Device with dual power sources

A wearable device includes a sensor, auxiliary electronics, a primary power supply configured to harvest radio frequency (RF) radiation received from an external reader and use the harvested RF radiation to power the sensor, and an auxiliary power supply configured to harvest energy other than that received from the external reader and use the harvested energy to supply power to the sensor and/or the auxiliary electronics. The external reader may supply less power in response to operation of the auxiliary power supply. Additionally or alternatively, in response to a determination that the auxiliary power supply is unable to supply power, the wearable device may disable all auxiliary electronics but for the sensor. In response to a determination that the primary power supply is unable to supply power but the auxiliary power supply is able to supply power, the wearable device may retain operating parameters in the memory storage unit using the auxiliary power supply.

BACKGROUND

An electrochemical amperometric sensor measures a concentration of an analyte by measuring a current generated through electrochemical oxidation or reduction reactions of the analyte at a working electrode of the sensor. A reduction reaction occurs when electrons are transferred from the electrode to the analyte, whereas an oxidation reaction occurs when electrons are transferred from the analyte to the electrode. The direction of the electron transfer is dependent upon the electrical potentials applied to the working electrode. A counter electrode and/or reference electrode is used to complete a circuit with the working electrode and allow the generated current to flow. When the working electrode is appropriately biased, the output current can be proportional to the reaction rate, so as to provide a measure of the concentration of the analyte surrounding the working electrode.

In some examples, a reagent is localized proximate the working electrode to selectively react with a desired analyte. For example, glucose oxidase can be fixed near the working electrode to react with glucose and release hydrogen peroxide, which is then electrochemically detected by the working electrode to indicate the presence of glucose. Other enzymes and/or reagents can be used to detect other analytes.

SUMMARY

Some embodiments of the present disclosure provide a method that includes a wearable device receiving a signal indicative of an availability of an auxiliary power supply to provide power to the wearable device. The wearable device may include: at least one sensor, a primary power supply configured to harvest radio frequency (RF) radiation received from an external reader and use the harvested RF radiation to power the at least one sensor, and an auxiliary power supply configured to harvest energy other than that received from the external reader and use the harvested energy to supply power to the at least one sensor. The method may further include receiving a signal indicative of an availability of the auxiliary power supply to provide power to the wearable device, and responsive to receiving the signal, the wearable device enabling the auxiliary power supply. The method may further include the wearable device operating the auxiliary power supply to supply power to the at least one sensor.

Some embodiments of the present disclosure provide a wearable device that includes a sensor, an antenna, and auxiliary electronics, including a memory storage unit. The wearable device may further include a first power supply configured to harvest radio frequency (RF) radiation received at the antenna from an external reader and a second power supply configured to harvest energy other than that received from the external reader. Each power supply is configured to supply power to the sensor and the auxiliary electronics. The wearable device may further include a controller electrically connected to the first power supply and the second power supply. In some embodiments, the controller can be configured to: enable the second power supply in response to a determination that the second power supply is able to supply power, disable all auxiliary electronics but for the sensor in response to a determination that the second power supply is unable to supply power, and retain operating parameters in the memory storage unit using the second power supply in response to a determination that the first power supply is unable to supply power but the second power supply is able to supply power.

Some embodiments of the present disclosure provide a non-transitory computer readable medium (CRM) having instructions stored thereon that, when executed by one or more processors associated with a wearable device, cause the wearable device to perform operations. Such operations may include receiving a signal indicative of an availability of an auxiliary power supply to provide power to the wearable device. The wearable device may include at least one sensor, a primary power supply configured to harvest radio frequency (RF) radiation received from an external reader and use the harvested RF radiation to power at least one sensor, and an auxiliary power supply configured to harvest energy other than that received from the external reader and use the harvested energy to supply power to the at least one sensor. The operations may further include responsive to receiving the signal, enabling the auxiliary power supply, and operating the auxiliary power supply to supply power to the at least one sensor.

DETAILED DESCRIPTION

An ophthalmic sensing platform or implantable sensing platform can include a sensor, control electronics and an antenna all situated on a substrate embedded in a polymeric material. The polymeric material can be incorporated in an ophthalmic device, such as an eye-mountable device or an implantable medical device. The control electronics can operate the sensor to perform readings and can operate the antenna to wirelessly communicate the readings from the sensor to an external reader via the antenna.

In some examples, the polymeric material can be in the form of a round lens with a concave curvature configured to mount to a corneal surface of an eye. The substrate can be embedded near the periphery of the polymeric material to avoid interference with incident light received closer to the central region of the cornea. The sensor can be arranged on the substrate to face inward, toward the corneal surface, so as to generate clinically relevant readings from near the surface of the cornea and/or from tear fluid interposed between the polymeric material and the corneal surface. Additionally or alternatively, the sensor can be arranged on the substrate to face outward, away from the corneal surface and toward the layer of tear fluid coating the surface of the polymeric material exposed to the atmosphere. In some examples, the sensor is entirely embedded within the polymeric material. For example, an electrochemical sensor that includes a working electrode and a reference electrode can be embedded in the polymeric material and situated such that the sensor electrodes are less than 10 micrometers from the polymeric surface configured to mount to the cornea. The sensor can generate an output signal indicative of a concentration of an analyte that diffuses through the lens material to the sensor electrodes.

The ophthalmic sensing platform can be powered via radiated energy harvested at the sensing platform. Power can be provided by light energizing photovoltaic cells included on the sensing platform. Additionally or alternatively, power can be provided by radio frequency energy harvested from the antenna. A rectifier and/or regulator can be incorporated with the control electronics to generate a stable DC voltage to power the sensing platform from the harvested energy. The antenna can be arranged as a loop of conductive material with leads connected to the control electronics. In some embodiments, such a loop antenna can also wirelessly communicate the sensor readings to an external reader by modifying the impedance of the loop antenna so as to modify backscatter radiation from the antenna.

Tear fluid contains a variety of inorganic electrolytes (e.g., Ca2+, Mg2+, Cl−, organic components (e.g., glucose, lactate, proteins, lipids, etc.), and so on that can be used to diagnose health states. An ophthalmic sensing platform configured to measure one or more of these analytes can thus provide a convenient non-invasive platform useful in diagnosing and/or monitoring health states. For example, an ophthalmic sensing platform can be configured to sense glucose and can be used by diabetic individuals to measure/monitor their glucose levels.

The sensing platform can be powered by an energy harvesting system to capture energy from incident radiation, rather than by internal energy storage devices requiring more space. For example, power can be provided by light energizing photovoltaic cells included on the sensing platform. Power may also be provided by radio frequency (RF) energy harvested via a loop antenna. A rectifier and/or regulator can be incorporated with the control electronics to generate a stable DC voltage to power the sensing platform from the harvested RF energy. Furthermore, the control electronics can wirelessly communicate the sensor readings to an external reader by modifying the impedance of the loop antenna so as to characteristically modify the backscatter from the antenna.

II. Example Ophthalmic Electronics Platform

FIG. 1is a block diagram of a system100that includes an eye-mountable device110in wireless communication with an external reader180. The exposed regions of the eye-mountable device110are made of a polymeric material120formed to be contact-mounted to a corneal surface of an eye. A substrate130is embedded in the polymeric material120to provide a mounting surface for a power supplies140aand14b, a controller150, bio-interactive electronics160, and a communication antenna170. The bio-interactive electronics160are operated by the controller150. Power supplies140aand140bsupply operating voltages to the controller150and/or the bio-interactive electronics160. The antenna170is operated by the controller150to communicate information to and/or from the eye-mountable device110. The antenna170, the controller150, power supply140a, power supply140b, and the bio-interactive electronics160can all be situated on the embedded substrate130. Because the eye-mountable device110includes electronics and is configured to be contact-mounted to an eye, it is also referred to herein as an ophthalmic electronics platform.

