Abstract:
The monitoring of UV radiation has received increased attention recently due to the hazards of accelerated skin ageing and even cancer following excessive exposure. Personalized monitoring gives a more accurate reading than crude weather forecasts of the ‘UV index’. This invention answers both these needs in a personal UV monitor that is incorporated into an existing display. Minimal processing changes are made to an existing display in order to achieve this added functionality, which is therefore achieved at little additional cost.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/205,782, filed on Jan. 23, 2009, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the device of monitoring UV, and in particular relates to the UV monitoring device integrated in the portable display device. 
     2. Description of the Related Art 
     The need for monitoring of the sun&#39;s UV radiation dose is well understood, in particular amongst those who sunbathe and who wish to minimize the risk of exceeding a healthy dose. Daily weather forecasts offer a crude UV index which gives a rough indication as to the likely ‘burn time’ of the average person in the sun, but since local exposure conditions are affected by effects such as cloud cover, this can only offer a very crude indication of the total dose. The monitoring of UV from sun exposure therefore requires a personal solution. 
     The spectral content of the sun&#39;s UV radiation is categorized by wavelength into UVA (400 nm to 320 nm), UVB (320 nm to 290 nm) and UVC (290 nm to 100 nm), based on its effect on the human skin. Whilst all wavelengths cause local heating, it is UVA that is responsible for skin ageing and UVB that is responsible for skin burning and non-melanoma skin cancer. UVC is largely filtered out by the earth&#39;s atmosphere. At low dose levels the damage to skin caused by UV is generally accepted to integrate over time, therefore the integrated dose must be measured over a period of sun exposure, and will account for time variations in the intensity due to for example cloud cover. 
     Existing solutions to monitoring the UV dose are available in the form of disposable patches which change color after a predetermined UV dose, bespoke monitoring units that are integrated into watches and wall-mounted weather station units that are used to monitor the UV dose in the user&#39;s back garden. However these all suffer from drawbacks. The disposable patches, whilst worn and therefore give a direct monitor of the dose, cannot be re-used and are therefore wasteful and require the user to carry an adequate supply. The sensors that are integrated into for example watches, require a dedicated photodetector and the corresponding filters in order to monitor the UV. The use of a dedicated photodetector in the sensing product increases cost and manufacturing complexity, and in some solutions requires a costly SiC or TiO 2  detector. The larger weather station wall-mounted units suffer from being bulky and are therefore non-portable. 
     Accordingly, a novel UV monitoring device without largely changing the existing processes is called for simplifying the manufacture and reducing the cost. In addition, this device should overcome the limitations of the related art, being incompatible with a portable unit, and eliminating the need for an expensive filter that is typically used in existing systems. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a portable UV monitoring device, comprising a standard display region, a reference region, and a UV sensitive region; wherein the device has a top substrate disposed between an array substrate and a fluorescent dye layer; and a plurality of photodetectors disposed on the top or bottom surface of the array substrate, or on the top or bottom surface of the top substrate, wherein the photodetectors corresponds to the reference region and the UV sensitive region, respectively, wherein the fluorescent dye layer corresponds to the UV sensitive region. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1A  is a cross sectional view showing a UV monitoring device; 
         FIG. 1B  shows optical spectra of the reference region of the device in  FIG. 1A ; 
         FIG. 1C  shows optical spectra of the UV sensitive region of the device in  FIG. 1A ; 
         FIG. 2  shows spectral distribution of the background optical radiation; 
         FIG. 3  shows transmission ratio versus different wavelengths of the commercial available glass sheet Corning&#39;s Eagle 2000 of 0.7 mm; 
         FIG. 4  shows transmission ratio versus different wavelengths of the color filters; 
         FIG. 5  shows fluorescent emission intensity as a function of a of wavelength of (a) sodium salicylate, (b) coronene, and (c) liumogen compared with the spectral response of a rear illuminated Si CCD; and 
         FIGS. 6-8  are cross sectional views showing UV monitoring devices; and 
