US2437912A

US2437912A - Quartz oscillator plate

Info

Publication number: US2437912A
Application number: US568324A
Authority: US
Inventors: Frondel Clifford
Original assignee: REEVES ELY LAB Inc
Current assignee: REEVES ELY LAB Inc; REEVES-ELY LABORATORIES Inc
Priority date: 1944-12-15
Filing date: 1944-12-15
Publication date: 1948-03-16
Anticipated expiration: 1965-03-16

Description

March 16, 1948. c. FRONDEL QUARTZ OSCILLATOR PLATE Filed Dec. 15. 1944 INVENTOR CLlFFORD FRONDEL ATTORNEYS Patented Mar. 16, 1948 UNITED STATES, PATENT OFFICE QUARTZ oscmmiron PLATE Clifl'ord Frondel, Flushing, N. Y., assig'nor to Reeves-Ely Laboratories, Inc., New York, N. Y., a corporation of New York Application December 15, 1944, Serial No. 568,324

1 21 Claims.

This invention relates to quartz oscillator plates and has for its object certain improvements in the method of manufacturing oscillator plates made of quartz or equivalent material.

In the manufacture of so-called BT quartz oscillator plates, for example, automatic or semiautomatic machines are generally employed in the initial and intermediate states. The final finishing of the plates is, however, still largely a hand operation, the work being done by highly skilled operatives, usually called finishers. In

finishing the plates, physical dimensions of the,

order of sub-millionths of an inch are involved. The finisher is usually provided with a frequencychecking device, a fiat glass plate, fine abrasive, an etching solution, water, a brush, cleaning solutions, lint-free towels, a, micrometer, an optical fiat, a small square, etc.

The finisher receives the plates, sometimes called blanks, as they come from mechanical lapping machines, the plates having been cut to substantially proper length and width and usually brought close to, but less than, the desired oscillating frequency. In a, platedesired to have a final frequency of, say, 8,000 kc., the machine lapping or other pre-hand-finishing treatment is stopped when the plate is from roughly a few hundred cycles up to ten or more kilocycles under the final desired frequency. A preliminary frequency check is then made by comparing the frequency of the plate withthat of a standard plate.

having a known frequency. This gives the finisher a general idea how much hand lapping the plate should be given. To reduce the plate to its proper thickness, and hence to increase its frequency, the finisher grinds the plate in a mixture of the abrasive and water on the fiat glass plate. keeping the faces of the plate as fiat and parallel as possible. The plate is next thoroughly cleaned and dried, after which its frequency is again tested. This is done by inserting the carefully cleaned plate in a holder, plugging the holder into an oscillator circuit and noting whether or not the plate has reached the desired oscillating frequency. The lapping of the major plane surfaces of the plates usually is accompanied by a lapping or beveling of the edges of the plates; this operation, by removing roughness and other imperfections from the edges and by altering the edge dimensions, gives the desired degree of activity, socalled, to the plate. v

The finishing of a plate to its desired frequency also may be accomplished in other ways, and a number of techniques other than handlapping have been and are being. developed in the oscillator-plate industry. Thus, in the so-called aclddip or etching process,,the plates as obtained at the completion of the machine lapping are brought up to the desired frequency by dipping them for the required length of time into a solvent for quartz. This solvent, which may be, for example, hydrofluoric acid, removes quartz from the surface of the plate and thus acts to reduce the thickness of the plate to the desired value.

This process, as with hand lapping, requires an intermittent, successive, series of treatments and measurements, especially in the final stages, to

ensure that the desired frequency is exactly attained. The rate of etching of difierent plates of the same initial frequency is not identical, due to variations in the cleanliness of the surface, the roughness of the surface, and other factors, so that a uniform, timed, procedure for all plates can not be set out. In still another method of finishing plates to the desired frequency, the plates are tumbled with an amount of coarse abrasive in a container until the frequency approaches that desired. The plates are then removed, cleaned, and

are adjusted to the desired frequency either by etching or hand lapping.

Alternate hand lapping, cleaning and testing are required until the plate reaches the desired frequency. The activity of the plate is determined by its dimensions, contour, parallelism, absence of The human factor is an exceedingly important 1 element in these finishing operations and the results obtained tend naturally to vary from person to person, depending upon the particular technique employed at the time by each finisher.

As a result of my investigation I have discovered that the frequency and certain other characteristics of piezo-electric bodies may be adjusted or varied without altering the physical dimensions or the body, such as by grinding, etching, or plating with a metal or other material.

