2900-202-T Report of Project MICHIGAN ELECTROLUMINESCENT- PIEZOELECTRIC FLAT-PANEL DISPLAYS S. NUDELMAN J. LAMBE J. MUDAR G. TRYTTEN October T960 INFRARED LABORATORY THE UNIVERSITY OF MICHIGAN Ann Arbor, Michigan

NOTICES Sponsorship. The work reported herein was conducted by Willow Run Laboratories for the U. S. Army Signal Corps under Project MICHIGAN, Contract DA-36-039 SC-78801. Contracts and grants to The University of Michigan for the support of research by Willow Run Laboratories are administered through the office of the Vice-President for Research. Distribution. Initial distribution is indicated at the end of this document. Distribution control of Project MICHIGAN documents has been delegated by the U. S. Army Signal Corps to the office named below. Please address correspondence concerning distribution of reports to: Commanding Officer U. S. Army Liaison Group Project MICHIGAN (6550) Ypsilanti, Michigan ASTIA Availability. Qualified requesters may obtain copies of this document from: Armed Services Technical Inofrmation Agency Arlington Hall Station Arlington 12, Virginia Final Disposition. After this document has served its purpose, it may be destroyed in accordance with provisions of the Industrial Security Manual for Safeguarding Classified Information. Please do not return it to Willow Run Laboratories.

The University of Michigan Willow Run Laboratories PREFACE Project MICHIGAN is a continuing research and development program for advancing the Army's long-range combat-surveillance and target-acquisition capabilities. The program is carried out by a full-time Willow Run Laboratories staff of specialists in the fields of physics, engineering, mathematics, and psychology, by members of the teaching faculty, by graduate students, and by other research groups and laboratories of The University of Michigan. The emphasis of the Project is upon basic and applied research in radar, infrared, acoustics, seismics, information processing and display, navigation and guidance for aerial platforms, and systems concepts. Particular attention is given to all-weather, long-range, high-resolution sensory and location techniques, and to evaluations of systems and equipments both through simulation and by means of laboratory and field tests. Project MICHIGAN was established at The University of Michigan in 1953. It is sponsored by the U. S. Army Combat Surveillance Agency of the U. S. Army Signal Corps. The Project constitutes a major portion of the diversified program of research conducted by Willow Run Laboratories in order to make available to government and industry the resources of The University of Michigan and to broaden the educational opportunities for students in the scientific and engineering disciplines. Progress and results described in reports are continually reassessed by Project MICHIGAN. Comments and suggestions from readers are invited. Robert L. Hess Technical Director Project MICHIGAN iii * *

The University of Michigan Willow Run Laboratories CONTENTS Notices................................ ii Preface............................... iii List of Figures............................vi Abstract............................... 1 1. Introduction............................ 1 2. Principles Involved in the Image Display........ 2 2.1. Electric-Field Sweep Design 2 2.2. Flat-Panel Display 4 2. 3. Feasibility Demonstrator 6 3. Further Device Development..................... 7 Reference............................... 8 Distribution List............................ 9 V

The University of Michigan Willow Run Laboratories FIGURES 1. Light-Spot Sweep Using Piezoelectric Cylinders and Wedges....... 3 2. Electrode Arrangement and Equivalent Circuit............. 4 3. Electroluminescent Panel Using Piezoelectric Cylinders........ 5 4. Electroluminescent Panel Using Piezoelectric Wedges......... 5 5. Single-Line-Scan Feasibility Model................. 6 6. Block Diagram for Electronic System Associated with ElectroluminescentPiezoelectric Flat-Panel Display................. 7 vi