         FIGS. 9A-9D  are cross sectional views showing a UV monitoring devices. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     The essential issue that the invention aims to overcome is that of sensing the UVB component of the sun&#39;s radiation in a cost effective manner. Sunburn is largely caused by UVB radiation which is orders of magnitude more effective per unit dose at causing sunburn than UVA. The problem to be solved is that low cost light sensors are invariably made from silicon, and unless special processing is employed, standard silicon is sensitive to visible light but insensitive to UV. Whilst more expensive TiO 2  or silicon carbide (SiC) detectors are available which are insensitive to the visible and only see the UV, their processing is incompatible with that of active matrix liquid crystal displays (in abbreviate AMLCD). This problem is typically overcome by using a UV-sensitive fluorescent layer to convert the UV spectral component of the radiation to visible light, and then detecting this visible radiation using a low cost silicon detector. Herein lies the problem. The background radiation being monitored contains both UV and visible light, and the fluorescent layers that are used to convert the UV to the visible are typically partially transparent to visible light, which is of course also detected by the silicon detector and therefore gives an additional rogue signal. The solution typically employed demands an expensive optical filter prior to the UV-Visible fluorescent layer, which transmits only the UV component. In order to eliminate the need for this expensive visible-light-blocking filter, in this invention the visible light is allowed to be partially transmitted through the fluorescent layer, and the spectral content of the transmitted visible radiation plus the fluorescence-converted UV to visible radiation is then analyzed into its red, green, and blue components. The original intensity of UVA plus UVB is then determined by subtracting the corresponding components in the red, green, and blue from those that are detected in the absence of the fluorescent layer. The fluorescent layer is also responsive to UVC, but owing to ozone absorption this is only present in the background sunlight radiation at a very low intensity (it is strongly absorbed by the earth&#39;s atmosphere) and will not therefore interfere with the measurement. In order to detect only UVB (which is largely responsible for skin cancer), a further embodiment relies on the use of a low cost UVA-absorbing dye filter that is dispersed into the UV transmitting plastic casing of the display. The optical analysis is performed by the low cost RGB filters on an array substrate of a standard display which are located above identical silicon photodetectors. The manufacturing complexity is minimal because no special processes are necessary to fabricate the photodetectors on the display glass of a standard AMLCD array substrate in a portable product such as watch, mobile phone, MP3 player, or Sat Nav guidance system. Photodetectors are currently being integrated onto AMLCD array substrate in order to make Ambient Light Sensors (ALS) in many display products. Therefore, the invention provides a portable and personal UV monitoring system, increasing the functionality of an existing mobile display with minimal additional manufacturing complexity. Moreover, the AMLCD which incorporates the described UV monitoring system can be reflective LCD, transmissive LCD, or transflective LCD. 
     Alternatively, the display mode of the invention is not only the described liquid crystal display but also an organic light emitting diode (in abbreviate OLED). 
     Embodiments 
     Embodiment 1 
     The construction of a UV monitoring device is shown in  FIG. 1A . The device of the  FIG. 1A  is subdivided into three regions in order to illustrate the differences from a standard mobile display construction. In the left third of  FIG. 1A  is the standard display region (I) in which light from the backlight  101  passes through the polarizer  103 , through the array substrate  105  having a plurality of TFT arranged in array, has its intensity modulated by the liquid crystal layer  107 , then passes through the color filter layer  109  on its top substrate  111  to generate the required intensity (the relative transmission of each RGB component within a pixel determining the net color and spectral content of the pixel), and finally passes through the compensation and bright enhancement films  113  and polarizer  115  where it is seen by the user. 
     The reference region (II) is used to monitor the intensity of the red, green, and blue components of visible light in the background radiation. The silicon photodetectors in this region are of course only sensitive to the visible components of detected light. The R, G, and B intensities will then be subtracted from the corresponding detected intensities in the UV sensitive region (III). The background optical radiation has a spectral distribution as shown in  FIG. 2 . The regions of interest here are the visible and UV regions to the left of the  FIG. 2 . The infrared region in  FIG. 2  shows the usual atmospheric gas absorption lines. The infrared is not of interest to the invention since the silicon detector will not detect wavelengths longer than 1100 nm. The UV region is subdivided into UVA (400 nm to 320 nm), UVB (320 nm to 290 nm) and UVC (290 nm to 100 nm), based on its effect on the human skin. As stated above, this embodiment aims to detect the combination of UVA plus UVB. As seen in  FIG. 2 , UVC has an almost-negligible contribution to the total UV signature as it is strongly absorbed by ozone in the earth&#39;s atmosphere and is therefore never detected by the detector. To eliminate the detection of UVC altogether, an additional glass sheet (not shown) is located between the optical radiation source and the fluorescent dye layer  117  in order to completely filter out the UVC component. The additional glass sheet can be Corning&#39;s Eagle 2000 having negligible UVC transmission as shown in  FIG. 3 . 
