Temperature sensitive interdigital sensor

Abstract

A temperature-sensitive sensor system for detecting a temperature above a specified threshold temperature can include an interdigital contact arrangement which can include a first contact with at least one elongated finger and a second contact with at least two elongated fingers, where the at least one elongated finger of the first contact can be interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers. The system can also include a temperature-sensitive medium, which can be configured to flow at least one of at or above the specified threshold temperature. The system can also include a delivery system, which can be configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature¬ sensitive medium flowing.

Description

TEMPERATURE SENSITIVE INTERDIGITAL SENSORCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Prov. Pat. Appl. No. 63 / 622,801, filed January 19, 2024, which is incorporated herein by reference in its entirety.TECHNOLOGICAL FIELD

[0002] The present disclosure relates to electronics, and more particularly, but not by way of limitation, to a temperature-sensitive interdigital sensor, such as can be used in an RFID system.BACKGROUND

[0003] Some products can benefit from being stored in temperature-controlled environments. For example, some medicines and food products need to be stored below a specified temperature (e.g., refrigerated). If a product has been exposed to temperatures outside of a desired range, identification of that product, disposal of that product, or both, can be desired.SUMMARY

[0004] A temperature-sensitive sensor system for detecting a temperature above a specified threshold temperature can include an interdigital contact arrangement which can include a first contact with at least one elongated finger and a second contact with at least two elongated fingers, where the at least one elongated finger of the first contact can be interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers. The system can also include a temperature-sensitive medium, which can be configured to flow at least one of at or above the specified threshold temperature. The system can also include a delivery system, which can be configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing.

[0005] A temperature-sensitive sensor system for detecting a temperature above a specified threshold temperature can include an interdigital contact arrangement which can include a first contact with at least one elongated finger and a second contact with at least two elongated fingers, where the at least one elongated finger of the first contact can be interleaved with the at least two elongated fingers of the second contact to create at least two contact gapsbetween the respective elongated fingers. The system can also include a temperature-sensitive medium, which can be configured to flow at least one of at or above the specified threshold temperature. The system can also include a delivery system, which can be configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing, where the delivery system can include an absorbent medium, which can be disposed near the temperature-sensitive medium and extending to near the contact gaps, which can be configured to flow the temperature-sensitive medium at least one of near or in contact with at least one of the contact gaps following the temperaturesensitive medium reaching the specified threshold temperature.

[0006] A method for using a temperature-sensitive sensor system can include placing the temperature-sensitive sensor system on a product to be monitored, the temperaturesensitive sensor system can include an interdigital contact arrangement which can include a first contact with at least one elongated finger and a second contact with at least two elongated fingers, where the at least one elongated finger of the first contact is interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers. The system can also include a temperature-sensitive medium, which can be configured to flow at least one of at or above a specified threshold temperature. The system can also include a delivery system, which can be configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperaturesensitive medium flowing. The method can also include measuring a property of the interdigital contact arrangement.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In the drawings, which may not be drawn to scale, like numerals can describe substantially similar components throughout one or more of the views. Like numerals having different letter suffixes can represent different instances of substantially similar components. The drawings illustrate generally, by way of example but not by way of limitation.

[0008] FIG. 1 is a perspective drawing of an example of portions of a temperaturesensitive sensor system.

[0009] FIG. 2 is a perspective drawing of an example of portions of the temperaturesensitive sensor system of FIG. 1, where the sensor has been at least partially activated.

[0010] FIG. 3 is a top-view drawing of an example of portions of a temperaturesensitive sensor system, including portions of an example of a radio frequency identification (RFID) system.

[0011] FIG. 4 is a graph showing an example of operating portions of a temperaturesensitive sensor system.

[0012] FIG. 5 is a diagram showing an example of a method for operating portions of a temperature-sensitive sensor system.DETAILED DESCRIPTION

[0013] Determining the historical temperature range of a product can be difficult, such as due to the product passing from the custody of one entity to another. For example, determining whether the product has been exposed to a temperature outside of a specified temperature range (e.g., above a high threshold temperature, below a low threshold temperature, etc.) can require keeping detailed logs of the products location throughout time. Even with detailed record keeping, mistakes can happen. For example, a transport vehicle carrying the product can differ from a desired temperature of the transport vehicle, or a transfer from one temperature-controlled region to another (e.g., from a refrigerated truck to a refrigerator) through a non-temperature-controlled environment can have an unknown effect on the products temperature range (e.g., can differ based on how long the transfer took, how much the transfer temperature differed from storage temperature, how much products near the edge of a package differ from products near a center of a package, etc.). Additionally, accurate historical information about the product may not be available for one or more reasons, such as one or more of loss of records related to handling, negligent misrepresentation of handling, or fraudulent misrepresentation of handling (e.g., stating that the product has been kept in a specific temperature range while knowing that is not true).

[0014] The present inventor has recognized, among other things, that it can be beneficial to have a temperature-sensitive sensor, such as can be included in a temperaturesensitive sensor system. The temperature-sensitive sensor can be disposed with a product or group of products (e.g., medicine, food products, etc.), and thereby monitor the temperature of the products. Additionally, the present inventor has recognized that it can be beneficial for the temperature-sensitive sensor to be one or more of passive (e.g., not requiring power to operate), irreversible (e.g., once the sensor has determined that it has been outside of a desired temperature range, the effects cannot be reversed, a fuse sensor, a one-shot sensor, etc.), or tamper proof (e.g., difficult to circumvent, disable, etc.).

[0015] In an approach, a sensor can be configured such that a temperature-sensitive medium is placed in contact with a first contact and a second contact when the sensor is above a specified threshold temperature. The temperature-sensitive medium can change a property ofthe contact arrangement, such as can be measured to determine if the sensor has been above the specified threshold temperature. The present inventor has recognized, among other things, that it can be beneficial to increase a level of contact that the temperature-sensitive medium has with the first contact and the second contact, such as through the use of an interdigital contact arrangement. This can increase a level of change in one or more properties of the contact arrangement due to the temperature sensitive medium (e.g., increase a change in resistance value).

[0016] FIG. 1 is a perspective drawing of an example of portions of a temperaturesensitive sensor system 100. FIG. 1 shows that the temperature-sensitive sensor system 100 can include an interdigital contact arrangement 110, a delivery system 120, a temperaturesensitive medium 130, an integrated circuit chip 160, and a substrate 170.

