Patent Publication Number: US-11029267-B2

Title: Method and a system for XRF marking and reading XRF marks of electronic systems

Description:
BACKGROUND AND GENERAL DESCRIPTION 
     The present invention is in the field of X-Ray Fluorescence (XRF) and particularly relates to XRF marking of electronic systems. 
     The present invention provides a novel technique for marking complementary (compatible) components of a composite system, such as an electronic system, by a unified marking/coding system/scheme (which is also referred to herein as One Board One code (OBOC) coding system/scheme. 
     More specifically the present invention provides for utilizing/employing elemental Id embedded in elemental (physical markings of components of electronic system) for providing brand protection and/or authentication of customized electronics, and/or providing liability of electronic components in medical devices (and in particular in wearable medical devices), and/or providing bridge liability for the coupling between virtual services or products and physical operational systems (for example the coupling between personal data and a smart clothing). 
     In various embodiments of the present invention the composite electronic system may be any system including an integrated circuit with plurality of components such as circuit boards (e.g. printed circuit boards (PCB) and/or flexible circuits), as well as electronic components to be electronically coupled/mounted on the circuit boards, such as processors and/or controllers and/or other chips and transistors of the circuit, data input/output/communication elements (e.g. RF and/or antenna modules), sensor modules (such as inertial sensors, camera, microphone as well as other sensors such as temperature and/or pressure and/or magnetic field sensors), user interface modules (e.g. screen, key-pad) and/or other electronic component of the composite electronic system which it to be electronically connected to the other components of the system (e.g. via the circuit board). Alternatively or additionally the composite system may be an electronic chip where one component thereof being the integrated circuit die of the chip and the second component may the packaging of the system (of the chip) in which the die is encapsulated. Yet alternatively or additionally the composite electronic system may be for example a distributed system including one or more separate components (which may be in this case separate devices) which are configured and operable together to carry out the operation of the composite system. For instance the composite electronic system may include an electronic system (e.g. an electronic control system), such as a health monitoring/treatment controller device and a complementary smart wearable product device (smart garment) connectable to the health monitoring/treatment controller, whereby the health controller device may be adapted for monitoring a condition of a user (e.g. by utilizing suitable sensors associated/connected thereto, and the smart wearable product may be configured to be responsive to signals from the health controller device for providing treatment to the user for example by releasing certain materials to the user&#39;s skin and/or applying pressure to one or more body parts of the user. Alternatively or additionally, the smart wearable device may be serving as the sensor measuring measurable health parameter of the user (e.g. measuring temperature and/or blood pressure and/or sweating rate and/or any other measurable health parameter of the user), and the health controller device may be responsive to signal from the smart wearable device and configured and operable for initiating the provision of treatment to the user, e.g. by issuing suitable alerts (via communication with the user and/or to other entities) and/or operating other treatment provider modules (such as cardiac pacemaker, insulin injector and/or other treatment provider modules). 
     In general the composite electronic system may include any number of complementary (compatible) components, where all or some of which may be marked with the OBOC coding scheme of the present invention. However for the sake of clarity and without limiting the scope of the invention, in the following description often discussed and exemplified are only two, first and second, complementary (compatible) components of the system, which are marked by the OBOC scheme of the present invention. 
     According to the OBOC marking technique of the present invention, at least two complementary/compatible components of the composite electronic system are marked by respective XRF identifiable marking compositions, which are coded to respectively carry/encode complementary XRF signatures, which may be similar- and/or matching- and/or corresponding-XRF signatures that are readable by XRF techniques. The first and second complementary/compatible components, which are marked by the XRF markings of complementary (similar/matching/corresponding) signatures, may for example include: (i) the electronic circuit board of the composite system and at least one electronic component mounted/connected thereon/thereto; and/or (ii) the packaging of the composite electronic system (e.g. the packaging of a chip) and the integrated circuit thereof (e.g. the die); and/or (iii) a first and second separated modules/devices of the composite system (e.g. a controller device and a smart wearable garment) which may be connectable to one another by wires or wirelessly. 
     In this regards it should be noted that the phrase similar signatures is used herein to specifically designate a case in which the XRF spectral response of the XRF marking of the two components of the composite system are similar in at least a predetermined portion thereof (e.g. at least one spectral part thereof), and/or that they are indicative of similar marking compositions. To this end, the similar XRF signatures may pertain to the similar concentrations of the active, XRF responsive, marker elements in the respective substrates from which the respective XRF signals carrying the signatures were emitted, but may have different actual XRF spectra due to the effects of the substrate (material and/or texture) to which the XRF marking is applied and/or due to the technique by which the marking is applied to the substrate. The phrase matching signatures is used herein to specifically designate a case in which a match between the signatures can be determined by processing the XRF signatures based on a certain predetermined formula/constraint to determine whether they are complementary (whether there exists a matching between them, e.g. without a need for utilizing external reference data to associated). In this sense, the similar signatures are a particular case of matching signature in which the match constraint is equality between them. Another way for determining a match between to signatures (after translating them to numerical values) is for example to check whether their addition sums up to a predetermined check sum value. The phrase corresponding XRF signatures is used herein to designate the case where a correspondence between the signatures can be verified by any suitable technique (e.g. utilizing reference data such as a lookup table (LUT) defining the correspondence between signatures. To this end matching signatures are generally a particular case of corresponding signatures, in which the match is determined by a predetermined relation between the signatures, thus not requiring use of external reference data. 
     The marking technique and the coding system of the present invention may be utilized in manufacturing customized electronics (cuslonomics) and personalized electronic components. For example, the code in a circuit embedded in a smart garment (e.g. for medical use), and the garment itself may be marked by a code associated with an individual. Such a smart garment for example may be custom made for a person with a medical condition (e.g. as a medical prescription) and the XRF marking may be used to verify that the customized garment is supplied to the right person. 
     The XRF marking can be used for the following purposes:
         Anti-counterfeit measure wherein the circuit board and various components may be marked. In particular, the XRF marking can be used for verifying, during the assembly, that the components to be assembled on the circuit board are ‘authentic’ and were manufactured by the original manufacturer. This aspect of the invention may provide authenticity and security measure for suppliers and end users as well. For example, upon receiving a circuit board the user can use the marking to authenticate the source, or type of the various components. Additionally, the marking allows the user to hand over the possession of the circuit (e.g. for repair or upgrade) and have the ability to verify that the circuit was not tampered with, for example the user can verify that none of the components has been replaced and that only authorized components have been installed. In addition, the marking can be used for verifying that the component is assembled at ‘correct’ position on the circuit board.   A component manufacturer can verify using such markings that the components are getting to the ‘right’ destination in order to prevent unauthorized trade of his components.   Supply chain management and control of supply chain diversion wherein the marking may include information relevant to the control of supply and production activities. For example, a number of marking composition may be applied at different stages of production and/or supply providing indication of the current production stage.   Manufacturer of smart clothing (wearable devices) can use such marking of one or both the garment (wearable object) and the circuits and electronic components which are to be assembled/attached to the garment are authentic and compatible. In particular, such marking may be of crucial importance in smart wearable objects that are used for medical purposes (see for example US 2016/0022982), wherein both the garment and the circuit board usually have special properties (the garment for example may include conductive threads) and must be of high quality.       

     The marking composition may be applied to the circuit board and the components at a single location or alternatively at different facilities. For example, the XRF markings of the components of the PCB may be applied at the facility of the of an authorized manufacturer. These marking may be read at the assembly facility of the circuit board authenticating the origin of the components. 
     The entire circuit and its components may be marked by same composition/the same XRF-signature/code-word. Alternatively, the various parts or components may be marked by the different code words of the same XRF-signature/code. For example, an XRF signature of a component may include a prefix containing information associated with the circuit board as a whole (indicating, for example the type of the circuit, the date of assembly, the destination or the client to which the circuit is to be sent) and a suffix including information associated with the component (type of component the manufacturer, the date of manufacturing, and so on). 
     The coding system associated with the marking may also include localized marking in different locations on a circuit board and/or on a single component, such that the configuration of the locations of the marking constitute part of the code. Namely, the specific locations of the markings would be incorporated in the code word associated with the marking. In other words, in some embodiments of the present invention the method/system (e.g. XRF reader) for reading the marking includes operating means, such as an imager and/or image recognition means) for identifying and determining the location of the marking on the marked component (on the marked circuit board), and for determining the code word read from the marking based on both (i) the XRF signal obtained from the marking; and (ii) the location of the marking on the marked component. 
     For the purpose of controlling the chain of supply (e.g. controlling unauthorized supply chain diversion) a number of marking compositions (each with a different XRF signature) may be applied to the circuit board at a number of location along the chain of supply or the assembly line such that reading the XRF markings provides information relating to the assembly of the circuit. 
     The XRF marking composition applied to a circuit board or to its components does not interfere with the electric or magnetic properties of the board or its components. Also the XRF marking composition may be configured such that it does not alter the appearance of the circuit board such that other legends markings and logos are not affected by the application of the marking composition (e.g. it may be by itself transparent and/or it may be embedded invisibly into the marked substrate material of the component). 
     The marking composition may also be applied to flexible circuits which may be included in wearable products and smart clothing used for medical purposes, fitness and workout as well as fashion and lifestyle. For example, smart shoes measuring biomechanical data, smart clothes that adjust to outside temperature and/or a garment that includes sensors measuring biometric indicators such as heart rate, skin moisture, and skin temperature. Smart garments may also be used for therapeutic purposes such as delivering electric shocks to the heart in case of cardiac arrest. 
     The smart garment may comprise of special materials and fabrics (for example breathable fabrics or fabrics which include conductive threads) and may be manufactured by different manufacturers. 
     The marking composition in this case may be applied to both flexible circuit (e.g. flexible circuit board), and to the fabric, authenticating both components. In addition, the marking may be used for quality control and control of chain of supply wherein only fabrics and associated circuit marked by suitable XRF signatures or codes may be assembled/combined together. 
     Thus according to a broad aspect of the present invention there is provided an electronic system including a plurality of components comprising at least a first and a second electronic components. The first electronic component includes a first XRF marking composition configured for emitting a first XRF signal having a first XRF signature in response to irradiation thereof by XRF exciting radiation. The second electronic component includes a second XRF marking composition configured for emitting a second XRF signal having a second XRF signature in response to irradiation thereof by XRF exciting radiation. The first and second XRF markings are respectively configured such that the first XRF signature of the first electronic component corresponds to the second XRF signature of the second electronic component thereby enabling verification that said first and second electronic components are respectively compatible components of said electronic system. 
     According to another broad aspect of the present invention there is provided a method for verifying compatibility of components of an electronic system that includes at least a first and a second electronic components. The method includes:
         providing a first component and a second components presumably associated with the electronic system;   irradiating the first and second components with XRF exciting radiation;   detecting one or more XRF response signals emitted in response to said irradiating from the first and second components;   processing the one or more XRF response signals to identify a first and a second XRF signatures associated respectively with first and second XRF marking compositions on said first and second components;   upon identification of the of the first and second XRF signatures, processing said first and second signatures to determine a correspondence between them, and verifying a verifying compatibility of said first and second components to the electronic system based on said correspondence.       

     It should be noted that in various embodiments and implementations of the present invention the marked components of the system may include respectively different substrates to which the XRF markings are applied. Accordingly there may be a need for calibrating the XRF measurements performed on different components of different substrates. 
     Therefore according yet another broad aspect of the present invention there is provided a method for calibrating XRF measurements of XRF markings applied to one or more substrate materials. The method includes carrying out the following:
         providing plurality of samples of including samples of various substrate material and various XRF marking compositions of different concentrations of XRF marker elements on the various substrate materials;   interrogating the plurality of samples of the particular substrate material by an XRF analyzer to determine for each sample a counts per second (CPS) value indicative of photons of a certain energy range(s) associated with the XRF marking elements;   determining and storing calibration data XRF for use on measurements of XRF markers applied to said substrate materials, whereby said calibration data includes data associating the predetermined/a-priory-known concentration of the XRF marker elements in the plurality of samples with the corresponding CPSs obtained from the respective samples. In this case, the calibration data may be used to determine the code-word of the marking based on the CPSs obtained from each sample.       

