Sept. 10, 1-946. ' “ ‘w, P, MASON ' 2,407,315 LIQUID MEDIUM FOR ULTRASONIC COMPRESSIONAL WAVE TRANSMISSION ‘ Filed Oc't. 6. 1943 . 2 Sheets-Sheet 1 FIG / INVENTOR By W . B MASON :f $ .47‘ TORNEP ‘ Sept. 10, 1,946. I w. P. MASON 2,407,315 LIQUID MEDIUM FOR ULTRASbNIC COMPRESSIONAL WAVE TRANSMISSION Filed Oct. s, 1943 ‘2 Shoals-Sheet 2 H612 .IQCOUSTIC IMPEDANCE 0F MIXTUIES 0MP Aw I"? AT "'6. AND IMKC. p - aumrr v - moan-r W, = 4:00am lumwvct L80 - I40 - 34% x: x L30 m: L30 " ‘ uo - L00 ' w ,9 msozv Patented set; 10, 1946 ‘ v ' 2,401,315 Q'UNI‘TED STATES PATENT OFFICE ‘ 2,407,315 ' - LIQUID MEDIUM FOR ULTRASONIC GOM PBESSIONAL WAVE TRANSMISSION Warren 1’. Mason, West Orange, N. 5., assignor' to Bell Telephone Laboratories, Incorporated, New York,'N. Y., a corporation of New York Application October '6, 1943, Serial No. 505,158 ' 2 Claims. (01. 252-1) . . This invention relates to ultrasonic compres sional wave transmission and has for its object the discovery and use of a medium which will support the transmission of high power. - It has been shown that the phenomenon of I‘ cavitation imposes a limit on the amount of power which may be transmitted by a transducer, the transducers provided having a capability of transmitting far greater power than can be sup ported by the surrounding medium.‘ ' One form of transducer in common use con sists of an array of piezoelectric crystals which respond to electrical excitation to produce com pressional waves in a surrounding medium such ,2 struction even after cavitation has been estab lished. _ Investigation has shown that when an object is moved in a liquid insuch a way as to put a ten sile strain on the liquid, if the movement is-of su?‘lcient rapidity voids are torn in the liquid. ‘ When these voids collapse the movement of the liquid has‘ acquired a certain momentum which leads to great and destructive forces being brought 10 to bear on anything in the path of such move- ‘ ment. It has further been found that this phe nomenon of cavitation starts somewhat more readily and has less destructive effect in a liquid in which a considerable amount of gas has been as sea water; but it has been found that sea 15 dissolved. Whereas in such a liquid, gaseous water will not transmit a great concentration of power before the phenomenon of cavitation sets bubbles may easily be formed, as by agitation, the bubbles so formed'are easily expanded by the forces which establish cavitation but are ?lled in and imposes a practical limit thereto and it has also been found that besides limiting the with vapor of the liquid .or the dissolved gas and power which may be transmitted, that cavitation 20 consequently do not collapse with such great leads to rapid physical destruction of the trans-‘ force as'would a void approaching a vacuum. ducer. Hence a transducer in such a liquid is not sub Some advance in the means to transmit greater ject to such rapid destruction as it would be if power has been made by immersing the trans operated in a non-gaseous liquid. But the gaseous ducers in another liquid which will support a turbulence set up in such a gaseous liquid has just greater power than sea water and then inter as limiting an effect as true cavitation on the ‘ posing between such surrounding liquid and the transmission of power. sea water in diaphragm having a much greater One means for increasing the power that may area than the effective area of the faces of the be transmitted through a liquid medium‘ is there transducers so that the power transmitted there 30 fore to use a non-gaseous or a degassed liquid. by per unit of area is comparatively small. In It has further been found that the cohesive this way the total power transmitted may be force which is related to the tensile strength of greatly increased. However, even in this case, the the liquid is the chief factor which determines power transmitted by. the transducer has to be the amount of power the liquid will .transmit be limited a reasonable amount below the point at 35 fore cavitation sets in. It is, therefore, desirable which cavitation will begin so as to avoid de to employ a liquid which has a high cohesive struction