Patent Publication Number: US-11652179-B2

Title: Methods and systems for real time UV monitoring for tracking and maintaining required vitamin D dosage

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of U.S. patent application Ser. No. 15/957,340, filed Apr. 19, 2018, entitled “PLZT THIN FILM CAPACITORS APPARATUS WITH ENHANCED PHOTOCURRENT AND POWER CONVERSION EFFICIENCY AND METHOD THEREOF,” which claims priority to, and the benefit of, U.S. Provisional Application No. 62/487,188, filed Apr. 19, 2017, titled “PLZT THIN FILM CAPACITORS APPARATUS WITH ENHANCED PHOTOCURRENT AND POWER CONVERSION EFFICIENCY AND METHOD THEREOF” and U.S. Provisional Application No. 62/599,434, filed Dec. 15, 2017, titled “METHODS AND SYSTEMS FOR REAL TIME UV MONITORING FOR TRACKING AND MAINTAINING REQUIRED VITAMIN D DOSAGE,” each of which is incorporated by reference herein in its entirety. 
    
    
     This invention was made with government support under EECS 943711 awarded by the National Science Foundation. The government has certain rights in the invention. 
    
    
     TECHNICAL FIELD 
     The disclosure generally relates a material system, and structure thereof, for a sensor or photovoltaic device, in particular, a ferroelectric thin film such as a lanthanum-doped lead zirconate titanate (PLZT) thin-film-based system. Further, the disclosure also relates to the use of such sensors, among others, e.g., for energy generation or for sensors. The disclosure real-time further relates to the monitoring of ultraviolet radiation exposure for health care applications, in particular ultraviolet B radiation, to track Vitamin D dosage. 
     BACKGROUND 
     Photosensitive materials which are sensitive to light (e.g., sunlight) are known to exhibit a current when exposed to sunlight. When exposed to light (e.g., photons), these photosensitive materials generate charge carriers which can be collected at respective electrodes giving rise to photocurrent and photovoltage. When these photosensitive materials are used, in a capacitor structure, to harvest energy to generate electricity, they may be considered as a photovoltaic (PV) device. However, magnitude of the resulting photocurrent and photovoltage are often very small, thereby making such photosensitive materials yet unsuitable for device applications. Many materials (oxides as well as metals) can be used as bottom and top electrodes to make capacitors from such films. Choice of bottom and top electrodes can affect the maximum electrical output from the capacitor structure derived therefrom. 
     Considering the rising demand for power, ferroelectric thin films provides an alternate material for use in solar technology (which currently uses semiconductor materials (e.g. Si, GaAs, CdTe), organic materials, and perovskite) if they can provide comparable photocurrent output and power conversion efficiency to such materials. Power conversion efficiency generally relates to the conversion of sunlight energy to usable electrical or thermal energy. 
     Ferroelectric material typically exhibits spontaneous electric polarization in absence of an electrical field. Such polarization properties induce an in-built electric field that enables the separation of photo-generated charge carriers. To this end, PV effects in ferroelectric materials can be realized without a p-n junction, as is the case in other semiconductor-based devices. 
     What are needed are devices, systems, and methods that can address such limitations, among others. 
     SUMMARY 
     The exemplified systems, and method thereof, includes a ferroelectric thin film such as a PLZT thin film (Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3 ) paired with a bottom metal and top transparent conductive oxide, that forms a capacitor structure with enhanced photocurrent and power conversion efficiency. The exemplified systems use metal electrode (platinum) as bottom electrode and a transparent oxide (Indium Tin Oxide—ITO) as the top electrode. Platinum as an electrode material facilitates ease of integration with the silicon technology. Indium tin oxide (ITO) is an established material and used in semiconductor process industry that provides high reliability and robustness in the process environment along with transparency, high electrical conductivity, and price. Combination of these two materials as electrodes along with a ferroelectric thin film such as (e.g., the Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3  (PLZT) thin film) demonstrated enhanced photocurrent and power conversion efficiency of a resulting capacitor structure formed therewith. Remarkably, when exposed to light, a device with this structure is observed to provide higher absorption of light, in particular, sunlight, and to exhibit high photocurrent, increased power efficiency, and higher output yield, as compared to material system of similar topology. 
     The exemplified device may be used as an ultraviolet (UV) sensor. 
     In some embodiments, embodiments of the present invention facilitates the monitoring of direct ultraviolet B (UVB) radiation exposure by a person via a system having a sensor (such as Lanthanum doped lead zirconate titanate (PLZT) thin-film sensors or other ferroelectric-based sensors) sensitive to UVB radiation. The system beneficially provides current real-time dosage information associated with Vitamin D production by the person as well as real-time indication of safe exposure and/or harmful exposure to current UVB radiation conditions. 
     In an aspect, apparatus (e.g., solar cell, a UV sensor, a UV index sensor, etc.) is disclosed. The apparatus includes a substrate; a bottom layer coupled to the substrate, the bottom layer forming an electrode that comprises a material that includes, in part, platinum (or LaNiO 3 LaAlO 3 , LSMO, LSCO, RuO x , Nb:SrTiO 3 , or ITO); a thin film layer coupled to the bottom layer, the thin film layer substantially spanning the bottom layer and comprising a lanthanum-doped lead zirconate titanate (PLZT) thin-film material (e.g., Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3 ); and an array of top electrodes that collectively form a top layer over the thin film layer so as to form a plurality of capacitors (e.g., with the bottom layer) (e.g., wherein a first top electrode of the array forms a capacitor with a second top electrode of the array), each of the top electrodes comprising a transparent oxide (e.g., indium tin oxide) layer. 
     In some embodiments, the lanthanum-doped lead zirconate titanate thin-film material comprises Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3 . 
     In some embodiments, the apparatus includes a seed layer comprising a material selected from the group consisting of Pb x TiO 3 , where x=1.0, 1.05, 1.1, or 1.2; PbO; PbZrO 3 ; LaNiO 3 , TiO x  where x≤2; SrTiO 3 ; SrRuO 3 ; LaxSr 1-x CoO 3 , where 0&lt;x&lt;1; and LaxSr 1-x MnO 3  where 0&lt;x&lt;1. 
     In some embodiments, the bottom layer comprises a material selected from the metal group consisting of Au, Pt, and a combination thereof. In some embodiments, the bottom layer comprises a material selected from an oxide group consisting of LaNiO 3 LaAlO 3 , LSMO, LSCO, RuO x , Nb:SrTiO 3 , ITO, and a combination thereof. In some embodiments, the bottom layer comprises a composite selected from the metal consisting of Au, Pt, and a combination thereof and an oxide group consisting of LaNiO 3 LaAlO 3 , LSMO, LSCO, RuO x , Nb:SrTiO 3 , ITO, and a combination thereof. 
     In some embodiments, the substrate comprises a material selected from the group consisting TiO 2 , SiO 2 , Si, and a combination thereof. 
     In some embodiments, each formed capacitor of the plurality of capacitors has a light-to-electricity conversion efficiency of at least 0.05%. 
     In some embodiments, each formed capacitor of the plurality of capacitors has a photocurrent density J sc  of at least −6.8×10 −5  A/cm 2  (Amp per cm 2 ). 
     In some embodiments, the thin film layer comprises a ferroelectric thin film material. 
     In some embodiments, two or more electrodes of the array are electrically linked by a connection member (e.g., in series, parallel, or combination thereof), the two or more electrodes forming a capacitor with a portion of the bottom layer across a portion of the thin film layer. 
     In some embodiments, two or more electrodes of the array are electrically linked by a connection member (e.g., in series, in parallel, or in combination thereof), the two or more electrodes forming a capacitor with another electrode of the array. 
     In some embodiments, the array of top electrodes comprises a plurality of structures that form gaps thereamong so as to form the plurality of capacitors, wherein the plurality of capacitors include a first top electrode of the array that forms a capacitor with a second top electrode of the array. 
     In some embodiments, each formed capacitor of the plurality of capacitors has an operational spectral wavelength range that, at least, spans a range consisting of between about 315 nm and about 400 nm, between about 280 nm and about 315 nm, and between about between 200-800 nm. 
     In some embodiments, the thin film layer has a peak photocurrent value about 350 nm. 
     In some embodiments, each of formed capacitor of the plurality of capacitors forms a solar cell. 
     In some embodiments, each of the formed capacitor of the plurality of capacitors forms an ultraviolet sensor. 
     In some embodiments, the thin film layer is configured as a sensing layer for the ultraviolet sensor. 
     In another aspect, an ultraviolet-light indexing device is disclosed comprising: a display; a sensing element; and electronic circuitry. The sensing element is configured to respond to UV radiation, the sensing element comprising: a substrate; a bottom layer coupled to the substrate, the bottom layer forming an electrode that comprises a material that includes, in part, platinum; a thin film layer coupled to the bottom layer, the thin film layer substantially spanning the bottom layer and comprising a ferroelectric thin film such as a lanthanum-doped lead zirconate titanate thin-film material (e.g., Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3 ); and, a top electrode of an array of top electrodes that collectively form a top layer over the thin film layer so as to form a plurality of capacitors with the bottom layer, each of the top electrodes comprising a transparent oxide (e.g., indium tin oxide) layer. The electronic circuitry is coupled to an output of the sensing element to receive an electric output (e.g., a current output), or a signal derived therefrom, generated from the sensing element in response to exposure of the sensing element by the UV radiation, the electronic circuitry being coupled to the display and configured to present an index parameter (e.g., an UV index parameter) generated from with the electric output. 
     In some embodiments, the device is wearable (e.g., comprises a wrist strap, an attachable pin, a chain (e.g., as a necklace), a bracelet, or an anklet). 
     In some embodiments, the device is embedded in an article of clothing (e.g., a shirt, a hat, sunglasses, or spectacles). 
     In some embodiments, the device includes a wireless transceiver, the wireless transceiver being coupled to the electronic circuitry and being configured to transmit to generated index parameter to a computing device. 
     In some embodiments, the device includes a processor; and a memory, the memory having instructions stored thereon, wherein execution of the instructions, cause the processor to: calculate (via a transfer function) an index parameter from a parameter derived (e.g., via ADC stage and/or filtering stage) from the electric output. 
     In some embodiments, the instructions, when executed by the processor, further cause the processor to, cause presentation of the index parameter. 
     In some embodiments, the instructions, when executed by the processor, further cause the processor to cause presentation of one of a plurality of pre-defined messages, each of the plurality of pre-defined messages being associated with a corresponding UV index tier to which the index parameter is compared (e.g., tiers may include low, moderate, high, very high, and extreme). 
     In some embodiments, the instructions, when executed by the processor, further cause the processor to cause presentation of one of a plurality of pre-defined messages, each of the plurality of pre-defined messages being associated with an amount of sun protection (e.g., use of sunscreen, rating of sunscreen, use of hat, use of shirt, and etc.). 
     In some embodiments, the instructions, when executed by the processor, further cause the processor to cause presentation of one of a plurality of pre-defined messages including a first message directed to presence, or degree of, UV-A, and a second message directed to presence, or degree, of UV-B. 
     In some embodiments, the sensing element has an operation range between about 315 to about 400 nm and between about 280 nm to about 315 nm. 
     In some embodiments, the instructions, when executed by the processor, further cause the processor to monitor the sensing element and to cause a reminder message (e.g., visual, audio, and etc.) (e.g., via the device) to be presented to the user (e.g., a remaining time for safe exposure or an action, e.g., to seek shading or more protection, and etc.). 
     In some embodiments, the instructions, when executed by the processor, further cause the processor to monitor the sensing element and to cause a reminder message (e.g., visual, audio, and etc.) (e.g., via SMS message or email) to be transmitted to the user (e.g., a remaining time for safe exposure or an action, e.g., to seek shading or more protection, and etc.). 
     In some embodiments, the electronic circuitry comprises: an amplifier circuit; an analog-to-digital conversion circuit; a processor; and, a memory, the memory having instructions stored thereon, wherein execution of the instructions, cause the processor to calculate (via a transfer function) an index parameter from a parameter derived, via the analog-to-digital convert circuit; from the electric output. 
