US3480906A - Transducer having a backing mass spaced a quarter wavelength therefrom - Google Patents

Transducer having a backing mass spaced a quarter wavelength therefrom Download PDF

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Publication number
US3480906A
US3480906A US712829A US3480906DA US3480906A US 3480906 A US3480906 A US 3480906A US 712829 A US712829 A US 712829A US 3480906D A US3480906D A US 3480906DA US 3480906 A US3480906 A US 3480906A
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Prior art keywords
transducer
impedance
quarter wavelength
inertia loading
transducer element
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US712829A
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John H Thompson
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Westinghouse Electric Corp
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Westinghouse Electric Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0644—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element
    • B06B1/0662—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface
    • B06B1/0674—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface and a low impedance backing, e.g. air

Definitions

  • a transducer for deep sea operation having a front radiating surface with an inertia loading mass extending around the remaining surfaces of the transducer element at a distance d therefrom.
  • the distance d is equal to a quarter wavelength (N4) of the operating frequency of the transducer.
  • the space between the inertia loading mass and the transducer element is filled with a pressure transmitting compliant material.
  • This invention in general relates to transducers, and more particularly to a pressure compensated transducer for use at great depths, for example, 20,000 feet, in the sea.
  • transducers include a transducer means in the form of an oscillatory transducer element which when suitably energized projects an acoustic beam, and conversely when acoustic energy of the proper frequency or frequency range is received a corresponding electrical output signal will be provided by the transducer element.
  • Such transducer elements are generally backed by a pressure release material which, in essence, simulates an air backing so that maximum acoustic energy is radiated from the front radiating surface of the transducer element.
  • a variety of pressure release materials may be used among them being foam epoxies, sponge rubber, and a form of cork and neoprene rubber composition known as corprene to name a few.
  • the transducer element is placed in a housing with a covering member and a transducer fluid, such as high grade castor oil, is introduced in order to equalize and distribute static pressures which may be encountered in the sea.
  • a transducer fluid such as high grade castor oil
  • the pressure release backing due to the Water pressure transmitted thereto through the covering member and transducer fluid becomes compressed to a point where all of the air is crushed out of the pressure release backing material thereby destroying the intended transducer operation.
  • transducers which utilize a sound absorbing material having the same characteristics of the sea water so that energy radiated from the sides and back of the transducer element is substantially absorbed and the desired beam characteristic is maintained.
  • This type of construction is satisfactory when operation is at elevated frequencies, for example, in the several hundred kilohertz (kHz.) range. At the lower frequencies however, for example below 100 kHz., the amount of sound absorbing material needed to do a satisfactory job can become prohibitive or impractical with present day sound absorbing mediums.
  • a transducer includes an oscillatory transducer means which is operable at one or more frequencies within a certain frequency range and includes front, rear and side surfaces.
  • An inertia loading mass extends around the back and up the sides at a distance d from the rear and side surfaces with the distance d chosen to be equal to a quarter wavelength, or any odd multiple of a quarter wavelength of the operating frequency (or an operating frequency within the said range).
  • Spaced between the transducer and the inertia loading mass is a pressure transmitting means, preferably of a compliant medium having a relatively low specific acoustic impedance.
  • FIGURE 1 illustrates a transducer element which may be used in the present invention
  • FIG. 2 represents a transmission line, to aid in an understanding of the present invention
  • FIG. 3 is an embodiment of the present invention in cross-sectional isometric view
  • FIG. 4 illustrates a transmission line analogy of the structure of FIG. 3
  • FIG. 5 is another embodiment of the present invention in cross-sectional isometric View
  • FIG. 6 illustrates a transmission line analogy of the structure of FIG. 5
  • FIG. 7 is a graph illustrating the relationship between operating frequency and relative mechanical impedance associated with the embodiment of FIG. 3;
  • FIG. 8 illustrates another embodiment of the invention, in cross-section and isometric view.
  • FIGURE 1 illustrates an oscillatory transducer means which may be utilized herein.
  • the oscillatory transducer means is a transducer element 10 which includes a front surface F, a rear surface R and a plurality of side surfaces of which one, S, is designated.
  • S one, S
  • operation of the transducer element 10 will be described in brief.
  • the side surfaces for example S will correspondingly oscillate in and out at a velocity which is approximately equal to one-third U. If the element 10 is considered to be surrounded by water, acoustic energy will be radiated from the front, rear and side surfaces of the element.
  • the power radiated into the water from a surface is:
  • V Z (real) 1 where V is the velocity of the surface and Z (real) is the real component of mechanical impedance which is presented to that surface by an adjacent medium.
  • the Z is in the form of a+jb where a is the real component and b is the imaginary, or reactive component, of impedance.
  • Reactive power [V Z (imaginary)] is also produced due to the reactive component of impedance and this reactive power tends to detune the transducer element.
  • the mechanical impedance is a function of the specific acoustic impedance adjacent the surface, the area of the surface and the thickness of the adjacent medium.
  • U/ 3 is the velocity V of Equation 1 and LT is the side area.
  • LT is the side area.
  • the power radiated from the side may be reduced by reducing L, the length of the transducer element. Reducing L however, will also reduce the power which is radiated from the front surface F since the L term is common to both equations. Such reduction in radiated power from the front surface F is undesirable.
  • Another way of reducing power out the side is to reduce T, however reduction of T will not allow operation at the lower frequencies.