of the transducer should the power be force. momentarily raised above the danger point. It is a speci?c object of the present invention to . - ' Applicant has discovered that a great amount of power may be transmitted by employing a liquid provide means whereby the power which the 40 which'is non-gaseous, has a high cohesive force liquid medium in contact with the transducer will and in addition has a high vapor pressure. This supportjmay'be transmitted freely and whereby last factor is one which causes the liquid'to act the tra'nsducer‘may be operated without de in the same manner as a gaseous liquid for due‘to 2,407,315 I ‘ 3 4 form a sealed chamber housing the electrical ap paratus and ?lled with a liquid medium 3 such as a mixture of dimethyl p'hthalate and xylene hexailuoride. The electrical apparatus consists of a plurality of piezoelectric crystal mosaics such as 4, 5 and 6, each with its resonator 1, 8 and 9 respectively mounted on a plate In. With in a housing H, also attached to the mounting the high vapor pressure voids torn in such liquid are filled with vapor of the liquid and hence do not collapse with the destructive effect of voids which more nearly approach a vacuum. There fore, given a liquid medium which will support a large power transmission before cavitation sets in, it may be employed up to the limit because like the turbulence set up in a gaseous liquid the plate l0, there is contained other electrical ap cavitation here set up is robbed of its destructive power through its, high vapor pressure and hence 10 paratus such as ?lters and delay networks ,used when such a transducer is connected as a prism if the limit is overstepped the transducer will not array. The device is shown as submerged in > be immediately ruined. water I2 and the vertical broken lines to the It can be said in general that as the cohesive right of the pc rubber cap represent a compres force of various liquids increases, the vapor pres sure thereof decreases. A feature of the present __ sional wave as being transmitted. The graphs of Fig. 2 represent the values of p the density, 12 the velocity and p1: the acoustic impedance of various mixtures of DMP and XHF. sure. Horizontal lines at values between, 1.5 and 1.6 While the above is a primary requirement, there are other qualities which such a liquid must 20 represent the po values of sea water so it will be ‘seen that DMP has a higher pu value and XHF have. It must have a very high electrical resist has a lower pv value than sea water. It will be ance so that no effective electrical connections noted that the density of the mixtures lies accu will be made thereover between electrodes which rately on a straight line between the terminal are immersed therein. It musthave low viscosity to avoid heating at the crystal face through the 25 values. The basis for this relationship is given invention therefore is a liquid characterized both by a high cohesive force and a high vapor pres by the formula violent mechanical agitation of the liquid there at. It must have a mechanical impedance equal to sea water and it must not physically or chem ically affect the devices and parts with which it comes in contact. Applicant has discovered that a mixture of dimethyl phthalate and xylene hexa?uoride most nearly ful?lls all of these requirements. Dimethyl phthalate, hereinafter referred to as 30" where p1 and p2 are the densities of the two com ponents, X is the proportion of the first com ponent‘and (l-X) that of the second. For this mixture of DMP and XHF this relation is quite accurate when used for the density but not for the velocity and impedance. The next plausible DMP, is a derivative of benzene and an ester of 35 assumption is that sound travels through the phthalic acid having the chemical formula liquid as if it went first through all of one pure CeH4(COOCH3) a. This liquid ranks among the component the-rest of a given distance. This highest in its cohesive force and at the same time leads to ‘the relation for the velocity. has a low viscosity. It has a low vapor pressure. Xylene hexa?uoride, hereinafter referred to as 40 XHF, is another derivative of benzene and has the chemical formula CaI-IdCFa) 2. While it‘has a low cohesive force it has a very high vapor pres _____ viva " T.