US2810883A

US2810883A - Frequency sensitive visual indicator

Info

Publication number: US2810883A
Application number: US501892A
Authority: US
Inventors: Robert L Carnine
Original assignee: RAYMOND M WILMOTTE Inc
Current assignee: RAYMOND M WILMOTTE Inc
Priority date: 1955-04-18
Filing date: 1955-04-18
Publication date: 1957-10-22
Anticipated expiration: 1974-10-22

Description

Oct. 22, 1957 R. L. CARNINE 2,810,883

FREQUENCY SENSITIVE VISUAL INDICATOR Filed April 18. 1955 .L I -4 ale VAL INPUT I 2 5 1: i E I CONDUCT! l/E 61145-5 ATTORNEY 2,810,883 FREQUENCY SENSITIVE VISUAL INDICATOR -Robert Lscarnineywashington', D. C.', as'signor' to Ray- -=mond -M.-'WilInotte, Inca WashingtonyD. C., a cor- --poration oif Mary-landv phois may be dispersed in asoli'd or liquid dielectric carrier, or may be disposed on a support independently ofany carrier, in either ever'ifconstituting an electro- I "luminous'rnedium. The medium may be sandwiched between a pair of electrodes, one of whichi'nay be transparent, and then constitutes the dielectric of an electrical cond'ens'er, which is luminous in response totheapplica- --tionthereto of timevaryingfvoltages. Such a-eondenser has been'described in the U. S. Patent to E. L. Mager, No. 2,624,857, to which reference is'niade for further detailedinformation as to preferredstructural' arrange- Inents.

In accordance with 'the'present'invcntion, in its preferred form, 'atransparentelectrically conductive plate is utilized as-a support" for a mass of electroluminescent phosphor, which 'is embeddedin ai'high resistance solid dielectric carrier. A 'signalinput terminalisconnected in par'allel to-corresponding' terminals ofia series of piezoelectric crystals, the emainingterminals of which are coriiiected with 'contactslocated at discrete points of the phosphor. Each piezo-electric. crystal is" fabricated to be 'seriesresonant to a' diiferen't frequency within a freq'uenc'y band. Iffde'sire'd', the selectivity curves" of the separatepiezoelectric crystals may o ierlap su'fliciently that atleastone piezo-electric' crystal of the plurality employed is responsive to every "frequency within=the bandf It is then-a characteristic of each 'piezo-electric crystal-that in response to a frequency towhic'hit is resonantit constitutescssentially ashortcircuit', while in} esponse to other frequenciesit constitutes an open circuit; The separatepiezo electric crystals accordingly applysignals'at differentfrequencies to' di'flerent points ofthe layer of electroluminescent phosphon-the signals passing through th e phosphor and viaa'tunilig indu'ctance to ground. A plurality of electroluminescent condensers are therebyformed, each one consisting'of (1) one of the contacts which proceed from the array of piezo-electric crystals,- (2:) the area of the transparenttelectrically conductingplate which immediately-mnderlies the* 'cont-act, and-(3 thephosphor in its high resistance, high dielect'ric constant'medium. The tuningcoih 'which is comrhon to all the electroluminescent condensers, resonates the individual condensers to the frequency of the band under examination. It is possible to accomplish this by means of a single coil, provided the band of frequencies is not unduly great, because the Q of the coil and its associated condenser or condensers is relatively low, of the order of 20 or 30, while the Q of the associated piezo-electric crystals is of the order of 10,000 or 10,000,000.

It is well known that piezo-electric crystals are series resonant not only to their fundamental frequencies, but also to harmonics of these frequencies. By virtue of the fact that the condenser and tuning coil in series with United States PatenfO "ice 2,810,883 Patented Oct ZZ, 1957 each piezo-electric crystal is a series'resonant circuit,- it

can in fact be resonant to only a single bandof frein-terms of voltage across the electroluminescent co'ndenser. For that frequency to which the electroluminescent condenser and its associated tuning coil is resonant aresonant rise of voltage takes place across-the coridenser, the resonant rise'bei'ngof the order of '20 o r;30.

