Systems and methods of flexible and fully printed passive RF resonators for contact-less solution sensing

Abstract

Microwave liquid sensing devices include a flexible substrate having embedded therein a flexible circuit including a microwave resonator with terminal sensing electrodes that extend outward within the substrate from a terminal portion of the microwave resonator. The microwave resonator has a resonant size dimension of between 100 µm and 50 mm. The terminal sensing electrodes have a lateral size dimension of between 100 µm and 50 mm. The microwave resonator is sensitive by contactless measurement to dielectric changes surrounding the extended terminal sensing electrodes.

Description

SYSTEMS AND METHODS OF FLEXIBLE AND FULLY PRINTED PASSIVE RF RESONATORS FOR CONTACT-LESS SOLUTION SENSINGCLAIM TO PRIORITY

[0001] This application relates to, incorporates by reference for all purposes, and claims priority to United States Application Serial Number 63 / 516,358, filed July 28, 2023.STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

[0002] This invention was made with government support under N-00014-19-12399 awarded by the Office of Naval Research. The government has certain rights in the invention.BACKGROUND

[0003] Microwave sensing platforms enable a wide range of measurements and characterization techniques across different fields of application, such as motion sensing, biomedicine, materials characterization as well as permittivity measurements of liquid samples. Aside from their general low-cost, their high-sensitivity and robustness against harsh environments, the key advantage of microwave liquid sensors resides in their capability for non-invasive, label-free sensing operability. In recent years, many different resonance-based microwave sensors have been proposed for monitoring solution properties, including the conductivity of aqueous electrolytes and the concentration of solutes. Despite their exceptional sensing performances, a large set of these technologies rely on physical connections to read-out electronics (i.e. , network analysers) or are implemented on rigid / semirigid substrates, requiring dedicated microfluidics to ensure appropriate exposure to solutions. Such characteristics limit the utility of these systems in real-life scenarios.SUMMARY

[0004] In recent years, several efforts have been dedicated to the development of portable and versatile microwave technologies for liquid sensing and characterization. Disclosed herein is a fully printed microwave sensor that allows untethered signal read-out when either immersed in or in proximity to the liquid under test, the latter thanks to its inherent mechanical flexibility. These characteristics, along with its cost-effectiveness and its ease of fabrication, favor the seamless integration of this device into fluidic and microfluidic systems, in real-life applications.

[0005] In some aspects, the techniques described herein relate to a microwave liquid sensing device including: a flexible substrate having embedded therein a flexible circuit including a microwave resonator with terminal sensing electrodes that extend outward within the substrate from a terminal portion of the microwave resonator, wherein the microwave resonator has a resonant size dimension of between 100 pm and 50 mm, including but not limited to, at least 100 pm, at least 5 mm, or at least 8 mm, and at most 50 mm, at most 20 mm, or at most 12 mm, wherein the terminal sensing electrodes have a lateral size dimension of between 100 pm and 50 mm, and wherein themicrowave resonator is sensitive by contactless measurement to dielectric changes surrounding the extended terminal sensing electrodes.

[0006] In some aspects, the techniques described herein relate to a method of making a microwave liquid sensing device, the method including: embedding a flexible circuit within a flexible substrate, the flexible circuit including a microwave resonator with terminal sensing electrodes that extend outward within the substrate from a terminal portion of the microwave resonator, wherein the microwave resonator has a resonant size dimension of between 100 pm and 50 mm, including but not limited to, at least 100 pm, at least 5 mm, or at least 8 mm, and at most 50 mm, at most 20 mm, or at most 12 mm, wherein the terminal sensing electrodes have a lateral size dimension of between 100 pm and 50 mm, and wherein the resonant sensing component is sensitive by contactless measurement to dielectric changes surrounding the extended terminal sensing region.

[0007] These and other systems, methods, objects, features, and advantages of the present disclosure will be apparent to those skilled in the art from the following detailed description of the preferred embodiment and the drawings.

[0008] All documents mentioned herein are hereby incorporated in their entirety by reference. References to items in the singular should be understood to include items in the plural, and vice versa, unless explicitly stated otherwise or clear from the text. Grammatical conjunctions are intended to express any and all disjunctive and conjunctive combinations of conjoined clauses, sentences, words, and the like, unless otherwise stated or clear from the context.BRIEF DESCRIPTION OF THE FIGURES

[0009] The disclosure and the following detailed description of certain embodiments thereof may be understood by reference to the following figures:

[0010] Fig. 1 depicts a) Schematic representation of the proposed sensor, composed of a Double Broadside-coupled Split-Ring Resonator (DBSRR) and two protruding metal fingers, extending the sensing area past the resonator, b) Simplified circuit diagram of the sensor, showing the DBSRR and fingers’ contributions respectively, c) Operating principle of the sensor: as the sensing area is exposed to media with different complex relative permittivity, the characteristic features of the resonance change, d) SI 1 scattering parameter plot, showing the DBSRR response upon exposition of the sensing area to different fluids, e) Mapping of the resonance frequency shift versus the real component of the complex permittivity for different fluids at 25°C, 500 MHz.

[0011] Fig. 2 depicts a) Schematic representation of the sensor operating in immersion and in contact-less mode. b,c) Return losses of an immersed device, demonstrating increased resonance depth as the LUT (i.e. DBPS, aqueous electrolyte) is gradually diluted in water (c), and resonance shift as ethanol concentration is increased in water (c). d,e) Comparison of two devices operating inimmersion and contact-less mode, measuring electrolyte conductivity (d) and ethanol content (e): each point represents the average over five separate measurements.

[0012] Fig. 3 depicts a,b) Schematic representation of the dual-band DBSRR sensor, constituted of two concentric DBSRRs, operating at approximately 525 MHz (inner DBSRR) and 265 MHz (outer DBSRR). c,d) Return losses of the same device operating in immersion (c) and contact-less mode (d).

