US3808563A - Filter and method for its manufacture - Google Patents

Filter and method for its manufacture Download PDF

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Publication number
US3808563A
US3808563A US00283277A US28327772A US3808563A US 3808563 A US3808563 A US 3808563A US 00283277 A US00283277 A US 00283277A US 28327772 A US28327772 A US 28327772A US 3808563 A US3808563 A US 3808563A
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Prior art keywords
resonators
resonator
filter
transducer
metal strips
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US00283277A
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English (en)
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M Borner
H Schussler
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Licentia Patent Verwaltungs GmbH
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Licentia Patent Verwaltungs GmbH
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/48—Coupling means therefor
    • H03H9/50—Mechanical coupling means
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/42—Piezoelectric device making

Definitions

  • An electromechanical filter having a first and a second transducer resonator and a plurality of additional resonators, each resonator having first and second end surfaces.
  • the resonators are arranged substantially parallel to one another.
  • Two longitudinally vibrating thin, coupling wires are respectively coupled to the first end surfaces and to the second end surfaces.
  • a plurality of thin, metal mounting strips are fastened to the resonators.
  • the thickness d, and length l, of each of the mounting elements corresponds approximately to the equation:
  • Such an electromechanical filter is manufactured by fixing each of the resonators to mounting elements, and removing material as required from at least one of the resonators to effect tuning.
  • This invention relates to an electromechanical filter and to a method of making the filter.
  • the present invention relates, more particularly, to an electromechanical filter having resonators of the flexural vibration type and longitudinally oscillating coupling elements as well as piezoelectrically acting transducer resonators at its input and its output.
  • One purpose is to eliminate production steps, if necessary at the sacrifice of higher quality, if this were to exceed, to too large an extent, the minimum requirement for the filter tolerances.
  • the present invention therefore resides in a combination of features which optimizes the total filter design in the desired manner.
  • the invention in its apparatus aspect, resides in an electromechanical filter having an input arrangement formed by a first piezoelectrically acting transducer resonator, having first and second end surfaces. An output arrangement is fonned by a second piezoelectrically acting transducer resonator, having first and second end surfaces.
  • a plurality of intervening resonators of the flexural vibrating type, each having first and second end surfaces, are provided.
  • the transducer resonators and the intervening resonators are arranged substantially parallel to one another.
  • Two longitudinally vibrating coupling elements in the form of thin coupling wires are provided. One of the coupling elements is coupled to each of the first end surfaces and the other coupling element is connected to each of the second end surfaces.
  • a plurality of mounting elements in the form of respective, thin, metal strips are fastened to the resonators of the plurality of resonators and to the transducer resonators. The thickness and the length of the mounting elements correspond approximately to the equation:
  • d is the thickness of the metal strips
  • I is the length of the metal strips
  • m is the angular (radial) frequency of the filter
  • p is the dei'tsity of the metal strips
  • E is the modulus of elasticity of the metal strips and a is a constant.
  • the end surfaces to which two of the coupling wires are fastened are preferably the frontal faces of the intervening resonators and transducer resonators so that the succession of end surfaces throughout the filter are connected together by at least one continuous wire.
  • the invention in its method aspect, involves the making of an electromechanical filter which includes providing a first transducer resonator, a second transducer resonator, and a plurality of intervening resonators, fixing each of the intervening resonators and each of the transducer resonators to mounting elements, and removing material as required from at least one of the resonators to effect tuning thereof.
  • FIG. I is a perspective view of one embodiment of an electromechanical filter constructed in accordance with the present invention, some of the resonators being absent, for the sake of clarity, and one resonator being shown in section.
  • FIG. 2 is a perspective view of a plurality of resonators coupled together by a wire.
  • FIG. 2A is a diagrammatic illustration of a resonator and an associated coupling wire of the single coupling wire type, with the coupling wire displaced from the center of the resonator.
  • FIG. 3 is a graphical representation of the coupling ratio (K/K plotted against the ratio of the distance that the coupling wire, as shown generally in FIG. 2A, is from an end of the resonator to the half length of the resonator (I /h).
  • FIG. 4 is a graphical representation of the frequency characteristics of an electromechanical filter constructed in accordance with the present invention.
  • FIG. 5 is a diagrammatic, perspective view of a mounting element suitable for use as part of an electromechanical filter constructed in accordance with the present invention.
