US2505364A - Compression wave transmission - Google Patents

Compression wave transmission Download PDF

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Publication number
US2505364A
US2505364A US653255A US65325546A US2505364A US 2505364 A US2505364 A US 2505364A US 653255 A US653255 A US 653255A US 65325546 A US65325546 A US 65325546A US 2505364 A US2505364 A US 2505364A
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United States
Prior art keywords
conduit
crystal
electrode
liquid
impedance
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Expired - Lifetime
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US653255A
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English (en)
Inventor
Herbert J Mcskimin
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AT&T Corp
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Bell Telephone Laboratories Inc
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Publication date
Priority to NL74171D priority Critical patent/NL74171C/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US653255A priority patent/US2505364A/en
Priority to GB17027/47A priority patent/GB658177A/en
Application granted granted Critical
Publication of US2505364A publication Critical patent/US2505364A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/18—Methods or devices for transmitting, conducting or directing sound
    • G10K11/22—Methods or devices for transmitting, conducting or directing sound for conducting sound through hollow pipes, e.g. speaking tubes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/30—Time-delay networks
    • H03H9/36—Time-delay networks with non-adjustable delay time

Definitions

  • This invention relates to compression wave transmission and particularly to systems in which a compression wave developed by signal pressures in one region of a liquid confined in a conduit travels a considerable distance-usually a large number of wavelengths-thereafter to actuate a receiver ,or pick-up device located at another region of the liquid.
  • a related object is to transmit a sharp pulse of energy from end to end of the conduit without substantial alteration of the pulse shape.
  • a subordinate object is to provide apparatus of the character described which shall be rugged, simple, and compact.
  • subsidiary objects for effectuating the principal objects of the invention are as follows: To reduce energv losses by absorption in the conduit walls; and to restrict the wave energy to the fundamental or zero-order mode, all higher order modes being absent or of negligible energy, so that distortion of transmitted signals is kept as low as possible.
  • a fluid medium which has the lowest possible intrinsic energy loss or attenuation characteristic for the desired frequency range.
  • Investigation of a number of different fluids indicates that for carrier frequencies in the 5-megacycle range, liquid mercury has the lowest internal losses.
  • a secondary advantage in mercury is that its mechanical impedance per square centimeter is sufficiently high to permit operation over a wide frequency range.
  • this probl m is in turn solved by making the wall impedance low compared with the fluid impedance, in which case an equally good impedance mismatch and reflection coefficient are obtained.
  • One of these surfaces is a ground or etched surface on a hardsubstance such as steel, glass. brass, Bakelite or the like.
  • the other is a lining of paper or other matted fibrous material, fitted snugly to the inside walls of the conduit and retained in place in any suitable fashion which does not involve saturation with glue or other hard adhesive which would destroy the matted structure.
  • the effective boundary impe'd'ance is the average value over a given area-o'f-t'heimpedance at each part of that area, and while the impedances at the high points or tips of the ground or etched surfaces and at individual fibres of the matted surface may be fairly high, their sum is small compared with the sum of the impedances of the other parts where the mercury bears only against air-and where the impedance is negligible.
  • the oscillatory component of the wave pressure at the walls vanishes ideally and actually .is very low; whereas, for effective propagation of substantial amounts of energy this pressure in the body of the fluid column must be comparatively high.
  • these conditions are compatible With various modal pressure distributions over .a crosssection of the conduit. Of all these one is greatly .to be preferred above all the others, i.
  • z is axial distance along the conduit from the driving end
  • the pressure p is derivable from the velocity potential and has the same distribution over any cross-section, though displaced in time phase. From the last expression it is evident that the phase velocity depends on the'mode number. This results in phase :distortion which increases progressively along the conduit. Similar considerations hold for conduit cross-sections other than circular.
  • This prevention is accomplished in accordance with the invention by causing the driving transducer face to exert pressures on the fluid medium which at all times and at all points of contact conform to the pressure distribution which characterizes the zero order oscillation mode.