[0017] The interdigital contact arrangement 110 can include a first contact 112 and a second contact 114. The first contact 112 and the second contact 114 can each have one or more fingers (e.g., one finger, two fingers, three fingers, four fingers, five fingers, six or more fingers). The fingers can be elongated, having a length that is substantially longer than their width. The fingers can all be of similar size and shape, or one or more fingers can differ in size or shape. The fingers of the first contact 112 can be at least partially interleaved with the fingers of the second contact 114, such as can create one or more contact gaps. In an example, the fingers of the first contact 112 can be inserted into the slots created by the fingers of the second contact 114 until the tips of the fingers of the first contact 112 are a specified distance from a base of the slots of the second contact 114, such as almost touching, or within a distance approximately equal to the contact gap width. In an example, the fingers of the first contact 112 might not be interleaved with the fingers of the second contact 114. For example, the tips of one or more fingers of the first contact 112 can be aligned with the tips of one or more fingers of the second contact 114 and there can be a specified length gap therebetween. In an example, the tips of one or more fingers of the first contact 112 are not aligned with the tips of one or more fingers of the second contact 114, but the contacts are not interleaved at all (e.g., the fingers of the first contact 112 are not inserted into the slots between the fingers of the second contact 114).

[0018] The interdigital contact arrangement 110 can be configured to one or more of increase a surface area of the contact arrangement (e.g., increasing a length of the fingers can increase a length of the arrangement and increasing a number of the fingers can increase a width of the arrangement), or increase a total length of contact gaps created between all of the contact gaps (e.g., a single contact gap has a length approximately equal to the length of thecontact fingers, adding similarly configured contact gaps increases the total contact gap length proportional to the number of gaps added (e.g., if a single contact gap has a length of 1 centimeter and there are 3 contact gaps, the total contact gap length is 3 centimeters)). FIG. 1 shows that the first contact 112 can include, for example only, a first finger 121, a second finger 122, a third finger 123, a fourth finger 124, and a fifth finger 125. FIG. 1 shows that the second contact 114 can include, for example only, a first finger 141, a second finger 142, a third finger 143, a fourth finger 144, and a fifth finger 145. One or more of the fingers can have a length and / or width that differs from one or more of the other fingers. The dimensions of one or more of the fingers can be configured for a desired application and / or resulting property of the interdigital contact arrangement 110.

[0019] In an example, one or more of the fingers may be in a shape (e.g., an elongated shape) other than linear, such as can include a curve, a spiral, or a wave. In an example, one or more of the contact fingers can be in the form of a spiral (e.g., a curve defined by a point rotating around a central origin with increasing distance from the central origin). In an example, the first contact 112 can include one or more spiral fingers, the second contact 114 can include one or more spiral fingers, and one or more of the spiral fingers of the first contact 112 can be interleaved (e.g., sized and shaped to within) one or more of the spiral fingers of the second contact 114. For example, the interdigital contact arrangement 110 can include an interdigital spiral capacitor. In an example, the interdigital contact arrangement 110 can include an interdigital concentric capacitor (e.g., an interdigital concentric sensor). In an example, the first contact 112 can include a first spiral finger that is interleaved with a first spiral finger of the second contact 114. In an example, the first contact 112 and / or the second contact 114 can include any combination of linear and spiral fingers. This disclosure is believed to apply, at least in part, to all interdigital contact arrangements.

[0020] The first contact 112 and the second contact 114 can include a conductive material, such as a metallic material (e.g., copper, gold, etc.), a doped semiconductor region (e.g., doped to provide a specified degree of conductivity), etc. The first contact 112 and the second contact 114 can be disposed on the substrate 170. The first contact 112 and the second contact 114 can be configured so that they do not touch each other. However, the first contact 112 and the second contact 114 can be configured so that the gaps between respective interdigital fingers have a specified width. For example, the interdigital contact arrangement 110 can include one or more contact gaps with a width that is approximately 0.1 millimeters, 0.5 millimeters, 1 millimeter, 2 millimeters, or any other specified width. Decreasing a width of one or more contact gaps and / or a width of one or more contact fingers can allow for anincreased total contact gap length for a given interdigital contact arrangement 110 surface area. The interdigital contact arrangement 110 can include a first contact gap 171 between the first finger 141 and the first finger 121, a second contact gap 172 between the first finger 121 and the second finger 142, a third contact gap 173 between the second finger 142 and the second finger 122, a fourth contact gap 174 between the second finger 122 and the third finger 143, a fifth contact gap 175 between the third finger 143 and the third finger 123, a sixth contact gap 176 between the third finger 123 and the fourth finger 144, a seventh contact gap 177 between the fourth finger 144 and the fourth finger 124, an eight contact gap 178 between the fourth finger 124 and the fifth finger 145, and a ninth contact gap 179 between the fifth finger 145 and the fifth finger 125. One or more of the contact gaps can have a length and / or width that differs from one or more of the other contact gaps. The dimensions of one or more of the contact gaps can be configured for a desired application and / or resulting property of the interdigital contact arrangement 110.

[0021] The substrate 170 can be an electrically insulating substrate, such as a glass epoxy laminate (e.g., FR-4) or other suitable dielectric. The substrate 170 can be configured to support and provide structure to one or more portions of the temperature-sensitive sensor system 100. For example, the substrate 170 can provide a generally flat and rigid surface for the construction of the remainder of the temperature-sensitive sensor system 100. One or more of the first contact 112 and the second contact 114 can include at least a portion that is printed or etched onto the substrate 170, such as in a process similar to a printed circuit board (PCB) manufacturing process.

[0022] The temperature-sensitive medium 130 can be a medium that flows at or above a specified threshold temperature. The temperature-sensitive medium 130 can be frozen (e.g., solid or having a viscosity above a specified level, such as can include being frozen on the molecular level, or rather, just behaving as a solid) or partially frozen below the specified threshold temperature. For example, the temperature-sensitive medium 130 can generally hold its shape when frozen and not flow. At or above the specified threshold temperature, the temperature-sensitive medium 130 can at least partially melt (e.g., become a liquid or have a viscosity below a specified level, such as can include melting on the molecular level, or rather, just behaving as a liquid), such as can allow the temperature-sensitive medium 130 to flow similar to a liquid or gel. The temperature-sensitive medium 130 can be composed of a single material (e.g., composed of a plurality of molecules with a shared or similar molecular formula) or can be composed of multiple materials. The temperature-sensitive medium 130 can include one or more of a pure substance, a homogeneous mixture, or a non-homogeneous mixture. Inan example where the temperature-sensitive medium 130 is composed of multiple materials, the temperature-sensitive medium 130 can include one or more of a solution (e.g., one material at least partially dissolved in another), a slurry (e.g., one material mixed with another material, such as a solid particle mixed with a liquid), or a suspension (e.g., one material suspended in another without dissolving, such as can include a stable suspension).