[0013] Fig 4 depicts the equivalent circuit of a DBSRR consists of a LC resonant circuit. In this model, the inductance L is approximated by the self-inductance of the two SRRs and R represent the dissipative losses due to the finite conductivity of the rings. The equivalent capacitance C results from the combination of the two split capacitances Cswith the mutual capacitance Co of the two SRRs.

[0014] Fig. 5 depicts inkjet printing allows the rapid variation of device geometry and size (a), which is strongly correlated to the operating frequency of the resonator, b) Su plots for devices of different lateral size (W, see also Figure SI3). c) Su plots for devices of same size but different fingers lengths, d) Su plots for devices with more than two superimposed SRRs (see Methods for fabrication).

[0015] Fig. 6 depicts the geometrical features of the resonator, here reported in terms of W, the lateral size of the square SRRs.

[0016] Fig. 7 depicts a) Schematic representation of the characterization set-up used for measuring the return losses of the DBSRRs. b) Photograph of the primary coils.

[0017] Fig. 8 depicts a) Photograph of the characterization set-up used for measuring the return losses of the DBSRR sensors operating in contact-less mode, through a portion of plastic tubing, b) Su plot of a DBSRR operating in air, with flat fingers (brown curve) and with the sensing area wrapped around an empty tube (green curve): the two curves are identical.

[0018] Fig. 9 depicts a,b) SI 1 plots of two different DBSRR operating in immersion mode (a, lateral size W: 10 mm) and in contact-less mode (b, lateral size W: 15 mm), when exposed to different dilutions of DPBS in deionised water. c,d) Dependence of the resonance depth (Si l magnitude at resonance) on DPBS concentration for the immersed device (c) and device operating contact-less (d): each point is the average of five separate measurements, standard deviation is not appreciable at this scale.

[0019] Fig. 10 depicts normalised response to different solution conductivities (S 11 magnitude at resonance versus DPBS concentration) for immersed devices of different sizes: each point is the average of five separate measurements, whiskers represent standard deviation. Black dots display the response from a standard benchtop conductivity probe (Mettler-Toledo SevenMulti).

[0020] Fig. 11 depicts a) the ability to sense in contact- less mode was evaluated by measuring the device response to deionised water and DPBS through a plastic layer of increasing thickness: to achieve this, up to 10 layers of Kapton tape were positioned on the fingers area, and Su spectra of both liquids were acquired for each layer by drop-casting -100 pL of solution on the sensing area, b) Thickness profile of the Kapton tape layer, acquired with a Bruker DektakXT Stylus Profilometer. c,d) Two graphs comparing the response of devices with different lateral size W (c) and gap width 5 (d) to deionised water and DPBS, through increasing layers of Kapton: the y-axis represent the difference between the S11 magnitude at resonance for the two liquids. The graphs highlight how, for devices of all size and gap width, the sensitivity decreases with separation, with larger resonators providing slightly better performances.

[0021] Fig 12 depicts a,b) Su plots of two different DBSRR operating in immersion mode (a, lateral size I : 10 mm) and in contact- less mode (b, lateral size IF: 15 mm), when exposed to different dilutions of ethanol in deionised water. c,d) Dependence of the resonance depth (Su magnitude at resonance) on ethanol concentration for the immersed device (c) and device operating contact-less (d): each point is the average of five separate measurements, standard deviation is not appreciable at this scale.DETAILED DESCRIPTION

[0022] Before the present disclosure is described in further detail, it is to be understood that the disclosure is not limited to the particular embodiments described. It is also understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. The scope of the present disclosure will be limited only by the claims. As used herein, the singular forms "a", "an", and "the" include plural embodiments unless the context clearly dictates otherwise.

[0023] In this application, unless otherwise clear from context, (i) the term “a” may be understood to mean “at least one”; (ii) the term “or” may be understood to mean “and / or”; (iii) the terms “comprising” and “including” may be understood to encompass itemized components or steps whether presented by themselves or together with one or more additional components or steps; and (iv) the terms “about” and “approximately” are used as equivalents and may be understood to permit standard variation as would be understood by those of ordinary skill in the art; and (v) where ranges are provided, endpoints are included.

[0024] Approximately: as used herein, the term “approximately” or “about,” as applied to one or more values of interest, refers to a value that is similar to a stated reference value. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%,1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

[0025] Composition: as used herein, may be used to refer to a discrete physical entity that comprises one or more specified components. In general, unless otherwise specified, a composition may be of any form - e.g., gas, gel, liquid, solid, etc. In some embodiments, “composition” may refer to a combination of two or more entities for use in a single embodiment or as part of the same article. It is not required in all embodiments that the combination of entities result in physical admixture, that is, combination as separate co-entities of each of the components of the composition is possible; however many practitioners in the field may find it advantageous to prepare a composition that is an admixture of two or more of the ingredients in a pharmaceutically acceptable carrier, diluent, or excipient, making it possible to administer the component ingredients of the combination at the same time.

[0026] Improve, increase, or reduce: as used herein or grammatical equivalents thereof, indicate values that are relative to a baseline measurement, such as a measurement in a similar composition made according to previously known methods.

[0027] Substantially: as used herein, the term “substantially” refers to the qualitative condition of exhibiting total or near-total extent or degree of a characteristic or property of interest. One of ordinary skill in the biological arts will understand that biological and chemical phenomena rarely, if ever, go to completion and / or proceed to completeness or achieve or avoid an absolute result. The term “substantially” is therefore used herein to capture the potential lack of completeness inherent in many biological and chemical phenomena.

[0028] It should be apparent to those skilled in the art that many additional modifications beside those already described are possible without departing from the inventive concepts. In interpreting this disclosure, all terms should be interpreted in the broadest possible manner consistent with the context. Variations of the term "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, so the referenced elements, components, or steps may be combined with other elements, components, or steps that are not expressly referenced. Embodiments referenced as "comprising" certain elements are also contemplated as "consisting essentially of" and "consisting of" those elements. When two or more ranges for a particular value are recited, this disclosure contemplates all combinations of the upper and lower bounds of those ranges that are not explicitly recited. For example, recitation of a value of between 1 and 10 or between 2 and 9 also contemplates a value of between 1 and 9 or between 2 and 10.