The frequency of oscillation of quartz oscillator plates, for example, may be varied continuously and this variation may be brought-under continu- 3 cos visual control as by an appropriate meter. This permits the frequency to be adjusted exactly to a predetermined value or range merely by following the frequency variation on a meter and stopping the treatment at the desired value or within the desired range. This is not possible in present methods of manufacture of piezo-electric bodies which. as noted above, involve a discontinuous alternating process of grinding or etching, cleaning and testing. The frequency of oscillation of quartz oscillator plates may, for example, be readily adjusted to a desired value with an accuracy up to 1 cycle or greater, depending primarlly on the accuracy of the measuring device employed. This accuracy cannot be accomplished by the conventional method of grinding or etching because the amount of grinding or etching on which the change of frequency and accuracy depends cannot be accurately controlled or measured, and the change in frequency itself cannot be observed continuously.

The frequency of a piezo-electric .body that has been put into a relatively stable state by means of baking, etching with a solvent for quartz, or other treatment, such as for the purpose of eliminating or reducing spontaneous variation with time in the frequency or activity of the piezo-electric body, can be adjusted without destroying the stability of the piezo-electric body. This is not possible by present methods of manufacture. For example, if a number of quartz oscillator plates are brought by grinding or etching to a desired frequency, and are then baked or otherwise treated, for the purpose of stabilization, it is found that the frequency often changes erratically from the original value and must then be adjusted by additional grinding or etching. This action then destroys the stabllity of the oscillator plate and the purpose of the original stabilizing operation is lost. This readjustment can now .be accomplished without grinding or etching and without loss of sta- 'bility.

The frequency of oscillator plates may be adjusted, for example, without wetting them with water or other liquids and in an entirely dry condition. Water is commonly used in the conventional method of finishing to frequency by lapping with an abrasive or by etching, and has been considered to contribute substantially to undesirable ageing and other phenomena in the finished oscillator plate. This diificulty may now be obviated.

The frequency of a piezo-electric body can be adjusted while it is contained in its permanent holder, whether this is of the contact (pressure), air gap, wire suspension or other type of mount. If desired, the frequency of the piezoelectric body may be adjusted before it is mounted in its permanent holder.

The change in frequency brought about by application of the invention is downwards from the initial value, but the downward change may be reversed, and the frequency restored to its original value, 'by suitable treatment. The new technique is especially advantageous in the recovery of oscillator plates that have been overshot by the ordinary methods of hand finishing, provided that the desired frequency change is within the range of the radiation technique. Oscillator plates that have increased in frequency over the upper tolerance due to ageing, or underplating, or aged low activity plates that have gone over the tolerance after cleaning to bring up the activity, may be similarly readjusted to their original frequency.

In accordance with the invention, the method comprises the step of treating quartz oscillator plates to the action of X-rays adapted to decrease their frequency of oscillation.

The change in frequency produced in oscillator plates by these radiations is downwards from the original value, as pointed out in my co-pertding application Serial No, 568,323, filed December 15, 1944. The change is progressive and continuous durin irradiation but finally reaches a limited value, determined by factors within the quartz, beyond which there is no further change. The rate of change appears to depend primarily on the kind and intensity of the radiation, but in part on variations in the properties of the quartz from specimen to specimen and on pre-treatment of the quartz. The continuity of the change is of great importance from a manufacturing point of view. The downward direction of the change is also of particular advantage.

The downward change in frequency brought about by the radiations is permanent under ordinary conditions, but can be reversed and the oscillator plate brought back to its original fre quency by baking at a suitably elevated temperature or by irradiating the plate with ultraviolet rays. Ultra-violet rays reverse the action of the other types of radiation. The ability to reverse the downward change is a great advantage. In other words, the oscillator plates may be adjusted downwards and upwards in frequency repeatedly by the proper treatment.

The rate at which the downward change in frequency of the oscillator plates can be effected and the total amount of change are influenced by the temperature at which the quartz is held during irradiation, and by previously baking the quartz at a suitably elevated temperature.

These and other features of the invention will be better understood by referring to the accompanying drawing, taken in conjunction with the following description, in which:

Fig. 1 is a diagrammatic representation of an X-ray tube showing a quartz oscillator plate positioned before its window for treatment with X-rays, illustrative of a practice of the invention; and

Fig. 2 is a similar diagrammatic representation showing the quartz oscillator plate mounted on a holder which is in turn connected to a frequency meter.

Referring first to Fig. 1, the apparatus shown comprises a lead housing 9, an X-ray tube l0 having mounted therein a cathode H, and an anode I2 terminating at its free end in a copper target l3 disposed laterally from a window or windows l4, M in the side of the housing. A quartz oscillator plate I5 is shown in front of window M, the plate being held on a sliding holder [6 movable in an upper track I! and a lower track l8 by means of a handle IS. A stack of plates I5 is shown in front of window l4.