  • this pressure distribution is given for the circular cross-section conduit by a being the conduit radius, and S1 the first root of Jo(a:),and by for the tube of rectangular cross-section, IX and ly being the half-lengths of the sides, and the origin being at the mid-point of the cross-section. Because of the high degree of damping of the crystal vibrations by radiation into the mercury, the movement of the crystal at each point of its face is substantially proportional to the voltage impressed on that point.
  • the driving electrode is rounded or domed to an appropriate shape and placed in central contact with the crystal so that there exists a separation between it and the crystal of a magnitude which increases progressively in a radial direction and in accordance with a certain formula.
  • the electrode shape is given by the formula:
  • Kc is the dielectric constant of the crystal
  • K5. is the dielectric constant of the medium separating the crystal from the driving electrode
  • d5. is the axial length of the separating medium.
  • FIG. 1 shows a compression wave transmission system in accordance with one form of the invention
  • Figs. 2 and 3 show, to an enlarged scale, a portion of the conduit of Fig. 1, broken open to reveal the low loss, high impedance propagation medium and two alternative forms of the low impedance conduit boundary walls of the invention;
  • Fig. 4 shows a geometrical arrangement alternative to Fig. 1;
  • Fig. 5 is a diagram showing the optimum pressure distribution over the face of a crystal driving :a liquid column of circular section;
  • Fig. 6 is a diagram showing the ideal form of a driving electrode for a crystal driving a tube of circular cross-section, together with its mathematical expression.
  • Fig. 1 shows a conduit or tube I of substantial overall length, bent back on itself for compactness. It may be constructed of steel tubing and block fittings at the bends to reduce reflection losses. There should be as few changes in diameter as possible, i. e., the inside diameter of each bend fitting should be equal to that of the straight portions.
  • the bend fittings are provided with reflecting plates '2 placed at angles of 45 degrees to th oncoming wave. The tube I is broken open to show one of these reflectors in place.
  • Fig. 2 shows the inner construction of the conduit I in one form to an enlarged scale.
  • the outer wall has been broken away to show the mercury medium 3 which has been broken away, in turn, to show the ground or etched wall surface 4 of the tube.
  • the surfaces of the reflectors 2 are preferably the same as the surfaces of the The grain of these surfaces may be of a fineness of approximately 200 to 1000 points to the inch, measured in any direction.
  • Fig. 3 is similar to Fig. 2, the tube wall I and the mercury 3 being broken away to show the paper lining 5 for the conduit walls and reflecting faces which affords an alternative construction to the etched or ground surfaces of Fig. 2. It is undesirable and unnecessary to employ any adhesive to hold the paper in place. The hydrostatic pressure of the mercury is suflicient for this purpose.
  • a pair of bend fittings may be conveniently made from a block of steel through which two holes are drilled of diameter equal to the inside diameter of the tubes, intersecting each other accurately at right angles. The block is then cut in half along its diagonal and a reflecting plate fastened, as by screws, over the opening at the intersection of the drilled holes. Care should be exercised to hold the reflecting plate in correct 45- degree alignment with the axis of the tube.
  • the tube I is provided at its head end with a driving crystal 6 and at its receiver end with a receiving crystal 1.
  • the crystals 6, 1 may be mounted in the tube by clamping between threaded washers or in any convenient manner.
  • the crystals may be of any desired type which is capable of vibrating axially in the thickness mode.
  • they may be of the well-known X cutvariety described in Electromechanical Transducers and Wave Filters by W. P. Mason, (Van Nostrand1942) at page 198. They are preferably one-half wavelength in thickness at the operating frequency. At a frequency of megacycles, for example, this is approximately 0.05 centimeter for X-cut, thickness mode, quartz crystals.
  • the tube 1 is filled'with mercury 3 which not only serves as the transmission medium but serves also as on electrode for each of the crystals 6, 1'. It may be connected to ground, thus avoiding any difficulties which might arise by reason of a potential difference between the conduit and ground.