[0029] As used herein, "silk fibroin" refers to silk fibroin protein whether produced by silkworm, spider, or other insect, or otherwise generated (Lucas et al., Adv. Protein Chem., 13: 107-242(1958)). Any type of silk fibroin can be used in different embodiments described herein. Silk fibroin produced by silkworms, such as Bombyx mori, is the most common and represents an earth-friendly, renewable resource. For instance, silk fibroin used in a silk film may be attained by extracting sericin from the cocoons of B. mori. Organic silkworm cocoons are also commercially available. There are many different silks, however, including spider silk (e.g., obtained from Nephila clavipes), transgenic silks, genetically engineered silks, such as silks from bacteria, yeast, mammalian cells, transgenic animals, or transgenic plants, and variants thereof, that can be used. See, e.g., WO 97 / 08315 and U.S. Pat. No. 5,245,012, each of which is incorporated herein by reference in their entireties.

[0030] Disclosed herein is a resonance-based microwave sensing platform that enables a wide range of measurements and characterization techniques across different fields of application, such as motion sensing, biomedicine, materials characterization as well as permittivity measurements of liquid samples. The disclosed microwave sensing platform exhibits low-cost, high- sensitivity and robustness against harsh environments, as well as a capability for non-invasive, label-free sensing operability. Examples of the disclosed microwave sensing platform are based on a fully untethered, contact-less and flexible technology, and are able to seamlessly integrate with existing fluidic systems. Disclosed herein is a resonant microwave solution sensor based on a Double Broadside- coupled Split-Ring Resonator (DBSRR) (See P. Tseng, B. Napier, L. Garbarini, D. L. Kaplan, F. G. Omenetto, Adv. Mater. 2018, 30, 1703257 and R. Marques, F. Mesa, J. Martel, F. Medina, IEEE Trans. Antennas Propag. 2003, 51, 2572, each of which are incorporated by reference in their entireties), entirely fabricated by inkjet printing onto a thin flexible polyimide substrate (thickness of approximately 50 pm). The typical SRR shape was modified by extending the sensitive area of the device, with the goal of improving responsivity as well as allowing the delocalization of the sensing region. This unique structure, along with the flexible device format, enables contact-less solution sensing through commercial plastic tubing, thus providing a cost-effective, passive and untethered solution monitoring device.

[0031] Disclosed herein is a microwave liquid sensing device. The microwave liquid sensing device includes a flexible substrate with an embedded flexible circuit including a microwave resonator with terminal sensing electrodes that extend outward within the substrate from a terminal portion of the microwave resonator. The microwave resonator has a resonant size dimension of between 100 pm and 50 mm. In some examples, the microwave resonator has a resonant size dimension of at least 100 pm. In some examples, the microwave resonator has a resonant size dimension of at least 5 mm. In some examples, the microwave resonator has a resonant size dimension of at least 8 mm. In some examples, the microwave resonator has a resonant size dimension of at most 50 mm. In some examples, the microwave resonator has a resonant sizedimension of at most 20 mm. In some examples, the microwave resonator has a resonant size dimension of at most 12 mm. The terminal sensing electrodes have a lateral size dimension of between 100 pm and 50 mm. The microwave resonator is sensitive by contactless measurement to dielectric changes surrounding the extended terminal sensing electrodes.

[0032] Disclosed herein is a method of making a microwave liquid sensing device. The method includes embedding a flexible circuit within a flexible substrate. The flexible circuit includes a microwave resonator with terminal sensing electrodes that extend outward within the substrate from a terminal portion of the microwave resonator. The microwave resonator has a resonant size dimension of between 100 pm and 50 mm. In some examples, the microwave resonator has a resonant size dimension of at least 100 pm. In some examples, the microwave resonator has a resonant size dimension of at least 5 mm. In some examples, the microwave resonator has a resonant size dimension of at least 8 mm. In some examples, the microwave resonator has a resonant size dimension of at most 50 mm. In some examples, the microwave resonator has a resonant size dimension of at most 20 mm. In some examples, the microwave resonator has a resonant size dimension of at most 12 mm. The terminal sensing electrodes have a lateral size dimension of between 100 pm and 50 mm. The microwave resonator is sensitive by contactless measurement to dielectric changes surrounding the extended terminal sensing electrodes. In the method, embedding at least partly includes printing the flexible substrate or the flexible circuit. Printing the flexible circuit includes printing a conductive ink and / or a nanoparticle dispersion. In the method, embedding includes printing a first portion of the flexible substrate, printing the flexible circuit, and printing a remaining portion of the flexible substrate.

[0033] Disclosed herein are example microwave liquid sensing devices of or made by any of the aforementioned methods disclosed herein. In the example microwave liquid sensing devices, the terminal sensing electrodes are a pair of electrodes, each of which extends from a respective terminal end of the microwave resonator. The pair of electrodes may be at least one of parallel, linear, or interdigitated. In the example microwave liquid sensing devices, the flexible substrate is composed of a plastic material, including but not limited to polyimide. In the example microwave liquid sensing devices, the flexible substrate is composed of a substrate material comprising, consisting essentially of, or consisting of a biomaterial, including but not limited to silk fibroin. In the example microwave liquid sensing devices, the flexible circuit is composed of a circuit material comprising, consisting essentially of, or consisting of a conductive metal, wherein the conductive metal is optionally copper, silver, gold, platinum, or a combination thereof. In the example microwave liquid sensing devices, the flexible circuit is composed of a circuit material comprising, consisting essentially of, or consisting of a conductive polymer. In examples, the microwave resonator is adouble-ring resonator. In examples, the microwave resonator is a broadside-coupled resonator. In examples, the microwave resonator is a double broadside-coupled microwave resonator.

