FIELD

The specification relates to a very small thermal imaging core and, in particular, to the design, test, and operational elements that enable the inclusion of thermal imaging into small devices such as smartphones, miniature drones, very small monitoring/security systems, and the like.

BACKGROUND

The increasing availability of high-performance, low-cost uncooled thermal imaging devices, such as those based on bolometer focal plane arrays (FPAs), is enabling the design and production of consumer-oriented thermal imaging cameras and sensors capable of quality thermal imaging. Such thermal imaging systems have long been expensive and difficult to produce, thus limiting the employment of high-performance, long-wave imaging to high-value instruments only available for aerospace, military, or large-scale commercial applications. Thermal imaging systems of a given design (produced in quantity) may have different design requirements than complex military or industrial systems. Providing thermal imagers for consumer applications with challenging cost and space requirements, such as thermal imagers for smartphones and other personal electronic devices (PED's), may benefit from new techniques spanning the design, manufacture, test, and operation of very small thermal imaging cores.

SUMMARY

Example embodiments described herein have innovative features, no single one of which is indispensable or solely responsible for their desirable attributes. Without limiting the scope of the claims, some of the advantageous features will now be summarized.

In some embodiments an ultra-small thermal imaging core, or micro-core, may be provided. The design of the micro-core may include substrates, for mounting optics and electronic connectors, that are thermally matched to the imaging Focal Plane Array (FPA). Tooling may be provided to position the optics to set the core focus, either by moving the lens and lens holder as one or by pushing and/or pulling the lens against a lens positioning element within the lens holder, while observing a scene. Test procedures that allow for full temperature calibration of each individual core, as well as providing data useful for uniformity correction during operation, may also be provided as part of the test and manufacture of the core.

In some embodiments, a thermal imaging micro-core comprises a thermal imaging Focal Plane Array, micro-fabricated at least in part of a first material; a substrate of a second material that has substantially the same thermal properties as the first material; at least one optical element; an optical housing; and a circuit element, wherein the FPA is bonded to the substrate, the optical element is attached to the housing, the housing is bonded to the substrate with the optical element disposed to expose the FPA to external scenes, and the circuit element is configured to provide connections between the FPA and a host system, and wherein the housing, substrate and FPA assembled together are less than 0.5″ in the longest dimension, and the micro-core with the circuit element assembled together are less than 1.5″ long and 0.5″ in all other dimensions.

In some embodiments, the first and second material are both silicon. In some embodiments, the substrate is a section diced from a silicon wafer of substantially the same thickness as a wafer the FPA is micro-fabricated from. In some embodiments, the circuit element comprises a flex circuit. In some embodiments, the flex circuit is bonded to the substrate. In some embodiments, flex circuit connections to the FPA are made by wire-bonding between contact pads on the flex circuit and contact pads on the FPA. In some embodiments, flex circuit connections to the FPA are made by connections fabricated into the substrate. In some embodiments, the flex circuit connections to the substrate are made by at least one of solder connections between contact pads on the flex circuit and contact pads on the substrate, or bump connections between contact pads on the flex circuit and contact pads on the substrate. In some embodiments, FPA connections to the substrate are made by at least one of solder connections between contact pads on the FPA and contact pads on the substrate, or bump connections between contact pads on the FPA and contact pads on the substrate. In some embodiments, the circuit element includes a connector configured to be compatible with internal host system connectors.

In another embodiment, a process for adjusting the focal distance of a lens for a thermal imager as recited in claim1comprises bonding the lens in the housing; placing the housing onto the substrate with the lens suitably positioned relative to the FPA; interfacing to the FPA all inputs and outputs required for operating and acquiring image data from the FPA; observing an imaged scene through the lens with the FPA to determine degree of focus; optimizing the observed image focus by changing the position of the housing relative to the substrate; and fixing the housing position relative to the substrate at the point of optimized focus.

In some embodiments, the fixing the housing position is done with a bonding element, the bonding element including at least one of glue, epoxy, solder, or fasteners. In some embodiments, the method further comprises applying the bonding element to the substrate and housing in an elastic state, finding the focus distance, and rendering the bonding element inelastic with the housing at the desired position. In some embodiments, the bonding agent is curable and the housing position is changed with the element in an uncured state and the element is cured in place at the desired position of the housing. In some embodiments, a change in position due to curing is factored into the positioning of the housing.