  • FIG. 6 is a perspective view of a second embodiment of a mounting element suitable for use as part of an electromechanical filter constructed in accordance with the present invention.
  • FIG. 7 is a perspective view of a mounting arrangement composed of a plurality of mounting elements formed by a common metal piece.
  • FIG. 8 is a perspective view of a transducer resonator suitable for use as part of an electromechanical filter constructed in accordance with the present invention.
  • FIG. 9 is a plan view of a plurality of intervening reso nators and a transducer resonator coupled together by wires in accordance with a preferred embodiment of the present invention.
  • FIG. 10 is a plan view of a plurality of resonators and a transducer resonator coupled together by wires in accordance with a further preferred embodiment of the present invention.
  • FIG. 11 is a perspective view of one embodiment of an electromechanical filter constructed in accordance with the present invention comprising additional cou pling wires between nonadjacent resonators.
  • FIG. 1 illustrates an embodiment of an electromechanical filter constructed in accordance with the pres ent invention.
  • the electromechanical filter according to the present invention includes electromechanical transducers and a mechanical filter structure which transmits purely mechanical waves, in its transmission range, and reflects them, in its blocking range.
  • a series of intervening resonators 2 which generally are made of a special metal alloy are disposed between an input piezoelectrically acting transducer resonator l and an output trans ducer resonator I.
  • FIG. 1 illustrates an embodiment of an electromechanical filter constructed in accordance with the pres ent invention.
  • the electromechanical filter according to the present invention includes electromechanical transducers and a mechanical filter structure which transmits purely mechanical waves, in its transmission range, and reflects them, in its blocking range.
  • intervening resonators 2 which generally are made of a special metal alloy are disposed between an input piezoelectrically acting transducer resonator l and an output trans ducer resonator I.
  • the housing includes a cover 6 which is shown broken away to expose elements [-4, connected, by conventional means, to a mounting plate 5 on which the mounting elements 4 are fixed.
  • the mounting elements 4 are, as shown in FIG. 1, thin metal strips fonned from parts of a thin metal member which is fixed, for example by welding, to the mounting plate 5.
  • a piezoelectric member 8, preferably in the form of a ceramic mem' her, is fixedly positioned on a surface of the second transducer resonator I.
  • a lead 7', on which the output signal from the filter appears, is connected to an electrode of the piezoelectric member 8.
  • Another similar piezoelectric member (not visible in FIG. 1) is fixedly attached to a surface of the first transducer resonator l, a lead 7 being provided to an electrode of this transducer to serve as the signal input lead of the filter.
  • All of the resonators I, l' and 2, as shown in FIG. I, are connected in succession by means of coupling elements 3, e.g. thin wires preferably connected to the resonator end faces.
  • Nonadjacent ones of the resonators may be additionally coupled together in any of many possible ways.
  • the electrical equivalent circuit diagram exhibits the characteristics ofa polynomial filter. With the additional coupling, it is possible to produce attenuation peaks at real and complex frequencies. It is also of importance that the coupling elements 3 have a given length which is related to the wavelength of the oscillation sought to be passed through the electromechanical filter.
  • a very decisive role is played by a plurality of substantially identically dimensioned, mechanical mounting elements 4 for the resonators l, l' and 2.
  • Two of the mounting elements 4 are provided for each of the resonators l, l and 2, and are fixed to spaced points of the respective resonators l, l and 2 inwardly of their end surfaces, to which the coupling elements 3 are fixed.
  • the mounting elements 4 serve to decouple the filter as completely as possible from the housing 5, 6.
  • the mounting elements 4 must be stable, can be produced inexpensively, and must not detune the resonators l, 1' and 2 or only detune them in a consistently repeatable manner, i.e. by the same amount from one production unit to the next.
  • the resonators l, I and 2 must not have additional resonant points (ancillary waves) as a result of their association with the mounting elements 4; any existing undesired resonances must be either attenuated or displaced intorioninterfering frequency regions.
  • the cover 6 is of importance because of the ancillary waves, if flexural resonators are used whose sound irradiation cannot be neglected, particularly in the range of about 50 kHz. Generally proven structures can be dependably used.
  • the coupling length in order to reduce the overall structural length, must be 25mm, i.e. practically a length of 5mm.