     Alternatively or additionally, the calibration procedure may include determining the XRF response spectra (e.g. the CPSs) obtained from a sample of a predetermined substrate (e.g. having known material and possibly known texture) to which a certain predetermined marking composition has been applied, and recording that XRF response as the code-word associated with the marked substrate, i.e. marking of the predetermined substrate by the predetermined marking composition. In this case, the XRF response spectra itself (possibly together with additional information such as the location of the marking on the object being marked) may represent the code word associated with that predetermined marking while on/in that predetermined substrate. That is, in this case the code-word is not related and not directly indicative of the concentrations/relative-concentrations of the marking elements, but is also associated with and affected by the properties of the substrate and the marking application technique, i.e. the unique XRF signature is formed by a combined response of the marked substrate to predetermined “reading” (exciting) radiation. For example, a lot of similar objects/substrates (i.e. objects produced by the same technique and having the same or very similar material composition and layout) may be associated with (identifiable by) the same reference/calibration XRF signature. Such signature is determined as stored to serve the reference one, upon applying the marking to one of the objects (or test object) and reading the XRF response therefrom. 
     Also in certain implementations the method also includes performing an SNR optimization step which is carried out by applying XRF interrogations with different XRF parameters, to said plurality of samples, to determine an optimized set of XRF parameters which optimizes an SNR of the XRF measurements of that substrate materials, and optionally storing said optimized set of XRF parameters in the calibration data. According to further yet another embodiment of the present invention there is provided an XRF reader including an XRF analyzer for interrogating an object and detecting an XRF response signal indicative of a spectral XRF signature of a marking composition applied to the object; and a signature calibration module associated with calibration data indicative of a correspondence between spectral XRF signature and concentrations of XRF marking elements of said object at which said XRF marking elements are included. The signature calibration module is adapted to utilize said spectral XRF signature to determine concentrations of XRF marking elements in said object based on the calibration data. 
     According to yet another broad aspect of the present invention there is provided An XRF readable mark, the XRF readable mark includes an XRF marking composition with specific relative concentrations of one or more chemical/atomic elements (generally a plurality of chemical/atomic elements); said relative concentrations are selected such that in response to irradiation of the XRF marking composition by XRF exciting radiation, the XRF marking composition emits an XRF signal indicative of a predetermined XRF signature associated with said the XRF readable mark. The XRF readable mark is configured and operable for placement on a substrate (e.g. an XRF responsive substrate associated with emission of XRF background clutter in response to said irradiation by the XRF exciting radiation). The XRF readable mark includes:
         an attenuation/mask layer including at least one element exhibiting high absorbance for at least one of: said XRF exciting radiation and said XRF background clutter; and   a marking layer comprising said XRF marking composition; and       

     The XRF readable mark is designated for placement on the substrate such that the attenuation/mask layer of the XRF readable mark intermediates (i.e. interposes/located between) between said substrate and the marking layer of the XRF readable mark. 
     In some embodiments the predetermined XRF signature of the XRF readable mark is characterized by one or more spectral peaks of said response to irradiation which are above a certain threshold, whereby the one or more spectral peaks include at least one spectral peak contributed by the XRF marking composition of the marking layer. For example the one or more spectral peaks may include at least one spectral peak contributed by one or more elements of the attenuation layer. 
     In some embodiments the predetermined XRF signature is characterized by one or more spectral peaks of the response to irradiation, which are above a certain threshold. The XRF background clutter from the XRF responsive substrate also includes at least one spectral peak above the certain threshold, and the attenuation/mask layer eliminates, or at least suppress the intensity of the at least one spectral peak of the XRF background clutter thereby enabling to read said predetermined XRF signature of the XRF readable mark while said XRF readable mark is placed over the substrate. 
     In some embodiments the attenuation layer is configured to extend over an area larger than an area of the marking layer. 
     In some embodiments the attenuation layer is configured with the parameters satisfying μ s ρx≥1/2, where x*ρ is area density of the attenuation layer (also known as areal or column density) and μ s  is the average mass absorption coefficient of the atomic element constituents of the attenuation layer. In some embodiments, the attenuation layer is configured with the parameters satisfying μ s ρx≥1. 
     According to some embodiments the at least one element exhibiting the high absorbance in the attenuation layer has an atomic number of at least 45. For example the at least one element exhibiting the high absorbance may include Lead (Pb). 
     In some embodiments the at least one element exhibiting the high absorbance in the attenuation layer is associated with substantial XRF response in at least one spectral regime. To this end the substantial XRF response may be a part of the predetermined XRF signature of the XRF readable mark. 
     According to yet another broad aspect of the present invention there is provided a component (e.g. an object or an electronic component) including:
         a substrate material; and   an XRF readable mark configured for emitting, an XRF signal having an XRF signature indicative of said component, in response to irradiation of the XRF readable mark by XRF exciting radiation;       

     The substrate may be an XRF responsive substrate including metallic atomic elements, and may be associated with emission of XRF background signal in response to irradiation thereof by the XRF exciting radiation. Accordingly the XRF readable mark may be configured as a multilayer XRF marker as described above an in more details below, including a marking layer and an attenuation layer, and is placed over a surface of said substrate such that the attenuation layer of the XRF readable mark intermediates/interposes between the surface of the substrate and the marking layer of the XRF readable mark. 
     According to yet another broad aspect of the present invention there is provided an electronic system including a plurality of components comprising at least a first and a second components, wherein:
         the first component includes a first XRF readable mark configured for emitting a first XRF signal having a first XRF signature in response to irradiation thereof by XRF exciting radiation;   the second component includes a second XRF readable mark configured for emitting a second XRF signal having a second XRF signature in response to irradiation thereof by XRF exciting radiation; and       

     The first and second XRF readable marks are respectively configured such that the first XRF signature of the first electronic component corresponds to the second XRF signature of the second electronic component thereby enabling verification that said first and second components are respectively compatible components of said electronic system. At least one of the components (e.g. the first component) is a component configured as defined above including: a substrate material, and an multilayer XRF readable mark placed over a surface of the substrate such that its attenuation/mask layer of the multilayer XRF readable mark intermediates between the surface of the substrate and the marking layer of the multilayer XRF readable mark. 
     In yet additional broad aspect of the present invention there is provided a method for producing an XRF readable mark. The method includes: 
     A. providing an XRF marking composition with specific relative concentrations of one or more chemical elements (generally a plurality of) whereby the relative concentrations are selected such that in response to irradiation of the XRF marking composition by XRF exciting radiation, the XRF marking composition emits an XRF signal indicative of a predetermined XRF signature; and 
     B. fabricating a multilayer structure of the XRF readable mark, whereby the fabrication includes:
         implementing an attenuation/mask layer including at least one element exhibiting high absorbance for at least one of: an XRF exciting radiation and an XRF background; and   implementing a marking layer including the XRF marking composition.       

     In some embodiments the implementation of the attenuation layer is configured such that parameters of the attenuation layer satisfy μ s ρx≥½, where x*ρ is area density (also known as areal or column density) of said attenuation layer is at least and U, is the average mass absorption coefficient of the atomic elements constituents of the attenuation layer. In some embodiments the implementation of the attenuation layer is such that parameters of said attenuation layer satisfy μ s ρx≥1. 
     In some embodiments the method further includes: furnishing the attenuation/mask layer (e.g. and the marking layer) over a substrate (e.g. an XRF responsive substrate which is associated with emission of XRF background clutter in response to said irradiation by an XRF exciting radiation). The furnishing is made such that the attenuation/mask layer intermediates between the substrate and the marking layer. 
     In some embodiments the at least one element exhibiting the high absorbance has higher atomic number than elements of the substrate. In some embodiments the at least one element exhibiting the high absorbance is lead (Pb). 
     In some embodiments the implementation of the attenuation/mask layer includes applying coating to at least a part of a surface of a substrate. The coating may include the at least one element exhibiting the high absorbance. 
     In some embodiments the coating includes a polymeric material embedded with one or more elements of high atomic number equal to or above 45. 
     In some embodiments the elements of high atomic number include one or more metallic elements. For example the one or more metallic elements may be embedded in the polymeric material by dissolving oxide or salt forms or organometallic compounds including said material in the polymeric material prior to the coating. The elements of high atomic number may be dispersed or suspended in the polymeric material. 
     In some embodiments the polymeric material may be polyamide. The polymeric material may be applied to the surface by at least one of the following: spraying, brushing, printing, injecting and stamping. In some embodiments the method further includes curing of the polymeric material by at least one of the following: heat, humidity, and UV radiation. 
     In some embodiments the implementation of the attenuation/mask layer includes depositing the at least one element exhibiting the high absorbance on at least a part of a surface of a substrate. For instance the deposition may be carried out utilizing at least one of CVD and PVD techniques. In some cases at least one element exhibiting the high absorbance is deposited in liquid, solid or granular form. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram of an electronic system according to an embodiment of the present invention including a plurality of components marked by XRF marking compositions;  FIGS. 2A to 2D  are block diagrams illustrating electronic systems configured according to various embodiments of the present invention which include XRF marking compositions embedded/applied to various components thereof; 
         FIG. 3  is a flow chart of a method for verifying compatibility of components of an electronic system according to an embodiment of the present invention; 
         FIGS. 4A to 4C  are flow chart of methods which may be carried out for verifying compatibility of components of an system according to various embodiments of the present invention; 
         FIG. 5A  is a schematic illustration of an XRF marker coupled with an object/component (e.g. an electronic component) having a substrate with substantial XRF response; 
         FIG. 5B  is a schematic graphical illustration of the XRF responses from the object/component of  FIG. 5A  with the XRF marker thereof; 
         FIG. 5C  is a flow chart of a calibration technique for use with XRF analyzer to enable accurate measurement of concentrations of XRF responsive marker materials in embedded/applied to various substrates. 
         FIG. 5D  is a block diagram of an XRF verification reader configured according to an embodiment of the present invention for verifying compatibility of electron components of an electronic system; 
         FIG. 6A  is a schematic illustration of a multilayered XRF marker according to an embodiment of the present invention coupled with an object/component (e.g. an electronic component) having a substrate with substantial XRF response; The multilayered XRF marker includes an attenuation layer and a marking layer. 
         FIG. 6B  is a schematic graphical illustration of the XRF responses from the object/component of  FIG. 5A  with the multilayered XRF marker; 
         FIG. 6C  is a flow chart of a method  600  for implementing a multilayered XRF mark according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference is made to  FIG. 1  which shows a block diagram of an electronic system  100  which includes a plurality of components marked by XRF markings. In this specific example the electronic system  100  is illustrated with two components C 1  and C 2  (herein after referred to as the first and second electronic components) that are respectively marked by XRF respective first and second marking compositions XRFM 1  and XRFM 2  associated with XRF signatures. It should be understood that generally more than two components marked with XRF marks may be included in the system  100 . 
     In various embodiments of the present invention the components C 1  and C 2  may include electronic components of the electronic system  100 , such as a circuit board and electrical components mounted thereon, and/or the components C 1  and C 2  may include separate devices of a distributed electronic system  100 , such as a control unit/device and a smart wearable device constituting together the system  100 , and/or the components C 1  and C 2  may include an electronic module and a casing/packaging/enclosure thereof. Also, in various embodiments of the present invention the first and second XRF marking compositions XRFM 1  and XRFM 2  on the components C 1  and C 2  may be marks indicative of one or more of the following: the brands of the respective components C 1  and C 2 , the manufacturing details (e.g. manufacturer, manufacturing place manufacturing date, LOT number, etc&#39;) of the components C 1  and C 2 , and/or indicative of the identification of the individual components such as serial numbers of the components C 1  and C 2 . Accordingly the XRF marking compositions XRFM 1  and XRFM 2  provide elemental identification of the components (e.g. their serial numbers brand and/or manufacture). 
     It should be noted that in various embodiments of the present invention the XRF markings XRFM 1  and XRFM 2  are applied to (e.g. applied on and/or embedded/blended) within different substrate materials in the different components (e.g. one component may include a polymer substrate at which the XRF marker in included while the other may include natural fibers serving as the substrate at which the XRF marker is included). In this regards the terms substrate and/or substrate materials is used herein to indicated the base material (e.g. media/substrate material) of the component of the electronic system with the XRF marking composition is applied/embedded. Accordingly the marking compositions of different components may include different promoters and/or different binder materials in accordance with the substrate to which the marking composition is to be applied in the different components of the system. 
     In this example the first electronic component C 1  includes a first XRF marking composition XRFM 1  configured for emitting, in response to irradiation thereof by XRF exciting radiation, a first XRF signal a first XRF signature XRFS 1 . The second electronic component C 2  includes a second XRF marking composition XRFM 2  configured for emitting a second XRF signal having a second XRF signature XRFS 2  in response to irradiation thereof by XRF exciting radiation. 
     According to the present invention the first and second XRF marking compositions, XRFM 1  and XRFM 2 , are respectively configured such that the first XRF signature XRFS 1  obtained from the first electronic component C 1  corresponds to the second XRF signature XRFS 2  from the second electronic component C 2 . The XRF marking compositions, XRFM 1  and XRFM 2 , thereby provide elemental identification codings enabling verification that the first and second electronic components are respectively compatible components (e.g. complementary components) of the electronic system. The elemental identification, which is elemental in the sense that it is based on markings associated with elements (herein after also referred to as active XRF elements to indicate chemical elements that emit X-Ray Fluorescence in response to irradiation thereof) embedded in the components C 1  and C 2 , may be, for example, used-for/facilitate brand protection, authentication of customized electronics, providing liability of electronic components in medical devices (e.g. in particular in wearable medical devices), and providing bridge liability for the coupling between virtual services or products and physical operational systems (for example the coupling between personal data and a smart clothing). 
       FIG. 1  also shows a table, Table 1, exemplifying possible relationships between the XRF signatures, XRFS 1  and XRFS 2 , of complementary marks, XRFM 1  and XRFM 2 , used for marking complementary/compatible components, C 1  and C 2 , of the electronic system  100  according to the present invention. In this regards, it should be understood that although only two components, C 1  and C 2 , are exemplified in this figure, system  100  may include any number of plurality of XRF marked components with the relationship between their marks similar to those exemplified in Table 1. 
     More specifically, in certain embodiments of the present invention the XRF marking compositions, XRFS 1  and XRFS 2 , on the respective components, C 1  and C 2 , of the system  100 , are configures such that a correspondence between the first and second XRF signatures, XRFS 1  and XRFS 2 , of the XRF signals emitted therefrom in response XRF exciting radiation (e.g. exciting radiation obtained by illuminating the system or its components by X-Ray or Gamma-Ray radiation) is based on a match between the XRF signatures, XRFS 1  and XRFS 2 . More specifically a match can be determined by utilizing/providing a certain predetermined mutual relationship condition (e.g. Function (XRFS 1 , XRFS 2 )&lt; or = or &gt; VALUE) between the XRF signatures, which should be satisfied by the XRF signatures XRFS 1  and XRFS 2  in cases there are matching. For instance, as exemplified in row 2 of table 1, the condition Functidon (XRFS 1 , XRFS 2 ) is that the superposition/addition of the signatures XRFS 1 , XRFS 2  equals a certain cumulative signature CXRFS, namely the following condition should be satisfied in this example:
 
Function (XRFS 1 ,XRFS 2 )=XRFS 1 +XRFS 2 =CXRFS.
 