     In another aspect, a method is disclosed of generating electric energy. The method includes exposing a solar cell to electromagnetic radiation in which the solar cell comprises: a substrate; a bottom layer coupled to the substrate, the bottom layer forming an electrode that comprises a material that includes, in part, platinum; a thin film layer coupled to the bottom layer, the thin film layer substantially spanning the bottom layer and comprising a ferroelectric thin film such as a lanthanum-doped lead zirconate titanate thin-film material (e.g., Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3 ); and, a top electrode of an array of top electrodes that collectively form a top layer over the thin film layer so as to form a plurality of capacitors with the bottom layer, each of the top electrodes comprising a transparent oxide (e.g., indium tin oxide) layer, wherein the exposure causes generation of a photocurrent from the thin film layer. 
     In another aspect, a method is disclosed of sensing ultra-violet radiation. The method exposing a sensor to electromagnetic radiation in which the sensor comprises: a substrate; a bottom layer coupled to the substrate, the bottom layer forming an electrode that comprises a material that includes, in part, platinum; a thin film layer coupled to the bottom layer, the thin film layer substantially spanning the bottom layer and comprising a ferroelectric thin film such as a lanthanum-doped lead zirconate titanate thin-film material (e.g., Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3 ); and one or more top electrodes of an array of top electrodes that collectively form a top layer over the thin film layer so as to form a plurality of capacitors with the bottom layer, each of the top electrodes comprising a transparent oxide (e.g., indium tin oxide) layer, wherein the exposure causes generation of a photocurrent from the thin film layer. 
     In another aspect, a method is disclosed for tracking (e.g. via real-time monitoring) and reporting estimated vitamin D dosage from direct exposure to sunlight. The method includes receiving, by a processor of a device, a plurality of data values derived from an acquired signal of a sensor (e.g., a Lanthanum doped lead zirconate titanate (PLZT) thin-film photodiode) having sensitivity to ultraviolet B intensity of sunlight; accumulating, by the processor, in a memory (e.g., persistent memory) of the device, for a pre-defined period of time, the plurality of data values; determining, by the processor, a value of estimated Vitamin D dosage for the pre-defined period of time based on the accumulated data values associated with the pre-defined period of time; and presenting, via a display (e.g., of the device or an external remote device), upon direction of the processor, a graphical representation of a parameter value (e.g., an estimated dosage value of Vitamin D obtained over a current day; an estimated dosage value of Vitamin D obtained over a current week; an estimated remaining amount value of Vitamin D dosage required or recommended for the current day (e.g., in time or dose); and/or an estimated remaining amount value of Vitamin D dosage required or recommended for the current week (e.g., in time or dose)) associated with obtained dosage of Vitamin D from exposure to direct sunlight over the course of the pre-defined period of time, wherein the parameter value is derived from the estimated vitamin D dosage for the pre-defined period of time. 
     In some embodiments, the parameter value is an estimated dosage value of Vitamin D obtained over a current day, over a current week, or over a user-defined period. 
     In some embodiments, the estimated dosage value of Vitamin D obtained over the current day, over the current week, or over the user-defined period is determined by a computing operation (e.g., multiplication, bit shifting, combination of multiplication and addition) that scales and/or offsets the accumulated data values associated with the pre-defined period of time with a set of pre-defined values (e.g., a scaling parameter and an offset parameter). 
     In some embodiments, the parameter value is associated with an estimated remaining amount value of Vitamin D dosage required or recommended for a current day, for a current week, or for over a user-defined period. 
     In some embodiments, the estimated remaining amount value of Vitamin D dosage required or recommended for the current day, for the current week, or for over the user-defined period is determined (e.g., from a look-up-table or a set of pre-defined transfer functions) based on a recommended exposure time to direct sunlight derived from a set of user-defined parameters (e.g., a first user-defined parameter associated with a user skin type or user skin sensitivity, and/or a second user-defined parameter associated with a degree of area of exposed body surface area and/or other user-defined parameter such as age, height, etc.). 
     In some embodiments, the method further includes determining, by the processor (e.g., from a look-up-table or a set of pre-defined transfer functions), a parameter value associated with a recommended exposure time to direct sunlight based on a set of user-defined parameters (e.g., a first user-defined parameter associated with a user skin type or a user skin sensitivity, and/or a second user-defined parameter associated with a degree of area of exposed body surface area and/or other user-defined parameter such as age, height, etc.). 
     In some embodiments, the set of user-defined parameters comprises a first user-defined parameter associated with a user skin type or user skin sensitivity (e.g., wherein the first user-defined parameter is determined based on a user input to a GUI of the device, based on a user input to a GUI of an application or website accessible on a remote device operatively connected to the device over a network, based on a derived value determined from a user-provided input (e.g., photo or image of the user) to the device or the application or website accessible on the remote device, or based on a scan of the user skin via a second sensor (e.g., optical sensor) located on the device). 
     In some embodiments, the set of user-defined parameters comprises a second user-defined parameter associated with a degree of area of exposed body surface area (e.g., wherein the second user-defined parameter is determined based on a user input to a GUI of the device (e.g., input of an exposed body area in percentage, a selection of a set of exposed body features from a predefined set of features, e.g., face, neck, hands, arms, legs, torso, etc.), based on a user input to a GUI of an application or website accessible on a remote device operatively connected to the device over a network, or based on a derived value determined from a user-provided input (e.g., photo or image of the user)). 
     In some embodiments, the method further includes presenting, via the display (e.g., of the device or the external remote device), upon direction of the processor, a graphical representation of a second parameter, and/or a visual cue, associated with a current UV exposure index, wherein the graphical representation of the second parameter, and/or the visual cue, indicate a current safe exposure to the direct sunlight or indicate a current harmful exposure to the direct sunlight (e.g., and generating audio or vibratory alert associated with current harmful exposure to the direct sunlight). 
     In some embodiments, the current UV exposure index is determined by comparing (e.g., via the processor or via digital circuitries) a parameter value derived from a last set of data values (e.g., one or more recently obtained data values, including or not including the last data value) of the plurality of data values received by the processor from the sensor to one or more UV threshold values, wherein at least one of the one or more UV threshold values is associated with the current safe exposure to the direct sunlight or the current harmful exposure to the direct sunlight. In other embodiments, the current UV exposure index is determined by comparing (e.g., via analog circuitries) a currently acquired signal of the sensor to one or more UV threshold signal levels, wherein at least one of the one or more UV threshold signal levels is associated with the current safe exposure to the direct sunlight or the current harmful exposure to the direct sunlight. 
     In some embodiments, the sensor comprises a PLZT thin-film (Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3 ) photodiode, a PbZr 1-x Ti x O 3 -based photodiode, or a (Pb 1-y La y )(Zr x Ti 1-x )O 3 -based photodiode wherein 0≤x≤1 (such as 0.5) and 0≤y≤0.1 (such as 0.05). 
     In some embodiments, the sensor is selected from the group consisting of a SiC-based (Silicon-Carbide-based) photodiode, a GaN-based (Gallium-Nitride-based) photodiode, an AlGaN (Aluminum-Gallium-Nitride-based) photodiode; a PbTiO 3 -based photodiode, a BaTiO 3 -based photodiode, a SrTiO 3 -based photodiode, a Ba x Sr 1-x TiO 3 -based photodiode, a (1-x)BaTiO 3 -(x)BiFeO 3 -based photodiode, a KNbO 3 -based photodiode, a ZnO-based photodiode, a MgZnS-based photodiodes, a LaAlO 3 -based photodiode, ZnMgO-based photodiode. 
     In some embodiments, the device is a hand-held device or a wearable device. In some embodiments, the device is a component of, or a set of components in, a mobile electronic device (e.g., smartphone or wearable device having a form of a watch, a hat, a headpiece, a neck piece, a neck band, a bracelet, a ring, an eye piece, an arm band). 
     In some embodiments, the method further includes transmitting, by the processor (e.g., via direct communication (e.g. Bluetooth/airdrop) or over a computing network), to a remote computing device (e.g., a user computing device or a third-party server), one or more device parameters values associated with i) the determined value of estimated Vitamin D dosage for the pre-defined period of time, ii) the accumulated data values associated with the pre-defined period of time, or iii) the presented parameter value associated with the obtained dosage of Vitamin D from the exposure to direct sunlight over the course of the pre-defined period of time (e.g., wherein the one or more transmitted device parameters values are stored over time, e.g., to create and display a Vitamin D dose profile, or for further analysis, e.g., to direct therapy for Vitamin D deficiency conditions or disorders). 
     In another aspect, an apparatus is disclosed for tracking (e.g., via real-time monitoring) and reporting estimated vitamin D dosage from direct exposure to sunlight. The apparatus includes a processor; and a memory having instructions stored thereon, wherein the instructions when executed by the processor, cause the processor to: receive a plurality of data values derived from an acquired signal of a sensor (e.g., a Lanthanum doped lead zirconate titanate (PLZT) thin-film photodiode, a SiC photodiode, a GaN photodiode, an InGaN photodiode, an AlGaN photodiode, a PbTiO 3 -based photodiode, a BaTiO 3 -based photodiode, a SrTiO 3 -based photodiode, a Ba x Sr 1-x TiO 3 -based photodiode, a (1-x)BaTiO 3 -(x)BiFeO 3 -based photodiode, a PbZr 1-x Ti x O 3 -based photodiode, a (Pb 1-y La y )(Zr x Ti 1-x )O 3 -based photodiode wherein 0≤x≤1 (such as 0.5) and 0≤y≤0.1 such as (0.05), a KNbO 3 -based photodiode, a ZnO-based photodiode, a MgZnS-based photodiodes, a LaAlO 3 -based photodiode, a ZnMgO-based photodiode) having sensitivity to ultraviolet B radiation of sunlight; accumulate, for a pre-defined period of time, the plurality of data values; determine a value of estimated Vitamin D dosage for the pre-defined period of time based on the accumulated data values associated with the pre-defined period of time; and cause graphical representation of a parameter value (e.g., an estimated dosage value of Vitamin D obtained over a current day; an estimated dosage value of Vitamin D obtained over a current week; an estimated remaining amount value of Vitamin D dosage required or recommended for the current day (e.g., in time or dose); and/or an estimated remaining amount value of Vitamin D dosage required or recommended for the current week (e.g., in time or dose)) associated with obtained dosage of Vitamin D from exposure to direct sunlight over the course of the pre-defined period of time, wherein the parameter value is derived from the estimated vitamin D dosage for the pre-defined period of time. 
     In some embodiments, the apparatus further includes a housing having a display coupled thereto, the housing forming a hand-held device or wearable system. 
     In some embodiments, the apparatus further includes a housing and an attachment member, collectively having a form of a watch, a hat, a headpiece, a neck piece, a neck band, a bracelet, a ring, an eye piece, an arm band. 
     In some embodiments, the instructions when executed by the processor, further cause the processor to: determine (e.g., from a look-up-table or a set of pre-defined transfer functions) a parameter value associated with recommended exposure time to direct sunlight based on a set of user-defined parameters (e.g., a first user-defined parameter associated with a user skin type or a user skin sensitivity, and/or a second user-defined parameter associated with a degree of area of exposed body surface area). 
     In some embodiments, the instructions when executed by the processor, further cause the processor to: compare a parameter value, derived from a last set of data values of the plurality of data values received by the processor from the sensor, to one or more UV threshold values, wherein at least one of the one or more UV threshold values is associated with a current safe exposure to the direct sunlight or a current harmful exposure to the direct sunlight; and present one or more graphical representations of a second parameter, and/or a visual cue, associated with a current UV exposure index, wherein the graphical representation of the second parameter, and/or the visual cue, indicate the current safe exposure to the direct sunlight or the current harmful exposure to the direct sunlight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments and together with the description, serve to explain the principles of the methods and systems: 