Since electroluminescent phosphors require a: minimum voltage for firing the response of the systemtoharmonic frequencies at considerable amplitude may be completely eliminated, while the response of the system to :relatively small amplitudes within a desired-band may be considerable.

: It isaccordingly a broad object of the'pr ese'ntrinvention toprovide a novelelectroluminescent indicator, in

which indications are produced at discrete points of an electroluminescent medium in response to signals of discrete frequencies, and in which responses of the system to frequencies harmonically-related to a desired band of frequencies are eliminated.

. It is a-more specific object of the presentinventio'n to provide a systememploying a'plurality of piezoelectric, crystals asfrequency separating devices, separate frequencies'being applied to discrete portions of. an electroluminescent medium, and the electroluminescent :mediumbeing tuned to a preselected band of; frequencies,

tothe practical exclusion offrequencies falling outside the" preselected band.

The above and still'further features, objects, andi advantages of theinvention will become apparcnt upon consideration of the following detailed description. of a specific embodiment ofthe invention,-especiallysyvlien taken in conjun'ction with the accompanying drawings, wherein the single figureof the drawings is-aschema'tic circuit diagram of a system in accordance with'the pres ent, invention. 40

Referring now more specifically to the accompanying drawings, thereference numeral '1 represents a'ftsig'nal input terminal to which may beapplied signalsderivin'g fromany source, such as from the intermediate-frequency amplifier of a radio receiver,-'a sonar'receiver; or the like, the band of frequencies being applied iniparallel to the input terminals 2, 3, 4, of an array of*:piezo electric crystals 6;7, 8, The output electrodesl10, 1-1, 12, of the'piezo-electric crystals 6, 7, 8,' respectively, are connected with or utilized asl'contacts, each directed to a different discretepoint of alayer M of electroluminescent phosphor. This phosphor may: be laid ona layer of dielectric material, or may befinc'orporat'ed thereinin-accordance with the teachings: of Ul S'. Patent to.E. L Mager-2,654,857. The l'ayero'fphosphor maybesupported on a sheet of electrically conductive glass 15, or other" transparent material, the reference 'le denoting a conductive coating on the glasstpla'te ISiE Th'e conductive layer'l6 is connected via a tuning "coil1 7to a1 l qund01other rcferencepointq 11 Thepiezoclectric crystals 6, 7, 8, inclusive, there being three such crystals illustrated 'for the sake of example only, and not by Way of limitation, may each be resonant to a different frequency, and the frequencies may be adjacent to one another, so that at least one of the crystals will be resonant to any frequency within a predetermined frequency band, ft to f2, which may be applied to the terminal 1. Accordingly, for any frequency falling within the predetermined band, an alternating current will appear at one of the

output terminals

10, 11, 12, Each of the contacts 10 to 12, in conjunction with that portion of the conductive layer 16 which immediately underlies it, represents a condenser having as its dielectric medium a portion of the electroluminescent layer 14. This condenser has a definite capacity which may be tuned by means of the inductance coil 17. Accordingly, each one of the piezoelectric crystals 68, inclusive, is connected in series with a further resonant circuit, tuned approximately to the same frequency as is the crystal. The Q of the piezo-electric crystal may be of the order of 10,000 to 10,000,000, depending upon the structure and mounting of the piezo-electric crystal. On the other hand the measured Q of a specific circuit consisting of a probe, a layer of electrically conductive plate, and an intermediate phosphor, in series with a tuning coil has been found to be approximately to 40. Accordingly, the series tuned circuit which includes the coil and electroluminescent condenser is relatively low Q and the piezo-electric crystals are each extremely high Q circuits. It follows that a large number of crystals may fall substantially within the resonance curve of the electroluminescent condenser and its tuning coil 17 Upon application to the terminal 1 of a signal falling within the predetermined band of frequencies, f1 and f2, one of piezo-electric crystals 6, 7, 8, represents a short circuit to the frequency of the signal, all the remaining crystals being essentially open circuits. The signal passes through the crystal which is conductive and thence through the phosphor and the tuning coil to ground. A resonant rise of voltage occurs across the condenser, and the phosphor which subsists immediately under the activated one of

