Patent Description:
As the surface area density of monitoring points on an asset increases, the associated size and/or weight of the electrical interconnects and the associated circuitry for those sensors also increases. Moreover, as the monitored surface area of an asset increases, so too can the difficulty in fabricating the large network of sensors. Manufacturing limitations can affect the ability to fabricate a sensor network for assets having a larger monitored surface area. A need exists for an extendable, flexible, substrate-free sensor system that is capable of being fabricated in a nominal form factor and then extended for conformal installation on a surface of a larger form factor asset, while minimally adding size and weight to the asset.

A prior art extendable sensor system having the features of the preamble to claim <NUM> is disclosed in <CIT>. Other prior art sensor systems are disclosed in <CIT>, <CIT> and "<NPL>.

From one aspect, the present disclosure provides a method of manufacturing a substrate-free extendable sensor system in accordance with claim <NUM>.

From another aspect, the present disclosure provides a method of manufacturing a substrate-free extendable sensor system in accordance with claim <NUM>.

Flexible Hybrid Electronic (FHE) based design and fabrication enables integration of a large number of sensors into assets to render them intelligent, while minimizing added weight and having no adverse effect on structural properties or function. In aerospace platforms, for example, many incidents are due to structural fatigue and impact damage. Use of newer, lightweight materials, including composites, introduces new failure mechanisms, such as delamination, to aircraft and automotive structures that require additional vigilance with respect to structural integrity.

Sensor nodes and extendable wiring, defined into a lattice topology, are printed on a thin sacrificial substrate and encapsulated using large screen printing or roll-to-roll (R2R) methods. The sensor system lattice is subsequently released from the thin substrate using pulsed femtosecond laser or chemical dissolution. Flexible and extendable interconnects between nodes, which transmit power and/or signals, are compliant when bonded to a curved surface. During the extension of the lattice network, a serpentine-pattern allows the lattice network to expand 20x or more in a linear dimension, thereby allowing a large-area network to be manufactured using existing equipment. Non-limiting examples of surfaces that can accommodate large-area networks include airplane wings and fuselages.

<FIG> is a process flow diagram showing steps in extending and deploying an extendable sensor system. Shown in <FIG> are monitored asset <NUM>, electrical network <NUM>, contact pads <NUM>, interconnects <NUM>, sensor <NUM>, sensor system <NUM>, fabricate sensor system step <NUM>, extended sensor system step <NUM>, and deploy sensor system step <NUM>. In the illustrated embodiment, monitored asset <NUM> is a nacelle on an aircraft. Sensor system <NUM> can also be referred to as an extendable sensor system because it can be extended in two dimensions (i.e., planar extension) to be deployed on the surface of asset <NUM>, thereby having an extended surface area that is greater than its fabricated surface area. Sensor system <NUM> includes electrical network <NUM>, contact pads <NUM>, and sensor <NUM>. Electrical network <NUM> includes interconnects <NUM> arranged in a lattice network, with interconnects <NUM> providing electrical connections between contact pads <NUM> and sensor <NUM>. Sensor <NUM> is mechanically and electrically connected to an underlying sensor node (not shown in <FIG>). Contact pads <NUM> and sensor <NUM> can also be referred to as interconnect nodes, because they provide interconnections throughout electrical network <NUM>. In the illustrated embodiment, sensor system <NUM> is fabricated in fabricate sensor system step <NUM> using an additive manufacturing process. Next, sensor system <NUM> is extended in two dimensions in extended sensor system step <NUM>.

The arrangement of interconnects <NUM> in electrical network <NUM> allows for a planar extension (i.e., expansion in two dimensions), as shown in <FIG>. Electrical network <NUM>, and accordingly, interconnects <NUM>, can be described as having appreciable stretchability. The serpentine pattern of interconnects <NUM> allows each particular interconnect <NUM> to be stretched, thereby allowing the sensor system <NUM> to be extended. In the illustrated embodiment, any particular interconnect <NUM> can be stretched in a linear dimension (i.e., an internodal distance) by a factor of approximately <NUM> from the fabricated state to the deployed state. This can also be referred to as a maximum expansion factor. Accordingly, sensor system <NUM> can undergo a linear expansion of up to approximately <NUM> in each of the x- and y-axis directions. Therefore, sensor system <NUM> can cover a surface area on monitored asset <NUM> that is approximately <NUM> times the surface area of sensor system <NUM> as produced in fabricate sensor system step <NUM>. In some embodiments, sensor system <NUM> can have an asymmetrical planar expansion ability, meaning that the maximum expansion factor in one planar dimension (e.g., along the x-axis) can be either greater than or less than the maximum expansion factor in the other planar dimension (e.g., along the y-axis). In other embodiments, the maximum expansion factor of particular interconnects <NUM> can be less than or greater than approximately <NUM>. It is to be appreciated that the maximum expansion factor of sensor system <NUM> in a particular dimension (i.e., along the x- or y-axis) is determined by the maximum expansion factor of the particular interconnects <NUM>. In other embodiments, the maximum expansion factor of sensor system <NUM> in a linear direction can range from about <NUM> - <NUM>. In yet other embodiments, the maximum expansion factor of sensor system <NUM> in a linear direction can be greater than <NUM>. There is no upper limit to the maximum expansion factor in a particular embodiment, and all values of the maximum expansion factor are therefore within the scope of the present disclosure. Extended sensor system step <NUM> will also be described in greater detail later, in <FIG>. It is to be appreciated that the stretching of interconnects <NUM> in a linear dimension (i.e., an internodal distance) is a result primarily of the straightening of the serpentine pattern of the various interconnects <NUM>. Whereas the materials that form interconnects <NUM> can allow some degree of elongation (i.e., stretchability) in some embodiments, the mechanical flexibility of interconnects <NUM> contributes to the intermodal expandability (i.e., the maximum expansion factor) by the straightening of interconnects <NUM>.