+“(1-Xiv‘. Applying this relation to the present components gives an over-connection. Actually, the experi sure and a low viscosity, Generally speaking these liquids having a high vapor pressure are good solvents and have a highly corrosive effect mental points, from which the graph for u were on the rubber which is used as a diaphragm. empirical relations, the line for v in Fig. 2 repre XHF is peculiar in this respect that while it has a high vapor pressure it nevertheless has a high plotted, lie closely half-way between these two senting the equation inertness to the materials with which it will come 50 in contact. The mixture of DMP and xl-IF has a cohesive From this relation and the values for p was de force between those of the two components but retains the high vapor pressure of the XHF. rived‘ the line for pr. This chart may be used ‘to determine the vol Through proper proportioning of the two com 55 ume proportions required to give any acoustic ponents it will provide an exact match in me impedance within the range of the components. chanical impedance to sea water. The mixture also has the low viscosity of the two components. Forinstance, the values of pi) for sea water at 25“l C. and at 15° C. are shown by dotted lines on Another feature ‘of the invention is a mixture of DMP and XHF in proportions to provide an 60 the chart. The curve for pc of the mixture shows that for the mixture at 25° C. to match sea water exact mechanical impedancematch to sea water. at 25° C., the components should be '73 per cent Other features will appear hereinafter. ‘ The drawings consist of two sheets having two DMP and 2'! per cent XHF. For the mixture to simulate sea water at ‘15° C. the components ?gures as follows: Fig. 1 is a side view, partly in section of an should be 66 per cent DMP and 34 per cent XHF. electromechanical transducer in which the liquid Finally for a mixture to match sea water when medium of the present invention may be em both are at 15° C. the rough temperature cor rection of three parts per thousand per degree ployed; and may be used. The impedance of the mixture Fig. 2 is a graphical representation of certain properties of various mixtures DMP and XHF. 70 should thus be about 1.504Xl0‘s ohm/cm.2 at 25°C. in order to become 1549x105. at 15° C. and The electromechanical transducer shown in the proportions shown by'the chart are 62 per Fig. 1 comprises a casing I of steel or other rigid cent DMP and 38 per cent XHF. and mechanically strong material and a cap 2 The method pointed out by the above example of plastic material such as that known as p0 rub ber. These two elements are bolted together to 75 may be used in determining the proper propor 2,407,315 6 - . tions of other mixturesof other liquids when the of BM? and three parts of XHF being some acoustic impedance of sea water is to be matched. where midway between the two. ' “ The following table gives the acoustic properties While other oils and mixtures have higher cavi tation pressures (directly relatedto the cohesive temperature at which these properties were 5 force) other properties prevent their use. measured is noted for the purpose of making As a i'urther guide to the selection of a. liq temperature corrections. uid medium a third table listing the general range of a number of liquids at one megacycle and the Table 1 Density p Liquid “mum in g/cc. Velocity 0 Tem mm" in m/sec. _ A071,?‘ ' Ethylene chloride Sea water. Do‘ ___ Alpha methyl nap" “me 010E101!- Distilled water H10 _- Peanut oil Corn oil Cottonseed oil . __ Dimethyl phthalate .... _. C5H4(C00CH;), ............ ._ Mineral oil Acetylated castor oil-P8 _____ ._ goat's-14311: nil rm 0 _- -- _ O ive oil. _ _ _ _ ohms/cm I 1. 073 1. 025 1. 730 1. 569 1. 027 1. 648 1.090 Fuel oil-99 g'rsv“ Castor oil D B ' Linseed 0" Mechanical impedance Temperature p nXlOl m m 5Q 1.495 _ . _ __ 1. 495 25 1. 472 l. 430 25 25 . 921 1. 353 24 . 936 . 914 1. 363 1. 333 25 24 . 912 1. 330 24 l. 176 1. 722 25 . 868 1. 263 24 . 956 1. 363 .g 1, 1g; . 912 26. 5 25 1. 308 25 1. 