ELECTROLUMINESCENT- PIEZOELECTRIC FLAT-PANEL DISPLAYS ABSTRACT A display panel consisting of electroluminescent phosphors deposited on piezoelectric crystals has been fabricated for the purpose of providing a controlled luminescent light spot. The scheme of operation provides for light-spot generation by using the electric fields generated at the piezoelectric-crystal surface, when the crystal is driven by voltages applied at the resonant frequency. The panel is made up of crystals connected electrically in parallel, but resonating at different frequencies. Light-spot sweep movement over the face of the panel and intensity variation are derived by frequency and amplitude modulation of the voltages applied to the piezoelectric crystal array. The device can be used immediately in the development of computer switches, character displays, luminescent dials, delay lines, and any displays requiring limited electric-field bandwidths. After additional phosphor research, it may have uses in the development of TV-like displays. 1 INTRODUCTION A display panel consisting of electroluminescent phosphors deposited on piezoelectric crystals has been fabricated at Willow Run Laboratories. The scheme of operation provides for sweep movement of a light spot over the face of the panel and intensity variation of the light spot by the frequency and amplitude modulation of a voltage applied to the piezoelectric crystals. The device is feasible for immediate use in developing switches for computers, character displays, luminescent dials, and any displays requiring a limited bandwidth of electric fields. TV-like display development, however, will first require extensive research on electroluminescent phosphors. Materials that operate efficiently with electric fields in the megacycle region are needed. To date, little is known about phosphor characteristics at such high frequencies. Flat-panel raster-type electroluminescent displays using a crossed-grid technique have been fabricated in the past. In such displays, the phosphor is part of a sandwich with a fine grid of transparent conducting parallel lines across the front surface, and a similar array of conducting lines on the back surface perpendicular to those on the front. By placing a potential difference across a pair of vertical and horizontal lines, a localized electric field is developed through the phosphor with a resultant luminescent light spot. Through the use of 1

The University of Michigan Willow Run Laboratories computer circuitry, the spot can be made to move in a raster-like manner, and by fieldstrength modulation, image reproduction can be obtained. This system has been demonstrated by Sylvania Electric Products, Inc. (Reference 1). It has, however, severe limitations in that, in order for a display to provide good resolution, the parallel lines must be placed close together. Consequently, more lines are necessary, which makes the switching problem for light-spot movement more difficult because more pairs of crossed lines must be handled and at higher rates of speed. The scheme of operation for the electroluminescent-piezoelectric display, on the other hand, minimizes the switching problem. Furthermore, color displays, which in the crossed-grid arrangement are virtually impossible unless efficient transparent phosphor layers can be developed, can be readily achieved with the approach described in this report, since any color component can be independently controlled. 2 PRINCIPLES INVOLVED in the IMAGE DISPLAY The success or any electroluminescent image display using a raster-type writing program depends on the development of an electric-field sweep and the ability to modulate the sweep with video information. The display panel proposed here will use the electric field that is generated at the surface of piezoelectric materials when they are operated in their resonant condition to excite electroluminescent phosphors. An electric-field sweep is generated by sweeping the frequency applied to the piezoelectric materials. 2.1. ELECTRIC-FIELD SWEEP DESIGN The operation of the device can be understood by referring to Figure l(a). A group of five barium titanate piezoelectric cylinders are placed electrically in parallel across a variablefrequency generator. Each of the cylinders has its own resonant frequency, different from the others. When the generator is tuned to one of the resonant frequencies, a cylinder will respond in its vibrational mode, and a strong polarization field is generated across its end surfaces. The intensity of the field is dependent on the voltage output of the generator, and an electroluminescent phosphor deposited on an end surface lights up with proportional intensity. This device also takes advantage of the voltage amplification possible from piezoelectric materials. The potential difference across the phosphor layer can be three to four times the voltage driving the piezoelectric cylinder for resonance operation. Sweeping the generator frequency causes the different cylinders to respond one at a time, with the light output following the tuned cylinder and the light-intensity modulation being achieved by modulation of the generator voltage. With minaturization of components, a fine-resolution panel display composed of a matrix of cylinders is readily conceivable. 2

The University of Michigan Willow Run Laboratories It is also possible to provide continuous light movement by using shaped bodies such as the quartz wedge shown in Figure l(b). Localized resonance is obtained in a wedge, since the resonant frequency is a sharp function of geometry. A light spot can then be made to move along the wedge simply by varying the generator frequency. Phosphor-Coated Surface Light Spot BaTiO3 Cylinders Phosphor-Coated Surface Light Spot Piezoelectric Wedge, Such as Quartz FIGURE 1. LIGHT-SPOT SWEEP USING PIEZOELECTRIC CYLINDERS AND WEDGES An important advantage in device applications that derive from the electric-field type of sweep is that a localized-field spot is generated without the need for electrodes to be placed in proximity to it. The field is generated by polarization charges appearing at the crystal surface. These changes can be made to appear at surfaces to which no electrical connections are made. If the piezoelectric crystal is shaped properly, the vibrational polarization field can be induced with electrodes placed along the crystal a significant distance away from the surface of interest. This arrangement is illustrated in Figure 2. The transparent grounded electrode placed across the phosphor layer provides the minimum path length for the field and therefore the maximum field intensity. An additional advantage derived from this arrangement is that the voltage applied directly at the electrodes also adds to the total field across the phosphor. This extra contribution is not large enough to make an electroluminescent phosphor glow, 3