[0023] The temperature-sensitive medium 130 can be configured to flow at or above the specified threshold temperature, such as through the selection of materials included in the temperature-sensitive medium 130 and the ratios of materials. For example, a material that flows at or above the specified threshold temperature can be selected for inclusion in the temperature-sensitive medium 130. In an example, two or more materials can be mixed to obtain a temperature-sensitive medium 130 that flows at or above the specified threshold temperature. For example, a material that flows below the specified threshold temperature can be mixed with a material that flows above the specified threshold temperature in a proper ratio to achieve a material that flows at or above the specified threshold temperature. In an example, one or more portions of the temperature-sensitive medium 130 can remain solid after the temperature-sensitive medium 130 flows. For example, a particle in a suspension or a slurry can remain solid, but can flow along with the melted surrounding material.

[0024] In an example, the temperature-sensitive medium 130 can be conductive. The temperature-sensitive medium 130 can include one or more conductive materials. For example, the temperature-sensitive medium 130 can include a conductive material that does not melt mixed with a non-conductive material that does melt, where the overall mixture is configured to flow at or above the specified threshold temperature The temperature-sensitive medium 130 can be configured to have a specified conductivity, such as through mixing a conductive material with another material in a sufficient quantity to achieve the desired level of conductivity.

[0025] The delivery system 120 can be configured to transfer the temperature-sensitive medium 130 to at least one of the contact gaps following the temperature-sensitive medium 130 flowing. The temperature-sensitive medium 130 can be initially disposed in a location one or more of away from or not touching one or more of the fingers and / or one or more of the contact gaps. Following the temperature-sensitive medium 130 flowing, the delivery system 120 can transfer the temperature-sensitive medium 130 into contact with one or more of the fingers and / or one or more of the contact gaps, such as can include transferring the temperaturesensitive medium 130 to at least one of the contact gaps such that the temperature-sensitivemedium 130 bridges between a finger of the first contact 112 and a finger of the second contact 114.

[0026] The interdigital contact arrangement 110 can have one or more properties between the first contact 112 and the second contact 114 (e.g., resistance, capacitance, inductance, reactance) before the temperature-sensitive medium 130 flows. One or more of these properties can be altered after the temperature-sensitive medium 130 has flowed and / or been transferred to at least one of the contact gaps, such as by the delivery system 120. For example, a resistance between the first contact 112 and the second contact 114 can initially be very high (e.g., above 10 kiloohms, above 100 kiloohms, above 1 megaohm) or near infinite, such as can be due to the first contact 112 and the second contact 114 not touching and the substrate 170 having a very high resistance. Following the temperature-sensitive medium 130 bridging one or more of the contact gaps, the resistance can drop if the temperature-sensitive medium 130 is conductive. For example, the resistance of the temperature-sensitive medium 130 bridging one of the contact gaps can be between 100 and 1500 ohms, 500 ohms, 1000 ohms, 1500 ohms, 2000 ohms, or any other resistance. A conductivity of the temperaturesensitive medium 130 can be limited, such as can be due to the temperature-sensitive medium 130 including conductive and non-conductive components. It can be desirable to reduce or otherwise tailor the resistance between the first contact 112 and the second contact 114 following the temperature-sensitive medium 130 flowing, such as can make it easier to detect that the temperature-sensitive medium 130 has flowed. This can make the introduction of additional contact gaps desirable. For example, if each contact gap has approximately the same properties (e.g., same length and width), each bridged contact gap can have similar properties, such as resistance. Adding additional contact gaps can simulate arranging resistors in parallel, such as can result in a resistance between the first contact 112 and the second contact 114 as shown in equation 1.Equation 1

[0027] In equation 1, R is the resistance between the first contact 112 and the second contact 114, Rgapis the resistance of a single bridged contact gap, and N is the number of bridged contact gaps. Accordingly, adding a second contact gap can reduce the resistance by half, adding a second and a third contact gap can cut the resistance to a third of the single gap resistance, etc.

[0028] In an example, a resistance between the first contact 112 and the second contact 114 can initially be a low value (e.g., 1 ohm, 10 ohms, 100 ohms, 1 kiloohm), such as due toone or more of the contact gaps being bridged by a material that is at least partially electrically conductive. Following the temperature-sensitive medium 130 flowing and reaching one or more of the contact gaps, the electrically conductive material in the one or more contact gaps can be diluted and / or displaced, such as can result in the resistance of the interdigital contact arrangement 110 changing. In an example, the temperature-sensitive medium 130 can be non- conductive, and can wash away a conductive film and / or ink that is bridging one or more of the contact gaps. This can increase a resistance of the interdigital contact arrangement 110.

[0029] In an example, the temperature-sensitive medium 130 can have a specified dielectric constant (e.g., the ratio of permittivity of the temperature-sensitive medium 130 to the permittivity of free space). The interdigital contact arrangement 110 can include a capacitance value between the first contact 112, such as can be affected by the dimensions of the one or more contact gaps. The capacitance of the interdigital contact arrangement 110 can be affected by the presence, or lack thereof, of a material near or in the contact gaps. Therefore, the capacitance of the interdigital contact arrangement 110 can change if the properties near or around the contact gaps change. When the temperature-sensitive medium 130 is transferred to the contact gaps, this can alter a capacitance of the interdigital contact arrangement 110. For example, the temperature-sensitive medium 130 can provide a material at the contact gaps where no material was present before (e.g., due to a vacuum or partial vacuum), or the temperature-sensitive medium 130 can displace a material near the contact gaps with a different dielectric constant (e.g., displacing air). The flowing of the temperature-sensitive medium 130 can affect the capacitance of the interdigital contact arrangement 110, such as can allow a capacitance measurement between the first contact 112 and the second contact 114 to be useful in determining if the temperature-sensitive medium 130 has flowed. The dielectric constant of the temperature-sensitive medium 130 can be any value, such as can include 1.5, 2, 2.5, 3, 5, 10, or greater than 10. The capacitance of the interdigital contact arrangement 110 can be approximately linearly related to the dielectric constant of the material between the fingers (e.g., similar to a parallel plate capacitor). The capacitance can go up by a factor approximately equal to the dielectric constant when the temperature-sensitive medium 130 is present. If the temperature-sensitive medium 130 does not completely surround the fingers, such as only surrounding on one side, such as due to the substrate 170 preventing the temperature-sensitive medium 130 from surrounding the fingers on all sides, the relation can be a multiple of the dielectric constant less than one. Equation 2 shows an example of the capacitance of the interdigital contact arrangement 110.C = CQ+ Cgap* N Equation 2

[0030] In equation 2, Cois the base capacitance between the first contact 112 and the second contact 114 before the temperature-sensitive medium 130 has flowed, Cgapis the differential capacitance increase of a single bridged contact gap vs the base capacitance, and N is the number or bridged contact gaps. Accordingly, adding a second contact gap can double the change in capacitance, adding a second and a third contact gap can triple the change in capacitance, etc.