Referring next to Fig. 2, the apparatus shown comprises a similar X-ray tube 10 with a quartz oscillator plate l5 located in front of window I4 of the tube. In this case, however, the oscillator plate is mounted in a holder 20 of conventional construction. The casing of the holder around the oscillator plate is shown broken away, for convenience. The holder is in turn connected with a frequency meter 2i by means of a pair of

leads

22 and 23. The frequency meter may be of conventional design, having a needle 24 adapted to move back and forth over a graduated frequency scale 25, preferably divided to indicate cycles per second.

The X-ray tube shown is of the evacuated, hot

element, type. when current is passed through the filament or cathode II, it is heated and resuits in a thermionic emission of a stream of high speed cathode rays or electrons 30, which are focussed on copper target H, from which theylating characteristics, the frequency in other words. The bombardment of the oscillator plates with the beamof X-rays may 'be conducted until the oscillating characteristics of'each oscillator plate fall within a predetermined range. In the case of the stack of plates IS, the plate nearest window I4 receives the greatest effect from the radiations, although the next succeedingplates are aflected less and less progressively by the radiations. 4

When using apparatussuch as that disclosed in Fig. 2, the predetermined frequency range just mentioned may be noted visually on frequency meter 2|. when needle 24 is deflected until it points at the desired frequency orfrequency range indicated by scale 25, the oscillator plate is taken out of the beam of X-rays or the beam of X-rays is shut off.

As pointed out, irradiation of the quartz oscillator plate with the X-rays decreases its frequency. The rate of change of frequency during irradiation is rapid at first but drops off with time and distance finally to approach a-li'miting values The magnitude of the limiting value varies with different specimens of quartz. This variation, which in the extreme cases so far encountered is about ten-fold, appears to depend primarily on a pre-disposing feature in the quartz itself. The actual rate of change in frequency in a given oscillator plate varies with the conditions of treatment, and primarily with the kind and intensity of radiation. The decrease in frequency during irradiation is accomplished with little, if any, significant change in activity. The observed changes are close in magnitude to the error of measurement, but in general appear to be downward and in some instances are of the order of 1%. c

presence of other absorbing material between the plate and the x-ray source, and on other factors. With low powered x-ray units and an oscillator plate to X-ray tube window distance of 10 or more, the exposure time needed toreach the limit of change was about 5 to or 12 hours. The rate of change of frequency obtained with such low powered X-ray equipment is too slow to be practical for most purposes.

The rate of change in frequency can be greatly increased, however, by increasing the intensity of the X-ray beam and in other ways. It is of advantage to place the oscillator plate as close to the target of the X-ray tube as possible, since the intensity of the radiation varies inversely as the square of the distance therefrom. On the other hand, most X-ray tubes at present available have a relatively fine focus, together with an anode screen, and the area of the X-ray beam at the window is only a few square millimeters. In order to irradiate the entire surface of a /2" or oscillator plate, it is therefore necessary to back off a few inches from the window pf the X-ray tube, and this results in a relatively large loss of intensity.

These dimculties can, of course, be compensated by using a broad focus X-ray tube with a relatively large window. The broad focus also makes it easier to cool the target and this permits an increase in the intensity rating of the tube itself. Getting very soft radiation out of the tube also is a factor. Quite rapid changes in frequency are effected by employing X-ray beams of high intensity. Changes of several hundred cycles have been brought about in 1 or 2 minutes exposure at 20 to 30 ma. and 45 to 60 kv. with a copper target. Comparable changes in not much longer time can be obtained with weak radiation if the oscillator plate is placed directly on or against the window. Extremely powerful X-ray units, such as 1000 kv. tungsten target tubes, are

The decrease in frequency'is continuous up to radiation and to follow the change in frequency visually on the meter. The oscillator plate may then be finished to a specified frequency by shutting ofl. the radiation or removing the plate at the proper value.

Working with BT quartz oscillator plates in the frequency range of 6 to 9 megacycles and with a conventional sealed-off filament type X- ray tube operating at 4 to 15 ma. and 25 to 45 kv. and affording copper radiation, such as is ordinarily employed for crystal diffraction work, a total change in frequency of from 500 to 3000 cycles was obtained in accordance with the invention. The rate of change of frequency depends on the intensity of the radiation, the distance of the oscillator plate from the X-ray target, the distance of the oscillator plate from the window of the X-ray tube, the amountof the total area of the oscillator plate that receives radiation, the distribution of the X-ray energy over the irradiated area of the oscillator, the

not necessarily better, however, because the controlling factor appears to be not the energy in the beam but the proportion of the available energy that is absorbed by the oscillator plate.

As noted above, the change of frequency of the oscillator plate during irradiation drops off with time and finally approaches a limiting value. The limiting value is found to vary widely in different oscillator plates of the same frequency. This variation occurs not only between plates cut from different mother crystalswhether from the same loc'ality or not, but sometimes also between oscillator plates cut from different parts of the same mother crystal. In a general sort of way, the least change in frequency is obtained in oscillator plates that have a natural dark smoky color. Entirely colorless oscillator plates vary widely in the degree of response to the radiation.