         FIG.  1    illustrates an apparatus (e.g., for use as a solar cell, a UV sensor, a UV index sensor, etc.) with ferroelectric-based photodiode (e.g., Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3  (PLZT)) thin film paired with a bottom metal and top transparent conductive oxide, that forms a capacitor structure with enhanced photocurrent and power conversion efficiency, in accordance with an illustrative embodiment. 
         FIG.  2    is a diagram showing a current-voltage characteristic of the apparatus of  FIG.  1   , in particular, the dark and illuminated current voltage curve, in accordance with an illustrative embodiment. 
         FIG.  3    is a diagram showing a light-to-electricity conversion curve of voltage corresponding to the current voltage curve of  FIG.  2   , in accordance with an illustrative embodiment. 
         FIG.  4 A  is a diagram showing a comparison of the dark and illuminated current voltage curve of the apparatus of  FIG.  1    (having an ITO/PLZT/Pt structure) to two alternative structures (e.g., Al/PLZT/Pt and Pt/PLZT/Pt), in accordance with an illustrative embodiment. 
         FIG.  4 B  is a diagram showing the light-to-electricity conversion curve of  FIG.  3    (corresponding to the apparatus of  FIG.  1   ) conversion curves of the two alternative structures (e.g., Al/PLZT/Pt and Pt/PLZT/Pt), in accordance with an illustrative embodiment. 
         FIGS.  5 A and  5 B  are diagrams of an apparatus thin film that includes a bottom metal and a top electrode/ITO layer that is formed with a seed layer of lead titanate, in accordance with an illustrative embodiment. 
         FIGS.  6 ,  7 ,  8 ,  9 ,  10 ,  11    each illustrates the apparatus (e.g., for use as a solar cell, a UV sensor, a UV index sensor, etc.) with a ferroelectric thin film such as Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3  (PLZT) thin film paired with a bottom metal and top transparent conductive oxide, that forms a capacitor structure with enhanced photocurrent and power conversion efficiency, in accordance with various illustrative embodiment. 
         FIG.  12    is a diagram showing an example structure of the electrode of the apparatus of  FIG.  11   , e.g., for use in a UV sensor, in accordance with an illustrative embodiment. 
         FIGS.  13 A and  13 B  each show cross-sectional views of one or more capacitor structures formed from top electrodes across the thin film layer (e.g., as shown, as applicable, in  7 ,  9 ,  10 , and  11 ), in accordance with an illustrative embodiment. 
         FIG.  14    is a diagram showing a current-voltage characteristic of the apparatus of  FIG.  11   , in particular, the dark and illuminated current voltage curve, in accordance with an illustrative embodiment. 
         FIG.  15    is a diagram showing a photocurrent response curve as a function of wavelength. 
         FIG.  16    is a diagram showing a process of fabricating the apparatus, e.g., of  FIG.  1    (as a solar cell, UV sensor, and etc.), in accordance with an illustrative embodiment. 
         FIG.  17 A  is a diagram showing a fabrication method for the thin film layer, in accordance with an illustrative embodiment. 
         FIG.  17 B  is a diagram showing a fabrication method for the thin film layer with a seed layer, in accordance with an illustrative embodiment. 
         FIG.  18    is a schematic of an example UV indexing sensor system (e.g., for skin-care application) that uses the apparatus, in accordance with an illustrative embodiment. 
         FIG.  19    is a table showing example UV index levels from the measured output of the ferroelectric UV sensor, in accordance with an illustrative embodiment. 
         FIG.  20    is a diagram illustrating an example exposure risk level based on the measured output of the ferroelectric UV sensor, in accordance with an illustrative embodiment. 
         FIG.  21    shows an example application of a UV index sensor, in accordance with an illustrative embodiment. 
         FIG.  22    is a diagram of an example system according to the present disclosure that monitors and/or tracks direct ultraviolet B (UVB) radiation exposure by a person to provide real-time Vitamin-D dose production information, in accordance with an illustrative embodiment. 
         FIG.  23    shows a table that includes different Vitamin D requirements or recommendations for a person based on the person&#39;s age, in accordance with an illustrative embodiment. 
         FIG.  24 A  shows a table that includes different exposure time requirements or recommendations to meet a daily dosage requirement in which the exposure time is varied based on the person&#39;s exposed body area and/or the persons&#39; skin type or sensitivity, in accordance with an illustrative embodiment. 
         FIG.  24 B  shows a table of example skin type and sensitivity, in accordance with an illustrative embodiment. 
         FIG.  25    shows a table that includes different calculated UVB dosage determined based on different values of exposure time to UVB radiation and on different values of UVB radiation intensity, in accordance with an illustrative embodiment. 
         FIG.  26    is a screenshot of an example graphical user interface of the exemplary system to track and monitor Vitamin D dosage production, in accordance with an illustrative embodiment. 
         FIG.  27    shows an example computing device which can be used to perform operations associated with the processes described herein, in accordance with an illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Before the present methods and systems are disclosed and described, it is to be understood that the methods and systems are not limited to specific methods, specific components, or to particular compositions. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 
     As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. 
     Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises,” means “including but not limited to,” and is not intended to exclude, for example, other additives, components, integers or steps. “Exemplary” means “an example of” and is not intended to convey an indication of a preferred or ideal embodiment. “Such as” is not used in a restrictive sense, but for explanatory purposes. Disclosed are components that may be used to perform the disclosed methods and systems. These and other components are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these components are disclosed that while specific reference of each various individual and collective combinations and permutation of these may not be explicitly disclosed, each is specifically contemplated and described herein, for all methods and systems. This applies to all aspects of this application including, but not limited to, steps in disclosed methods. Thus, if there are a variety of additional steps that may be performed it is understood that each of these additional steps may be performed with any specific embodiment or combination of embodiments of the disclosed methods. 
       FIG.  1    illustrates an apparatus  100  (e.g., for use as a solar cell, a UV sensor, a UV index sensor, etc.) with ferroelectric-based photodiode (e.g., Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3  (PLZT)) thin film paired with a bottom metal and top transparent conductive oxide, that forms a capacitor structure with enhanced photocurrent and power conversion efficiency, in accordance with an illustrative embodiment. 
     As shown in  FIG.  1   , the apparatus  100  includes a substrate  102  (shown as “TiO 2 /SiO 2 /Si Substrate”  102 ), a bottom layer  104  (shown as “Pt (111) Bottom contact”  104 ), a thin film layer  106  (shown as “PLZT (210 nm)”  106 ) comprising a ferroelectric-based photodiode such as a lanthanum-doped lead zirconate titanate (PLZT) thin-film material (e.g., Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3 ), and an array of top electrodes  108  (shown as “ITO (Top contact)”  108 ). Each individual electrode of the array  108  is referenced herein as  110 . In some embodiments, the bottom layer  104  and the top electrodes  110  each forms back-to-back Schottky contacts with the thin film layer  106 . The Schottky barriers formed at the interfaces between each of the thin film layer  106  and the electrodes (e.g.,  104 ,  110 ) create polarization independent interface electric field. 
     In some embodiments, the thin film layer  106  is formed of a ferroelectric-based photodiode comprising a PbZr 1-x Ti x O 3 -based device or a (Pb 1-y La y )(Zr x Ti 1-x )O 3 -based device, where 0≤x≤1 (such as 0.5) and 0≤y≤0.1 (such as 0.05). In some embodiments, the ferroelectric-based photodiode comprises a Lanthanum doped lead zirconate titanate (PLZT) thin-film such as Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  as noted above. 
     Referring still to  FIG.  1   , the bottom layer  104  is coupled to the substrate  102  and forms an electrode, in some embodiments, that comprises a material that includes, in part, platinum. In some embodiments, and as shown in  FIG.  1   , the bottom layer  104  is comprised of a platinum (111) structure. Other platinum-based alloys and structure and composition may be used. The substrate  102 , as shown in the example of  FIG.  1   , may be a TiO 2 , SiO 2 , or Si. Other substrate material such as Nb:SrTiO 3 , Quartz, among others, can be used. 
     Referring still to  FIG.  1   , the thin film layer  106  is coupled to, and substantially spans, the bottom layer  104 . The thin film layer  106  comprises predominantly, ferroelectric-based photodiode such as a lanthanum-doped lead zirconate titanate thin-film material, e.g., Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  or other ferroelectric-based photodiode as described herein. Description of Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  thin films, and like films, can be found, for example, in Harshan et al., “Influence of work-function of top electrodes on the photovoltaic characteristics of Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  thin film capacitors”, Applied Physics Letters 100.17 (2012); Nampoori, “Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  Thin Films For Photovoltaic Applications,” arXiv preprint arXiv:1304.1611 (2013); Batra, Vaishali et al., “Optical constants and band gap determination of Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  thin films using spectroscopic ellipsometry and UV-visible spectroscopy,” Optical Materials 49, pp. 123-128 (2015); and Harshan et al., “Photovoltaic and Ferroelectric Properties of Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  Thin Films under Dark and Illuminated Conditions,” Ferroelectrics 470.1, pp. 99-106 (2014), each of which is incorporated by reference in its entirety. 
     The PV effects of the thin film layer  106  can be tuned, for example, by controlling the polarization in ferroelectric materials. When exposed to sunlight, ferroelectric material in a given device absorbs photons, which can generate charge carriers, also called photogenerated carriers. These photogenerated carriers are often separated by in-built electric field present in the photoactive ferroelectric layer and can cause the flow of electric current or photocurrent. Because this electric field can be present throughout the bulk region of the material—that is, the PV effect in such materials is a bulk phenomenon, which is limited to depletion region in the semiconductor based devices—this phenomenon of photons absorption and separation of charge carriers can generate photovoltage between a top and a bottom electrode. This photovoltage value in ferroelectric material devices is not limited to bandgap of the material, the value can exceed higher than bandgap which is not true for semiconductor based devices. 
     Referring still to  FIG.  1   , the array of top electrodes  108  collectively forms a transparent oxide (e.g., indium tin oxide—ITO) top layer over the thin film layer  106  so as to form a plurality of capacitors. ITO has desirable transparent nature and high electrical conductivity, which is demonstrated to increase the transport mechanism in the apparatus  100  of  FIG.  1   . In some embodiments, the capacitor structure is formed between one or more top electrodes  110  and the bottom layer  104  across the thin film layer  106 . In other embodiments, the capacitor structure is formed among electrodes of the array of top electrodes across the thin film layer  106 . The electrodes  108 , in some embodiments, is made of a metal or a metal-based alloy that at least includes Pt, Au, Al, Ag, Ti, Cr, and/or Ir. In some embodiments, the electrodes  108  is a transparent conducting oxides (e.g., such as In 2 O 3 , In doped Tin oxide (In—SnO 2  or ITO)), or combinations thereof. Other electrode material can be used. 
       FIG.  2    is a diagram showing a current-voltage characteristic of the apparatus  100  of  FIG.  1   , in particular, the dark and illuminated current voltage curve, in accordance with an illustrative embodiment.  FIG.  3    is a diagram showing a light-to-electricity conversion curve of voltage corresponding to the current voltage curve of  FIG.  2   , in accordance with an illustrative embodiment. 
       FIG.  4 A  is a diagram showing a comparison of the dark and illuminated current voltage curve of the apparatus  100  of  FIG.  1    (having an ITO/PLZT/Pt structure) to two alternative structures (e.g., Al/PLZT/Pt and Pt/PLZT/Pt), in accordance with an illustrative embodiment.  FIG.  4 B  is a diagram showing the light-to-electricity conversion curve of  FIG.  3    (corresponding to the apparatus  100  of  FIG.  1   ) conversion curves of the two alternative structures (e.g., Al/PLZT/Pt and Pt/PLZT/Pt), in accordance with an illustrative embodiment. Notably, as shown in  FIG.  4 B , the apparatus  100  of  FIG.  1    has a demonstrated conversion efficiency about 3 orders of magnitude higher than that of a Pt/PLZT/Pt structure and about 2 orders of magnitude higher than that of an A/PLZT/Pt structure. Table 1 illustrates comparison results, per  FIGS.  4 A and  4 B , of the apparatus  100  of  FIG.  1    and the two alternative structures (e.g., Al/PLZT/Pt and Pt/PLZT/Pt) with respect to open circuit voltage V oc  (in volts), photocurrent density J sc  (in Amp per cm 2 ), and conversion efficiency (in percent). 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Capacitors 
                 V oc  (V) 
                 J sc  (A/cm 2 ) 
                 Efficiency (%) 
               