574 1. 155 2A 1. 645 24 24.3 25 Decalin._ ____ CmHu Dibutyl phthalate __________________ _.__ 01114000041510; ........... .- .8765 1. 032 1. 245 1. 455 Tricresyl phosphate" 1. 153 1. 620 24 ___ 1. 158 1. 630 24 CH1COCH;C(CH|OH), ____ -_ 013K031): ................ -_ . 910 . 854 . 810 1. 280 1.150 1. 072 24 24 25 D0. Diacetone alcohol ____________________ __ Diethyl benzene ..................... -_ Kerosene____ __ _ Pentanediol __________________________ ._ ' 1-2-4 trichlor-benzene..Carbon tetrachloride _________________ -_ ' 24 . 1. 104 Chlor nated diphenyl- 25 .998 .990 .969 . Diethf'l phthslate .................... .. CQHKGOOCMHI)! .... _-. .... ._ 25 25 15 éCHrhCOHCH: ............ __ ‘H101. ___ . 913 1. 441 l. 192 1. 849 C014 .................. ._ l. 595 1. 478 24 24. 25 X lene bexa?uoride __________________ _- O¢H4(OF;):.. 1. 370 1. 205 25 D +DMP (equal parts of castor oil 1. 080 1. 585 20 D B and dimethyl-phthelate) . of viscosity and vapor pressures’ is here given. From this table various mixtures may be pro duced whose impedance will match that of sea 40 In the column of viscosity the ?guresrepresent water. Providing other properties of the liquids viscosity ranges as follows: meet given requirements, the proportions of the liquids to be used may thus be readily deter mined. 1. 2; 3. 4. For the purposes hereinabove set forth in or der to provide a liquid which has 5 high cavita Carbon tetrachloride Kerosene Olive oil Castor oil i tion pressure the following values have been de termined and are herein set forth in: In the column oi’ vapor pressures the letters irep resent vapor pressure ranges of the following' orders: » 50 Table 2 A. 1 cm. Hg or more . B. .1 cm. H8 Prefssurtehon the ietgci 0 e crys C. ' .01 Cm. Hg ag8mstthenquid_ Liquid _ expresedinatmos D. .001 cm. H8’ . 55 > pheres per cent ' Table 3 Olive oil_____‘____~_ 7.5 DB (caster 011) ..... __ P8 (acetylated caster o 3% . 6.5 DMP _______ _.' _________ __ 6.1 85% DM P+15% DB__ Peanut oil .......... _. 5.3 5.2 5.2 perm 4 parts DMP+3 parts XHF. Soy been 011.. _ 3 parts DM P+1 part DB Carbon tetrachloride Kerosene ___________________ __ - vs cos- ' ity v a or presgure 'oxlo‘ ’ P 0.969 4 C 1.43 1.477 (P8) ................ -- 4 C 1.387 1.451 .956 3 3 3 3 3 3 B B B B B B 1.308 1.333 1.363 1.362 1.333 1.353 1.431 1.463 1.458 1.461 1.463 1.468 .912 .914 .936 .919 .912 .921 4.4 4.2 4.0 3.9 3.9 3.7 L d i] _. 2.8 3.4 @rennoiL. erosene ............. -_ 3 B 1.022 1.268 1.324 1.440 .81 Xylene hexa?uoride _______________________ __ 2.6 aMethylnaphthalene“ Dimeth lphthalate____ 1 234 A 1) 1.643 1.510 1.722 1.463 1.090 1.176 1.595 4! Methyl naphthalene ' . Cestoroil (DB) ______ __ Acetylated eastor oil 5.0 ________________________ __ Linseed oil Liquid 60 3 B .88 70 Xylene exailuoride-.._ '1 A 1.205 .879 1.37 Carbontetrachloride.._ 1 A 1.595 .926 From this table it will be seen that dimethyl phthalate ranks among the highest in cavitation pressures and that xylene hexa?uoride is the ' of the above table it appears that ‘ On the basis lowest here recorded, the mixture of four parts 75. a methyl naphthalene and carbon tetrachloride 2,407,315 7 ~ . are both suitable from the standpoint 01' high What is claimed is: vapor pressure but it will be noted that both of 1. A mixture or 57 per cent by volume of these liquids have too high a mechanical imped ance (pv) for mixture with DMP to provide a match with sea, water and in addition both will attack rubber. ‘ . ' It therefore appears that the mixture of dimethyl phthalate and xylene hexa?uoride is a peculiar and novel combination oi’ liquids produc ing a liquid medium for electromechanical trans ducers and other like apparatus having the great est combination of desirable properties. v dimethyl phthaiate and 43 per cent by volume of xylene hexa?uoride.’ 2. In a mixture of liquids having high cohesive force to support large power transmission and high vapor pressure to reduce the destructive ei fect of cavitation, the combination of dimethyl phthalate and xylene hexa?uoride in substantially 10 the proportions of tour volumes of dimethyl phthalate and three volumes of xylene hoxaiiuo ride. . ‘WARREN P. MASON.