[0031] The fingers of the interdigital contact arrangement 110 can be raised off the substrate 170, such as through a height of the material forming the contacts or by another material. This can increase a surface area of the contact gaps, or allow the temperature-sensitive medium 130 to flow more completely between the contact gaps.

[0032] The delivery system 120 can include an absorbent medium 132, and a reservoir 150. The reservoir 150 can be configured to contain the temperature-sensitive medium 130 in solid form, and can be configured to direct the temperature-sensitive medium 130 onto the absorbent medium 132 when the temperature-sensitive medium 130 flows. The absorbent medium 132 can be disposed near the temperature-sensitive medium 130 before the temperature-sensitive medium 130 has flowed, such as can include in the reservoir 150, and can extend to near the contact gaps. The absorbent medium 132 can be configured to flow the temperature-sensitive medium 130 one or more of near or in contact with one or more contact gaps.

[0033] The absorbent medium 132 can include a fabric, mat, or wick, such as can be configured to flow a material, such as through intermolecular forces (e.g., capillary action). The absorbent medium 132 can be a substantially planar piece of material, such as can include a length and width much greater (e.g., five times, 10 times, 100 times, etc.) than a thickness. In an example, the absorbent medium 132 can be an absorbent organic material, such as can include blotter paper.

[0034] In the example of FIG. 1, the absorbent medium 132 can extend from a first end 134 to a second end 136, such as along axis 138. The first end 134 can be positioned away from the interdigital contact arrangement 110, and the second end 136 can be positioned over the interdigital contact arrangement 110. The reservoir 150 can be positioned, for example, over the first end 134. In an example, the reservoir 150 can be positioned under the first end 134.

[0035] The reservoir 150 can include a receptacle of any shape configured for containing the temperature-sensitive medium 130. The reservoir 150 can be configured tosurround the temperature-sensitive medium 130 on any number of sides (e.g., top, bottom, front, back, left, right), such as can include completely surrounding the temperature-sensitive medium 130 (as shown in FIG. 1), such as can include surrounding the temperature-sensitive medium 130 on all sides. In an example, the reservoir 150 may only surround the temperaturesensitive medium 130 on four sides, such as can include the top and bottom of the reservoir 150 being open. The reservoir 150 can be configured to transfer the temperature-sensitive medium 130 to the absorbent medium 132 when the material flows, such as through an aperture or other opening in the bottom of the reservoir 150.

[0036] The delivery system 120 can be configured to transfer the temperature-sensitive medium 130 to one or more of the contact gaps following the temperature-sensitive medium 130 flowing independent of an orientation (e.g., right side up, sideways, upside down, etc.) of the sensor system, or at least in some orientations other than precisely right side up. For example, the delivery system 120 can be configured to transfer the temperature-sensitive medium 130 to one or more of the contact gaps through a property such as wicking and / or capillary action. The force that causes the wicking and / or capillary action can be large enough to overcome a gravitational or other acceleration-based force that is acting on the temperaturesensitive medium 130. In an example, the reservoir 150 can be a tube with a sufficiently small diameter such that the force of capillary action within the tube draws the temperature-sensitive medium 130 towards the absorbent medium 132 regardless of orientation. As discussed above, capillary action within the absorbent medium 132 can allow the absorbent medium 132 to transfer the temperature-sensitive medium 130 to one or more of the contact gaps regardless or orientation (e.g., wicking vertically up the absorbent medium 132 from the first end 134 to the second end 136).

[0037] In an example, the delivery system 120 may not include a reservoir 150. For example, the temperature-sensitive medium 130 can be initially disposed one or more of on the surface of the first end 134 or impregnated within the material of the first end 134. Following the temperature-sensitive medium 130 melting, the temperature-sensitive medium 130 can one or more of wick into the absorbent medium 132 or wick from the first end 134 to the second end 136. In an example, the absorbent medium 132 may not include a first end 134, but may be positioned largely over the interdigital contact arrangement 110. Whether or not a reservoir 150 is used, the absorbent medium 132 can initially one or more of hold the temperaturesensitive medium 130 or separate the temperature-sensitive medium 130 from the interdigital contact arrangement 110. In an example, the delivery system 120 might not include a reservoir 150 or a first end 134, and the temperature-sensitive medium 130 can be disposed on a surfaceof the absorbent medium 132 opposite the interdigital contact arrangement 110. Following the temperature-sensitive medium 130 flowing, the temperature-sensitive medium 130 can wick through the absorbent medium 132 into contact or nearly into contact with one or more contact gaps of the interdigital contact arrangement 110.

[0038] The temperature-sensitive sensor system 100 can be configured such that once the temperature-sensitive medium 130 has flowed and the delivery system 120 has transferred the temperature-sensitive medium 130 to one or more of the contact gaps, the temperaturesensitive medium 130 remains at the one or more contact gaps, such as can result in the properties of the interdigital contact arrangement 110 remaining the same as when the temperature-sensitive medium 130 was above the specified threshold temperature, or distinct from a property of the interdigital contact arrangement 110 before the temperature-sensitive medium 130 flowed. This can allow the temperature-sensitive sensor system 100 to determine if it has ever been above the specified threshold temperature, even if it later went back below the specified threshold temperature. For example, the temperature-sensitive medium 130 can solidify or stop flowing but remain in the absorbent medium 132 on the second end 136.

[0039] In an example, there can initially be a conductive material (e.g., a conductive ink) applied to the portion of the absorbent medium 132 overlaying the interdigital contact arrangement 110 (e.g., the second end 136), applied directly to one or more portions of the interdigital contact arrangement 110, or both. This conductive material can form a conductive path between one or more of the contact fingers. Following the temperature-sensitive medium 130 flowing, the conductive material may be displaced, which can result in breaking the conductive path, altering a property of the interdigital contact arrangement 110 (e.g., increasing a resistance), or both. In this example, the temperature-sensitive medium 130 might not be conductive.