     Indeed other mutual condition may also be used—for example that a difference XRFS 1 −XRFS 2  between the signatures equals a certain value, and/or that the signatures are similar XRFS 1 =XRFS 2 . The latter case, similarity between the signatures XRFS 1  and XRFS 2 , being a particular case of a matching between them is exemplified in row 1 of the table 1. 
     It should be noted that embodiments of the present invention in which the correspondence between the signatures, XRFS 1  and XRFS 2 , is determined by matching them utilizing a predetermined condition, such as similarity between the or other, may be advantageous in certain implementation in which in situ verification that components C 1  and C 2  are compatible/complementary (e.g. in-situ in the sense that there is no need for utilizing external reference data for associating the signatures of complementary components, but only providing a predetermined mutual relationship condition (e.g. similarity) that should be satisfied thereby. Accordingly an XRF verification reader (e.g. such as that exemplified in  FIG. 5B ), may be furnished with a memory storing the predetermined condition, and may utilize that condition to examine the components of the system, and determine, in situ, whether two or more components of an electronic system are complementary or compatible, without a need for accessing external data sources. 
     Alternatively or additionally, the electronic system, a correspondence between the first and second XRF signatures is determined based on a reference data (e.g. lookup table (LUT)), such as the REFERENCE-LUT in table 1, associating the XRF signatures of complementary/compatible components, C 1  and C 2 , of the system  100 . This is illustrated in self-explanatory manner in row 3 of table 1 in the figure. Indeed in this case the reference data may also be included in a memory/storage of an XRF verification reader (e.g. such as that of  FIG. 5B ) to enable in-situ verification operation, however, in that case the memory storage may need to be updated at each time additional components/systems with different complementary markings are released. 
     It should be generally understood that the terms XRF signatures are used herein to indicate at least one portion/region of the spectral response of the components, e.g. C 1  and C 2  of the system  100  to XRF exciting radiation, which is associated with at least a part of the spectral band at which XRF signals are expected (and not necessarily the entire XRF spectral band). Accordingly, XRF signatures of interest, XRFS 1  and XRFS 2 , may be “hidden” at certain designated spectral regions of the entire XRF response obtained from the XRF marking XRFM 1  and XRFM 2 . 
     The XRF markings according to the present invention may be applied to various substrates including metals, plastic and fabrics. The novel marking technique of the invention is highly generic, insensitive to materials and structure of the objects (components of the system  100 ) to which marking, and thus permits verification of authenticity of a great variety of types or components of the electrical system  100 , (e.g. circuit boards, electronic components, and fabrics). According to some embodiments the present invention, the present invention also provide a calibration technique and an XRF reading system optionally utilizing this calibration technique enabling to accurately read XRF markings which are applied to different types of substrate materials of different components of the system. This is illustrated for example in  FIGS. 5A and 5B  which are further described below. Accordingly, the XRF marking technique of the present invention may be insensitivity to the different substrate/materials of the components to which the XRF markings may be applied in the system  100 . 
     The XRF markings (also referred to as marking composition) applied to a component (object) generally includes a low concentration of a marking system, which typically comprises a plurality of marker materials (herein “markers”). Each of the markers being XRF sensitive/responsive in the sense that they emit an X-Ray response signal in response to interrogation (irradiation) by X-Ray or gamma ray radiation. 
     In certain embodiments of the invention one or more of the marker composition(s) used in the system  100  include at least one XRF-sensitive marker (which is also referred to herein as XRF responsive marker element and/or active XRF marker) and at least one surface binding material (permitting association of said marker to at least a surface region of an object, e.g., a binder material and/or an adhesive material). In certain implementations the concentration of the at least one marker is between 0.1 and 10,000 ppm. In some embodiments, the composition is suitable for application onto at least one region of a surface of the component e.g. C 1  or C 2  of the electrical system  100 . 
     In certain embodiments the XRF marking composition that is used for marking one or more of the components C 1  and C 2  includes at least one XRF-sensitive marker, at least one surface binding material, and may also include at least one adhesion promoter and at least one etching agent. The concentrations or amounts of the marker(s) and the binding material(s) within any marking composition of the invention may be set according to a preselected code, which can be measured by XRF analysis, after application of the composition onto the component of the system. In general, the marking composition may include one or more markers with concentrations within the range of 0.1 to 10,000 ppm. 
     In certain embodiments of the present invention, the marker composition which is used for marking one or more of the components of the system  100  includes a plurality of XRF marker elements, each being present in different concentrations or form. This may be used to provide a unique signature of the marking composition with spectral features characteristic not only of the specific elements in the combination but also of their concentrations or relative concentrations. 
     Alternatively or additionally, in some embodiments of the present invention, each marking composition that is to be used is prepared with a certain (possibly unique) concentrations of the marking elements (which may be determined/set arbitrarily and possibly event not measured). Then, only after the marking composition is applied to a predetermined substrate (e.g. a sample substrate having certain material and/or texture) by a certain application technique (e.g. CVD, PVD and/or embedding, as described below) the XRF response is read from the marking that is applied to the specific substrate, and that XRF response is set as the code-word of the marking on that substrate. In this case the concentrations of the marking elements are not determined a-priory based on a preselected code, but instead, the code is determined/measured post-priori only after the marking composition (possibly including arbitrary concentrations of marking elements) is applied to the sample substrate. In other words here the code word may be considered to be associated not only with the marking composition but also with the substrate to which it is applied. 
     Thus, the concentrations and/or relative concentrations of the marking elements may or may not be determined a priority based on the desired code word of the marking, but in some cases the code words is determined post-priory only after a marking composition having certain (not necessarily known) concentrations of elements applied to an object (e.g. a reference object/component) of the type/material similar to that of the component that is to be marked by the marking composition. Then, during a calibration process, the XRF spectra (signal/signature) of the marking composition after being applied to the marked object (e.g. to the reference object) is measured, to determine the code word of the marking. This is because, in some implementations, the XRF spectra/signature is not only affected by the concentrations of the marking elements in the marking composition, but may also be affected by the material composition of the object itself being marked and/or by the method of application of the marking composition to the object/component. Accordingly, it should be understood that in such implementations the code-word of the marking, although being affected by the concentrations of the marker elements, may not be indicative of the concentrations of the marking elements and may not be constituted by those concentrations, but may be affected also by additional factors such as the material of the object being marked, the method of application of the marking to the object, and possibly also the location of the marking on the object as indicated above. To this end, two different objects marked by the same marking compositions may yield different code-words. 
     The XRF marker(s) in a marker combination or independent of other markers in an XRF marking composition may be in a metal form, a salt form, an oxide form, a polymer comprising (in a chemical or a physical interaction) the one or more XRF marking elements, an organometallic compound, or a complex which includes one or more of the XRF marking elements. 
     In some embodiments of the present invention the surface binding material used in compositions of the invention is a material which binds or promotes binding of the marker to a surface of an object. The at least one surface binding material may be a single material or a combination of materials, which independently or in combination permits irreversible association of the marker/marker combination or any other component of the marking composition to a surface region. The at least one surface binding material is one or more of a binder material, an adhesive material, an adhesive promoter material, a polymer and a pre-polymer, as known in the art. For instance in some implementations, the at least one surface binding material is at least one binder and at least one adhesion promoter. Alternatively or additionally in some implementations, the at least one surface binding material is at least one binder material and/or at least one adhesion promoter, independently of the other, or in combination promote binding of the marker material or any component of the marking composition to the surface of the object. 
     The etchant or etching agent is selected to cause surface modifications to improve adhesion or generally association, being optionally irreversible, of the marking composition to the surface region of the object. 
     The following table, Table 2, specifies possible chemical compositions of XRF markings which may be used according to the present invention for marking various components of the electronic system  100 . 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Etching 
               
               
                 Markers 
                 Binder 
                 Adhesion promoter 
                 agent 
               
               
                   
               
             
            
               
                 Elements 
                 thermoplastic 
                 Chlorinated Polyolefin 
                 Fumaric 
               
               
                 with an 
                 polyurethane 
                   
                 acid 
               
               
                 identifi- 
                 thermoplastic 
                 Ethylene butyl acrylate 
                 Halogen 
               
               
                 able XRF 
                 polyurethane 
                 copolymer functionalized with 
                 base acid 
               
               
                 signature 
                   
                 maleic anhydride (MAH) 
               
               
                   
                 poly-ether- 
                 Styrene ethylene butylene 
                 Carbox- 
               
               
                   
                 urethane 
                 block copolymer functionalized 
                 ylic acid 
               
               
                   
                   
                 with maleic anhydride 
               
               
                   
                 polyethylene- 
                 Ethylene octen copolymer 
               
               
                   
                 terephthalate 
                 functionalized with maleic 
               
               
                   
                   
                 anhydride 
               
               
                   
                 polybutylene- 
                 copolymerizable olefinic 
               
               
                   
                 terephthalate 
                 monomer 
               
               
                   
                 polyvinyl- 
                 Functionalized polyolefins 
               
               
                   
                 acetate 
                 Functionalized ethylene-vinyl- 
               
               
                   
                   
                 acetate copolymers 
               
               
                   
                 epoxy-acrylate 
                 Functionalized ionomers 
               
               
                   
                 Epoxy 
                 Functionalized polyalkylene 
               
               
                   
                   
                 oxide polyester block 
               
               
                   
                   
                 copolymer 
               
               
                   
                 Urethane 
                 Functionalized derivatives of 
               
               
                   
                   
                 carboxymethylcellulose 
               
               
                   
                 acrylate 
                 Homopolymers and copolymers 
               
               
                   
                   
                 derived from dicarboxylic 
               
               
                   
                   
                 acids, diamines and 
               
               
                   
                   
                 aminocarboxylic acids 
               
               
                   
               
            
           
         
       
     
