RADIOFREQUENCY RESONANT CIRCUIT SENSING DEVICE, METHOD OF ITS PRODUCTION, AND USES

Abstract: A radiofrequency resonant circuit sensing device, a method of its production, an apparatus and sensing device comprising it; and its use for the detection of fluid levels, empty containers, and leak of fluids from containers and bodies containing said fluids; e.g. for monitoring collection of drain of fluid from a human or for monitoring leak of fluid from a human suffering from urinary and/or faecal incontinence.

Description: RADIOFREQUENCY RESONANT CIRCUIT SENSING DEVICE, METHOD OF ITS PRODUCTION, AND USES DESCRIPTION 1. BACKGROUND OF THE INVENTION The present invention relates to a radiofrequency resonant circuit sensing device, a method of its production, and use thereof for a fluid sensing device for detecting a fluid in an article or a container; for containing a fluid, in particular a human or animal body fluid; and use thereof for radiofrequency resonant circuit tags in detection of theft of articles for sale. The Technical Field Generally, radiofrequency resonant circuit devices comprise layered structures of electrically conducting means comprising inductive and capacitive elements, and electrically insulating means separating the electrically conductive layers which are electrically connected through separate perforations of the electrically insulating layers. Prior art radiofrequency resonant circuit devices include conductive paths that are etched out of various strong metal foils which are laminated on both sides of a flexible insulating carrier foil. Conductive connections are established by through-contacts through the foil which is a rather time consuming process. Further, through-contacts cannot be imprinted because this would damage the layers. Through-contacts may be avoided by using conductive paths divided into at least two parts electrically connected and applied to one side of the insulating carrier foil so that the two parts of the conductive paths can be brought to overlap by folding with carrier foil therebetween, thereby providing a capacitive element. One-sided conductive paths on carrier foils can be mass- produced by methods known in the art thereby facilitating cheap production of single-use radiofrequency resonant circuit devices. However, the variability of degree of overlap m the folding process introduces variability m the values of especially the capacitive element of the resonant circuit, thereby deceasing the reliability of the device m some applications. Variability of the capacitive element may be important in applications of radiofrequency resonant circuit devices for sensing external parameters affecting the function of the resonant circuit. One such application is detection or deactivation of the resonant circuit by the presence of a fluid such as humidity or a body fluid from a human or an animal. Generally detection of a fluid, e.g. for detecting the level of a fluid m a container or for detecting a leak of fluid from a body such as a container or a human or animal body discharging said fluid comprises production of a sensor signal of the fluid and detection of the produced sensor signal by appropriate detection electronics . In applications of e.g. detecting levels or leaks of stationary oil containers, or detecting leak of body fluids from patients or elderly confined to a " bed, the sensor of the fluid and the detection electronics are typically interconnected by electrically conducting connectors e.g. wires or cables, or by optical wave guides such as optical fibres. However, such connections can be sensitive to damage and for patients or elderly confined to a bed they can be very inconvenient and put severe constraints on their movability. Particularly for patients or elderly who are able to walk around, such sensor-detector connections cannot be used without restricting their movability. Since lack of movability of patients and elderly requires an increased level of monitoring of e.g. wounds and urinary and faecal incontinence by personnel, such a monitoring often being considered inconvenient and cumbersome, sensor-detector connections of monitoring devices implicitly contribute to bad sanitary conditions for patients and elderly and contaminated environments of wound healing sections, incontinence sections and the like of hospitals and nursery homes. Wireless sensor-detector connection based on suitable receiver/transmitter electronics at the sensor and detection electronics can be contemplated. However, in order to function, such electronics requires a portable power supply such as an electric battery. This is impractical because of the necessary exchange or recharge of discharged batteries. Consequently there is a need for wireless connection of fluid sensor and detection electronics which does not require portable power supply as well as sensors suited for sensing exposure of a fluid without requiring external power supply. Such sensors should be reliable m use and easy to mass- produce, particularly when such sensors are based on radiofrequency resonant circuit devices, these should be reliable and cheap. The term "wireless sensor-detector connection" is intended to mean that the connection between the sensor and detector is operated with or actuated by electromagnetic waves. Specific ranges of electromagnetic waves include radiowaves or microwaves, m particular radiowaves . Prior Art Disclosures US 4,792,790 discloses a tag-like strip affixable to an article comprising a flexible, non-conductive substrate, at least one inductive element formed from a planar conductive path, a capacitive element formed from superimposed conductive path parts, and a dielectric interposed therebetween, the conductive paths being arranged m at least two surfaces which are superimposed by folding the substrate together forming a closed resonant circuit with the inductive element; said folded substrate avoiding contacts between conductive paths to be pressed through an insulating foil therebetween as m prior art layered structures of resonant circuits. US 5,291,180 discloses similar LC structures of flexible msulative layers folded back on itself and having on one surface an electrically conductive layer forming multi- turn spirals m a counter turning relationship m a like folded superposition. US 6,031,458 discloses a polymeric radio frequency resonant tag and method of its manufacture for use m detection of theft of articles for sale, said tag comprising a substrate, and first and second conductive pattern layers based on a polymeric binder and connected to form an inductive element and further connected to first and second capacitor electrodes having a dielectric film therembetween; said layers being sequentially applied, cross-linked and bonded together and adhered onto the substrate. The conductive pattern layers are applied using screen-printing with conductive printable ink. The dielectric film is screen-printed using e.g. a UV curable dielectric medium. The first and second conductive layers are connected through contacts via perforations m the dielectric film, specifically provided by impressing a dowel at the point of connection . US Patent No. 4 646 066 discloses an indicator device and method of measuring incremental environmental exposure of an environmental parameter; said method comprising measuring responses of a target to an electromagnetic interrogation signal; said target including a tuned circuit and an element that is sensitive to environmental exposure, especially exposure to specified fluids e.g. liquids and water vapour, influencing the electronic or ionic conductivity. There is no teaching of parameter influences including the capacitance of the tuned circuit, nor of a measuring method based on changes of transmission of electromagnetic energy of oscillators transmitting electromagnetic energy to the tuned circuits . 