The University of Michigan Willow Run Laboratories Electroluminescent-Phospor Layer Transparent Conducting/ / Layer A r1A 1^ _L \ Electrode FIGURE 2. ELECTRODE ARRANGEMENT AND EQUIVALENT CIRCUIT. / = piezoelectric material. I:-~.t:' I = electroluminescent-phosphor layer. r2 = electrical resistance of upper half of piezoelectric slug. rl = electrical resistance of lower half of piezoelectric slug. A = signal generator. PA = amplified signal voltage at phosphor layer during resonance. but is large enough to reduce the requirement on the polarization field. It can be independently adjusted by placing a variable resistor between ground and the transparent conducting surface. 2.2. FLAT-PANEL DISPLAY When the electric-field spot sweep is coupled with an electroluminescent phosphor for a flat-panel display, essentially performing as a TV-type display, the construction of the panel may look either like Figure 3 or Figure 4. In Figure 3, a mosaic of spots appears at the panel surface sufficient for good resolution and spaced to conform with some scan pattern. Each spot represents the surface of a piezoelectric cylinder. The length of the cylinder and the material of which it is made determine the resonant frequency of the cyliner. All cylinders may be placed electrically in parallel and are tuned to oscillate independently of one another so that only one spot lights up at a time. By frequency modulation of the generator, the light spot then can be moved in any desired scan pattern. Video information is displayed by amplitude modulation. If the state of the art of electroluminescent phosphors or piezoelectric materials places restrictions on the electrical bandwidth of operation, the mosaic of spots can be 4

The University of Michigan Willow Run Laboratories Transparent Conducting Surface Piezoelectric Cyliner Phosphor Layer \^s J/ ^^^ Transparent Plate FIGURE 3. ELECTROLUMINESCENT PANEL USING PIEZOELECTRIC CYLINDERS Transparent Conducting Surface Piezoelectric Wedge Phosphor Layer Transparent Plate FIGURE 4. ELECTROLUMINESCENT PANEL USING PIEZOELECTRIC WEDGES arranged in lines, so that one line at a time may be scanned by frequency modulation. Then, by simple one-dimensional switching techniques, all lines can be scanned in any desired sequence. The scheme of Figure 4 is based upon the use of wedges of piezoelectric materials, rather than cylinders. Each line viewed at the panel surface represents the surface of a wedge or a series of adjacent wedges placed end to end, depending on the materials used and the panel size. The resolution available with a wedge is determined mainly by the piezoelectric material and the slope of the wedge. Device operation is the same as for the mosaic of cylinders. 5

The University of Michigan Will iow Run Laboratories At one particutlar frequeilcy, only onle spot on one wedcge will lig~ht up., Chan~t-ging the frecquency cautses the light to move. If bandnc width req~r~fuirements permitti, all wedges can- be placed electr~ically in parallel, and by onse traversal through the fr~equency range, the lightt spot can be mart e toc m~tove over the rvhole Panel. If bandwidth reqeclirecnec ts aretoos sever~e, t~hen iderntical lines of wedges can be placedt side b~ty side! and swept one at a tinte in ally sequentle by switchzing devices. Th'fus, thle lightl-spot mnoven-ien catm 1be Ia;L e to cover' the enltireC panel wine victeo iniformation dtisplayed by aaiplitude niodulatimi of the electric-~fieldt generator. 2. 3. FEAS11XX:31 1.4IIV X)Y J)P iMSMONSTRA."tI\"OR~ A device has~ beeni assetubleci consisting of a rcow of 23 clectroltiti ineseciit-piezoelectritri elementes, all placed in conitact wvith a rectangularr shcct of tr~ansparent, conducting glass. Eatch elementz resonates at a Diffferent frequeney, each is op~erated wit-h thle electrode arralngemenxt o>f Figure 2, and3 all are placect electr~ica lly in parallel., Th1e uttit provides a lumin~escent ligh-t spot which can be~J made to move anxd ctla.rge in~tettsity int a colztrolled manner. I~* t demnonstrates readily tfte fea~sibility of a clectroluiiiiticeseeerz t-pier zolectric display. Thls device is shownx in Figurme 5. A block dtiagram. of thex associatedt electroanic systeln used is shown in Figure 6. Thte electrontic sweeping oscillator oper~ates autolnaticafly to provide ttte necessary range; of frequlencies to drive all piezoelectric efeenc nts. It cail te adjustedcc ~ to sweep at dif~fer-....................~~I....................................................................................................................1.11,.......................................................................................................................................................'l.............................................................................................................................''I..........................................................................................................................................................................................-'''.........1........'Ill'.......' —............................................................................................................................................................................................... ~ ~ ~~~Q ~~~~~~~~r* ~ ~................................................................................................................. B a " i i.~~~~~~.....................................................................................................................................................................................~r.