[0034] In the example microwave liquid sensing devices, the microwave resonator is a single-ring resonator. In the example microwave liquid sensing devices, the device is substantially planar.

[0035] Disclosed herein is an example method of using the microwave liquid sensing device made by any of the methods disclosed herein, including a) placing the terminal sensing electrodes within a sensing distance of between direct contact and 50 mm of a liquid of interest, and b) measuring a resonant property of the microwave resonator while the terminal sensing electrodes are within the sensing distance of the liquid of interest. The method of using further includes estimating a property of the liquid of interest based on the measured resonant property of the microwave resonator or a change in the property based on a change in the measured resonant property. In an example method of using, the placing of step a) includes immersing at least a portion of the flexible substrate having the terminal sensing electrode embedded therein in the liquid of interest. In an example method of using, the placing of step a) includes contacting at least a portion of the flexible substrate having the terminal sensing electrode embedded therein with the liquid of interest. In an example method of using, the placing of step a) includes positioning the terminal sensing electrode adjacent to the liquid of interest without contacting the flexible substrate with the liquid of interest. In an example method of using, the placing of step a) includes wrapping the flexible substrate around a section of tubing, such that at least a portion of the terminal sensing electrode is adjacent to the tubing, wherein the liquid of interest if located within the tubing. In some examples, the tubing has a thickness of between 50 pm and 50 mm. In some examples, the tubing has a thickness of at least 50 pm. In some examples, the tubing has a thickness of at least 100 pm. In some examples, the tubing has a thickness of at least 500 pm. In some examples, the tubing has a thickness of at most 50 mm. In some examples, the tubing has a thickness of at most 5 mm. In some examples, the tubing has a thickness of at most 3 mm.

[0036] Unless otherwise specified or indicated by context, the terms “a”, “an”, and “the” mean “one or more.” For example, “a molecule” should be interpreted to mean “one or more molecules.”

[0037] As used herein, “about”, “approximately,” “substantially,” and “significantly” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, “about” and “approximately” will mean plus or minus <10% of the particular term and “substantially” and “significantly” will mean plus or minus >10% of the particular term.

[0038] As used herein, the terms “include” and “including” have the same meaning as the terms “comprise” and “comprising.” The terms “comprise” and “comprising” should be interpreted asbeing “open” transitional terms that permit the inclusion of additional components further to those components recited in the claims. The terms “consist” and “consisting of’ should be interpreted as being “closed” transitional terms that do not permit the inclusion of additional components other than the components recited in the claims. The term “consisting essentially of’ should be interpreted to be partially closed and allowing the inclusion only of additional components that do not fundamentally alter the nature of the claimed subject matter.

[0039] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0040] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0041] Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the abovedescribed elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

[0042] The methods and systems described herein may be deployed in part or in whole through a machine having a computer, computing device, processor, circuit, and / or server that executes computer readable instructions, program codes, instructions, and / or includes hardware configured to functionally execute one or more operations of the methods and systems disclosed herein. The terms computer, computing device, processor, circuit, and / or server, as utilized herein, should be understood broadly.

[0043] Any one or more of the terms computer, computing device, processor, circuit, and / or server include a computer of any type, capable to access instructions stored in communication thereto such as upon a non-transient computer readable medium, whereupon the computer performs operations of systems or methods described herein upon executing the instructions. In certain embodiments, such instructions themselves comprise a computer, computing device, processor, circuit, and / or server.Additionally or alternatively, a computer, computing device, processor, circuit, and / or server may be a separate hardware device, one or more computing resources distributed across hardware devices, and / or may include such aspects as logical circuits, embedded circuits, sensors, actuators, input and / or output devices, network and / or communication resources, memory resources of any type, processing resources of any type, and / or hardware devices configured to be responsive to determined conditions to functionally execute one or more operations of systems and methods herein.

[0044] Network and / or communication resources include, without limitation, local area network, wide area network, wireless, internet, or any other known communication resources and protocols. Example and non-limiting hardware, computers, computing devices, processors, circuits, and / or servers include, without limitation, a general purpose computer, a server, an embedded computer, a mobile device, a virtual machine, and / or an emulated version of one or more of these. Example and non-limiting hardware, computers, computing devices, processors, circuits, and / or servers may be physical, logical, or virtual. A computer, computing device, processor, circuit, and / or server may be: a distributed resource included as an aspect of several devices; and / or included as an interoperable set of resources to perform described functions of the computer, computing device, processor, circuit, and / or server, such that the distributed resources function together to perform the operations of the computer, computing device, processor, circuit, and / or server. In certain embodiments, each computer, computing device, processor, circuit, and / or server may be on separate hardware, and / or one or more hardware devices may include aspects of more than one computer, computing device, processor, circuit, and / or server, for example as separately executable instructions stored on the hardware device, and / or as logically partitioned aspects of a set of executable instructions, with some aspects of the hardware device comprising a part of a first computer, computing device, processor, circuit, and / or server, and some aspects of the hardware device comprising a part of a second computer, computing device, processor, circuit, and / or server.

[0045] A computer, computing device, processor, circuit, and / or server may be part of a server, client, network infrastructure, mobile computing platform, stationary computing platform, or other computing platform. A processor may be any kind of computational or processing device capable of executing program instructions, codes, binary instructions and the like. The processor may be or include a signal processor, digital processor, embedded processor, microprocessor or any variant such as a co-processor (math co-processor, graphic co-processor, communication co-processor and the like) and the like that may directly or indirectly facilitate execution of program code or program instructions stored thereon. In addition, the processor may enable execution of multiple programs, threads, and codes. The threads may be executed simultaneously to enhance the performance of the processor and to facilitate simultaneous operations of the application. By way of implementation, methods, program codes, program instructions and the like described herein may be implemented inone or more threads. The thread may spawn other threads that may have assigned priorities associated with them; the processor may execute these threads based on priority or any other order based on instructions provided in the program code. The processor may include memory that stores methods, codes, instructions and programs as described herein and elsewhere. The processor may access a storage medium through an interface that may store methods, codes, and instructions as described herein and elsewhere. The storage medium associated with the processor for storing methods, programs, codes, program instructions or other type of instructions capable of being executed by the computing or processing device may include but may not be limited to one or more of a CD-ROM, DVD, memory, hard disk, flash drive, RAM, ROM, cache and the like.