2. DISCLOSURE OF THE INVENTION Object of the Invention It is an ob ect of the present invention to provide a radiofrequency resonant circuit device which avoids through-contacts through insulting layers between conductive layers. Further, it is the object to provide such a device which can be produced by mass production with high reproducibility of the parameters of the resonant circuit, m particular the capacitance of the capacitive element. It is another object of the present invention to provide a method and apparatus for detecting a fluid without using any physical connection between a sensor of the fluid and an electronic detection system therefore and without requiring a portable power supply for the fluid sensor . It is another object of the present invention to provide a method and apparatus for detecting the level of a fluid m a container, m particular the level of a human body fluid collected in a container; or for detecting the level of an infusion liquid m a container, m particular the level of an infusion liquid m a plastic bag, e.g. of soft plastic that collapses during emptying thereof. It is another object of the present invention to provide a method and apparatus for detecting a body fluid from a human or animal body, m particular a leak of body fluid from a human suffering from e.g. urinary and/or faecal incontinence, a human or animal undergoing surgery requiring a drain of body fluid, or a human or animal having e.g. a bleeding wound. Further objects will be apparent from the description. Solution According to the Invention In an aspect of the present invention there is provided a radiofrequency resonant circuit sensing device comprising (a) a substrate having a surface; (b) a layered structure comprising: (i) at least one first electrically conducting means comprising an inductance (L) ; (ii) at least one second electrically conducting means; and (iii) at least one electrically insulating means which separates at least a part of said first electrically conducting means from said second electrically conducting means; either of said at least one first or second electrically conducting means being positioned on said substrate; the first and second electrically conducting means and the electrically insulating means being electrically connected to form a resonant circuit (LC) ; wherein parts of the at least first and second electrically conducting means provide the electrodes of at least one capacitance (C) , and parts of said first and second electrically conducting means provide at least one connection between the first and second electrically conducting means, and a sensing means for sensing a change of resonance conditions of the resonant circuit, whereby the feature of providing at least one connection between the first and second electrically conducting means ensures that through-contacts through the electrically insulating means can be avoided. In a preferred embodiment the at least one connection between the first and second electrically conducting means is constituted by contact between parts of said first and second electrically conducting means, whereby it is obtained that connections of first and second electrically conducting means can be realized by contacting the two. In a preferred embodiment the first and second electrically conducting means comprises a material selected from the group consisting of electrical conducting polymers, paints or inks, whereby particularly cost-effective mass-production of resonant circuits can be obtained using printing techniques such as screen-printing. In particular for applications where a large inductance value is required under conditions of small dimensions, more layers of resonant circuits can be provided. Accordingly, m a preferred embodiment, the device further comprises more layered structures comprising more at least one first and second electrically conducting means and more at least one electrically insulating means; parts of said more first and second electrically conducting means providing contacting each other for providing at least one connection therebetween. Generally, the sensing means for sensing a change of resonance conditions of the resonant circuit comprises any of the parameters inductance, capacitance, and resistance, or a combination thereof. In a preferred embodiment the at least one first electrically conducting means comprises an inductive element having a coil with separated windings for receiving a fluid, whereby the fluid may short cut the windings and change the resonance conditions. In order to further improve the ability of the resonant circuit sensing device to sense a fluid, either the inductive element, the capacitive element, the substrate, or a combination of these can be made particular attractive to the fluid, e.g. by coating thereof with a hydrophilic material. In a preferred embodiment the substrate is attractive to said fluid, whereby m an embodiment of the resonant circuit having the induction element positioned on the substrate, the windings of the coil are more likely to get into contact with the fluid. If the fluid is water or urine, it may short cut the windings and deactivate the resonant circuit . Accordingly, m a preferred embodiment, the resonant circuit is deactivated by presence of a fluid. Some applications do not allow the influence of a fluid, e.g. water, which could produce unintended signals, e.g. in theft security systems. Accordingly, m a preferred embodiment, the layered structure is coated with a fluid protection layer, m particular a water repellent layer. In many applications, it is desired to be able to deactivate the resonant circuit, e.g. to authorize release of articles of sale, whereby the deactivated resonant circuit is allowed to pass the electromagnetic detection field without triggering an alarm. For this purpose it is known to include a fuse m series in the resonant circuit. Accordingly, m a preferred embodiment, the resonant circuit further comprises a fuse. In another aspect of the invention there is provided a method of providing a resonant circuit sensing device comprising (a) providing a substrate having a surface; (b) providing a layered structure comprising: (I) at least one first electrically conducting means comprising an inductance (L) ; (n) at least one second