[0040] In an example, the delivery system 120 can be configured to deliver the temperature-sensitive medium 130 to a point at or near the center of a set of interleaved spiral fingers (e.g., a spiral finger of the first contact 112 interleaved with a spiral finger of the second contact 114), such as can change a capacitance and / or resistance of the spiral finger arrangement. In an example, spiral fingers may be able to provide more change in capacitance per unit area, such as can allow spiral fingers to create a more sensitive sensor.

[0041] In an example, as shown in FIG. 1, the first end 134 can be on a first side of the contact gaps and the second end 136 can be on a second side of the contact gaps. The axis 138 extending from the first end 134 to the second end 136 can be substantially orthogonal to the contact gaps, as shown in FIG. 1. One or more of the absorbent medium 132 or the temperature-sensitive medium 130 can be configured such that when the temperature-sensitive medium 130 flows, it is transported by the absorbent medium 132 at a specified rate (e.g., such as a number of centimeters per second the absorbent medium 132 transports the temperature-sensitive medium 130), such as from the first end 134 to the second end 136. The specified rate can include a range of rates. The specified rate can be selected such that the temperature-sensitive sensor system 100 must be above the specified threshold temperature for a specified amount of time before the temperature-sensitive medium 130 reaches one or more of the contact gaps. In an example, the length of time that the temperature-sensitive sensor system 100 has been at or above the specified threshold temperature can be determined based on how far the temperature-sensitive medium 130 has flowed through the absorbent medium 132 such as can include by determining how many contact gaps are bridged.

[0042] In an example, the temperature-sensitive sensor system 100 might not include a delivery system 120. For example, the temperature-sensitive medium 130 can be disposed on one or more of the fingers and configured such that when the temperature-sensitive medium 130 flows, it bridges at least one of the contact gaps. For example, the temperature-sensitive medium 130 can be mounded high enough that the temperature-sensitive medium 130 flows to one or more of the contact gaps, such as due to gravity or adhesion. In an example, a flux can be applied to the surface of one or more portions of the interdigital contact arrangement 110, such as can include the contact gaps, to help attract and / or hold onto the temperature-sensitive medium 130.

[0043] The integrated circuit chip 160 can be any processor, computer, or other integrate circuit chip. The integrated circuit chip 160 can be disposed on the substrate 170. The integrated circuit chip 160 can be coupled to the first contact 112 and the second contact 114. The integrated circuit chip 160 can be configured to measure a property of the interdigital contact arrangement 110, such as can include measuring a property between the first contact 112 and the second contact 114. The integrated circuit chip 160 can be configured to measure one or more of resistance or capacitance corresponding to the interdigital contact arrangement 110.

[0044] The integrated circuit chip 160 can be configured to determine whether the temperature-sensitive medium 130 has flowed to one or more of the contact gaps, such as can determine if the temperature-sensitive sensor system 100 has been exposed to a temperature above the specified threshold temperature. The integrated circuit chip 160 can compare one or more measured properties of the interdigital contact arrangement 110 to one or more corresponding thresholds (e.g., a high threshold, a low threshold). For example, the integratedcircuit chip 160 can compare a measured resistance value to a low threshold. If the resistance value is below the low threshold, the integrated circuit chip 160 can determine that the temperature-sensitive sensor system 100 has been exposed to a temperature above the specified threshold temperature. The integrated circuit chip 160 can determine how far the temperaturesensitive medium 130 has flowed, such as can include how far the temperature-sensitive medium 130 has been transported by the absorbent medium 132, such as using a look up table or equation to determine how many contact gaps are bridged. For example, the integrated circuit chip 160 can compare a measured capacitance to various look up table values corresponding to the capacitance when each additional contact gap is bridged, and determine the number of bridged contact gaps.

[0045] In an example, the integrated circuit chip 160 can compare a property of the interdigital contact arrangement 110 to a threshold, such as without directly measuring the property of the interdigital contact arrangement 110 (e.g., without determining a numerical representation of a property of the interdigital contact arrangement 110, such as not determining a resistance value in ohms). For example, the integrated circuit chip 160 can compare the resistance of the interdigital contact arrangement 110 to a reference resistor included in the temperature-sensitive sensor system 100, and determine if the reference resistor is larger than the resistance of the interdigital contact arrangement 110 (e.g., compare a resistance of the interdigital contact arrangement 110 to a reference resistor included on the temperature-sensitive sensor system 100 without determining a resistance value corresponding to the interdigital contact arrangement 110, such as by passing a matching or nearly matching test current through both the interdigital contact arrangement 110 and the reference resistor and using a comparator measuring the voltage across both the interdigital contact arrangement 110 and the reference resistor to determine which has a larger resistance value). The result of this comparison can be used to determine if the temperature-sensitive sensor system 100 has been exposed to a temperature at or above the specified threshold temperature.

[0046] In an example, the temperature-sensitive medium 130 can include two or more materials that are initially separated. One or more of the two or more materials can be configured similarly to the temperature-sensitive medium 130 described above (e.g., mixtures, slurries, including multiple components, etc.). These two or more materials can be at least partially miscible, such that when the temperature-sensitive medium 130 flows, the two or more materials at least partially mix when they come into contact. For example, a first material could be configured to have a first dielectric constant and a second material could be configured to have a second dielectric constant, such as can be different than the first dielectric constant.When the temperature-sensitive medium 130 flows and the two or more materials at least partially mix, the dielectric constant of the temperature-sensitive medium 130 can change, such as to a dielectric constant of the two or more materials combined. In this example, the temperature-sensitive medium 130 can be transferred by the delivery system 120, such as described above. Additionally or alternatively, the temperature-sensitive medium 130 could initially be placed on or near the interdigital contact arrangement 110 (e.g., over the interdigital contact arrangement 110, in one or more contact gaps of the interdigital contact arrangement 110). Then, when the temperature-sensitive medium 130 flows, the two or more materials can combine, and a property of the interdigital contact arrangement 110 can change, such as due to a mixing of the two or more materials.

[0047] FIG. 2 is a perspective drawing of an example of portions of the temperaturesensitive sensor system 100 of FIG. 1, where the sensor has been at least partially activated. In the example of FIG. 2, the temperature-sensitive medium 130 has been at or above the specified threshold temperature and has flowed partially across the interdigital contact arrangement 110. FIG. 2 shows that the temperature-sensitive medium 130 has flowed across the first contact gap 171, the second contact gap 172, the third contact gap 173, the fourth contact gap 174, and at least a portion of the fifth contact gap 175. The integrated circuit chip 160 can determine a property of the interdigital contact arrangement 110, such as can indicate that 4 contact gaps are completely bridged by the temperature-sensitive medium 130.