In another embodiment, a process for adjusting the focus of a lens for a thermal imager, wherein the thermal imager comprises a Focal Plane Array (FPA), a lens, and a lens housing which holds the lens in relation to the FPA, comprises placing the lens in the housing, wherein the housing is configured to allow positioning adjustment within the housing, and lens tooling is configured to pull and/or push the lens within the housing; inserting a position adjustment element in the housing between the lens and the FPA, wherein the position adjusting element is configured to allow at least a partial unobstructed view of the FPA through the lens; bringing the lens in contact with the positioning adjustment element using the lens tooling wherein the tooling push/pull pressure applied to the lens against the position element allows for temporarily stable positioning of the lens within the housing; observing an image scene through the lens with the FPA to determine degree of focus; optimizing the observed image focus by changing the position of the lens in the housing; fixing the lens position at the point of optimized focus; and removing the positioning element from the housing.

In some embodiments, the positioning element is a tapered shaft oriented substantially perpendicular to the lens focus axis and the lens tooling pushes the lens against the tapered shaft and the temporarily stable position is changed by the tapered shaft being drawn in and out of the housing. In some embodiments, the tapered shaft is at least one of a round tapered shaft or a wedge shaped tapered shaft. In some embodiments, the positioning element is a spring oriented substantially perpendicular to the lens focus axis and the lens tooling pushes the lens against the spring and the temporarily stable position is changed by the balancing of the lens tooling pushing action against the spring's reverse pressure. In some embodiments, the spring is a leaf spring. In some embodiments, the fixing the lens position comprises applying a bonding agent to at least one of the lens and a lens holder, thereby fixing the lens in place. In some embodiments, the housing and the lens are configured with a channel for the bonding agent to be applied that ensures mutual contact of the bonding agent with both lens and housing. In some embodiments, the bonding agent is at least one of glue, epoxy, a rubber sealant, or a spot weld. In some embodiments, the lens holder is at least one of fixed relative to the housing or attached to a fine focus element. In some embodiments, the lens positioning range achievable by the positioning element is greater than 10 microns and the positioning resolution is less than 1 micron. In some embodiments, the lens positioning range achievable by the positioning element is greater than 50 microns. In some embodiments, the micro-core is manufactured on a panel holding a plurality of micro-cores configured for assembly operations on multiple micro-cores. In some embodiments, the micro-core is tested on a panel holding a plurality of micro-cores configured for test operations on multiple micro-cores. In some embodiments, the micro-core's focus is set on a panel holding a plurality of micro-cores configured for focus operations on multiple micro-cores.

In another embodiment, a process for testing a thermal imaging micro-core as recited in claim1comprises: placing at least one micro-core in a test fixture; interfacing the micro-core to test electronics configured to operate and acquire image data from the micro-core; exposing the micro-core to a plurality of controlled ambient temperatures; recording the temperature sensor reading representative of each controlled ambient temperature; exposing the micro-core to a plurality of controlled temperature scenes at each controlled ambient temperature and recording the signal level for at least a portion of the pixels for the micro-core acquired image of the scenes; and creating at least one data set for each micro-core comprising of at least one of the signal representative of scene temperature vs. ambient temperature, or pixel-to-pixel variation vs. scene temperature vs. ambient temperature and wherein the tables are at least one of stored for use in each micro-core, or provided with the each micro-core for storage in a processor interfaced to the micro-core when the micro-core is in operation.

In some embodiments, the ambient temperature is controlled by mounting the micro-core to a heat sink whose temperature is controlled. In some embodiments, the heat sink temperature is controlled by at least one of a thermo-electric device or temperature controlled fluid flowed through channels in the heat sink. In some embodiments, the controlled temperature scenes are a plurality of individually temperature controlled black-bodies sequentially presented for viewing by the micro-core. In some embodiments, the black-body temperatures are measured by a pyrometer, and the pyrometer measured temperature is stored in the data set. In some embodiments, the controlled ambient FPA temperatures are varied at least one of continuously or semi-continuously and FPA temperature sensor readings taken during image acquisition are stored in the data set as the ambient temperature data.