electrically conducting means; and in) at least one electrically insulating means which separates at least a part of said first electrically conducting means from said second electrically conducting means; either of said at least one first or second electrically conducting means being positioned on said substrate; the first and second electrically conducting means and the electrically insulating means being electrically connected to form a resonant circuit (LC) ; wherein parts of the at least first and second electrically conducting means are provided with electrodes of at least one capacitance (C) , and (c) bringing parts of said first and second electrically conducting means to provide at least one connection between the first and second electrically conducting means, whereby a very cost-effective method of mass-production of resonant circuits allowing use of printing techniques such as screen-printing is provided. According to the invention it surprisingly turns out that electrically conducting connectors between cheap, mass produced sensing devices of fluid and the detection electronics, and battery power supply of the sensor, and receiver circuits for receiving and detecting responses of resonant circuits of the sensors can be avoided. This provides a number of advantages e.g. that the sensor of the fluid can be separated from the detection electronics for detecting changes in the sensor. This is particularly advantageous when monitoring bodies containing fluid wherein the sensor and the detection electronics used cannot be connected permanently by electrically conducting connectors, or when they ' can only be connected by such connectors with great difficulties or inconveniences. Also, the oscillators and detection electronics can be simplified. , Uses of the resonant circuit sensing device for detecting a fluid" Accordingly, m still another aspect according to the invention there is provided uses of the method or the apparatus as claimed for detection of fluid level m one or more containers, m particular incontinence containers, specifically diapers; and use for detecting whether a container containing a fluid has been emptied for the fluid m particular emptying of an infusion containing use for monitoring leak of fluid from a container, or a human or animal body, m particular from a human suffering from urinary and/or faecal incontinence; whereby the health care personnel can monitor the hygienic condition of e.g. a diaper. When a body leak has been detected proper care of e.g. changing the diaper can then be taken. w Sensing devices of a fluid" Still another aspect of the present invention relates to sensors usable for such methods and apparatus m sensing a fluid, more specifically it relates to sensing devices comprising resonant circuits which are responsive to parameters that are able to influence the impedance thereof, e.g. responsive to a fluid. "Articles comprising the sensing device" In another aspect of the present invention there is provided an article comprising the sensing device. Preferred articles include, but are not limited to, articles for containing or for taking up fluid or for delivering fluid; such container e.g. being monitored for being filled or being emptied. In a preferred embodiment, the article consists of a hygienic article for healthy development and maintenance of health. In a particularly preferred embodiment, the article consists of an absorbent or a bandage m form of a wrap or a trapping used to protect, cover or immobilise an injured or diseased part of a human or an animal, or used during surgery. In a particularly preferred embodiment, the article consists of an absorbent for urine or faeces, m particular a diaper. λ, Use of articles comprising the sensing device" Articles comprising a sensing device according to the present invention are preferably used m a method of monitoring hygienic conditions of one or more patients; said method comprising applying one or more hygienic articles according to the invention to one or more patients, each article having a sensing device with a resonant circuit that differ from each other; and transmitting electromagnetic energy to said resonant circuits. In an embodiment, the method further comprises monitoring at least one response of said resonant circuits, thereby allowing the prior art techniques of interrogating the resonant circuit to be used. In a preferred embodiment, the method further comprises monitoring changes of the transmission of electromagnetic energy of one or more oscillators transmitting electromagnetic energy to said resonant circuits, thereby obtaining the advantages of the method according to the present invention. Further advantages will be apparent from the detailed description. Sensing Devices In its broadest aspect, the sensing device according to the present invention does not necessarily depend on the method of detecting changes of one or more characteristics of the resonant circuit, i.e. for example by detecting the change of the transmission of electromagnetic energy of the oscillators according to the invention, or by detecting a response of the resonant circuit according to prior art methods. However, the specific resonant circuit used typically depends on the parameter to be detected, e.g. a fluid. Known methods include those referenced in US 4 646 066, e.g. US 4 321 586. According to the aspect of the invention relating to detecting a fluid, a resonant circuit has one or more characteristics which change by contact between the resonant circuit and a fluid. In a preferred embodiment of both aspects, the characteristics comprise resistance, capacity, inductance, or any derivative thereof. By contact of the resonant circuit with the fluid, one or more of the characteristics resistance R, capacitance C and inductance L, or any derivative thereof, e.g. the resonance frequency co=(LC) _1~ , or higher harmonics thereof, or the quality factor Q=ωL/R, e.g. at resonance ω=ω , change . When one or more of the characteristics change, the ability of the resonant circuit to receive electromagnetic energy changes. This can be detected by detecting changes in one or more characteristics of one or more oscillators transmitting electromagnetic energy to said resonant circuit. Generally, sensing devices can be manufactured m any suitable way that allow the external parameters to affect the impedance of the respective resonant circuits. In the particular aspect of the invention relating to detecting a fluid, resonant circuits can be prepared m any suitable way that ensures the penetration of fluid into the resonant circuit to such an extent that one or more of its characteristics are changed. In the particular aspect of the method of detecting a fluid, the change of characteristics of the resonant circuit causes a detectable change m one or more of the characteristics of the one or more oscillators. In a preferred embodiment, the resonant circuit consists of a coil having separated windings which can receive the fluid and short cut the circuit. The windings can be of any suitable material. In a preferred