The lattice structure of sensor system <NUM> depicted in <FIG> can be described as having a rectangular structure (i.e., net-like). Accordingly, interconnects <NUM> can be generally referred to as being approximately oriented in either an x- or y-axis orientation, with respect to the coordinate axes depicted in <FIG>. It is to be appreciated that the x- and y-axes are depicted arbitrarily, for the sake of description, and that in a particular embodiment, sensor system <NUM> can be oriented in any specific orientation.

Interconnects <NUM> provide electrical conductivity throughout electrical network <NUM>. As will be described later in <FIG>, each interconnect <NUM> can include a flexible electrically-conductive trace (i.e., strand) that is sandwiched between flexible dielectric material (not shown in <FIG>). In some embodiments, two or more electrically-conductive strands can be included in one or more interconnects <NUM>. In some of these embodiments, the two or more electrically-conductive strands can be parallel to each other in the same layer, with an electrically-insulating region separating them. In other of these embodiments, the two or more electrically-conductive strands can be stacked one upon the other, with an electrically-insulating dielectric layer separating them. In yet other of these embodiments, some of the multiple electrically-conductive strands can be parallel to each other, and/or others of the multiple electrically-conductive strands can be stacked upon each other in separate layers, as described above.

Referring again to <FIG>, after performing extend sensor system step <NUM>, the x-axis-oriented interconnects <NUM> intersect the y-axis-oriented interconnects <NUM> at approximately right angles. The series of interconnects <NUM> (i.e., electrical network <NUM>) is joined at contact pads <NUM> and/or at sensor <NUM> at each intersection, the details of which will be described more fully in <FIG>, <FIG>, and <FIG>. Each intersection of interconnects <NUM> can also be referred to as a routing junction. The flexibility (i.e., mechanical flexibility) of interconnects <NUM> allow sensor system <NUM> to be deployed on the curved surface of monitored asset <NUM>, as depicted in deploy sensor system step <NUM>. In the illustrated embodiment, sensor system <NUM> conforms to the surface of monitored asset <NUM> having a radius of curvature primarily in one direction. In other embodiments, sensor system <NUM> can conform to an irregular surface profile because of the flexibility and stretchability of interconnects <NUM>, whereby each particular interconnect <NUM> can stretch by a factor that can be different from that of any of the other interconnects <NUM>.

In deploy sensor network step <NUM>, sensor system <NUM> can be handled by contact pads <NUM>. Accordingly, contact pads <NUM> can also be referred to as handling tabs, because contact pads <NUM> have adequate mechanical strength to support the weight of sensor system <NUM> during handling. In deploy sensor network step <NUM>, the lattice network of sensor system <NUM> is positioned on the desired surface of monitored asset <NUM>, and is then adhered by one or more processes. In one embodiment, sensor system <NUM> can be bonded to the surface of monitored asset <NUM> by use of a separate bonding agent (not shown). In another embodiment, sensor system <NUM> can be bonded to the surface of monitored asset <NUM> by activating an adhesive layer (not shown) on sensor system <NUM> and/or on monitored asset <NUM>. In yet another embodiment, sensor system <NUM> can be embedded in or under the surface of monitored asset <NUM>. In any of these embodiments, an overcoat (not shown) can be applied over sensor system <NUM> during or after deploy sensor system step <NUM>. After sensor system <NUM> is deployed (i.e., installed) on monitored asset <NUM>, sensor system <NUM> can be connected to external circuitry (not shown) by means of contact pads <NUM>.

It is to be appreciated that <FIG> depicts exemplary sensor system <NUM> having a single sensor <NUM>, thereby representing a relatively uncomplicated lattice structure. <FIG> is provided to illustrate and to help describe an exemplary embodiment of the present disclosure. In other embodiments, sensor system <NUM> can include a greater number of sensors <NUM>, and a correspondingly larger electrical network <NUM>. As will be described in greater detail later in <FIG>, there is no upper bound to the complexity of the lattice structure of sensor system <NUM>.

<FIG> is a process flow diagram showing steps in fabricating sensor system <NUM> (i.e., the extendable sensor system). Shown in <FIG> are polyethylene terephthalate (PET) sheet <NUM>, polyvinyl alcohol (PVA) coating <NUM>, chemically-removable substrate <NUM>, electrical network <NUM>, contact pads <NUM>, sensor node <NUM>, interconnects <NUM>, sensor <NUM>, sensor system <NUM>, mounting frame <NUM>, fabricate substrate step <NUM>, fabricate electrical network step <NUM>, deposit electrical components step <NUM>, release sensor system step <NUM>, expand sensor system step <NUM>, and frame-mounting step <NUM>.

In fabricate substrate step <NUM>, PVA coating <NUM> is applied to both sides of PET sheet <NUM> and allowed to dry, thereby forming chemically-removable substrate <NUM>. Chemically-removable substrate <NUM> can also be referred to as a sacrificial substrate because it is later sacrificed (i.e., removed) from sensor system <NUM>. Next, in fabricate electrical network step <NUM>, the structure of electrical network <NUM> is formed. As described above with regard to <FIG>, electrical network <NUM> includes a series of contact pads <NUM>, interconnects <NUM>, and sensor node <NUM>, whereby interconnects <NUM> are capable of flexing and stretching once released from chemically-removable substrate <NUM>. The structure of electrical network <NUM> will be show in greater detail later, in <FIG>. In the illustrated embodiment, chemically-removable substrate <NUM> includes PET sheet <NUM> as a base substrate, with a coating of PVA <NUM> on both sides. In some embodiments, chemically-removable substrate <NUM> can be made entirely or primarily of PVA. In other embodiments, chemically-removable substrate <NUM> can include PET sheet <NUM> having PVA coating <NUM> on a single side.