     It should be noted that additional possible XRF marking compositions, including XRF marking compositions which may be particularly suited for marking metal objects/substrates are described for example in PCT application No. PCT/IL2017/050121, which is assigned to the assignee of the present application, and included herein by reference. Reference is now made to  FIG. 2A  showing an electronic system  100  configured according to an embodiment of the present invention. It should be noted that here and in all of the figures of the present application described in the following, similar reference numerals are used to designate similar/like elements/method-operations having the similar configurations and/or functionalities. 
     In this example the first component C 1  of the system  100  is an electronic circuit board PCB (which may be rigid or flexible circuit board) and the second component C 2  is a component (e.g. electronic component) associated with a designated place on the circuit board C 1 . Additional components, C 3  and C 4 , which may be also mounted/mountable on the first component C 1  (circuit board PCB) and which may or may not include XRF markings, are also exemplified in the figure. 
     In various implementations of the system  100 , the first marking composition XRFM 1  is embedded in/on the circuit board PCB by utilizing one or more of the following: 
     (a) The first marking composition XRFM 1  may be blended with the polymers comprising the solder mask applied to the circuit board PCB during its fabrication. For example embedding the XRF marker elements in solder mask based on epoxy and epoxy-acrylate polymers, and\or in photoimageable solder mask (LPSM) inks, and/or in liquid photoimageable solder mask commonly called LPI or LPISM; and/or in dry film photoimageable solder mask (DFSM). 
     (b) The first marking composition XRFM 1  may be blended with ink of prints (e.g. logos/legends and so forth) which may be printed on the circuit board PCB. For example by mixing/embedding XRF marker elements with one or more of the following: UV cure polymer or thermal cure polymers inks, such as epoxy or urethane, or acrylate polymers, which are applied as silk screen printing or as liquid photo polymers or as ink jet printing. Alternatively, the marking applied to the surface of the circuit board may be an invisible composition. 
     (c) The marking composition may be dispensed or deposited the onto the surface of the object by various additional techniques such as printing (such as ink jet printing), stamping, spraying, injecting, brushing, and air brushing. 
     (d) Alternatively or additionally, the marking composition may be applied to the surface of the circuit by vacuum deposition methods wherein the deposition process is carried out at pressure which is well below atmospheric pressure or in vacuum (i.e. in a vacuum chamber). Preferably, the vacuum deposition process which may be used in such marking techniques utilizes Chemical Vapor Deposition (CVD) including various processes such as low-pressure chemical vapor deposition (LPCVD), Plasma-Enhanced Chemical Vapor Deposition (PECVD), Plasma-Assisted CVD (PACVD), and Atomic Layer Deposition (ALD). Alternatively, or additionally, the process of depositing the marker material(s) on the object includes Physical Vapor Deposition (PVD) in which the vapor source is solid or liquid. A PVD process may use techniques such as sputtering, cathodic arc deposition, thermal evaporation, laser ablation serving as a (solid) precursor to generate vapor, and electron beam deposition, to generate the deposited particles in a vapor phase. 
     (e) The first marking composition XRFM 1  may be blended with the compounds comprising the under-fill binding of one or more components to the circuit board PCB. For example, blending the XRF marking elements with under fill adhesives based on low viscosity epoxy polymers, and/or with urethane polymers, and/or with acrylate polymers. 
     (f) The first marking composition XRFM 1  may be blended with polymers of the packaging of some of the components on the circuit board PCB. For example, blending the XRF marking elements with Thermoset Electronic Polymers (such as: Epoxies, Polyimides, Silicones, Phenolics, Polyurethanes) and/or with Thermoplastic Polymers (such as: Polysulfone, Polyethersulfone, Nylon 66-polyamide, Polyphenylene Sulfide, PBT—Polybutylene Terephthalate, PET—Polyethylene Terephthalate). The marking composition may be blended during the melt process of the polymer (e.g. injection molding, compression molding, thermoforming). 
     (g) The marking composition XRFM 1  may be embedded in an overly, or coating, of the solder mask or of components of the circuit board PCB. For example, the overly, or coating may include: thermoplastic polyurethane, thermoplastic polyurethane, poly-ether-urethane, polyethylene-terephthalate, polybutylene-terephthalate, polyvinyl-acetate, epoxy, epoxy-acrylate, urethane, acrylate based polymers. 
     (h) The marking composition XRFM 1  may be blended with polymers applied to through vertical interconnect access (VIA) holes on the circuit board PCB. For example, XRF marker elements blended in polymers based on low viscosity epoxy polymers, or urethane polymers or acrylate polymers 
     (i) The PCB may include a special ‘fake’ component mounted thereon for carrying the marking composition XRFM 1 , and the marking composition XRFM 1  may be contained/carried on/at the special ‘fake’ component according to any one of the techniques described above. 
     In this embodiment, the second component C 2  may be for example an electronic component, such as a chip, that is mountable on the circuit board PCB. The second marking composition XRFM 2  may be embedded in the electronic component C 2  in one or more of the following: 
     (a) The second marking composition XRFM 2  may be blended with ink of prints printed on the electronic component. The chemical composition of the marking composition XRFM 2  may be this case similar to the ink marking composition described above with regards to XRFM 1 . 
     (b) The second marking composition XRFM 2  may be blended with polymers of the packaging of the second component C 2 . The chemical composition of the marking composition XRFM 2  may be this case similar to marking composition XRFM 1  applied to the polymers of the PCB as described above. 
     (c) The marking composition XRFM 2  may also alternatively or additionally be blended with polymers applied to through vertical interconnect access (VIA) holes of the second component C 2 . 
     Reference is now made to  FIG. 2B  showing an electronic system  100  configured according to another embodiment of the present invention, and in which the first electronic component C 1  is a printed circuit board PCB, and the second component is an electronic component mountable on the circuit board PCB at a designated location LC 2 . Here, the first XRF marking XRFM 1  is spatially located on the PCB at the designated location LC 2  at which the second component C 2  should be mounted on the circuit board PCB. This thereby enabling to utilize a scanning (e.g. spatially focused) XRF analyzer to scan the circuit board PCB to identify the designated location LC 2  for mounting of the second component C 2 , based on a correspondence (e.g. match or similarity) between the first and second signatures, XRFS 1  and XRFS 2  of the first and second XRF markings XRFM 1  and XRFM 2 . The may be used to determine/verify the proper placement location LC 2  of the second component C 2  on the circuit board PCB. 
     Optionally, as also illustrated in  FIG. 2B , the designated location LC 3  and LC 4  at which to mount additional components C 3  and C 4  of the system  100  are also marked with respective XRF marking compositions XRFM 13  and XRFM 14 . Accordingly, the components C 3  and C 4 , which are also illustrated in the figure, are also marked with the at which the XRF marking compositions XRFM 13  and XRFM 44  which respectively correspond to the XRF marking compositions XRFM 13  and XRFM 14  on the PCB. Accordingly this enables to utilize the scanning XRF analyzer to scan the circuit board PCB to determine/verify the proper placement locations for the components C 2 , C 3  and C 4  prior or after their assembly/mounting on the PCB and thereby enable, either automatic assembly of the electronic system  100 , and/or enabling carrying out quality assurance (QA) checks on the assembled system  100 , to verify proper placement of compatible components in their proper locations. 
     Reference is made to  FIG. 2C  showing an electronic system  100  according to another embodiment of the present invention in which the first component C 1  marked by the XRF marking composition XRFM 1  is an electronic component and the second component C 2  marked by the XRF marking composition XRFM 2  is a casing/packaging of the electronic component C 1 . The electronic component C 1  may be located/enclosed within the packaging C 2 , and accordingly in the figure a region RG of the packaging is illustrated semitransparent to reveal the XRF marking XRFM 1  of the electronic component C 1 . 
     For example the electronic system  100  may be in this case a chip (e.g. assembled chip), whereby the first component C 1  may be a semiconductor die of the chip  100  and second component C 2  may be a package of the chip  100  which encloses the die C 1 . Accordingly the package may be for example made of, or may include polymer materials and the second XRF marking composition XRFM 2  may be embedded in the polymer materials of the package C 2  in the manner described above for embedding XRF marks in polymers, or it may be included/embedded in an under-fill material in between the die and the package. The first XRF marking composition XRFM 1  may be in this case embedded/included in the material of electrical inter-connect (e.g. indium bumps) and/or in the material fillings VIA holes of the die C 1 , 
     To this end according to certain embodiments of the present invention the first and second XRF marking compositions, XRFM 1  and XRFM 2  are selected/configured such that in response to irradiation of the system by XRF exciting radiation, they emit together a composite XRF signal (e.g. referenced CXRFS in  FIG. 1 ) including the first and second XRF signals from both the components C 1  and C 2 . The XRF marking compositions, XRFM 1  and XRFM 2 , (specifically the contents of active XRF responsive materials therein) may be specifically selected/configured such that the composite XRF signal CXRFS is indicative of the first and second XRF signatures XRFM 1  and XRFM 2  (namely that the first and second XRF signatures XRFM 1  and XRFM 2  can be distinguishably identified therein), and such that the first and second XRF signatures XRFM 1  and XRFM 2  do not interfere with one another (e.g. such that they complement on another) in the composite XRF signal CXRFS. This may be achieved for example by respective configuration of the first and second XRF marking compositions, XRFM 1  and XRFM 2 , with specifically selected set of active XRF responsive materials in each of them such that the spectra (set of wavelengths (k)) in their respective XRF signatures XRFS 1  and XRFS 2 , are mutually exclusive (e.g. the do not emit/have XRF spectral response peak at the same wavelength). This is illustrated for example in row 2 of table 1 in  FIG. 1  showing the signatures XRFS 1  and XRFS 2  having mutually exclusive spectral peaks. Accordingly the signatures XRFS 1  and XRFS 2  do not interfere with one another and can be read together to determine whether the components C 1  and C 2  (e.g. the inner component C 1  and the outer component enclosing it C 2 ) are compatible components (e.g. and whether the system  100  is authentic). In this regards, it should be noted that since the XRF technique is used, which is generally based on irradiation and detection of X-Ray or Gamma-rays, determining whether the component is authentic can be done non-invasively without opening the package/casing C 2  (e.g. by irradiating the entire system with X-Ray or Gamma-rays and detecting the composite XRF signal CXRFS emitted therefrom in response). 
     Reference is now made to  FIG. 2D  showing an electronic system  100  according to yet another embodiment of the present invention. In this embodiment the first and second electronic components C 1  and C 2 , are generally first and second electronic devices each associated or includes a respective data storage module MEM 1  and MEM 2 , and at least one of them includes, or is associated with a pairing and activation controller ACTRL capable of connecting to both the memory/data storage modules MEM 1  and MEM 2 . The memory modules may be for example in the form of computer memory modules, flash memory, RFID module and/or any other usable data carrying/storing module device. 
     To this end in this example the first component C 1  is a first electronic device including a first data storage module MEM 1  (hereinafter without loss of generality referred to also as memory) capable of storing a first data portion indicative of a correspondence between said first and second XRF signatures XRFS 1  and XRFS 2 . The second component C 2  is a second device including a second data storage module MEM 2  capable of storing a second data portion indicative of a correspondence between the first and second XRF signatures XRFS 1  and XRFS 2 . In this regards, it is noted that during a pairing operation (e.g. which may be carried out for example at a plant where the first and second devices are paired and/or at the distributor/shop at which they first and/or second device are soled/distributed) may include reading the XRF marking (e.g. XRFS 2  of one of the devices) for storing it (or a code corresponding to it) in the memories MEM 1  and MEM 2  of the first and second devices. Accordingly an elemental ID coding is introduced in to the memories of the first and second devices enabling elemental pairing between them based on the correspondence between their XRF marks. The pairing/activation controller ACTRL is configured and operable for carrying out the following before enabling activation of mutual operation of the devices C 1  and C 2  (e.g. upon existence of wired or wireless connation between the first and second devices C 1  and C 2 ): 
     (i) accessing the first and the second data storage modules, MEM 1  and MEM 2 , upon wired or wireless connation between the first and second devices; 
     (ii) retrieving the first data portion from the first memory MEM 1  and retrieving the second data portion from the second memory MEM 2 ; and 
     (iii) processing the first and second data portions to determine whether the first component/device C 1  is paired with the component/second device C 2 . 
     In this connection the processing to determine whether the components/devices C 1  and C 2  are paired includes determining whether exists based a correspondence between the codes which are stored in the memories MEM 1  and MEM 2  of the first and second devices. This provides elemental identifications that devices C 1  and C 2  are compatible and are allowed for working together, which is based on the compatibility of the first and second XRF signatures of the first and second devices (as indicated by the reference data stored in the memories MEM 1  and MEM 2 . To this end the activation controller ACTRL provides/enables conditioned activation of mutual operation of the first and second devices C 1  and C 2  based on a pairing (elemental pairing) between them. 
     In this particular example of  FIG. 2D  one of the devices, specifically the second component C 2 , is a smart wearable/garment device. For instance the electronic system  100  may be a healthcare system, wherein at least one of the first and second devices, C 1  and C 2 , is configured for monitoring one or more conditions of a user using the system  100 , and at least one of the first and second devices C 1  and C 2  is configured and operable for providing treatment to the user based on the monitored condition. Indeed in this case, since the healthcare system (the monitoring properties and/or the treatment properties) might be customized for use by specific user and might damage other users, it is advantageous to use the elemental pairing between the first and second devices C 1  and C 2 , to thereby provide inherent verification that the correct treatment device (e.g. garment C 2 ) is connected to the correct monitoring device (e.g. C 2 ) of the same user. 
     According to various embodiments of the present invention the smart wearable device (garment) C 2  may include one or more fabrics made with natural and/or synthetic fibers. 
     In some embodiments the fabric is made/includes with natural fibers the XRF marking composition may be included in the dyes used for dying the natural fibers. Accordingly the active XRF responsive materials may be added to the natural fibers of the fabric in the dying stage of the fabric production. 
     Typically natural fibers are dyed by utilizing Mordants, whereby herein the term Mordants is used for chemicals which usually have a metal with a valency of at least two or more, (they may also include other types of compound as well). More specifically mordants are mineral salts that bind dyes into fiber (dyes for natural fibers require use of a mordant to fix the pigment to the fabric and prevent the color from fading or washing out). Commonly used mordants for natural dyes include for example one or more of the following: alum, potassium aluminum sulfate, tin and bluevitriol, chrome, potassium dichromate, potassium bichromate, blue vitriol, copper sulfate, ferrous sulfate, stannous chloride, sodium dithionite, sodium hydrosulfite, ammonia hydroxide, cream of tartar, potassium bitartrate, “Glauber&#39;s salt”, sodium sulfate, lime, lye, sodium hydroxide, oxalic acid, tannic acid, uria, vinegar, acetic acid, washing soda or sodium carbonate. 
     This provides a variety of potential XRF markers which can be used/included in various quantities in the Mordants material used in dying of the natural fibers to thereby obtain a desired XRF signature of the fiber. To this end in natural fabrics/fibers the XRF marking composition (e.g. XRFM 2  in the figure) may be included in the Mordants used for dying the fabric and with the Mordants composition specifically selected to provide the desired XRF signature (e.g. XRFM 2  in the figure). 
     Alternatively or additionally the fabric may be made, or may include synthetic fibers made from the polymer materials such as: Linear polyamides (Nylon 6-6, 6-10, 6, 7), Acetate cellulose, Lyocell, Polyester—PET (e.g. Dacron,™ Terylene™), Lycra, Spandex, Kevlar, and Acrylic fibers. In this case dying of the fibers/fabric is performed the production of the fibers of the fabric (typically during the extrusion process). Accordingly XRF marking compositions (e.g. XRFM 2 ) may be in this case introduced into the fiber by during the extrusion process (e.g. by—blending the XRF marker elements with the other materials of the synthetic fibers). 
     Reference is now made to  FIG. 3  which is a flow chart of a method  200  for verifying compatibility of components (e.g. C 1  and C 2 ) of an electronic system (e.g.  100 ) which includes at least two, first and second, components. 
     The method includes the following operations: 
     Operation  210  includes providing a first component C 1  that is presumably associated with the electronic system  100 . 
     Operation  220  includes providing a second component C 2  that is presumably associated with the electronic system  100 ; 
     Operation  230  includes irradiating the first and second components C 1  and C 2  with XRF exciting radiation. In various implementations of the present invention the irradiation of the components by the XRF exciting radiation (e.g. by X-Ray or Gamma rays) may be performed by separately irradiating separate components, and/or by irradiating both/several of the components together. 
     Operation  240  includes detecting one or more of the XRF response signals from first and second components, C 1  and C 2 , which are emitted in response to the irradiation of the first and second components, C 1  and C 2  by the XRF exciting radiation. In this regards it should be noted that dependent of the XRF signatures which are expected to be detected (e.g. whether they are expected to interfere with one another or not), the detection of the XRF response from several/two or more components may be done separately for separate components, or may be done for several components together. Then, the one or more XRF response signals may be processed to identify a first and a second XRF signatures, XRFS 1  and XRFS 2 , which are respectively associated with the first and second XRF marking compositions XRFM 1  and XRFM 2  on the first and second components, C 1  and C 2 . For instance the processing of the one or more XRF response signals at this stage may include certain signal to noise enhancement and background filtration, to enhance the SNR of the signals. For example, such SNR filtration may be carried out by utilizing the XRF analyzer (reader/system) and/or the method described in PCT patent application No. PCT/IL2016/050340, which is assigned to the assignee ofthe present application and incorporated herein in its entirety by reference, for removing the trend and/or the periodic spectral components from the detected XRF signals. Also the processing of the one or more XRF response signals at this stage may include filtering certain portions (spectral bands) of the detected signal(s), to leave only those spectral bands at which the XRF signatures of interests XRFS 1  and XRFS 2  should be found. This provides for identifying/extracting from the detected XRF signals, the signatures XRFS 1  and XRFS 2  and/or a cumulative/composite signature CXRFS including both the signatures XRFS 1  and XRFS 2 . 
     Operation  250  is carried out upon identification of the first and second XRF signatures, XRFS 1  and XRFS 2 , or the cumulative/composite signature CXRFS including them both, and includes processing the identified signatures to determine whether exists a correspondence between. The correspondence may be determined based on a similarity between the signatures, and/or based on a matching between them according to a predetermined condition, and/or by utilizing reference data (e.g. LUT) associating corresponding signatures, as discussed above in more details in illustrated in Table 1 of  FIG. 1 . To this end operation  250  of method  200  may optionally include provision of a certain predetermined condition indicative of a predetermined mutual relationship between matching XRF signatures (e.g. which are complementary/corresponding signatures), and determining whether the first and second XRF signatures satisfy said predetermined condition (this as indicated above enable in situ verification that the first and second components are compatible while obviating a need for using external reference data). For instance the predetermined condition may be that the first and second XRF signatures are similar in the at least one spectral region thereof, and wherein the processing may thus include comparing this spectral region in the first and second XRF signatures XRFS 1  and XRFS 2 . Alternatively or additionally the correspondence between the first and second XRF signatures may be determined based on a reference data associating signatures of compatible components. In this case the processing in  250  includes obtaining the reference data (e.g. from a memory and/or from an external source) and processing the first and second XRF signatures against the reference data to determine whether there is an indication of a correspondence between them a in the reference data. 
     In case the conclusion in operation  250  is that the detected signatures are not complementary, the components C 1  and C 2  are thus determined to be not compatible with one another and method  200  may end, while possibly providing/outputting indication that the components are not compatible. 
     In case the conclusion in operation  250  is that the detected signatures are complementary, the components C 1  and C 2  may thus be determined to be compatible with one another and/or with the electronic system  100 . In this case operation  260  may optionally be carried out to provide/output suitable indication of the compatibility of the components in the system  100  (which may be in turn an indication that the system and/or the components are authentic and not counterfeit system/components). 
     Accordingly, in this case whereby the components C 1  and C 2  are compatible with one another (e.g. can be suitably used together in the system  100 ), additional operations  270   280  and/or  290  of method  200  may optionally be further carried out. For instance, operation  270  may optionally be carried out for determining/verifying correct arrangement of the first and second the electronic components C 1  and C 2  in the electronic system  100 . This was described/exemplified above with reference to  FIG. 2B  and is also further described in more detail with reference to  4 A below. Alternatively or additionally, upon identifying that the components C 1  and C 2  are compatible, operation  280  may be carried out for assembling the electronic system  100  (e.g. possibly based on the locations/arrangement of the components as may be determined in optional operation  270 ). Yet alternatively or additionally, upon identifying that the components C 1  and C 2  are compatible operation  290  may be carried out for pairing the first and second electronic components C 1  and C 2  of the electronic system  100 . This was described/exemplified above with reference to  FIG. 2D  and is also further described in more detail below with reference to  4 C. 
