Early warning thermal sensor system and method

Abstract

Systems and methods for temperature detection include an antenna, a transmitter, a passive thermal sensor, and a power source. The passive thermal sensor defines an electrical discontinuity establishing an incomplete circuit between the power source and the transmitter. The passive thermal sensor includes a metal alloy provided in proximity to the electrical discontinuity. The metal alloy may be configured to change state from a solid state to a liquid state in a narrow temperature range such that the metal alloy in the liquid state bridges the electrical discontinuity to provide electrical connection between the power source and the transmitter to enable temperature detection. The metal alloy may be a shape memory alloy configured to provide an electrical connection between the power source and the transmitter above a certain threshold temperature and break the connection when the temperature falls below the threshold temperature.

Description

EARLY WARNING THERMAL SENSOR SYSTEM AND METHODFIELD

[0001] The present disclosure relates generally to sensors, and more particularly to thermal sensors and associated methods.BACKGROUND

[0002] Forest fires have become an increasing threat to human life and property over the past several years. Loss of human life can arise from one or more of: the speed with which a fire can travel; lack of early detection relative to the required evacuation time; and / or lack of fire position knowledge relative to the known evacuation routes. In addition, forest fires can start in remote areas, for example by lightning strike, which can make it difficult to detect before the fire grows or spreads at dangerous levels.

[0003] Detecting thermal events, such as forest fires, in which a thermal limit has been exceeded can be difficult due to factors such as: the failure (e.g., melting) of sensor components at high temperatures; determining the location where the thermal event begins and / or where it is spreading; and / or loss of battery life for sensors placed in remote areas requiring frequent replacement.

[0004] In addition, the detection of over temperature events, such as in industrial process management, can also be desirable as a protection to equipment operators and / or to mitigate damage to equipment or the surrounding area. Sensor systems that require reduced or no maintenance, such as battery replacement, and which can be built into line equipment is desirable.

[0005] Accordingly, it remains desirable to develop improvements and advancements in relation to thermal sensors, to overcome shortcomings of known techniques, and to provide additional advantages thereto.

[0006] This section is intended to introduce various aspects of the art, which may be associated with the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

[0008] FIG. 1 illustrates a system for temperature detection according to an embodiment of the present disclosure.

[0009] FIG. 2A illustrates a side view of a passive thermal sensor having one portion of a metal alloy coupled to a first electrical contact according to an embodiment of the present disclosure.

[0010] FIG. 2B illustrates a side view of the passive thermal sensor of FIG. 2A after the metal alloy has melted and formed an electrical connection between a first and second electrical contacts.

[0011] FIG. 3 illustrates a side view of a passive thermal sensor having a first portion and a second portion of a metal alloy decoupled from first and second electrical contacts, respectively, according to an embodiment of the present disclosure.

[0012] FIG. 4 illustrates a side view of a passive thermal sensor having a first portion and second portion composed of different metal alloys, where each portion is decoupled from first and second electrical contacts, respectively, according to an embodiment of the present disclosure.

[0013] FIG. 5 illustrates a system for temperature detection in which multiple sensors are electrically arranged in parallel according to an embodiment of the present disclosure.

[0014] FIG. 6A illustrates a system for temperature detection in which a plurality of sensors is electrically arranged in series according to an embodiment of the present disclosure.

[0015] FIG. 6B illustrates two sensors from the system of FIG. 6A according to an embodiment of the present disclosure.

[0016] FIG. 6C illustrates the two sensors of FIG. 6B, in which one sensor has reached a temperature within or above the narrow temperature range corresponding to one or more of the metal alloy(s), causing the metal alloy(s) to melt and shorten the circuit such that a resistive element is bypassed.

[0017] FIG. 7 illustrates a system for temperature detection in which multiple sensors are spatially arranged in different orientations according to an embodiment of the present disclosure.

[0018] Throughout the drawings, sometimes only one or fewer than all of the instances of an element visible in the view are designated by a lead line and reference character, for thesake only of simplicity and to avoid clutter. It will be understood, however, that in such cases, in accordance with the corresponding description, that all other instances are likewise designated and encompassed by the corresponding description.DETAILED DESCRIPTION

[0019] The present disclosure describes a system and method for temperature detection. The system for temperature detection may have a circuit comprising an antenna, a transmitter, a power source, and a passive thermal sensor. The passive thermal sensor may be positioned between the power source and the transmitter and further defines an electrical discontinuity that prevents the transmitter from receiving power from the power source. The electrical discontinuity may be a physical separation between two electrical contacts. The passive thermal sensor may comprise a metal alloy in proximity to the electrical discontinuity. The metal alloy may be configured to change from a solid state to a liquid state in a narrow temperature range such that the metal alloy in the liquid state bridges the electrical discontinuity. When the electrical discontinuity is bridged by the metal alloy in its liquid state, an electrical connection is formed between the power source and the transmitter, which completes the circuit and permits the transmitter to transmit a signal.

[0020] In an aspect, the present disclosure provides a system for temperature detection, the system comprising: an antenna; a transmitter electrically coupled to the antenna; a passive thermal sensor electrically coupled to the transmitter; and a power source electrically coupled to the passive thermal sensor. The passive thermal sensor may define an electrical discontinuity establishing an incomplete circuit between the power source and the transmitter. The passive thermal sensor may comprise a metal alloy provided in proximity to the electrical discontinuity. The metal alloy may be configured to change state from a solid state to a liquid state in a narrow temperature range such that the metal alloy in the liquid state bridges the electrical discontinuity to provide electrical connection between the power source and the transmitter to enable temperature detection.

[0021] In an embodiment, the passive thermal sensor comprises first and second electrical contacts positioned on a substrate, the first electrical contact being spaced apart from the second electrical contact to define the electrical discontinuity.