embodiment, the windings are made of an electrically conducting material selected from the group consisting of metals such as aluminium, copper, tin; an electrically conducting polymer such as polyanilme; and an electrically conducting polymer blend such as poly(p- phenylene vmylene) , polyacryla ide, polyanilme and polyethylene, or electrically conducting silicone, or combinations of these. Specifically useful electric conducting polymers include a flexible, crease resistant, one component, carbon filled ink and coating sold by Emerson & Cummg Speciality Polymers under the trademark Amicon C 932-74. Another useful electric conducting polymer is a highly flexible, crease resistant, one component, silver filled, ink and coating sold by Wacker-Chemie under the trademark Elastosil N 189. Both products are environmentally acceptable . In the particularly aspect of detecting temperature changes, the resonant circuits can be prepared m any suitable way that ensures the influence of different temperatures to affect the impedance of the resonant circuit to such an extent that one or more of its characteristics are changed. In the particular aspect of the method of detecting a temperature change, the change of the characteristics of the resonant circuit causes a detectable change one or more of the characteristics of the one or more oscillators . The fluid sensing device can be placed any suitable position to detect the desired fluid. In preferred embodiments, the fluid sensing device is contained m or attached onto a container; or it is embedded a diaper; or it is embedded a carrier with an adhesive, such as a sticker, to be attached on a desired location, e.g. onto said container or diaper. Several resonant circuits can be positioned one location to encode for given patterns of frequencies, e.g. several small resonant circuits of e.g. different frequencies placed m a diaper can provide a unique identification of e.g. individual patients or elderly being monitored m a hospital or a nursing home. In a particular aspect the present invention relates to a sensing device for sensing a fluid as claimed claim 46 that can be mass produced by a printing process or a dispensing process. A sensing device according to the invention has a number of advantages. It can be produced by an application process such as a printing process or a dispensing process comprising a series of steps providing a layered structure of the first electrical conducting means, the electrical insulating means, and the second electrical conducting means. Printing or dispensing of suitable electrical conducting materials and electrical insulating materials, respectively, allows very fast and easily controllable production processes to be used. A particular advantage is obtained, compared to prior art productions techniques of prior art resonant circuits using e.g. copper or tin as the electrical conducting means, in that a flexible resonant circuit can be produced. This is important for many applications wherein the resonant circuit is to be applied on or embedded m a carrier, e.g. a diaper, which can be bent and possible folded. -, « Further, sensing devices according to the present invention are advantageous that environmentally acceptable materials and/or smaller amounts can be used thereby avoiding discharging used sensing devices including e.g. copper to the environment. Thus, by selecting a suitable flexible substrate of a material such as paper, textile, woven, non-woven, suitable polymer, plastics, and a flexible electrical conducting polymer for the first and second electrical conducting means, which polymer can be the same or different for the two conducting means, and a suitable flexible insulating material such as polyurethane lacquer for the insulating means, flexible resonant circuits can be provided. A suitable porous material allowing penetration of humidity and/or liquids is Tyvek© supplied by DuPont . In a preferred embodiment, the first and second electrical conducting means is composed of a material selected from the group consisting of electrical conducting polymers such as electrical conducting silicones . The electrical insulating means is composed of any suitable material for providing electrical insulation. In a preferred embodiment the electrical insulating means consists of polyurethane laquer. Consequently, m still a further aspect the present invention relates to a method of producing a sensing device . In a preferred embodiment, the application process involves applying the suitable electrical insulating material onto the first electrical conducting means covering all or parts thereof, e.g. leaving parts for connecting points and areas to be exposed to the fluid during operation of the sensing device uncovered. In a preferred embodiment, the application process is a printing process such as stencil printing and/or a dispensing process. The term "'dispensing" is intended to mean that a material, here a suitable electrical conducting material or a suitable insulating material which as dispensable, is applied to a substrate material by a suitable application means, including but not limited to application of a continuous fluid of the material, and application of droplets of the material by spraying. Oscillators According to the invention an oscillator operates m functional proximity of a resonant circuit. In the present context the expression * functional proximity of a resonant circuit" is intended to mean that an oscillator one location radiates electromagnetic energy, e.g. m form of radiowaves or microwaves, which can be fully or partly transferred to a resonant circuit another location. Generally, any suitable oscillator can be used, i.e. an oscillator which is able to produce electromagnetic oscillations and to emit electromagnetic energy e.g. m form of radiowaves or microwaves which is fully or partly received by the resonant circuit. It should be understood that more than one oscillator can operate functional proximity of said resonant circuits e.g. if more oscillators operates at different frequency ranges, and if changes m different characteristics of the resonant circuit are to be detected. Generally, an oscillator comprises a generator which generates a high frequency signal of radiant energy e.g. an ac current or voltage, or an impulse, of a frequency around that of the resonant circuit. Generators can be any suitable generator known the art, e.g. radio frequency signal generators. In a preferred embodiment, the oscillator comprises a generator generating a signal of electromagnetic energy of a frequency comprising that of the resonant circuit. An oscillator comprises one or more inductors. The inductors can be internal or external to a cabinet housing the oscillator. Preferably there is one or more inductors for each different band of operation for each resonant circuit. Preferably more inductors can be interchanged either manually or automatically. The inductors can be of any suitable form. In a preferred embodiment the inductors are external inductors m form coils . Functional proximity between the