To facilitate contact-mounting, the polymeric material120can have a concave surface configured to adhere (“mount”) to a moistened corneal surface (e.g., by capillary forces with a tear film coating the corneal surface). Additionally or alternatively, the eye-mountable device110can be adhered by a vacuum force between the corneal surface and the polymeric material due to the concave curvature. While mounted with the concave surface against the eye, the outward-facing surface of the polymeric material120can have a convex curvature that is formed to not interfere with eye-lid motion while the eye-mountable device110is mounted to the eye. For example, the polymeric material120can be a substantially transparent curved polymeric disk shaped similarly to a contact lens.

The polymeric material120can include one or more biocompatible materials, such as those employed for use in contact lenses or other ophthalmic applications involving direct contact with the corneal surface. The polymeric material120can optionally be formed in part from such biocompatible materials or can include an outer coating with such biocompatible materials. The polymeric material120can include materials configured to moisturize the corneal surface, such as hydrogels and the like. In some embodiments, the polymeric material120can be a deformable (“non-rigid”) material to enhance wearer comfort. In some embodiments, the polymeric material120can be shaped to provide a predetermined, vision-correcting optical power, such as can be provided by a contact lens.

The substrate130includes one or more surfaces suitable for mounting the bio-interactive electronics160, the controller150, the power supplies140aand140b, and the antenna170. The substrate130can be employed both as a mounting platform for chip-based circuitry (e.g., by flip-chip mounting to connection pads) and/or as a platform for patterning conductive materials (e.g., gold, platinum, palladium, titanium, copper, aluminum, silver, metals, other conductive materials, combinations of these, etc.) to create electrodes, interconnects, connection pads, antennae, etc. In some embodiments, substantially transparent conductive materials (e.g., indium tin oxide) can be patterned on the substrate130to form circuitry, electrodes, etc. For example, the antenna170can be formed by forming a pattern of gold or another conductive material on the substrate130by deposition, photolithography, electroplating, etc. Similarly, interconnects151,157between the controller150and the bio-interactive electronics160, and between the controller150and the antenna170, respectively, can be formed by depositing suitable patterns of conductive materials on the substrate130. A combination of microfabrication techniques including, without limitation, the use of photoresists, masks, deposition techniques, and/or plating techniques can be employed to pattern materials on the substrate130. The substrate130can be a relatively rigid material, such as polyethylene terephthalate (“PET”) or another material configured to structurally support the circuitry and/or chip-based electronics within the polymeric material120. The eye-mountable device110can alternatively be arranged with a group of unconnected substrates rather than a single substrate. For example, the controller150and a bio-sensor or other bio-interactive electronic component can be mounted to one substrate, while the antenna170is mounted to another substrate and the two can be electrically connected via the interconnects157.

In some embodiments, the bio-interactive electronics160(and the substrate130) can be positioned away from the center of the eye-mountable device110and thereby avoid interference with light transmission to the central, light-sensitive region of the eye. For example, where the eye-mountable device110is shaped as a concave-curved disk, the substrate130can be embedded around the periphery (e.g., near the outer circumference) of the disk. In some embodiments, however, the bio-interactive electronics160(and the substrate130) can be positioned in or near the central region of the eye-mountable device110. Additionally or alternatively, the bio-interactive electronics160and/or substrate130can be substantially transparent to incoming visible light to mitigate interference with light transmission to the eye. Moreover, in some embodiments, the bio-interactive electronics160can include a pixel array164that emits and/or transmits light to be received by the eye according to display instructions. Thus, the bio-interactive electronics160can optionally be positioned in the center of the eye-mountable device so as to generate perceivable visual cues to a wearer of the eye-mountable device110, such as by displaying information (e.g., characters, symbols, flashing patterns, etc.) on the pixel array164.

The substrate130can be shaped as a flattened ring with a radial width dimension sufficient to provide a mounting platform for the embedded electronics components. The substrate130can have a thickness sufficiently small to allow the substrate130to be embedded in the polymeric material120without influencing the profile of the eye-mountable device110. The substrate130can have a thickness sufficiently large to provide structural stability suitable for supporting the electronics mounted thereon. For example, the substrate130can be shaped as a ring with a diameter of about 10 millimeters, a radial width of about 1 millimeter (e.g., an outer radius 1 millimeter larger than an inner radius), and a thickness of about 50 micrometers. The substrate130can optionally be aligned with the curvature of the eye-mounting surface of the eye-mountable device110(e.g., convex surface). For example, the substrate130can be shaped along the surface of an imaginary cone between two circular segments that define an inner radius and an outer radius. In such an example, the surface of the substrate130along the surface of the imaginary cone defines an inclined surface that is approximately aligned with the curvature of the eye mounting surface at that radius.

Power supply140ais configured to harvest energy to power the controller150and bio-interactive electronics160. For example, a radio-frequency energy-harvesting antenna142can capture energy from incident radio radiation. The energy harvesting antenna142can optionally be a dual-purpose antenna that is also used to communicate information to the external reader180. That is, the functions of the communication antenna170and the energy harvesting antenna142can be accomplished with the same physical antenna.

Power supply140bis also configured to harvest energy to power the controller150and bio-interactive electronics160; however, power supply140bis configured to harvest ambient energy other than incident radio radiation. For example, in the embodiment depicted inFIG. 1, power supply140bmay include solar cell(s)144(“photovoltaic cells”) that can capture energy from incoming ultraviolet, visible, and/or infrared radiation. However, in other embodiments, other types of power sources can be used. For instance, in one example embodiment, power supply140bmay include an inertial power scavenging system that captures energy from ambient vibrations. In another example embodiment, power supply140bmay include a biofuel cell that generates electrical energy in response to chemical reactions occurring at the bio fuel cell. Tear fluid may be used as the fuel for such chemical reactions, although other fuels are possible as well. Alternatively or additionally, power supply140bmay include one or more charge storage devices, such as rechargeable batteries or capacitor arrangements. Other types of power supplies are possible as well.

Rectifier/regulators146aand146bcan be used to condition the captured energy to stable DC supply voltages141aand141bthat are supplied to the controller150. For example, the energy harvesting antenna142can receive incident radio frequency radiation. Varying electrical signals on the leads of the antenna142are output to the rectifier/regulator146a. The rectifier/regulator146arectifies the varying electrical signals to a DC voltage and regulates the rectified DC voltage to a level suitable for operating the controller150. Additionally, output voltage from the solar cell(s)144or other types of energy capture/storage devices can be regulated to a level suitable for operating the controller150. The rectifier/regulator146aand146bcan itself include one or more energy storage devices to mitigate high frequency variations in the ambient energy gathering antenna142and/or solar cell(s)144. For example, one or more energy storage devices (e.g., a capacitor, an inductor, etc.) can be connected in parallel across the outputs of the rectifier146aand/or146bto regulate the DC supply voltages141aand141band configured to function as a low-pass filter.

Additionally or alternatively, power supply140bmay include a DC-DC converter that may convert a larger (or smaller) voltage supplied from photovoltaic cells144, an inertial power scavenging system, a bio fuel cell, and/or a charge storage device, as the case may be, to a more suitable unregulated voltage. In one example, the DC-DC converter may convert a 5V DC supply to 1.2V DC, thereby yielding additional power savings before it is regulated. Other examples of voltage conversion are possible as well.

The controller150is turned on when the DC supply voltage141aor141bis provided to the controller150, and the logic in the controller150operates the bio-interactive electronics160and the antenna170. The controller150can include logic circuitry configured to operate the bio-interactive electronics160so as to interact with a biological environment of the eye-mountable device110. The interaction could involve the use of one or more components, such an analyte bio-sensor162, in bio-interactive electronics160to obtain input from the biological environment. Additionally or alternatively, the interaction could involve the use of one or more components, such as pixel array164, to provide an output to the biological environment.