[0022] In an embodiment, the metal alloy comprises a first portion and a second portion, the first portion being electrically decoupled from the first electrical contact, the secondportion being either electrically coupled or decoupled from the second electrical contact when the metal alloy is in the solid state. The first portion may be electrically coupled to the first electrical contact and the second portion may be electrically coupled to the second electrical contact after the metal alloy changes from the solid state to liquid state, to provide electrical connection between the power source and the transmitter.

[0023] In an embodiment, the metal alloy comprises a first portion composed of a first metal alloy and a second portion composed of a second metal alloy. The narrow temperature range may comprise a first narrow temperature range and a second narrow temperature range, the first portion composed of the first metal alloy configured to change state from the solid to liquid state in the first narrow temperature range, and the second portion composed of the second metal alloy configured to change state from the solid to liquid state in the second narrow temperature range, to provide electrical connection between the power source and the transmitter.

[0024] In an embodiment, the passive thermal sensor comprises a first passive thermal sensor and a second passive thermal sensor, wherein the narrow temperature range comprises a first narrow temperature range and a second narrow temperature range, the first passive thermal sensor comprises a first metal alloy configured to change from solid to liquid state within the first narrow temperature range, and the second passive thermal sensor comprises a second metal alloy configured to change from solid to liquid state within the second narrow temperature range.

[0025] In an embodiment, the first passive thermal sensor is electrically arranged in parallel with the second passive thermal sensor.

[0026] In an embodiment, the first passive thermal sensor is electrically arranged in series with the second passive thermal sensor.

[0027] In an embodiment, the transmitter comprises a first transmitter associated with the first passive sensor and a second transmitter associated with the second passive thermal sensor, wherein: changing from solid to liquid state within the first narrow temperature range provides the electrical connection between the power source and the first transmitter, and changing from solid to liquid state within the second narrow temperature range provides the electrical connection between the power source and the second transmitter.

[0028] In an embodiment, the metal alloy comprises a solder preform.

[0029] In an embodiment, the transmitter transmits a signal in response to the electrical connection between the power source and the transmitter.

[0030] In an embodiment, the transmitter is configured to transmit the signal to a cellular base transceiver station or a satellite communication system.

[0031] In an embodiment, the transmitter transmits the signal on a radio frequency.

[0032] In an embodiment, the radio frequency is distinct from a licensed Industrial, Scientific, and Medical (ISM) radio frequency band.

[0033] In an embodiment, the signal comprises a signal identifier based on a location code applied to the sensor.

[0034] In an embodiment, the first narrow temperature range does not overlap with the second temperature range.

[0035] In an embodiment, the passive thermal sensor further comprises a third electrical contact between the first electrical contact and the second electrical contact, the third electrical contact being approximately aligned with the metal alloy, wherein the third electrical contact is spaced apart from the first and second electrical contacts.

[0036] In an embodiment, the substrate comprises a pattern configured to receive the metal alloy in the liquid state.

[0037] In an embodiment, the substrate is thermally conductive.

[0038] In an embodiment, the substrate is composed of graphite, and at least one insulating layer electrically separates the first and second electrical contacts from the substrate.

[0039] In an embodiment, the substrate comprises a magnet and the metal alloy is ferromagnetic.

[0040] In an embodiment, the power source is a battery, a thermoelectric generator, a thermoelectric cooler, or a supercapacitor.

[0041] In an embodiment, the metal alloy is a shape memory alloy configured to revert to an original shape when the metal alloy is below the narrow temperature range.

[0042] For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the features illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications, and any further applications of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. It will be apparent to those skilled in the relevant art that some features that are not relevant to the present disclosure may not be shown in the drawings for the sake of clarity.

[0043] Certain terms used in this application and their meaning as used in this context are set forth in the description below. To the extent a term used herein is not defined, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Further, the present processes are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments and terms or processes that serve the same or a similar purpose are considered to be within the scope of the present disclosure.

[0044] “Solidus” can mean the highest temperature at which a metal alloy is completely solid. A metal alloy in a “solidus state” is completely solid.

[0045] “Liquidus” can mean the lowest temperature at which a metal alloy is completely liquid. A metal alloy in a “liquidus state” is completely liquid.

[0046] “Solid state” can mean the metal alloy is in a substantially solid state or a completely (solidus) solid state.

[0047] “Liquid state” can mean the metal alloy is in a substantially liquid state or a completely (liquidus) liquid state.

[0048] FIG. 1 illustrates a system 100 for thermal detection, which may be used to detect the presence and / or location of a thermal event. A thermal event may be any occurrence or phenomenon that causes a temperature increase, such as a fire (e.g., forest fires), machinery overheating or failure, explosions, and / or natural phenomena. The system 100 has an antenna 110, a transmitter 120 electrically coupled to the antenna 110, a passive thermal sensor 130 electrically coupled to the transmitter 120, and a power source 140 electrically coupled to the passive thermal sensor 130. The passive thermal sensor 130 may be positioned between the power source 140 and the transmitter 120 and may further define an electrical discontinuity 132. The electrical discontinuity 132 may form or establish an incomplete circuit that prevents the transmitter 120 from receiving power from the power source 140, thereby preventing the transmitter 120 from transmitting a signal.