The University of Michigan Willow Run Laboratories ent rates. By feeding video pulses into the modulator, synchronized properly with the sweep rate, one can generate a corresponding localized light-pulse pattern on the display. This is identical in nature to Z-axis modulation of a single-line sweep in a cathode-ray oscilloscope. A luminescent thermometer-type meter can be readily derived by having the video gate modulate the field sweep. Thus, for example, a controlled luminescent line can be generated through the use of a thermocouple signal to determine a gate width for the sweep-frequency oscillator, starting from the frequency necessary to light up the first element. Video Electronic Sweeping Modulator Driver Flat-Panel Oscillator Amplifier Display FIGURE 6. BLOCK DIAGRAM FOR ELECTRONIC SYSTEM ASSOCIATED WITH ELECTROLUMINESCENT-PIEZOELECTRIC FLAT-PANEL DISPLAY 3 FURTHER DEVICE DEVELOPMENT The display panels described in this report make use of electroluminescent phosphors. They might equally well have made use of electric-field-sensitive fluorescent liquids, gels, or gases with suitable discharge characteristics. These materials could be contained in a thin panel, wherein one surface of the container might be the piezoelectric material itself. The container could be one thin unit complete in itself, or broken down into some form of an array of encapsulated cells. Three-dimensional displays are also possible when the gases or lumiescent materials are transparent, since piezoelectric materials such as quartz are also transparent. Dials for instrument panels might be developed in a relatively simple manner. For example, if a luminescent circle designating some particular area were needed, a dial could be formed from a piezoelectric disc. The disc would be flat on one surface, have a conical hole bored in the other, and be coated on the flat surface with an electroluminescent phosphor. The application of a single driving frequency would cause a luminescent circle to appear. Changes in the driving frequency would cause the circle to get larger or smaller, and might thereby delinate a varying target area. 7

The University of Michigan Willow Run Laboratories One- and two-dimensional delay lines can be obtained from simple display panels such as those described above. The important features here are that a spot of light can be made to move in any desired path and with a controlled velocity. The speed with which a light spot moves along the surface is determined by the speed with which the electrical generator frequency is changed. When a panel is coupled to an array of photodetectors, any desired sequence of events can be triggered, with complete and independent control of the timing of these events. Since the panel is a fabricated solid-state device requiring no internal electronics or gadgetry for its operation, and since photodetectors, such as CdS, meet the same description, panels and photodetectors can be fabricated in a unit package. These can be shaped and positioned to fit unusual compartment requirements. Furthermore, it is clear that multiple arrays and panels can be formulated so that any number of identical sequences can be triggered at the same time. It follows from these applications that computer circuitry may well be simplified and expanded. Display panels such as we have described can also serve admirably as frequency-spectrum analyzers. Any signal fed into the display can have its frequency components examined by the luminescent pattern on the panel. Another useful device naturally evolves from this kind of application. One can readily conceive of a character display, where a signal consisting of a mixture of frequencies is fed to the panel so that a number, letter, or figure will appear and be sustained as long as the signal is applied. Therefore, keyed characters, or automated character sequences, are well within the possibilities for this technique. REFERENCE 1. Aviation Week, "Thin-Panel Radar Possible with Electro-luminescence Technique," July 1957, Vol. 67, p. 32. 8