oscillators and the resonant circuits can be achieved in any suitable way. In a preferred embodiment, the inductors are external inductors m form of coils which surrounds the resonant circuit. In a particularly preferred embodiment, the coils are embedded a bed for monitoring leak of body fluids of a human. In another preferred embodiment, the oscillators comprise one or more antennas whereby the direction of the electromagnetic radiation, e.g. radio waves, can be more accurately defined. An antenna can be any suitable antenna known in the art, e.g. a dipole. In a preferred embodiment, the antenna comprises a radiator element, transmission lines, and optional transformers, coupled to the inductor, or constituting a part of the inductor. Detectors The apparatus further comprises one or more detectors for detecting one or more changes m one or more characteristics of said oscillators upon changes m the characteristics of one or more resonant circuits. The characteristics of the oscillators comprise any suitable characteristic. In a preferred embodiment the characteristics of the oscillator comprise current, voltage, or a derivative thereof such as power, whereby one or more characteristics, or derivatives thereof, of the resonant circuit are detected, e.g. change frequency, particularly the resonance frequency; change m quality factor; and wholly or partial suppression or restoration of any of these. In a preferred embodiment one or more of the detectors detect an increase or a decrease of energy loss of one or more of the oscillators. Further, preferred embodiments of the invention and uses appear from the following detailed description and claims. 3. BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention is further disclosed with detailed description of preferred embodiments, reference being made to the drawings in which FIGS. 1A and IB show a preferred embodiment of a sensing device according to the invention for sensing a fluid; FIGS. 2A-2C and 3A-3C show a preferred embodiment of a method for the production of a sensing device according to the invention; FIGS. 4A-4C show another preferred embodiment of a method of producing another sensing device according to the invention; FIGS. 5A-5C show applications of the sensing device shown FIG. 1 where fluid droplets affects the resonant circuit without penetrating the electrical conducting means (FIG. 5A) , or with penetration thereof (FIG. 5B) ; FIGS. 7A-7C and FIGS. 8A-8C are similar to FIGS. 2A-2C and FIGS. 3A-3C; FIGS. 9A and 9B show adjustment of the position of first and second flat extended conductors; FIGS. 10A and 10B illustrate diaper production; FIG. 11 illustrates production of resonant circuits using single step application; FIGS. 12A and 12B and FIGS. 13A and 13B show a resonant circuit sensor coated partly with a fluid protective layer; FIGS. 14, 15, and 16A and 16B show different embodiments of applications of the resonant circuit; and FIGS. 17A and 17B and FIGS. 18A and 18B show applications of the resonant circuit inside and outside a collection bag and an infusion bag, respectively. 4. DETAILED DESCRIPTION Embodiment of sensing devices according to the invention FIGS. 1A and IB show a preferred embodiment of a sensing device for sensing a fluid according to the invention. It comprises a substrate having a surface, here exemplified by a flexible material 10 such as paper, textile, plastic, etc. m the form of e.g. a sheet or a foil. On its surface opposite to the layered structure, or on any other suitable position, the substrate can have an adhesive layer whereby the sensing device can be adhered to the surface of e.g. a diaper, like a sticker, a label or a tag. At least one first electrical conducting means comprising an inductance (L) , here exemplified by a winding or a coil 12 of a conducting polymer such as an electrical conducting silicone of Wacker Silicones e.g. Semicosil 970 from Wacker-Chemie, and typically m form of a flat winding but not limited thereto, which inductance is positioned on the substrate surface, and parts thereof 11, here exemplified by a first extended conductor which provides a first electrode of at least one capacitance (C) and parts thereof, here a connecting point " 15 which provides a connection to at least one second electrical conducting means, here exemplified by a second flat extended conductor 13 which provides a second electrode of said at least one capacitance and a flat connecting conductor extending from the second flat extended conductor to the connecting point. At least one electrical insulating means, here an electrical insulating layer 14, separates at least a part of said first conducting means from said second conducting means, here the flat extended conductor and the flat connecting conductor are insulated from the windings and the first extended conductor. The first and second electrical conducting means and the electrical insulating means are electrically connected to form a resonant circuit, the equivalence diagramme (LC) of which is shown m FIGS. 1A and IB. It should be understood that a resonant circuit of a physical sensing device deviates from the idealized equivalence diagramme of FIG. 1, mainly due to loss factors, such as resistive losses m the leads, energy lost from the circuit by radiation etc. Therefore, the actual performance of the circuit is more closely approximated by including a resistor m the LC equivalence diagramme (not shown m FIG. 1) . Also, a dedicated resistor may be included in the circuit order to modify the circuit performance m a particular fashion. The resistor, whether it is merely a representation of loss factors of it signifies a combination of loss factors together with one or more dedicated resistors, may be coupled m parallel, or series, or both, with the other components of the resonant circuit. Determining suitable values of the components in the equivalence diagramme and " of the resistor is considered to lie within the capabilities of those skilled the art. It should be noted that the term "being positioned on the surface of said substrate" is intended to include any such positioning wherein the material of the at least one first or second electrical conducting means penetrates wholly or partly into the substrate. Principle of Design The method of manufacturing a response circuit provided by the present invention enables an extensive range of options of size and arrangement of device. The invention allows a range of printing techniques to be applied the method including continuously rotating printing methods for printing the conductive and dielectric patterns . Generally, there is no requirement for a separate mechanical or other process for making the connection between the individual conductive layers. The design enables the printing process itself to connect the two conductive layers at the required position. The design minimizes the size of the capacitor dielectric which is only printed where layers need to be separated. Many conductive layers may be printed on top of each other using simple printing techniques without recourse to