               
                   
               
             
            
               
                 Pt/PLZT/Pt 
                 0.17 
                 −6.4 × 10 −7   
                 ~6.31 × 10 −5   
               
               
                 Al/PLZT/Pt 
                 0.37 
                 −3.6 × 10 −6   
                 ~7.08 × 10 −4   
               
               
                 ITO/PLZT/Pt 
                 1.31 
                 −6.8 × 10 −5   
                  ~4.5 × 10 −2   
               
               
                   
               
            
           
         
       
     
       FIGS.  5 A and  5 B  are diagrams of an apparatus thin film that includes a bottom metal and a top electrode/ITO layer (that forms a capacitor structure with enhanced photocurrent and power conversion efficiency) and formed on a seed layer  502  of lead titanate, in accordance with an illustrative embodiment. 
     In some embodiments, the seed layer  502  of lead titanate comprises Pb x TiO 3 , where x=1.0, 1.05, 1.1, or 1.2. In other embodiments, the seed layer  502  includes PbO, PbZrO 3 , LaNiO 3 , and/or TiO x  (x≤2). In yet other embodiments, the seed layer  502  includes SrTiO 3  and/or SrRuO 3 . In yet other embodiments, the seed layer  502  includes La x Sr 1-x CoO 3 , where 0&lt;x&lt;1 and/or La x Sr 1-x MnO 3  where 0&lt;x&lt;1. 
     In some embodiments, the seed layer  502  of lead titanate is configured to promote (001) orientation and suppress (110) orientation in the PLZT thin film layer  106 . Such orientation of the PLZT thin film layer  106 , e.g., as produced by inclusion of the seed layer, enhances the magnitude of both short circuit current and open circuit voltage of the capacitor structure that is formed, e.g., in an electrode/PLZT/Pt structure in which the electrode is a metal or a metal-based alloy that at least includes Pt, Au, Al, Ag, Ti, Cr, Ir (see  FIG.  5 A ). In some embodiments, electrode/PLZT/Pt structure is formed with an ITO top layer, such as In 2 O 3 , In-doped Tin oxide (In—SnO 2  or ITO) (see  FIG.  5 B ). As noted above, other materials can be used. 
       FIGS.  6 ,  7 ,  8 ,  9 ,  10 ,  11    each illustrates the apparatus  100  (e.g., for use as a solar cell, a UV sensor, a UV index sensor, etc.) with a ferroelectric thin film such as a Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  PLZT thin film paired with a bottom metal and top transparent conductive oxide, that forms a capacitor structure with enhanced photocurrent and power conversion efficiency, in accordance with various illustrative embodiment. It is noted that the structures shown in  FIGS.  6 ,  7 ,  8 ,  9 ,  10 ,  11    can be applied to the apparatus  100  of  FIG.  1   ,  FIG.  5 A  or  FIG.  5 B , as well as in combination with one another. 
     In  FIG.  6   , the capacitor structure  600  is formed between a top electrode  110  of the array  108  and a portion of the bottom layer  104  across a corresponding portion of the ferroelectric thin film such as the Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  thin film layer  106 . In some embodiments, each layer (e.g.,  104 ,  106 , 108 ) are parallel to each other and/or deposited on over one other. 
     In  FIG.  7   , the capacitor structure (e.g., shown by polarity  600 ) is formed (lateral configuration) between two top electrodes (shown as  110   a  and  110   b ) of the array  108  across a corresponding portion of the ferroelectric thin film such as the Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3  thin film layer  106 . In some embodiments, electrodes (e.g.,  110 ), which are separated by a finite distance, are deposited on the surface of the thin film layer  106 . 
     In  FIG.  8   , the capacitor structure (e.g., shown by polarity  600 ) is formed (as a vertical configuration with plurality of electrodes connected in series, parallel, or combination thereof) between a plurality of top electrodes  802  serially connected to one another, via a connection member  804 , and a corresponding portion of the bottom layer  104  (generally corresponding to the area of the plurality of top electrodes  802 ) across the a corresponding portion of the ferroelectric thin film such as the Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3  thin film layer  106  (generally corresponding to the area of the plurality of top electrodes  802 ). This parallel plate electrode configuration provides an increased surface area over that of a single electrode. 
     In  FIGS.  9  and  10   , the capacitor structure (e.g., shown by polarity  600  as a lateral configuration with a plurality of electrodes connected in series, parallel, or combination thereof) is formed between a first plurality of top electrodes  902  serially connected to one another and a second plurality of top electrodes  904  across the a corresponding portion of the ferroelectric thin film such as the Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3  thin film layer  106 . In some embodiments, the electrodes structure (e.g.,  902 ,  904 ) are symmetric to one another. In addition to being serially connected, the plurality of top electrodes  902  and  904  may be configured as a parallel circuit or a combination of serial and parallel circuit. Without wishing to be bound to a particular theory, array of electrodes can provide a means of increasing the effective exposure area of the device so as to increase light absorption and in turn can result in higher photovoltaic parameters. 
     Although shown in  FIGS.  6 - 10    as circular electrodes, the top electrodes  110  can be configured in any closed, coiled, patterned, or opened shapes, including oval, square, rectangle, rhombus, and etc. 
     In  FIG.  11   , the capacitor structure (e.g., shown by polarity  600 ) is formed between a first top electrode  1102  and a second top electrode  1104 , which collectively forms a structure that forms gaps thereamong so as to form the plurality of capacitors. In some embodiments, the structure is formed on a plane. In other embodiments, the structure is formed on more than one planes. 
     Ultraviolet Sensor Using a Ferroelectric Thin Film 
       FIG.  12    is a diagram showing an example structure of electrode of the apparatus  100  of  FIG.  11   , e.g., for use in a UV sensor, in accordance with an illustrative embodiment. 
     As shown in  FIG.  12   , the structure may be defined by geometric parameters, including, as those shown, a device-width parameter w ( 1202 ), a lead width parameter w L  ( 1204 ), a device length parameter L ( 1206 ), a lead length parameter L L  ( 1208 ), a sensor grid length parameter L S  ( 1210 ), a finger width parameter b ( 1212 ), a comb finger length parameter a ( 1214 ), a finger-overlap length parameter a o  ( 1216 ), a lead-finger gap parameter g ( 1218 ), a comb-pitch parameter p ( 1220 ), and a number of finger on each comb parameter N. Other parameters, shapes, and structures may be formed. 
       FIGS.  13 A and  13 B  each show cross-sectional views of one or more capacitor structures formed from top electrodes across the thin film layer (e.g., as shown, as applicable, in  7 ,  9 ,  10 , and  11 ), in accordance with an illustrative embodiment. In  FIG.  13 A , the capacitor structure is formed over a distance g ( 1302 ) in a lateral configuration. In  FIG.  13 B , the capacitor structure is formed across a set of the interdigitated fingers (e.g., of  FIGS.  11  and  12   ). 
       FIG.  14    is a diagram showing a current-voltage characteristic of the apparatus  100  of  FIG.  11    in particular, the dark and illuminated current voltage curve, in accordance with an illustrative embodiment.  FIG.  15    is a diagram showing a photocurrent response curve as a function of wavelength. As shown in  FIG.  15   , the apparatus  100  is operable, and highly sensitive, over the UV wavelength ranges (e.g., “UV-A” at about 315 nm to about 400 nm wavelength; “UV-B” at about 280 nm to about 315 nm wavelength). A maximum photocurrent of about 14.5 nA is observed at about 350 nm. 
     Method of Fabrication 
       FIG.  16    is a diagram showing a process  1600  of fabricating the apparatus  100  of  FIG.  1    (as a solar cell, UV sensor, and etc.), in accordance with an illustrative embodiment. As shown in  FIG.  16   , an initial structure, in step  1602 , comprising the substrate  102 , the bottom layer  104 , and the thin film layer  106  is provided. In step  1604 , a layer of ITO ( 1606 ) is deposited to the initial structure  1602  to form an ITO layered structure. In step  1608 , a layer of photo-resist ( 1610 ) is applied to the ITO layer  1606 , and ion milling process is performed (in step  1611 ) to generate a pattern  1614  in the photo-resist layer ( 1610 ). In step  1616 , the exposed portion of the ITO layer  1606  is etched and then the photo-resist layer is removed. 
       FIG.  17 A  is a diagram showing a fabrication method  1700  for the thin film layer, in accordance with an illustrative embodiment. The method  1700  includes generating a PLZT solution, e.g., using a metal organic decomposition (MOD) method. Precursors including Pb and La acetates, Zr-propoxide, and Ti-butoxide are used with 2-Methoxyethanol solvent. The PLZT thin film is formed, for example, with a chemical solution deposition (CSD) method. Additional description of the fabrication method for the PLZT thin film is provided in Harshan et al., “Effect of Annealing on Ferroelectric Properties of Lanthanum Modified Lead Zirconate Titanate Thin Films,” Integrated Ferroelectrics, Vol. 130, pp. 73-83 (2011), which is incorporated by reference herein in its entirety. 
       FIG.  17 B  is a diagram showing a fabrication method  1702  for the thin film layer with inclusion of a seed layer, in accordance with an illustrative embodiment. The method is a modification to the chemical solution deposition method as described in relation to  FIG.  17 A , and further includes first spin coating (step  1704 ) the seed layer material, e.g., Pb x TiO 3 , onto the substrate (e.g., Pt/TiO 2 /SiO 2 /Si) and processing the seed layer prior to spin coating (step  1706 ) the PLZT solution on the formed seed layer material and processing the PLZT layer as, for example, described in relation to  FIG.  17 A . 
     Ferroelectric UV Indexing Sensor for Skin Care Application 
       FIG.  18    is a schematic of an example UV indexing sensor system  1800  (e.g., for skin-care application) that uses the apparatus  100 , in accordance with an illustrative embodiment. The system  1800  includes a ferroelectric UV sensor  1802  configured to output an electric current  1804  corresponding to a measured UV exposure. Notably, the ferroelectric UV sensor  1802  is sensitive to UV-A and UV-B (as well UV-C) (e.g., as shown in  FIG.  15   ). The output of the ferroelectric UV sensor  1802  is amplified and digitized. In  FIG.  18   , an amplifier circuit  1806  is shown along with an analog-to-digital conversion (ADC) circuit  1808 . The output of the ADC circuit  1808  is received by a microcontroller  1810  configured to process the digitized signal and present a UV index value on a display  1812  (shown as “LCD”  1812 ). Display  1812  includes OLED (organic light emitting display) panels, and the likes. Other types of processor or controller may be used. A processor can be microcontrollers, microprocessors, or logic circuits such as ASICs (Application Specific Integrated Circuit), CPLDs (Complex Programmable Logic Device), FPGA (Field Programmable Gate Array), or other programmable logic integrated circuits. In some embodiments, a processor is configured to execute instruction stored in a memory of the device. 
     In some embodiments, the current output flows over a sensing load to facilitate sensing as a voltage. 
     In some embodiments, the LCD is mounted to a wearable device such as a watch having a wrist strap, an attachable pin, a chain (e.g., as a necklace), a bracelet, or an anklet. In some embodiments, the system  1800  is embedded, or fastened, in an article of clothing (e.g., a shirt, a hat, sunglasses, spectacles etc.). 
