical property which varies in response to temperature change, can be implemented as part of an electrical sensing system. A sensor for monitoring thermal transport properties of an object can be created by combining one or more temperature sensors with one or more thermal actuators as part of a sensing system. By measuring the temperature change of an object in response to actuation by the thermal actuator, various thermal transport properties can be determined, such as thermal conductivity, heat capacity, diffusivity, and other related parameters. Different spatial locations of temperature sensors relative to the thermal actuator result in different thermal responses to thermal actuation. Some arrangements of temperature sensors and thermal actuators additionally enable measurement of convective thermal transport properties induced by the movement of fluids near to the thermal actuator. While fluid flow sensors based on thermal actuation, such as hot-wire anemometers, are often desired to be in direct contact with a fluid, certain sensor arrangements enable fluid flow measurements through a solid media, without direct contact with the fluid. For example, such designs can enable body- mountable sensors for noninvasive measurement of biological fluid flow beneath the skin surface without directly contacting the biological fluid.

[0005] There are several challenges associated with making skin-mountable thermal sensors, and in particular, non-invasive thermal fluid flow sensors which are precise, accurate, and reliable. One of such challenges is minimizing the thermal resistance between actuators and / or sensors and the measurement object, which may be a bodily fluid beneath the skin. Some of the currently existing conventional designs employ materials between the sensors / actuators and the skin which create thermal resistance, thereby limiting the accuracy and reliability of the measurements. Some existing sensors are mechanically rigid, which limits their ability to intimately conform to a skin surface without high resistance air gaps. Furthermore, conventional electronic constructions may create a low thermal resistance between thermal actuators and multiple temperature sensors, thereby limiting relative signal response to the object of interest. Additional challenges may also exist due to influence of undesirable external factors, such as air flow over the sensors, which may reduce the signal reliability of body tissues below the skin. In the case of thermal fluid flow sensors, a specific orientation of the sensor relative to the underlying conduit may provide improved signal levels. Some mechanical designs may optimize usability of the sensor for alignment to an underlying conduit. Embodiments described herein serve to address one or more of these challenges by employing multiple constructions to optimize signals by modifying the mechanical designs. Furthermore, wearable thermal sensors require a combination of intimate thermal sensor contact and comfortable wearability from a combination of low mass and comfortable form factor. Some of the currently existing designs may be unable to achieve each parameter simultaneously due to either large mass or rigid and uncomfortable form factor.

[0006] Embodiments disclosed herein describe constructions to resolve each issue simultaneously. In addition to the above-mentioned challenges, other challenges related to electrical signals may exist with skin-mountable thermal sensors. Thermal actuators applied to tissue, such as skin, may represent a hazard to the user if the thermal actuation creates excess heat. Conventional skin-mounted thermal actuators do not account for possible tissue variations in constant power systems, or possible component failure in constant temperature systems, or do not account for expected component variability in manufacturing. Embodiments disclosed herein describe constructions for creating hardware-controlled, software-controlled, and redundant thermal failsafe systems. Further, conventional skinmounted thermal actuation sensors require large batteries, suffer short shelf-life, or require mechanical openings to charge or replace batteries, which may act as ingress points fordamage, safety issues, or signal perturbations. Some embodiments disclosed herein enable solutions for compact, long shelf-life, and hermetically sealed designs.

[0007] As a non-limiting example, Hydrocephalus, represents an exemplary condition for spinal fluid flow measurements. Hydrocephalus is a common and costly condition caused by the accumulation of cerebrospinal fluid (CSF) in the brain, with symptoms that include headaches, seizures, coma, or death. It particularly afflicts children, occurring in 1-5 of every 1,000 live births. Hydrocephalus may be treated with the surgical implantation of a catheter, known as a ventricular shunt, which diverts the excess CSF in the brain to a distal absorptive site, such as the peritoneal cavity. Overall, 40,000 shunts are implanted or replaced annually in United States, with costs estimated at $2 billion per year. Unfortunately, shunts have extremely high failure rates due to a diverse set of factors including occlusion, mispositioning, or kinking. Up to 51% of shunt recipients exhibit symptoms that require a shunt repair surgery, known as a “revision,” in the first year and 99% of shunts are replaced at least once within 10 years of implantation. It is also estimated that nearly half of all healthcare expenditures related to shunt surgery are spent on revisions. Non-specific symptoms like headaches and nausea make diagnosing shunt malfunction extremely challenging. Consequently, physicians rely on a complicated, expensive, and often inconclusive suite of tests, including those that expose patients to significant radiation, to make clinical decisions.

[0008] On average, a single pediatric hydrocephalus patient with an implanted shunt is admitted to the hospital multiple times each year, with a high number of emergency department presentations. The standard-of-care methods used to assess shunt malfunction today include (i) aspiratory CSF sampling, an invasive procedure used to assess pressure in the shunt, (ii) injection of a radionucleotide tracer into the ventricular system and monitoring the movement of the radiotracer into the abdomen, (iii) an x-ray “shunt series” exam to check for mechanical shunt damage, and (iv) Computerized Tomography (CT) or Magnetic Resonance Imaging (MRI) to assess ventricle size. Notably, CT and x-ray shunt series expose the patient to significant radiation. Also, the only test that directly measures CSF flow in the shunt, the radiotracer test, is invasive, painful, and carries a risk of infection. Moreover, the diagnostic performance of these tests is poor. X-ray shunt series, for example, has a sensitivity of approximately 18% for the determination of shunt failure in symptomatic patients. Finally, MRI and CT have poor performance because shunt failure is often not concomitant to ventriculomegaly. These tests are regularly employed despite their serious limitations because they are, unfortunately, the best tools currently available to clinicians. Inaddition to their poor performance, frequent CTs expose children to sizeable radiation doses, increasing their risk of brain cancer. Although MRI is seen as a viable alternative to CT for evaluation of hydrocephalus, access and cost are significant barriers. Significantly, only -17% of the CTs performed lead to a revision surgery within a week, implying that the vast majority of these scans are unnecessary. Therefore, the current standard of care, ventricular catheters (shunts), is prone to failure, which can result in nonspecific symptoms such as headaches, dizziness, and nausea. Current diagnostic tools for shunt failure such as CT, MRI, radionuclide shunt patency studies (RSPSs), and ice pack-mediated thermodilution have disadvantages including high cost, poor accuracy, inconvenience, and safety concerns. As an example, ShuntCheck® utilizes an ice-pack based thermal cooling system connected to a Windows PC DAQ to address a need for shunt monitoring. That technology, however, is limited as it requires wires connected to a patient and the use of a transient icepack, thereby reducing patient comfort, and prohibiting extended use. Accordingly, there is a need for a precise, rapid, easy-to-use, wireless, non-invasive shunt diagnostic that can be used continuously and in patients’ homes.SUMMARY

[0009] Embodiments of the present disclosure provide systems and methods of monitoring fluid flow beneath the skin surface on a body. Disclosed herein are exemplary systems and methods of measurements of flow follow from localized thermal actuation and sensing using a flexible, non-invasive device gently laminated onto the surface of the skin at the location a subdermal fluid conduit such as a blood vessel or a cerebrospinal fluid (CSF) shunt. The results presented here extend these concepts into a user-friendly, fully wireless system that enables continuous, noninvasive monitoring of flow performed by clinicians or by patients themselves in real-world settings. Advanced designs and integration schemes exploit low- cost commercial components and flexible circuit board manufacturing techniques in optimized layouts guided by theoretical and numerical models of thermal transport and system-level mechanics. A Bluetooth Low-Energy System on a Chip (BLE-SoC) embedded system architecture allows for robust, high-quality data transfer during normal patient activities, where a miniaturized on-board, rechargeable battery supports continuous operation over hours to days. User-replaceable adhesive patches and wireless power charging enable user-friendly designs for using disclosed sensors repeatedly over extended periods.