In one example, the controller150includes a sensor interface module152that is configured to operate analyte bio-sensor162. The analyte bio-sensor162can be, for example, an amperometric electrochemical sensor that includes a working electrode and a reference electrode. A voltage can be applied between the working and reference electrodes to cause an analyte to undergo an electrochemical reaction (e.g., a reduction and/or oxidation reaction) at the working electrode. The electrochemical reaction can generate an amperometric current that can be measured through the working electrode. The amperometric current can be dependent on the analyte concentration. Thus, the amount of the amperometric current that is measured through the working electrode can provide an indication of analyte concentration. In some embodiments, the sensor interface module152can be a potentiostat configured to apply a voltage difference between working and reference electrodes while measuring a current through the working electrode.

The controller150can optionally include a display driver module154for operating a pixel array164. The pixel array164can be an array of separately programmable light transmitting, light reflecting, and/or light emitting pixels arranged in rows and columns. The individual pixel circuits can optionally include liquid crystal technologies, microelectromechanical technologies, emissive diode technologies, etc. to selectively transmit, reflect, and/or emit light according to information from the display driver module154. Such a pixel array164can also optionally include more than one color of pixels (e.g., red, green, and blue pixels) to render visual content in color. The display driver module154can include, for example, one or more data lines providing programming information to the separately programmed pixels in the pixel array164and one or more addressing lines for setting groups of pixels to receive such programming information. Such a pixel array164situated on the eye can also include one or more lenses to direct light from the pixel array to a focal plane perceivable by the eye.

The controller150can also include a communication circuit156for sending and/or receiving information via the antenna170. The communication circuit156can optionally include one or more oscillators, mixers, frequency injectors, etc. to modulate and/or demodulate information on a carrier frequency to be transmitted and/or received by the antenna170. In some examples, the eye-mountable device110is configured to indicate an output from a bio-sensor by modulating an impedance of the antenna170in a manner that is perceivable by the external reader180. For example, the communication circuit156can cause variations in the amplitude, phase, and/or frequency of backscatter radiation from the antenna170, and such variations can be detected by the reader180.

The controller150is connected to the bio-interactive electronics160via interconnects151. For example, where the controller150includes logic elements implemented in an integrated circuit to form the sensor interface module152and/or display driver module154, a patterned conductive material (e.g., gold, platinum, palladium, titanium, copper, aluminum, silver, metals, combinations of these, etc.) can connect a terminal on the chip to the bio-interactive electronics160. Similarly, the controller150is connected to the antenna170via interconnects157.

The controller150can also include logic configured to couple to and operate other auxiliary electronics166that may be mounted on substrate130. For instance, auxiliary electronics166can include a radio transceiver, configured to communicate via Bluetooth, WiFi, cellular, or another type of communications protocol. Additionally or alternatively, auxiliary electronics166can include a type of memory storage, such a volatile or non-volatile memory. Other types of auxiliary electronics are possible as well. Controller150is connected to the auxiliary electronics via interconnects153.

It is noted that the block diagram shown inFIG. 1is described in connection with functional modules for convenience in description. However, embodiments of the eye-mountable device110can be arranged with one or more of the functional modules (“sub-systems”) implemented in a single chip, integrated circuit, and/or physical component. For example, while rectifier/regulators146aand146bare illustrated in power supply blocks140aand14b, respectively, the rectifier/regulators146aand146bcan be implemented in a chip that also includes the logic elements of the controller150and/or other features of the embedded electronics in the eye-mountable device110. Thus, the DC supply voltage141aor141bthat is provided to the controller150from power supplies140aor140bcan be a supply voltage that is provided to components on a chip by rectifier and/or regulator components located on the same chip. That is, the functional blocks inFIG. 1shown as the power supply blocks140aand140band controller block150need not be implemented as physically separated modules. Moreover, one or more of the functional modules described inFIG. 1can be implemented by separately packaged chips electrically connected to one another.

Additionally or alternatively, the energy harvesting antenna142and the communication antenna170can be implemented with the same physical antenna. For example, a loop antenna can both harvest incident radiation for power generation and communicate information via backscatter radiation.

The external reader180includes an antenna188(or a group of more than one antennae) to send and receive wireless signals171to and from the eye-mountable device110. The external reader180also includes a computing system with a processor186in communication with a memory182. The memory182is a non-transitory computer-readable medium that can include, without limitation, magnetic disks, optical disks, organic memory, and/or any other volatile (e.g. RAM) or non-volatile (e.g. ROM) storage system readable by the processor186. The memory182can include a data storage183to store indications of data, such as sensor readings (e.g., from the analyte bio-sensor162), program settings (e.g., to adjust behavior of the eye-mountable device110and/or external reader180), etc. The memory182can also include program instructions184for execution by the processor186to cause the external reader180to perform processes specified by the instructions184. For example, the program instructions184can cause external reader180to provide a user interface that allows for retrieving information communicated from the eye-mountable device110(e.g., sensor outputs from the analyte bio-sensor162). The external reader180can also include one or more hardware components for operating the antenna188to send and receive the wireless signals171to and from the eye-mountable device110. For example, oscillators, frequency injectors, encoders, decoders, amplifiers, filters, etc. can drive the antenna188according to instructions from the processor186.

The external reader180can be a smart phone, digital assistant, or other portable computing device with wireless connectivity sufficient to provide the wireless communication link171. The external reader180can also be implemented as an antenna module that can be plugged in to a portable computing device, such as in an example where the communication link171operates at carrier frequencies not commonly employed in portable computing devices. In some instances, the external reader180is a special-purpose device configured to be worn relatively near a wearer's eye to allow the wireless communication link171to operate with a low power budget. For example, the external reader180can be integrated in a piece of jewelry such as a necklace, earing, etc. or integrated in an article of clothing worn near the head, such as a hat, headband, etc.

In some embodiments, the system100can operate to non-continuously (“intermittently”) supply energy to the eye-mountable device110to power the controller150and electronics160. For example, radio frequency radiation171can be supplied to power the eye-mountable device110long enough to carry out a tear film analyte concentration measurement and communicate the results. For example, the supplied radio frequency radiation can provide sufficient power to apply a potential between a working electrode and a reference electrode sufficient to induce electrochemical reactions at the working electrode, measure the resulting amperometric current, and modulate the antenna impedance to adjust the backscatter radiation in a manner indicative of the measured amperometric current. In such an example, the supplied radio frequency radiation171can be considered an interrogation signal from the external reader180to the eye-mountable device110to request a measurement. By periodically interrogating the eye-mountable device110(e.g., by supplying radio frequency radiation171to temporarily turn the device on) and storing the sensor results (e.g., via the data storage183), the external reader180can accumulate a set of analyte concentration measurements over time without continuously powering the eye-mountable device110.

Further, some embodiments of the system may include privacy controls which may be automatically implemented or controlled by the wearer of the device. For example, in embodiments in which a wearer's collected physiological parameter data and health state data are uploaded to a cloud computing network for trend analysis by a clinician, the data may be treated in one or more ways before it is stored or used, so that personally identifiable information is removed. For example, a wearer's identity may be treated so that no personally identifiable information can be determined for the wearer, or a wearer's geographic location may be generalized where location information is obtained (such as to a city, ZIP code, or state level), so that a particular location of a user cannot be determined.

Additionally or alternatively, wearers of a device may be provided with an opportunity to control whether or how the device collects information about the wearer (e.g., information about a user's medical history, social actions or activities, profession, a wearer's preferences, or a wearer's current location), or to control how such information may be used. Thus, the wearer may have control over how information is collected about him or her and used by a clinician or physician or other user of the data. For example, a wearer may elect that data, such as health state and physiological parameters, collected from his or her device may only be used for generating an individual baseline and recommendations in response to collection and comparison of his or her own data and may not be used in generating a population baseline or for use in population correlation studies.