Referring again to <FIG>, in fabricate electrical network step <NUM>, electrical network <NUM> can be printed (i.e., additively-manufactured) on chemically-removable substrate <NUM>. As used in this disclosure, "printing" is an additive-manufacturing process that can refer to any of a number of processes that can deposit material for fabricating a component or components. Chemically-removable substrate <NUM> can be a plate, sheet, or continuous roll of material, and can be thick or thin, and/or rigid or flexible. In a particular embodiment, chemically-removable substrate <NUM> can be a thin-film material on a roll, with fabricate electrical network step <NUM> using a roll-to-roll (R2R) manufacturing process. In another particular embodiment, chemically-removable substrate <NUM> can be a sheet of rigid or semi-rigid material, with fabricate electrical network step <NUM> using a large screen printing manufacturing process. Chemically-removable substrate <NUM> can later be removed from sensor system <NUM> by using a chemical dissolution process. In fabricate electrical network step <NUM> (i.e., print, additively manufacture), the lattice topology of interconnects <NUM>, as well as contact pads <NUM> and the sensor node, can be delivered by one of several possible additive manufacturing and/or printing methods, with non-limiting examples including screen printing, R2R, gravure printing, ink jet printing aerosol jet (AJ) deposition, extrusion direct-write microdispensing, micro-cold spray deposition, thermal-spray deposition, and mesoplasma spray (i.e., miniaturized thermal spray). The structure of interconnects <NUM> will be described in more detail later, in <FIG>.

Next, in deposit electrical components step <NUM>, sensor <NUM> is electrically and mechanically connected to sensor node <NUM>, thereby providing electrical connection to electrical network <NUM>. This establishes the proper electrical conduction paths necessary for sensor <NUM> to operate within sensor system <NUM>. In the illustrated embodiment, sensor <NUM> can be an integrated circuit (IC) that is deposited onto electrical network <NUM> to create sensor system <NUM>. In a particular embodiment, sensor <NUM> is a conventional monolithic semiconductor circuit package that is set onto electrical network <NUM> using a pick-and-place (PnP) manufacturing process, thereby providing a flexible hybrid electronic network. In other embodiments, sensor <NUM> can be an additively-manufactured sensor that is fabricated in place by using any of several processes that can be used to additively-manufacture (i.e., print) a sensor. Accordingly, as used in this disclosure, sensor <NUM> refers to any electronic device that can act as a sensor, transducer, and/or circuit, regardless of the method of manufacture or placement. Any particular sensor <NUM> can be a sensing element that is configured to provide an electrical signal in response to one or more sensed parameters. Non-limiting examples of sensed parameters include pressure, temperature, stress, strain, acceleration, vibration, acoustical energy (i.e., sound), and photonic energy (i.e., light). Any particular sensor <NUM> can be configured to respond to one or more parameters. In a particular embodiment, any particular sensor <NUM> can be configured to respond to a particular range of parameters. In some embodiments, any particular sensor <NUM> can provide an electrical signal in response to a sensed parameter without requiring an electrical supply. Sensors <NUM> can be any type of sensor, now known or later developed. Non-limiting examples of sensors that can be used for a particular sensor <NUM> can include thermocouples, resistance temperature detectors (RTDs), piezoelectric wafers, photocells, electrical resistance cells, electrical resistance bridges (e.g., Wheatstone bridge), electrical capacitance cells, and micro-electro-mechanical systems (MEMS) cells. Moreover, as used in this disclosure, depositing electrical components step <NUM> can be performed by a PnP manufacturing process and/or a printing (i.e., additive-manufacturing) process.

Next, in release sensor system step <NUM>, sensor system <NUM> is released from chemically-removable substrate <NUM> by a dissolution process. In the illustrated embodiment, sensor system <NUM> being attached to chemically-removable substrate <NUM> is immersed in water, dissolving PVA coating <NUM>, and thereby releasing sensor system <NUM> from chemically-removable substrate <NUM>. In other embodiments, chemically-removable substrate <NUM> can be made of, or coated with (i.e., have a surface coating) any material that is chemically-dissolvable, thereby allowing the removal of chemically-removable substrate <NUM> from sensor system <NUM> by the use of a dissolvent. Non-limiting examples of chemical dissolvents include water, alcohol, limonene, and alkali solutions. Non-limiting examples of chemically-dissolvable (i.e., soluble) substrates include polyimide (e.g., KAPTON®), polyethylene terephthalate, and polycarbonate having a thin film soluble surface coating. Non-limiting examples of chemically-dissolvable (i.e., soluble) surface coatings include polyvinyl alcohol (e.g., water soluble), soluble acrylates (e.g., alkali soluble), and polystyrene (e.g., limonene soluble). In yet another embodiment, a sacrificial substrate that is not chemically-removable can be used, whereby mechanical removal can be used to remove the sacrificial substrate from sensor system <NUM> by any mechanical removal process. A non-limiting example of a mechanical removal process is using a laser to cut away a sacrificial substrate, for example, by the use of a pulsed femtosecond laser.