[0010] In one aspect of the disclosure, a wireless, flexible thermal sensor mountable on a body is disclosed. The wireless, flexible thermal sensor may comprise a barrier film, anenclosure, a first region with a first width, a second region with a second width, a thermal actuator disposed within the first region, a temperature sensor disposed within the first region, a power source disposed within the second region, and a third region with a third width, wherein the third width is smaller than the first width and the second width, and wherein the thermal actuator, the temperature sensor and the power source are disposed within a cavity formed by the combination of the barrier film and the enclosure.

[0011] In another aspect of the disclosure, a wireless, flexible thermal sensor mountable on a body is disclosed. The wireless, flexible thermal sensor may comprise a first region, a support layer disposed within the first region, a second region, a thermal actuator supported by the support layer, a first axis passing through the thermal actuator, a second axis orthogonal to the first axis and passing through the thermal actuator, and a plurality of temperature sensors supported by the support layer and disposed within the first region aligned to the first axis, wherein the support layer in the first region comprises a plurality of discontinuities which are symmetric about both the first axis and the second axis.

[0012] In yet another aspect of the disclosure, a wireless, flexible thermal sensor mountable on a body is disclosed. The wireless, flexible thermal sensor may comprise a support layer, a thermal actuator supported by the support layer, a first temperature sensor supported by the support layer, a second temperature supported by the support layer, and a conductive trace supported by the support layer, wherein the conductive trace is electrically coupled to the thermal actuator, and wherein the conductive trace approximately bisects a virtual line formed between the first temperature sensor and the second temperature sensor.

[0013] In yet another aspect of the disclosure, a wireless, flexible thermal sensor mountable on a body is disclosed. The wireless, flexible thermal sensor may comprise a barrier film, an enclosure, a first region, a thermal actuator disposed within the first region, a temperature sensor disposed within the first region, a second region, a power source disposed within the second region, and an electrically conductive coil disposed within the second region and configured for receiving inductive power, wherein the thermal actuator, the temperature sensor, the power source and the conductive coil are disposed within a cavity formed by the combination of the barrier film and the enclosure.

[0014] In yet another aspect of the disclosure, a system configured for monitoring fluid flow in a body is disclosed. The system may comprise a thermal flow sensor. The thermal flow sensor may comprise a thermal actuator, a temperature sensor, a power source, an electrically conductive coil configured for receiving inductive power, and a charging apparatus comprising an electrically conductive coil configured for transmitting inductive power.

[0015] In yet another aspect of the disclosure, a system configured for monitoring fluid flow in a body is disclosed. The system may comprise a thermal flow sensor. The thermal flow sensor may comprise a thermal actuator, a temperature sensor, a power source, and an adhesive patch comprising a first adhesive surface and a second adhesive surface, wherein the first adhesive surface is approximately geometrically matched to the footprint of the thermal flow sensor and the second adhesive surface is on the opposite face of the adhesive patch as the first adhesive surface

[0016] Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figs. 1A and IB are schematic illustrations of an exemplary wireless thermal flow sensor including electronics and an enclosure, consistent with disclosed embodiments.

[0018] Fig. 2 is a schematic illustration of exemplary layered structures of a wireless thermal flow sensor, consistent with disclosed embodiments.

[0019] Fig. 3 is a schematic illustration of an exemplary wireless thermal flow sensor temperature sensing component arrangement including lines corresponding to exemplary sensing axes, consistent with disclosed embodiments.

[0020] Fig. 4 is a schematic illustration of an exemplary wireless thermal flow sensor including device regions with different patterning, consistent with disclosed embodiments.

[0021] Figs. 5A-5E are schematic illustrations of an exemplary wireless thermal flow sensor including sensing regions with various examples of symmetric pattering, consistent with disclosed embodiments.

[0022] Figs. 6A-6C are schematic illustrations of an exemplary wireless thermal flow sensor including device regions for improving mechanical properties, consistent with disclosed embodiments.

[0023] Fig. 7 is a schematic illustration of an exemplary wireless thermal flow sensor including exemplary actuator and sensor electrical trace routing, consistent with disclosed embodiments.

[0024] Fig. 8 is a schematic illustration of metallic trace dimensions, consistent with disclosed embodiments.

[0025] Fig. 9 is a schematic illustration of exemplary layered structures associated with a raised wireless communication antenna component, consistent with disclosed embodiments.

[0026] Fig. 10 is a schematic illustration of exemplary layered structures associated with a raised wireless communication antenna component including other layered structures of a thermal flow sensor, consistent with disclosed embodiments.

[0027] Fig. 11 is a schematic illustration of exemplary layered structures associated with a raised wireless communication antenna component including other layered structures of a thermal flow sensor, consistent with disclosed embodiments.

[0028] Fig. 12 is a schematic illustration of exemplary layered structures associated with a battery region of a thermal flow sensor, consistent with disclosed embodiments.

[0029] Fig. 13 is a schematic illustration of an exemplary wireless thermal flow sensor including a wireless charging coil and a battery, consistent with disclosed embodiments.

[0030] Figs. 14A and 14B are schematic illustrations of an exemplary wireless thermal flow sensor including a wireless charging coil and a battery, consistent with disclosed embodiments.

[0031] Figs. 15A and 15B are schematic illustrations of an exemplary wireless thermal flow and a wireless charging apparatus including a mechanical alignment inset and accessory structure, consistent with disclosed embodiments.

[0032] Fig. 16 is a schematic illustration of exemplary layered structures of a removable adhesive patch for use with a wireless thermal flow sensor, consistent with disclosed embodiments.

[0033] Fig. 17 is a schematic illustration of exemplary layered structures of a removable adhesive patch for use with a wireless thermal flow sensor, consistent with disclosed embodiments.

[0034] Fig. 18 is a schematic illustration of exemplary layered structures of a removable adhesive patch applied to a wireless thermal flow sensor, consistent with disclosed embodiments.

[0035] Fig. 19 is a schematic illustration of exemplary layered structures of a removable adhesive patch for use with a wireless thermal flow sensor, consistent with disclosed embodiments.

[0036] Figs. 20A, 20B, and 20C are schematic illustrations of a removable adhesive patch including bonding to a wireless thermal flow sensor, consistent with disclosed embodiments.

[0037] Fig. 21 is a schematic illustration of a removable adhesive patch including bonding to a wireless thermal flow sensor, consistent with disclosed embodiments.

[0038] Fig. 22 is a schematic illustration of wireless thermal flow sensor applied to a removeable adhesive patch with a pull tab structure, consistent with disclosed embodiments.

[0039] Figs. 23A and 23B are schematic illustrations of exemplary release liners for a removable adhesive patch for use with a wireless thermal flow sensor, consistent with disclosed embodiments.

[0040] Fig. 24 is a schematic illustration of components associated with a control system of a wireless thermal flow sensor, consistent with disclosed embodiments.

[0041] Fig. 25 is a schematic illustration of components associated with a control system of a wireless thermal flow sensor, consistent with disclosed embodiments.

[0042] Fig. 26 is a schematic illustration of components associated with a wireless thermal flow sensor system, consistent with disclosed embodiments.

[0043] Fig. 27 is a process flow diagram associated with thermal actuator control associated with a wireless thermal flow sensor, consistent with disclosed embodiments.

[0044] Fig. 28 is a process flow diagram associated with thermal actuator control associated with a wireless thermal flow sensor, consistent with disclosed embodiments.

[0045] Fig. 29 is a set of exemplary process flow diagrams associated with thermal actuator control associated with a wireless thermal flow sensor, consistent with disclosed embodiments.

[0046] Fig. 30 is a process flow diagram associated with user guidance associated with a wireless thermal flow sensor, consistent with disclosed embodiments.