     Reference is now made to  FIG. 4A  which is a flow chart of a method  200 A for verifying compatibility of components (e.g. C 1  and C 2 ) of an electronic system (e.g.  100 ) and determining/verifying corrected placement/arrangement of the components in the electronic system. Method  200 A may be carried out for example in cases where the first component C 1  is an electronic circuit board and the second component C 2  is an electronic component associated with a designated place LC 2  on the circuit board C 1 . It should be noted, that method  200 A includes operations that are similar to those described above with reference to the method  200  of  FIG. 3 , which are marked by similar reference numerals in the flow chart  200 A and are therefore not described in details in the following. 
     Operation  230  of method  200 A includes irradiating, operations  232  and  234 , of the first and second components C 1  and C 2  with XRF exciting radiation. In this example, one of the components, (e.g. the first component C 1  being the circuit board) may be irradiated operation  232  with spatially scanning XRF exciting radiation, to thereby determined the location (e.g. LC 2  designated for the second component, or a location indicative of the location LC 2 ) on the first component C 1 . 
     In this case the first XRF marking composition XRFM 1  is spatially located on the circuit board at the designated location LC 2  of the second component (or a location indicative thereof) and therefore spatially located on said circuit board at said designated location of the second component on the circuit board. 
     In this embodiment, operation  240  for detecting XRF response signals from the components of the system includes the operation  242  for determining a location LC 2  of the first XRF mark XRFM 1  on the first component C 1  (PCB). This may be for example achieved by monitoring the state (position/angular orientation of the radiation beam) of the spatially scanning XRF exciting radiation from the scanning XRF analyzer, at the time the first XRF signature XRFS 1  (e.g. of a signature corresponding/matching the signature XRFS 2  from the second component C 2 ) is identified and thereby determining the location LC 2  of the first XRF mark XRFM 1  on the PCB. This location LC 2  is thus indicative of a designated placement of the second component C 2  on the PCB/first component C 1 . 
     Accordingly in this embodiment the method  200 A further includes operation  270  which is carried out to determine the correct arrangement (and proper placement location LC 2 ) of the second component C 2  on the first component (circuit board) C 1 . Indeed identifying the designated location is based on a correspondence between the first signature obtained from the designated location LC 2  and the second signature obtained from the second component. Optionally, method  200 A includes operation  272  for assembling (e.g. automatically assembling) the second component C 2  on the first component C 1  at the proper placement location LC 2 . Optionally, alternatively or additionally, method  200 A includes operation  274  for performing quality assurance (QA) by verifying that the second component is correctly assembled on said first component at the proper placement location. Indeed in this case the component C 2  may already be mounted on the designated location LC 2 , and accordingly the XRF signatures XRFS 1  and XRFS 2  may be obtained together as in a cumulative/composite signature CXRFS including them both. This is described in more details with reference to  FIG. 4B . 
       FIG. 4B  is a flow chart  200 B of a method according to an embodiment of the present invention for determining whether a two or more components C 1  and C 2  of an electronic system  100 , which are located/connected together, are compatible with one another. It should be noted that generally the method  200 B may be combined with the method  200 A (which as described above utilizes the scanning XRF analyzer), for the purpose of carrying out QA and/or authenticity and/or counterfeit checks of assembled electronic systems. It should also be noted that where method  200 B includes operations that are similar to those described above with reference to the method  200  of  FIG. 3  and/or to the method of  FIG. 4A , such operations are marked by similar reference numerals in the flow chart  200 B and are not described in details in the following. 
     Thus in operations  210  and  220  of method  200 B includes providing a first and a second components C 1  and C 2  presumably associated with the electronic system  100  and optionally assembled together, whereby the first component has a first XRF mark and the second component has a second XRF mark. Optionally ( 228  in the figure) the first and second XRF marks of the first and second components the first and second XRF marks should match in case the components C 1  and C 2  are complementary associated with the system  100 , and should be also respectively configured for providing non-interfering XRF signals/signatures. 
     Operation  230  of method  200 B for irradiating the first and second components with XRF exciting radiation includes operation  236  for irradiating the first and second components together with XRF exciting radiation. Operation  240  of method  200 B for detecting XRF response signal(s) indicative of the XRF signatures of components C 1  and C 2 , includes in method  200 B detection of an composite XRF response signal indicative of a super position of the first and a second XRF signatures of the first and second components. Accordingly operation  250  in the method  200 B for determining whether there is a match between the first and second XRF signatures, includes operation  252  for determining whether the first and second components are complementary is based on a matching between the first and second XRF signatures that are represented in the cumulative/composite XRF signature CXRFS (see for example row 2 in table 1 of  FIG. 1 ). 
     This allows verifying if the components, C 1  and C 2 , assembled together are complementary and thus allows to authenticate the electronic system based on the match between the first and second XRF signatures (as indicated in operation  262 ). In this regards the first component C 1  may be an electronic component and the second component C 2  may be a casing/packaging thereof. For example the first and second components may constitute parts of a chip assembly, as described above with reference to  FIG. 2C . 
     Reference is now made to  FIG. 4C  which shows a flow chart  200 C of a method according to an embodiment of the present invention for pairing between two components of an electronic system (e.g. providing elemental pairing between the components), possibly only in case the components are compatible. 
     It should also be noted that where method  200 C includes operations that are similar to those described above with reference to the method  200  of  FIG. 3  and/or with reference to the methods of  FIGS. 4A and 4B , such operations are marked by similar reference numerals in the flow chart  200 C and are not described in details in the following. It is also noted that the non-essential/optional operations of this method  200 C (e.g. operation  250  for verifying/determining whether the components C 1  and C 2 ) are compatible are marked in the figure with dashed lines. 
     Method  200 C includes operation  290 , which is carried out in addition to one or more of the above described operations  210  to  280  (some of which may be optional as illustrated in the figure). Operation  290  is carried out for pairing the first and second electronic components C 1  and C 2  of the electronic system  100 , which may be two electronic devices of a distributed electronic system. Operation  290  includes operation  292  registering a code (a first data portion) associated with the XRF signature (e.g. XRFS 2 ) of a certain component (e.g. C 2 ) of the electronic system  100  in a data storage module (e.g. memory MEM 1 ) of another component (e.g. C 1 ) of the system  100 . Optionally, operation  290  also includes carrying out optional operation  294 . This optional operation should be carried out for example case a code (e.g. a second data portion) corresponding to the XRF signature of that certain component C 2  is not stored in a data storage module (memory MEM 2 ) of that component C 2  (e.g. generally such code (second data portion) may already be stored in the memory of the component C 2  during its manufacture). Optional operation  294  includes registering the code (second data portion) corresponding to the XRF signature of that certain component C 2  in the memory MEM 2  of that certain component C 2 , or at least verifying that such code (second data portion) is indeed registered/stored in the memory MEM 2 . 
     Thus operation  290  enables enabling activation of the electronic system  100  based on particular identification that the specific components of the system are connected together (identifying that the connection between the certain component C 2  and the another component C 1 ). 
     Method  200 C, and particularly operation  290  may be for example carried out for pairing to devices, C 1  and C 2  such as those illustrated in  FIG. 2D  above. In such examples the first component C 1  is a first electronic device including a memory, for storing a first data portion (code) indicative of a correspondence between said first and second XRF signatures. The second component C 2  is a second device comprising a second memory capable of storing a second data portion (e.g. the same code or a corresponding code) which is indicative of a correspondence between first and second XRF signatures. At least one of said first and second devices, C 1  and C 2 , may include or be associated with a pairing/activation controller ACTRL that is configured and operable for obtaining the first and second data portions (codes) from the memories MEM 1  and MEM 2  and processing them to determine whether the first and second devices are paired to enable conditioned activation of mutual operation of the first and second devices based on a pairing between them. 
     As indicated above, in various embodiments of the present invention the XRF markings XRFM 1  and XRFM 2  may be applied to (e.g. applied on and/or embedded/blended) different substrate materials of different components of the electronic system  100 , and accordingly different marking compositions of different components may be configured-with, or include, different promoters and/or different binder materials in accordance with the substrate to which they are to be applied. Indeed the different substrate materials and/or the different binder and/or promoters) used in different marking compositions may result with detection of different XRF background clutter, when measuring the XRF of different components of the system which are made from different substrates. Additionally, different textures and surface topologies (e.g. the surface of the substrate may be smooth or on the other hand may include recesses and/or protrusion) may also affect the measured XRF signals (for instance, due to variance in angles between the radiation source the surface of the substrate and the detector). The XRF signals measured by the detector will therefore include other components in addition to the XRF signature which is determined by the different substrates. This difference in the clutter and other components might affect the XRF signature emanating from the object and the code word identified/determined. 
     In this regard reference is made together to  FIGS. 5A and 5B .  FIG. 5A  is a block diagram illustrating an XRF marker mXRF configured according to an embodiment of the present invention with an XRF marking composition including active XRF elements ME with predetermined relative concentrations furnished with a component, such as an electronic component, having a substrate material SB. It should be understood that in this example XRF marker mXRF may not be necessarily furnished on the component in the form of a marking layer ML, but the marking composition ME may also be alternatively or additionally coupled to the component in other ways, e.g. embedded in the materials of the component or its substrate SB. The XRF marker mXRF and the component (or at least its substrate SB) form together an XRF marked component C. In this particular non-limiting example the XRF marker mXRF is illustrated as a layer ML of the XRF marking composition ME furnished on a substrate SB of a component, such as an electronic component, and these together form an XRF marked electronic component C. The substrate SB in this example is XRF responsive substrate which is associated with emission of significant XRF background clutter in response to said irradiation by the XRF exciting radiation. In general the responsive substrate may be a metallic substrate or a substrate including metallic elements which may be plastic or ceramic substrate with metallic elements or compositions thereof included therein. For illustrative purposes, XRF exciting radiation R from radiation source  412  are illustrated in the figure, as well as corresponding XRF responses, XRFS and XRFB, reaching an XRF detector  415  from the layer ML of the XRF marker mXRF and the substrate SB respectively.  FIG. 5B , is a graphical illustration schematically showing the spectral profile of: (i) a graph RSP of the spectral profile of the total XRF response reaching the detector  415  from the XRF marked electronic component C; (ii) a graph XRFS of the spectral profile of the XRF response reaching the detector  415  from the layer ML of the XRF marker mXRF; and (iii) a graph XRFB of the spectral profile of the XRF response reaching the detector  415  from the substrate SB of the component C. The graphs are provided as intensity INT (Y axis) vs. Spectra (frequency—X axis) in arbitrary units. As shown the spectral profile of the total XRF response reaching the detector  415 , which is graph RSP, is about equal to a sum of the XRF responses from the substrate SB and the XRF marker mXRF: RSP˜=XRFB+XRFS. Dashed horizontal lines in each of these graphs illustrate the threshold above which signal detection is considered valid/authentic measurement. For clarity, in this particular non limiting example the detection threshold is illustrated as a horizontal line constant across the spectrum, however it should be understood that in a general implementation of the present invention the detection threshold may be spectrally dependent (may not be fixed across the spectral regime of the measurement) and may be determined based on various factors, such as the detection signal to noise/clutter ratio(s) (SNR/SCR), the background radiation during the measurement, and/or based on other factors such as trend and seasonality components of the XRF response, as described for example in U.S. Pat. No. 10,539,521 co-assigned to the assignee of the present invention. As shown in this example, the spectral profile of the total XRF response RSP includes 7 spectral peaks P 1  to P 7 , of which only spectral peaks P 1 , P 2 , P 4 , P 6  and P 7  are above the threshold. It is noted that spectral peaks P 1 , P 3 , P 6  and P 7  are contributed by the XRF marking composition ME of the XRF marker mXRF. In this particular non-limiting example these peaks are contributed only by the XRF marker mXRF and not from the substrate—however it will be appreciated that this is not necessary and generally the technique of the present invention as described in details in  FIGS. 5C and 5D  below, will operate also when one or more peaks are contributed from both the XRF responses of the substrate SB and the XRF marker mXRF. The spectral peaks P 2 , P 4  and P 5  (which are marked in dashed-dotted line in the total response graph RSP) are contributed by the XRF response of the substrate SB. 
     To this end the graphs of  FIG. 5B  demonstrate a problem which arises in some cases where various components having are to be marked by XRF markings. The resulting XRF signature, (e.g. being the part of the total XRF response RSP which is above the threshold) may include contribution not only from only from the marking composition ME) but also from the substrate/material SB of the marked component C itself, or from the different binder and/or promoter materials in the XRF marker mXRF. Accordingly, different components C (e.g. including different respective substrate materials SB), or different components include different binder and/or promoter materials of the XRF markers mXRF used to mark different components, may yield different XRF signatures, even in cases where the different components are marked by the by the similar marking composition ME. 
     As shown in  FIG. 5C  the present invention provides a novel calibration technique/method  500 A for calibrating XRF analyzers. Advantageously the technique/method  500 A provides a simple way to determine the calibration data for marking new types of substrates while obviating a need to perform specific calibration per each type substrate to account for the specific material composition and/or texture of the substrate and/or the technique used marking the substrate. This calibration method may be used for calibrating XRF analyzers in order to allow accurate measurements of XRF signatures (e.g. XRFS 1  and XRFS 2 ) of XRF marking compositions, which are embedded/located at different components (e.g. C 1  and C 2 ) of the system  100 , possibly embedded located on different substrate materials of those components. This technique may be used in various implementations of the present invention to facilitate accurate detection and measurement of the XRF signatures XRFS 1  and XRFS 2  of the different components and to enable reliable comparison between them (e.g. using the predetermined condition and/or reference data as described above) to reliably determine whether the components are compatible. This calibration technique is described in the following with reference to  FIG. 5C . Advantageously the calibration technique of  FIG. 5C  provides a simple way to determine the calibration data for marking new types of substrates without having to perform specific calibration to each new type substrate, which is to be marked by the XRF marking of the invention. 
     Reference is made to  FIG. 5C  which is a flow chart of a method  500 A for multi-substrate calibration of an XRF analyzer according to an embodiment of the present invention. 
     The method  500 A provides for obtaining an optimal calibration of XRF analyzers, enabling the accurate identification of one or more XRF marking elements/materials, which may be deposited on various substrates (e.g. media) by various deposition methods as exemplified for example in Table 2 and/or in sections (a) to (i) above. 
     In general the calibration method  500  provides for generating a calibration data (e.g. in the form of, or indicative of, a curve/plot) associating the counts collected in a time period (e.g. counts per second (CPS)) of x-ray photons within certain energy range(s) that are received from a component (e.g. C 1 ) of the electronic system  100  with the concentration of a corresponding XRF marker element/material (which emits XRF in the same energy range(s)) that is included in the component (e.g. C 1 ), and practically regardless of the substrate at which the XRF marker is deposited in the component. In other words, the method  500 A provides for translating the CPS of one or more peak of an x-ray spectrum of XRF emission received from the component, into concentration (commonly measured in particles per million (ppm)) of the XRF marking element in that component, while being substantially indifferent to the substrate of the components on to which the XRF marking composition is applied and/or also regardless of the types of the additional materials (e.g. adhesives/binders/promoters) which are used in the XRF marking compositions for binding the XRF marking element(s) to the particular substrate of particular components, and the type of the substrate. This facilitates utilizing the technique of the present invention with various types of components of the electronic systems and embedding the XRF markers at different substrates. 
     Calibration method  500 A is performed by utilizing a plurality of samples (also referred to herein as standards) in which one or more XRF marking element(s) is/are present in various known concentration(s) in a various media or substrates (where typically there are a number of samples with a number of concentrations for each substrate type). The standards/samples are then interrogated using the XRF analyzer. That is, the standards/samples are irradiated with x-ray or gamma-ray radiation and the secondary radiation arriving from the standards/samples in response are measured, thus receiving a CPS value for each of the samples/samples which are respectively associated with known concentration(s) of the XRF marking elements. Then reference calibration data for the calibrating XRF signals is based on the data acquired from the standard samples. The pair (CPS value, concentration) represents a point in the CPS Vs. concentration (PPM) plane and the calibration curve is generated by fitting a curve to the set of measured points (e.g. by the method of least squares which generates the ‘best’ linear curve). 
     Commonly, the samples standards are made of known materials containing varying concentrations of the XRF marker element(s), and the calibration is intended to be used for finding concentrations of the XRF marker element in a media of the type used in the samples/standards (e.g. metals, polymers, fabric). Therefore calibration is performed while using each type of media/substrate which may include XRF markings in the components of interest. This is because each substrate generates different background x-ray radiation, therefore calibration (calibration curve) made with samples/standards of one group of substrates would generally not be suitable for measurements taken with other types of substrates). More specifically, method  500 A includes performing the following operations  520  to  540  which are carried out for the plurality of various substrate (e.g. media) material on to which XRF markings are to be applied by various binding techniques:
         Operation  520  includes providing plurality of samples/standards of a plurality of substrate materials whereby for each substrate there may be several samples with XRF marking compositions having different predetermined concentration(s) of XRF marker element(s).   Operation  530  includes interrogating the plurality of samples/standards by an XRF analyzer to determine counts per second (CPS) value for each standard/sample having the predetermined concentration(s) of XRF marking elements, whereby the CPS is indicative of photons of a certain energy range(s) corresponding the XRF emission from those marking elements arriving from the standard/sample in response to the interrogation; and   Operation  540  includes utilizing data indicative of the predetermined concentration(s) (CNCTR) of active XRF marker elements in the various standards/samples (CNCTR), and the corresponding CPSs obtained from the respective samples/standards respectively to generate XRF-calibration-data for calibration of XRF measurements/signatures of XRF markings applied to various substrates. The XRF-calibration-data includes data associating different concentration(s) of the XRF markers in the samples/standard with the respective CPSs obtained therefrom. Accordingly, the XRF-calibration-data allows for calibration the spectral response of XRF signatures determine (represent those signatures) in terms of the concentrations of the XRF marking elements located at the substrate.   Thus, according to various embodiments of the present invention an XRF reader system that is configured for carrying out XRF measurements of XRF markings on different substrates, may be equipped with the calibration data as obtained by method  500 A above and may be configured to utilize the calibration data to convert/translate the XRF signatures obtained from XRF markings on different substrates to a common basis (e.g. being the marking material concentration bases instead of the spectral basis at which the signatures are initially obtained from the XRF analyzer). Accordingly, this allows accurate and reliable processing and/or comparison XRF markings applied to different components made with different substrates (e.g. comparison of between the XRF markings of the components and/or between them and a reference data.       