Referring again to <FIG>, in expand sensor system step <NUM>, sensor system <NUM> is now free of chemically-removable substrate <NUM>, and is expanded in a plane (i.e., planar expansion, expansion in the x- and y-axis directions). During expand sensor system step <NUM>, the structure of interconnects <NUM> is shown partially expanded as depicted in <FIG>. In the illustrated embodiment, the structure of interconnects <NUM> can be referred to as a serpentine pattern of interconnects <NUM>. The structure of interconnects <NUM> can also be referred to as a zig-zag pattern, or switch-backs, folds, S-curves, and the like. Contact pads <NUM> (i.e., handling tabs) can be used to expand sensor system <NUM> by being pulling outward (i.e., away from a central region of sensor system <NUM>). As described above in regard to <FIG>, contact pads <NUM> can also function as handling tabs, thereby having adequate mechanical strength to be used in expand sensor system step <NUM>. In some embodiments, precision tooling can be used to pull outward on the various interconnects <NUM>, contact pads <NUM>, and/or sensor <NUM>, thereby assisting in the planar expansion of sensor system <NUM>. In the embodiment shown in <FIG>, sensor system <NUM> is a 3x3 lattice network (i.e., three segments in each of the x- and y-axis dimensions) of interconnects <NUM>. In some embodiments, a larger lattice network can be used for sensor system <NUM>. For example, in a particular embodiment, a 7x13 lattice network can be used for sensor system <NUM>. In some embodiments, sensor system can have a lattice network that exceeds <NUM> segments in either or both of the x- and y-axis directions. All lattice network configurations are within the scope of the present disclosure, regardless of the number of segments in either direction. Accordingly, it is to be appreciated that in some of these other embodiments, expand sensor system step <NUM> can include using precision tooling, and/or other methods, at various points and/or throughout various regions of sensor system <NUM>.

In the illustrated embodiment, expand sensor system step <NUM> involves fully expanding, or substantially fully expanding, sensor system <NUM>. In some embodiments, sensor system can be only partially expanded. For example, sensor system <NUM> can be partially expanded prior to being deployed on monitored asset <NUM> having an irregular surface profile, thereby allowing portions of sensor system <NUM> to more fully expand while conforming to an irregular surface profile of monitored asset <NUM>.

Referring again to <FIG>, sensor system <NUM> is placed on mounting frame <NUM> in frame-mounting step <NUM>, which can be a temporary storage condition prior to installing sensor system <NUM> on monitored asset <NUM>. In some embodiments, sensor system <NUM> can be stored using other storage method steps, with non-limiting examples including lying flat, hanging, and rolling around a roller or drum. In other embodiments, frame-mounting step <NUM> can be omitted, and sensor system <NUM> can be installed immediately on an asset (e.g., as shown above in regard to <FIG>). Accordingly, in some embodiments, frame-mounting step <NUM> can be optional. It is to be appreciated that in most embodiments, frame-mounting step <NUM> is to provide for the temporary storage and/or transport of sensor system <NUM> prior to the step of deploying sensor system <NUM> on an asset (not shown in <FIG>).

<FIG> is a top view showing electrical network <NUM> of sensor system <NUM> shown in <FIG>. It is to be appreciated that <FIG> depicts electrical network <NUM> following fabricate electrical network step <NUM> and prior to deposit electrical components step <NUM>, as described above in regard to <FIG>. Shown in <FIG> are chemically-removable substrate <NUM>, electrical network <NUM>, contact pads <NUM>, sensor node <NUM>, and interconnects <NUM>. Contact pads <NUM> describe the various points that can be used for making an electrical connection to electrical network <NUM>. In the illustrated embodiment, contact pads <NUM> surround the perimeter of electrical network <NUM>, being located in the corners and along the edges between the corners. In some embodiments, either a greater or lesser number of contact pads <NUM> can be used on electrical network <NUM> than is illustrated in <FIG>. In other embodiments, contact pads <NUM> can also be located within an interior region of electrical network <NUM> (i.e., not in the corners or around the perimeter). The serpentine pattern of each individual interconnect <NUM> is shown in <FIG>. In the illustrated embodiment, contact pads <NUM> are between about <NUM> - <NUM> across (i.e., from one side to the other), as can be seen from the <NUM> scale mark in <FIG>. In other embodiments, contact pads <NUM> can be smaller and/or larger than shown in <FIG>. Referring again to <FIG>, sensor node <NUM> is the point on electrical network <NUM> where sensor <NUM> (not shown in <FIG>) will be located. Sensor node <NUM> will be described in more detail later, in <FIG>.

<FIG> is a top view of a second embodiment of the electrical network of an extendable sensor system. Shown is <FIG> are chemically-removable substrate <NUM>, electrical network <NUM>, contact pads <NUM>, sensor node <NUM>, and interconnects <NUM>. The descriptions of chemically-removable substrate <NUM>, electrical network <NUM>, contact pads <NUM>, sensor node <NUM>, and interconnects <NUM> are substantially similar to that provided above in regard to <FIG>. It is to be appreciated that in the illustrated embodiment, the serpentine pattern of interconnects <NUM> involves fewer switchbacks than shown in the embodiment of <FIG>. Accordingly, the maximum expansion factor of electrical network <NUM> is about <NUM> (i.e., a smaller value than that described above in regard to <FIG>).