[0046] A processor may include one or more cores that may enhance speed and performance of a multiprocessor. In embodiments, the process may be a dual core processor, quad core processors, other chip- level multiprocessor and the like that combine two or more independent cores (called a die).

[0047] The methods and systems described herein may be deployed in part or in whole through a machine that executes computer readable instructions on a server, client, firewall, gateway, hub, router, or other such computer and / or networking hardware. The computer readable instructions may be associated with a server that may include a file server, print server, domain server, internet server, intranet server and other variants such as secondary server, host server, distributed server and the like. The server may include one or more of memories, processors, computer readable transitory and / or non-transitory media, storage media, ports (physical and virtual), communication devices, and interfaces capable of accessing other servers, clients, machines, and devices through a wired or a wireless medium, and the like. The methods, programs, or codes as described herein and elsewhere may be executed by the server. In addition, other devices required for execution of methods as described in this application may be considered as a part of the infrastructure associated with the server.

[0048] The server may provide an interface to other devices including, without limitation, clients, other servers, printers, database servers, print servers, file servers, communication servers, distributed servers, and the like. Additionally, this coupling and / or connection may facilitate remote execution of instructions across the network. The networking of some or all of these devices may facilitate parallel processing of program code, instructions, and / or programs at one or more locations without deviating from the scope of the disclosure. In addition, all the devices attached to the server through an interface may include at least one storage medium capable of storing methods, program code, instructions, and / or programs. A central repository may provide program instructions to be executed on different devices. In this implementation, the remote repository may act as a storage medium for methods, program code, instructions, and / or programs.

[0049] The methods, program code, instructions, and / or programs may be associated with a client that may include a file client, print client, domain client, internet client, intranet client and other variants such as secondary client, host client, distributed client and the like. The client may include one or more of memories, processors, computer readable transitory and / or non-transitory media, storage media, ports (physical and virtual), communication devices, and interfaces capable of accessing other clients, servers, machines, and devices through a wired or a wireless medium, and the like. The methods, program code, instructions, and / or programs as described herein and elsewhere may be executed by the client. In addition, other devices utilized for execution of methods as described in this application may be considered as a part of the infrastructure associated with the client.

[0050] The client may provide an interface to other devices including, without limitation, servers, other clients, printers, database servers, print servers, file servers, communication servers, distributed servers, and the like. Additionally, this coupling and / or connection may facilitate remote execution of methods, program code, instructions, and / or programs across the network. The networking of some or all of these devices may facilitate parallel processing of methods, program code, instructions, and / or programs at one or more locations without deviating from the scope of the disclosure. In addition, all the devices attached to the client through an interface may include at least one storage medium capable of storing methods, program code, instructions, and / or programs. A central repository may provide program instructions to be executed on different devices. In this implementation, the remote repository may act as a storage medium for methods, program code, instructions, and / or programs.

[0051] The methods and systems described herein may be deployed in part or in whole through network infrastructures. The network infrastructure may include elements such as computing devices, servers, routers, hubs, firewalls, clients, personal computers, communication devices, routing devices and other active and passive devices, modules, and / or components as known in the art. The computing and / or non-computing device(s) associated with the network infrastructure may include, apart from other components, a storage medium such as flash memory, buffer, stack, RAM, ROM and the like. The methods, program code, instructions, and / or programs described herein and elsewhere may be executed by one or more of the network infrastructural elements.

[0052] The methods, program code, instructions, and / or programs described herein and elsewhere may be implemented on a cellular network having multiple cells. The cellular network may either be frequency division multiple access (FDMA) network or code division multiple access (CDMA) network. The cellular network may include mobile devices, cell sites, base stations, repeaters, antennas, towers, and the like.

[0053] The methods, program code, instructions, and / or programs described herein and elsewhere may be implemented on or through mobile devices. The mobile devices may include navigation devices, cell phones, mobile phones, mobile personal digital assistants, laptops, palmtops, netbooks, pagers, electronic books readers, music players, and the like. These mobile devices may include, apart from other components, a storage medium such as a flash memory, buffer, RAM, ROM and one or more computing devices. The computing devices associated with mobile devices may be enabled to execute methods, program code, instructions, and / or programs stored thereon.Alternatively, the mobile devices may be configured to execute instructions in collaboration with other devices. The mobile devices may communicate with base stations interfaced with servers and configured to execute methods, program code, instructions, and / or programs. The mobile devices may communicate on a peer to peer network, mesh network, or other communications network. The methods, program code, instructions, and / or programs may be stored on the storage medium associated with the server and executed by a computing device embedded within the server. The base station may include a computing device and a storage medium. The storage device may store methods, program code, instructions, and / or programs executed by the computing devices associated with the base station.

[0054] The methods, program code, instructions, and / or programs may be stored and / or accessed on machine readable transitory and / or non-transitory media that may include: computer components, devices, and recording media that retain digital data used for computing for some interval of time; semiconductor storage known as random access memory (RAM); mass storage typically for more permanent storage, such as optical discs, forms of magnetic storage like hard disks, tapes, drums, cards and other types; processor registers, cache memory, volatile memory, non-volatile memory; optical storage such as CD, DVD; removable media such as flash memory (e.g., USB sticks or keys), floppy disks, magnetic tape, paper tape, punch cards, standalone RAM disks, Zip drives, removable mass storage, off-line, and the like; other computer memory such as dynamic memory, static memory, read / write storage, mutable storage, read only, random access, sequential access, location addressable, file addressable, content addressable, network attached storage, storage area network, bar codes, magnetic ink, and the like.