[0048] FIG. 3 is a top-view drawing of an example of portions of a temperaturesensitive sensor system 100, including portions of an example of a radio frequency identification (RFID) system 300. In the example of FIG. 3, the substrate 170 is on the bottom. FIG. 3 shows that the RFID system 300 can include an RFID chip 360 and an antenna 310. The RFID system 300 can be a near-field or far-field RFID system.

[0049] The RFID system 300 can be a passive system (e.g., operating based on power received with the antenna 310), such as can allow the RFID system 300 to operate without any power storage system (e.g., battery). The RFID system 300 can be configured to receive a “read” signal from an RFID reader 380 and send back a “return” signal. The “read” signal can include information, or can just be a wave at a carrier frequency that powers the RFID system 300, such as through the antenna 310. For example, the RFID system 300 might only be powered on when it is being read, such as can make it desirable for the temperature-sensitive sensor system 100 to be an irreversible sensor as the RFID system 300 might not be powered on when the temperature-sensitive sensor system 100 is above the specified threshold temperature to record the event.

[0050] The antenna 310 can be any type of antenna. The antenna 310 can be configured as a near field antenna (e.g., designed to couple to another antenna magnetically, such as when a distance to the other antenna is less than approximately one wavelength of the carrier frequency), such as a near field coil (as shown in FIG. 3). The antenna 310 can be configured as a far field antenna (e.g., designed to interact with an electromagnetic wave generated by another antenna, such as when a distance to the other antenna is greater than approximately one wavelength of the carrier frequency), such as a dipole antenna. In an example, the RFID system 300 can include a near field antenna and a far field antenna, such as can allow the RFID system 300 to be read by an RFID reader 380 from a larger range of distances. The antenna 310 can be energized by the carrier frequency generated by the RFID reader 380, such as can provide a voltage and current on the antenna 310. This voltage and current can be used to power the RFID chip 360 while the antenna 310 is receiving the carrier frequency. In an example, there can be an insulating material placed between the absorbent medium 132 and / or the delivery system 120 and the antenna 310, which can help prevent the temperature-sensitive medium 130 from shorting out one or more portions of the antenna 310. The antenna 310 can be configured to operate in close proximity to a conductive material, such as the temperaturesensitive medium 130.

[0051] The RFID chip 360 can take the place of the integrated circuit chip 160 of FIG. 1, and can be configured similarly, or can differ in one or more ways. The RFID chip 360 can be coupled to the interdigital contact arrangement 110 and the antenna 310. The RFID chip 360 can be configured to communicate with the RFID reader 380. The RFID chip 360 can communicate with the RFID reader 380 by one or more of altering an impedance of the antenna 310, such as can be sensed by the RFID reader 380, or sending back a signal using the antenna 310, such as can be received by the RFID reader 380. In a near-field system, altering an impedance of the antenna 310 can be used. In a far-field system, sending back a return signal can be used.

[0052] The RFID chip 360 can be configured to transfer one or more pieces of information when it is scanned by the RFID reader 380. For example, the RFID chip 360 can transfer one or more of: one or more pieces of identifying information (e.g., a serial number, reference number, product number, etc.), one or more representations of one or more properties of the temperature-sensitive sensor system 100 (e.g., a measured or determined capacitance value, a measured or determined resistance value, an indication of whether the temperaturesensitive sensor system 100 has been exposed to a temperature above the specified threshold temperature, a result of a comparison between a reference resistor and the resistance of theinterdigital contact arrangement 110, a number of contact gaps that have been determined to have been bridged, etc.), or one or more pieces of security information (e.g., a security code to verify that the temperature-sensitive sensor system 100 has not been replaced or otherwise tampered with, such as a key that only a manufacturer would know and would be difficult for a third party to guess or spoof).

[0053] FIG. 4 is a graph showing an example of operating portions of a temperaturesensitive sensor system 100. The conceptual (not simulated or experimental) data of FIG. 4 shows the resistance value 402 of the interdigital contact arrangement 110 and the capacitance value 404 of the interdigital contact arrangement 110. FIG. 4 shows an example where the temperature-sensitive medium 130 can flow across the interdigital contact arrangement 110 through the absorbent medium 132 at a specified rate. FIG. 4 shows that initially, the resistance value 402 can be very large (e.g., near infinite), and the capacitance value 404 can be at a base capacitance (e.g., a capacitance before the temperature-sensitive medium 130 is near the interdigital contact arrangement 110) such as, for example only, approximately 25 picofarads. At time 410, the temperature-sensitive medium 130 can hit the first contact gap. FIG. 4 shows that the properties of the interdigital contact arrangement 110 can change over a period of time 414 between time 410 and time 412, such as can be due to the temperature-sensitive medium 130 not bridging all portions of the contact gap simultaneously. In the example of FIG. 4, the temperature-sensitive sensor system 100 has five contact gaps, which are reached by the temperature-sensitive medium 130 at time 410, time 420, time 430, time 440, and time 450, respectively.

[0054] FIG. 4 shows that the capacitance value 404 can increase by the differential gap capacitance each time a contact gap is bridged, such as according to equation 2. In the example of FIG. 4, the differential gap capacitance can be, for example only, approximately 10.5 picofarads. Following all of the contact gaps being bridged, the capacitance value 404 can increase to about 77 picofarads, approximately three times the original value. This can be due to a dielectric constant of the temperature-sensitive medium 130 being approximately 3.

[0055] FIG. 4 shows that the resistance value 402 of a single bridged contact gap can be, for example only, approximately 4200 Ohms. Following the bridging of additional contact gaps, the resistance value 402 can change according to equation 1. For example, the resistance value 402 can be approximately 2100 ohms (e.g., 4200 / 2) following the second contact gap bridging and 1400 ohms (e.g., 4200 / 3) following the third contact gap bridging.

[0056] FIG. 4 also shows a resistance threshold 462 and a capacitance threshold 464. The resistance threshold 462, in this example, is set at approximately 3400 ohms, such that atleast two contact gaps can be bridged for the resistance value 402 to cross below the threshold. This can increase a reliability of the system and / or reduce false positive readings. The capacitance threshold 464, in this example, is set at approximately 33 picofarads, such that at least two contact gaps can be bridged for the capacitance value 404 to cross above the capacitance threshold 464.