[0049] The passive thermal sensor 130 may comprise a metal alloy 134 in a solid state that is in proximity to the electrical discontinuity 132 such that when the metal alloy 134 changes from a solid state to a liquid state (i.e., melts), for example in response to the temperature(s) of a thermal event, the liquid metal alloy bridges the electrical discontinuity. Bridging the electrical discontinuity 132 with the metal alloy 134 provides or establishes an electrical connection between the power source 140 and the transmitter 120 to form a complete circuit such that the transmitter 120 may transmit a signal. The transmitter 120 may beconfigured to automatically transmit a signal via the antenna 110 to indicate that the sensor 130 been activated when the transmitter 120 is powered by the power source 140. For example, the signal may contain information, such as the location of the sensor (e.g., a location code), the sensor’s electronic signature, the sensor’s serial number, the sensed temperature, and / or the sensor’s GPS location. In an embodiment, the information about the sensor may be formatted into a code. The information in the signal may further contain a message or notification.

[0050] The metal alloy 134 may comprise a composition of elements that forms a metallic compound or solution. The selection of elements and their relative ratios for the metal alloy 134 can be used to produce a metal alloy with specific material properties. For example, the solidus temperature and the liquidus temperature of the metal alloy 134 can be engineered to be equal, approximately equal, or within a narrow range of temperatures. For example, in reference to Table 1, in some embodiments the narrow temperature range may be less than about 20 degrees Celsius, or the narrow temperature range may be less than about 1 degree Celsius. The liquidus is the lowest temperature at which an alloy is completely liquid; the solidus temperature is the highest temperature at which an alloy is completely solid. References to a “narrow temperature range” in this disclosure refer to the temperature range between the solidus temperature and the liquidus temperature of a metal alloy. The metal alloy 134 may be configured to change state from a completely solid state to a completely liquid state in a narrow temperature range, e.g., according to the solidus and liquidus temperatures of the metal alloy 134.

[0051] Table 1 shows examples of metal alloys, their composition, and respective solidus and liquidus temperatures. The alloys listed below are by way of example only. Other metal alloys that have solidus and liquidus temperatures that are approximately equal, or within a narrow temperature range may be used.

[0052] Table 1: Metal Alloy Examples

[0053] In some embodiments, there is provided a system for temperature detection, the system comprising: an antenna; a transmitter electrically coupled to the antenna; a passive thermal sensor electrically coupled to the transmitter; and a power source electrically coupled to the passive thermal sensor, the passive thermal sensor defining an electrical discontinuity establishing an incomplete circuit between the power source and the transmitter, the passive thermal sensor comprising a metal alloy provided in proximity to the electrical discontinuity, the metal alloy configured to change state from a solidus state to a liquidus state in a narrow temperature range such that the metal alloy in the liquidus state bridges the electrical discontinuity to provide electrical connection between the power source and the transmitter to enable temperature detection.

[0054] Referring again to FIG. 1, the passive thermal sensor 130 may have a first electrical contact 136 and a second electrical contact 138 that are physically separate and spaced a distance apart on a substrate 150 to form the electrical discontinuity 132. For example, the first and second electrical contacts 136, 138 may be spaced apart on the substrate 150 to define a gap. The gap or distance between the electrical contacts may beabout 20 mm. When the metal alloy 134 changes from the solid state to the liquid state, the liquid metal alloy 134 may bridge the first and second electrical contacts 136, 138 to form an electrical connection between the contacts, which completes the circuit between the power source 140 and the transmitter 120.

[0055] In another embodiment, a third electrical contact (not shown in FIG. 1) may be positioned in the gap between the first and second electrical contacts 136, 138 with gaps separating each of the contacts to maintain the electrical discontinuity when the metal alloy 134 is in the solid state (as shown particularly in FIGs 3 and 4). The third electrical contact (not shown) may help the liquid metal alloy 134 bridge the first and second electrical contacts 136, 138, for example, to help form the electrical connection between the electrical contacts 136, 138. If the temperature of the sensor 130 decreases below the melting point of the metal alloy 134, and / or below the solid temperature, the metal alloy 134 may partially or completely resolidify. Depending on the material properties of the metal alloy 134 and / or the configuration of the substrate 150, the re-solidification of the metal alloy 134 may or may not maintain the electrical connection between the electrical contacts 136, 138. For example, in some embodiments the metal alloy 134 may be a shape memory alloy that changes shape at temperatures within or above the narrow temperature range to form an electrical connection between the electrical contacts 136, 138. When the temperature of the sensor decreases to a temperature at or below the solidus temperature after the thermal event, the shape memory alloy may revert to its original shape such that the metal alloy 134 does not maintain the electrical connection between electrical contacts 136, 138, i.e., the electrical discontinuity 132 may be re-established. Using shape memory alloy may in some cases improve temperature accuracy, survivability, and / or sensitivity of the passive thermal sensor 120. In some embodiments, the melting of the metal alloy 134 may be irreversible. In some embodiments, the metal alloy may be a solder preform.

[0056] The metal alloy 134 may bridge the electrical discontinuity as a result of magnetic forces, for example, when the metal alloy 134, or a portion of the metal alloy 134, is ferromagnetic and the substrate 150 comprises a magnet (see e.g., FIG. 4). Other mechanisms or forces may be present that help the liquid metal alloy 134 bridge the electrical discontinuity to form an electrical connection on and between the electrical contacts 136, 138. The metal alloy 134 may bridge the electrical discontinuity as a result of interfacial forces (e.g., surface tension, capillary forces, etc.). In some embodiments, the sensor 130 may operateindependent of, and not rely (in part or in whole), on gravitational forces to help bridge the electrical discontinuity.

[0057] Since the metal alloy 134 may bridge the electrical discontinuity with the assistance of magnetic forces and / or interfacial forces, the passive thermal sensor 130 may be configured or positioned in any orientation (e.g., upward, downward, on its side) when the system 100 is deployed. This positional independence permits the sensor 130 to be deployed using methods that may not control the final orientation of the sensor 130, such as by airborne drop or by foot. The positional independence may permit more efficient distribution of the thermal sensors 130 by overcoming limitations of existing sensors that require setup, calibration, and / or positioning (i.e. , specific orientations), which take additional time and may require trained personnel.