  • radiation from the side and rear surfaces is substantially reduced by placing around the side and rear surfaces a backing means which effectively reduces the mechanical impedance presented to the surface by the reduction of the specific acoustic impedance, the C term in the above power equations, presented to the side and rear surfaces.
  • FIG. 2 representing a transmission line of length d having a characteristic impedance of Z
  • a mechanical physical system has a direct analogy in a corresponding electrical system and the transmission line of FIG. 2 is presented in order to better understand the mechanical concepts involved herein.
  • the impedance Z looking in at the terminals A, B relative to the characteristic impedance Z is given by the formula:
  • Z is the impedance at terminals C, D and:
  • Equation 5 0 in Equation 5 would be 1r/2 and Equation 4 would reduce to:
  • Equation 7 Z will be relatively low if Z is low and Z made high as practical.
  • Equation 7 Application of Equation 7 to a mechanical system by the analogy to mechanical impedance in place of electrical impedance will be discussed with respect to FIGURES 3 and 4 to which reference is now made.
  • the transducer of FIG. 3 includes an oscillatory transducer means such as the transducer element 10 of FIG. 1.
  • Backing means for the transducer element 10 includes an inertia loading mass 12 which extends around the back, and up the side surfaces of the transducer element 10 and spaced at a distance d therefrom.
  • the inertia loading mass 12 also forms the transducer housing.
  • the inertia loading mass 12 may be of any dense material offering resistance to dynamic movement.
  • One example of a material which may be utilized as the inertia loading mass 12 is metal such as aluminum, lead, brass, gold, etc. For those metals which have little sea Water corrosion resistance a suitable coating or metallic jacket may be provided thereon.
  • a pressure transmitting means 14 Interposed in the space between the transducer element 10 and the inertia loading mass 12 is a pressure transmitting means 14.
  • the pressure transmitting means 14 be a compliant material having a relatively low specific acoustic impedance C).
  • the term compliance is the reciprocal of stiffness, that is the displacement corresponding to the application of a specific force.
  • One type of material which may be utilized is a butyl rubber composition, and to aid in the absorption of acoustic energy radiated from the rear and side surfaces of the transducer element 10 the butyl rubber composition may include metallic particles such as aluminum powder or flakes embedded therein thus forming a sound absorbing medium.
  • a sound absorbing butyl rubber material having the embedded aluminum flakes exhibits a compliance of approximately 10" inches per inch per pound, and a specific acoustic impedance approximately equal to that of sea water, which is approximately l.5 l0 MKS units.
  • an inertia loading mass formed of aluminum exhibits a specific acoustic impedance of l7 l0 MKS units, over 11 times that of the sea water.
  • the sound absorbing material described may be suflicient to prevent acoustic radiation from the rear and sides of the transducer; however, at the lower frequencies such as below kilohertz the amount of sound absorbing medium required becomes prohibitive.
  • inertia loading masses 20 and 21 which therefore aid in maintaining a proper beam pattern.
  • the transducer is provided with a covering member 24 and the housing is filled with a transducer fluid 26, the covering member 24 and transducer fluid 26 both having approximately the same acoustic transmission characteristics as sea water, such materials being well known to those skilled in the art. Static forces encountered at depth are applied to the covering member 24 and transmitted through the transducer fluid 26 to the pressure transmitting means 14 which then balances the pressure within the transducer to that of the surrounding water medium.
  • the backing means including the inertia loading mass 12 and pressure transmitting means 14 of FIG. 3 cooperate in a manner to substantially reduce undesired acoustic propagation from the rear and sides of the transducer element 10 and consequently from the rear and sides of the transducer, and also keeps to a minimum reactive power tending to detune the transducer element.
  • An important consideration in the fabrication of the backing means is the selection for the distance d. To accomplish the desired result the distance d is made equal to M4 where A is the wavelength of the operating frequency of the transducer.
  • FIG. 4 illustrates a transmission line analogy of a portion of the backing means of FIG. 3.
  • the line from terminals A, B to terminals C, D is analogous to the pressure transmitting means 14, which has been made equal to a quarter wavelength, and therefore a quarter wavelength transmission line (as in FIG. 2) is represented between terminals A, B and C, D.
  • the impedance looking in at terminals A, B of FIG. 4 represents the impedance presented to a side surface (or the rear surface) of the trans ducer element 10. From the power equation 1 it is seen that the lower the impedance presented, the lower will be the power radiated from that particular surface.
  • the impedance 32 of the water load is arbitrarily normalized to unity and it may be assumed that it is substantially resistive, then the impedance of the inductor representing the inertia loading mass 12, assuming approximately 1 inch thick aluminum and transducer operation at 60 kHz., will be in the order of 20. Referring back to FIG.
  • the impedance at terminals C, D is equivalent to Z while the impedance at terminals A, B is equivalent to Z
  • a quarter wavelength of pressure transmitting means 14 is utilized coupled with the relatively high Z impedance at terminals C, D cooperate to provide a relatively low Z at terminals A, B thereby reducing the power andaccordingly the acoustic energy propagated from the side and rear surfaces of the transducer element while maximizing the power radiated from the front surface F. That is, with'the specific acoustic impedance of the water being normalized to 1, and the value of inductance of the inductor 30 being therefore equal to approximately 20, then from Equation 7 the impedance at terminals A, B will be:
  • Equation 9 Z is of the form a+jb where the real component a is 1/401 and the imaginary or reactive component b is The real component of mechanical impedance presented to the side and rear surfaces of transducer element 10 therefore is approximately that of the mechanical impedance (real component) presented to it, were it coupled directly to the water. Similarly, 'detuning of the transducer element is substantially kept to a minimum since the'reactive component of impedance contributing to reactive power is negligible.
  • FIG. 5 illustrates another embodiment wherein acoustic radiation from the side and rear surfaces of a transducer element is further reduced.
  • the transducer of FIG. 5 includes a transducer element 10 and spaced from the rear and "side surfaces therefrom by a distance d is a first inertia loading mass 35 which may, for example, be of a lead composition. interposed between the transducer element 10 and the first inertia loading mass is a first pressure transmitting means 38 which may be identical to the pressure transmitting means 14 of FIG. 3.