[0055] Certain operations described herein include interpreting, receiving, and / or determining one or more values, parameters, inputs, data, or other information. Operations including interpreting, receiving, and / or determining any value parameter, input, data, and / or other information include, without limitation: receiving data via a user input; receiving data over a network of any type; reading a data value from a memory location in communication with the receiving device; utilizing a default value as a received data value; estimating, calculating, or deriving a data value based on other information available to the receiving device; and / or updating any of these in response to a laterreceived data value. In certain embodiments, a data value may be received by a first operation, and later updated by a second operation, as part of the receiving a data value. For example, when communications are down, intermittent, or interrupted, a first operation to interpret, receive, and / or determine a data value may be performed, and when communications are restored an updated operation to interpret, receive, and / or determine the data value may be performed.

[0056] Certain logical groupings of operations herein, for example methods or procedures of the current disclosure, are provided to illustrate aspects of the present disclosure. Operations described herein are schematically described and / or depicted, and operations may be combined, divided, reordered, added, or removed in a manner consistent with the disclosure herein. It is understood that the context of an operational description may require an ordering for one or more operations, and / or an order for one or more operations may be explicitly disclosed, but the order of operations should be understood broadly, where any equivalent grouping of operations to provide an equivalent outcome of operations is specifically contemplated herein. For example, if a value is used in one operational step, the determining of the value may be required before that operational step in certain contexts (e.g. where the time delay of data for an operation to achieve a certain effect is important), but may not be required before that operation step in other contexts (e.g. where usage of the value from a previous execution cycle of the operations would be sufficient for those purposes). Accordingly, in certain embodiments an order of operations and grouping of operations as described is explicitly contemplated herein, and in certain embodiments re-ordering, subdivision, and / or different grouping of operations is explicitly contemplated herein.

[0057] The methods and systems described herein may transform physical and / or or intangible items from one state to another. The methods and systems described herein may also transform data representing physical and / or intangible items from one state to another.

[0058] The elements described and depicted herein, including in flow charts, block diagrams, and / or operational descriptions, depict and / or describe specific example arrangements of elements for purposes of illustration. However, the depicted and / or described elements, the functions thereof, and / or arrangements of these, may be implemented on machines, such as through computer executable transitory and / or non-transitory media having a processor capable of executing program instructions stored thereon, and / or as logical circuits or hardware arrangements. Example arrangements of programming instructions include at least: monolithic structure of instructions; standalone modules of instructions for elements or portions thereof; and / or as modules of instructions that employ external routines, code, services, and so forth; and / or any combination of these, and all such implementations are contemplated to be within the scope of embodiments of the present disclosure Examples of such machines include, without limitation, personal digital assistants, laptops, personal computers, mobile phones, other handheld computing devices, medical equipment,wired or wireless communication devices, transducers, chips, calculators, satellites, tablet PCs, electronic books, gadgets, electronic devices, devices having artificial intelligence, computing devices, networking equipment, servers, routers and the like. Furthermore, the elements described and / or depicted herein, and / or any other logical components, may be implemented on a machine capable of executing program instructions. Thus, while the foregoing flow charts, block diagrams, and / or operational descriptions set forth functional aspects of the disclosed systems, any arrangement of program instructions implementing these functional aspects are contemplated herein. Similarly, it will be appreciated that the various steps identified and described above may be varied, and that the order of steps may be adapted to particular applications of the techniques disclosed herein. Additionally, any steps or operations may be divided and / or combined in any manner providing similar functionality to the described operations. All such variations and modifications are contemplated in the present disclosure. The methods and / or processes described above, and steps thereof, may be implemented in hardware, program code, instructions, and / or programs or any combination of hardware and methods, program code, instructions, and / or programs suitable for a particular application. Example hardware includes a dedicated computing device or specific computing device, a particular aspect or component of a specific computing device, and / or an arrangement of hardware components and / or logical circuits to perform one or more of the operations of a method and / or system. The processes may be implemented in one or more microprocessors, microcontrollers, embedded microcontrollers, programmable digital signal processors or other programmable device, along with internal and / or external memory. The processes may also, or instead, be embodied in an application specific integrated circuit, a programmable gate array, programmable array logic, or any other device or combination of devices that may be configured to process electronic signals. It will further be appreciated that one or more of the processes may be realized as a computer executable code capable of being executed on a machine readable medium.

[0059] The computer executable code may be created using a structured programming language such as C, an object oriented programming language such as C++, or any other high-level or low- level programming language (including assembly languages, hardware description languages, and database programming languages and technologies) that may be stored, compiled or interpreted to run on one of the above devices, as well as heterogeneous combinations of processors, processor architectures, or combinations of different hardware and computer readable instructions, or any other machine capable of executing program instructions.

[0060] Thus, in one aspect, each method described above and combinations thereof may be embodied in computer executable code that, when executing on one or more computing devices, performs the steps thereof. In another aspect, the methods may be embodied in systems that performthe steps thereof, and may be distributed across devices in a number of ways, or all of the functionality may be integrated into a dedicated, standalone device or other hardware. In another aspect, the means for performing the steps associated with the processes described above may include any of the hardware and / or computer-readable instructions described above. All such permutations and combinations are contemplated in embodiments of the present disclosure.

[0061] While the invention has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. For example, any of the features or functions of any of the embodiments disclosed herein may be incorporated into any of the other embodiments disclosed herein.

[0062] The following examples illustrate some embodiments and aspects of the invention. It will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be performed without altering the spirit or scope of the invention, and such modifications and variations are encompassed within the scope of the invention as defined in the claims which follow. The following examples do not in any way limit the invention.