     Referring still to  FIG.  18   , in some embodiments, the system  1800  includes a wireless transceiver  1814 . As shown in  FIG.  18   , in this example, the wireless transceiver  1814  is coupled to the electronic circuitry (e.g., microcontroller  1810 ) and is configured to transmit, over a communication channel, the generated index parameter to another computing device (not shown). In some embodiments, the transmission is over a near-field communication channel (e.g., Bluetooth, Wi-Fi, infrared, and the like) to facilitate presentation of the UV index data to a person, e.g., on a portable computing device and portable computing watch) or over a combination of near-field and far-field communication channel to store, e.g., in the cloud. A cloud-based application may send notification and alerts based on the measured UV index and/or corresponding exposure risk level. 
       FIG.  19    is a table showing example UV index levels from the measured output of the ferroelectric UV sensor  1802 , in accordance with an illustrative embodiment. As shown, the UV index levels may be tiered based on sensed output of the ferroelectric UV sensor  1802 . The UV index levels may include a first tier ( 1902 —having a UV index of 0-2.9), a second tier ( 1904 —having a UV index of 3-5.9), a third tier ( 1906 —having a UV index of 6-7.9), a fourth tier ( 1908 —having a UV index of 8.0-10.9) and a fifth tier ( 1910 —having a UV index of greater than 11). Each UV index tiers may be mapped to an exposure risk level. 
       FIG.  20    is a diagram illustrating an example exposure risk level based on the measured output of the ferroelectric UV sensor  1802 , in accordance with an illustrative embodiment. In  FIG.  20   , a UV index between about 0 and 2.9 is characterized as a low exposure risk ( 2002 ); a UV index between 3 and 5.9 is characterized as a moderate exposure risk ( 2004 ); a UV index between 6.0 and 7.9 is characterized as a high exposure risk ( 2006 ); a UV index between 8.0 and 10.9 is characterized as a very high exposure risk ( 2008 ); and a UV index higher than 11 is characterized as an extreme exposure risk ( 2010 ). Other UV index values and associated exposure risk levels may be used. 
     Referring still to  FIG.  20   , in some embodiments, the UV safety message is presented as icons having an associated meaning to the message (e.g., an icon  2012  indicating that eye protection is desired; an icon  2014  indicating that shading is desired; an icon  2016  indicating that protective clothing is desired; an icon  2018  indicating that sunscreen and the like is desired; an icon indicating a degree of sunscreen rating (e.g.,  2020   a ,  2020   b ,  2020   c ,  2020   d ) is desired; an icon  2022  indicating that shelter is desired; an icon  2024  indicating the additional head protection is desired, among others). Other types of messages maybe used. For example, in some embodiments, a UV safety message may be presented based on the measured UV index via the LCD or display. In some embodiments, the UV safety message may be presented as text (e.g., indicating whether eye protection may be desired, whether shading may be desired, whether protective clothing may be desired, whether sunscreen and the like may be desired, a degree of sunscreen rating may be desired, and whether shelter may be desired). In some embodiments, the UV safety alert is a generated as audio message. In some embodiments, the UV safety alert is selectable, via a user interface, by the user with regard to the type of notification presented, the format of the presentation, the means of the notification being provided or generated, among others. 
     In some embodiments, the processor, is configured, via instructions, to monitor the sensed UV sensor  1802  and to cause a reminder message to be transmitted to the user. The reminder message, in some embodiments, includes a remaining time for safe exposure. In some embodiments, when the safe exposure time is passed or approaching, the processor is configured, via the instructions, to provide a reminder and an alert to the user, e.g., to seek shading or additional protection. 
     In some embodiments, the processor is configured, via instructions, to interrogate a user for a skin type. Based on the information entered by the user, the processor, via the instructions, can cause a display of UV hazards according to skin type and sensitivity, e.g., so as to provide safe exposure time which will be dependent on skin type and present UV index. In some embodiments, the processor, via the instructions, can present via the display selectable option of selecting a format (icon, text or audio) to receive the message. 
       FIG.  21    shows an example application of a UV index sensor, in accordance with an illustrative embodiment. 
     Real Time UV Monitoring for Tracking and Maintaining Required Vitamin D Dosage 
     The section of the disclosure relates to the use of such sensors made from lanthanum-doped lead zirconate titanate (PLZT) thin-film-based system, among others, e.g., for use in the real-time monitoring of ultraviolet radiation exposure for health care applications, in particular ultraviolet B radiation, to track Vitamin D dosage. 
     It is noted that Vitamin D deficiency has become a global health problem—more than a billion people worldwide are reported to be deficient in Vitamin D. In the United States, approximately 85% of the people have been reported in some studies to have some form of Vitamin D deficiency. Vitamin D has a role of helping with the absorption of calcium in the human body, which is essential for bone health and the maintenance of the skeleton, and Vitamin D deficiency has been reported to be associated or linked with autoimmune diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), inflammatory bowel disease (IBD), multiple sclerosis (MS), type 1 diabetes (T1DM), among others. 
     Vitamin D can be formed endogenously when sunlight strikes the skin. One form of Vitamin D, Vitamin D3 (cholecalciferol), is synthesized in the skin by the reaction of 7-dehydrocholesterol with short-wave ultraviolet B (“UVB”) radiation present in sunlight. While direct exposure to sunlight can be beneficial to the treatment of Vitamin D deficiency, overexposure to UV radiations can be harmful in causing sun burn and can have chronic results associated with premature aging of the skin, suppression of the immune system, damage to the eyes, and skin cancer. 
     Treatment for Vitamin D deficiency often includes Vitamin D supplements that can be injected into the blood stream or taken orally. In severe cases of Vitamin D deficiency, blood tests are periodically conducted to monitor Vitamin D levels in the body. 
     Indeed, monitoring of direct ultraviolet B (UVB) radiation exposure by a person via a system having a sensor (such as Lanthanum doped lead zirconate titanate (PLZT) thin-film sensors or other ferroelectric-based sensors) sensitive to UVB radiation would beneficially provide current real-time dosage information associated with Vitamin D production by the person as well as real-time indication of safe exposure and/or harmful exposure to current UVB radiation conditions. 
       FIG.  22    is a diagram of an example system  2200  according to the present disclosure that monitors and/or tracks direct ultraviolet B (UVB) radiation exposure by a person to provide real-time Vitamin-D dose production information, in accordance with an illustrative embodiment. The system  2200  includes an UVB sensor  2202  sensitive to UVB radiation, such as a ferroelectric-based photodiode, e.g., as those described herein. In some embodiments, the UVB sensor  2202  is based on the UV sensor  1802 , as described for example in relation to  FIG.  18   , or the apparatus  100  as described for example in relation to  FIGS.  1 - 17   , among others. In some embodiments, the ferroelectric-based photodiode comprises a PbZr 1-x Ti x O 3 -based device or a (Pb 1-y La y )(Zr x Ti 1-x )O 3 -based device, where 0≤x≤1 (such as 0.5) and 0≤y≤0.1 (such as 0.05). In some embodiments, the ferroelectric-based photodiode comprises a Lanthanum doped lead zirconate titanate (PLZT) thin-film such as Pb 0.95 La 0.5 Zr 0.54 Ti 0.46 O 3 . 
     Short-wave ultraviolet radiation (UVB radiation) may exhibit different changes in intensity as compared to long-wave ultraviolet radiation (UVA radiation) due to different environment conditions, for example, that are caused by different cloud coverage, weather condition, and outdoor condition and/or structures. Indeed, measurement of UVB radiation via sensors sensitive to this range of the electromagnetic spectrum will provide a more accurate and direct assessment and/or estimate of endogenous production of Vitamin D as compared to the use of sensors that measure UVA radiation. 
     In other embodiments, an UVA sensor is used to provide measurements of UVA radiation levels to which estimates of UVB radiation levels can be derived therefrom. 
     As shown in  FIG.  22   , in some embodiments, the UVB sensor  2202  is coupled to short-wave ultraviolet-transparent filter  2204  configured to allow UVB radiation to pass through. The ultraviolet-transparent filter  2204  can be glass, crystals, or any other material that does not substantially attenuate or substantially block the transmission of UVB radiation. The ultraviolet-transparent filter  2204  can be integrated into the UVB sensor  2202 , or it can be a component that is separately integrated into a system housing  2206  having the UVB sensor  2202 . In some embodiments, the ultraviolet-transparent filter  2204  is configured to substantially block long wave ultraviolet radiation (i.e., UVA radiation). 
     In some embodiments, the apparatus includes a substrate (e.g., a TiO 2 /SiO 2 /Si Substrate), a bottom layer (e.g., Platinum bottom contact), a thin film layer of PLZT comprising a Lanthanum doped lead zirconate titanate (PLZT) thin-film material (e.g., Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3 ), and an array of top electrodes comprising an ITO top contact. In some embodiments, the bottom layer and the top electrodes each forms back-to-back Schottky contacts with the thin film layer. The Schottky barriers formed at the interfaces between each of the thin film layer and the electrodes create polarization independent interface electric field. Other ferroelectric-based photodiodes can be used including those discussed herein. 
     The UVB sensor  2202  is further coupled to a signal processing stage and analog-to-digital conversion stage (collectively shown as  2208 ). In some embodiments, when the UVB sensor  2202  is a photodiode that outputs electric current levels corresponding to the intensity of UVB radiation exposure by the sensor  2202 , the signal processing stage includes a current-to-voltage conversion circuit  2210  (e.g., a transimpedance amplifier circuit, a resistive network, etc.) that converts the current output of the UVB sensor  2202  to a voltage output. The signal processing stage includes, in some embodiments, a voltage amplifier  2212  configured to amplify the voltage prior to analog-to-digital conversion. In  FIG.  22   , the voltage amplifier  2212  is coupled to a microcontroller  2214  having a processor and an analog-to-digital conversion input. An example of the microcontroller  2214  that can be used is the MSP430 family microcontroller manufactured by Texas Instrument (Dallas, Tex.). The MSP430 family microcontroller is a self-contained low-cost and low-power microcontroller having integrated ferroelectric-based RAM and integrated static RAM (collectively referred to as memory), integrated sigma delta analog-to-digital converter, general purpose IOs, bus IOs, and/or other peripheral components. 
     Other microcontrollers and circuitries for signal processing and analog-to-digital conversion can be used. In some embodiments, the various subcomponents described herein can be implemented in field-programmable gate arrays (FPGAs), complex programmable logic devices (CPLDs), application-specific integrated circuits (ASICs), and/or other custom digital or mixed-signal circuitries. 