[0047] Fig. 31 is a process flow diagram associated with user guidance associated with a wireless thermal flow sensor, consistent with disclosed embodiments.DETAILED DESCRIPTION

[0048] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the disclosure. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the subject matter recited in the appended claims. The following detailed description refers to the accompanying drawings. While several illustrative embodiments are described herein, modifications, adaptations and other implementations are possible. For example, substitutions, additions, or modifications may be made to thecomponents and steps illustrated in the drawings, and the illustrative methods described herein may be modified by substituting, reordering, removing, or adding steps to the disclosed methods. Accordingly, the following detailed description is not limited to the disclosed embodiments and examples. Instead, the proper scope of the invention is defined by the appended claims.

[0049] Relative dimensions of components in drawings may be exaggerated for clarity. Within the following description of drawings, the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described.

[0050] As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a database may include A or B, then, unless specifically stated otherwise or infeasible, the database may include A, or B, or A and B. As a second example, if it is stated that a database may include A, B, or C, then, unless specifically stated otherwise or infeasible, the database may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0051] In general, the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. The following definitions are provided to clarify their specific use in the context of the invention.

[0052] “ Soft” refers to a material that may be comfortably positioned against the skin without discomfort or irritation to the underlying skin by the material itself deforming to conform to the skin without unduly exerting force on the underlying skin with corresponding devicegenerated skin deformation. Softness / hardness may be optionally quantified, such as in terms of durometer, or a material's resistance to deformation. For example, the substrate may be characterized in terms of a Shore 00 hardness scale, such as a Shore 00 that is less than 80. Soft may also be characterized in terms of a modulus, such as a Young's modulus that is less than or equal to 100 kPa.

[0053] “Stretchable” refers to a material's ability to undergo reversible deformation under an applied strain. This may be characterized by a Young's modulus, a ratio of stress to strain. A bulk or effective Young's modulus refers to a composite material formed from materials having different Young's modulus, so that the bulk or effective Young's modulus is influenced by each of the different materials and provides an overall device-level modulus.

[0054] “Flexible” refers to a material's ability to undergo a bending without fracture or permanent deformation, and may be described in terms of a bending modulus.

[0055] Any of the devices may be described herein as being “mechanically matched” to skin, specifically the skin over which the device will rest. This matching of device to skin refers to a conformable interface, for example, useful for establishing conformal contact with the surface of the tissue. Devices and methods may incorporate mechanically functional substrates comprising soft materials, for example exhibiting flexibility and / or stretchability, such as polymeric and / or elastomeric materials. A mechanically matched substrate may have a modulus less than or equal to 100 MPa, less than or equal to 10 MPa, or less than or equal to 1 MPa. A mechanically matched substrate may have a thickness less than or equal to 0.5 mm, and optionally for some embodiments, less than or equal to 1 cm, and optionally for some embodiments, less than or equal to 3 mm. A mechanically matched substrate may have a bending stiffness less than or equal to 1 N / m, optionally less than or equal to 0.1 N / m.

[0056] A mechanically matched device, and more particularly a substrate is characterized by one or more mechanical properties and / or physical properties that are within a specified factor of the same parameter for an epidermal layer of the skin, such as a factor of 10 or a factor of 2. For example, a substrate may have a Young's Modulus or thickness that is within a factor of 20, or optionally for some applications within a factor of 10, or optionally for some applications within a factor of 2, of a tissue, such as an epidermal layer of the skin, at the interface with a device of the present invention. A mechanically matched substrate may have a mass or modulus that is equal to or lower than that of skin.

[0057] “Encapsulate” refers to the orientation of one structure such that it is at least partially, and in some cases completely, surrounded by one or more other structures, such as a substrate, adhesive layer, or encapsulating layer. “Partially encapsulated” refers to the orientation of one structure such that it is partially surrounded by one or more other structures, for example, wherein 30%, or optionally 50%, or optionally 90% of the external surface of the structure is surrounded by one or more structures. “Completely encapsulated” refers to the orientation of one structure such that it is completely surrounded by one or more other structures.

[0058] “Polymer” refers to a macromolecule composed of repeating structural units connected by covalent chemical bonds or the polymerization product of one or more monomers, often characterized by a high molecular weight. The term polymer includes homopolymers, or polymers consisting essentially of a single repeating monomer subunit. The term polymer also includes copolymers, or polymers consisting essentially of two or more monomer subunits, such as random, block, alternating, segmented, grafted, tapered and other copolymers. Useful polymers include organic polymers or inorganic polymers that maybe in amorphous, semi-amorphous, crystalline or partially crystalline states. Crosslinked polymers having linked monomer chains are particularly useful for some applications. Polymers useable in the methods, devices and components disclosed include, but are not limited to, plastics, elastomers, thermoplastic elastomers, elasto-plastics, thermoplastics and acrylates. Exemplary polymers include, but are not limited to, acetal polymers, biodegradable polymers, cellulosic polymers, fluoropolymers, nylons, polyacrylonitrile polymers, polyamide-imide polymers, polyimides, polyacrylates, polybenzimidazole, polybutylene, polycarbonate, polyesters, polyetherimide, polyethylene, polyethylene copolymers and modified polyethylenes, polyketones, poly(methyl methacrylate), polymethylpentene, polyphenylene oxides and polyphenylene sulfides, polyphthalamide, polypropylene, polyurethanes, styrenic resins, sulfone-based resins, vinyl-based resins, rubber (including natural rubber, styrene-butadiene, polybutadiene, neoprene, ethylene-propylene, butyl, nitrile, silicones), acrylic, nylon, polycarbonate, polyester, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyolefin or any combinations of these.

[0059] “Elastomer” refers to a polymeric material which can be stretched or deformed and returned to its original shape without substantial permanent deformation. Elastomers commonly undergo substantially elastic deformations. Useful elastomers include those comprising polymers, copolymers, composite materials or mixtures of polymers and copolymers. Elastomeric layer refers to a layer comprising at least one elastomer. Elastomeric layers may also include dopants and other non-elastomeric materials. Useful elastomers include, but are not limited to, thermoplastic elastomers, styrenic materials, olefinic materials, polyolefin, polyurethane thermoplastic elastomers, polyamides, synthetic rubbers, PDMS, polybutadiene, polyisobutylene, poly(styrene-butadiene-styrene), polyurethanes, polychloroprene and silicones. Exemplary elastomers include, but are not limited to silicon containing polymers such as poly siloxanes including poly(dimethyl siloxane) (i.e. PDMS and h-PDMS), poly(methylsiloxane), partially alkylated poly(methyl siloxane), poly(alkyl methyl siloxane) and poly(phenyl methyl siloxane), silicon modified elastomers, thermoplastic elastomers, styrenic materials, olefinic materials, polyolefin, polyurethane thermoplastic elastomers, polyamides, synthetic rubbers, polyisobutylene, poly(styrene-butadiene-styrene), polyurethanes, polychloroprene and silicones. In an embodiment, a polymer is an elastomer.

[0060] “ Conformable” refers to a device, material or substrate which has a bending stiffness that is sufficiently low to allow the device, material, or substrate to adopt any desired contour profile, for example a contour profile allowing for conformal contact with a surface having a pattern of relief features. In certain embodiments, a desired contour profile is that of skin.