[0057] FIG. 4 and the example values included therein are just examples to help illustrate the embodiments of the present disclosure, but they are not limiting. For example, the temperature-sensitive sensor system 100 can be configured with one or more of: other numbers of fingers, other numbers of contact gaps, other single gap resistance values, other base capacitance values, other differential gap capacitance values, etc.

[0058] FIG. 5 is a diagram showing an example of a method 500 for operating portions of a temperature-sensitive sensor system, such as the temperature-sensitive sensor system 100. At step 505, a temperature-sensitive sensor system can be place on a product to be monitored. The temperature-sensitive sensor system can include an interdigital contact arrangement including a first contact with at least one elongated finger and a second contact with at least two elongated fingers, where the at least one elongated finger of the first contact is interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers. The temperature-sensitive sensor system can also include a temperature-sensitive medium, configured to flow at least one of at or above a specified threshold temperature. The temperature-sensitive sensor system can also include a delivery system, configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing. The temperature sensitive sensor system can include a system similar to or identical to the temperature-sensitive sensor system 100, or can include a differing system. The product to be monitored can include medical product (e.g., a medicine, a drug, a donor organ, a vaccine, a medical dye or marker, etc.) a food product (e.g., a perishable food product, a refrigerated product, a frozen product), or another product that is temperature sensitive (e.g., sensitive electronics). Placing the temperature-sensitive sensor system on the product can include affixing (e.g., gluing, taping) the temperature-sensitive sensor system on the product or otherwise disposing the temperaturesensitive sensor system with the product (e.g., placing the temperature-sensitive sensor system in a box with the product).

[0059] At step 510, a property of the interdigital contact arrangement can be measured, such as using an integrated circuit chip, such as the integrated circuit chip 160. Measuring a property of the interdigital contact arrangement can include generating any piece ofinformation indicative of a state of the interdigital contact arrangement, such as can include an indication of a resistance value or capacitance value, or an indication of how a resistance or capacitance of the interdigital contact arrangement compares to one or more thresholds or reference components.

[0060] At step 515, a representation of the measured property can optionally be transmitted, such as using a radio frequency identification (RFID) system, such as the RFID system 300. The information can be requested by and / or transferred to an RFID reader, such as the RFID reader 380.

[0061] At step 520, a piece of identifying information can optionally be transmitted, such as using a radio frequency identification (RFID) system, such as the RFID system 300.

[0062] The shown order of steps is not intended to be a limitation on the order the steps are performed in. In an example, two or more steps may be performed simultaneously or at least partially concurrently.Additional Notes & Examples

[0063] Example l is a temperature-sensitive sensor system for detecting a temperature above a specified threshold temperature, the sensor system comprising: an interdigital contact arrangement including a first contact with at least one elongated finger and a second contact with at least two elongated fingers, wherein the at least one elongated finger of the first contact is interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers; a temperature-sensitive medium, configured to flow at least one of at or above the specified threshold temperature; and a delivery system, configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing.

[0064] In Example 2, the subject matter of Example 1 optionally includes wherein the first contact and the second contact include a conductive material, wherein the first contact and the second contact are disposed on an insulating substrate.

[0065] In Example 3, the subject matter of Example 2 optionally includes a radio frequency identification (RFID) system, the RFID system comprising: an RFID chip, the RFID chip coupled to the first contact and the second contact and configured to determine a property of the interdigital contact arrangement; and an antenna, coupled to the RFID chip.

[0066] In Example 4, the subject matter of Example 3 optionally includes wherein the RFID chip and the antenna are disposed on the insulating substrate.

[0067] In Example 5, the subject matter of any one or more of Examples 3-4 optionally include wherein the temperature-sensitive medium has a different dielectric constant than a medium near the contact gaps before the temperature-sensitive medium flowing.

[0068] In Example 6, the subject matter of Example 5 optionally includes wherein to determine a property of the interdigital contact arrangement includes to measure a capacitance corresponding to the interdigital contact arrangement.

[0069] In Example 7, the subject matter of any one or more of Examples 3-6 optionally include wherein the temperature-sensitive medium is electrically conductive.

[0070] In Example 8, the subject matter of Example 7 optionally includes wherein to determine a property of the interdigital contact arrangement includes to determine if a resistance corresponding to the interdigital contact arrangement is below a threshold resistance.

[0071] In Example 9, the subject matter of Example 8 optionally includes wherein a resistance value for the interdigital contact arrangement resulting from the temperaturesensitive medium bridging at least one of the contact gaps is between 100 Ohms and 1500 Ohms.

[0072] In Example 10, the subject matter of any one or more of Examples 3-9 optionally include wherein the RFID chip is configured to transmit a representation of the determined property and transmit a piece of identifying information when an RFID reader scans the RFID system.

[0073] In Example 11, the subject matter of Example 10 optionally includes the RFID reader.

[0074] In Example 12, the subject matter of any one or more of Examples 3-11 optionally include wherein the delivery system includes an absorbent medium, disposed near the temperature-sensitive medium and extending to near the contact gaps, configured to flow the temperature-sensitive medium at least one of near or in contact with at least one of the contact gaps following the temperature-sensitive medium reaching the specified threshold temperature.

[0075] In Example 13, the subject matter of Example 12 optionally includes wherein the delivery system is configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing independent of an orientation of the sensor system.

[0076] In Example 14, the subject matter of any one or more of Examples 12-13 optionally include wherein the absorbent medium includes a first end and a second end, wherein the first end is on a first side of the contact gaps, wherein the second end is on anopposite side of the contact gaps, wherein an axis extending from the first end to the second end is substantially orthogonal to the contact gaps, wherein the temperature-sensitive medium is placed near the first end of the absorbent medium, wherein the absorbent medium is configured to transport the temperature-sensitive medium from the first end to the second end at a specified rate.

[0077] In Example 15, the subject matter of Example 14 optionally includes wherein to determine a property of the interdigital contact arrangement includes to determine how far the temperature-sensitive medium has been transported by the absorbent medium.

[0078] In Example 16, the subject matter of any one or more of Examples 1-15 optionally include wherein the delivery system is configured to maintain the transferred temperature-sensitive medium at the contact gaps following the sensor system falling below the specified threshold temperature.

[0079] In Example 17, the subject matter of any one or more of Examples 1-16 optionally include at least three contact gaps.