[0063] EXAMPLES

[0064] Example 1

[0065] Figure la shows a schematic representation of the device structure, where two conductive fingers protrude from the split of the DBSRR. The equivalent electrical circuit for this microwave element is that of an LC oscillator, where the self-inductances of the two antiparallel SRRs compose the overall inductance Lo, while the capacitive element Co combines the contributions of the split regions of both SRRs and their mutual capacitance (see Figure 4). It is important to note that the characteristic inductance and capacitance of the resonators can be tuned by adjusting the device size and structure, and inkjet printing allows to quickly prototype several device configurations, operating at different resonance frequencies (Figure 5 and 6). The contribution from the fingers (i.e., the sensing area) is accounted as an additional parallel RC circuit (see Figure lb), where the values of and Rf are respectively determined by the real and imaginary components of the sample solution permittivity. In fact, as different liquid media are placed in proximity to the fingers, changes in Q and Ry respectively translate in variations of the resonance frequency fo and the resonance depth of the oscillator (Figure 1c), which can be easily measured by monitoring the reflection losses (.S' / / scattering parameter) from a primary coil adjacent to the DBSRR (see Figure 7 and Tseng, 2018). Figure Id shows the Su plot for a single device whose sensing area has been exposed to different solutions, ranging from water and water-based electrolytes to organic solvents. In accordance with the proposed device behaviour, when compared to the dry condition, Liquids Under Test (LUTs)with higher relative permittivity determine a larger shift of the resonance frequency, where Af0= fory~ foUT(Figure le).

[0066] Immersion and contact-less solution sensing

[0067] The proposed resonator structure can thus be used to monitor changes in solution conductivity and permittivity, employing the device in either immersion or in contact-less mode (Figure 2). The former is implemented by submerging the sensing region (i.e., the fingers, protected by a 70 pm-thick layer of Kapton tape) directly in the LUT, while the latter is achieved by wrapping the fingers around a plastic tube (see Figure 8). As a common aqueous electrolyte (Dulbecco’s Phosphate Buffer Saline, DPBS) is gradually mixed to deionised water, the solution conductivity increases from approximately 6 pS / cm to 16 mS / cm, thus decreasing the Rf component in the equivalent circuit. For this reason, the Sii plot shows a decrease in resonance depth of -7 dB for both immersion and contact-less measurements, as shown in Figure Id (full spectra and analysis in Figs. 4is the magnitude of the return losses at resonance. A notable discrepancy between the two approaches emerges when they are used to evaluate ethanol content in deionised water, visible through the shift in resonance frequency of the resonators: while the immersed device displays a 15% shift in resonance frequency when transitioning from water to ethanol, the contactless approach is limited to -0.5% (see Figure 12 for full spectra). The lower sensitivity is likely due to the contribution of the plastic tubing to the overall permittivity, as well as to the smaller sensing area exposed to the LUT: while in immersion mode the fingers are exposed on both sides of the device for a geometrical depth of -1 cm, the contact-less mode limits the proximity area to only one side of the device along the tube diameter (-0.9 cm).

[0068] Differential measurements

[0069] The utility and versatility of this device structure can be enhanced by recurring to a differential-mode sensing scheme, which is generally adopted to improve the robustness of measurements to undesired environmental and instrumental effects. Examples of differential-mode liquid sensors have been reported in the literature, operating on both microfluidic platforms and in immersion mode. In this disclosure, the differential reading is achieved by introducing an additional, smaller concentric DBSRR to the structure depicted in Figure 1. As shown in Figure 3a, the modified sensor embeds two resonating elements, where the outer DBSRR is still exposed to the LUT through its protruding fingers, while the inner DBSRR provides a reference value at higher frequency, given its reduced size. The Si] plots in Figure 3c highlight the relative variation in resonance frequency and depth of the low-frequency feature compared to the high-frequency one, when the device is immersed in different LUTs and air. The same trends are maintained when the device is operated incontact-less mode, with a reduction in sensitivity that is comparable with what is seen for the initial device (single DBSRR).

[0070] This disclosure demonstrates a microwave liquid sensing platform that can operate in multiple sensing modalities, thanks to its inherent mechanical flexibility and the versatility of the involved fabrication techniques. This untethered, fully printed sensing platform is in fact able to monitor changes of both the real and the imaginary components of the relative permittivity of fluids, while allowing for either immersion or contact-less monitoring through plastic tubing. The ease of fabrication allows for the fast prototyping of devices with modified characteristics, enabling for example differential-mode sensing or rapid tuning of the operating frequency. These characteristics are promising for real-life liquid sensing applications in industrial and laboratory settings, where these sensors could be seamlessly integrated in pre-existing fluidic and microfluidic systems, without requiring structural changes to the fluid circulation apparatus. Further developments of this sensing platform will require a proper optimisation of device structure and geometry to enable operation on a larger set of tubing samples, for example by customizing the fingers configuration to grant deeper penetration of the fringing fields into plastic materials. Finally, the integration of the proposed resonator geometry on different substrates, including bio- and skin-conformable materials, may enable biosensing and wearable applications.

[0071] Experimental Methods

[0072] Materials and inks: Polyimide substrates (~50 pm thick) were donated by FLEXcon Company, Inc. and used without cleaning or surface treatment. The silver nanoparticle dispersion (Silverjet DGP-40LT-15C, silver ink) and the organic solvents used for solution sensing were purchased from Sigma Aldrich. Dulbecco’s Phosphate Buffer Saline (DPBS) was purchased from Thermo Fisher Scientific. The tubing for the contact-less measurement (hard nylon plastic tubing) was purchased from McMaster-Carr.

[0073] Sensor fabrication: The SRR structures were prepared by inkjet printing (Fujifilm Dimatix, DMP2800) the silver nanoparticle dispersion directly on the untreated substrates, followed by a sintering step (180°C, 15 minutes); after sintering, the procedure was then repeated to increase the conductivity of the pattern. These steps were performed on both side of the substrate to achieve the broadside-coupled structure. When operated in immersion mode, the fingers region was coated with a layer of Kapton tape (~70 pm thick) to avoid electrode degradation and or delamination due to interactions with the liquid.