[0058] The transmitter 120 of the system 100 may be a broadcast type transmitter suitable for transmitting a signal. In an embodiment, the transmitter 120 may be compatible to transmit a signal to a cellular base transceiver station. For example, the transmitter 120 may be configured to transmit a signal to local authorities, a fire department, community group, or other local group / authority. The transmitter 120 may be configured to transmit the signal to one or more different recipients, for example to provide an alert or notification to recipients in an order of increasing importance, based on stored signal transmission protocol data or rules. The transmitter 120 may transmit the signal on a radio frequency. For example, the transmitter 120 may transmit a signal on a radio frequency that does not overlap with a licensed Industrial, Scientific, and Medical (ISM) radio band. The radio frequency may be 433.92 MHz. In some embodiments, the transmitter may be compatible to transmit a signal to and / or via a satellite communication system. In embodiments comprising more than one passive thermal sensor, such as the embodiments described in reference to FIGs 5-7, the system may comprise a transmitter configured to transmit a unique signal corresponding to each sensor, when the respective sensors are activated. In another embodiment, multiple transmitters may each correspond to one or more sensors. The unique signal may comprise information about the sensor, as previously described, which may be further formatted into a code.

[0059] The power source 140 may be any power source suitable for powering a transmitter 120, such as a battery or a supercapacitor. The power source 140 may be a thermoelectric generator (TEG), a thermoelectric cooler (TEC), or a combined TEG / TEC cell. The TEG may be partially or wholly powered by the temperatures and / or temperature gradients stemming from the thermal event. Multiple or combinations of power sources 140 may be used.The power source 140 may be rechargeable, and in some embodiments, the system 100 may include a passive charging element to charge the power source 140 and / or a secondary power source. For example, a solar cell may be used to enable passive charging of the power source 140 over time. Since the power source 140 is disconnected from the transmitter until the metal alloy melts to bridge the electrical discontinuity, the power source 140 may remain viable in the field without requiring replacement for extended periods of time as compared to a sensor having a complete circuit and battery such that the battery must be regularly replaced due to a constant power draw.

[0060] The substrate 150 may be any substrate suitable for a passive thermal sensor 130 comprising electrodes (i.e., the first and second electrical contacts 136, 138). The substrate 150 may have grooves, ridges, or otherwise be patterned in a manner to guide the metal alloy 134 into a shape or configuration for bridging the first and second electrical contacts 136, 138. The configuration of the substrate may help the metal alloy 134 bridge the electrical discontinuity 132 regardless of the system’s orientation. The substrate 150 may be patterned, or shaped and constructed, such that the first and second electrical contacts 136, 138 remain electrically connected if the metal alloy 134 resolidifies (e.g., if the temperature decreases after a thermal event) and / or if the metal alloy 134 reliquefies (e.g., in a subsequent thermal event or when the metal alloy 134 is in a reflow state).

[0061] The location of the system 100 comprising the passive thermal sensor 130 may be recorded based on the location of the drop point, for example, if the system 100 is dropped via airborne drop or by a person on foot. The location of the system 100 may be determined based on the sensor’s 130 electronic signature, serial number, and / or other identifying information that may be transmitted by the transmitter 120 when the sensor 130 is activated in a thermal event.

[0062] Based on the number of sensors 130, the placement of the sensor(s) 130, and / or the melting point of the metal alloy(s) 134 of the sensor(s) 130, information about a thermal event may be generated, obtained and / or inferred when one or more signals are received from the transmitter 120 of the system 100.

[0063] The system 100 may comprise redundancies to help ensure a sensor 130 is activated when a thermal event occurs and / or to prevent false positives. For example, the sensor 130 may comprise more than one electrical discontinuity such that both electrical discontinuities must be bridged to complete the circuit to help prevent a false positive if one electrical discontinuity is bypassed by an electrical short, e.g., when there is no thermal event.The system 100 may comprise one or more additional sensors 130 that are identical to the sensor 130 that may help ensure a signal is transmitted in the event one or more sensors 130 fail before or during a thermal event.

[0064] FIGs 2-4 illustrate example configurations of the passive thermal sensor 130 according to some embodiments of the present disclosure.

[0065] FIG. 2A illustrates a side view of a passive thermal sensor 230 having a first portion 234a of a metal alloy 234 coupled to a first electrical contact 236 according to an embodiment of the present disclosure. The metal alloy 234 may comprise a first portion 234a and a second portion 234b. The first portion 234a and second portion 234b may be located at the respective or opposite ends of the metal alloy 234. For example, the metal alloy 234 may comprise a solder preform with a first end and second end that respectively form the first and second portions 234a, 234b. In some embodiments, the metal alloy 234 may be a shape memory alloy having an open state and / or a closed state. Changing between the open state and closed state may occur within and / or above the narrow temperature range. For example, the metal alloy 234 that comprises a shape memory alloy may be in an open state such that the electrical discontinuity 232 is not bridged at temperatures at or below the solidus temperature, and the shape memory alloy may be in a closed state such that the electrical discontinuity 232 is bridged at temperatures within or above the narrow temperature range. If the temperature of the sensor 230 decreases below the narrow temperature range, the shape memory alloy may revert to its original shape. A shape memory alloy may allow the sensor 230 to be used to detect more than one thermal event.

