Patent Description:
Thermal mass-flow meters, also called thermal anenometers, are simpler to employ. However, they are limited to a defined continuum of flow of fluid having a constant and well-known density and heat capacitance within the volume stream passing the sensor. Thermal anenometers are therefore incapable of measuring water flow in, for example, aqueous solutions of unknown composition exhibiting unknown thermo-physical parameters.

Therefore, there is a need for a high-precision measurement device that can reliably and precisely determine the flow rate of an aqueous solution, circulating in a known environment (such as a microfluidic system), that is inexpensive, and deployable in a wide variety of settings function in the above-noted flow regime.

<NPL>, discloses: Micro-traces of water in gases have been determined by using a combination of a conversion reactor column and a high sensitivity hydrogen gas sensor (abbreviated here to CRHSGC). A special purge installation was designed to clean the system with dried and purified liquid nitrogen. Micro-traces of water in gases first were introduced into the reactor column. The column was prepared by filling with a mixture of lithium and aluminium hydride (LiAIH4) and glass fibre in a vacuum box, where the water present reacted with LiAIH4 at about <NUM>. Hydrogen was released and determined by the hydrogen gas sensor, which was calibrated by a series of standard micro-trace hydrogen mixture gases. The experimental results showed that this method can be used to determine micro-traces of water in gases quickly, accurately and at a low cost. Only about <NUM>-<NUM> litresof sample were needed during each analysis. The method developed does not have the shortcoming of direct determination of micro-traces of water in gases that is caused by the absence of appropriate traceable calibration gases.

<CIT> discloses skin moisture content measuring devices.

The figures illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. For simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity of presentation. Furthermore, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. References to previously presented elements are implied without necessarily further citing the drawing or description in which they appear. The number of elements shown in the Figures should by no means be construed as limiting and is for illustrative purposes only.

The following description sets forth various details to provide a thorough understanding of the invention and it should be appreciated, by those skilled in the art, that the present invention may be practiced without these specific details. Furthermore, well-known methods, procedures, and components have been omitted to highlight the present invention.

Turning now to the figures, <FIG> is a schematic, cross-sectional side-view of a measurement device <NUM> and includes two primary elements; a reactor <NUM> that directly or indirectly engages with and/or is in fluid communication with transducing element <NUM>, according to the invention. Reactor <NUM> includes, for example, a (e.g., polymeric) housing <NUM> that may at least partially encase a hydrophilic porous filter <NUM> for capturing moisture and filtering impurities, a gas donor <NUM> characterized by its ability to generate (e.g., hydrogen) gas upon reaction with water, and a hydrophobic filter membrane <NUM> operative to capture unreacted water and other reactants. Transducing element <NUM> is operative to transduce the gas into an electrical signal <NUM> and can be implemented in various configurations as will be further discussed.

In some embodiments, hydrophilic porous filter <NUM> can be disposed such to be in fluid communication with a fluid source <NUM>.

In some embodiments, gas donor <NUM> may be disposed between hydrophilic porous filter <NUM> and hydrophobic filter membrane <NUM>. In some embodiments, hydrophobic filter membrane <NUM> may be disposed between gas donor <NUM> and transducing element <NUM>. Optionally, hydrophilic porous filter <NUM>, hydrophobic filter membrane <NUM>, gas donor <NUM> and/or transducing element <NUM> may be disposed in a layered manner. Optionally, housing <NUM> may extend laterally from an upper surface 5A of hydrophobic filter membrane <NUM> to a lower surface 4B of hydrophilic porous filter <NUM>. Housing <NUM> may therefore laterally encase hydrophilic porous membrane <NUM>, gas donor <NUM> and hydrophobic filter membrane <NUM>. In some embodiments, as exemplified in <FIG>, transducing element <NUM> may extend over the upper surface 5A of hydrophobic filter membrane <NUM> and the upper surface or edge 3A of housing <NUM>. Optionally, the upper surfaces 3A and 5A may be flush. In some other embodiments, the upper surfaces 3A and 5A may not be flush. Further, in some other embodiments, transducing element <NUM> may be sized such to not extend over the later edges of hydrophobic filter membrane <NUM>. Optionally, housing <NUM> may be arranged to laterally extend over the lateral edges of transducing element <NUM>.

The lower surface 4B of hydrophilic porous filter <NUM> is exposed to allow for the continuous measurement of water content in liquid discharged by the skin of a living mammalian.

In some embodiments, measurement device <NUM> may comprise a fastener for allowing operably (and optionally, removably) coupling measurement device <NUM> with an animal body such to allow for the measurement of water content contained in bodily fluid discharged from the animal body. The fastener may include, for example, an adhesive, staple, tack, suture, and/or the like.

In accordance with the invention, measurement device <NUM> is configured as a patch-like structure.