     To estimate the endogenous Vitamin D production or the estimated remaining amount of Vitamin D dosage production, the processor (e.g., of the microcontroller  2214 ) is configured, via instructions, to accumulate the measured values of the UVB sensor  2202  and to store that accumulated value in the system&#39;s memory. The measured values of the UVB sensor  2202 , in some embodiments, can be stored as a measured UV intensity or a value associated therewith. The accumulation may be performed, in some embodiments, by updating a counter value (i.e., a total measured UV intensity) using each measured UV intensity sampled from the signal of UVB sensor  2202  as the measured UV intensity is sampled. In other embodiments, each measured intensity value is stored in memory and then accumulated when the accumulated information is requested or triggered to be displayed or notified to the user. The measurement can be sampled at a frequency of about 1 Hz or more. In some embodiments, the sampling frequency is less than 1 Hz (e.g., 0.2 Hz, 0.25 Hz, 0.5 Hz, 0.75 Hz, etc.). In some embodiments, the sampling frequency is about 10 Hz or more. In some embodiments, the sampling frequency is about 100 Hz or more. 
     In some embodiments, the raw measured UV intensity values (e.g., the raw ADC values) can be stored. In some embodiments, the raw measured UV intensity can be converted to other units (energy, measured current output of the sensor, measured voltage output of the current-to-voltage converter) for storage. 
     Referring still to  FIG.  22   , the system  2200  includes, in some embodiments, a display  2218  (shown as an OLED (organic light-emitting diode) display  2218 ) configured to provide a graphical indication of an estimated dosage value ( 2220 ) of Vitamin D obtained over a current day or over a current week and/or an estimated remaining amount value of Vitamin D dosage required or recommended for the current day or week. The presented information can be in exposure time (e.g., seconds, minutes, fractions of hours, hours, etc.) or in dosage produced (e.g., in IU/day or IU/week, mcg/day, mcg/week, etc.). In some embodiments, the presented units and information relating to estimated dosage value or estimated remaining amount value of Vitamin D dosage needed can be selectable by the user. The graphical indication can be a numerical value or an icon (or widget) having a representation of a gauge (e.g., a dial or a level, etc.). The graphical indication may present values of a parameter normalized to a pre-defined goal (i.e., determine required or recommended Vitamin D dosage). 
     Referring still to  FIG.  22   , in some embodiments, the system is configured to receive one or more inputs  2222  from the user to determine a required or recommended Vitamin D dosage for a given day or week.  FIGS.  23  and  24    each shows a table of required or recommended Vitamin D dosage (for a given time period) for a person in which the required dosage can vary based on the person&#39;s age, the person&#39;s skin type or sensitivity, and the person&#39;s exposed body region or parts. 
     Specifically,  FIG.  23    shows a table  2300  that includes different Vitamin D requirements or recommendations for a person based on the person&#39;s age, in accordance with an illustrative embodiment. As shown in  FIG.  23   , the Vitamin D requirements or recommendations (shown as  2302 ) for a person is generally the same for a male or for a female between the age of 6 months and 70 years. Newborns (e.g., 0-6 months old) (shown with  2304 ), people over 70 years old (shown with  2306 ), and pregnant women and new mothers (shown with  2308 ) may have different Vitamin D needs. 
     In some embodiments, the system is configured to receive, from the user, an input associated with the age or condition of the user. In some embodiments, the system is configured to prompt the user to answer questions associated with their age or condition (e.g., whether they are older than 70 years and/or whether they are pregnant or breast-feeding, or whether they are diagnosed as being Vitamin D deficient). Indeed, when the user selects these conditions, calculations for vitamin D requirements are adjusted accordingly. For example, if diagnosed with being Vitamin D deficient, a person would need more IU/day to make up the deficient levels. 
     In some embodiments, the system is configured to receive, from the user, a direct input associated with Vitamin D dosage requirement (e.g., daily requirement or weekly requirement). 
       FIG.  24 A  shows a table  2400  that includes different exposure time requirements or recommendations to meet a daily dosage requirement in which the exposure time is varied based on the person&#39;s exposed body area and/or the persons&#39; skin type or sensitivity, in accordance with an illustrative embodiment.  FIG.  24 B  shows a table of example skin type and sensitivity, in accordance with an illustrative embodiment. 
     As shown in  FIG.  24 A , the exposure time for a person requiring 400 IU/day dosage of Vitamin D (shown in columns  2402   a    2402   b ) and for a person requiring 1000 IU/day dosage of Vitamin D (shown in columns  2404   a ,  2404   b ) can vary based on skin type ( 2406   a  and  2406   b ), or exposed body areas (shown in column  2406  based on percentage and shown in column  2408  based on corresponding set of exposed body areas). A look-up-table may be stored with similar information to that of table  2400 , e.g., for the different types of skin types or sensitivity, for different dosage requirement, and for different exposed body area. The information can be stored in memory in other structure. 
     In some embodiments, multiple sets of exposure time information can be stored in the look-up-table or memory which each set include recommended or required exposure time for each of the different skin types or sensitivity. In this example, shown in  FIGS.  24 A and  24 B , the skin type and sensitivity is segmented into 6 skin types, including skin type “1”, skin type “2” (shown in  FIG.  24 A ), skin type “3”, skin type “4”, skin type “5” (shown in  FIG.  24 A ), and skin type “6”, in which each skin type has an associated pigment coloration. Other levels for skin types or sensitivity can be used. 
     Further description of recommended or required exposure time for each of the different skin types or sensitivity is provided in O. Engelsen, “The Relationship between Ultraviolet Radiation Exposure and Vitamin D Status,” Nutrients 2010, Vol 2(5), pp. 482-495 and Webb et al., “Ultraviolet exposure scenarios: risks of erythema from recommendations on cutaneous vitamin D synthesis,” Adv. Exp. Med. Biol. Vol. 624, pp. 72-85 (2008), each of which is incorporated by reference herein in its entirety. 
     In some embodiments, a single set of exposure time information is stored along with scaling multipliers for each of the respective skin type or sensitivity. In some embodiments, the scaling multipliers can be stored as a pre-defined transfer function. To this end, the exposure time for a person with a given skin type or sensitivity can be determined or generated by multiplying the single set of exposure time information with a scaling multiplier corresponding to a selected skin type or sensitivity. 
     To provide an accurate exposure time estimates for the user, in some embodiments, the system is configured to receive, from the user, an input associated with the person&#39;s skin type or sensitivity. In some embodiments, the input can be received in a configuration pane of a graphical user interface of the system. In other embodiments, the input can be received in a prompted set of questions presented to the user during a setup sequence. In other embodiments, the input can be received in a website or user portal to which the input is then communicatively provided, e.g., over a network, from a server operatively coupled to the website or user portal to the system. In some embodiments, different skin colors can be presented to the user to aid the user in the selection of the user&#39;s skin type or sensitivity. 
     In some embodiments, the system is configured to estimate a value for the person&#39;s skin type or sensitivity, for example, based on an assessed skin fairness, assessed skin darkness, and/or assessed skin color tone as determined from a person photo or image. In some embodiments, the system is configured to receive an image from the user or to capture an image of the user and then using the received images to determine the skin type or sensitivity of the user for the purpose of determining required or recommended exposure time. 
     Referring still to  FIG.  24 A , the table  2400  includes exposure time for a person requiring 400 IU/day dosage of Vitamin D (shown in columns  2402   a ,  2402   b ) and for a person requiring 1000 IU/day dosage of Vitamin D (shown in columns  2404   a ,  2404   b ) in which the exposure time varies based on exposed body areas (shown in columns  2406  and  2408 ). 
     In some embodiments, the system is configured to receive an input from the user relating body regions or parts of the user that are, or would be, exposed to direct sunlight. As shown in column  2408 , exposed body area can be segmented, for example, based on the face, the neck region, the hands, the arms, and the legs. Other body region can include the torso. 
     In some embodiments, a set of exposure time can be stored for each set of body part combination, for example, as shown in  FIG.  24 A . In other embodiments, a scaling value (e.g., a multiplier value) can be stored for each body region or part to which an aggregated exposed body area value can be determined from such scaling values and associated selection by the user. The aggregated exposed body value (e.g., in percentage) can be used to determine a required or recommended exposure time. 
     In some embodiments, the system can determine the user exposed body regions or parts based on one or more user&#39;s inputs associated with clothing. For example, the system can estimate that the face is exposed or not exposed based on an input from the user associated with whether the user is wearing a hat. The system can estimate that the arm is exposed or not exposed based on an input from the user associated with whether the user is wearing a long-sleeve or a short-sleeve upper body garment. The system can estimate that the legs are exposed or not exposed based on an input from the user associated with whether the user is wearing a long or a short lower body garment. In some embodiments, the system can present, e.g., via a display and/or user interface, a set of selectable tiers to the user associated with each combination of exposed body region or parts. In some embodiments, the system can present, e.g., via the display and/or user interface, a set of selectable exposed body regions or parts. In some embodiments, the system can estimate a set of exposed or not exposed body regions or parts based on assessed environment conditions, e.g., temperature, humidity, and weather conditions. The estimate may be presented to the user with a set of default values for the user to accept and/or to adjust. 
     In yet another embodiment, the system can determine a required or recommended exposure time without consideration of exposed or unexposed body areas. In some embodiments, an average exposed area is used. In other embodiments, a minimal value of the exposed or unexposed body areas is used to which the system can monitor or track UVB exposure for the user with respect to over-conservative requirement or recommendation of UVB exposure. This requirement can be adjusted based on seasonality information. 
     Referring back to  FIG.  22   , and as discussed in relation to  FIG.  22   , the system is configured to estimate and present a dosage value ( 2220 ) of Vitamin D obtained over a current day or over a current week and/or an estimated remaining amount value of Vitamin D dosage required or recommended for the current day or week. In some embodiments, to estimate a current dosage value ( 2220 ) of Vitamin D obtained for the day, the system maintains a counter of UVB dosage (D obtained ). In some embodiments, the UVB dosage can be determined by Equation 1.
 