     It should be noted that optionally according to some embodiments of the present invention, operation  530  which is carried out for interrogating the plurality of samples/standards by an XRF analyzer, includes an SNR optimization step  535  which is carried out to optimize/determine the parameters of the XRF exciting radiation which should be emitted during the XRF interrogation in order to optimize the SNR of the XRF signatures read from the standards/samples. SNR optimization step  535  may for example include the following: 
     (I) Applying XRF measurements to the plurality of samples for measuring the XRF spectrum arriving from each sample (spectrum of secondary x-ray radiation arriving from each sample in response to x-ray or gamma-ray radiation). 
     (II) Processing the XRF spectrum arriving from each sample to determine an XRF signature of the sample/standard—(by identifying the peak (or peaks) associated with the XRF marker elements for each spectrum). 
     (III) Evaluating the signal to noise ratios (SNR) of the XRF signatures of the samples/standards and selecting from the samples/standards, a sample/standard having medium (‘average’) SNR. E.g. selecting a sample/standard whose SNR is closest to the average SNR of all the standards, and/or alternatively, randomly choosing a standard, whose SNR is not too close (closer than a preselected distance) to one of the extreme values (best or worst)).
 
(IV) Varying the XRF measurement parameters (e.g. XRF tube voltage, XRF tube current, XRF filter, and distance from the standard) to optimizing the SNR of the XRF signature from the selected standard/sample.
 
(V) Then, carrying the operation  530  as described above for interrogating/measuring the XRF spectrum (signatures) of all of the standards/samples of all substrates but with the selected/optimized XRF measurement parameters.
 
(VI) Optionally, discarding spectrum measurements of standards whose SNR is lower than a preselected value.
 