Irradiated quartz oscillator plates begin to revert back to their original frequency when heated over about C. Oscillator plates irradiated below about 170 C. have not been found to differ substantially in their stability or behavior from ordinary non-irradiated plates. At temperatures over about 350 C. the reversion to the. original frequency is substantially complete and immediate, but at about 300 C. an appreciable amount of time is required for the reversion. At 220 C. the complete change required several hours. A group of irradiated plates, together with nonirradiated control plates, heated at C. for 384 hours gained roughly half of the frequency originally lost on irradiation. Oscillator plates continuously increased in temperature from- 24 to 250 C. over a period of three hours showed the first change in frequency at about 180 C. but a complete change was not efiected until about 230 C. was reached.

Changes that could be ascribed to a reversal of the eflect of radiation could not be detected in oscillator plates heated continuously over long periods at 160 0., 145 C. and 125 C. In one experiment agroup of irradiated oscillator plates was heated at 125 C. for 861 hours, and the fre- 1o quency was measured at intervals. In the first 200 hours there was a small gradual rise in frequency in both the irradiated and the control plates but thereafter there was no change in frequency. At the end of the run the oscillator plates still had their original color and gained in baking to 500 C. the amount of frequency originally lost on irradiation. The initial gain in frequency may be due to unloading of the oscillator plates by dehydration or otherwise and to ageing. No

changes in frequency or activity have been observed in irradiated plates that have stood at room temperature upwards of one year other than those ordinarily encountered in high frequency oscillator plates and due to ageing. Irradiated oscillator plates also stood up under repeated cycling over the temperature run from -55 C. to +90 C. and under continuous oscillation for a period of days.

The rate of change of freqi icy of a quartz oscillator plate during irradiation is rapid at first but then decreases and approaches zero at saturation. At this point there is no further change in frequency on continued exposure to the X-rays.

The total change of frequency that can be effected 3 is variable and depends on a number of'factors. Among these are the type of cut of the plate, the treatment given to the plate prior to irradiation, the kind of radiation employed, and the initial frequency, or thickness, of the plate itself. There is also a considerable variation in response among different specimens of raw quartz and hence between diiferent plates of the same frequency cut therefrom. The time needed to efiect saturation appears to be constant for plates of a given frequency regardless of the total amount of change provided that the conditions of irradiation are identical. The observed variation in saturation value in 8000 kc., BT-cut,' plates is roughly from 500 to 3000 cycles decrease, with an average change of approximately 1400 cycles decrease. These and other data refer, unless so stated, to quartz plates exposed to unfiltered copper X-rays without special provision to increase the effect by prior sensitization of the quartz or otherwise.

The change in frequency appears to be a photoelectric eifect in the quartz by the absorption of radiant energy, The X-ray energy absorbed by the quartz apparently is able not only to effect a momentary transfer of electrons from low to higher levels, but also permanently to eject electrons from the atom. The alteration in the interatomic bonding forces thus brought about is reflected by the variation in the elastic constants the irradiated plate.

The principal factors influencing the rate of change of frequency during irradiation are the intensity of the X-ray beam, the distance of the and, in turn, in the oscillating characteristics of plate from the window and anode of the X-ray tube, and the initial frequency of the plate itself.

The rate of change of frequency is found to be directly proportional to the intensity of the X-ray beam. The beam intensity itself increases as the square of the voltage and directly as the cur-rent passed. It may be noted that the peak wave-length of the continuous radiation yielded by the tube decreases with increasing voltage so that there is an accompanying slight decrease in the percentage absorption of the beam.

Using copper radiation from an x ray tube operated at 25 ma. and 60 kv., with a plate to window distance of approximately 1 mm., ordinary unsensltized 8 megacycle plates can be changed in frequency on the average about 40 cycles a minute. At 20 me. and 40 kv. on a slightly different type of tube an average rate was obtained of roughly 18 cycles a minute; and at 4 ma. and 20 kv. on still another tube, a rate of about 5 cycles a minute. Charges of from 200 to 400 cycles have been obtained in one minute on tubes operated intermittently at 60 ma. and 50 kv. with the plate directly on the window. If the quartz plate has been sensitized before irradiating, or other steps taken to increase the response, these rates may be increased several-fold at the same beam intensities.

If absorbing material is interposed between the window and the quartz plate, the rate of change of frequency is reduced due to diminution in intensity of the beam. Wire suspension mounted plates that are irradiated through their holders while oscillating change much more slowly than when irradiated at the same window distance and and out of their holders. In such work, every effort should be made to reduce the thickness of the wall or housing of the holder to a minimum and to use holder materials that arerelatively transparent to X-rays. Plastics, thin aluminum or beryllium foil, and very thin copper foil, are relatively transparent to copper X-rays. Metals, such as iron or lead, are relatively opaque to X-rays, even in thin sheets, and X-ray beams of the intensity heredescribed cannot penetrate through the steel electrodes used in clamp-type holders.