     Returning to  FIG. 1A , the Sun&#39;s solar spectrum initially passes through the UV transmitting plastic casing  121  that forms the existing protective cover of the mobile display. Different product manufacturers use different plastics for this layer, in which they currently care largely about the visible transmission. In the invention it is critical that this UV transmitting plastic casing  121  transmits visible light as well as both UVA and UVB. Some pure clear polymers (e.g. PMMA (poly(methyl methacrylate)), or Plexiglass) has sufficient UV transmission, but many manufacturers will use dyes dispersed in this UV transmitting plastic casing  121  for enhancing the UV absorption. This invention requires a UV-transmitting window between the background radiation source and the fluorescent dye layer in the UV sensing region (III), and the widow is made from, for example, Plexiglass. A thin polytetrafluoroethylene layer  119  passing all three wavelength regions, slightly attenuating the visible, and acting to scatter the incident radiation, can be optionally disposed between the UV transmitting plastic casing  121  and the fluorescent dye layer  117  to give the sensor a cosine response to incident radiation. Therefore, the visible plus UVA plus UVB optical radiations pass through the optional polytetrafluoroethylene layer. In the reference region (II), the relative components of the visible spectrum in red, green, and blue are then measured by the photodetectors  106  located on the array substrate  105  behind the color filters  109  after the light passes through the standard LCD layers such as polarizer  115 , compensation and brightness enhancement films  113 , and top substrate  111 . The color filters  109  can be the standard color filter plate or the color filter on array (COA) used in general all full-color displays, and acts as optical filters in order to separate these three components of the visible spectrum. Whilst there is typically some overlap between the transmission spectra of these three phosphors as shown in  FIG. 4 , the separation of the visible light into these three components using the color filters  109  is sufficient for this invention. The photodetector  106  such as silicon photodiodes is readily implemented on the array substrate  105  in both amorphous and polysilicon with few process changes since these are currently being deployed as ambient light sensors in displays. Following their amplification and measurement using transimpedance or switched capacitor charge amplifiers (not shown and can be fabricated on the array substrate  105 ), the optical intensities from the photodetectors  106  in red, green, and blue pixels yield electrical signals (as shown in  FIG. 1B ) which correspond to the relative intensities of these three optical components in the visible spectrum. These signals measured in the reference region (II) are then subtracted from the signals measured in the UV sensitive region (III). 
     The UV sensitive region (III) in the sensing system is identical to that of the reference region (II) except that it contained a fluorescent dye layer  117 . After passes through the optional polytetrafluoroethylene layer  119 , the visible plus UVA plus UVB optical radiations are incident upon the fluorescent dye layer  117 , such that the UVA and UVB are converted to a visible radiation. Suitable dyes for the fluorescent dye layer  117  includes Liumogen and Coronene, whose fluorescence signatures and quantum efficiencies are shown in  FIG. 5 . Liumogen is the preferable dye of the invention, and is usually used in greenish fluorescent dye marker pens. Essentially, Liumogen has a flat quantum efficiency across the UV from 50 nm to 420 nm, so a photon anywhere in this wavelength region excited an electron-hole pair (and subsequently another photon in the visible) with the same probability. Coronene, with its emission spectrum centered at 520 nm is less attractive as it had a dip in its quantum efficiency between 390 and 420 nm which will complicate the detection process. As shown in  FIG. 5 , the Liumogen has a central emission wavelength of green light at 530 nm. However, Liumogen is partially transparent to visible light. The spectrum of the light transmitted by the fluorescent dye will therefore be visible light that is enhanced in the green region due to excitation of the phosphor by UVA plus UVB. This is a combination of the background visible light and the wavelength-converted UV radiation. The optical spectra of the light arriving at the phosphor layers prior to their detection into R, G and B are shown as dotted lines in  FIG. 1C . In  FIG. 1C , the transmission spectra of the phosphors are represented as dotted lines for clarity, showing that since the transmission of the green color filter is closely aligned with the emission of the fluorescent phosphor, good detection is achieved with this system. The greenish emission of the Liumogen fluorescent phosphor is clearly better aligned with that of the green color filter than that of Coronene. 
     In order to monitor the UV dose, the electrical signals corresponding to the red, green, and blue spectral from the UV sensitive region (III) as shown in  FIG. 1C  are subtracted from their corresponding red, green, and blue signals in the reference region (II) as shown in  FIG. 1B  by a subsequent electrical circuit of the array substrate  105 . This result signal from the circuit is then transferred to the display region (I) array of the array substrate  105  for pointing out the UVA plus UVB content of the background radiation in order to advise the exposed sunbather. It can also subsequently be integrated over time in order to provide the user with the accumulated dose. Note that the photodetectors  106  in the reference region (II) and the UV sensitive region (III) are separated devices without contacting to each other. If the photodetectors  106  contact, the electrons should interference to each other. 
     Note that the polarizer  103  can be disposed between the color filters  109  and the liquid crystal layer  107  as well as between the fluorescent dye layer  117  and the top substrate  111  in  FIG. 1A . This type is so-called in-cell polarizer. In addition, the photodetectors  106  can be formed on the top or bottom surface of the top substrate  111  or formed on the bottom surface of the array substrate  105  as well as on the top surface of the array substrate  105  in  FIG. 1A . 
     Embodiment 2 
     Embodiment 2 incorporates a UVA filter (not shown) on the optical radiation side of the fluorescent dye layer  117 . The filter selectively absorbs only the UVA radiation and therefore prevents it from contributing to the detected signals. Such dyes are available commercially and can be incorporated into various polymers such as Plexiglass and polycarbonate which is in widespread use in products such as sunglasses. 