In accordance with the invention, measurement device <NUM> is configured to be operably engaged with a skin surface portion of an animal body.

Hydrophilic porous filter <NUM> provides a constant flow resistance to both liquid and gas states in the above-noted flow regime, and the hydrophilic properties do not hinder passage or facilitate passage of liquid water at the low pressures that may be associated with low flow rate regimes towards gas donor <NUM>. For example, the hydrophilic properties of porous filter <NUM> may facilitate the passage of water-containing liquid from fluid source <NUM> towards gas donor <NUM>. Filter <NUM> may be made, for example, of glass, ceramic, metal, and/or cellulose and may, for example, have a pore size of <NUM> enabling passage of liquid and vapor while filtering particles or salt compounds.

In another embodiment, Hydrophilic porous filter <NUM> is implemented as Anodic Aluminum Oxide or Anodic Titanium Oxide with a pore size of, e.g., <NUM>-<NUM>.

As shown, gas donor <NUM> is disposed at the downstream side of filter <NUM> to enable reaction with filtered water vapor conveyed by pressure exerted by the water source through primary porous filter <NUM>. In certain filters <NUM>, the liquid water is also conveyed through via capillary action from the outside to the inside of upstream reactor <NUM>.

In some embodiments, CaH<NUM> is employed as the gas donor. Alternative donors of hydrogen include, for example, metal-hydrides such as MgH<NUM>, NaAlH<NUM>, LiAlH<NUM>, LiH, LiBH<NUM>, LiBH4, non-metal hydrides, and/or some carbohydrates. The gas donor can act as a battery substitute and may define the upper limit of the cumulative electrical power that can be generated.

Hydrophobic filter membrane <NUM> is implemented as a barrier to enclose the CaH<NUM>, H<NUM>O and Ca(OH)<NUM> and prevent them from entering the downstream fuel cell, in a certain embodiment. In another embodiment, filter membrane <NUM> is implemented as combination cellulose/polyester cloth.

Transducing element <NUM> translates the gas into an electrical signal by any of a variety of transducing element embodiments, as will be now discussed.

The measurement device <NUM> may be configured such that hydrogen gas generated thereby is released into the environment. In this way, hydrogen gas can be continuously generated in response to (e.g., continuously) subjecting hydrophyilic porous filter <NUM> with (e.g., flowing) media that may contain water.

<FIG> are schematic, cross-sectional side-views of various embodiments of transducing element <NUM>.

Specifically, <FIG> depicts an embodiment of transducing element <NUM> implemented as a proton-exchange membrane (PEM) fuel cell in which hydrogen contacting a downstream gas diffusion electrode (GDE) 8C is oxidized and the electrons exit the cell on the anode side <NUM> through an electrical conductor. The resulting cations traverse PEM 8B. At GDE 8D the hydrogen ions recombine with electrons and form water through reaction with oxygen. In a certain embodiment PEM 8B is implemented as Nafion.

<FIG> depicts an embodiment of transducing element <NUM> employing a polymer stack of the PEM fuel cells.

<FIG> depicts an embodiment of transducing element <NUM> that employs a heating filament <NUM> cooled by the flow of gas. As shown, at least some of the gas is directed over a resistance heated wire <NUM>. The resulting change in resistance or temperature distribution profile is measured by circuitry <NUM> and output, e.g., via leads <NUM> and/or a wireless transmitter. It should be appreciated that the above noted deficiencies of an anemometer are removed through conversion of any fluid media (e.g., aqueous solution) operably engaging with the device into a pure gas. It is noted that fluid media may be characterized by its composition-dependent density and heat capacity.

<FIG> depicts an embodiment of transducing element <NUM> that employs a porous material <NUM> whose dielectric constant changes as it fills with gas. The resulting change in capacitance is processed by circuitry <NUM> and outputs a signal via leads <NUM> and/or a wireless transmitter. Zeolite is an example of a such a porous material.

<FIG> depicts an embodiment of transducing element <NUM> that employs a differential pressure sensor to transduce gas pressure into an electrical signal. As shown, a differential pressure is created as gas passes through orifice <NUM> and is transduced into an electric signal by circuitry <NUM>, and signal output, e.g., via leads <NUM> and/or a wireless transmitter.

<FIG> depicts an embodiment of transducing element <NUM> that employs a cantilever or stretchable membrane configured to deflect responsively to the local pressure field generated by the gas-stream. As shown, gas applies a pressure to flexible element <NUM> and the resulting deformation is quantified through an electromechanical transducer or circuitry <NUM>, and a signal output, e.g., via leads <NUM> and/or a wireless transmitter.

<FIG> depicts an embodiment of measurement device <NUM> applied as a sweat gauge mounted to sweating skin <NUM>.