contacts

10, 11, 12, glows. shunt capacity of the remaining crystals, or which occurs at frequencies harmonically related to those desired, produces no response in the phosphor, unless they are of extremely high amplitude, because the phosphor possesses a firing threshold, and does not glow in response to any voltage lower than its required firing voltage. This firing voltage is a function of the constitution of the phosphor, the constitution of its medium, if any, and the thickness of the layer of phosphor. Firing voltages having values of volts R. M. S. have been observed, at frequencies 1 of several mc., and luminous efiects have been observed in electroluminescent phosphors of the general type described in the Mager patent at frequencies as high as mc./s. and as low as 10 C. P. S.

While I have described and illustrated one specific example of the present invention it will be clear that variations of the specific details of construction may be resorted to without departing from the true spirit of the invention as defined in the appended claims.

What I claim is:

1. A frequency sensitive visual indicator, including a thin layer of electroluminescent phosphor material, said layer having a high electrical resistance in the direction of its thickness, a first electrically conductive electrode in contact with one side of said layer, a further plurality of electrically conductive electrodes in contact with discrete points of the other side of said layer, which are opposed to said first electrode, a plurality of piezoelectric crystals, each resonant to a different frequency in a frequency band, means connecting each of said piezo-electric crystals in series with one of said further plurality of electrically conductive electrodes, means for supplying signals within said frequency band to said piezo-electric crystals in Any signal which leaks through the associated parallel, and means for tuning the condensers formed by said further conductive electrodes and said first electrically conductive electrode to series resonance over said frequency band.

2. The combination in accordance with claim 1, wherein said means for tuning is an inductance.

3. A frequency sensitive visual indicator, including a thin layer of material including electroluminescent phosphor, said layer having high electrical resistance in the direction of its thickness, a pair of conductive electrodes on opposite sides of said layer, a piezo-electric crystal filter in series with one of said pair of electrodes, and means for tuning the condenser formed by said electrodes and said phosphor to a frequency equal to one response frequency of said piezo-electric crystal filter.

4. A frequency sensitive visual indicator, including a thin layer of material including electroluminescent phosphor, said layer having high electrical resistance in the direction of its thickness, a pair of conductive electrodes on opposite sides of said layer, a band-pass filter in series with said pair of electrodes, and means for series tuning the condenser formed by said electrodes and said layer of material to a frequency equal to a response frequency of said filter.

5. The combination in accordance with claim 4 wherein said means for series tuning is a coil in series with said pair of electrodes.

6. A frequency indicating system including an electroluminescent condenser, a band-pass filter in series with said electroluminescent condenser, and means for series tuning said electroluminescent condenser to resonate over the band-pass of said filter.

7. The combination in accordance with claim 6 wherein said means for series tuning is a coil.

8. A frequency indicating system including a plurality of electroluminescent condensers, a relatively narrow band-pass filter in series with each of said electroluminescent condensers, each of said filters tuned to a different mean frequency, and a single tuning element for simultaneously tuning all said condensers broadly to all the frequencies passed by said filters.

9. The combination in accordance with claim 8 wherein said means for tuning is a single coil.

10. A frequency indicating system including an electroluminescent condenser, a band-pass filter in series with said electroluminescent condenser, and means for tuning said electroluminescent condenser to resonate in the bandpass range of said filter.

11. A frequency sensitive visual indicator, including a thin layer of material including electroluminescent phosphor, said layer having high electrical resistance in the direction of its thickness, a pair of conductive electrodes on opposite sides of said layer, a band-pass filter in series with one of said pair of electrodes, and means for tuning the condenser formed by said electrodes and said phosphor to a frequency in the band-pass range of said filter.

References Cited in the file of this patent UNITED STATES PATENTS 1,814,399 Meissner July 14, 1931 2,556,586 Johnson June 12, 1951 2,624,857 Mager Jan. 6, 1953 2,698,915 Piper Jan. 4, 1955