[0061] “ Conformal contact” refers to contact established between a device and a receiving surface, specifically skin. In one aspect, conformal contact involves a macroscopic adaptation of one or more surfaces (e.g., contact surfaces) of a device to the overall shape of a surface. In another aspect, conformal contact involves a microscopic adaptation of one or more surfaces (e.g., contact surfaces) of a device to a surface resulting in an intimate contact substantially free of voids. In an embodiment, conformal contact involves adaptation of a contact surface(s) of the device to a receiving surface(s) such that intimate contact is achieved, for example, wherein less than 20% of the surface area of a contact surface of the device does not physically contact the receiving surface, or optionally less than 10% of a contact surface of the device does not physically contact the receiving surface, or optionally less than 5% of a contact surface of the device does not physically contact the receiving surface. Devices of certain aspects are capable of establishing conformal contact with internal and external tissue. Devices of certain aspects are capable of establishing conformal contact with tissue surfaces characterized by a range of surface morphologies including planar, curved, contoured, macro-featured and micro-featured surfaces and any combination of these. Devices of certain aspects are capable of establishing conformal contact with tissue surfaces corresponding to tissue undergoing movement.

[0062] “Young’s modulus” is a mechanical property of a material, device or layer which refers to the ratio of stress to strain for a given substance. “Low modulus” refers to materials having a Young's modulus less than or equal to 10 MPa, less than or equal to 5 MPa or less than or equal to 1 MPa.

[0063] “Bending stiffness” is a mechanical property of a material, device or layer describing the resistance of the material, device, or layer to an applied bending moment. Generally, bending stiffness is defined as the product of the modulus and area moment of inertia of the material, device or layer. A material having an inhomogeneous bending stiffness may optionally be described in terms of a “bulk” or “average” bending stiffness for the entire layer of material.

[0064] Reference is now made to Fig. 1A, which illustrates an exemplary structure of a wireless thermal sensor device, such as a wireless thermal flow sensor 100. In some embodiments, the thermal flow sensor 100 may comprise electronic circuitries, one or more supporting layers 101, and an enclosure structure 102. Fig. IB shows an isometric view of wireless thermal flow sensor 100.

[0065] Referring now to Fig. 2, a thermal flow sensor 200 may comprise multiple layers arranged in a manner conducive to thermal sensing, and especially thermal flow sensing forsensing flow through a subdermal conduit, such as cerebrospinal fluid in a shunt or blood in a blood vessel beneath the skin. In some embodiments, a thermal flow sensor may comprise surface mount electrical components, one or more patterned conductive layers, a supporting layer such as Kapton, an insulating media such as, but not limited to, foam or air, an enclosure structure, and a barrier layer such as a barrier film, for example. In one exemplary construction, as part of the multilayer construction of the device, a barrier film may be applied to outermost Kapton layer of the device to form the outermost layer of the device substrate. The barrier film may be comprised of a bonding adhesive on one side and a plastic film such as polyester on the other side. The bonding adhesive may preferably have an adhesion strength to the device such as 16N / 25mm to provide an effectively permanent bond to the device. The plastic film backing may preferably have a thickness less than 0.1mm and preferably less than 0.05mm, such as 0.03mm. Such a construction may enable a high degree of mechanical flexibility and minimal thermal resistance through the barrier film. The barrier film layer may be used to protect the device from ingress by sealing the internal device components from the outside environment. The plastic polyester side of the barrier film may also feature a suitable surface finish or release coating be to promote the selective application and removal of an adhesive patch to and from the device. Various layers in a thermal flow sensor may be patterned to create a variety of shapes and structures conducive to thermal measurements and product use. In other embodiments layers may be repeated, omitted, or replaced with other layers. For example, in yet another embodiment, one or more regions of a thermal flow sensor may comprise rigid composite supporting layers, such as FR-4 commonly used in printed circuit board manufacturing and may include a laminate of multiple patterned conductive layers, such as 4 or 6 distinct patterned conductive layers, with surface mount components disposed on the top and bottom layers. A thermal flow sensor may further comprise additional components useful to wireless thermal flow sensing, such as a power components, various sensing and actuating components, processing components, control components, wireless communication components, illuminating components, haptic components, and the like.

[0066] In some applications of thermal flow sensing it may be useful to utilize a plurality of temperature sensing components in a thermal flow sensor. Reference is made to Fig. 3, which shows a plurality of temperature sensing components 301 spatially arranged along a first axis 302. A further plurality of temperature sensing components may be spatially arranged along a second axis 303 perpendicular to the first axis 302. The plurality of temperature sensing components along each axis may be spatially arranged such that they are symmetric about acentral thermal actuator 304. For example, the temperature sensing components may be arranged as equidistant pairs on opposing sides of a thermal actuator. In some embodiments, the first axis may align spatially to other features on a thermal flow sensor which aid alignment of the first axis 302 to a subdermal fluid conduit, such as a CSF shunt or a blood vessel.

[0067] The skin mounted flow sensor may further comprise one or more additional temperature sensing components 305 which may be thermally decoupled from the central thermal actuator 304. Additional temperature sensing components 305 are herein referred to as ambient temperature sensors. The presence of one or more ambient temperature sensors may be useful in recording temperature fluctuations of the skin environment independent of those induced by the thermal actuator. In some embodiments, a temperature sensor may substantially record temperatures independent of a circular thermal actuator when a critical ratio between the distance of the temperature sensor from the center of the heater element to the power per unit area of the heater element exists. In some embodiments, this distance may be between 5 mm and 15 mm and the heater power per unit area may be between 0.1-10.0 mW / mm2, and preferably between 1.0-5.0 mW / mm2, and more preferably between 1.5-2.5 mW / mm2, creating a critical ratio preferably in the range of 3.0 - 4.0 mm3 / mW. Such a ratio of distance of a temperature sensor from a thermal actuator relative to thermal actuator power can result in a design such that the temperature sensor increases by less than 1 degree Celsius, and preferably less than 0.5 degrees Celsius, as a result of heat produced by the thermal actuator when the thermal flow sensor is applied to skin. Such heating power densities may be beneficial because they enable a suitably large thermal signal strength for measurement without cause damage to human skin. Such critical ratios to the ambient sensor may be beneficial by enabling a sensor design with a suitably small geometrical footprint while also having an ambient sensor experience a temperature rise due to the thermal actuator of less than 1.0° C and preferably less than 0.5° C within 10 minutes of beginning to supply power to the heater actuator when the device is applied to human skin. It will be appreciated that for alternative heater element geometries, a similar critical ratio exists relating the distance of the ambient sensor from the heater element to the power supplied to the heater element.