The distance of the plate from the window and anode of the X-ray tube is one of the most-important single factors in irradiating oscillator plates, Broadly speaking, a given frequency change produced in a few minutes when the plate is 0.5 mm. from the window will require an exposure time of hours when the plate is 20 mm. from the window and an exposure of many days at a distance of a foot. Although the intensity of radiation drops ofi? inversely as the square of the distance from the source, it is found in the present instance that the time needed to effect a given frequency change decreases much more rapidly than would be excepted from this law as the plate closely approaches the Window. This is due in part to the fact that the X-rays proceed from a relatively broad area on the target and not from a. point source, and to the relatively high absorption of the longer, and more effective, wavelengths inthe beam during their passage in the air after emerging from the window.

The average saturation value increases with increasing frequency of the plate. The average rate at which saturation is reached also is found to increase with increasing plate frequency, or decreasing plate thickness, at constant intensity of the X-ray beam. The increase in rate with decreasing thickness appears to be much more pronounced than the accompanying increase in saturation value., This presumably is due to the relatively strongly absorbed but weakly penetrating long wave-length components of the incident beam, which, while they penetrate to the same depth in a thin as in a thick plate, expose a larger percentage of the total mass of quartz as the plate thickness decreases Only part of the total area of a BT-cut plate has to be irradiated in order to gain the maxi-,

' for maximumresults. Frequency change of 100 irradiated to change frequency more rapidly.

The increase in rate brought about by baking between 250? and 350? C. ranges up to two-fold,

and there is an accompanying increase in the total frequency range. It is often advantageous to heat the plates to 300 to 570 C. in order markedly to sensitize them prior to irradiation with X-rays. Such baking has a stabilizing effect on the irradiated plates. In this connection it may be noted that a'former objection to the baking of the plates, that of erratic increase in frequency which often brought the plates out of tolerance, is 'readily overcome by the irradiation method without destroying the stability of the plates.

If a thin quartz plate isplaced in an X-ray beam, a large part of the incident radiation is transmitted through the plate. The transmitted radiation is wasted, since only the absorbed radiation can produce frequency shift in the with a more pentrating radiation, such as from a tungsten tube operated at from 40 to 80 kv.

Irradiated quartz ,plates revert back to their original frequency when heated to a sumciently high temperature. The change is a time-temperature reaction. No frequency changes have been observed in irradiated plates, stabilized by baking and deep etching before irradiation, and left on time tests for periods over six months at room temperature and for periods of weeks at temperatures up to about 170 C. Repeated cycling over the range of 55 to +90? C. has not been found to affect the stability. In the neighborhood of 170 to 180 C. a .true reversal of frequency begins, which is extremely slow and requires a period of weeks for completion. The rate of reversal increases rapidly with increasing temperature. In the range of about 210 to 230 C. complete reversal requires a few hours, and at 350 to 400 C.a few minutes. Over 450 C. the change is almost instantaneous.

The increase in frequency brought about by baking is found to be exactly the same as the initial decrease brought about by irradiation. This is true, however, only if the plate has been stabilized before irradiation and does not undergo an added increase in frequency due to ageing when it is later baked. Stabilized plates can be cycled downwards by irradiation and upwards by baking indefinitely by the same amount of frequency if the conditions of irradiationand baking are exactly duplicated.

The action of heat and of ultra-violet light in reversing the frequency change brought about plate. The efilciency of utilization of the X-ray beam can be increased by stacking a number of plates, one behindor above the'other. All of the incident beam can be absorbed if the stack of plates is sufilciently thick. If a mono-chromatic beam of X-rays is employed. the decrease in intensity of the-transmitted beam, or absorption in each plate in the stack as measured by an ioniza tion chamber is found to follow an exponential v law. That is. the intensity of the transmitted beam decreases by a constant percentage in passing through each successive plate.

The wave-length of the X-rays employed ing power is relatively low and hence the greater part of theenergy in the X-ray beam might be transmitted through a relatively thin crystal.