  • One electrode for the driving crystal may be supplied by the mercury 3 in contact therewith, mercury being a good conductor of electricity.
  • the other electrode is the external electrode 8, shaped as hereinafter described.
  • These electrodes are supplied with voltage from a suitable source, for example a source of high-frequency carrier waves, divided from an oscillator 9, and
  • the modulated output may be supplied by way of a transformer l i to the electrode 8 which may be directly connected to the secondary winding of the transformer H and to the mercury column 3 by way of one electrode E? which passes through the tube wall I and the paper lining 5, if present.
  • the etched or ground surface 4 When the etched or ground surface 4 is employed, electric connection with the mercury 3 may be directly established by way of the tube wall I.
  • One electrode of the output crystal l is provided by the mercury 3, electric contact with one terminal l3 of an external load circuit I4, 55, being established as described above.
  • the impedance offered by the load circuit Hi, IE to the crystal generator comprising the elements 3, I, It, is preferably of a relatively low value.
  • the other output crystal electrode 15 may be of conventional form and may be connected to the other terminal of the load circuit. However, improved results may be secured when the output electrode 56 is domed according to the same formula as the input electrode.
  • a mercury end 'cell which may comprise an extension 2i! of the tube l terminated by a plate 2
  • Fig. 4 shows modified apparatus in which the cross-section is rectangular. This offers certain advantages of compactness as compared with the arrangement of Fig. 1.
  • the crystals 6' and 1' may be cut to rectangular peripheral shape and may otherwise b the same as the iii) crystals 6 and 1 of Fig. 1.
  • the external electrodes 8 and I6 may be domed, but the formula expressing their shape differs from that which expresses the shape of the electrodes 8 and I6 of Fig. 1.
  • Thoseof Fig. 1 are shaped in accordance with the Formula 7 while those of Fig. 4 are shaped in accordance with the Formula 8, specialized, in each case, for air as the medium between the crystal and the external domed electrode.
  • the right-hand portion of Fig. 6 is a plot, to the same scale, of the function a 0( 1 I. show) (9) i. e., of the thickness function '7 for air as a medium between a, quartz crystal and a metal electrode.
  • the left-hand portion of Fig. 6 is a cross-sectional diagram to the same scale of onehalf of the driving electrode of the invention, domed in accordance with the above equation. The magnitudes do and do. are indicated on the figure.
  • each condenser is proportional to its area and the dielectric constant of the medium, and inversely to its thickness
  • a domed electrode may be designed to excite zero order mode (plane) waves in a conduit of cross-section other than circular; in particular, a conduit of rectangular cross-section, for which the electrode form is given by Formula 8.
  • Qr Qp cos cos 3%; (17) for the tube of rectangular cross-section, where Qp is the charge released on the crystal surface due to piezoelectric action and all other symbols have the meanings given them above.
  • JoUCzT JoUtsT
  • JoUCnr any combination of these, where a being the radius of the conduit, as before; i. e., successive values of ka are the successive roots or zeros of the Jo function.
  • A is a constant of proportionality
  • the propagation speed of compression waves in unconfined mercury is 1.5 10 centimeters per second at standard temperature and pressure. At a frequency of 5 megacycles per second, the wavelength is 0.03 centimeter.
  • a transmission line of the type described, one inch in diameter, provided with a half wavelength, thickness mode, quartz crystal at each end and a driving electrode of the type described can carry signal energy, for example short pulses, of a fundamental frequency of 5 megacycles for a distance of 24 feet, i. e., over 200,000 wavelengths, without excessive transmission loss or distortion, to give rise in the output load circuit to a faithful replica of the input signal, delayed by 5 milliseconds with respect thereto.
  • the apparatus is characterized by simplicity, ruggedness, compactness and reliability in operation.
  • the conduit may, of course, be extended in a straight line, if desired. Usually folding will be resorted to for the sake of compactness.