 D   obtained =UVB intensity value×exposure time  (Equation 1)
 
in which D obtained  is in units of milliWatt-second/cm 2  (or Joules/cm 2 ); UVB intensity value is expressed in units of mW/cm 2 , and the exposure time is in units of seconds.
 
     The estimated dosage value ( 2220 ) of Vitamin D obtained over a current day or over a current week can be stored, in some embodiments, as a time-series dataset as a historical profile for the user. 
       FIG.  25    shows a table  2500  that includes different calculated UVB dosage determined based on different values of exposure time to UVB radiation and on different values of UVB radiation intensity, in accordance with an illustrative embodiment. Specifically, table  2500  shows calculated UVB dosage, in Joules per cm 2  based on measured UVB radiation intensity of about 2 mW/cm 2  ( 2502 ); about 10 mW/cm 2  ( 2504 ); about 12 mW/cm 2  ( 2506 ); about 15 mW/cm 2  ( 2508 ); and about 20 mW/cm 2  ( 2510 ). 
     In some embodiments, the system can determine the estimated remaining amount value of Vitamin D dosage (D remaining ) required or recommended for the current day based on Equation 2.
 
 D   remaining   =D   required −(Σ V   raw   *T   s )  (Equation 2)
 
in which D remaining  is the estimated remaining amount of required or recommended UVB dosage for the current day expressed in seconds, D required  is the required or recommended UVB dosage expressed in Joules/cm 2 , V raw  is the measured input of the sensor expressed in Watt/cm 2 , and T s  is the sampling time expressed in seconds. Other units and unit scales can be used.
 