Considering the various factors involved, including the practicalities of tube design and flexibility of application, copper radiation appears at present to be best for general use. Radiation of a longer wave-length and hence more easily absorbed, such as from iron, cobalt, chromium, manganese, or titanium target, would be especially suited for very high frequency plates, of a; thickness of 0.008 inch or less. quency plates may perhaps best be irradiated Thick low freby X-rays oifers the possibility of adjusting the frequency of irradiated plates on the up-grade. Thus, plates, overshot by X-rays on the downgrade, can be recovered, or plates can be deliberately overshot in'bulk by a very powerful and relatively cheap source of radiation and then individually adjusted upwards to the desired frequency by heat or ultra-violet. Mounted plates can be adjusted to frequency by heat in this way, but only if the holder does not contain plastic or soldered or other parts which are affected by the degree of heat necessary. Adjustment by ultra-violet light requires that the plate be directly exposed to the, beam, because the ordinary holder materials are opaque to, do not transmit, the ultra-violet wave-lengths.

- In the frequency adjustment of unmounted, nonoscillating, plates, the method is especially applicable to plates in which the frequency need merely be reduced below a certain tolerance and a precise adjustment is not desired. This situation is commonly met in the case of plates that have been overshot in frequency during the final finishing, or that have' been underplated; that have increased in frequency over tolerance due to ageing; or that have gone over tolerance after cleaning, baking, or other treatment to effect stabilization. In order to gain full advantage of the irradiation technique, it may be advantageous to readjust the finishing tolerances used in production, so that the percentage of undershot plates is reduced with acorresponding increase in the percentage of over-frequency plates.

In practice, the plate frequency is measured,

the amount of reduction in frequency needed to ference frequencies. There is a significant vari tion in the degree of response of different plates of the same frequency, as already pointed out, so that it may be necessary in the case of plates that respond much less than average to run them again after the first irradiation. It is usually found advantageous in the case of reruns to turn the plate so that the original back surface is in front. This change is also of advantage when relatively large frequency changes are to be effected and in irradiating low frequency plates. The benefit is derived from the fact that the front side is quickly saturated in a thin surface layer by the soft, weakly penetrating, components of the incident beam leaving the rearward portions of the quartz plate less affected and hence relatively more responsive when the plate is turned over.

In the frequency adjustment of mounted, oscillating, plates, full advantage of the method is gained only if the plate can be irradiated while mounted in its permanent holder. This requires a wire suspension or clip mounting in which the major portion of the plate is not shielded by heavy metal parts. Plates mounted between conventional contact (pressure) electrodes cannot be irradiated directly because the metal parts shield off the X-ray beam. In such cases, it is desirable to measure the plate beforehand and to determine the amount of frequency change desired. to transfer the plate to a temporary holder in which it can be oscillated and,simultaneously irradiated to its desired frequency, and then to place the plate in its permanent holder.

In the treatment of quartz oscillator plates just described, primary X-rays were employed. The invention may also be practiced with secondary X-rays which are emitted when a beam of primary X-rays strikes or passes through certain materials. There are, in general, two kinds of secondary X-rays: (1) scattered rays of exactly the same, and in part ofslightly longer, wave length as the original primary beam; and (2) characteristic rays characteristic of the material from which they are radiated, being identical with the characteristic X-rays emitted by the same material when used as the target of an X-ray tube. The secondary X-rays are useful in the practice of the invention because the surface of the quartz oscillator plate to be treated is covered or coated with a suitable powder, film or layer of a foreign metal, chemical compound or other material which will scatter the incident X-rays and also yield its own characteristic rays (secondary radiation) of definite wave length when it is struck by a primary beam of X-rays, or other radiation. This secondary X-radiation then acts on the quartz plate. The foreign material can be so selected as to yield characteristic, secondary, X-rays of a relatively long wavelength which are more highly absorbed by the irradiated plates than the primary X-rays. Primary X-rays tend to be hard while secondary X-rays tend to be soft and more strongly absorbed. Also, the intensity of the irradiation is increased, as can be seen, for example, from the fact that if the side of the plate away from the incident beam is coated with or is immediately adjacent to a foreign material which strongly emits secondary X-rays, part of the secondary X-rays proceeding therefrom radiates backwards into the quartz plate where it adds to the effect of the incident, primary, beam of X-rays. When using primary copper X-rays, it is advantageous, for example, to place a piece of nickel or cobalt 12 foil directly behind the plate, or in front of the plate, or both. The use of secondary X-rays is more particularly described and claimed in my copending application Serial No. 568,325, filed December 15, 1944.

X-rays are dangerous to humans and every care should be taken to shield the operator of the method and apparatusfrom direct or primary, as well as scattered or secondary, radiations. To this end the apparatus employed should be shielded with leadsheets of sufficient thickness to prevent penetration and emission of the X-rays.

As previously noted, the frequency of quartz oscillator plates also undergoes a change when the plates are treated with ultra-violet rays; the change in frequency, however, .being upwardly instead of downwardly. Oscillator plates irradiated as described above in order to decrease their frequency may be reverted in frequency to their initial or intermediate value when exposed, for example, to a powerful quartz-mercury lamp. The change is accelerated by heating the quartz oscillator plates to IOU- C. during irradiation with the ultra-violet rays. The use of ultraviolet rays offers an important advantage. If for some reason the frequency of an oscillator plate should be decreased too much by the other types of radiation disclosed, its frequency may be increased to the desired value. This method is more particularly described and claimed in my co-pending application Serial No. 568,330, filed December 15, 1944.