FIG. 2Ais a bottom view of an example eye-mountable electronic device210(or ophthalmic electronics platform).FIG. 2Bis an aspect view of the example eye-mountable electronic device shown inFIG. 2A. It is noted that relative dimensions inFIGS. 2A and 2Bare not necessarily to scale, but have been rendered for purposes of explanation only in describing the arrangement of the example eye-mountable electronic device210. The eye-mountable device210is formed of a polymeric material220shaped as a curved disk. The polymeric material220can be a substantially transparent material to allow incident light to be transmitted to the eye while the eye-mountable device210is mounted to the eye. The polymeric material220can be a biocompatible material similar to those employed to form vision correction and/or cosmetic contact lenses in optometry, such as polyethylene terephthalate (“PET”), polymethyl methacrylate (“PMMA”), polyhydroxyethylmethacrylate (“polyHEMA”), silicone hydrogels, combinations of these, etc. The polymeric material220can be formed with one side having a concave surface226suitable to fit over a corneal surface of an eye. The opposite side of the disk can have a convex surface224that does not interfere with eyelid motion while the eye-mountable device210is mounted to the eye. A circular outer side edge228connects the concave surface224and convex surface226.

The eye-mountable device210can have dimensions similar to a vision correction and/or cosmetic contact lenses, such as a diameter of approximately 1 centimeter, and a thickness of about 0.1 to about 0.5 millimeters. However, the diameter and thickness values are provided for explanatory purposes only. In some embodiments, the dimensions of the eye-mountable device210can be selected according to the size and/or shape of the corneal surface of the wearer's eye.

The polymeric material220can be formed with a curved shape in a variety of ways. For example, techniques similar to those employed to form vision-correction contact lenses, such as heat molding, injection molding, spin casting, etc. can be employed to form the polymeric material220. While the eye-mountable device210is mounted in an eye, the convex surface224faces outward to the ambient environment while the concave surface226faces inward, toward the corneal surface. The convex surface224can therefore be considered an outer, top surface of the eye-mountable device210whereas the concave surface226can be considered an inner, bottom surface. The “bottom” view shown inFIG. 2Ais facing the concave surface226. From the bottom view shown inFIG. 2A, the outer periphery222, near the outer circumference of the curved disk is curved to extend out of the page, whereas the central region221, near the center of the disk is curved to extend into the page.

A substrate230is embedded in the polymeric material220. The substrate230can be embedded to be situated along the outer periphery222of the polymeric material220, away from the central region221. The substrate230does not interfere with vision because it is too close to the eye to be in focus and is positioned away from the central region221where incident light is transmitted to the eye-sensing portions of the eye. Moreover, the substrate230can be formed of a transparent material to further mitigate effects on visual perception.

The substrate230can be shaped as a flat, circular ring (e.g., a disk with a centered hole). The flat surface of the substrate230(e.g., along the radial width) is a platform for mounting electronics such as chips (e.g., via flip-chip mounting) and for patterning conductive materials (e.g., via microfabrication techniques such as photolithography, deposition, plating, etc.) to form electrodes, antenna(e), and/or interconnections. The substrate230and the polymeric material220can be approximately cylindrically symmetric about a common central axis. The substrate230can have, for example, a diameter of about 10 millimeters, a radial width of about 1 millimeter (e.g., an outer radius 1 millimeter greater than an inner radius), and a thickness of about 50 micrometers. However, these dimensions are provided for example purposes only, and in no way limit the present disclosure. The substrate230can be implemented in a variety of different form factors, similar to the discussion of the substrate130in connection withFIG. 1above.

A loop antenna270, controller250, and bio-interactive electronics260are disposed on the embedded substrate230. The controller250can be a chip including logic elements configured to operate the bio-interactive electronics260and the loop antenna270. The controller250is electrically connected to the loop antenna270by interconnects257also situated on the substrate230. Similarly, the controller250is electrically connected to the bio-interactive electronics260by an interconnect251. The interconnects251,257, the loop antenna270, and any conductive electrodes (e.g., for an electrochemical analyte bio-sensor, etc.) can be formed from conductive materials patterned on the substrate230by a process for precisely patterning such materials, such as deposition, photolithography, etc. The conductive materials patterned on the substrate230can be, for example, gold, platinum, palladium, titanium, carbon, aluminum, copper, silver, silver-chloride, conductors formed from noble materials, metals, combinations of these, etc.

As shown inFIG. 2A, which is a view facing the concave surface226of the eye-mountable device210, the bio-interactive electronics module260is mounted to a side of the substrate230facing the concave surface226. Where the bio-interactive electronics module260includes an analyte bio-sensor, for example, mounting such a bio-sensor on the substrate230to be close to the concave surface226allows the bio-sensor to sense analyte concentrations in tear film near the surface of the eye. However, the electronics, electrodes, etc. situated on the substrate230can be mounted to either the “inward” facing side (e.g., situated closest to the concave surface226) or the “outward” facing side (e.g., situated closest to the convex surface224). Moreover, in some embodiments, some electronic components can be mounted on one side of the substrate230, while other electronic components are mounted to the opposing side, and connections between the two can be made through conductive materials passing through the substrate230.

The loop antenna270is a layer of conductive material patterned along the flat surface of the substrate to form a flat conductive ring. In some instances, the loop antenna270can be formed without making a complete loop. For instances, the antenna270can have a cutout to allow room for the controller250and bio-interactive electronics260, as illustrated inFIG. 2A. However, the loop antenna270can also be arranged as a continuous strip of conductive material that wraps entirely around the flat surface of the substrate230one or more times. For example, a strip of conductive material with multiple windings can be patterned on the side of the substrate230opposite the controller250and bio-interactive electronics260. Interconnects between the ends of such a wound antenna (e.g., the antenna leads) can then be passed through the substrate230to the controller250.

FIG. 2Cis a side cross-section view of the example eye-mountable electronic device210while mounted to a corneal surface22of an eye10.FIG. 2Dis a close-in side cross-section view enhanced to show the tear film layers40,42surrounding the exposed surfaces224,226of the example eye-mountable device210. It is noted that relative dimensions inFIGS. 2C and 2Dare not necessarily to scale, but have been rendered for purposes of explanation only in describing the arrangement of the example eye-mountable electronic device210. For example, the total thickness of the eye-mountable device can be about 200 micrometers, while the thickness of the tear film layers40,42can each be about 10 micrometers, although this ratio may not be reflected in the figures. Some aspects are exaggerated to allow for illustration and facilitate explanation.

The eye10includes a cornea20that is covered by bringing the upper eyelid30and lower eyelid32together over the top of the eye10. Incident light is received by the eye10through the cornea20, where light is optically directed to light sensing elements of the eye10(e.g., rods and cones, etc.) to stimulate visual perception. The motion of the eyelids30,32distributes a tear film across the exposed corneal surface22of the eye10. The tear film is an aqueous solution secreted by the lacrimal gland to protect and lubricate the eye10. When the eye-mountable device210is mounted in the eye10, the tear film coats both the concave and convex surfaces224,226with an inner layer40(along the concave surface226) and an outer layer42(along the convex layer224). The tear film layers40,42can be about 10 micrometers in thickness and together account for about 10 microliters.

The tear film layers40,42are distributed across the corneal surface22and/or the convex surface224by motion of the eyelids30,32. For example, the eyelids30,32raise and lower, respectively, to spread a small volume of tear film across the corneal surface22and/or the convex surface224of the eye-mountable device210. The tear film layer40on the corneal surface22also facilitates mounting the eye-mountable device210by capillary forces between the concave surface226and the corneal surface22. In some embodiments, the eye-mountable device210can also be held over the eye in part by vacuum forces against corneal surface22due to the concave curvature of the eye-facing concave surface226.