  • transducers for example, an electromagnetically actuated diaphragm, or array of diaphragm's, can .also be employed, and that actuation of such diaphragms in such a manner as to suppress oscillations of higher ,rnodesis within the spirit of the invention; that the transducer corn-pr-i sirigv the crystal plate and t enie l ir e er f r a fin s dependent of the wave guiding conduit in connection with which it has been described; and “that advantage :may "equally be "taken of the low wall impedance feature of the invention when the driving means is a transducer other than "a crystal or when the wave carrying fluid medium is other than mercury.
  • a conduit 'of circular cross section a fluid of high characteristic impedance substantially filling said "conduit, the inner surfaces of "the Walls of said conduit offering a low impedance to said fluid, and an electromechanical transducer 'at one end of'said conduit for generating longitudinal waves inthe fluid
  • transducer comprises a piezoelectric crystal disc having a face in contact with the fluid and normal to the conduit axis, and an external electrode in cooperative association with the other face .of said crystal, the face of said external electrode in contact with said crystal being domed to the 'form a conduit of rectangular cross-section, a 'fluid of high characteristic'impedance substantially n11- ing'said conduit,the inner surfaces of the walls 'of 'said conduit offering a low impedance to said fluid, and an electromechanical transducer atone end ,of said conduit for generating longitudinal waves in the fluid, "which transducer comprises 'a'thin rectangular piezoelectriccrystal having
  • K is the dielectric constant oi the crystal
  • K2. is the dielectric constant "of the separating medium, I V e lx is the'half length of one "edgeof thetrectangular crystal wafer, and p 7 1 is the half length of an adjacent edge of the rectangular crystal wafer, the origin being at the center of the crystal wafer.
  • Compression Wave transmission apparatus which comprises a supporting conduit having at least two substantially straight portions of uni form cross-section interconnected by a bend, at least one reflector -rnounte d ingsaid bend and oriented to direct wave energy incident thereon from one straight portion into an adjacent straight portion, a liquid of high intrinsic impedance, high surface tension, and low absorptivity to gases substantially filling .said conduit and being supported thereby and by said reflector, thereby constituting a bent liquid column adapted to support compression waves propazg ated from end to end thereof, a piezoelectric crystal driving element mounted at an end of said conduit in position to launch compression Waves into said liquid column, ;a 'wave receiver at the other .end of said conduit, the internal wall surfacesof said conduit and of2said reflector having .a roughness of grain sizeof the order of /5 :to /50 of a compression Wavelength :in :said liquid, the spaces between the high :points of :said rough surfaces constituting L
  • a wave guide conduit a liquid of high ins c i p dan e a d hi urfacetee i n 1bstantially filling said conduit, the interior surfaces of the conduit walls being ground to a texture such that substanial" areas of said interior surfaces remain unwetted by said liquid,
  • a wave guide conduit a liquid of high intrinsic impedance and high surface tension substantially filling said conduit, the interior surfaces of the conduit walls being etched to a texture such that substantial areas of said interior surfaces remain unwetted by said liquid, whereby a low-impedance reflecting boundary is presented to said liquid, means for applying high frequency pressures to said liquid at one part of said conduit, and means for utilizing the energy of high frequency compression waves propagated through said liquid to another part of said conduit.
  • a wave guide conduit a liquid of high intrinsic impedance and high surface tension substantially filling said conduit, a thin layer of a matted, fibrous material lining the interior surfaces of the conduit walls and of a texture such that substantial areas of said interior surface lining remain unwetted by said liquid, whereby a low-impedance reflecting boundary is presented to said liquid, means for applying high frequency pressures to said liquid at one part of said conduit, and means for utilizing the energy of high frequency compression waves propagated through said liquid to another part of said conduit.