[0066] The first portion 234a of the metal alloy 234 may be coupled to the first electrical contact 236 and the second portion 234b of the metal alloy 234 may be decoupled from the second electrical contact 238 when the metal alloy 234 is in an initial solid state (e.g., when the sensor 230 is deployed). When the sensor 230 is exposed to temperatures that are within or exceed the narrow temperature range corresponding to the melting point of the metal alloy 234, the metal alloy 234 will change from the solid state to the liquid state such that the second portion 234b couples to the second electrical contact 238, for example as shown in FIG. 2B. When the second portion 234b of the metal alloy 234 couples to the second electrical contact 238, an electrical connection is formed between the first and second electrical contacts 236, 238 to complete a circuit (as shown in FIG. 1, for example), which causes a transmitter (not shown in FIGs 2A and 2B) to receive power from a power source (not shown in FIGs 2A and 2B) to transmit a signal indicating that the sensor 230 has been activated. In someembodiments, multiple transmitters may be used, for example, to correspond with each sensor 230.

[0067] FIG. 3 illustrates a side view of a passive thermal sensor 330 having a metal alloy 334 comprising a first portion 334a and a second portion 334b decoupled from first and second electrical contacts 336, 338, respectively, according to an embodiment of the present disclosure. The use of two decoupled portions of the metal alloy 334 may lower the possibility of a false positive connection as the electrical contacts 336, 338 may only be electrically connected when both the first portion 334a and the second portion 334b melt. A false positive connection may occur as a result of manufacturing process variability and / or mechanical shock as a result of deployment.

[0068] The first and second portions 334a, 334b of the metal alloy 334 may be composed of the same metal alloy 334. The metal alloy 334 may comprise a third portion 334c between the first and second portions 334a, 334c to form an approximate U-shape in which the first and second portions 334a, 334b are offset from the third portion 334c. The third portion 334c may be provided in the gap between the first electrical contact 336 and the second electrical contact 338. The third portion 334a may be affixed to a third electrical contact 337 that is physically separate from the first and second electrical contacts 336, 338, or the third portion 334c may be affixed to the substrate 350 or other supporting structure.

[0069] In an embodiment, the first portion 334a, second portion 334b, and third portion 334c may be composed of the same metal alloy 334. When the metal alloy 334 melts, the first, second, and third portions 334a, 334b, 334c melt to bridge the first and second electrical contacts 336, 338. The third portion 334c may help guide the position of the first and second portions 334a, 334b to help form an electrical connection between the first and second electrical contacts 336, 338. In another embodiment, the third portion 334c may be composed of a second metal alloy that is different from the first metal alloy that makes up the first and second portions 334a, 334b. The second metal alloy may have a second narrow temperature range corresponding to the melting point that is less than the first narrow temperature range corresponding to the melting of the first metal alloy such that the third portion 334c will melt first and may help guide the positions of the first and second portions 334a, 334b when they subsequently melt at a temperature within or above the second narrow temperature range.

[0070] In some embodiments, the metal alloy 334 may be a shape memory alloy having an open state and / or a closed state, and changing between the open state and closed state occurs within and / or above the narrow temperature range. For example, the metal alloy334 that comprises a shape memory alloy may be in an open state such that the electrical discontinuity 332 is not bridged at temperatures at or below the solidus temperature, and the shape memory alloy may be in a closed state such that the electrical discontinuity 332 is bridged at temperatures within or above the narrow temperature range. If the temperature of the sensor 330 decreases below the narrow temperature range, the shape memory alloy may revert to its original shape. A shape memory alloy may allow the sensor 330 to be used to detect more than one thermal event.

[0071] The first electrical contact 336 and the second electrical contact 338 (and / or the third electrical contact 337) may be separated from the substrate by an electrically insulating layer 352, such SiC>2 or any other suitable electrically insulating material. For example, an insulating layer 352 in between the electrical contacts 336, 338 (and / or 337) may be used when the substrate 350 is composed of an electrically conductive material, such as graphite. The insulating layer 352 may inhibit the formation of a short circuit that bypasses the metal alloy 334.

[0072] FIG. 4 illustrates a side view of a passive thermal sensor 430 having a metal alloy 434 comprising a first portion 434a and second portion 434b decoupled from first and second electrical contacts 436, 438, respectively, and a substrate 450 comprising a magnet 454, according to an embodiment of the present disclosure.

[0073] The metal alloy 434 may comprise a first portion 434a and a second portion 434b composed of a first metal alloy. In an embodiment, the metal alloy 434 may comprise a third portion 434c composed of the first metal alloy of the first and second portions 434a, 434b. In another embodiment, the third portion 434c may be composed of a second metal alloy that has a different narrow temperature range than the first metal alloy that makes up the first and second portions 434a, 434b. Thus, the first and second metal alloys may be different such that they have respective first and second narrow temperature ranges.

[0074] The first metal alloy may be ferromagnetic such that when the first metal alloy changes from the solid state to the liquid state, attraction between the magnet 454 in the substrate 450 and the first metal alloy may help the first metal alloy form an electrical connection with the electrical contacts 436, 438. The second narrow temperature range corresponding to the melting point of the second metal alloy may be less than the first narrow temperature range corresponding to the melting point of the first metal alloy such that the third portion 434c melts before the first and second portions 434a, 434b. The third portion 434c comprising the second metal alloy may conform to the substrate 450 or a third electrical contact437. The third portion 434c may help guide the position of the first and second portions 434a, 434b to help form the electrical connection between the first and second electrical contacts 436, 438. In some embodiments, when the third portion 434c melts, the first and / or second portions 434a, 434b will form an electrical connection with the first and second electrical contacts 436, 438, respectively, in the solid state to bridge the first and second electrical contacts 436, 438 via the third portion 434c.