<FIG> is a schematic cross-sectional side view of a particular interconnect <NUM> shown in <FIG>. Shown in <FIG> are chemically-removable substrate <NUM>, interconnect <NUM>, first dielectric layer <NUM>, conductor layer <NUM>, and second dielectric layer <NUM>. First and second dielectric layers <NUM>, <NUM> can be referred to as dielectric/mechanical support ink, and conductor layer <NUM> can be referred to as conductor/printed sensor ink. First dielectric layer <NUM> can also be referred to as a bottom dielectric layer, being in contact with chemically-removable substrate <NUM>. Second dielectric layer <NUM> can also be referred to as a top dielectric layer. Also shown in <FIG> are interconnect width W, interconnect thickness T, first dielectric layer thickness A, conductor layer thickness B, and second dielectric layer thickness C. Interconnect <NUM> consists of conductor layer <NUM> sandwiched between first and second dielectric layers <NUM>, <NUM>, as shown in <FIG>. Interconnect <NUM> has interconnect width W and interconnect thickness T, with interconnect thickness T being the combination of first dielectric layer thickness A, conductor layer thickness B, and second dielectric layer thickness C. In the illustrated embodiment, interconnect width W is approximately <NUM> microns wide (i.e., <NUM>), and interconnect thickness T is approximately <NUM> microns thick (i.e., <NUM>). First dielectric layer thickness A and second dielectric layer thickness C are each about <NUM> microns thick, and conductor layer thickness B is about <NUM> microns thick. In some embodiments, interconnect width W can range between <NUM> - <NUM> microns. In other embodiments, interconnect width W can be less than <NUM> microns, or greater than <NUM> microns. In some embodiments, interconnect thickness T can range between <NUM> - <NUM> microns. In other embodiments, interconnect thickness T can be less than <NUM> microns, or greater than <NUM> microns. In some embodiments, first dielectric layer thickness A and second dielectric layer thickness C can be different from each other.

Referring again to <FIG>, an interconnect aspect ratio (W/T) can be defined as the ratio of interconnect width W to interconnect thickness T. In the illustrated embodiment, W/T is approximately <NUM> (i.e., <NUM>/<NUM>). In some embodiments, W/T can range between <NUM> - <NUM>. In other embodiments, W/T can range between <NUM> - <NUM>. In yet other embodiments, W/T can be less than <NUM>, meaning that interconnect thickness T is greater than interconnect with W. This can be beneficial, for example, for larger expansion factors of interconnect <NUM> (i.e., larger expansion factors of sensor system <NUM>), whereby the serpentine pattern of electrical network <NUM> can be more dense. In some embodiments, a value of W/T < <NUM> can be beneficial in reducing the tendency of interconnects <NUM> to curl out of the expansion plane. In other embodiments, it can be beneficial to have W/T in the range from about <NUM> - <NUM>, which can help reduce the tendency of interconnects <NUM> to roll or curl out of the expansion plane. In yet other embodiments, W/T can be less than <NUM> or greater than <NUM>. In some of these embodiments, other measures can be taken to reduce the tendency of interconnects <NUM> to roll or curl during the extension. In some embodiments, it can be tolerable to allow some or all of interconnects <NUM> to roll or curl during expansion.

Referring to <FIG>, first and second dielectric layers <NUM>, <NUM> can be made from photoset and thermoset polymer dielectric inks, extruded thermoplastics, and the like. Conductor layer <NUM> can be made from conductive inks containing silver, copper, aluminum, gold, platinum, ruthenium, carbon, and/or alloys of these metals. In other embodiments, some or all conductor layers can be made from combinations of these metals, partial conductors, and/or composites. In the illustrated embodiment, electrical network <NUM> (i.e., interconnects <NUM>) is printed (i.e., additively manufactured) on chemically-removable substrate <NUM> in three layers (i.e., first dielectric layer <NUM>, conductor layer <NUM>, and second dielectric layer <NUM>). First dielectric layer <NUM> defines the lattice topology (i.e., structure), conductor layer <NUM> establishes the electrical conduction paths of interconnects <NUM> and other circuitry components, and second dielectric layer <NUM> provides encapsulation. Additional fabrication steps will be described in greater detail later in <FIG>. In the illustrated embodiment, the various printing inks (i.e., fluid materials) that form first dielectric layer <NUM>, conductor layer <NUM>, and second dielectric layer <NUM> can be made using a curable resin. In some embodiments, the curable resin can be a photopolymer (i.e., light-activated resin) that changes properties when exposed to light. A photopolymer that is optimized to respond to ultraviolet (UV) light is known as a UV-curable resin. The photopolymer can be comprised of monomers and/or oligomers, and photoinitiators, thereby allowing the printing inks to be soft and flowable in an uncured condition, then becoming sufficiently viscous or solid as a result of the cross-linking of the monomers and/or oligomers during the light-activating process. The process by which printing ink (e.g., photopolymer resin) becomes more viscous or solidifies is also known as curing. A photopolymer cures by the action of photoinitiators that absorb photon energy during exposure to light of a particular wavelength or range of wavelengths. As the printing ink (i.e., photopolymer resin) cures, it becomes sufficiently viscous or solid, while also bonding to any solid material that it is in contact with. In some embodiments, the printing ink can be selected to be responsive to ultraviolet light having a wavelength of about <NUM> - <NUM> nanometers (nm). In some of these embodiments, the printing ink can be selected to be responsive to ultraviolet light having wavelengths of about <NUM> - <NUM>. Ultraviolet light sources of about <NUM> and <NUM> wavelengths may be commercially available and readily adaptable to the process of the present disclosure. In some embodiments, the printing ink (i.e., photopolymer resin) can cure as a result to a broader range of wavelengths. In some of these embodiments, visible light can initiate the curing process (e.g., the shorter wavelengths of visible light near the violet end of the visible light spectrum). Accordingly, in some embodiments, special precautions may need to be taken to prevent the premature curing (i.e., viscofication or solidification) of the printing ink (i.e., photopolymer).