It will be clear to those skilled in this art that the invention lends itself to numerous modifica tions, The oscillator plates may be irradiated whether plated or unplated, coated or uncoated. In accordance with the invention the oscillator plates may, for example, be plated with a, metal such as gold, silver, aluminum or an alloy which may serve the purpose of making a better or more intimate electrical contact with or act as electrodes; or which may serve as protective or stabilizing films. The plates may, for example, be

coated with amorphous silica or organic plastic or other material which may serve the purpose of protective or stabilizing films. In the case of oscillator plates that have been protected or stabilized by a plating, coatin or other treatment, including heating and ageing, the radiations herein contemplated are adapted nevertheless to modify the oscillator plates so as to vary their oscillating characteristics; and irradiation of the plates may be conducted until their frequency of oscillation reaches the desired value without substantial loss of stability. The plates may be ad justed upwards or downwards in frequency repeatedly by use of the proper radiations.

It also is possible to adjust the plate to have a desired frequency at a given temperature by irradiating the plate, and bringing it to frequency, while it is held at that temperature in a suitable heating or cooling contrivance. This is not easily accomplished by the conventional lapping or etching techniques of finishing plates,

The rate of change of frequency of the plate during irradiation and also the total amount of frequency change that can be obtained (saturation value) can be modified by baking the quartz plate at a suitable temperature before it is irradiated. Thus, baking the quartz plate at a suitably elevated temperature has been found to increase both the rate of change and the amount of change of frequency over that which would obtain if the plate had notbeen baked beforehand.

The oscillator plates may be irradiated whether mounted or, unmounte'd. It is advantageous to' irradiate the plates while they are mounted in a temporary or permanent holder and whilethe plates are oscillating. It is particularly advantageous to conduct the irradiation operation while the oscillator plates are mounted in a permanent holder connected with a suitable meter, so that the change in frequency of oscillation which takes place may be visually observed and the irradiation stopped'when the plates have attained the desired frequency. The type of permanent holder, for example, may be of the pressure orclamp, air-gap, combined pressure and airgap, wire-support, mechanically or hermetically sealed, temperature-controlled or temperature protected, or themultiple-type. If the oscillator c plates are mounted in a permanent holder,-the

radiations go right through the plastic, glass or metal shell or housing of the'holder, A sumciently penetrating radiation must, of course, be

employed. This practice is especially useful in the case of oscillator plates supported between wire suspension mounts in thin-walled vacuum holders. If theoscillator plates are not mounted in a holder, they may be held, for example, in paper or aluminum foil envelopes which protect them from moisture, dust and grease spots from handling. i

It also is convenient under certain circumstances to irra'diate a large number of plates simultaneously. This can be done, for example, by stacking the plates together and placing the stack directly in front of the window, face on. The amount of frequency change thus brought about is not uniform through the stack, but is greatest in the first plate, considerably less in the second, and then decreases more slowly in succeeding plates. beam of X-rays the frequency decrease in successive plates appears to follow an exponential With a homogeneous (monochromatic) holder and to decrease the frequency of oscilla-' 4. In the manufacture of quartz oscillator plates, the improvement which comprises treating each plate while mounted in a holder connected to a frequency meter-to the action of X- rays adapted to pass through the housing of the tion of the plate, and'terminating the treatment of each plate with said X-rays when its frequency of oscillation reaches a predetermined value.

5. In the manufacture of quartz oscillator plates, the improvement which comprises maintainlngeach oscillator plate at a predetermined temperature, treating each plate while at said temperature with X-rays adapted to decrease its frequency of oscillation, and terminating the r treatment of each plate with said X-rays when I its frequency of oscillation-reaches a predetermined value; I

6. In the manufacture of quartz oscillator plates, the improvement which comprises main-- taining each oscillator plate at a predetermined temperature while mounted in a holder connected with a frequency meter, treating the plate while at said temperature with X-rays adapted to decrease the frequency of oscillation of the plate,

and terminating the treatment. of each plate with said X-rays when its frequency of oscillation reaches a predetermined value. v

7. In the manufacture of quartz oscillator plates, the improvement which comprisesmain; taining each oscillator plate at a. predetermined temperature while mounted in a holder connected with a frequency meter, treating each plate to the action of X-rays adapted to pass through plates, the improvement which comprises treating each oscillator plate with X-rays adapted to decrease -its frequencyof oscillation.