Water and other sweat constituents are captured by primary hydrophilic porous filter <NUM>, the non-aquatic constituents are filtered out, and the remaining water content conveyed downstream where it contacts the hydrogen donor CaH<NUM> <NUM> disposed at the downstream edge of primary filter <NUM>. There the CaH<NUM> reacts with water to form a stoichiometric volume of hydrogen that creates a pressure gradient driving the hydrogen through secondary filter <NUM>. Water filter <NUM> filters unreacted water, CaH<NUM> and Ca(OH)<NUM> and has a low flow resistance relative to primary filter <NUM>. This filtering may become increasingly significant in protecting transducing element <NUM> as reaction efficiency diminishes with time and the quantity of unreacted water increases. The hydrogen continues downstream and contacts transducing element <NUM> implemented in this example as a single-cell membrane electrode assembly (MEA) having a proton exchange membrane PEM 8B sandwiched between two gas diffusion electrodes GDEs 8C and 8D, as noted above. Each of GDEs 8C and 8D has an electrically conductive supporting cloth enabling gas distribution and an electrode with a catalyst where the chemical reactions occur. The catalyst coated surfaces are in contact with PEM electrolyte 8B.

As shown, GDE 8C hydrogen is oxidized to cations H+ and the electrons leave measurement device <NUM> at anode <NUM>. The cations pass the solid-state electrolyte PEM 8B and the oxygen is reduced and combines with cations to produce water at cathode <NUM>, as noted above.

The PEM 8B is a gas selective permeable membrane resulting in a hydrogen and oxygen gradient across the membrane thickness. It acts as convey path for protons supply the GDE 8D with protons H+, while blocking oxygen and ions thereof. The GDE 8D in contact with the PEM promotes a high conversion rate of the protons to water.

MEA 8A is in communication with gas distribution channel 8F to maximize hydrogen contact with to the membrane surface. A high conversion rate is obtained by using MEAs. Non-converted excess hydrogen can leave the system after passing membrane surface 8D in a certain embodiment.

In another embodiment, a bypass channel (not shown) directs a known, fixed fraction of hydrogen directly out of housing <NUM> and does not produce an electrical signal to prevent saturation of the fuel cell and facilitate miniaturization of MEA 8A. Measurement device <NUM> can be self-actuated and deactivated in accordance with stoichiometric limitation set by the amount of water available.

As taught, the required precision measurement is achieved through the capture of sweat in static and/or any flowing state and the conversion of the sweat, based on the amount of water contained therein, into a corresponding collective electrical signal.

Furthermore, in addition to its measuring capacity, the sensor also generates harnessable electricity.

Measurement device <NUM> may be comparatively efficient and effective for static and non-static states and have a high sensitivity down to flow rates of the less than, for example, 10uL/min. Measurement device <NUM> is also effective for liquid, gaseous, and vapor states over a temperature range like, for example, <NUM>-<NUM>, has a fast response time of some seconds, has a slew rate of, e.g., <NUM>-<NUM> seconds to reach the nominal output power, and has a comparatively low cost. Its dynamic range spans, e.g., at least five orders of magnitude and is highly selective in that its capable of identifying and measuring the amount of water included in any media that may comprise, for example, aqueous solutions among a variety of other compositions.

<FIG> is a flowchart of the processing steps employed by the measurement device (e.g., water sensor) and can be divided into three stages, gas generation <NUM>, signal generation <NUM>, and output <NUM>.

Specifically, in gas generation stage <NUM>, water is captured at step <NUM> as a liquid, gas or vapor with a hydrophilic material, as noted above. In step <NUM>, the water is contacted with a reactant characterized by its gas generation properties as a reaction product. In step <NUM> the liberated gas is conveyed through a hydrophobic membrane <NUM> while filtering unreacted water and reacted CaH<NUM>.

In stage <NUM>, the liberated gas is transduced into an electrical signal at step <NUM> through any of the transducing element embodiments noted above. In step <NUM>, the signal is measured either as a current or a voltage in accordance with the type of transducing element employed. In step <NUM>, the measured signal is rendered into a quantitative measurement of the flow rate of water fluid in accordance with a given reaction conversion.

Claim 1:
A measuring device (<NUM>) operably engageable with a skin surface portion of a skin surface of an animal body for measuring water content in a bodily media discharged by the skin surface, the measurement device being configured as a patch-like structure, wherein the measuring device (<NUM>) is characterized by:
a reactor (<NUM>) comprising a reactant gas donor (<NUM>), wherein the reactor (<NUM>) is configured to liberate a hydrogen stream having a stoichiometric equivalent to water in the media, the reactant gas donor (<NUM>) having an ability to liberate hydrogen gas upon reaction with water; and
a transducing element (<NUM>) configured to transduce the hydrogen stream into an electrical signal,
wherein the reactor (<NUM>) is configured such that the reactant gas donor (<NUM>) can be continuously subjected to flow of the bodily media.