  • the backing means further includes a second inertia loading mass 42 which forms the transducer housing and may be aluminum.
  • the second inertia loading mass 42 is spaced from the first inertia loading mass 35 by a distance of d and the space therebetween is filled with a second pressure transmitting means 46.
  • the transducer of FIG. 5 includes inertia loading masses 49 and 50, covering member 52 and transducer fluid 54.
  • the transmission line analogy for the backing means of the transducer in FIG. 5 is illustrated in FIG. 6.
  • the impedance at terminals A, B is the impedance presented to a side or rear surface of transducer element 10 and is equivalent to the Z of FIG. 2.
  • the transmission line from terminals A, B to C, D is a quarter wavelength long and is equivalent to the first pressure transmitting means 38.
  • Inductor 57 is representative of the impedance of the first inertia loading mass 35 and the inductor 60 is representative of the impedance of the second inertia loading mass, or housing 42.
  • Impedance 61 represents the water load impedance.
  • the transmission line from terminals A, B to C, D is of a distance d and is representative of the second pressure transmitting means 46.
  • the impedance looking in at terminals A, B toward C, D is governed by Equation 4 and depending upon the length d, the value of inductor 60, the impedance of the water load 61 (assumed to be normalized to unity) there will be present at terminals A, B a certain impedance Z illustrated in dotted lines.
  • the impedance at terminal A, B therefore is governed by the value of impedance Z the inductance value of inductor 57 and Equation 7 since a quarter Wavelength transmission line is utilized. In general the higher the value of X the lower will be the impedance at terminals A, B.
  • Results similar to those demonstrated with respect to FIGS. 4 and 6 may be achieved by using odd multiples of quarter wavelength pressure transmitting means and accordingly in general the spacing d of the first inertia mass from the transducer element 10 in FIG. 3 and FIG. 5 would be where n is an odd integer.
  • the operating frequency of the transducer is selected and accordingly a quarter wavelength distance may be calculated and the backing means of the trans ducer fabricated accordingly with the thickness of the inertia mass or masses chosen in accordance with the desired side and rear sound attenuation (decibels).
  • the operating frequency may vary somewhat within a limited range. If the operating frequency is chosen by way of example to be 60 kilohertz then M4 would be equal to inch and with the first inertia mass spaced from the transducer element at a distance of inch a minimum mechanical impedance is provided. If operation should be increased to a higher frequency or decreased to a lower frequency the A inch spacing would no longer represent a quarter wavelength.
  • the impedance curve 64 is a minimum at frequency f A theoretical construction for a. 20 decibel attenuation utilizing inch lead as an inertia mass and A inch of sound absorbing rubber would, at a frequency f of 60 kHz. yields a Z/Z of approximately 0.05.
  • the transducer may be designed to operate at a chosen frequency for which a quarter wavelength section may be determined and for which a minimum mechanical impedance results in accordance with the desired attenuation and the inertia loading mass utilized.
  • the transducer can operate at certain other frequencies with one or more frequency ranges to still provide, although not optimum, at least satisfactory results.
  • the designed operating frequency falls within the range and accordingly the distance d is equal to where A is the wavelength of one of the frequencies and n is an odd integer.
  • FIG. 8 there is illustrated another embodiment of the present invention which utilizes a different type of pressure transmitting means not illustrated in FIGS. 3 and 5. Only one inertia loading mass 68 is illustrated in FIG. 8 although it is to be understood that a plurality of such inertia loading masses such as illustrated in FIG. may be utilized.
  • the distance between the side and rear surfaces of transducer element 10 and the inertia loading mass 68 is equal to a quarter wavelength and the space therebetween is filled with a fluid 71.
  • Various types of silicon fluids are available which exhibit a specific acoustic impedance below that of the sea Water and in addition the use of a fluid allows for pressure balancing when used at depth.
  • a plurality of spacer means 73 In order to center the transducer element 10 there is provided a plurality of spacer means 73, an example of such spacer means being undulating or corrugated metal, the corrugations being provided in order to insure a spring action to decouple the element 10 from the mass 68.
  • the present invention has been described with a certain degree of particularity it should be understood that the present disclosure has been made by way of example.
  • An important consideration in the fabrication of the transducer is the selection of distance d, in conjunction with at least one inertia loading mass.
  • the size or shape of the transducer element may vary according to desired use. If such element is, for example, discshaped then such element would have a front and rear surface in addition to a curved side surface; such curved side surface could be thought of as an infinite number of surfaces and hence the terminology, side surfaces, used herein is applicable to various shapes of transducer elements. It is apparent that various modifications and variations of the present invention are made possible in light of the above teachings.
  • a transducer comprising:
  • oscillatory transducer means for operation within a frequency range, and including front, rear and side surfaces;
  • backing means including (1) an inertia loading mass extending around said back and up said side surface and spaced at a distance d therefrom,
  • the pressure transmitting means is a compliant material having a specific acoustic impedance C approximately equal to that of the fluid medium in which the transducer operates.
  • the compliant material has metallic particles embedded therein to form a sound absorbing medium.
  • the pressure transmitting means includes a fluid.
  • the pressure transmitting means includes spacer means contacting the transducer means and the inertia loading mass.
  • a transducer comprising:
  • oscillatory transducer means for operation within a frequency range and including front, rear and side surfaces;
  • each of said pressure transmitting means having a lower specific acoustic impedance than those of said inertia loading masses.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Transducers For Ultrasonic Waves (AREA)
US712829A 1968-03-13 1968-03-13 Transducer having a backing mass spaced a quarter wavelength therefrom Expired - Lifetime US3480906A (en)