secondary processes for completing the device. FIGS. 2A-2C and 3A-3C show a preferred embodiment of a method for the production of a sensing device according to the invention. FIGS. 2A-2C illustrates three consecutive steps of application of the at least one first electrical conducting means 11, 12, 15 (FIG. 3A) , the at least one second electrical conducting means 13, 15 (FIG. 3C) and the at least one electrical insulating means 14 (FIG. 3B) , here exemplified by a printing process. The respective layers are shown in FIGS. 3A-3C. FIG. 3A shows the first conductive pattern to be printed. Item 11 is the first layer of the capacitor, item 12 is the coil and position 15 is the location for the contact to the second layer of the capacitor. This same location would be used for contact to any subsequent layers of the conductive patterns. In this instance, this location is positioned outside of the coil. FIG. 3C shows the second conductive layer of capacitor, item 13, printed on top of the dielectric mask. This second layer makes the connection for each side of the capacitor at location 15. This procedure may be repeated providing as many layers as necessary. FIGS. 4A, 4B and 4C illustrate a variation providing a response circuit with a double capacitor and coil combination. This variation has the connection between the conductive patterns located both inside and within the coil at locations 15A and 15B. The two capacitors are formed from conductive areas 11A and B, dielectric masks 14A and B and conductive layers 13A and B. FIGS. 4A-4C show another preferred embodiment of the method of producing a sensing device according to the invention wherem it is illustrated that more complex resonant circuits, e.g. including two capacitances Ci and C_, can be provided. The substrate is not shown. The first electrical conducting means includes two extended conductors 11A, 11B, and two connecting points 15A, 15B (FIG. 4A) . The two extended conductors are then covered by respective electrical insulating layers 14A, 14B (FIG. 4B) . Finally, the second electrical conducting means in form of two extended conductors 13A, 13B are applied on the electrical insulating layers. Examples of suitable application apparatus to be used in carrying out the method of producing a sensing device according to the invention are screen printers and stencil printers from e.g. EKRA, Eduard kraft GmbH Maschinen Fabrik, Bόnnigheim, Germany. Specific apparatus can be mentioned e.g. El™ Semi-automative Screen Printer and M2™ Semi-automatic Thick-Film Screen Printer, the latter being particularly suited for printing of solder pastes, through-hole coating using vacuum techniques, and multilayer systems. Further suitable apparatus are dispensing apparatus from e.g. Asymtek. FIGS. 5A-5C show an application of the sensing device wherein fluid droplets affects the resonant circuit without penetrating therethrough (FIG. 5A) , and with penetration (FIG. 5B) . FIG. 5C provides a top view. FIGS. 6-8 illustrate that more resonant circuits can be produced in parallel. FIGS. 7A-7C and 8A-8C are similar to FIGS. 2A-2C and 3A- 3C. FIGS. 6A-6C illustrate production of resonant circuits 13 in parallel process lines on a single continuous foil 10. In FIG. 6C, there is illustrated means to assist m controlling the printing process, here illustrated by an antenna 61 positioned above a resonant circuit 13 and connected to a control unit 62. The control unit 62 feeds control signal to the application apparatus the various process steps for adjusting e.g. the speed of the foil, amounts and speed of applied layers, based on the measured quantities of the resonant circuit. General control test parameters include the frequency of the resonant circuit, but other parameters such as the Q- value or frequency dependent impedance can be contemplated for use m control purposes. FIGS. 9A and 9B illustrate the adjustment of the position of the first and second electrically connecting means, here the first 11 and second 13 flat extended conductors providing electrodes of the capacitive element and the connecting point 15 are moved with respect to each other. In FIG. 9A, the two electrodes fully overlap whereas they are displaced with respect to each other m FIG. 9B . The control parameter measured for controlling this type of adjustment typically includes the capacitance of the resonant circuit, e.g. measured by the Q-value, because the degree of overlap of the capacitor electrodes is changed significantly. FIGS. 10A and 10B illustrate diaper production wherem several parallel resonant circuits 13 on separate foils 10, they could also be positioned on the same foil, are fed from a drum A and laminate on both sides by diaper compatible materials fed from drums B and C and controlled by compression rollers D. The actual diaper produced may include other materials not shoVn, e.g. water absorbents and water repellent front cover foils. At E, individual sections are punched out. In another application, the same set up can be used to produce resonant circuit tags for theft security of sales products, such products the resonant circuit is usually laminated with water repellent foils. FIG. 10B illustrates perforations 101 m the foil 10 for controlling the movement thereof. FIG. 11 illustrates the production of resonant circuits using a single step application apparatus 112 of pairs of resonant circuits B,C according to the invention wherem the conductive layers, here connecting points 11, are brought into contact with each other by folding the substrate about the folding line A by means of folding guide 110. Between the parts to be folded against each other there is inserted an insulating intermediate layer 111. An antenna 61 and control unit 62 are positioned of the folding step and function to control the folding process m providing the desired contact between the two conductors. In an embodiment, curement of the conductive UV-curable layers is obtained by UV-irradiation of the folded foil with the connecting points of the conductive paths m contact thereby providing fixed contacts. In another embodiment, not shown, the connecting point 11 is placed closer to the folding line thereby providing a hinge-type contact which is useful m applications where the intermediate layer is constituted by available capacitive element e.g. a plastic bag. The hinge-type resonant circuit is able to sense whether the bag has a content or not or the bag is being filled or emptied. FIGS. 12A and 12B and FIGS. 13A and 13B illustrate means to modify the sensitivity to a fluid of the resonant circuit sensor by coating with a fluid protective layer 120. In FIG. 12A, the protective layer covers fully the one side of the resonant circuit and covers partially the other side. In FIG. 13A, only one side is covered. In another embodiment, the fluid protective layer can be a fluid attracting layer to enhance the sensitivity to fluids . FIGS. 14, 15, and 16A and 16B show different embodiments of applications of the resonant circuit, m particular for a sensing device according to the present invention. FIG. 14 