  • a wave guide conduit a liquid of high intrinsic impedance and high surface tension substantially filling said conduit, a thin layer of paper lining the interior surfaces of the conduit walls and of a texture such that substantial areas of said interior surface lining remain unwetted by said liquid, whereby a low-impedance reflecting boundary is presented to said liquid, means for applying high frequency pressures to said liquid at one part of said conduit, and means for utilizing the energy of high frequency compression waves propagated through said liquid to another part of said conduit.
  • Compression wave transmission apparatus which comprises a supporting conduit having at least two substantially straight portions interconnected by a bend, at least one reflector mounted in said bend and oriented to direct Wave energy incident thereon from one straight portion into an adjacent straight portion, a liquid of high intrinsic impedance, high surface tension, and low absorptivity to gases substantially filling said conduit and being supported thereby and by said reflector and providing a bent path for compression waves propagated from end to end thereof, a piezoelectric crystal driving element mounted at an end of said conduit in position to launch compression waves into said liquid, and a wave receiver at the other end of said conduit, the front face of said reflector being roughened to a texture such that it remains substantially unwetted by said liquid, whereby a lowimpedance reflecting surface is presented to said liquid.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
  • Apparatuses For Generation Of Mechanical Vibrations (AREA)
US653255A 1946-03-09 1946-03-09 Compression wave transmission Expired - Lifetime US2505364A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
NL74171D NL74171C (en, 2012) 1946-03-09
US653255A US2505364A (en) 1946-03-09 1946-03-09 Compression wave transmission
GB17027/47A GB658177A (en) 1946-03-09 1947-06-27 Compressional wave transmission devices

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Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2590405A (en) * 1946-08-13 1952-03-25 Rca Corp Signal to noise ratio of radar systems
US2626992A (en) * 1949-02-26 1953-01-27 Bell Telephone Labor Inc Signal delay device
US2664547A (en) * 1950-02-17 1953-12-29 Raytheon Mfg Co Delay line device
US2685067A (en) * 1948-03-12 1954-07-27 Raytheon Mfg Co Means for delaying electrical signals
US2727214A (en) * 1949-11-02 1955-12-13 Bell Telephone Labor Inc Acoustic delay line using solid rods
US2728868A (en) * 1951-09-24 1955-12-27 Northrop Aircraft Inc Liquid filled accelerometer
US2746019A (en) * 1951-09-19 1956-05-15 Lab For Electronics Inc Delay line
US2748369A (en) * 1951-12-07 1956-05-29 Birmingham Small Arms Co Ltd Transducer
US2753528A (en) * 1948-09-21 1956-07-03 Robert M Ashby Ultrasonic delay lines
US2777997A (en) * 1951-11-06 1957-01-15 David L Arenberg Ultrasonic delay lines
US2781494A (en) * 1953-03-18 1957-02-12 Lab For Electronics Inc Ultrasonic delay lines
US2823355A (en) * 1950-05-17 1958-02-11 David L Arenberg Ultrasonic delay line
US2826745A (en) * 1956-08-05 1958-03-11 Irving H Page Grid-type liquid delay line
US2922966A (en) * 1953-11-30 1960-01-26 Marconi Wireless Telegraph Co Ultrasonic delay devices
US2945984A (en) * 1959-07-17 1960-07-19 Sylvania Electric Prod Piezoelectric device
US2984800A (en) * 1951-10-26 1961-05-16 Irving H Page Delay line for wave signals
US3137836A (en) * 1955-08-25 1964-06-16 Clyde P Glover Support for electro-acoustic transducer
US3794937A (en) * 1972-04-20 1974-02-26 Westinghouse Electric Corp Folded path acoustic delay line and optical processor