     After performing the operation  530  in the way to optimize the SNR, the method further continues to operation  540  for obtaining a calibration data/curve. 
     Thus, the calibration data for the different substrates, as obtained in operation  540  indicates a fit between the XRF signatures measured in terms of CPS vs. wavelengths/energy (λ) to the XRF signatures in terms of the concentrations of the XRF marking elements in different substrates, as illustrated in Table 3 above. Optionally the calibration data may also include data indicative of the XRF measurement parameters (e.g. XRF tube voltage, XRF tube current, XRF filter, and distance from the standard) which are obtained in operation  535  and which should be used for measuring the XRF responses from different substrates. 
     Reference is now made to  FIG. 5D  which is a block diagram of an XRF verification reader  400  for use for verification of compatibility of components of electronic system according to an embodiment of the present invention. 
     The XRF verification reader  400  includes an XRF analyzer  410  adapted for performing XRF measurements on different components (e.g. C 1  and C 2 ) of electronic systems (e.g.  100 ), and providing data indicative of XRF signatures XRFS 1  and XRFS 2  obtained from XRF markings thereon. The XRF verification reader  400  also includes a XRF signature correspondence data provider  430  and XRF signature correspondence processor  440  which may be used together to determine whether the XRF signatures XRFS 1  and XRFS 2  obtained from the XRF analyzer  410  correspond to one another, and in that case issue indication that IND that the components (e.g. C 1  and C 2 ) which XRF markings are measured by the XRF analyzer  410  are compatible or otherwise issue indication IND that the components are not compatible. 
     In certain embodiments the XRF signature correspondence data provider  430  includes a data storage facility (e.g. memory) that stores data, such as a predetermined condition data indicative of a predetermined condition according to which a match between different XRF signatures, XRFS 1  and XRFS 2 , should be determined, and and/or storing reference data, such as a LUT that associates corresponding XRF signatures. Alternatively or additionally, in certain embodiments the XRF signature correspondence data provider  430  includes communication utility adapted for communicating, e.g. with a remote data source, to obtain the reference data indicative of the correspondence between the XRF signatures. 
     Accordingly, the XRF signature correspondence processor  440  may be connected, directly or in directly to the XRF analyzer  410  for receiving therefrom data indicative of the XRF signatures, XRFS 1  and XRFS 2 , and may also be connected to the signature correspondence data provider  430  for receiving data/condition indicative of correspondence/matching between the signatures. The XRF signature correspondence processor  430  processes the XRF signatures, XRFS 1  and XRFS 2  based on the correspondence data and determines whether they correspond, according to any one of the techniques described above. 
     The XRF analyzer  410  generally include an interrogation radiation emitter  411  which includes an X-Ray and/or Gamma-ray radiation source  412  for emitting interrogation radiation towards an inspected object/component, and an XRF detector  415 , possibly comprising a spectrometer  416 , adapted for detecting the XRF radiation response from the interrogated object and possibly obtaining data indicative of its spectral composition. 
     The XRF analyzer  410  may also include one or more filters  417  for filtering the detected XRF response. These may include a spectral filter  418  for filtering out les relevant spectral components form the response, leaving in the detected XRF signatures only the spectral regions at which an XRF response of interest is expected from the interrogated object/component. Also the filters  417  may include a trend and/or periodicity filter  419  (such as that described for example in PCT patent application No. PCT/IL2016/050340 which is incorporated herein by reference), which is operable for enhancing the SNR of the XRF signals/signatures by removing the trend and/or the periodic spectral components therefrom. 
     In some embodiments the interrogation radiation emitter  411  includes a radiation beam scanner  413  which is configured and operable for spatially directing and/or focusing the interrogation radiation beam outputted from the radiation source  412  so as to scan an interrogated object (e.g. electronic system  100 ) with the beam, and thereby provide data indicative of the locations (e.g. LC 1  and LC 2  in  FIG. 2B ) at which various components of the system may be assembled. 
     Optionally, in some embodiments the XRF verification reader  400  also includes an XRF signature calibration module  420  and a calibration DATA Provider  425  which are operable together to calibrate the XRF signatures, XRFS 1  and XRFS 2  which may be obtained from XRF markings which are embedded/applied to different components made/including different substrate materials. The calibration DATA Provider  425  may be for example a storage facility/memory for XRF calibration data for different substrates. The calibration data may for example similar to that obtained by method  500 A above and may include curve fitting (e.g. curve fitting) data indicative of a substrate specific relationship between the spectral curves (obtained as a function of CPS vs. wavelength/energy) in the XRF signatures XRFS 1  and XRFS 2  and the concentration of XRF marking elements in the XRF marking compositions marking the substrates of the components C 1  and C 2  from which the XRF signatures XRFS 1  and XRFS 2  were obtained. Accordingly the XRF signature calibration module  420  may utilize the calibration data to convert the XRFS t  and XRFS 2  from the spectral basis to respective XRF signatures, XRFMC 1  and XRFMC 2 , represented in the basis of the concentrations of the XRF markers in the marking compositions used to mark the respective substrates from which the XRF signatures were obtained. This allows comparing XRF markings of different components and/or form different substrates. 
     Optionally the calibration data from the calibration DATA Provider  425  also includes the data indicative of the XRF measurement parameters (e.g. XRF tube voltage, XRF tube current, XRF filter, and distance from the standard) as obtained in operation  535  described above, Accordingly the interrogation radiation emitter  411  may optionally include an Interrogation controller  414  configured and operable for receiving the reference data about the XRF measurement parameters corresponding to the substrate(s) of the component(s) on which XRF interrogation is to be applied, and adjusting the emission properties of the radiation emitter accordingly, thereby calibration the radiation emission of the interrogated components at which the XRF marking resides. 
     It should be understood both the XRF signature calibration module  420  and a calibration DATA Provider  425  are optional and may be obviated. For example, as discussed above in some cases in the code word of an XRF signature is not indicative of the concentrations of the XRF marking elements in the marking composition but is associated with XRF signature that is read from the marked object/component as a whole, including the marking composition as well as the effects of the substrate of the component to which the marking composition is applied and the method of application of the marking. In that case there may be not need to determine the concentrations of the marker elements but instead the XRF signature from the component itself may represent the code-word of the marking. Accordingly, in this case calibration module may be obviated, while possibly relaying on the XRF signature correspondence data provider  430  and XRF signature correspondence processor  440  to determine whether the XRF signatures XRFS 1  and XRFS 2  (which may be obtained from the same marking composition applied to different components/substrates) correspond to one another. 
     Thus the technique of the present invention described with reference to  FIGS. 5A to 5D  above demonstrate how the problem of clutter/background XRF radiation emanating from a substrate/material SB may be solved according to the present invention by suitable processing/analysis of the XRF response signals RSP emanating from the component C and the XRF marker. 
     An alternative solution to the similar problem is provided according to an embodiment of the present invention by utilizing a novel XRF marker configuration, referred to herein a multilayered XRF marker. In this regard, reference is made together to  FIGS. 6A and 6B  schematically illustrating how the above indicated problem of clutter/background XRF radiation emanating from a substrate/material SB (or other materials of an electronic component at which the XRF marking composition is implemented) of a component C with which an XRF marking composition ME is implemented, are mitigated by a multilayered XRF marker mXRF configured according to an embodiment of the present invention. It should be understood that any of the XRF markings discussed with reference to the embodiments above (e.g. XRFM 1 , XRFM 2 , XRFM 13 , XRFM 14 , XRFM 33 , XRFM 34 ) may be configured and operable according to the present invention as multilayer XRF readable mark as was described above and is described and exemplified in more details in the following. 
       FIG. 6A  is a block diagram illustrating a multilayered XRF marker mXRFM configured according to an embodiment of the present invention. The multilayer XRF readable mark mXRFM is shown in the figure to be implemented with a component/object C e.g. on a substrate/material SB of an electronic component (i.e.  FIG. 6  also illustrates the electronic component C including the multilayerXRF readable mark mXRFM). The multilayer XRF readable mark mXRFM according to this embodiments of the present invention is configured and operable for diminishing (reducing/attenuating or practically eliminating) the XRF clutter/background XRFC emanated by the substrate SB, while still emitting the XRF signal XRFS (e.g. serving as signature of component/object). For illustrative purposes  FIG. 6  shows a radiation source  412  emitting XRF exciting radiation R, and an XRF detector  415  capable of detecting XRF responses emitted in response to the exciting radiation R. In this regards the XRF responses including XRF signals/signatures XRFS emitted by the active XRF elements ME of the XRF readable mark mXRFM as well as clutter/background XRF responses XRFC emitted by other substrate/materials of the electronic component C. It would be appreciated that the radiation source  412  and the XRF detector  415  as well as the radiation and XRF signals/clutter (R, XRFS and XRFC), and also the electronic component C or its substrate/material SB, are not part of the multilayer XRF readable mark mXRFM, and are shown in the figure for illustration purposes. Also, illustratively the thicknesses of the arrows, which are used in the figure to illustrate exciting radiation R and the XRF signals/clutter, are selected to indicate illustratively how the intensity of these radiation and XRF responses vary during passage in the respective layers of the multilayer XRF readable mark mXRFM. 
     In this example, the substrate SB of the object/component C is XRF responsive substrate associated with emission of significant XRF background clutter in response to said irradiation by the XRF exciting radiation. For instance the XRF responsive substrate may be a metallic substrate or a substrate including metallic elements, which may be plastic or ceramic substrate with metallic elements or compositions thereof included therein. Typically the metallic elements of the substrate are associated with significant XRF responses which might, if not otherwise attenuated, in some implementations interfere or prevent accurate measurement of the XRF response of the marking composition of the XRF readable mark. As shown in the figure, according to some embodiments of the present invention the multilayer XRF readable mark mXRFM includes: 
     a. an attenuation/mask layer AL comprising one or more materials HAE exhibiting high absorbance for at least one of: (i) the XRF exciting radiation R; and (ii) the XRF response(s)—i.e. at least the background XRF clutter XRFC being the response from the substrate; and 
     b. a marking layer ML comprising an XRF marking composition ME with specific active XRF elements/material whose types and relative concentrations are selected to emit, in response to irradiation by the XRF exciting radiation, the XRF signal XRFS having a characterizing XRF signature indicative of the XRF mark mXRFM (i.e. a signature indicative of the components C with which the XRF mark to be implemented). 
     According to an embodiment of the present invention, the XRF readable mark mXRFM is implemented with the component C such that the XRF readable mark mXRFM is placed on top of a surface S of a certain substrate/material SB of the component C whereby such that the attenuation/mask layer AL of the multilayer XRF readable mark mXRFM intermediates (i.e. is located in between) the surface S of the substrate SB and the marking layer ML of the XRF readable mark. 
     Accordingly, the attenuating layer AL may attenuate the part of exciting X-ray or Gamma-ray radiation R which propagates to the substrate (as well as attenuating XRF emissions from the marking layer which are directed to the substrate), thereby reducing the amount of XRF exciting radiation reaching the substrate and attenuating an XRF response XRFC from the substrate (which is background clutter in respect to the XRF signal/signature XRFS of the XRF marker mXRFS that is to be identified. This mechanism is illustrated in the figure by the reduction in the thickness of the arrows of the exciting radiation R during its passage through the attenuation layer AL. Alternatively or additionally, the attenuating layer AL may also operate to attenuate the XRF response XRFC emitted by the substrate SB (which is as said background clutter) by absorbing all, or a substantial part of, the XRFC background clutter from the substrate SB, when the later propagates through the attenuating layer AL along a propagation path to the detector  115 . This mechanism is illustrated in the figure by the reduction in the thickness of the arrows of the XRF response clutter XRFC emitted by the substrate SB during its passage through the attenuation layer AL. The above one or both mechanisms provide that the attenuation layer AL effectively reduces the intensity of the background clutter XRFC from the substrate, from reaching the detector  115 . 
     In general the attenuation of an X-ray beam (or equivalently XRF response) of a given wavelength after traveling a distance x within the media of the attenuation layer AL (hereinafter referred to as attenuation media) is given by the formula:
 
 I=I   0 exp(−μ s   ρx )
 
where μ i  in the intensity after passage via an attenuating media, I 0  is the initial intensity of the radiation (prior to passage via the media), ρ is the density of the sample (gram/cm 3  i.e. mass per unit volume), and μ s  is the mass absorption coefficient (e.g. in units of cm 2 /gram) of the sample as a whole. The sample mass absorption coefficient μ s  is given by the following sum:
 
               μ   s     =       ∑   i     ⁢       μ   i     ⁢     C   i               
wherein μ i  is the mass absorption coefficient (e.g. in units of cm 2 /gram) of a particular element in the media, and C i  (percentage) is the relative concentration of the element indexed in the media. Thus the sum μ s  presents the average mass absorption coefficient of the media considering the relative concentrations C i  of all the materials/atomic-elements present in the media. To this end ρ*x is the average aerial density of the attenuation media.
 