shows a resonant circuit 11 embedded a diaper or bandage 60 able to absorb the fluid, e.g. urine or a body fluid, e.g. blood from a wound, by an absorbing material 61. FIG. 15 shows a laminated resonant circuit 11 having the resonant circuit 11 embedded between two materials 71, 72 or which one 71 is compatible with human skin and allows humidity and body fluid to penetrate. The laminated circuit can be applied directly on the skin wholly or partly covering a bleeding wound 73. It can be fixed to the skin either by means of a plaster or a tape 75. FIG. 16A shows an attachable resonant circuit 80 of the type shown m FIG. 15 wherem the resonant circuit is embedded between a carrier material wholly or partly covered with adhesive, e.g. a skin compatible adhesive, material 81 for affixing the resonant circuit to e.g. the skin, or a diaper, and a releasable cover material 82 covering said adhesive properties thereof before use. It should be noted that the resonant circuit can be of the laminated type, or it can be directly adhered to or incorporated m the carrier material. FIG. 16B shows several attachable resonant circuits 80 similar to that of FIG. 16A provided on an "endless" releasably cover material 81, particularly useful for fast and easy handling and application of many sensing devices, e.g. fluid, to a human body or an article, e.g. a diaper. FIGS. 17A and 17B with cross sectional views show application of a fluid sensing device, i.e. a resonant circuit 91 e.g. of the type shown m FIG. 5C or FIG. 15, contained m a container 92, e.g. a collection bag, or dram bag, for monitoring the level of the collected fluid, e.g. dram fluid 12. The characteristics of the resonant circuit are changed upon contact with the fluid, see FIG. 17B. FIGS. 18A and 18B show another application of a resonant circuit 101, e.g. of the type which can be used m combination with a hinge-type resonant circuit according to an embodiment discussed with respect to FIG. 11, attached to the outside of a container 102, e.g. an infusion bag, at the fluid level A-A for monitoring the level of a fluid 12 contained therein, when the level of the fluid sinks below the level A-A, the ability of the resonant circuit to receive electromagnetic energy from an oscillator changes because the capacitor between the serially connected coils changes as the container sides collapse against each other. This embodiment can be used to monitor infusion liquids and indicate an alarm, when the infusion bag is empty.

Claims: RADIOFREQUENCY RESONANT CIRCUIT SENSING DEVICE, METHOD OF ITS PRODUCTION, AND USES CLAIMS 1. A radiofrequency resonant circuit sensing device comprising (a) a substrate (10) having a surface; (b) a layered structure comprising: (I) at least one first electrically conducting means (11,12) comprising an inductance (L) ; (II) at least one second electrically conducting means (13) ; and (111) at least one electrically insulating means (14) which separates at least a part of said first electrically conducting means from said second electrically conducting means; either of said at least one first or second electrically conducting means being positioned on said substrate; the first and second electrically conducting means and the electrically insulating means being electrically connected to form a resonant circuit (LC) ; wherem parts (11,13) of the at least first and second electrically conducting means provide the electrodes of at least one capacitance (C) , and parts (15) of said first and second electrically conducting means provide at least one connection between the first and second electrically conducting means, and a sensing means for sensing a change of resonance conditions of the resonant circuit. 2. A device according to claim 1 wherem the at least one connection between the first and second electrically conducting means is constituted by contacts between parts (15) of said first and second electrically conducting means . 3. A device according to claims 1 or 2 wherem the first and second electrically conducting means comprises a material selected from the group consisting of electrical conducting polymers, paints or inks. 4. A device according to claims 1-3 further comprising more layered structures comprising more at least one first and second electrically conducting means and more at least one electrically insulating means; parts of said more first and second electrically conducting means providing contacts with each other for providing at least one connection therebetween. 5. A device according to claims 1-4 wherem the at least one first electrically conducting means comprises an inductive element having a coil with separated windings for receiving a fluid. 6. A device according to claims 1-5 wherein the substrate is attractive to said fluid. 7. A device according to claims 1-6 wherem the layered structure is coated with a fluid protection layer. 8. A device according to claims 1-7 wherein the resonant circuit is deactivated by presence of a fluid. 9. A device according to claims 1-8 wherein the resonant circuit further comprises a fuse. 10. A method of producing a resonant circuit sensing device comprising (a) providing a substrate (10) having a surface; (b) providing a layered structure comprising: (i) at least one first electrically conducting means (11,12) comprising an inductance (L) ; (ii) at least one second electrically conducting means (13) ; and (iii) at least one electrically insulating means (14) which separates at least a part of said first electrically conducting means from said second electrically conducting means; either of said at least one first or second electrically conducting means being positioned on said substrate; the first and second electrically conducting means and the electrically insulating means being electrically connected to form a resonant circuit (LC) ; wherem parts (11,13) of the at least first and second electrically conducting means are provided with electrodes of at least one capacitance (C) , and (c) bringing parts (15) of said first and second electrically conducting means to provide at least one connection between the first and second electrically conducting means. 11. A method according to claim 10 wherem the at least one connection between the first and second electrically conducting means is established contacting parts (15) of said first and second electrically conducting means with each other. 12. A method according to claims 10 or 11 wherem the first and second electrically conducting means comprises a material selected from the group consisting of electrical conducting polymers, paints or inks. 13. A method according to claims 10-12 further comprising providing more layered structures comprising more at least one first and second electrically conducting means and more at least one electrically insulating means; contacting parts of said more first and second electrically conducting means with each other for providing at least one connection therebetween. 14. A method according to claims 10-13 wherein the layered structure is provided by printing. 