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US (1) US3480906A (enrdf_load_stackoverflow)
JP (1) JPS4930743B1 (enrdf_load_stackoverflow)
FR (1) FR2003837A1 (enrdf_load_stackoverflow)
GB (1) GB1257836A (enrdf_load_stackoverflow)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4068209A (en) * 1974-11-08 1978-01-10 Thomson-Csf Electroacoustic transducer for deep submersion
US4380808A (en) * 1981-02-06 1983-04-19 Canadian Patents & Development Limited Thinned array transducer for sonar
US5047996A (en) * 1989-11-22 1991-09-10 Westinghouse Electric Corp. Sonar transducer
US5335209A (en) * 1993-05-06 1994-08-02 Westinghouse Electric Corp. Acoustic sensor and projector module having an active baffle structure
US5532980A (en) * 1994-11-14 1996-07-02 Sciencetech Inc. Vibrational anti-fouling system
DE19957125A1 (de) * 1999-11-26 2001-06-21 Siemens Ag Ultraschall-Wandler
EP2401966A1 (en) * 2010-06-30 2012-01-04 Kabushiki Kaisha Toshiba Ultrasound probe and ultrasound imaging apparatus
CN102798670A (zh) * 2011-05-20 2012-11-28 Ge传感与检测技术有限公司 用于超声换能器的多部件式安装装置
KR101411232B1 (ko) 2011-03-29 2014-06-24 도시바 메디칼 시스템즈 코포레이션 초음파 프로브와 초음파 프로브의 제조 방법