[0068] Reference is now made to Fig. 4, which illustrates an exemplary wireless thermal flow sensor 400 including device regions with different patterning, consistent with disclosed embodiments. In some embodiments sensing and / or actuating elements, such as one or more temperature sensing components and thermal actuators, may be supported by a supporting layer 401 to provide mechanical support and electrical isolation. Supporting layer 401 maycomprise, but is not limited to, a plastic layer, such as polyimide in the commercial form of Kapton®. In some embodiments, supporting layer 401 may be a solid, continuous, unpatterned film in one region 402, while in a different device region 403, the layer may be patterned. The patterns may comprise regions 404 of no support layer (e.g., patterned holes, cutouts, serpentines, or other patterns, such as greater than 25 pm thick in one region and zero thickness in other regions), or regions of varying thickness of supporting layer (e.g., supporting layer having reduced thickness in one location relative to another, such as 50 pm thick in one region and 12.5 pm thick in another). Such spatial structuring of the Kapton® may provide increased device flexibility in the regions with cutouts or reduced thicknesses and may also improve the ability of the device regions to conform to three dimensional surfaces. For example, in some embodiments, it may be advantageous for a sensing region 403 with a patterned support layer to have at least 20% of the region containing no support material (such as via cutouts in Kapton®) and preferably at least 50% of the region containing no support material. Additionally, it may be advantageous for support material to be removed from regions local to individual sensors to improve mechanical conformation to surfaces, such as by having cutouts in support material on at least two sides of a temperature sensor 405.[0069J Reference is now made to Figs. 5A-5E, which are schematic illustrations of an exemplary wireless thermal flow sensor including sensing regions with various examples of symmetric pattering, consistent with disclosed embodiments. In some embodiments, it may be advantageous for patterned cutouts 501a-d in support layer 502a-d to impart symmetry about a thermal actuator 503a-d and / or about one or more sensing axes 504a-d. Some embodiments may feature a further plurality of patterned cutouts 50 le in support layer 502e to impart symmetry about a thermal actuator 503e and / or one or more sensing axes 504e enabling a multitude of sensor configurations. Such a symmetry may be beneficial by enabling symmetric thermal diffusion of heat generated by a thermal actuator through the thermal flow sensor such that each temperature sensor that is disposed at a given distance away from a thermal actuator experiences equal temperature increases due to thermal conduction of heater from the thermal actuator through the thermal flow sensor. Such a design may improve measurement accuracy by reducing measurement offsets due to asymmetry in the thermal design.[0070J Referring to Fig. 6A-6C, which illustrate exemplary wireless thermal flow sensors including device regions for improving mechanical properties, consistent with disclosed embodiments. Thermal flow sensor 600 may comprise a plurality of spatial regions whereinthe regions have differing mechanical properties. A first region 601 may be optimized for conformal contact to the skin where the second region 602 may be optimized for mechanical strength of rigid surface mounted components. The regions with different intended mechanical properties may be mechanically decoupled from one another such that the mechanical properties of any one of the regions may not interfere with intended mechanical properties of a different region. For example, the first region 601 and second region 602 may be separated by a bridge 603. Bridge 603 may have a narrower width than at least one of regions 601 and 602. For example, in some embodiments a length of at least 5 millimeters, such as 16.0 millimeters, and width of less than 20 millimeters, such as 4.05 millimeters, may enable mechanically decoupling the regions from one another. The presence of the bridge region 603 may enable improved conformal mechanical contact of the first region 601 to an uneven or moving surface, such as the surface of skin. In some embodiments, first region 601 may comprise one or more sensing and / or actuating element which may provide improved signals with improved contact to the surface. The relatively narrow width of the bridge region 603 may serve to decrease the second polar moment of area of the bridge region 603, thereby minimizing the resistance to torsional deformation, and rotationally decoupling the regions from one another, and also providing an axis of reduced bending resistance enabling improved flexibility between the regions. The length of the bridge region 603 may reduce the shear strain enabling further rotational decoupling of the regions from one another. In some embodiments, an enclosure 604 may enclose the thermal flow sensor. Enclosure 604 may be contoured to enclose the first region 601, the second region 602 and the third region 603. In some embodiments, third region 605 of the enclosure 604 may be made from a flexible material such as a thermoplastic elastomer with a Shore A hardness of less than 100 and preferably less than 80, and more preferably with wall thickness of less than 2 millimeter and even more preferably of 1 millimeter or less. In some embodiments, the height of the enclosure in the third region 605 may be reduced to provide improved flexibility of the third region 605. In some embodiments, the same material and wall thickness preferences may be useful in the enclosure surrounding the first region 601 to improve flexibility of the sensing region.

[0071] In some embodiments, the entire enclosure 604 may comprise the same material. In some embodiments, the enclosure 604 may be made from different materials or different wall thicknesses in different regions, such as a construction with higher mechanical strength and less flexibility in the enclosure surrounding the second region 602, which may aid in robustness of mechanical components in the second region 602. In some embodiments, theenclosure 604 may further comprise visual alignment features 606, shown in Fig. 6b, which may be configured to align with a sensing axis of a sensing region. Fig. 6c illustrates an isometric view of an exemplary wireless thermal flow sensor showing an exemplary third region 605.

[0072] Reference is now made to Fig. 7, which is a schematic illustration of an exemplary wireless thermal flow sensor 700 including exemplary actuator and sensor electrical trace routing, consistent with disclosed embodiments. In some embodiments, electrically conductive traces 701 may be employed to supply electrical power and / or voltage signals to sensing and / or actuation components disposed within a region of a thermal actuator 702. In some embodiments, additional electrically conductive traces 703 may further be connected to other components, such as temperature sensing components, which are disposed outside of a region of the thermal actuator 702. Common highly electrically conductive traces, such as metallic traces, are typically also highly thermally conductive. As a result, conductive traces 701 electrically routed through a region of the thermal actuator 702 may be prone to conducting thermal energy, or heat generated by the thermal actuator 702 through the conductive traces 701. If the conductive traces 701 are further routed such that they are disposed locally to temperature sensing components 704 outside of the region of the thermal actuator 702, they may transfer thermal energy through the conductive traces 701 from the thermal actuator 702 to the temperature sensing component 704.

[0073] In some embodiments, such as a thermal flow sensor configured for monitoring flow of a subdermal fluid, it may be desirable to minimize thermal conduction of energy from the thermal actuator 702 through the conductive traces 701 to other temperature sensing components 704, as this heat conduction may serve to reduce the sensitivity of heat conduction through the skin due to subdermal fluid flow. Further, if the conductive traces 701 are routed such that they conduct heat unevenly between different temperature sensing components 704, an uneven heating of different temperature sensing components 704 may occur. Therefore, it may be desirable to minimize heat transferred through conductive traces 701 from the thermal actuator 702 to other temperature sensing components 704. In some embodiments, such heat transfer imbalance may be minimized by routing conductive traces 701 to and from the thermal actuator 702 such that the nearest temperature sensing components 704 may be approximately equidistant from conductive trace 701. For example, such trace routing may be employed such that the nearest temperature sensing components 704 to a given conductive trace 701 may be symmetric about the line of the conductive trace 701.

[0074] Reference is now made to Fig. 8, which is a schematic illustration of an exemplary conductive trace 800, consistent with disclosed embodiments. In some embodiments, heat conduction through conductive trace 800 (analogous to conductive trace 701) may be further minimized by reducing the thermal conduction of traces. For example, in an embodiment which employs copper traces the surface mounted components in the sensing region of the device may be electrically connected via electrical traces featuring a critical ratio between the thermal resistance of the electrical traces and the power per unit area of the heater element. The thermal resistance of a trace may be defined as the fraction of the trace length L3 relative to the product of the cross-sectional area L1*L2 of the trace with the thermal conductivity K of the trace material, combined to yield a trace thermal resistance of K*L3 / (L1*L2). This may improve device sensitivity to flow induced thermal anisotropy. Such a construction may reduce thermal conduction from the central heater element to the adjacent temperature sensors, thereby increasing the specificity of changes in recorded temperature of the temperature sensors. Such a construction may also decrease the net in-plane thermal conduction leading to a faster and larger temperature rise of the heater. In another example, traces may be formed of copper by standard flexible printed circuit manufacturing techniques to be less than 0.25 millimeters in width, and preferably less than 0.125 millimeters in width, and more preferably less than 0.075 millimeters in width.

[0075] In some embodiments, a thermal flow sensor may comprise electronic surface mount components, as shown in Fig. 2, wherein surface mount components may include one or more wireless communication components such as an antenna component, for example. In embodiments wherein a thermal flow sensor is configured for application to body tissue such as skin, close proximity of antenna components to skin can in some instances may adversely affect the wireless strength of the system, such as when a 2.4 Gigahertz (GHz) antenna used as part of a Bluetooth Low Energy communication system is applied in close proximity to skin.

[0076] Reference is now made to Fig. 9, which is a schematic illustration of an exemplary layered structure 900 associated with a raised wireless communication antenna component, consistent with disclosed embodiments. In some embodiments, a thermal flow sensor (e.g., wireless thermal flow sensor 100 of Fig. 1) may be constructed such that one or more antenna components are elevated further away from a skin-contacting surface, such a barrier film surface, relative to other electronic components. In an example, a supporting layer may be a flexible support layer such as Kapton such that a space may be disposed beneath an antenna component, with the supporting layer bending over the support layer, such that the antennacomponent is spaced at a great distance from the skin-contacting surface, which is a barrier film surface. In some embodiments, the spacer may be at least 0.5 millimeters thick, and preferably greater than 1 millimeter thick and more preferably 3 millimeters thick. In some embodiments, a space may comprise one or more materials such as foam, adhesive, plastic, polymer, or composite.