[0075] FIG. 5 illustrates a system 500 for temperature detection in which multiple sensors 530a, 530b are electrically arranged in parallel according to an embodiment of the present disclosure. The system 500 may comprise an antenna 510, a transmitter 520, and a power source 540. The system 500 may comprise a first passive thermal sensor 530a comprising a first metal alloy 534a and a second passive thermal sensor 530b comprising a second metal alloy 534b. While two sensors 520a and 530b are illustrated in FIG. 5, in other embodiments, the system 500 may comprise a plurality of passive thermal sensors 530 comprising metal alloys 534 with different narrow temperature ranges. The melting points of the first and second metal alloys 534a, 534b may be different. The first and second passive thermal sensors 530a, 530b may each establish electrical discontinuities 532a, 532b according to any of the embodiments described herein. The transmitter 520 may be configured to transmit a unique signal corresponding to each of the first and second passive thermal sensors 530a, 530b.

[0076] For example, when the system 500 reaches a temperature within or above the first narrow temperature range corresponding to the melting point of first metal alloy 534a of the first sensor 530a, the transmitter 520 may receive power from the power source 540 to transmit a first signal that indicates the first sensor 530a has been activated. When the system 500 reaches a temperature within or above the second narrow temperature range corresponding to the melting point of second metal alloy 534b of the second sensor 530b, the transmitter 520 may be configured to transmit a second signal that indicates the second sensor 530b has been activated. For example, in some embodiments determination of how many sensors are activated may be through a current sensor in the transmitter that detects the increase in current resulting from progressive bridging of the electrical discontinuity in each sensor. Accordingly, the system 500 may be used to monitor the increasing temperature of the environment around the system 500. The temperature information may be used to infer the strength or severity of a thermal event, such as a forest fire, at the location of the system 500.

[0077] FIG. 6A illustrates a system 600 for temperature detection comprising a plurality of passive thermal sensors 630 electrically arranged in parallel according to an embodiment of the present disclosure. The chain of passive thermal sensors 630 may be arranged such that the current flow between the power source 640 and the transmitter 620 increases as each sensor 630 is activated by a thermal event (or one or more thermal events), which may be used to determine which sensor(s) and / or how many sensors have been activated. A pair of sensors at the end of a chain of sensors may be configured as an open circuit such that the transmitter 620 only receives power from the power source 640 when at least one of the plurality of sensors 630 is activated. The system 600 may have more than one chain of passive thermal sensors 630. Each passive thermal sensor 630 may be spaced a distance apart from the next or adjacent sensor 630, which may help detect a thermal event, such as a forest fire, at a distance from the remainder of the system 600 comprising the transmitter 620 and power source 640. The activation of one or more of the sensors 630 may allow for detection of the location and / or rate of movement and / or presence of additional thermal events based on which sensors 630 are activated and / or how many sensors 630 are activated. For example, the system 600 may not be arranged with uniform spacing as shown in FIG. 6, and there may be a large distance in the order of many feet or many metres in between adjacent sensors 630.

[0078] In an example embodiment in relation to FIG. 6A, as well as FIG. 6B and FIG.6C, multiple sensors may be used to determine a distance between a thermal event and the transmitter 620. For example, the sensors 630 may close in parallel progressively shortening the loop between the sensor 630 and the transmitter 620. The change in distance may be determined from the increase in current through the loop which can have resistive elements incorporated. When all sensors 630 are inactivated the resistance may be infinite and the current flow zero, or the circuit may be open. As sensors 630 fuse shut as a result of the heat from the thermal event, the current circulating to the transmitter will progressively increase. This is one example of how the current may be detected or the distance to each sensor determined. Other methods may be used.

[0079] FIG. 6B illustrates two sensors 630a and 630b of the system 600 of FIG. 6A. The sensors 630a, 630b may have one or more respective metal alloys 634a-d that are positioned to form an electrical connection between the circuit wires of system 600 when the metal alloy(s) 634a-d reach a temperature within or above their respective narrow temperature ranges. The electrical connection between the circuit wires may shorten the loop between the respective sensor (e.g., 630a, 630b, ...) and the transmitter such that one or more resistiveelements (e.g., 660a-b, ...) are bypassed. By bypassing one or more resistive elements (e.g., 660a-b, ...), the current of the circuit may increase, thus providing information about which sensor was activated, which may be further communicated via the transmitted signal.

[0080] The sensors 630a, 630b may have respective substrates 650a, 650b that are patterned with patterned elements 652a, 652b (e.g., by etching, deposition, or any other suitable microfabrication techniques) to facilitate the flow of the metal alloy(s) 634a-d between the circuit wires to form an electrical connection that shortens the circuit loop. The patterned element 652a, 652b may help maintain an electrical connection if the metal alloy(s) re-melt or reflow. In some embodiments, each sensor (630a, 630b, ...) may have more than one metal alloy to provide redundancy, as discussed elsewhere in the specification. The sensors (630a, 630b, ...) may have only one metal alloy to form the electrical connection between wires. In some embodiments, the circuit wires may be electrically coupled to electrical contacts to which the metal alloys (634a-d, ...) form an electrical connection to shorten the circuit loop. In some embodiments, the configuration illustrated in FIG 4 may also be employed to form a connection between the two parallel wires of 630a and 630b of FIG 6B.