[0074] Resonators with multiple (i.e., more than two) broadside-couple SRRs (see Figure SI2), were realized by first fabricating a DBSRR, which was then covered with a layer of Kapton tape ((~70 pm thick). After this step, another antiparallel SRR was inkjet printed on the resonator area, to obtain a triple broadside-coupled resonator. This procedure was repeated up to 7 stacks of SRRs.

[0075] RF measurements: The scattering parameters were acquires using a primary coil connected to a Tektronix TTR506A Vector Network Analyzer. The immersion measurements were performed with DBSRR of 10 mm lateral size, while 15 mm size DBSRR were preferred for contact-less measurements through the plastic tubing (ID: 2.38 (3 / 32"); OD: 3.175 mm (1 / 8")).

Claims

CLAIMSWhat is claimed is:

1. A microwave liquid sensing device comprising: a flexible substrate having embedded therein a flexible circuit comprising a microwave resonator with terminal sensing electrodes that extend outward within the substrate from a terminal portion of the microwave resonator, wherein the microwave resonator has a resonant size dimension of between 100 m and 50 mm, including but not limited to, at least 100 pm, at least 5 mm, or at least 8 mm, and at most 50 mm, at most 20 mm, or at most 12 mm, wherein the terminal sensing electrodes have a lateral size dimension of between 100 pm and 50 mm, and wherein the microwave resonator is sensitive by contactless measurement to dielectric changes surrounding the extended terminal sensing electrodes.

2. A method of making a microwave liquid sensing device, the method comprising: embedding a flexible circuit within a flexible substrate, the flexible circuit comprising a microwave resonator with terminal sensing electrodes that extend outward within the substrate from a terminal portion of the microwave resonator, wherein the microwave resonator has a resonant size dimension of between 100 pm and 50 mm, including but not limited to, at least 100 pm, at least 5 mm, or at least 8 mm, and at most 50 mm, at most 20 mm, or at most 12 mm, wherein the terminal sensing electrodes have a lateral size dimension of between 100 pm and 50 mm, and wherein the resonant sensing component is sensitive by contactless measurement to dielectric changes surrounding the extended terminal sensing region.

3. The method of claim 2, wherein the embedding at least partly comprises printing the flexible substrate.

4. The method of claim 2, wherein the embedding at least partly comprises printing the flexible circuit.

5. The method of claim 4, wherein printing the flexible circuit comprises printing a conductive ink and / or a nanoparticle dispersion.

6. The method of claim 2, wherein the embedding comprises printing a first portion of the flexible substrate, printing the flexible circuit, and printing a remaining portion of the flexible substrate.

7. The micro wave liquid sensing device of or made by the method of any one of the preceding claims, wherein the terminal sensing electrodes are a pair of electrodes, each of which extends from a respective terminal end of the microwave resonator.

8. The microwave liquid sensing device of or made by the method of claim 7, wherein the pair of electrodes is parallel.

9. The microwave liquid sensing device of or made by the method of claim 7, wherein the pair of electrodes is linear.

10. The microwave liquid sensing device of or made by the method of claim 7, wherein the pair of electrodes is interdigitated.

11. The microwave liquid sensing device of or made by the method of any one of the preceding claims, wherein the flexible substrate is composed of a plastic material, including but not limited to polyimide.

12. The microwave liquid sensing device of or made by the method of any one of the preceding claims, wherein the flexible substrate is composed of a substrate material comprising, consisting essentially of, or consisting of a biomaterial, including but not limited to silk fibroin.

13. The micro wave liquid sensing device of or made by the method of any one of the preceding claims, wherein the flexible circuit is composed of a circuit material comprising, consisting essentially of, or consisting of a conductive metal, wherein the conductive metal is optionally copper, silver, gold, platinum, or a combination thereof.

14. The microwave liquid sensing device of or made by the method of any one of the preceding claims, wherein the flexible circuit is composed of a circuit material comprising, consisting essentially of, or consisting of a conductive polymer.

15. The micro wave liquid sensing device of or made by the method of any one of the preceding claims, wherein the microwave resonator is a single-ring resonator.

16. The microwave liquid sensing device of or made by the method of any one of claims 1 to 14, wherein the microwave resonator is a double-ring resonator.

17. The micro wave liquid sensing device of or made by the method of any one of claims 1 to 14 or 16, wherein the microwave resonator is a broadside-coupled resonator.

18. The micro wave liquid sensing device of or made by the method of claim 16 or 17, wherein the microwave resonator is a double broadside-coupled microwave resonator.

19. The micro wave liquid sensing device of or made by the method of any one of the preceding claims, wherein the device is substantially planar.

20. A method of using the microwave liquid sensing device of or made by the method of any one of the preceding claims, the method comprising: a) placing the terminal sensing electrodes within a sensing distance of between direct contact and 50 mm of a liquid of interest; and b) measuring a resonant property of the microwave resonator while the terminal sensing electrodes are within the sensing distance of the liquid of interest.

21. The method of claim 20, the method further comprising: c) estimating a property of the liquid of interest based on the measured resonant property of the microwave resonator or a change in the property based on a change in the measured resonant property.

22. The method of claim 20, wherein the placing of step a) comprises immersing at least a portion of the flexible substrate having the terminal sensing electrode embedded therein in the liquid of interest.

23. The method of claim 20, wherein the placing of step a) comprises contacting at least a portion of the flexible substrate having the terminal sensing electrode embedded therein with the liquid of interest.

24. The method of claim 20, wherein the placing of step a) comprises positioning the terminal sensing electrode adjacent to the liquid of interest without contacting the flexible substrate with the liquid of interest.

25. The method of claim 20, wherein the placing of step a) comprises wrapping the flexible substrate around a section of tubing, such that at least a portion of the terminal sensing electrode is adjacent to the tubing, wherein the liquid of interest if located within the tubing.

26. The method of claim 25, wherein the tubing has a thickness of between 50 pm and 50 mm, including but not limited to, at least 50 pm, at least 100 pm, or at least 500 pm, and at most 50 mm, at most 5 mm, or at most 3 mm.

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