15. A method according to claims 10-14 wherem the printing is controlled by monitoring resonant circuit parameters the produced resonant circuits on line and adjusting the printing process conditions to obtain desired parameters therefor. 16. An apparatus for detecting a fluid comprising: one or more oscillators (10) for transmitting electro-magnetic energy; one or more resonant circuits (11) for receiving electromagnetic energy from said oscillators; and one or more detectors for detecting changes m one or more characteristics of the one or more oscillators upon changes m characteristics of the resonant circuits by contact thereof with the fluid wherem the resonant circuit is according to claims 1-9. 17. Apparatus according to claim 16, where the one or more resonant circuits comprise coils having separated windings for receiving the fluid and short cut the circuit. 18. Apparatus according to claims 16 or 17, wherem the windings are made of an electrically conducting material selected from the group consisting of electrically conducting polymers such as polyanilme; or electrically conducting polymer blends such as blends of poly(p- phenylene vmylene) , polyacrylamide, polyanilme and polyethylene . 19. Apparatus according to claims 16-18, wherem the one or more resonant circuits are contained m or attached onto one or more containers. 20. Apparatus according to claims 16-19, wherem the one or more resonant circuits are embedded m a diaper. 21. Apparatus according to claims 16-20, wherem the one or more resonant circuits are embedded m a carrier with an adhesive such as a sticker. -, « 22. Use of an apparatus according to claims 16-21 for detecting the level of fluid m one or more containers. 23. Use as claim 22, wherem the containers comprise containers and infusion containers. 24. Use of an apparatus according to claims 16-21 for detecting whether a container containing a fluid has been emptied for the fluid or an empty container has been filled. 25. Use as claimed m claim 24, wherem the container comprises an infusion container. 26. Use of an apparatus according to claims 16-21 for monitoring a leak of fluid from a container. 27. Use of an apparatus according to claims 16-21 for monitoring a leak from or a supply of fluid to a human or animal body. 28. Use as claimed m claim 27, wherem the leak of fluid is a fluid from a human suffering from urinary and/or faecal incontinence. 29. A sensing device for sensing a fluid; said device comprising a radiofrequency resonant circuit sensing device as claimed claims 1-9. 30. A sensing device according to claim 29, wherem said resonant circuit further comprises a resistance means. 31. A sensing device according to claims 29-30, wherem said resistance means consists of a thermally responsive resistor. 32. A sensing device according to claims 29-31, wherem said capacitance is constituted by a pair of electrodes and a spacer means . 33. A sensing device according to claim 32, wherem said spacer means is a variable distance between said pair of electrodes . 34. A sensing device according to claim 33, wherem said spacer means is an absorber. 35. A sensing device according to claims 29-31, wherem said at least two parts of the substrate are brought m a mutual overlaying relationship by folding. 36. A sensing device according to claims 29-31 comprising an electromagnetic antenna. 37. A sensing device according to claim 36, wherem said inductance provides said antenna. 38. The sensing device according to claims 29-37 wherem the sensing means is constituted by said first electrical conducting means, said second electrical conducting means, said at least one capacitance, alone or m combinations thereof. 39. Device according to claims 29-37, wherem the one or more resonant circuits consist of coils having separated windings for receiving the fluid and short cut the circuit . 40. A method of producing a sensing device for sensing a fluid; said method comprising providing a sensing device as claimed in claim 30, wherem the at least one electrically conducting means is provided on or embedded m said sides of the substrate by printing m a printing process and/or by dispensing m a dispensing process. 41. A method according to claim 40, wherem the printing is affected by means of at least one set rotational impression drums. 42. A method according to claims 40-41, further comprising the step of providing a resistance means connected with said conducting means. 43. A method according to claims 40-42, further comprising the step of providing said conducting means consisting of inductance means and resistance means sequentially on or embedded m said substrate and separated by at least one insulating means. 44. A method according to claim 43, wherem said step consists m providing said induction means on or embedded m said substrate, providing said insulation means on said induction means without covering the electrodes thereof, providing said resistance means on said insulating means, and connecting said electrodes of the induction means. 45. A method according to claims 40-44, wherem said conducting means are provided on or embedded m said substrate m one operation. 46. A transmitter/receiver combination comprising a sensing device as claimed m claims 29-37, or a sensing device produced according to the method as claimed m claims 40-45. 47. An article comprising a sensing device as claimed m claims 29-37, or a sensing device produced according to the method as claimed m claims 40-45, for containing or for taking up or for delivering of fluid. 48. An article comprising a sensing device as claimed m claims 29-37, or a sensing device produced according to the method as claimed m claims 40-45, for healthy development and maintenance of health. 49. An article according to claim 48 consisting of an absorbent or a bandage m form of a wrap or a trapping used to protect, cover or immobilise an injured or diseased part of a human or an animal, or used during surgery. 50. An article according to claim 48 consisting of an absorbent for urine or faeces, m particular a diaper. 51. A method of monitoring hygienic conditions of one or more patients; said method comprising applying one or more articles according to claims 47-50 to one or more patients, each article having a sensing device with a resonant circuit which differs from those of the other articles; and transmitting electromagnetic energy to said resonant circuits. 52. A method according to claim 51, further comprising monitoring at least one response of said resonant circuits . 53. A method according to claims 51 or 52, further comprising monitoring changes of the transmission of electromagnetic energy of one or more oscillators transmitting electromagnetic energy to said resonant circuits . 54. Use of a radiofrequency resonant circuit sensing device for acting in detection of theft of articles for sale .

Inventors: BENSEN BENT THORNING, BENSEN, BENT, THORNING
Applicants: BENSEN BENT THORNING, BENT THORNING BENSEN AS, BENSEN, BENT, THORNING, BENT THORNING BENSEN A/S
Application year: 2000
Main classification: G08B13
IPC codes: A61F5, A61F13, G01F23, G08B13