     The attenuated fraction of the XRF response from the substrate SB (i.e. the part diminished by the attenuation layer AL, is therefore F Response =1−exp(−μ s ρx). In practical implantations of the invention it is desired to achieve an attenuation F Response  of about 60% or more of the XRF response from the substrate (e.g. more preferably attenuation layer providing higher attenuation of 75% or even more 90% is used). 
     Accordingly, in order to obtain attenuation of at least 60% the attenuation layer is configured such that μ s ρx≥1. I.e. the thickness x of the attenuation layer AL multiplied by its density ρ multiplied by the average mass absorption coefficient μ s  is equal or greater than one. 
     It should also be noted the attenuation layer adds to the distance between the emitter and the responsive substrate and the distance between the responsive substrate and the detector. Therefore, the attenuating layer generally reduces the signal XRFC of the XRF responsive substrate at the detector even if the attenuating layer is composed of light materials. This mechanism of utilizing the thick attenuation layer for reduction of the signal XRFC of the responsive substrate SB is more effective the for lower energy XRFC signals from the XRF responsive substrate (e.g. for XRFC response of photon energy up to 5-10 Key emitted by lighter materials present in the XRF responsive substrate). Moreover the attenuation by this mechanism, depends on the thickness of the attenuation layer (greater attenuation is achieved with thicker layer), and therefore in some embodiments of the present invention where this mechanism is exploited, the attenuation layer is implemented with relatively high thickness x (e.g. thickness x of hundreds of microns). 
     Alternatively or additionally, in some embodiments of the present invention attenuation layer is not necessarily so thick, as a thin attenuation layer AL with atomic elements of relatively high atomic number (i.e. having relatively high mass absorption coefficient(s) μ i ), may provide sufficient absorbance of either the exciting XRF radiation R and/or of the XRF response XRFC from the substrate SB, and may also provide sufficient attenuation for radiation/XRF-response with photon of energy higher than energy 10 Kev. 
       FIG. 6B , is a graphical illustration schematically showing the spectral profile of: (i) a graph RSP of the spectral profile of the total XRF response reaching the detector  415  from the XRF marked electronic component C; (ii) a graph XRFS of the spectral profile of the XRF response reaching the detector  415  from the layer ML of the multilayered XRF marker mXRFM; (iii) a graph ATN of the spectral profile of the XRF response reaching the detector  415  from the attenuation layer AL of the multilayered XRF marker mXRFM; and (iv) a graph XRFC of the spectral profile of the XRF response (background clutter) from the substrate SB of the component C (this response is attenuated by the attenuation layer AL as illustrated by the diminished peaks in the dashed-dotted parts of the total XRF response graph RSP). The graphs are provided as intensity INT (Y axis) vs. Spectra SPCT (frequency—X axis) in arbitrary units. As shown, the spectral profile of the total XRF response reaching the detector  415 , which is graph RSP, is about equal to a sum of the XRF responses from the attenuation layer AL and the XRF marker mXRFM, plus substantially diminished part (fraction F) of the background XRF clutter XRFC from the substrate SB: RSP˜ 32  XRFB+XRFS+(1−F)*XRFC. Dashed horizontal lines in each of these graphs schematically illustrate the detection threshold above which signal detection is considered valid/authentic measurement. The detection threshold may be set by several factors including the signal to noise ratio (SNR) and/or the signal to clutter ratio (SCR) and/or the intensity background radiation in the corresponding spectral regime, and the required accuracy of the measurement. For clarity, in this particular non-limiting example the detection threshold is illustrated as a horizontal line constant across the spectrum, however it should be understood that in a general implementation of the present invention the detection threshold may be spectrally dependent (may not be fixed across the spectral regime of the measurement) and may be determined based on various factors, such as trend and seasonality components of the XRF response, as described for example in PCT application U.S. Pat. No. 10,539,521 co-assigned to the assignee of the present invention. As will be further clarified below the diminished part (fraction F) of the background XRF clutter XRFC from the substrate SB depends on the types of the one or more materials HAE exhibiting high XRF absorbance in the attenuation layer AL of the multilayered XRF marker mXRFM and on their concentrations and the thickness of the attenuation layer AL. The concentrations of the materials HAE exhibiting the high XRF absorbance and the thickness of the attenuation layer AL define the aerial/column density of these materials HAE in the attenuation layer AL. Generally, the higher the aerial/column density of these high XRF absorbance materials HAE in the attenuation layer AL, the larger if the fraction F of the background XRF response from the substrate XRFC which is absorbed/diminished by the attenuation layer AL. 
     As shown in this example, the spectral profile of the total XRF response RSP includes 7 spectral peaks P 1  to P 7 , of which only spectral peaks P 1 , P 3 , P 6  and P 7  are above the detection threshold. It is noted that spectral peaks P 1 , P 3 , P 6  and P 7  are contributed by the XRF marking composition ME of the multilayered XRF marker mXRFM. The spectral peak P 3  is contributed not only by the XRF marking composition but also contributed by the XRF response ATN of the attenuation layer AL (see e.g. in the figure ATN-C indicating the part of peak P 3  contributed by the attenuation layer and MRK-C indicating the part of peak P 3  contributed by the marking layer ML). Note that in this particular example, in the absence of the contributions from any one of the attenuation layer AL and the marking layer ML the spectral peak P 3  would have remained below the detection threshold and would therefore not be a part of the XRF signature of the multilayered XRF marker mXRFM. To this end, in this particular example the attenuation layer also form part of the XRF signature of the multilayer XRF marker mXRFM (as in the absence of the attenuation layer the XRF signature would be different—e.g. without peak P 3 ). This is however not necessarily so in other implementations of the multilayered XRF marker mXRFM, and in some cases one or more spectral peaks contributed by the attenuation layer AL and/or the marking layer ML or both, may be below or above the detection threshold as the case may be. The spectral peak P 7  is contributed not only by the XRF marking composition but also contributed by the XRF response XRFC of the substrate SB (see e.g. in the figure SBT-C indicating the part of peak P 7  contributed by the substrate SB layer and MK-C indicating the part of peak P 7  contributed by the marking layer ML). Note that in this particular example, the fact that the contribution SBT-C to peak P 7  by the substrate SB is significantly diminished (see the height of the contribution SBT-C as compared to the corresponding peak in the graph XRFC) provides that the height of the peak P 7  in the total response signal RSP is not substantially affected by the substrate SB. This in turn increases the achievable resolution by which XRF signatures can be resolved from total response signal RSP obtained from different substrates, permits to utilize the height/intensity of the peaks in the total response signal RSP as indicators to the XRF signature embedded in the response signal RSP, and thus enabling to encoded large verity of signatures in the XRF response signal even with XRF markers placed on different substrates. 
     The spectral peaks P 2 , P 4  and P 5  (which are marked in dashed-dotted line in the total response graph RSP) are contributed by the XRF response (background clutter) XRFC of the substrate SB. Comparing these peaks between the graphs XRFC and the graph RSP of the total XRF response reaching the detector  415 , one can appreciate that due to the attenuation layer AL these peaks are diminished by substantial fraction F, or even totally eliminated before reaching the detector. To this end, the multilayered XRF marker mXRFM provides a novel technique for masking the XRF response of an a-priori unknown substrate/material SB of an object/component C which is to be marked by the multilayered XRF marker mXRFM. To achieve said masking, an attenuation layer AL is introduced in the multilayered XRF marker mXRFM to interpose/intermediate between the substrate/material SB of the object/component C and the marking layer ML of the marker. In some embodiments the attenuation layer AL has only small and not significant XRF response, in which case its function is mainly to mask the XRF response of the substrate SB to diminish it by at least a certain fraction F (which may be generally spectrally dependent), in at least a certain spectral domain of interest for determining the XRF signature of the marking mXRFM. In some embodiments, as illustrated in  FIG. 6B , the attenuation layer AL, with or without the marking layer ML, also contributes for peaks (e.g. P 3 ) in the XRF spectral response that are above the detection threshold of the measurement, thereby contributing also for the XRF signature of the multilayered XRF marker mXRFM. 
     To this end the graphs of  FIG. 6B  demonstrate how the problem arising from marking various components having XRF responsive substrate by XRF markers can be solved by utilizing the multilayered XRF marker mXRFM of the present invention. The resulting XRF signature, (e.g. being the part of the total XRF response RSP which is above the detection threshold) may include contribution from the marking composition ME, and possibly from the attenuation layer AL (which is a priori known) while the possibly unknown XRF contribution from the substrate/material SB of the marked component C is masked and diminished. Accordingly, by this technique different components C (e.g. including different respective substrate materials SB) may be marked by the similar multilayered XRF marker to yield the similar XRF signatures. 
     Turing back to  FIG. 6A , it is noted that in some embodiments the multilayered XRF marker mXRFM is fabricated/configured such that the attenuation layer AL extends over an area larger than the area of the marking layer ML (as shown for instance on the left side of the XRF marker mXRFM in the figure, so that the attenuation layer can also attenuate exciting XRF radiation R reaching to the substrate SB not through the marking layer ML and/or attenuate XRF response XRFC from the substrate SB which is directed to the detector not through the marking layer ML. 
     As indicated above, the fraction F of the XRF response XRFC which is diminished (e.g. diminished by any of: (i) by attenuating the exciting XRF radiation R to the substrate SB and/or (ii) by attenuating the XRF response XRFC from the substrate SB) depends on aerial/column density of the one or more elements HAE exhibiting the high absorbance in the attenuation layer ML, and the types of these elements. Elements of higher atomic number have generally better absorbance for exciting XRF radiation R (i.e. for X-rays or Gamma-rays) and also better absorbance for XRF response. Therefore in some embodiments of the present invention at least one element exhibiting the high absorbance in the attenuation layer has an atomic number of at least 13 (this embodiment is particularly suitable for attenuation of relatively low energy XRFC signals from the substrate XRFC e.g. with photon&#39;s energy up to 5 Kev); in another example the atomic number of element is at least 22 (this embodiment is particularly suitable for attenuation of moderate energy XRF signal from the substrate XRFC e.g. with photon&#39;s energy up to 10 Kev); in yet another example the atomic number is at least 45 (this embodiment is suitable attenuation of higher energy XRFC signals from the substrate XRFC e.g. with photon&#39;s energy up to 30 Kev). For example the at least one element exhibiting the high absorbance may be Lead (Pb) having atomic number  82  which therefore absorbs also very high energy XRF photons (e.g. with photon&#39;s energy up to 50 Kev). 
     In some embodiments the attenuation layer AL is configured to provide sufficient diminishing fraction F of the XRF response from the substrate, in the order of F≃60% of the intensity of the XRF response from the substrate XRFC. In cases were the multilayer XRF marker mXRFM is intended/designed to be arranged on the component C such that the part of the XRF exciting radiation R reaching the substrate SB would pass through the attenuation layer AL, the attenuated fraction of the XRF exciting radiation R reaching the substrate would also be F Excitation =[1−exp(−μ s ρx)] The cumulative effects of these two attenuations F excitation  and F Response  generally yield the total diminishing fraction F that is larger than F Response  alone. Thus, in some embodiments of the present invention the attenuation layer may be configured with the parameters satisfying μ s ρx≥½ (where x is the thickness of the attenuation layer AL ρ is its density and μ s  is the average mass absorption coefficient thereof). In such configuration a total diminishing fraction F of at least 60% is obtained whereby the total diminishing fraction F is contributed by both the attenuations of the exciting XRF radiation R reaching the substrate F Excitation  and the attenuation of the XRF response from the substrate F Response . 
     It should be noted that the total thickness x of the attenuation layer AL may depend on the method of applications. In an example, a high absorbance elements (i.e. elements of high atomic number) may be blended in a polymeric coating applied to the responsive layer. The thickness of the attenuation layer may not exceed hundreds of microns. 
     In another example the thickness would not exceed ten of microns or even less than ten microns, while still providing sufficient aerial/column density ρ*x of these elements and such that the attenuation layer yields sufficiently high diminishing fraction F for the XRF response form the substrate SB. As indicated above, in some embodiments the at least one element HAE exhibiting the high absorbance in the attenuation layer AL is associated with substantial XRF response. For example the intensity of the response of the attenuation layer may be higher than 10% of the intensity of the marking layer; in another example the intensity of response of the elements in the attenuation layer may be comparable to (e.g. in the same order of) the intensity of the marking layer in at least one region of the spectral regime of the XRF signature by the XRF readable mark mXRFM. Accordingly, the attenuation layer AL may also contribute to the XRF signature of the XRF readable mark mXRFM. 
       FIG. 6A  also shows the component C including the substrate material SB the multilayered XRF readable mark mXRFM furnished over a surface of the substrate SB. As indicated above, the substrate SB in this case may be an XRF responsive substrate whose material(s) includes metallic elements (typically metallic elements are associated with significant emission of XRF background in response to irradiation thereof by the XRF exciting radiation). Accordingly the multilayered XRF readable mark mXRFM according to the present invention is placed over a surface S of said substrate SB such that the attenuation/mask layer of the XRF readable mark intermediates between the surface S of the substrate and the marking layer ML of XRF readable mark. 
     Some embodiments of the present invention provide an electronic system including at least a first and a second components, wherein the first component includes a first XRF readable mark and the second component includes a second XRF readable mark. The first and second XRF readable marks are respectively configured such that the first XRF signature of the first electronic component corresponds to the second XRF signature of the second electronic component thereby enabling verification that said first and second components are respectively compatible components of said electronic system. In some implementations at least said first component is an electronic component having the XRF responsive substrate as defined above. Accordingly, the first XRF readable mark may be configured as a multilayered XRF mark configured according to the technique of the present invention and placed over a surface of the substrate SB of the first component such that its attenuation/mask layer intermediates between the surface of the substrate and its marking layer. In some embodiments both or all the components of the electronic system are marked by multilayered XRF marks mXRFM(s) (e.g. irrespective of whether their substrates are associated with significant XRF responses). This obviates a need to measure/characterize the XRF responses of the components&#39; substrates, and facilitates straight forwards implementation of the XRF markings. 
     Reference is made to  FIG. 6C  which is a flow chart of a method  600  for implementing a multilayered XRF mark mXRFM according to an embodiment of the present invention. The method includes: 
       610 —providing an XRF marking composition AE with specific relative concentrations of one or more chemical elements whereby the relative concentrations are selected such that in response to irradiation of the XRF marking composition by XRF exciting radiation, the XRF marking composition emits an XRF signal indicative of a predetermined XRF signature; and 
     Fabricating a multilayer structure of the XRF readable mark by carrying out the following: said fabricating comprising: 
       620 —implementing an attenuation/mask layer AL including at least one element exhibiting high absorbance for at least one of: an XRF exciting radiation and an XRF background; and 
       630 —implementing a marking layer ML comprising the XRF marking composition AE. The marking layer ML is implemented over at least a part of the attenuation/mask layer AL, while not necessarily implemented directly on top of the attenuation/mask layer AL (e.g. it may be spaced from the marking layer ML by one or more additional layers). 
     Optionally the method includes  640  for furnishing the attenuation/mask layer AL over an XRF responsive substrate SB of an object/component. Furnishing the attenuation/mask layer AL may be performed together the implementation of the attenuation/mask layer AL (i.e. implementing the layer directly on the substrate) or after the implementation of the attenuation/mask layer AL (e.g. before or after implementation of the marking layer ML). Optionally the attenuating layer may be furnished to cover the entire surface (or surfaces) of the substrate SB, or alternatively it may be applied locally such that only preselected areas of the substrate are coated. 
     In some embodiments the implementing of the attenuation/mask layer is performed by applying coating to at least a part of a surface S of the substrate SB and by utilizing a coating that included at least one element HAE exhibiting high XRF/X-ray/Gamma-ray absorbance. The coating may for instance include a polymeric material embedded with one or more HAE elements (the atomic number therefor may be selected to be at least 13 or more preferably equal to or above 22 or even more preferably equal to or above 45). In some case the HAE elements of high atomic number include one or more metallic elements. In some implementations the one or more metallic elements are embedded in the polymeric material by dissolving oxide or salt forms or organometallic compounds including these elements in the polymeric material prior to said coating. In some implementations the HAE elements are dispersed or suspended in the polymeric material. The polymeric material may be for example polyamide. The polymeric material may be applied to the surface S of the substrate SB by any one or more of the following: spraying, brushing, printing, injecting and stamping. In some cases the method further includes curing the polymeric material by at least one of the following: heat, humidity, and UV radiation. 
     Alternatively, or additionally, in some embodiments the attenuation/mask layer is implemented by depositing the one or more elements HAE exhibiting the high absorbance on at least a part of the surface S of the substrate SB. The deposition may be for example performed by utilizing CVD or PVD techniques. The HAE elements may be deposited in liquid, solid or granular form.