     Referring back to  FIG.  22   , the system in some embodiments is configured to further provide indication  2226  of estimated remaining amount of required or recommended UVB dosage for the current week. In some embodiments, a second counter is maintained for an estimated cumulated UVB dosage produced for the week. The required or recommended UVB dosage for the current week can be determined based on the required or recommended UVB dosage for the current day. 
     Referring back to  FIG.  22   , the system in some embodiments is configured to further provide indication  2224  of a current safe exposure to the direct sunlight or indicate a current harmful exposure to the direct sunlight. In some embodiments, the indication is a graphical output, via the display  2218 , of a graphical icon indicating safe or unsafe conditions. The determination of current safe exposure or current harmful exposure, in some embodiments, is based on the current measured UVB intensity. For example, in some embodiments, the processor is configured to compare the current measured UVB intensity to a pre-defined threshold for safe exposure or a pre-defined threshold for unsafe exposure. In some embodiments, the pre-defined threshold for safe exposure or a pre-defined threshold can be fixed or it can vary based on factors such as the user&#39;s skin type or sensitivity. 
     In some embodiments, the system generates a current UV exposure index by comparing (e.g., via the processor or via digital circuitries) a parameter value derived from a last set of data values (e.g., one or more recently obtained data values, including or not including the last data value) of the plurality of data values received by the processor from the sensor to one or more UV threshold values, at least one of the one or more UV threshold values is associated with the current safe exposure to the direct sunlight or the current harmful exposure to the direct sunlight. In other embodiments, the system generates the current UV exposure index by comparing (e.g., via analog circuitries) a currently acquired signal of the sensor to one or more UV threshold signal levels, wherein at least one of the one or more UV threshold signal levels is associated with the current safe exposure to the direct sunlight or the current harmful exposure to the direct sunlight. 
     In some embodiments, the indication  2224  is an auditory alert or a vibratory alert that is associated with the current harmful exposure to the direct sunlight. 
     To this end, the exemplary system can provide information about a person&#39;s vitamin D dosage obtained from the sun exposure, keep a track of daily dosage, and warn the user when it is not safe to be exposed to the sun. The system can be used to bring awareness to the safe or recommended exposure time (for a given season, weather pattern, and geographic location) and a duration to UV radiations (specifically UVB radiation). 
     The system can help a person in naturally maintaining vitamin D levels via endogenous Vitamin D production and minimize the risk and likelihood of harmful effects from such exposure such as burns, activation of cancer cells, etc. In some embodiments, the system is used to augment or replace oral vitamin D dosage as a way to treat Vitamin D deficiency. In some embodiments, the system is used to help reduce the periodicity of monitoring Vitamin D levels in the body via blood tests. 
     Referring back to  FIG.  22   , the system can be configured as a wearable device or a hand-held device (such as smart-phone or a standalone device). In some embodiments, the system  2200  is a component of, or a set of components in, a mobile electronic device. In other embodiments, the system  2200  is integrated or can operate with a smartphone or wearable device having a form of a watch, a hat, a headpiece, a neck piece, a neck band, a bracelet, a ring, an eye piece, an arm band (e.g., as part of a pendant, bracelet, clip, cocktail ring, fit bit, smart watch, etc. or be embedded in garments such as a hat, shirt, etc.) 
     In some embodiments, the system  2200  includes a wireless transceiver, which can be coupled to the processor and is configured to transmit, over a communication channel, to another computing device (not shown), the produced Vitamin D dosage or a parameter derived therefrom and/or a remaining exposure time to meet the required or recommended exposure time. In some embodiments, the transmission is over a near-field communication channel (e.g., Bluetooth, Wi-Fi, infrared, and the like) to facilitate presentation of the produced Vitamin D dosage or a parameter derived therefrom and/or a remaining exposure time to meet the required or recommended exposure time to the person, e.g., on a portable computing device and portable computing watch) or over a combination of near-field and far-field communication channel to store, e.g., in the cloud. A cloud-based application may send notification and alerts based on the measured UV index and/or corresponding exposure risk level and produced Vitamin D dosage. 
     Example Experimental Test System for Real Time UV Monitoring of Required Vitamin D Dosage 
       FIG.  26    is a screenshot of an example graphical user interface  2600  of the exemplary system  2200  to track and monitor Vitamin D dosage production as described herein, in accordance with an illustrative embodiment. 
     As shown in  FIG.  26   , the graphical user interface  2600  includes a first graphical input  2602  for the user to provide a selection of a skin type, a second graphical input  2604  for the user to provide a selection of skin sensitivity, a third graphical input  2606  for the user to provide the user&#39;s age, and a fourth graphical input  2608  for the user to provide status of whether the user has been diagnosed with Vitamin D deficiency. As discussed herein, in some embodiments, the input of the system  100  and associated with the first graphical input  2602 , the second graphical input  2604 , the third graphical input  2606 , and the fourth graphical input  2608  can be received in an initial configuration pane of a graphical user interface of the system. It is noted that the first graphical input  2602  for the user to provide a selection of a skin type and the second graphical input  2604  for the user to provide a selection of skin sensitivity are directed to the same factor and only one selection is needed for the determination of the exposure time to meet the daily requirement or recommendation for Vitamin D dosage. 
     The graphical user interface  2600  further includes a set of selectable icons  2610  each associated with an exposed body region or part including a first icon  2612  associated with the face area, a second icon  2614  associated with the neck region, a third icon  2616  associated with the hand region, a fourth icon  2618  associated with the arm region, a fifth icon  2620  associated with the leg region, and a sixth icon  2622  associated with the torso region. In some embodiments, the input of the system  2200  and associated with the selectable icons  2610  can be presented for each selection by the user on a daily basis and based on each prolonged exposure anticipated by the user. To this end, accurate UVB dosage production can be determined based on exposed body area and UV intensity. The graphical user interface  2600  further includes a dial gauge output  2624  that presents area of body exposed as a percentile that is calculated based on inputs of the set selectable icons  2610 . 
     The graphical user interface  2600  further includes a graphical output  2626  associated with a UV intensity measurement that is derived from a sensor measurement. 
     The graphical user interface  2600  further includes a graphical output  2628  associated with a determined recommended or required Vitamin D dosage as determined based on the inputs provided by the user (e.g., based on the user&#39;s age as provided to the input  2606 ). 
     The graphical user interface  2600  further includes a graphical output  2628  associated with a determined recommended or required Vitamin D dosage as determined based on the inputs provided to the user (e.g., based on the user&#39;s age as provided to the input  2606 ), for example, as discussed in relation to  FIG.  23   . 
     The graphical user interface  2600  further includes a graphical output  2630  associated with a determined UV dosage as determined based on the measured UV intensity and exposure time and based on the inputs provided to the user, including the exposed body regions or parts as provided to inputs  2610 , for example, as discussed in relation to  FIG.  24 A . 
     The graphical user interface  2600  further includes a graphical output  2632  associated with a determined indication  2224  of a current safe exposure to the direct sunlight (e.g., assessed UV index is lower than 3) or indicate a current harmful exposure (e.g., assessed UV index is greater than 3) to the direct sunlight, for example, as described in relation to  FIG.  22   . 
     The graphical user interface  2600  further includes a graphical output  2634  associated with a determined indication that required or recommended exposure time has been met. 
     Discussion of Real Time UV Monitoring of Required Vitamin D Dosage 
     It is noted that few devices in the market are UV index sensors or Vitamin D trackers that has the capability of providing information about safe exposure time for obtaining Vitamin D dosage. In addition, the current devices in the market are often based on pure Silicon or compound semiconductor based materials such as SiC, GaN, InGaN, etc. These materials are difficult to fabricate and require vacuum deposition techniques, which adds to the overall cost of the development of the system. Further, the existing devices are either large or are not stand alone/wearable devices. Some of these devices may require GPS trackers to track the location to get information on UV index or can work only with smartphone apps. With that said, the system as described herein can nevertheless, in some embodiments, be used in systems with GPS trackers or with other types of UVB sensitive sensors, such as SiC-based (Silicon-Carbide-based) photodiode, a GaN-based (Gallium-Nitride-based) photodiode, an InGaN (an Indium-Gallium-Nitride-based) photodiode, an AlGaN (Aluminum-Gallium-Nitride-based) photodiode; a PbTiO 3 -based photodiode, a BaTiO 3 -based photodiode, a SrTiO 3 -based photodiode, a Ba x Sr 1-x TiO 3 -based photodiode, a (1-x)BaTiO 3 -(x)BiFeO 3 -based photodiode, a PbZr 1-x Ti x O 3 -based photodiode, a (Pb 1-y La y )(Zr x Ti 1-x )O 3 -based photodiode wherein 0≤x≤1 (such as 0.5) and 0≤y≤0.1 such as (0.05), a KNbO 3 -based photodiode, a ZnO-based photodiode, a MgZnS-based photodiodes, a LaAlO 3 -based photodiode, and a ZnMgO-based photodiode. 
     By using ferroelectric material such as PbZr 1-x Ti x O 3 -based device or a (Pb 1-y La y )(Zr x Ti 1-x )O 3 -based device, where 0≤x≤1 (such as 0.5) and 0≤y≤0.1 (such as 0.05). In some embodiments or Lanthanum doped lead zirconate titanate (PLZT) thin-film such as Pb 0.95 La 0.05 Zr 0.54 Ti 0.46 O 3 , the UVB sensor  2202  can still be fabricated on Si substrate, which is inexpensive, and can easily be integrated with CMOS technology. To this end, the system can be miniaturized and integrated with existing consumer electronics such as an iPod or other storage device so that a person can save and enjoy music while soaking in Vitamin D. As a further example, the Vitamin D tracker can be integrated into a heart rate monitor or a pedometer to allow an individual to maintain an account of their fitness routine at the same time in a single all-in-one device. 
     While the methods and systems have been described in connection with preferred embodiments and specific examples, it is not intended that the scope be limited to the particular embodiments set forth, as the embodiments herein are intended in all respects to be illustrative rather than restrictive. 
     As used herein, “computing device” may include a plurality of computers. The computers may include one or more hardware components such as, for example, a processor, a random access memory (RAM) module, a read-only memory (ROM) module, a storage, a database, one or more input/output (I/O) devices, and an interface. Alternatively and/or additionally, controller may include one or more software components such as, for example, a computer-readable medium including computer executable instructions for performing a method associated with the exemplary embodiments. It is contemplated that one or more of the hardware components listed above may be implemented using software. For example, storage may include a software partition associated with one or more other hardware components. It is understood that the components listed above are exemplary only and not intended to be limiting. 
       FIG.  27    shows an example computing device which can be used to perform operations associated with the processes described herein, in accordance with an illustrative embodiment. 
     Processor may include one or more processors, each configured to execute instructions and process data to perform one or more functions associated with a computer for indexing images. Processor may be communicatively coupled to RAM, ROM, storage, database, I/O devices, and interface. Processor may be configured to execute sequences of computer program instructions to perform various processes. The computer program instructions may be loaded into RAM for execution by processor. As used herein, processor refers to a physical hardware device that executes encoded instructions for performing functions on inputs and creating outputs. 
     RAM and ROM may each include one or more devices for storing information associated with operation of processor. For example, ROM may include a memory device configured to access and store information associated with controller, including information for identifying, initializing, and monitoring the operation of one or more components and subsystems. RAM may include a memory device for storing data associated with one or more operations of processor. For example, ROM may load instructions into RAM for execution by processor. 
     Storage may include any type of mass storage device configured to store information that processor may need to perform processes consistent with the disclosed embodiments. For example, storage may include one or more magnetic and/or optical disk devices, such as hard drives, CD-ROMs, DVD-ROMs, or any other type of mass media device. 
     Database may include one or more software and/or hardware components that cooperate to store, organize, sort, filter, and/or arrange data used by controller  1320  and/or processor. For example, database may store hardware and/or software configuration data associated with input-output hardware devices and controllers, as described herein. It is contemplated that database may store additional and/or different information than that listed above. 
     I/O devices may include one or more components configured to communicate information with a user associated with controller. For example, I/O devices may include a console with an integrated keyboard and mouse to allow a user to maintain a database of images, update associations, and access digital content. I/O devices may also include a display including a graphical user interface (GUI) for outputting information on a monitor. I/O devices may also include peripheral devices such as, for example, a printer for printing information associated with controller, a user-accessible disk drive (e.g., a USB port, a floppy, CD-ROM, or DVD-ROM drive, etc.) to allow a user to input data stored on a portable media device, a microphone, a speaker system, or any other suitable type of interface device. 
     Interface may include one or more components configured to transmit and receive data via a communication network, such as the Internet, a local area network, a workstation peer-to-peer network, a direct link network, a wireless network, or any other suitable communication platform. For example, interface may include one or more modulators, demodulators, multiplexers, demultiplexers, network communication devices, wireless devices, antennas, modems, and any other type of device configured to enable data communication via a communication network. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the specification. 
     Throughout this application, various publications may be referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the methods and systems pertain. 
     It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope or spirit. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit being indicated by the following claims.