US4193049A (en) * 1978-06-12 1980-03-11 Deere & Company Ultrasonic touch control panel
US4196406A (en) * 1978-06-12 1980-04-01 General Electric Company Ultrasonic control device

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1775775A (en) * 1926-08-07 1930-09-16 American Telephone & Telegraph Method of and means for wave retardation
US1783014A (en) * 1927-01-21 1930-11-25 Rca Corp Semirigid crystal mounting
FR711667A (fr) * 1930-05-26 1931-09-15 Appareil retardateur électro-acoustique
US1954238A (en) * 1925-10-29 1934-04-10 Rca Corp Mounting of piezo-electric resonators
US2015836A (en) * 1933-01-26 1935-10-01 Telefunken Gmbh Quartz crystal oscillator
US2202220A (en) * 1939-04-10 1940-05-28 Power Patents Co Movable core spark plug
US2263902A (en) * 1938-02-08 1941-11-25 Emi Ltd Delay device for use in transmission of oscillations
US2423306A (en) * 1945-08-01 1947-07-01 Forbes Gordon Donald Transmission line

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1954238A (en) * 1925-10-29 1934-04-10 Rca Corp Mounting of piezo-electric resonators
US1775775A (en) * 1926-08-07 1930-09-16 American Telephone & Telegraph Method of and means for wave retardation
US1783014A (en) * 1927-01-21 1930-11-25 Rca Corp Semirigid crystal mounting
FR711667A (fr) * 1930-05-26 1931-09-15 Appareil retardateur électro-acoustique
US2015836A (en) * 1933-01-26 1935-10-01 Telefunken Gmbh Quartz crystal oscillator
US2263902A (en) * 1938-02-08 1941-11-25 Emi Ltd Delay device for use in transmission of oscillations
US2202220A (en) * 1939-04-10 1940-05-28 Power Patents Co Movable core spark plug
US2423306A (en) * 1945-08-01 1947-07-01 Forbes Gordon Donald Transmission line

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2590405A (en) * 1946-08-13 1952-03-25 Rca Corp Signal to noise ratio of radar systems
US2685067A (en) * 1948-03-12 1954-07-27 Raytheon Mfg Co Means for delaying electrical signals
US2753528A (en) * 1948-09-21 1956-07-03 Robert M Ashby Ultrasonic delay lines
US2626992A (en) * 1949-02-26 1953-01-27 Bell Telephone Labor Inc Signal delay device
US2727214A (en) * 1949-11-02 1955-12-13 Bell Telephone Labor Inc Acoustic delay line using solid rods
US2664547A (en) * 1950-02-17 1953-12-29 Raytheon Mfg Co Delay line device
US2823355A (en) * 1950-05-17 1958-02-11 David L Arenberg Ultrasonic delay line
US2746019A (en) * 1951-09-19 1956-05-15 Lab For Electronics Inc Delay line
US2728868A (en) * 1951-09-24 1955-12-27 Northrop Aircraft Inc Liquid filled accelerometer
US2984800A (en) * 1951-10-26 1961-05-16 Irving H Page Delay line for wave signals
US2777997A (en) * 1951-11-06 1957-01-15 David L Arenberg Ultrasonic delay lines
US2748369A (en) * 1951-12-07 1956-05-29 Birmingham Small Arms Co Ltd Transducer
US2781494A (en) * 1953-03-18 1957-02-12 Lab For Electronics Inc Ultrasonic delay lines
US2922966A (en) * 1953-11-30 1960-01-26 Marconi Wireless Telegraph Co Ultrasonic delay devices
US3137836A (en) * 1955-08-25 1964-06-16 Clyde P Glover Support for electro-acoustic transducer
US2826745A (en) * 1956-08-05 1958-03-11 Irving H Page Grid-type liquid delay line
US2945984A (en) * 1959-07-17 1960-07-19 Sylvania Electric Prod Piezoelectric device
US3794937A (en) * 1972-04-20 1974-02-26 Westinghouse Electric Corp Folded path acoustic delay line and optical processor
US4193049A (en) * 1978-06-12 1980-03-11 Deere & Company Ultrasonic touch control panel
US4196406A (en) * 1978-06-12 1980-04-01 General Electric Company Ultrasonic control device

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Publication number Publication date
NL74171C (en, 2012)
GB658177A (en) 1951-10-03

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