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5920234B2 (ja) * 1979-09-27 1984-05-11 沖電気工業株式会社 超音波送受波器

Citations (7)

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Publication number Priority date Publication date Assignee Title
US2534918A (en) * 1948-12-11 1950-12-19 Westinghouse Electric Corp Apparatus for balancing rotors
US2753543A (en) * 1952-08-28 1956-07-03 Raytheon Mfg Co Transducers
US2761117A (en) * 1952-01-16 1956-08-28 Charles E Green Directional transducer
US2894317A (en) * 1954-06-07 1959-07-14 Spence T Marks Method for constructing a barium titanate blast velocity gauge
US2925582A (en) * 1956-02-22 1960-02-16 Oflice Nat D Etudes Et De Rech Acoustical firing indicator
US2956278A (en) * 1957-10-22 1960-10-11 Branchu Paul Joseph Aircraft-guidance system
US3396286A (en) * 1965-01-21 1968-08-06 Linden Lab Inc Transducer assembly for producing ultrasonic vibrations

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2534918A (en) * 1948-12-11 1950-12-19 Westinghouse Electric Corp Apparatus for balancing rotors
US2761117A (en) * 1952-01-16 1956-08-28 Charles E Green Directional transducer
US2753543A (en) * 1952-08-28 1956-07-03 Raytheon Mfg Co Transducers
US2894317A (en) * 1954-06-07 1959-07-14 Spence T Marks Method for constructing a barium titanate blast velocity gauge
US2925582A (en) * 1956-02-22 1960-02-16 Oflice Nat D Etudes Et De Rech Acoustical firing indicator
US2956278A (en) * 1957-10-22 1960-10-11 Branchu Paul Joseph Aircraft-guidance system
US3396286A (en) * 1965-01-21 1968-08-06 Linden Lab Inc Transducer assembly for producing ultrasonic vibrations

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4068209A (en) * 1974-11-08 1978-01-10 Thomson-Csf Electroacoustic transducer for deep submersion
US4380808A (en) * 1981-02-06 1983-04-19 Canadian Patents & Development Limited Thinned array transducer for sonar
US5047996A (en) * 1989-11-22 1991-09-10 Westinghouse Electric Corp. Sonar transducer
US5335209A (en) * 1993-05-06 1994-08-02 Westinghouse Electric Corp. Acoustic sensor and projector module having an active baffle structure
US5532980A (en) * 1994-11-14 1996-07-02 Sciencetech Inc. Vibrational anti-fouling system
DE19957125A1 (de) * 1999-11-26 2001-06-21 Siemens Ag Ultraschall-Wandler
US6825594B1 (en) 1999-11-26 2004-11-30 Siemens Aktiengesellschaft Ultrasonic transducer
EP2401966A1 (en) * 2010-06-30 2012-01-04 Kabushiki Kaisha Toshiba Ultrasound probe and ultrasound imaging apparatus
KR101411232B1 (ko) 2011-03-29 2014-06-24 도시바 메디칼 시스템즈 코포레이션 초음파 프로브와 초음파 프로브의 제조 방법
CN102798670A (zh) * 2011-05-20 2012-11-28 Ge传感与检测技术有限公司 用于超声换能器的多部件式安装装置
US20130019702A1 (en) * 2011-05-20 2013-01-24 York Oberdoerfer Multi-part mounting device for an ultrasonic transducer
US8997590B2 (en) * 2011-05-20 2015-04-07 Ge Sensing & Inspection Technologies Gmbh Multi-part mounting device for an ultrasonic transducer

Also Published As

Publication number Publication date
FR2003837A1 (enrdf_load_stackoverflow) 1969-11-14
JPS4930743B1 (enrdf_load_stackoverflow) 1974-08-15
GB1257836A (enrdf_load_stackoverflow) 1971-12-22

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