In other embodiments, the curable resin can be responsive to an elevated temperature for initiating the curing process. A material that is responsive to an elevated temperature for curing can also be referred to as a thermoset material. Higher temperatures may accelerate the curing rate of the printing ink, with a temperature of about <NUM> (<NUM> °F) resulting in a noteworthy rate of curing. Temperatures ranging from about <NUM> (<NUM> °F) to about <NUM> (<NUM> °F) can be used to effectuate a noteworthy rate of curing the printing ink during fabricate step <NUM>. In some embodiments, the curable resin can be a thermoplastic resin that solidifies (i.e., cures) by cooling. In other embodiments, the curable resin can be a thermally-cured ink that uses a thermal solvent for evaporation/sintering of the ink. In yet other embodiments, non-resin materials can be used for one or more of the various layers of a sensor system. As used in this disclosure, "curable material" describes any material that can undergo viscofication, hardening, and/or solidification during a fabrication process. Accordingly, both resins (i.e., photoresins, thermal-resins) and non-resins can be curable materials. Non-limiting examples of curable non-resins include thermoplastics, inks, metals, and/or other materials that can be deposited (i.e., printed) as powders, molten materials, liquids, and the like by one or more additive-manufacturing processes (e.g., cold spray, thermal spray, thermal solvent evaporation, sintering). It is to be appreciated that the various layers of interconnects <NUM> can be made of different curable materials, for example, as described above. Accordingly, in some embodiments the curable materials that are used for an electrically-conductive layer and a dielectric layer can be referred to as "first" and "second" curable materials, respectively. In some of these embodiments, the first and second curable materials can be similar to each other, or substantially the same as each other.

In some embodiments, conductor layer <NUM> can be an electrically-conductive layer that is fabricated by a direct material deposition process using a metal or alloy. Accordingly, in these embodiments, it is not necessary for conductor layer <NUM> to contain curable materials in addition to electrically-conductive materials. In the illustrated embodiment, fabricated sensor structure <NUM> has a single layer of conductor layer <NUM>. In other embodiments, two or more layers of conductor layer <NUM> can be used, each being sandwiched between alternating layers of a dielectric layer, thereby providing two or more electrically-conductive strands in a particular interconnect <NUM> (e.g., as described above in regard to <FIG>). Accordingly, in some of these other embodiments, a second, third, etc. conductor layer can be used, and a third, fourth, etc. dielectric layer can be used.

<FIG> is a schematic top view of a sensor node. <FIG> is a schematic top view of a second embodiment of a sensor node. <FIG> is a schematic top view of a second embodiment of a sensor node. Shown in <FIG> are chemically-removable substrate <NUM>, interconnects <NUM>, dielectric <NUM>, sensor nodes <NUM>, 44A, 44B, sensor edge contact <NUM>, center bond pad <NUM>, side conductor <NUM>, and corner conductor <NUM>. Chemically-removable substrate <NUM> and interconnects <NUM> are substantially similar to those described above in regard to <FIG>. Sensor nodes <NUM>, 25A, 25B depict exemplary electrical connections that can be provided to later attach a particular sensor (not shown in <FIG>) to interconnects <NUM>. Dielectric <NUM> provides electrical isolation between sensor edge contact <NUM>, center bond pad <NUM>, side conductor <NUM>, and/or corner conductor <NUM> in various embodiments. Sensor edge contact <NUM>, center bond pad <NUM>, side conductor <NUM>, and corner conductor <NUM> can also be referred to as sensor connection pads, because they can be used to provide electrical connections to a particular sensor when so attached. Side conductor <NUM> and corner conductor <NUM> can also be referred to as routing junctions, because they provide electrical connections (i.e., routing) between interconnects <NUM>. In some embodiments, routing junctions (i.e., side conductor <NUM>, and corner conductor <NUM>) can be used without an associated sensor. In embodiments where a sensor is attached to sensor node <NUM>, 25A, 25B, the various sensor connection pads can also be used to provide a mechanical connection between that sensor and sensor nodes <NUM>, 25A, 25B.

Referring to <FIG>, center bond pad <NUM> can be used to provide a mechanical connection (i.e., bonding) between sensor node <NUM> and a sensor if so attached. However, center bond pad <NUM> is not electrically connected to interconnects <NUM>. In some embodiments, two or more electrically-conductive strands (i.e., layers) layers can be used in a particular interconnect <NUM>, as was described above in regard to <FIG>. In some of these embodiments, an electrical connection can be made between a particular interconnect <NUM> and center bond pad <NUM>, thereby allowing an electrical connection to be made to a sensor attached thereon.

Referring to <FIG>, side conductor <NUM> can provide electrical connectivity between interconnects <NUM> that are positioned on opposite sides of sensor node 25A. In some embodiments, side conductor <NUM> can also provide an electrical connection to a sensor if so attached. Similarly, corner conductor <NUM> can provide electrical connectivity between interconnects <NUM> on a corner of sensor node 25B. In some embodiments, corner conductor <NUM> can also provide an electrical connection to a sensor if so attached. It is to be appreciated that other configurations of sensor connection pads beyond the exemplary embodiments shown in <FIG>. As a non-limiting example, a side-corner conductor (not shown in <FIG>) could be used to provide an electrical connection between three interconnects <NUM>.