As shown in the cross-sectional views inFIGS. 2C and 2D, the substrate230can be inclined such that the flat mounting surfaces of the substrate230are approximately parallel to the adjacent portion of the concave surface226. As described above, the substrate230is a flattened ring with an inward-facing surface232(closer to the concave surface226of the polymeric material220) and an outward-facing surface234(closer to the convex surface224). The substrate230can have electronic components and/or patterned conductive materials mounted to either or both mounting surfaces232,234. As shown inFIG. 2D, the bio-interactive electronics260, controller250, and conductive interconnect251are mounted on the inward-facing surface232such that the bio-interactive electronics260are relatively closer in proximity to the corneal surface22than if they were mounted on the outward-facing surface234.

III. Example Ophthalmic Electrochemical Analyte Sensor

FIG. 3is a functional block diagram of a system300for electrochemically measuring a tear film analyte concentration. As a general matter, the tear film is an aqueous layer secreted from the lacrimal gland to coat the eye. The tear film is in contact with the blood supply through capillaries in the structure of the eye and includes many biomarkers found in blood that are analyzed to characterize a person's health condition(s). For example, the tear film includes glucose, calcium, sodium, cholesterol, potassium, other biomarkers, etc. The biomarker concentrations in the tear film can be systematically different than the corresponding concentrations of the biomarkers in the blood, but a relationship between the two concentration levels can be established to map tear film biomarker concentration values to blood concentration levels. For example, the tear film concentration of glucose can be established (e.g., empirically determined) to be approximately one tenth the corresponding blood glucose concentration. Although another ratio relationship and/or a non-ratio relationship may be used. Thus, measuring tear film analyte concentration levels provides a non-invasive technique for monitoring biomarker levels in comparison to blood sampling techniques performed by lancing a volume of blood to be analyzed outside a person's body. Moreover, the ophthalmic analyte bio-sensor platform disclosed here can be operated substantially continuously to enable real time monitoring of analyte concentrations.

The system300depicts a select set of components in order to illustrate certain functionality. It should be understood that system300can include other components not depicted here. As depicted, system300includes an eye-mountable device310with embedded electronic components powered by an external reader340. The eye-mountable device310includes an antenna312for capturing radio frequency radiation341from the external reader340. The eye-mountable device310includes a rectifier314, an energy storage316, and regulator318for generating power supply voltages330,332to operate the embedded electronics. The eye-mountable device310includes an electrochemical sensor320with a working electrode322and a reference electrode323driven by a sensor interface321. The eye-mountable device310includes hardware logic324for communicating results from the sensor320to the external reader340by modulating the impedance of the antenna312. An impedance modulator325(shown symbolically as a switch inFIG. 3) can be used to modulate the antenna impedance according to instructions from the hardware logic324. Similar to the eye-mountable devices110,210discussed above in connection withFIGS. 1 and 2, the eye-mountable device310can include a mounting substrate embedded within a polymeric material configured to be mounted to an eye.

The electrochemical sensor320can be situated on a mounting surface of such a substrate proximate the surface of the eye (e.g., corresponding to the bio-interactive electronics260on the inward-facing side232of the substrate230) to measure analyte concentration in a tear film layer interposed between the eye-mountable device310and the eye (e.g., the inner tear film layer40between the eye-mountable device210and the corneal surface22). In some embodiments, however, an electrochemical sensor can be situated on a mounting surface of such a substrate distal the surface of the eye (e.g., corresponding to the outward-facing side234of the substrate230) to measure analyte concentration in a tear film layer coating the exposed surface of the eye-mountable device310(e.g., the outer tear film layer42interposed between the convex surface224of the polymeric material210and the atmosphere and/or closed eyelids).

With reference toFIG. 3, the electrochemical sensor320measures analyte concentration by applying a voltage between the electrodes322,323that is sufficient to cause products of the analyte catalyzed by the reagent to electrochemically react (e.g., a reduction and/or oxidization reaction) at the working electrode322. The electrochemical reactions at the working electrode322generate an amperometric current that can be measured at the working electrode322. The sensor interface321can, for example, apply a reduction voltage between the working electrode322and the reference electrode323to reduce products from the reagent-catalyzed analyte at the working electrode322. Additionally or alternatively, the sensor interface321can apply an oxidization voltage between the working electrode322and the reference electrode323to oxidize the products from the reagent-catalyzed analyte at the working electrode322. The sensor interface321measures the amperometric current and provides an output to the hardware logic324. The sensor interface321can include, for example, a potentiostat connected to both electrodes322,323to simultaneously apply a voltage between the working electrode322and the reference electrode323and measure the resulting amperometric current through the working electrode322.

The rectifier314, energy storage316, and voltage regulator318operate to harvest energy from received radio frequency radiation341. The radio frequency radiation341causes radio frequency electrical signals on leads of the antenna312. The rectifier314is connected to the antenna leads and converts the radio frequency electrical signals to a DC voltage. The energy storage316(e.g., capacitor) is connected across the output of the rectifier314to filter out high frequency components of the DC voltage. The regulator318receives the filtered DC voltage and outputs both a digital supply voltage330to operate the hardware logic324and an analog supply voltage332to operate the electrochemical sensor320. For example, the analog supply voltage can be a voltage used by the sensor interface321to apply a voltage between the sensor electrodes322,323to generate an amperometric current. The digital supply voltage330can be a voltage suitable for driving digital logic circuitry, such as approximately 1.2 volts, approximately 3 volts, etc. Reception of the radio frequency radiation341from the external reader340(or another source, such as ambient radiation, etc.) causes the supply voltages330,332to be supplied to the sensor320and hardware logic324. While powered, the sensor320and hardware logic324are configured to generate and measure an amperometric current and communicate the results.

The sensor results can be communicated back to the external reader340via backscatter radiation343from the antenna312. The hardware logic324receives the output current from the electrochemical sensor320and modulates (325) the impedance of the antenna312in accordance with the amperometric current measured by the sensor320. The antenna impedance and/or change in antenna impedance is detected by the external reader340via the backscatter signal343. The external reader340can include an antenna front end342and logic components344to decode the information indicated by the backscatter signal343and provide digital inputs to a processing system346. The external reader340associates the backscatter signal343with the sensor result (e.g., via the processing system346according to a pre-programmed relationship associating impedance of the antenna312with output from the sensor320). The processing system346can then store the indicated sensor results (e.g., tear film analyte concentration values) in a local memory and/or an external memory (e.g., by communicating with the external memory through a network).

In some embodiments, one or more of the features shown as separate functional blocks can be implemented (“packaged”) on a single chip. For example, the eye-mountable device310can be implemented with the rectifier314, energy storage316, voltage regulator318, sensor interface321, and the hardware logic324packaged together in a single chip or controller module. Such a controller can have interconnects (“leads”) connected to the loop antenna312and the sensor electrodes322,323. Such a controller operates to harvest energy received at the loop antenna312, apply a voltage between the electrodes322,323sufficient to develop an amperometric current, measure the amperometric current, and indicate the measured current via the antenna312(e.g., through the backscatter radiation343).

Whereas the device described herein is described as comprising the eye-mountable device110and/or the eye-mountable device310, the device could comprise other devices that are mounted on or in other portions of the human body.

For example, in some embodiments, the body-mountable device may comprise a tooth-mountable device. In some embodiments, the tooth-mountable device may take the form of or be similar in form to the eye-mountable device110and/or the eye-mountable device310. For instance, the tooth-mountable device could include a polymeric material or a transparent polymer that is the same or similar to any of the polymeric materials or transparent polymers described herein and a substrate or a structure that is the same or similar to any of the substrates or structures described herein. With such an arrangement, the tooth-mountable device may be configured to detect at least one analyte in a fluid (e.g., saliva) of a user wearing the tooth-mountable device.