[0077] In some embodiments, the raised antenna structure may be disposed within a thermal flow sensor device enclosure, such as shown in Figs. 10 and 11. Such a construction may be configured to improve wireless communication operations by raising the radiating plane of the antenna relative to the skin plane which may reduce absorptive losses from the body across a range of radio frequencies.

[0078] In some embodiments, a thermal flow sensor 1200 may include one or more elements of a power system. In one such embodiment, a thermal flow sensor may include a rechargeable battery, as depicted in Fig. 12. In some such embodiments, a thermal flow sensor may feature a layered construction comprising one or more layers of polymer films, adhesives, and electronics, at least one temperature sensor, a battery, and a device enclosure. The temperature sensor may be configured to be disposed at the interface between the layers of electronics and the battery to monitor the temperature at this interface. Such a construction may be useful as a safety element for monitoring internal device temperatures and alerting a user. For example, in such an embodiment the measured temperature from the temperature sensors may be incorporated into a battery protection circuit to prevent overheating of the battery or adjacent components. Such a configuration may be useful as part of a control system for one or more processes related to operation of the device, such as for providing a means to shut down a process if a battery exceeds a predetermined temperature threshold.

[0079] Reference is now made to Fig. 13, which illustrates an exemplary wireless thermal flow sensor 1300 including a wireless charging coil and a battery, consistent with disclosed embodiments. In some embodiments, thermal flow sensor 1300 may comprise an antenna 1301 to be used for wireless communication and / or wireless power transfer implemented in accordance with a standard such as near-field communication (NFC) or Qi. In some embodiments the antenna 1301 may be disposed near the bottom plane of the device, such as the plane represented by the barrier film in Fig. 1. In such a configuration, the device may be set on a flat surface during charging. In such an embodiment, as shown in Fig. 13, the geometric center of the antenna 1301 may be laterally offset from any metallic objects, such as the casing of a battery 1302, which may improve power transmission and charging efficiency.

[0080] Fig. 14A shows a top plan view of an exemplary wireless thermal flow sensor 1400 including a wireless charging coil 1401 and a battery, consistent with disclosed embodiments. In some embodiments, thermal flow sensor 1400 may have a wireless charging coil 1401 disposed in a location that enables convenient wireless charging by a user, such as, but not limited to, on top of a battery cavity. Some embodiments may feature an additional ferromagnetic material layer spanning beyond the area of the antenna which may further improve power transmission and charging efficiency. Fig. 14B shows a side view of thermal flow sensor 1400.

[0081] Fig. 15A illustrates an isometric view of an exemplary thermal sensor system 1505, consistent with embodiments of the present disclosure. Thermal sensor system 1505 may include a docking assembly for a thermal flow sensor 1500. In some embodiments, a docking assembly may include a charging station 1550 comprising a mechanical inset 1551 approximately matched to the footprint of a thermal flow sensor 1500 and configured to receive thermal flow sensor 1500 for charging, as an example. Charging station 1550 may further comprise a wireless charging coil 1560 (shown in Fig. 15B), such as a Qi charging transmitter coil, positioned such that the mechanical inset 1551 supports aligning wireless charging coil 1510 disposed within thermal flow sensor 1500 to the charging transmitter coil 1560. Such a structure may enable improved usability of thermal flow sensor 1500 by an end user by ensuring proper alignment of a thermal flow sensor 1500 for efficient wireless battery charging.

[0082] In some embodiments, charging station 1550 may further include a hold slot 1552 for holding extra adhesive patches for the thermal flow sensor 1500. Such an additional structure may enhance usability of thermal flow sensor system 1500. In some embodiments, slot 1552 may have an approximate length and width of 9.8 cm x 0.4 cm. It is to be appreciated that other dimensions of slot 1552 are possible as well.

[0083] Fig. 16A shows a schematic illustration of an exemplary adhesive laminate patch 1600 which may be applied to and removed from a thermal flow sensor by a user, consistent with embodiments in the present disclosure. In some embodiments, adhesive patch 1600 may comprise a first adhesive layer for adhesion to a device, such as a thermal flow sensor, and a second adhesive layer for adhesion to skin of the user. Each of the first and the second adhesive layers may be supported by an adhesive backing layer such as a polyurethane layer. In some embodiments a first adhesive layer may comprise a rubber or an acrylic material, and second adhesive layer may comprise a silicone or an acrylic material.

[0084] In a preferred embodiment the adhesion strength of the first adhesive layer to a barrier layer of a thermal flow sensor may be strong enough to support continuous adhesion to the thermal flow sensor during extended wear and motion by a user, but weak enough to enable intentional removal of the adhesive from the thermal flow sensor by a user with manual peeling. In the same preferred embodiment, the adhesion strength of the second adhesive layer to skin may be strong enough for the device to remain adhered to skin during extended wear by a user, but weak enough to support intentional removal from skin by the user. For example, an adhesion strength to stainless steel during 180-degree peel of approximately 5.9 N / 25mm for the first adhesive layer and of approximately 1.1 N / 25mm for the second adhesive layer represent exemplary preferable adhesion strengths.

[0085] In some embodiments, adhesive patch 1600 may further comprise a skirt layer featuring a single sided adhesive with a spunlace nonwoven backing adhered to the first adhesive layer. The adhesive patch 1600 may further comprise release liner layers disposed on the exposed first and second adhesive layers, with the release liners preferably having adhesion strength measured during 180-degree peel of less than 1.0 N / 25mm, and preferably less than 0.5 N / 25mm. Removal of the release liner disposed on the first adhesive layer (device adhesive) may enable exposure of the first adhesive layer for bonding to a thermal flow sensor (e.g., thermal flow sensor 100 of Fig. 1). Fig. 16B shows an exemplary embodiment comprising a release liner laminated to the first adhesive layer, wherein the release liner is surrounded by the skirt and nonwoven backing materials. In other embodiments, release liners may extend all the way to the perimeter of an adhesive patch. When such a first adhesive liner is removed, the first adhesive layer becomes exposed enabling adhesive to a thermal flow sensor, as shown in Fig. 16C.

[0086] Fig. 17 shows an exemplary embodiment of a layer structure 1700 created when a thermal flow sensor 1710 is applied to the first device adhesive layer of an adhesive patch (e.g., adhesive patch 1600) as herein described.

[0087] Reference is now made to Fig. 18, which shows schematic illustrations 1800a, 1800b, and 1800c of exemplary layered structures of a removable adhesive patch 1805 applied to a wireless thermal flow sensor, consistent with disclosed embodiments. Layers of removable adhesive patch 1805 may have different dimensions, such some layers may extend beyond the footprint of other layers in order to further form a skirt layer for improving shear strength adhesion to skin. In some embodiments, adhesive patch 1805 may also be configured such that the top skirt layer extends beyond the edge of the skin adhesive footprint. In doing so, the delamination interface may be extended away from the edge of the device enclosure and asecond delamination interface may be created. With such embodiments, two different adhesives may simultaneously be in contact with the skin increasing the effective adhesive strength of the patch during extended wear.

[0088] Fig. 19 shows an exemplary embodiment of a layer structure 1900 created when a thermal flow sensor 1910 is applied to the first device adhesive layer of an adhesive patch 1905, as herein described.