<FIG> is a schematic top view of a second embodiment of the extendable sensor system. Shown in <FIG> are sensor system <NUM>, corner pads <NUM>, contact pads <NUM>, interconnects <NUM>, routing junctions <NUM>, piezoelectric wafers <NUM>, resistance temperature detectors (RTDs) <NUM>, and Wheatstone bridges <NUM>. Corner pads <NUM>, contact pads <NUM>, and interconnects <NUM> are substantially similar to those described above in regard to <FIG>, being greater in number than the embodiment illustrated in <FIG>. The embodiment illustrated in <FIG> depicts a 13x7 lattice structure. Routing junctions <NUM> provide electrical connections between adjacent interconnects <NUM>, and are substantially similar to those described above in regard to <FIG>. Routing junctions <NUM> can also be referred to as interconnect nodes. The illustrated embodiment shown in <FIG> includes three types of sensors, described as follows. Piezoelectric wafers <NUM> can be used as sensors to provide an indication of the structural health of a system. RTDs <NUM> can be used as sensors to provide an indication of a temperature at a point on a system. Wheatstone bridges <NUM> can be used as sensors to provide in indication of material strain in a system. In some embodiments, other types of sensors can be used in addition and/or in lieu of those shown in <FIG>. Non-limiting examples of other types of sensors that can be used in sensor system include thermocouples, photocells, electrical resistance cells, electrical capacitance cells, and micro-electro-mechanical systems (MEMS) cells, as described above in regard to <FIG>. Any type of sensor, now known or later developed, in sensor system <NUM> is within the scope of the present disclosure. The illustrated embodiment depicts exemplary electrical connections between corner pads <NUM>, contact pads <NUM>, interconnects <NUM>, routing junctions <NUM>, and the various sensors (e.g., piezoelectric wafers <NUM>, RTDs <NUM>, and Wheatstone bridges <NUM>) in sensor system <NUM>.

<FIG> is a schematic cross-sectional side view of sensor system <NUM> before and after a chemical release process. Shown in <FIG> are fabricated sensor structure <NUM>, chemically-removable substrate <NUM>, first dielectric layer <NUM> (i.e., dielectric/mechanical support ink), conductor layer <NUM> (i.e., conductor/printed sensor ink), second dielectric layer <NUM> (i.e., dielectric/mechanical support ink), integrated circuits <NUM>, chemical release process <NUM>, and sensor structure <NUM>. Fabricated sensor structure <NUM> depicts a representative sensor (e.g., as described above in regard to <FIG>). Chemically-removable substrate <NUM> is substantially similar to that described above in regard to <FIG>. During the fabrication of fabricated sensor structure <NUM>, various layers (i.e., first dielectric layer <NUM>, conductor layer <NUM>, second dielectric layer <NUM>, integrated circuits <NUM>) are deposited (e.g., printed, additively manufactured) using printing ink. It is to be appreciated that curing of the printing ink can occur following the printing of each of the various layers, with the curing (i.e., viscofication or solidification) of the printing ink (i.e., curable material) being either partial or complete. Those who are skilled in the art of additive manufacturing using curable materials (i.e., curable resins or non-resins) are familiar with the various methods that can be used to cure or to partially cure printed layers of a curable material.

Referring again to <FIG>, first dielectric layer <NUM> is printed on to chemically-removable substrate <NUM>. First dielectric layer <NUM> provides an electrical dielectric (i.e., insulating layer), while also providing mechanical support (i.e., structural integrity) for sensor system <NUM>. Next, conductor layer <NUM> is printed over first dielectric layer <NUM>. Conductor layer <NUM> can be electrically conductive, being formed of a mixture of metallic elements and curable materials. Examples of metallic elements include those described above in regard to <FIG>. Conductor layer <NUM> can be connected to associated interconnects (not shown in <FIG>). Next, integrated circuits <NUM> are deposited onto conductor layer <NUM> while establishing the proper electrical conduction paths necessary for a particular integrated circuit <NUM> (i.e., a sensor) to operate. In the illustrated embodiment, integrated circuits <NUM> are conventional monolithic semiconductor circuit packages that are set onto conductor layer <NUM> using a pick-and-place (PnP) manufacturing process, thereby providing a flexible hybrid electronic network. Next, second dielectric layer <NUM> is printed over integrated circuits <NUM>, thereby providing an electrical dielectric (i.e., insulating layer), while also providing mechanical support (i.e., structural integrity). In other embodiments, integrated circuits <NUM> can be additively-manufactured sensors that are manufactured in place by using any of several processes that can be used to additively-manufacture (i.e., print) a sensor. Accordingly, as used in this disclosure, integrated circuit <NUM> refers to any electronic device that can act as a sensor, transducer, and/or circuit. Moreover, as used in this disclosure, depositing integrated circuit <NUM> can be performed by a PnP manufacturing process and/or a printing (i.e., additive-manufacturing) process. In some embodiments, conductor layer <NUM> can be an electrically-conductive layer that is fabricated by a direct material deposition process using a metal or alloy, as described above in regard to <FIG>. Accordingly, in these embodiments, it is not necessary for conductor layer <NUM> to contain curable materials in addition to electrically-conductive materials. In the illustrated embodiment, fabricated sensor structure <NUM> has a single layer of conductor layer <NUM>. In other embodiments, two or more layers of conductor/printed sensor ink <NUM> can be used, each being sandwiched between alternating layers of dielectric/mechanical support ink <NUM>, thereby providing two or more electrically-conductive strands in a particular interconnect as described above in regard to <FIG>. It is to be appreciated that the accompanying interconnects, routing junctions, handling tabs, and contact pads (not shown in <FIG>) are fabricated concurrently with fabricated sensor structure <NUM>.