[0081] FIG. 6C illustrates the two sensors 630a and 630b of FIG. 6B, in which the sensor 630a has reached a temperature within or above the narrow temperature range of one or more of the metal alloy(s) 634a, 634b, causing the metal alloy(s) 634a, 634b to melt and complete the circuit such that the transmitter 620 may receive power from the power source 640. When additional sensors are activated, the circuit may be shortened such that one or more resistive elements (e.g., 660a, 660b..) is bypassed. The melted one or more metal alloys 634a, 634b in this example may combine to form a metal alloy 634e that bridges the circuit wires or electrical contacts. In this example embodiment, the current of the circuit increases due to the reduced resistance and permits the transmitter to receive power from the power source to transmit a signal. The resistive elements (650a-c, ...) may be positioned on the substrate or physically elsewhere in the circuit. The resistance value of the resistive elements (660a-b, ...) may be selected such that when none of the sensors (630a, 630b, ...) are activated, the current is zero (or effectively zero), and when one or more of the sensors (630a, 630b, ...) is activated, the resistance is low enough such that power from the power source 640 is routed to the transmitter 620 to transmit a signal. In some embodiments, the series of sensors (630a, 630b, ...) may be electrically configured to increase or decrease the resistance (or other electrical parameter) of the circuit loop to effectuate a current change (or other relatedelectrical parameter) in the circuit as an indication that one or more sensors have been activated.

[0082] FIG. 7 illustrates a system 700 for temperature detection comprising a plurality of passive thermal sensors 730 spatially arranged in different orientations according to an embodiment of the present disclosure. The plurality of passive thermal sensors 730 may comprise a passive thermal sensor according to any of the embodiments described herein, such as those described in reference to FIGs 2A-4. In an embodiment, the plurality of passive thermal sensors are each the same, for example the same type of sensor and / or having the same melting point or temperature range. In another embodiment, one or more sensors of the plurality of passive thermal sensors 730 may be different from another sensor. For example, one or more sensors may have a different configuration according to the embodiments described herein and / or a different melting points or temperature range of the metal alloy(s). Each of the sensors in the plurality of passive thermal sensors 730 may have the same narrow temperature range, which may provide redundancy in the event one or more sensors fail. Each of the sensors in the plurality of passive sensors may have different narrow temperature ranges.

[0083] In the embodiments described above, the present disclosure provides systems and methods for detecting a thermal event. The system may comprise a passive thermal sensor configured to activate at a specific temperature or within a narrow temperature range corresponding to the melting point of the metal alloy(s) in the passive thermal sensor. When the metal alloy melts, the metal alloy bridges an electrical discontinuity between a power source and a transmitter such that a complete circuit is formed. The complete circuit allows the transmitter to receive power from the power source to transmit a signal indicating that the sensor has been activated, and the signal may include information about the sensor, such as its location.

[0084] Since the circuit is not complete until the sensor is activated when the metal alloy melts, the power source is not depleted while the systems comprising the sensor(s) are out in the field. Similarly, the power source may comprise thermoelectric properties that may further generate power. This allows the system to remain deployed in the field longer than previous systems since the power source, such as a battery, does not need to be replaced as often. Methods of protecting the system from environmental and / or passive degradation may be provided, which may further extend the lifetime of the system while deployed in the field.

[0085] The methods and systems described herein may allow the early detection, warning, and / or monitoring of a thermal event, such as a forest fire, and can further provide additional information about the thermal event, such as the maximum temperature reached based on which sensors are activated. Such information may further be used to infer the severity of a thermal event. In the context of a forest fire, systems comprising the passive thermal sensors may be distributed across a geographical region such that when a sensor is activated, the path and breadth of a forest fire may be monitored, which may facilitate safe management of the forest fire. Thus, the systems and methods according to the present disclosure may provide early warning of the start of flame and its general location relative to population centers, which may facilitate timely extinction or management of the fire and / or evacuation. Knowing the position and / or trajectory of the forest fire may facilitate the selection of safer evacuation routes and the approximate time to evacuate from an area based on the approximate rate of fire spread.

[0086] Multiple sensors with different respective melting points may also be positioned in a geographical region to provide information about the maximum temperature reached during a forest fire. Sensors that are not activated may indicate that a temperature was not reached, while sensors that have been activated may indicate that a temperature was reached and / or exceeded.

[0087] Since metal alloys may be engineered to have melting points at a specific temperature and / or within a narrow temperature range, the activation or lack of activation of a sensor may provide information about the temperatures of a thermal event and / or may be selected to align with or be close to temperatures of interest according to the context. For example, in the context of early detection and monitoring of a forest fire, the flash point of wood can be around 250 °C to 500 °C (or higher / lower, depending on the tree type or variety). Sensors corresponding to a temperature at or around the flash point of certain tree types may be selected for monitoring a forest fire in a specific geographical region to facilitate early warning and monitoring of forest fires in that region.

[0088] According to the embodiments described herein, the systems may be deployed by various methods, such as an airborne drop or by foot. The metal alloy may bridge the electrical discontinuity according to forces or structures other than gravity (such as interfacial forces, magnetic forces, and / or structures / patterning on the substrate of the passive thermal sensor), which may allow systems comprising the passive thermal sensor(s) to be deployed in any orientation without inhibiting the sensor from activating (e.g., if the sensor is “upsidedown”). This may reduce the effort, time, and / or training required to deploy the sensors since the sensors do not require specific positioning and / or calibration compared to other sensors.

[0089] While forest fires are used as an example thermal event in the preceding description, the systems and methods described herein may be used for the early warning detection, and / or monitoring of other thermal events, such as systems, products, and environments in which a prior thermal limit has been exceeded. In some embodiments, the thermal event may be a localized high temperature hazard condition susceptible to spontaneous combustion or catastrophic failure due to overheating resulting from an increase in temperature (e.g., in applications such as locomotive wheels, oil wells, coal mines, electrical system, critical equipment shut down, failure logging, etc.). In some embodiments, the systems and methods described herein may be used to detect fires in a residential context, for example on the surrounding property of a home or community in a rural area to detect a fire outside the home or building.