[0089] Reference is now made to Fig. 20A, in which an adhesive patch 2000 is applied to the thermal flow sensor 2050. In some embodiments, the adhesive patch 2000 may have an exposed first adhesive layer 2010 corresponding substantially to the footprint of thermal flow sensor 2050. Such a construction will adhere the entirety of the bottom face of the device to the adhesive patch and by proxy with bond the entirety of the device footprint to skin when the combination is applied such that the second adhesive layer (skin adhesive) is exposed by removal of the release liner and applied to skin. This may increase the robustness of the adhesion between the device and the skin thereby decreasing the likelihood of a delamination event occurring during wear.

[0090] Fig. 20B illustrates the thermal flow sensor 2050 being attached to the exposed adhesive layer of adhesive patch 2000. In some embodiments, a portion of adhesive patch 2000 may have a depth such that thermal flow sensor 2050 may be placed inside the portion of adhesive patch. In some embodiments, the depth of the portion of adhesive path 2000 may be substantially same as the height of the base layer of thermal flow sensor 2050. Base layer of thermal flow sensor 2050 may include a barrier film, or a combination of barrier film and bonding adhesive (as shown in Fig. 2). Fig. 20C illustrates the assembled form 2050C of combined thermal flow sensor 2050 and adhesive patch 2000.

[0091] In some embodiments, as illustrated in Fig. 21, the adhesive patch 2100 may have an exposed first adhesive layer 2110 corresponding only to a specific region of the thermal flow sensor 2150, such as the region comprising the sensing elements. In such a construction, the sensor region is adhered to adhesive patch 2100 and by proxy to the skin, once the skin-side second adhesive layer is exposed and applied to skin, leaving other region 2120 of the thermal flow sensor 2150 not adhered to the adhesive patch and thereby not adhered to the skin. This construction may improve the conformability of the sensor region to skin.

[0092] Reference is now made to Fig. 22, which is a schematic illustration of wireless thermal flow sensor 2200 applied to a removeable adhesive patch with a pull tab structure, consistent with disclosed embodiments. In some embodiments, the adhesive patch 2200 may also include an extended portion 2201 on one side of the patch without any exposed adhesiveto be used to grip the patch during application and removal of the patch from the skin. The extended portion herein referred to as a pull-tab 2201, may decrease the required applied force to remove the adhesive patch from the skin by the user by facilitating the patch into entering a 180-degree peel delamination mode.

[0093] Referring now to Figs. 23A and 23B, a removeable adhesive patch 2300 may include a set of release liners, including a first adhesive layer release liner 2301 and second adhesive layer release liner 2302 (including elements 2302a and 2302b), to prevent adhesive degradation prior to application to the skin. In some embodiments, a release liner may be composed of multiple individual release liner pieces such as represented by elements 2302a and 2302b. In an exemplary embodiment, adhesive patch 2300 may have a release liner 2301 overlaying the device adhesive side of the patch featuring the same footprint as the device. The patch may also have a release liner pair of elements 2302a and 2302b on the skin adhesive side of the patch. The skin adhesive side liner may be comprised of multiple independent release liners which are to be removed in a particular order to assist with the application of the adhesive patch onto the skin. Fig. 23A illustrates the removable adhesive patch 2300 comprising a first adhesive layer release liner 2301 overlaying the device adhesive side and a second adhesive layer release liner 2302 on the skin adhesive side of adhesive patch 2300. Alternatively, as shown in Fig. 23B, the removable adhesive patch 2300 may comprise a first adhesive layer release liner 2301 on the skin adhesive side of adhesive patch 2300 and a second adhesive layer release liner 2302 on the overlaying the device adhesive side of adhesive patch 2300.

[0094] Referring now to Fig. 24, which illustrates a thermal flow sensor sensing system 2400 including one or more actuators, one or more sensors, and a control system comprising a memory, a processor, and a microcontroller. A microcontroller 2410 may control the actuation and sensing of the one or more actuators 2420 and one or more sensors 2430, based on sets of instructions, which may be stored in one or more memory structures, executed by the processor. Sensor data may be stored in memory and further utilized by the processor utilizing additional computing instructions from memory to further control the one or more sensors and / or one or more sensors.

[0095] Reference is now made to Fig. 25, which illustrates a sensing system 2500 of a thermal flow sensor, consistent with disclosed embodiments. In some embodiments, sensing system 2500 may comprise a memory 2510 storing thermal sensor data from one or more thermal sensors and optionally also storing sensor data from an inertial measurement unit (IMU) sensor. Sensor data may be processed by a processor 2520 to determine subsequentcontrol, by a microcontroller 2530, of a thermal actuator 2540, one or more thermal sensors 2550, and an inertial measurement unit 2560. In some embodiments, a memory and / or a processor may, in whole or in part, be embedded within the physical structure of a thermal flow sensor, or alternatively embedded within a physical separate device in wireless communication with a thermal flow sensor.

[0096] Reference is now made to Fig. 26, which illustrates a memory and processor module may be embedded within a system-on-chip integrated circuit physically disposed as part of the electronics within a thermal flow sensor 2601. In another example, a memory or processor module may be embedded within a computing device 2602 in wireless communication with a thermal flow sensor, such as a smartphone or tablet computer, or a remote server 2603 as part of a cloud computing environment. In yet other embodiments, portions of the memory storage may be distributed between any number of memory storage devices which may be a combination of memory storage physically located within a flow sensor 2601, located within a wireless computing device 2602, and / or located within a remote server 2603. For example, a portion of memory storage may be physically contained within a processor within the thermal flow sensor as volatile memory, and another portion of memory may be physically located within a wireless computing device 2602 or within a remoter server 2603. Similarly, portions of the processor tasks may be distributed between any number of processor which may be physically located within a flow sensor 2601, located within a wireless computing device 2602, or located within a remote server 2603.

[0097] In some embodiments, the actuation of a thermal actuator may be controlled by a processor based in part on data from one or more sensors. In one such example data from an IMU may be stored in memory. A memory, which may the same memory where data is stored or a different memory, may also comprise computing instructions for reading sensor data stored in memory, determining a state based at least in part on the sensor data stored in memory, and actuating a thermal actuator based at least in part on the determined state.

[0098] Fig. 27 shows a process flow diagram 2700 associated with thermal actuator control which is associated with a wireless thermal flow sensor, consistent with disclosed embodiments. In some embodiments, a thermal actuator may only be transitioned from an ‘off to an ‘on’ state if parameters related to the IMU data are below a threshold, indicating a period of reduced motion. Such a control scheme may be beneficial by enabling a system wherein active thermal flow measurements are taken during low motion periods, which may have lower levels of noise relative to high motion states. This system also prioritizes power consumption of the system to periods most likely to yield the lowest noise data, therebyimproving the effective power efficiency of the sensor relative to the value of data collected. In other embodiments, one or more thresholds may exist for one or more datasets stored in memory, such as thresholds based on data from one or more thermal sensors, thresholds based on time or counts, and other data stored in memory, with various examples shown in Figs. 28 and Fig. 29.

[0099] In some embodiments the average power output of a thermal actuator may be controlled by pulse width modulation (PWM) of a thermal actuator. PWM provides a means of effectively using software to control power output of the heater without any changes to hardware. Proper configuration of PWM switching speed relative to the thermal mass of the thermal actuator and surrounding system can enable a system wherein the PWM control of heater power does not introduce any significant noise into the measurement. For example, a heater may be configured for 50% power output by cycling the heater on and off at equal intervals with a 1 kHz frequency, such that each heater ‘on’ and heater ‘off period is 500 microseconds. In some thermal flow sensor systems, the thermal mass of the thermal actuator is large enough such that the average temperature of the thermal actuator does not shift significantly, such as by less than 0.1 degrees Celsius, during the individual ‘on’ and ‘off cycles.