The University of Michigan Willow Run Laboratories PROJECT MICHIGAN DISTRIBUTION LIST 5 1 October 1960-Effective Date Copy No. Addressee Copy No. Addressee 1 Army Research Office, ORCD, DA 47-48 Commander, Army Rocket & Guided Missile Agency Washington 25, D. C. Redstone Arsenal, Alabama ATTN: Research Support Division ATTN: Technical Library, ORDXR-OTL 2 Office, Assistant Chief of Staff for Intelligence 49 Commanding Officer Department of the Army, Washington 25, D. C. U. S. Army Transportation Research Command Fort Eustis, Virginia ATTN: Chief, Research & Development Branch Fort Eustis irgi ATTN: Research Reference Center 3 Commanding General, U. S. Continental Army Command Fort Monroe, Virginia 50 Commanding General ~~~~~~~ATTN: ATSWD-G ~Ordnance Tank-Automotive Command, Detroit Arsenal 28251 Van Dyke Avenue 4-5 Commanding General Centerline, Michigan 4-5 Commanding General U. S. Army Combat Surveillance Agency ATTN: Chief, ORDMC-RRS 1124 N. Highland Street Arlington 1, Virginia 51 Commanding Officer, Ordnance Weapons Command Rock Island, Illinois 6-8 Office of the Chief Signal Officer ORDOW Department of the Army, Washington 25, D. C. 52 Commanding Officer (6) ATTN: Chief, Combat Development 52 Commanding Officer (6) ATTN Chif, C bat Development U. S. Army Diamond Ordnance Fuze Laboratories Branch, Research & Development Division Washington 25, D. C. (7-8) ATTN: Chief, Signal Research Office ATTN: ORDTL-300 Research & Development Division ~~9-37 Commanding Officer ~53-55 Director, U. S. Army Engineer Research & Development Laboratories U. S. Army Signal Research & Development Laboratory Development Laboratores Fort Monmouth, New Jersey ~~~ATTN-~:~ SIGFM/EL-DR ^(53) ATTN: Chief, Topographic, Engineer Department ATTN: SIGFM/EL-DR (54) ATTN: Chief, Electrical Engineering Department 38 Commanding General UJ. S. Army Electronic Proving Ground U. S. Army Electronic Proving Ground (55) ATTN: Technical Documents Center Fort Huachuca, Arizona Fort Huachuca, Arizoa 56 Director, Human Engineering Laboratory ATTN: SIGPG-DXP Aberdeen Proving Ground, Aberdeen, Maryland 39 Office of the Director 57 Commandant, U. S. Army Command & General Staff College Defense Research & Engineering Technical Library Fort Leavenworth, Kansas Department of Defense, Washington 25, D. C. ATTN: Archives ATTN: Archives 40 Director, Weapons Systems Evaluation Group 5 C U. S. Roo 1E880, The Pentagon58 Commandant, U. S. Army Infantry School Room 1E880, The Pentagon Fort Benning, Georgia Washington 25, D. C. ATTN: Combat Developments Office 41 Chief of Engineers Department of the Army, Washington 25, D. C. 59-60 Assistant Commandant U. S. Army Artillery & Missile School ATTN: Research & Development Division Fort Sill, Oklahoma 42 Chief, Chief of Ordnance, Research & Development Division 61 Assistant Commandant, U. S. Army Air Defense School Department of the Army, Washington 25, D. C. Fort Bliss, Texas ATTN: ORDTB, Research & Special Projects 62 Commandant, U. S. Army Engineer School Fort Belvoir, Virginia 43 Commanding Officer, Army Map Service, Corps of Engineers U. S. Army, Washington 25, D. C. ATTN: ESSY-L ATTN: Document Library 63 President, U. S. Army Infantry Board Fort Benning, Georgia 44 Commanding General Quartermaster Research & Engineering Command 64 President, U. S. Army Artillery Board U. S. Army, Natick, Massachusetts Fort Sill, Oklahoma 45-46 Chief, U. S. Army Security Agency 65 President, U. S. Army Air Defense Board Arlington Hall Station, Arlington 12, Virginia Fort Bliss, Texas 9