[0080] Example 18 is a temperature-sensitive sensor system for detecting a temperature above a specified threshold temperature, the sensor system comprising: an interdigital contact arrangement including a first contact with at least one elongated finger and a second contact with at least two elongated fingers, wherein the at least one elongated finger of the first contact is interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers; a temperature-sensitive medium, configured to flow at least one of at or above the specified threshold temperature; and a delivery system, configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing, wherein the delivery system includes: an absorbent medium, disposed near the temperature-sensitive medium and extending to near the contact gaps, configured to flow the temperature-sensitive medium at least one of near or in contact with at least one of the contact gaps following the temperature-sensitive medium reaching the specified threshold temperature.

[0081] Example 19 is a method for using a temperature-sensitive sensor system, the method comprising: placing the temperature-sensitive sensor system on a product to be monitored, the temperature-sensitive sensor system comprising: an interdigital contact arrangement including a first contact with at least one elongated finger and a second contact with at least two elongated fingers, wherein the at least one elongated finger of the first contact is interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers; a temperature-sensitive medium,configured to flow at least one of at or above a specified threshold temperature; and a delivery system, configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing; and measuring a property of the interdigital contact arrangement.

[0082] In Example 20, the subject matter of Example 19 optionally includes transmitting, using a radio frequency identification (RFID) system, a representation of the measured property; and transmitting, using the RFID system, a piece of identifying information.

[0083] Example 21 is at least one machine-readable medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations to implement of any of Examples 1-20.

[0084] Example 22 is an apparatus comprising means to implement of any of Examples 1-20.

[0085] Example 23 is a system to implement of any of Examples 1-20.

[0086] Example 24 is a method to implement of any of Examples 1-20.

[0087] Each of the non-limiting aspects above can stand on its own or can be combined in various permutations or combinations with one or more of the other aspects or other subject matter described in this document.

[0088] In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc., are used merely as labels, and are not intended to impose numerical requirements on their objects.

[0089] Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like.Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Such instructions can be read and executed by one or more processors to enable performance of operations comprising a method, for example. The instructions are in any suitable form, such as but not limited to source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like.

Claims

What is claimed is:

1. A temperature-sensitive sensor system for detecting a temperature above a specified threshold temperature, the sensor system comprising: an interdigital contact arrangement including a first contact with at least one elongated finger and a second contact with at least two elongated fingers, wherein the at least one elongated finger of the first contact is interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers; a temperature-sensitive medium, configured to flow at least one of at or above the specified threshold temperature; and a delivery system, configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing.

2. The sensor system of claim 1, wherein the first contact and the second contact include a conductive material, wherein the first contact and the second contact are disposed on an insulating substrate.

3. The sensor system of claim 2, further comprising a radio frequency identification (RFID) system, the RFID system comprising: an RFID chip, the RFID chip coupled to the first contact and the second contact and configured to determine a property of the interdigital contact arrangement; and an antenna, coupled to the RFID chip.

4. The sensor system of claim 3, wherein the RFID chip and the antenna are disposed on the insulating substrate.

5. The sensor system of claim 3 or 4, wherein the temperature-sensitive medium has a different dielectric constant than a medium near the contact gaps before the temperaturesensitive medium flowing.

6. The sensor system of claim 5, wherein to determine a property of the interdigital contact arrangement includes to measure a capacitance corresponding to the interdigital contact arrangement.

7. The sensor system of any one of claims 3 to 6, wherein the temperature-sensitive medium is electrically conductive.

8. The sensor system of claim 7, wherein to determine a property of the interdigital contact arrangement includes to determine if a resistance corresponding to the interdigital contact arrangement is below a threshold resistance.

9. The sensor system of claim 8, wherein a resistance value for the interdigital contact arrangement resulting from the temperature-sensitive medium bridging at least one of the contact gaps is between 100 Ohms and 1500 Ohms.

10. The sensor system of any one of claims 3 to 9, wherein the RFID chip is configured to transmit a representation of the determined property and transmit a piece of identifying information when an RFID reader scans the RFID system.

11. The sensor system of claim 10, further comprising the RFID reader.

12. The sensor system of any one of claims 3 to 10, wherein the delivery system includes an absorbent medium, disposed near the temperature-sensitive medium and extending to near the contact gaps, configured to flow the temperature-sensitive medium at least one of near or in contact with at least one of the contact gaps following the temperature-sensitive medium reaching the specified threshold temperature.

13. The sensor system of claim 12, wherein the delivery system is configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing independent of an orientation of the sensor system.

14. The sensor system of claim 12 or 13, wherein the absorbent medium includes a first end and a second end, wherein the first end is on a first side of the contact gaps, wherein the second end is on an opposite side of the contact gaps, wherein an axis extending from the first end to the second end is substantially orthogonal to the contact gaps, wherein the temperature-sensitive medium is placed near the first end of the absorbent medium, wherein the absorbent medium is configured to transport the temperature-sensitive medium from the first end to the second end at a specified rate.

15. The sensor system of claim 14, wherein to determine a property of the interdigital contact arrangement includes to determine how far the temperature-sensitive medium has been transported by the absorbent medium.

16. The sensor system of any one of claims 1 to 10 or 12 to 15, wherein the delivery system is configured to maintain the transferred temperature-sensitive medium at the contact gaps following the sensor system falling below the specified threshold temperature.

17. The sensor system of any one of claims 1 to 10 or 12 to 16, comprising at least three contact gaps.

18. A temperature-sensitive sensor system for detecting a temperature above a specified threshold temperature, the sensor system comprising: an interdigital contact arrangement including a first contact with at least one elongated finger and a second contact with at least two elongated fingers, wherein the at least one elongated finger of the first contact is interleaved with the at least two elongated fingers of the second contact to create at least two contact gaps between the respective elongated fingers; a temperature-sensitive medium, configured to flow at least one of at or above the specified threshold temperature; and a delivery system, configured to transfer the temperature-sensitive medium to at least one of the contact gaps following the temperature-sensitive medium flowing, wherein the delivery system includes: an absorbent medium, disposed near the temperature-sensitive medium and extending to near the contact gaps, configured to flow the temperature-sensitive medium at least one of near or in contact with at least one of the contact gaps following the temperature-sensitive medium reaching the specified threshold temperature.

19. A method for using a temperature-sensitive sensor system, the method comprising: placing the temperature-sensitive sensor system of any one of claims 1 to 10 or 12 to18 on a product to be monitored; and measuring a property of the interdigital contact arrangement.

20. A method for using a temperature-sensitive sensor system, the method comprising:placing the temperature-sensitive sensor system of any one of claims 3 to 10 or 12 to on a product to be monitored; measuring a property of the interdigital contact arrangement; transmitting, using the RFID system, a representation of the measured property; and transmitting, using the RFID system, a piece of identifying information.

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