Moreover, in some embodiments, the body-mountable device may comprise a skin-mountable device. In some embodiments, the skin-mountable device may take the form of or be similar in form to the eye-mountable device110and/or the eye-mountable device310. For instance, the skin-mountable device could include a polymeric material or a transparent polymer that is the same or similar to any of the polymeric materials or transparent polymers described herein and a substrate or a structure that is the same or similar to any of the substrates or structures described herein. With such an arrangement, the skin-mountable device may be configured to detect at least one analyte in a fluid (e.g., perspiration, blood, etc.) of a user wearing the skin-mountable device.

FIG. 4Ais a flowchart of a process400for operating an amperometric sensor in an eye-mountable device to measure a tear film analyte concentration. Radio frequency radiation is received at an antenna in an eye-mountable device including an embedded electrochemical sensor (402). Electrical signals due to the received radiation are rectified and regulated to power the electrochemical sensor and associated controller (404). For example, a rectifier and/or regulator can be connected to the antenna leads to output a DC supply voltage for powering the electrochemical sensor and/or controller. A voltage sufficient to cause electrochemical reactions at the working electrode is applied between a working electrode and a reference electrode on the electrochemical sensor (406). An amperometric current is measured through the working electrode (408). For example, a potentiostat can apply a voltage between the working and reference electrodes while measuring the resulting amperometric current through the working electrode. The measured amperometric current is wirelessly indicated with the antenna (410). For example, backscatter radiation can be manipulated to indicate the sensor result by modulating the antenna impedance.

FIG. 4Bis a flowchart of a process420for operating an external reader to interrogate an amperometric sensor in an eye-mountable device to measure a tear film analyte concentration. Radio frequency radiation is transmitted to an electrochemical sensor mounted in an eye from the external reader (422). The transmitted radiation is sufficient to power the electrochemical sensor with energy from the radiation for long enough to perform a measurement and communicate the results (422). For example, the radio frequency radiation used to power the electrochemical sensor can be similar to the radiation341transmitted from the external reader340to the eye-mountable device310described in connection withFIG. 3above. The external reader then receives backscatter radiation indicating the measurement by the electrochemical analyte sensor (424). For example, the backscatter radiation can be similar to the backscatter signals343sent from the eye-mountable device310to the external reader340described in connection withFIG. 3above. The backscatter radiation received at the external reader is then associated with a tear film analyte concentration (426). In some cases, the analyte concentration values can be stored in the external reader memory (e.g., in the processing system346) and/or a network-connected data storage.

For example, the sensor result (e.g., the measured amperometric current) can be encoded in the backscatter radiation by modulating the impedance of the backscattering antenna. The external reader can detect the antenna impedance and/or change in antenna impedance based on a frequency, amplitude, and/or phase shift in the backscatter radiation. The sensor result can then be extracted by associating the impedance value with the sensor result by reversing the encoding routine employed within the eye-mountable device. Thus, the reader can map a detected antenna impedance value to an amperometric current value. The amperometric current value is approximately proportionate to the tear film analyte concentration with a sensitivity (e.g., scaling factor) relating the amperometric current and the associated tear film analyte concentration. The sensitivity value can be determined in part according to empirically derived calibration factors, for example.

IV. Example Electrochemical Sensor with Dual Power Sources

FIG. 5Ais a functional block diagram of an example electrochemical sensor system500including a measurement power supply510and an auxiliary power supply520. The electrochemical sensor system500can also include a working electrode502, a reference electrode504, an antenna522, measurement and communication electronics524, photocell526and auxiliary electronics528. Although, it is noted the functional block diagram of the system500shown inFIG. 5Aillustrates separate functional modules, they are not necessarily implemented as physically distinct modules. For example, the measurement power supply510and measurement and communication electronics524can be packaged in a common chip that includes terminals connected to the antenna522and the sensor electrodes502,504. Further, while not specifically illustrated, it is noted that a reagent layer can be provided on or near the working electrode502to sensitize the electrochemical sensor to an analyte of interest. For example, glucose oxidase may be fixed around the working electrode502(e.g., by incorporating glucose oxidase in a gel or medium) to cause the electrochemical sensor system500to detect glucose.

As shown, measurement power supply510and auxiliary power supply520are electrically connected to the measurement and control electronics524in order to supply power (e.g., a DC supply voltage) to the system500. For brevity, the measurement and control electronics524is alternately referred to herein as the “measurement electronics” or the “measurement module.” Generally, the measurement and control electronics524, which receive power from the measurement power supply510and/or the auxiliary power supply520, may apply a voltage across the sensor electrodes502,504while obtaining an amperometric current measurement (e.g., similar to the operation of a potentiostat).

In accordance with one embodiment, the measurement power supply510depicted inFIG. 5Aoperates to harvest energy from incident radio frequency radiation and generate a DC supply voltage to turn on the measurement and communication electronics524, thereby causing the system500to obtain an amperometric current measurement through the working electrode502and communicate the sensor result through antenna522. The measurement power supply510may be a power supply that is dedicated to providing power to the measurement and control electronics524. The measurement power supply510can generally be similar to the energy harvesting power supply system described in connection withFIGS. 1 and 3and may include one or more rectifiers, energy storage devices, and/or voltage regulators/conditioners configured to harvest energy in radio frequency electrical signals on leads of the antenna522caused by incident radiation and output a DC supply voltage to power the measurement and communication electronics524.

In accordance with one embodiment, the auxiliary power supply520depicted inFIG. 5Aoperates to harvest energy other than that received from the from the radio frequency energy harvesting antenna522. For example, in some embodiments, the auxiliary power supply520may comprise a photovoltaic cell (e.g., the photovoltaic cell526) that outputs a voltage across two terminals in response to incident light radiation. The terminals of the photovoltaic cell526can then be connected to the measurement and communication electronics524, so that voltage output from the photovoltaic cell526can turn on the measurement and communication electronics524, thereby causing the system500to obtain an amperometric current measurement through the working electrode502.

The photovoltaic cell526can be, for example, a solar cell or a combination of such solar cells. The photovoltaic cell can be activated in response to the receipt of light at a range of different wavelengths, such as visible light, ultraviolet light, near infrared light, etc. Although, a particular photovoltaic cell may be configured to be activated at a selected range of wavelengths as desired. In an embodiment in which the electrochemical sensor is included in an eye-mountable device (e.g., embedded in a transparent polymeric material configured to be contact-mounted to an eye surface) the photovoltaic cell526can be embedded in the eye-mountable device and can receive incident light radiation that is transmitted through the eye-mountable device.

In other embodiments, however, the auxiliary power supply520is additionally or alternatively powered via another energy harvesting source, such as an inertial motion energy harvesting system, a biofuel cell, and/or a charge storage device. The biofuel cell may be configured to facilitate a chemical reaction and generate a responsive electric potential. In one example, the biofuel cell facilitates oxidation of the ascorbate naturally present in tear fluid. However, other types of bio fuel cells are possible as well. Still additionally, the auxiliary power supply may comprise a charge storage device, such as a rechargeable battery or an arrangement of capacitors. The charge storage device may be arranged to store electric charge generated by the photovoltaic cell, inertial motion energy harvesting system, biofuel cell, antenna, or other charge generating device.

In some embodiments, the measurement power supply510and the auxiliary power supply520include components similar to the voltage regulator and/or rectifier314,318described in connection withFIG. 3that outputs both an analog voltage332to the sensor interface321, and a DC supply voltage330to the circuit logic324. With reference to the system500inFIG. 5A, the voltage applied across the sensor electrodes502,504may be analogous to the analog voltage output of the energy harvesting system, while the DC supply voltage provided to the measurement and communication electronics524can be analogous to the digital voltage output of the energy harvesting system. Thus, some embodiments of the measurement power supply510and auxiliary power supply520may include a rectifier, a low-pass filter (e.g., one or more capacitors), and/or voltage regulation/conditioning modules that may be similar in some respects to the rectifier314, energy storage316, and/or voltage regulator/conditioner318described in connection withFIG. 3above.