The University of Michigan Willow Run Laboratories Distribution List 5, 1 October 1960-Effective Date Copy No. Addressee Copy No. Addressee 66 President, U. S. Army Aviation Board 103-106 Central Intelligence Agency Fort Rucker, Alabama 2430 E Street, N. W. Washington 25, D. C. 67-68 President, U. S. Army Intelligence Board ATTN: OCR Mail Room Fort Holabird, Baltimore 19, Maryland 69 Office, Deputy Chief of Naval Operations 107-112 National Aeronautics & Space Administration Department of the Navy 1520 H Street, N. W. The Pentagon, Washington 25, D. C. Washington 25, D. C. ATTN: Op-07T 113 Combat Surveillance Project 70-73 Office of Naval Research, Department of the Navy Cornell Aeronautical Laboratory, Incorporated 17th & Constitution Avenue, N. W. Box 168, Arlington 10, Virginia Washington 25, D. C. ATTN: Technical Library (70-71) ATTN: Code 463 114 The RAND Corporation (72-73) ATTN: Code 461 11 e R rratin 1700 Main Street 74-76 Chief, Bureau of Shipsanta Monica alifornia Department of Navy, Washington 25, D. C. ATTN: Library (74) ATTN: Code 335 (74) ATTN: Code 335 115-116 Cornell Aeronautical Laboratory, Incorporated (75) ATTN: Code 684C 4455 Genesee Street (76) ATTN: Code 690 Buffalo 21, New York ATTN: Librarian 77 Director, U. S. Naval Research Laboratory VIA: Bureau of Naval Weapons Representative Washington 25, D. C. 4455 Genesee Street ATTN: Code 2027 Buffalo 21, New York 78 Commanding Officer U. S. Navy Ordnance Laboratory 117-118 Director, Human Resources Research Office Corona, California The George Washington University P. O. Box 3596, Washington 7, D. C. ATTN: Library ATTN: Library 79 Commanding Officer & Director U. S. Navy Electronics Laboratory San Diego 52, California a. S. Navy Electronics Laboratory 119 Chief Scientist, Department of the Army'~~San Diego 52, California ~Office of the Chief Signal Officer ATTN: Library Research & Development Division, SIGRD-2 Washington 25, D. C. 80-81 Department of the Air Force, Headquarters, USAF Washington 25, D. C. 120 Columbia University, Electronics Research Laboratories (80) ATTN: AFDRT-ER 632 W. 125th Street 632 W. 125th Street (81) ATTN: AFOIN-1B1 New York 27, New York ATTN: Technical Library 82 Aerospace Technical Intelligence Center, U. S. Air Force Wright-Patterson AFB, Ohio VIA: Commander, Rome Air Development Center Griffiss AFB, New York ATTN: AFCIN-4Bla, Library ATTN: RCKCS 83-92 ASTIA (TIPCR) Arlington Hall Station, Arlington 12, Virginia 121 Coordinated Science Laboratory, University of Illinois Urbana, Illinois 93-100 Commander, WrightAir Development Division Wright-Patterson AFB, Ohio ATTN: Librarian (93-96) ATTN: WWDE VIA: ONR Resident Representative 605 S. Goodwin Avenue (97) ATTN: WWAD-DIST Ilo Urbana, Illinois (98-100) ATTN: WWRNOO (Staff Physicist) 122 Polytechnic Institute of Brooklyn 101 Commander, Rome Air Development Center 122 Polytechnic Institute of Brooklyn 55 Johnson Street Griffiss AFB, New York B rookyn 1, New Yor Brooklyn 1, New York ATTN: RCOIL-2 ATTN: Microwave Research Institute Library 102 APGC (PGTRI) VIA: Air Force Office of Scientific Research Eglin Air Force Base, Florida Washington 25, D. C. 10

The University of Michigan Willow Run Laboratories Distribution List 5, 1 October 1960- Effective Date Copy No. Addressee Copy No. Addressee 123 Visibility Laboratory, Scripps Institution of Oceanography 125 U. S. Continental Army Command University of California Liaison Officer, Project MICHIGAN San Diego 52, California Willow Run Laboratories, Ypsilanti, Michigan VIA: ONR Resident Representative University of California Scripps Institution of Oceanography, Bldg. 349 La Jolla, California 124 Cooley Electronics Laboratory 126 Commanding Officer, U. S. Army University of Michigan Research Institute Liaison Group, Project MICHIGAN Ann Arbor, Michigan Willow Run Laboratories, Ypsilanti, Michigan 11

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