[0090] In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details are not required. In other instances, well-known electrical structures and circuits are shown in block diagram form in order not to obscure the understanding. For example, specific details are not provided as to whether the embodiments described herein are implemented as a software routine, hardware circuit, firmware, or a combination thereof.

[0091] Embodiments of the disclosure can be represented as a computer program product stored in a machine-readable medium (also referred to as a computer-readable medium, a processor-readable medium, or a computer usable medium having a computer-readable program code embodied therein). The machine-readable medium can be any suitable tangible, non-transitory medium, including magnetic, optical, or electrical storage medium including a diskette, compact disk read only memory (CD-ROM), memory device (volatile or non-volatile), or similar storage mechanism. The machine-readable medium can contain various sets of instructions, code sequences, configuration information, or other data, which, when executed, cause a processor to perform steps in a method according to an embodiment of the disclosure. Those of ordinary skill in the art will appreciate that other instructions and operations necessary to implement the described implementations can also be stored on the machine-readable medium. The instructions stored on the machine-readable medium can beexecuted by a processor or other suitable processing device, and can interface with circuitry to perform the described tasks.

[0092] The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A system for temperature detection, the system comprising:an antenna;a transmitter electrically coupled to the antenna;a passive thermal sensor electrically coupled to the transmitter; anda power source electrically coupled to the passive thermal sensor,the passive thermal sensor defining an electrical discontinuity establishing an incomplete circuit between the power source and the transmitter, the passive thermal sensor comprising a metal alloy provided in proximity to the electrical discontinuity, the metal alloy configured to change state from a solid state to a liquid state in a narrow temperature range such that the metal alloy in the liquid state bridges the electrical discontinuity to provide electrical connection between the power source and the transmitter to enable temperature detection.

2. The system of claim 1 , wherein the passive thermal sensor comprises first and second electrical contacts positioned on a substrate,the first electrical contact being spaced apart from the second electrical contact to define the electrical discontinuity.

3. The system of claim 2, wherein the metal alloy comprises a first portion and a second portion,the first portion being electrically decoupled from the first electrical contact, the second portion being either electrically coupled or decoupled from the second electrical contact when the metal alloy is in the solid state; andthe first portion being electrically coupled to the first electrical contact and the second portion being electrically coupled to the second electrical contact after the metal alloy changes from the solid state to liquid state, to provide electrical connection between the power source and the transmitter.

4. The system of claim 1 , wherein the metal alloy comprises a first portion composed of a first metal alloy and a second portion composed of a second metal alloy, and wherein the narrow temperature range comprises a first narrow temperature range and a second narrow temperature range,the first portion composed of the first metal alloy configured to change state from the solid to liquid state in the first narrow temperature range, andthe second portion composed of the second metal alloy configured to change state from the solid to liquid state in the second narrow temperature range, to provide electrical connection between the power source and the transmitter.

5. The system of claim 1 , wherein the passive thermal sensor comprises a first passive thermal sensor and a second passive thermal sensor,wherein the narrow temperature range comprises a first narrow temperature range and a second narrow temperature range,the first passive thermal sensor comprises a first metal alloy configured to change from solid to liquid state within the first narrow temperature range, andthe second passive thermal sensor comprises a second metal alloy configured to change from solid to liquid state within the second narrow temperature range.

6. The system of claim 5, wherein the first passive thermal sensor is electrically arranged in parallel with the second passive thermal sensor.

7. The system of claim 5, wherein the first passive thermal sensor is electrically arranged in series with the second passive thermal sensor.

8. The system of claim 5, wherein the transmitter comprises a first transmitter associated with the first passive sensor and a second transmitter associated with the second passive thermal sensor, wherein:changing from solid to liquid state within the first narrow temperature range provides the electrical connection between the power source and the first transmitter, and changing from solid to liquid state within the second narrow temperature range provides the electrical connection between the power source and the second transmitter.

9. The system of claim 1 , wherein the metal alloy comprises a solder preform.

10. The system of claim 1 , wherein the transmitter transmits a signal in response to the electrical connection between the power source and the transmitter.

11. The system of claim 10, wherein the transmitter is configured to transmit the signal to a cellular base transceiver station or a satellite communication system.

12. The system according to any one of claims 10 or 11, wherein the transmitter transmits the signal on a radio frequency.

13. The system of claim 12, wherein the radio frequency is distinct from a licensed Industrial, Scientific, and Medical (ISM) radio frequency band.

14. The system according to any one of claims 10 to 13, wherein the signal comprises a signal identifier based on a location code applied to the sensor.

15. The system according to any one of claims 4 to 14, wherein the first narrow temperature range does not overlap with the second temperature range.

16. The system according to any one of claims 2 to 15, wherein the passive thermal sensor further comprises a third electrical contact between the first electrical contact and the second electrical contact, the third electrical contact being approximately aligned with the metal alloy,wherein the third electrical contact is spaced apart from the first and second electrical contacts.

17. The system according to any one of claims 2 to 16, wherein the substrate comprises a pattern configured to receive the metal alloy in the liquid state.

18. The system according to any one of claims 2 to 17, wherein the substrate is thermally conductive.

19. The system of claim 18, wherein the substrate is composed of graphite, and at least one insulating layer electrically separates the first and second electrical contacts from the substrate.

20. The system according to any one of claims 1 to 19, wherein the substrate comprises a magnet and the metal alloy is ferromagnetic.

21. The system according to any one of claims 1 to 20, wherein the power source is a battery, a thermoelectric generator, a thermoelectric cooler, or a supercapacitor.

22. The system according to any one of claims 1 to 21, wherein the metal alloy is a shape memory alloy configured to revert to an original shape when the metal alloy is below the narrow temperature range.

Images