Referring again to <FIG>, chemical release process <NUM> is performed to separate fabricated sensor structure <NUM> from chemically-removable substrate <NUM>. Accordingly, the accompanying interconnects, routing junctions, handling tabs, and contact pads (not shown in <FIG>) are separated from chemically-removable substrate <NUM> concurrently during chemical release process <NUM>. Therefore, the resulting fabricated sensor structure <NUM> can be referred to as a substrate-free manufactured extendable sensor system. In the illustrated embodiment, chemical release process <NUM> can be substantially similar to one of the exemplary methods described above in regard to <FIG>, thereby yielding sensor structure <NUM> (e.g., sensor structure <NUM>, as shown in <FIG>).

<FIG> is a schematic cross-sectional side view of a third embodiment of the extendable sensor system before and after a laser cutting process. Shown in <FIG> are substrate <NUM>, fabricated sensor structure <NUM>, conductor/printed sensor ink <NUM>, encapsulant layer <NUM>, integrated circuits <NUM>, laser cutting process <NUM>, and sensor structure <NUM>. Fabricated sensor structure <NUM>, substrate <NUM>, conductor/printed sensor ink <NUM>, integrated circuits <NUM>, and sensor structure <NUM> are all substantially similar to those described above in regard to <FIG>. In the illustrated embodiment, encapsulant layer <NUM> is a dielectric overcoat that can also provide exterior surface protection to sensor structure <NUM>. In some embodiments, substrate <NUM> provides sufficient mechanical support for sensor structure <NUM>, and a mechanical support ink is not required (e.g., dielectric/mechanical support ink, as shown in <FIG>). Accordingly, in these embodiments, conductor/printed sensor ink <NUM> can be deposited directly on substrate <NUM> which has a dielectric property. In these or other embodiments, encapsulant layer <NUM> can be a dielectric/mechanical support ink.

In the illustrated embodiment, fabricated sensor structure <NUM> includes a single layer of conductor/printed sensor ink <NUM>. In other embodiments, two or more layers of conductor/printed sensor ink <NUM> can be used, each being sandwiched between alternating layers of encapsulant later <NUM>, thereby providing two or more electrically-conductive strands in a particular interconnect (e.g., as described above in regard to <FIG>).

Referring again to <FIG>, laser cutting process <NUM> uses a laser beam for cutting (i.e., ablation) of sensor structure <NUM> (i.e., conductor/printed sensor ink <NUM>, encapsulant layer <NUM>, integrated circuits <NUM>) from substrate <NUM>. In a particular embodiment, laser cutting process <NUM> can use a pulsed femtosecond laser that provides an ultrashort pulse of high-energy light. A pulsed femtosecond laser can be useful in performing precision micro-machining of the various materials associated with sensor structure <NUM>, while providing minimal impact on the surrounding materials (i.e., a heat-affected zone) because of the ultrashort laser pulse duration (i.e., close to or less than one femtosecond, 1x10-<NUM> sec. ) In other embodiments, other lasers can be used for laser cutting process <NUM>. Those who are skilled in the laser art are familiar with the various types of lasers that can be used for precision-machining of microelectronic components and associated materials.

Laser cutting process <NUM> can be referred to as a release process, because sensor structure <NUM> is released (i.e., cut away) from substrate <NUM>. Accordingly, the resulting sensor structure <NUM> following the release process includes the portions of substrate <NUM> that are under the various electrically-conductive traces (i.e., conductor/printed sensor ink <NUM>), but the remainder of substrate <NUM> is released from sensor structure <NUM>. Laser cutting process <NUM> can also be referred to as a trimming process and as a precision micro-machining process.

Claim 1:
A method of manufacturing an extendable sensor system (<NUM>; <NUM>), the method comprising:
additively manufacturing, on a sacrificial substrate (<NUM>;<NUM>), the extendable sensor system (<NUM>;<NUM>) by performing the steps of:
(a) depositing a first dielectric layer (<NUM>) defining a lattice topology, the first dielectric layer (<NUM>) comprising a curable material, and the lattice topology defining a perimeter;
(b) depositing an electrically-conductive layer (<NUM>) over the first dielectric layer (<NUM>), wherein:
the electrically-conductive layer (<NUM>) comprises a curable electrically-conductive material;
the electrically-conductive layer (<NUM>) is configured to provide electrical connections to a sensor array; and
the electrically-conductive layer (<NUM>) defines a pattern of interconnects (<NUM>; <NUM>; <NUM>);
(c) depositing one or more sensors (<NUM>) on the lattice topology, each of the one or more sensors (<NUM>) being disposed at a point defined by an intersection of interconnects (<NUM>;<NUM>;<NUM>) and electrically connected to the electrical connections;
(d) depositing a second dielectric layer (<NUM>) over the electrically-conductive layer (<NUM>);
(e) performing a release process, thereby releasing the extendable sensor system from the sacrificial substrate (<NUM>;<NUM>);
(f) at least partially extending the extendible sensor system (<NUM>;<NUM>) prior to deploying the extendible sensor system (<NUM>;<NUM>); and
(g) deploying the extendible sensor system (<NUM>;<NUM>) by positioning the system on a surface of an asset and adhering the system to the surface;
wherein:
the pattern of interconnects (<NUM>;<NUM>;<NUM>) comprises a plurality of extendable interconnects (<NUM>;<NUM>;<NUM>);
at least some of the plurality of extendable interconnects (<NUM>;<NUM>;<NUM>) are arranged in a serpentine pattern that is configured to be expanded by straightening of the serpentine pattern, thereby extending the extendable sensor system (<NUM>;<NUM>);
the extended extendable sensor system (<NUM>; <NUM>) defines an extended sensor system topology; and
the extended sensor system topology is configured to be disposed on the surface of an asset (<NUM>).