The measurement and communication electronics524are shown and described in connection withFIG. 5Aas a functional module that receives a DC supply voltage, obtains an amperometric current measurement measured through the working electrode, and then operates the antenna522to communicate the measured current. However, the measurement and communication electronics may include one or more of the functional modules shown and described in connection withFIG. 3above, such as a sensor interface (e.g., a potentiostat), an antenna interface (e.g., a backscatter radiation modulator, one or more oscillators, etc.), and/or logic elements configured to cause the module524to function as described. Moreover, while the measurement and communication electronics are shown and described as a single physical module, it is noted that the measurement and communication electronics524can include a combination of one or more modules, or can be combined with other modules (e.g., rectifier, regulator and/or other related power supply modules) in a single physical implementation, such as an integrated circuit or chip.

In accordance with some embodiments, system500also includes auxiliary electronics528. Auxiliary electronics528are shown and described in connection withFIG. 5Aas a functional module that receives a DC supply voltage from auxiliary power supply520. The auxiliary electronics528may include one or more of the functional modules shown and described in connection withFIG. 1above, such a pixel array, radio transceiver, memory storage, and/or logic elements configured to cause the auxiliary electronics528to function as described. Moreover, while auxiliary electronics528are shown as a single physical module, it is noted that the auxiliary electronics528can include a combination of one or more modules, or can be combined with other modules (e.g., rectifier, regulator and/or other related power supply modules) in a single physical implementation, such as an integrated circuit or chip.

In operation according to some embodiments, system500may contain an appropriate mechanism that operates to determine when the auxiliary power supply520is able to provide power to the system500and responsively enable the auxiliary power supply520. For example, in embodiments in which the auxiliary power supply is powered by a photovoltaic cell526, auxiliary power supply520may contain an ambient light detector that operates to detect the presence of ambient light sufficient enough for the photovoltaic cell526to provide an operating voltage (e.g., 5.0V) to the measurement and communication electronics524and/or the auxiliary electronics528. In embodiments in which the auxiliary power supply is powered by a biofuel cell, auxiliary power supply520may recognize when the biofuel cell is producing a voltage level (e.g., 5.0V) that is sufficient enough to operate the measurement and communication electronics524and/or the auxiliary electronics528. In embodiments in which the auxiliary power supply is powered by a charge storage device, auxiliary power supply520may determine whether the charge storage device has stored a sufficient level of electric charge (e.g., 5.0V) to operate the measurement and communication electronics524and/or the auxiliary electronics528. In embodiments in which the auxiliary power supply520is powered by an inertial motion energy harvesting system, the auxiliary power supply520may contain a motion detector that operates to determine when there is motion sufficient enough for the motion detector to provide an operating voltage (e.g., 5.0V) to the measurement and communication electronics524and/or the auxiliary electronics528. However, in other embodiments, other mechanisms for determining whether the auxiliary power supply520is able to provide power to the system500are possible as well.

As mentioned above, in response to determining that the auxiliary power supply520is able to provide sufficient power to the communication electronics524and/or the auxiliary electronics528, the auxiliary power supply520may operate to enable the auxiliary power supply520. In some embodiments, this is carried out by providing to a switch or other logic a signal indicative of the availability of the auxiliary power supply520to provide power to the system500. The switch or other logic may responsively enable and operate the auxiliary power supply520to provide power to the measurement and communication electronics524and/or the auxiliary electronics528(e.g., by closing a circuit, thereby electrically coupling the auxiliary power supply to either or both of the measurement and communication electronics524and the auxiliary electronics528). However, other ways of enabling the auxiliary power supply520are possible as well.

In practice, opportunistic enabling of auxiliary power supply520may have several operational advantages. For instance, in a situation in which the auxiliary electronics528are being powered by measurement power supply510, enabling auxiliary power supply520may result in additional power being supplied to the auxiliary electronics528from the auxiliary power supply520. As such, the additional power may result in an improved performance of one or more of the auxiliary electronics. For example, when the auxiliary electronics528include a Bluetooth radio, providing additional power to the radio may enable the radio to transmit a farther distance. Other examples of improved performance are possible as well.

In another example of an operational advantage, enabling auxiliary power supply520to provide power to the system500may allow the measurement power supply510to reduce the amount of power it supplies to the system500. As such, while the auxiliary power supply520powers the system500, power may be preserved at the measurement power supply510and/or an external reader associated with the measurement power supply510. In some embodiments, the auxiliary power supply520in conjunction with the measurement and communication electronics524include logic configured for determining whether the auxiliary power supply520is supplying power to the system500and responsively causing the measurement power supply510to reduce the amount of power supplied to the system500. In one example of this, the measurement and communication electronics524operate to characteristically modify RF backscatter at antenna526to communicate with an external reader. Accordingly, this communication may cause the external reader to temporarily reduce or stop the external reader's transmission of power to the measurement power supply510. However, other ways of conserving power are possible as well.

In another example of an operational advantage, enabling auxiliary power supply520to provide power to auxiliary electronics528may allow system500to retain an operating state during periods in which the measurement power supply510is unable to provide power to the system500. For instance, when auxiliary electronics528include a volatile memory storage unit (i.e., a memory storage unit that loses its contents when power is removed from the memory storage unit) that stores certain operating parameters (e.g., measurement results), those parameters may be lost when power is removed from the volatile memory storage unit. Therefore, when the auxiliary power supply520provides power to the volatile memory storage unit, the operating parameters contained therein may not be lost when the measurement power supply510stops providing power to system500. In addition, in some embodiments, system500may contain logic configured for determining that the measurement power supply is (or will soon be) unable to provide power but the auxiliary power supply is able to provide power. In response to this determination, the system500may enable the auxiliary power supply520to provide power to the volatile memory storage unit. In one example, the system500determines that the measurement power supply510is (or will soon be) unable to provide power by receiving an instruction (e.g., in the form of RF radiation received at antenna522from an external reader) that indicates that the external reader is powering down. However, other ways of determining that the measurement power supply510is (or will soon be) unable to provide power are possible as well.

In operation according to additional or alternative embodiments, system500may contain logic configured for determining an intention to operate auxiliary electronics528and responsively enabling and operating the auxiliary power supply520to provide power to the auxiliary power electronics528. For instance, system500may receive an instruction (e.g., in the form of RF radiation received at antenna522from an external reader) that instructs system500to operate at least part of auxiliary electronics528, such as pixel array164. In response, auxiliary power supply520may provide to a switch or other logic a signal indicative of an intent to operate the auxiliary electronics528. The switch or other logic may responsively enable and operate the auxiliary power supply520to provide power to the auxiliary electronics528(e.g., by closing a circuit, thereby electrically coupling the auxiliary power supply to the auxiliary electronics528). In this way, auxiliary electronics embedded within the eye-mountable device, such as a Bluetooth radio or a pixel array, can be opportunistically operated when there is sufficient power able to be harvested from sources other than the external reader, thereby conserving battery life of the external reader.

In operation according to additional or alternative embodiments, system500may contain logic configured for determining that the auxiliary power supply is unable to currently supply power and responsively entering a lower power mode in which the system500disables all auxiliary electronics but for the sensor501. Entering a low power mode, such as this one, may help the system500generally, and the measurement power supply510(as well as an associated external reader) in particular, conserve power. Depending on the embodiment, the system500may determine that the auxiliary power supply520is unable to supply power by detecting that there is insufficient light for the photovoltaic cell526to provide an operating voltage (e.g., 5.0V) to the measurement and communication electronics524and/or the auxiliary electronics528, the biofuel cell is not producing a voltage level (e.g., 5.0V) that is sufficient enough to operate the measurement and communication electronics524and/or the auxiliary electronics528, the charge storage device has stored an insufficient level of electric charge (e.g., <5.0V) to operate the measurement and communication electronics524and/or the auxiliary electronics528, there is not sufficient enough motion for the motion detector to provide an operating voltage (e.g., 5.0V) to the measurement and communication electronics524and/or the auxiliary electronics528, or in other ways as well.