     Embodiment 3 
     In Embodiment 1, the display mode of the display region (I) is transmissive or transflective type, and the pixel electrode of the array substrate  105  must be all transparent or semi-transparent to match the backlight. In Embodiment 3, the display mode of the display region (I) is reflective type, wherein the pixel electrode of the array substrate  105  is reflective material such as metal. As shown in  FIG. 6 , the backlight  101  and the polarizer  103  in  FIG. 1A  are omitted in Embodiment 3. 
     Embodiment 4 
     In Embodiment 4, the color filters in the reference region (II) and the UV sensitive region (III) are omitted. As such, the photodetector  106  in the reference region (II) will detect the visible light such as white light not divided into red, green, and blue light by the color filters. Moreover, the photodetector  106  in the UV sensitive region (III) will detect the visible light (white light) and the UV light (being transferred to visible light by the fluorescent dye layer  117 ). As described above, the signals of the reference region (II) and the UV sensitive region (III) can be calculated by the circuit of the array substrate  105 . The result signal from the circuit is then transferred to the display region (I) array of the array substrate  105  for pointing out the UVA plus UVB content of the background radiation in order to advise the exposed sunbather. It can also subsequently be integrated over time in order to provide the user with the accumulated dose. Similarly, the UV monitoring device in this embodiment can be reflective type, such that the backlight  101  and the polarizer  103  can be omitted as shown in  FIG. 8 . 
     Embodiment 5 
     In Embodiments 1-4, the display mode is LCD and therefore needing liquid crystal layer  107 . In Embodiment 5, the display mode is replaced to OLED, such that the crystal layer  107  can be omitted. Moreover, the OLED display does not need the back light unit  101 , the polarizer  103 , and compensation and bright enhancement films  113 . The other layers/elements such as array substrate  105 , photodetectors  106 , top substrate  111 , fluorescent dye layer  117 , optional polarizer  115 , thin polytetrafluoroethylene layer  119 , and UV transmitting plastic casing  121  are similar to that of the LCD mode as described in Embodiment 1. As shown in  FIG. 9A , the OLED stack  108 , sequentially formed of an anode, a hole transfer layer, an illumination layer, an electron transfer layer, a cathode, and the likes, is formed on the array substrate  105 , wherein the OLED stack  108  corresponds to the standard display region (I). In  FIG. 9A , the OLED stack  108  illuminates white light, such that the color filter layer  109  is adopted to display full color image. 
     Embodiment 6 
     In embodiment 5, the OLED stack  108  illuminates white light and therefore needing color filter layer  109 . In Embodiment 6, the OLED stack  108  arranged as pixels illuminates red, green, and blue lights, respectively. As shown in  FIG. 9B , the standard display region (I) of the device in Embodiment 6 is free of the color filter layer  109 . 
     Embodiment 7 
     The device in Embodiment 7 is similar to Embodiment 5, the only difference in Embodiment 7 is the color filter layer  109  in the reference region (II) and the UV sensitive region (III) are omitted. As shown in  FIG. 9C , the photodetector  106  in the reference region (II) will detect the visible light such as white light not divided into red, green, and blue light by the color filters. Moreover, the photodetector  106  in the UV sensitive region (III) will detect the visible light (white light) and the UV light (being transferred to visible light by the fluorescent dye layer  117 ). As described above, the signals of the reference region (II) and the UV sensitive region (III) can be calculated by the circuit of the array substrate  105 . The result signal from the circuit is then transferred to the display region (I) array of the array substrate  105  for pointing out the UVA plus UVB content of the background radiation in order to advise the exposed sunbather. 
     Embodiment 8 
     The device in Embodiment 8 is similar to Embodiment 6, the only difference in Embodiment 8 is the color filter layer  109  in the reference region (II) and the UV sensitive region (III) are omitted too. As shown in  FIG. 9D , the photodetector  106  in the reference region (II) will detect the visible light such as white light not divided into red, green, and blue light by the color filters. Moreover, the photodetector  106  in the UV sensitive region (III) will detect the visible light (white light) and the UV light (being transferred to visible light by the fluorescent dye layer  117 ). As described above, the signals of the reference region (II) and the UV sensitive region (III) can be calculated by the circuit of the array substrate  105 . The result signal from the circuit is then transferred to the display region (I) array of the array substrate  105  for pointing out the UVA plus UVB content of the background radiation in order to advise the exposed sunbather. 
     Note that the photodetectors  106  can be formed on the top or bottom surface of the top substrate  111  or on the bottom surface of the array substrate  105  as well as on the top surface of the array substrate  105  in  FIG. 9A-9D . 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.