2. In the .manufacture of quartz oscillator plates, the improvement which comprises treatdecrease its frequency of oscillation, and terminating the treatment of each plate with said X- rays when its frequency of oscillation reaches a predetermined value.

3. In the manufacture ofquartz oscillator plates, the improvement which 'comprises treating each oscillator plate while mounted in a holdor connected to a frequency meter to the action of X-rays adapted to decreasethe frequency of oscillation of the plate, and terminating the treatment of each plate with said X-rays when its frequency of oscillationreaches a, predator-- mined value.

the housing of the holder and to decrease the I frequency of oscillation of the plate, and terminating the treatment of each plate with said X-rays when its frequency of oscillation reaches a predetermined value.

8. In the manufacture of quartz oscillator plates, the'improvement which comprises grinding each oscillator plate to a thickness beyond that required to increase its frequency to a predetermined value, and treating each ground plate with X-rays adapted to decrease its frequency of oscillation.

9. In the manufacture of plates, the improvement which comprises grinding each oscillator plate to a thickness beyond that required to increase its frequency to a predetermined value, treating each ground-plate with X-rays adapted to decrease its frequency of oscillation, and terminating the treatment of each ground plate with said X-rays when itsfrequency of oscillation reaches-a'predetermined value.

10. In the .manufacture of quartz oscillator plates, the improvement which comprises etching each oscillator plate to athickness beyond that required to increase its frequency to a'predetering each oscillator plate with X-rays adapted to mined value, treating each etched plate with X- rays adapted to decrease its frequency of oscillation, and terminating the treatment ofeach etched plate with said x-rays when its frequency of oscillation reaches a predetermined value.

11. In the manufacture of quartz oscillator plates that have been stabilized by baking, acid washing or other treatmentand that have a frequency of oscillation higher than desired, the improvement which comprises treating each stabilized oscillator plate with X-rays adapted to decreaseits frequency-of oscillation, and terminating the treatment of each stabilized plate with said X-rays when its frequency of oscillation reaches apredetermined value.

12.111 the manufacture of quartz oscillator quartz oscillator 13. In the manufacture of quartz oscillator plates, the improvement which comprises treating each oscillator plate with X-rays adapted to de-,

crease its frequency of oscillation, treating each plate to the action of ultra-violet light rays adapted to increase its frequency of oscillation, and terminating the treatment of each plate with said ultra-violet light rays when its frequency of oscillation reaches a predetermined value.

14. In the manufacture of quartz oscillator plates, the improvement which comprises heating each oscillator plate to an elevated temperature to sensitize it to frequency change, treating each sensitized plate to the action of X-rays adapted to decrease its frequency of oscillation, and terminating the treatment of each plate with said X-rays when its frequency of oscillation reaches a predetermined value.

15. In the manufacture of quartz oscillator plates, the improvement which comprises heating each oscillator plate to an elevated temperature to sensitize it to frequency change, treating each sensitized plate to the action of X-rays adapted to decrease its frequency of oscillation, treating each plate to the action of ultra-violet light rays adapted to increase its frequency of oscillation, and terminating the treatment of each plate with said ultra-violet light rays when its frequency of oscillation reaches a predetermined value.

16. In the manufacture of quartz oscillator plates, the improvement which comprises heating each oscillator plate to an elevated temperature to sensitize it to frequency change, treating each sensitized plate to the action of X-rays adapted to decrease its frequency of oscillation, heating each oscillator plate so treated to increase its frequency of oscillation, and terminating the heating of each plate when its frequency reaches a predetermined value.

17. In the manufacture of quartz oscillator plates, the improvement which comprises treating each oscillator plate with copper X-rays adapted to decrease its frequency of oscillation.

18. Inthe manufacture of quartz oscillator plates, the improvement which comprises treating each oscillator plate with copper X-rays adapted to decrease its frequency of oscillation, and terminating the treatment of each plate with said copper X-rays when its frequency of oscillation reaches a predetermined value.

19. In the manufacture of quartz oscillator plates, the improvement which comprises treating each oscillator plate while mounted in a holder connected to a frequency meter to the action of copper X-rays adapted to decrease the frequency of oscillation of the plate, and terminating the v treatment of each plate with said copper X-rays when its frequency of oscillation reaches a predetermined value.

20. In the manufacture of quartz oscillator plates, the improvement which comprises treating each plate while mounted in a holder connected to a frequency meter to the action of copper X-rays adapted to pass through the housing of the holder to decrease the frequency of oscillation of the plate, and terminating the treatment of each plate with said copper X-rays when its frequency of oscillation reaches a predetermined value.

21. In the manufacture of oscillator plates the step comprising decreasing the frequency of the oscillator plate by treating the same by X rays.

CLIFFORD FRONDEL.

REFERENCES CITED UNITED STATES PA'I'EN'I'B Name Date Bond June 12, 1945 Number