In another embodiment, a process for operating a thermal imaging system containing a micro-core tested according to the present technology comprises: applying a Scene-Based Non-Uniformity Correction (SBNUC) comprising of generating a continuously updated Fixed-Pattern Noise (FPN) correction of pixel-by-pixel FPN correction terms, the process comprising reading the temperature sensor; interpolating data from a data set of pixel-to-pixel variations, the closest value to the data set corresponding to both the ambient and black-body temperature corresponding to the actual temperature sensor reading; and using the derived data set as at least one of the gain and offset correction of the image frame or the initial FPN correction term. In some embodiments, the process further comprises scaling and normalizing the data set.

In another embodiment, a thermal imaging system containing a micro-core tested according to the present technology is configured to: apply a Scene-Based Non-Uniformity Correction (SBNUC) comprised of generating a continuously updated Fixed-Pattern Noise (FPN) correction of pixel-by-pixel FPN correction term; read the temperature sensor; interpolate data from a data set of pixel-to-pixel variations, the closest value to the data set corresponding to both the ambient and black-body temperature corresponding to the actual temperature sensor reading; and use the derived data set as at least one of the gain and offset correction of the image frame or the initial FPN correction term. In some embodiments, the thermal imaging system is further configured to scale and normalize the data set.

In some embodiments, a micro-core further comprises an electromechanical actuator between the lens and the lens holder configured to impart motion to at least one of the lens or the micro-core to cause the FPN term to update if the thermal imaging system acquired images are not continuously subject to motion. In some embodiments, the imparted motion is used to develop sub-pixel resolution.

In another embodiment, a thermal imaging micro-core comprises a substrate; a thermal imaging Focal Plane Array (FPA) bonded to the substrate; at least one optical element; an optical housing coupled to the at least one optical element, the optical housing bonded to the substrate such that the at least one optical element is disposed to expose the FPA to external scenes; a circuit element coupled to the substrate and configured to provide one or more electrical connections between the FPA and a host system; and an oscillator circuit configured to set the frame rate of the FPA, the oscillator circuit mounted to the circuit element, wherein at least a portion of the oscillator is disposed between the circuit element and at least a portion of the housing such that the housing prevents removal of the oscillator circuit from the micro-core.

In another embodiment, a method of displaying fused data from a thermal imager and a visible imager imaging at least partially the same scene comprises: extracting edge information from the visible image; selecting a color table for display of the thermal image; and blending the visible edge data with thermal image data for corresponding scene pixels according to a blending coefficient, wherein the blending coefficient is automatically chosen based on the thermal color table selected.

In another embodiment, a method for correcting for offset drift in a thermal imager including a focal plane array (FPA) of photodetectors, including a FPA ambient temperature sensor configured to observe a thermal scene and convert the thermal scene information to a plurality of image frames whose pixels correspond to individual photodetectors in the array, comprises: providing a non-uniformity correction in the form of an offset value from a desired value for at least one pixel at a given FPA ambient temperature; updating the non-uniformity correction at at least one different FPA ambient temperature; developing a relationship between offset variation and temperature sensor reading; using the relationship to apply an offset correction derived from the temperature sensor reading to image data during imaging operation of the thermal imager.

In some embodiments, the non-uniformity correction is performed by a calibration operation that is part of the initial testing of the imager. In some embodiments, the offset correction is based on an offset collection operation performed at manufacturing testing, and wherein the relationship is stored for use during operation. In some embodiments, the offset correction is determined at a discrete number of temperature sensor readings and the relationship is a curve fit to the offset correction data points. In some embodiments, the offset correction is performed during actual use of the imager and is used to update or replace any preexisting offset drift correction data. In some embodiments, the offset correction is performed during operation of the imager by: observing a flat scene at a first temperature sensor value and determining a NUC offset data set; observing the flat scene at at least one different temperature sensor value and determining the difference in offset data set; developing the relationship from the operationally observed flat scenes at different FPA temperature and apply offsets derived from the relationship at other temp sensor readings. In some embodiments, the imager is directed at a flat scene by a user and the offset correction is initiated by an input from the user. In some embodiments, the imager detects a flat scene is being imaged and initiates the offset correction. In some embodiments, observing the flat scene at at least one different temperature sensor value comprises, responsive to an initiation of the offset correction and subsequent to observing the flat scene at the first temperature sensor value, initiating at least one of power saving or power using operations, wherein an increase or decrease in resistive heating associated with the power saving or power using operations at least partially causes a local ambient temperature change from a first temperature associated with the first temperature sensor value to a second temperature associated with the different temperature sensor.