FIG. 5Bis a flowchart of an example process530for operating the example electrochemical sensor system500ofFIG. 5A. The example process530may include one or more operations, functions, or actions, as depicted by one or more of blocks532,534, and/or536, each of which may be carried out by any of the systems described herein; however, other configurations could be used.

Furthermore, those skilled in the art will understand that flow diagrams described herein illustrate functionality and operation of certain implementations of example embodiments. In this regard, each block of each flow diagram may represent a module, a segment, or a portion of program code, which includes one or more instructions executable by a processor (e.g., a processor of controller150described above with respect toFIG. 1) for implementing specific logical functions or steps in the process. The program code may be stored on any type of computer readable medium (e.g., computer readable storage medium or non-transitory media), for example, such as a storage device including a disk or hard drive. In addition, each block may represent circuitry that is wired to perform the specific logical functions in the process. Alternative implementations are included within the scope of the example embodiments of the present application in which functions may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art.

The process530begins at block532where the system500receives a signal indicative of the availability of the auxiliary power supply to supply power to the system500. As described, in embodiments in which the auxiliary power supply receives power from a photovoltaic cell, such a signal may take the form of the output of an ambient light detector. In one example, the signal comprises a determination that the level of ambient light incident upon the photovoltaic cell is at or above a threshold level of ambient light. Generally, in this example, the threshold level of ambient light is a level at which the photovoltaic cell and the auxiliary power supply can provide a sufficient DC voltage (e.g., 5.0 Volts) to operate the auxiliary electronics and/or the measurement and communication electronics. In embodiments in which the auxiliary power source receives power from another type of energy-harvesting device, the signal may be one that is generally indicative of that device's ability to imminently provide a DC power supply to the auxiliary electronics and/or the measurement and communication electronics sufficient to power such electronics.

The process continues at block534, where the system500enables the auxiliary power supply. As described, in some embodiments, enabling the auxiliary power supply includes a switch or other actuating device that can electrically couple the auxiliary power supply to the auxiliary electronics and/or the measurement and communication electronics upon receipt of the signal described in connection with block532. And finally, in block536, the system operates the auxiliary power supply to provide power to the electrochemical sensor. As described, in one embodiment, operating the auxiliary power supply to provide power may include receiving incident light at the photovoltaic cell and converting the light into a DC supply voltage. In another embodiment, operating the auxiliary power supply to provide power may include harvesting motion energy and converting such energy into a DC supply voltage. In other embodiments, other energy harvesting devices are possible and in those embodiments, operating the auxiliary power supply generally includes converting the harvested energy into a DC supply voltage.

FIG. 5Cis another flowchart of an example process540for operating the example electrochemical sensor system500ofFIG. 5A. The example process540may include one or more operations, functions, or actions, as depicted by one or more of blocks542,544, and/or546, each of which may be carried out by any of the systems described herein; however, other configurations could be used.

The process540begins at block542where the system500receives a signal indicative of an intention to operate an auxiliary device. As described, in embodiments in which the auxiliary electronics include a pixel array, such a signal may take the form of an instruction to operate the pixel array. In some embodiments, this instruction may be generated at a controller of system500(e.g., controller150described in connection withFIG. 1). Additionally or alternatively, this instruction may be received from an external reader (e.g., external reader180described in connection withFIG. 1).

The process continues at block544, where the system500enables the auxiliary power supply. Similar to that described above in connection with block534ofFIG. 5B, the auxiliary power supply may include a switch or other actuating device that can electrically couple the auxiliary power supply to the auxiliary electronics and/or the measurement and communication electronics upon receipt of the signal described in connection with block542. And finally, in block546, similar to that described above in connection with block536ofFIG. 5B, the system operates the auxiliary power supply to provide power to the auxiliary device. As described, in one embodiment, operating the auxiliary power supply to provide power may include receiving incident light at the photovoltaic cell and converting the light into a DC supply voltage. In another embodiment, operating the auxiliary power supply to provide power may include harvesting motion energy and converting such energy into a DC supply voltage. In other embodiments, other energy harvesting devices are possible and in those embodiments, operating the auxiliary power supply generally includes converting the harvested energy into a DC supply voltage.

FIG. 5Dis a flowchart of an example process550for operating the example electrochemical sensor system500ofFIG. 5A. The example process550may include one or more operations, functions, or actions, as depicted by one or more of blocks552and/or554, each of which may be carried out by any of the systems described herein; however, other configurations could be used.

The process550begins at block552where the system500receives a signal indicative of the inability of the auxiliary power supply to supply power to the system500. As described, in embodiments in which the auxiliary power supply receives power from a photovoltaic cell, such a signal may take the form of the output of an ambient light detector. In one example, the signal comprises a determination that the level of ambient light incident upon the photovoltaic cell is below a threshold level of ambient light. Generally, in this example, the threshold level of ambient light is a level at which the photovoltaic cell and the auxiliary power supply can provide a sufficient DC voltage (e.g., 5.0 Volts) to operate the auxiliary electronics and/or the measurement and communication electronics. In embodiments in which the auxiliary power source receives power from another type of energy-harvesting device, the signal may be one that is generally indicative of that device's inability to imminently provide a DC power supply to the auxiliary electronics and/or the measurement and communication electronics sufficient to power such electronics.

The process continues at block554, where the system500enters a low power mode in which it disables all the auxiliary electronics but for the sensor501. As described, in some embodiments, entering the low power mode may enable the system500generally and the measurement power supply in particular to conserve power by not having to power the auxiliary electronics.

FIG. 6depicts a computer-readable medium configured according to an example embodiment. In example embodiments, the example system can include one or more processors, one or more forms of memory, one or more input devices/interfaces, one or more output devices/interfaces, and machine-readable instructions that when executed by the one or more processors cause the system to carry out the various functions, tasks, capabilities, etc., described above.

As noted above, in some embodiments, the disclosed techniques can be implemented by computer program instructions encoded on a non-transitory computer-readable storage media in a machine-readable format, or on other non-transitory media or articles of manufacture (e.g., the instructions184stored on the memory storage182of the external reader180of the system100).FIG. 6is a schematic illustrating a conceptual partial view of an example computer program product that includes a computer program for executing a computer process on a computing device, arranged according to at least some embodiments presented herein.

In one embodiment, the example computer program product600is provided using a signal bearing medium602. The signal bearing medium602may include one or more programming instructions604that, when executed by one or more processors may provide functionality or portions of the functionality described above with respect toFIGS. 1-5C. In some examples, the signal bearing medium602can be a non-transitory computer-readable medium606, such as, but not limited to, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, memory, etc. In some implementations, the signal bearing medium602can be a computer recordable medium608, such as, but not limited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In some implementations, the signal bearing medium602can be a communications medium610, such as, but not limited to, a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.). Thus, for example, the signal bearing medium602can be conveyed by a wireless form of the communications medium610.

The one or more programming instructions604can be, for example, computer executable and/or logic implemented instructions. In some examples, a computing device such as the processor-equipped external reader180ofFIG. 1is configured to provide various operations, functions, or actions in response to the programming instructions604conveyed to the computing device by one or more of the computer readable medium606, the computer recordable medium608, and/or the communications medium610.

The non-transitory computer readable medium606can also be distributed among multiple data storage elements, which could be remotely located from each other. The computing device that executes some or all of the stored instructions could be an external reader, such as the reader180illustrated inFIG. 1, or another mobile computing platform, such as a smartphone, tablet device, personal computer, etc. Alternatively, the computing device that executes some or all of the stored instructions could be remotely located computer system, such as a server.

Where example embodiments involve information related to a person or a device of a person, some embodiments may include privacy controls. Such privacy controls may include, at least, anonymization of device identifiers, transparency and user controls, including functionality that would enable users to modify or delete information relating to the user's use of a product.