[0100] In some embodiments, such a system may be useful for controlling the power output or temperature of one or more thermal actuators via software. For example, such a system may enable controlling output to a thermal actuator to maintain a constant temperature of one or more temperature sensors, or for maintaining temperature above or below a threshold, such as below a threshold of 60 degrees Celsius for up to 60 seconds, or below a threshold of 48 degrees Celsius for up to 10 minutes, or below a threshold of 43 degrees Celsius, in accordance with various medical device thermal standards described in IEC 60601-1.

[0101] Reference is now made to Fig. 30, which shows a process flow diagram 3000 associated with user guidance associated with a wireless thermal flow sensor, consistent with disclosed embodiments. In some embodiments, thermal flow sensor system may include a set of computing instructions stored in memory for determining a quality of contact of the sensor with skin. In some embodiments, the system may include a device comprising a graphical user interface, such as a smartphone or tablet computer, for a user wherein the user is instructed to modify the position of the flow sensor when the quality of contact of the sensor with skin is determined to be outside of a predetermined acceptable range. Such a systemmay enable a user to take higher quality measurements, which may provide improved accuracy.[00102 J Reference is now made to Fig. 31, which shows a process flow diagram 3100 associated with user guidance associated with a wireless thermal flow sensor, consistent with disclosed embodiments. In some embodiments, the thermal flow sensor system may include a set of computing instructions stored in memory for transitioning the sensor between different power states. In some embodiments, the computing instructions may comprise the steps of reading one or more sets of sensor data stored in memory and altering a power state based on one or more thresholds related to the sensor data. In one example, a set of sensor data may include temperature sensor data, and a set of computing instructions may transition the sensor to a lower power state if the temperature sensor data indicates that the sensor is not applied to skin, such as by determining that the temperatures are below a threshold, preferably below 32 degrees Celsius. In another embodiment, a set of sensor data may include IMU sensor data and a set of computing instructions may transition the sensor to a lower power state if the IMU sensor data is below a threshold. In yet another embodiment, the computing instructions may be configured such that sensor is transitioned between multiple power states based on sets of sensor data from multiple sensor data. For example, a sensor may be transitioned to a low power mode if both the temperature sensor data and the IMU sensor data are below a threshold, which may reduce the possibility of transitioning to low power states when applied to skin during periods of relatively little motion, such as during sleep.[00.1.03] In some applications it may be useful for a thermal flow sensor to be designed such that is has a maximum effective temperature of a thermal actuator even in the event of catastrophic software failure. In one exemplary embodiment, a combination of voltage applied to a thermal actuator, electrical resistance of a thermal actuator, and effective thermal distribution area of a thermal actuator can be selected such that the highest temperature expected when the thermal flow sensor is in contact with skin is below a specific temperature. For example, a thermal flow sensor with an applied voltage of 2.5 V, with a total thermal actuator electrical resistance of 235.2 Ohms and circular thermal actuator area of 12.5 square millimeters will generally remain below 43 degrees Celsius when applied to human skin even under full power. Similarly, a thermal flow sensor with an applied voltage of 2.5 V, with a total thermal actuator electrical resistance of 141.6 Ohms (Q) and circular thermal actuator area of 12.5 square millimeters (mm2) will generally remain below 48 degrees Celsius (°C) when applied to human skin even under full power. Such a construction may be useful for thermal flow sensor designs that require robust maximum temperatures of a thermal actuatorwithout any dependence on software. Additional useful thermal safety systems can include electrical designs which prevent power application to a thermal actuator when a temperature sensor embedded within the thermal actuator is in an open circuit condition, which may indicate a fault in a system for monitoring the temperature of a thermal actuator. Further useful thermal safety systems can include electrical designs which prevent power application to a thermal actuator when a temperature sensor embedded within the thermal actuator is above or below a resistance, which may be useful when a temperature sensor changes resistance as a function of temperature, such as with a negative temperature coefficient thermistor or a positive temperature coefficient thermistor, and may enable preventing power to a thermal actuator when the thermal actuator exceeds a temperature. Any of the previously described systems may be implemented in systems that are independent of any programmed software.[00104J It will be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure has been described in connection with various embodiments, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.[00105J The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

WHAT IS CLAIMED IS:

1. An apparatus configured for monitoring fluid flow in a body, the apparatus comprising: a thermal flow sensor comprising: a thermal actuator; a plurality of temperature sensors; a power source; a processor; and at least one memory storage device, wherein the processor is configured to control power delivery to the thermal actuator based on at least one of a signal from a temperature sensor, a parameter stored in the memory storage device, or time, and wherein the at least one memory storage device is configured to store values corresponding to at least one of the plurality of temperature sensors.

2. The apparatus of claim 1, wherein the at least one memory storage device comprises a set of instructions accessible by the processor and configured to: control power delivered to the thermal actuator; receive values corresponding to the plurality of temperature sensors; and store values corresponding the plurality of temperature sensors in at least one memory storage device.

3. The apparatus of claim 2, further comprising a wireless communication module,wherein the wireless communication module is configured to transmit data read from the at least one memory storage device to a second memory storage device physically disposed within a wireless communication device.

4. The apparatus of claim 3, further comprising a motion sensor.

5. The apparatus of any of claims 2-4, wherein the instructions of the at least one memory storage device further comprise instructions accessible by the processor and configured to: apply increased power to the thermal actuator; receive values corresponding to at least one of the plurality of temperature sensors; compare the values to a threshold value stored in a memory storage device; and reduce power to the thermal actuator if a value corresponding to a temperature sensor exceed the threshold value.

6. The apparatus of claim 1, wherein the plurality of temperature sensors comprises at least a first temperature sensor, a second temperature sensor and a third temperature sensor, and wherein the first temperature sensor is disposed within the region of the thermal actuator; the second temperature sensor is disposed outside of the region of the thermal actuator; and the third temperature sensor is disposed outside of the thermal actuator on anopposing side of the thermal actuator as the second temperature sensor.

7. A system configured for monitoring fluid flow in a body, the system comprising: a thermal flow sensor comprising: a thermal actuator; a temperature sensor; a power source; and an adhesive patch comprising a first adhesive surface and a second adhesive surface, wherein the first adhesive surface is configured for releasable bonding to a surface of the thermal flow sensor, the second adhesive surface is configured for releasable bonding to human skin, and the first adhesive surface has an adhesive strength greater than that of the second adhesive surface.

8. The system of claim 7, wherein the first adhesive surface is geometrically matched to a surface of the thermal flow sensor.

9. The system of claim 8, wherein the first adhesive surface further comprises a perimeter region with reduced adhesive strength.

10. The system of claim 9, wherein the perimeter region is comprised a woven material.

11. The system of claim 9, wherein the perimeter region is comprised of a nonwoven material.

12. The system of claim 7, wherein the thermal flow sensor comprises at least a firsttemperature sensor, a second temperature sensor and a third temperature sensor, wherein: the first temperature sensor is disposed within the region of the thermal actuator; the second temperature sensor is disposed outside of the region of the thermal actuator; and the third temperature sensor is disposed outside of the thermal actuator on an opposing side of the thermal actuator as the second temperature sensor.

13. A wireless, flexible thermal sensor mountable on a body, the sensor comprising: a barrier film; an enclosure; a first region; a thermal actuator disposed within the first region; a temperature sensor disposed within the first region; a second region; a power source disposed within the second region; and an electrically conductive coil disposed within the second region and configured for receiving inductive power, wherein the thermal actuator, the temperature sensor, the power source, and the conductive coil are disposed within a cavity formed by the combination of the barrier film and the enclosure.

14. The sensor of claim 13, wherein the first region comprises at least a first temperature sensor, a second temperature sensor and a third temperature sensor, wherein:the first temperature sensor is disposed within the region of the thermal1005 actuator; the second temperature sensor is disposed outside of the region of the thermal actuator; and the third temperature sensor is disposed outside of the thermal actuator on an opposing side of the thermal actuator as the second temperature sensor.

Images