  • Ni-Span-C is a Ni-Fe alloy consisting of 42,5 Ni, 5 Cr, l Al and Ti, remainder Fe.
  • the components of Therrnelast are as follows: 42 Ni, 9 Mo, l Be, remainder Fe.
  • A-wire material consists of Ni, Fe and Mo.
  • the coupling wire 11 must have a cross section which is greater by the factor l/0.37 2.7 (FIG. 3) as can be learned from an article in the publication AEU I6 (1962) (Archiv der Elektrischen Ubertragung), S. Hir zel Verlag, Stuttgart, West Germany, pages 355-358.
  • AEU I6 (1962) (Archiv der Elektrischen Ubertragung), S. Hir zel Verlag, Stuttgart, West Germany, pages 355-358.
  • the diameter of the coupling wire 11 is about 0.45mm. If two wires serving as the coupling members 3 (FIG.
  • the diameter of these coupling wires reduces to 0.45 l/ V? l/ 2.7mm 0.]9mm. This reduction in the cross section is very decisive in another respect.
  • the coupling ratio decreases as the single coupling wire 11 is moved away from the center point, reaching zero at a l ratio of about 0.3 and thereafter reaching l.0 when l, is zero; i.e., the wire 11 is at the end of the resonator 10.
  • FIG. 4 shows graphically how strongly the frequencies shift at the upper (f,) and lower (L) edges of the band as well as at the center band frequency f when the length of a coupling member I differs from M4.
  • the frequencies are standardized to the prealignment frequency f, of the resonators inherent to them before the coupling members or wires are welded on.
  • K is the coupling factor of the resonators.
  • the steep rise of the curves directly shows that for f, and f at I, )t/4 the maintaining of an accurate coupling length is very critical.
  • the permissible tolerances for the filter result in a manufacturing accuracy of the length I of Al, 2 i4p.
  • the position of the welding point for welding the coupling wire to the flexural resonator must be corre spondingly accurate.
  • the advantage of using two coupling wires, in accordance with this invention, each having a diameter of 190p. instead of one wire with a diameter of 450p. becomes immediately evident.
  • a wire of 190p. can be welded much more accurately than a wire of 45044..
  • Added to this advantage is a further advantage when the proposed two coupling wires are welded to the two frontal faces of the resonators, in accordance with the present invention.
  • the position of a coupling wire and its thickness are decisive, with regard to the degree (strength) of the coupling effected by the coupling wire, but not its accurate positioning on the frontal face of the resonators.
  • the accurate positioning of this point is also decisive as can be seen from FIG. 3 (with I, z l,).
  • the value K K is thus dependably achieved in the arrangement of the present invention over the entire frontal face. This is of importance for the manufacture of the filters.
  • An electromechanical filter according to FIG. I is to be manufactured in such a way that first all parts of the filter shown in FIG. I, except for the coupling elements (wires) 3, are connected together, for example, by electrical spot welding, soldering or cementing. Then the individual resonators 2 and the transducer resonators l and 1' are accurately frequency tuned.
  • the weld ing jig in which the resonators 2 and the transducer resonators I and l are welded to the mounting elements 4 need not meet any extreme precision requiremenLs.
  • a spacing tolerance of about :0. lmm in the alignment of these parts ,to one another is sufficient for the type of filters according to the present invention.
  • the difficulty here again is the attainment of relatively short mounting elements 4.
  • ultrasonic vibrations will always propagate along the mounting elements 4.
  • the mounted resonators I, I and 2 are detuned or attenuated.
  • the magnitude of these effects can be reduced by providing a cross section for the mounting element 4 which just suffices for mounting purposes, so that the coupling of the mounted resonators 1, l' and 2 with the cover 6 and the mounting plate 5 is reduced in that the acoustically effective length of these mounting elements 4 is made about M4.
  • the torsional vibrations transmitted from the holding pins would be optimally decoupled from the housing.
  • the mounting elements 4 in FIG. 1 each substantially consist of an actual supporting part which is shown, in an enlarged view, in FIG. 5 and which has a length L, a width b and a thickness d.
  • This element is torsionally stressed by that one of the resonators l, l' and 2 with which it is associated, and performs flexural vibrations in the plane of the resonators l, l' and 2. If this mounting element is imagined to be separated into parallel sections along the dashed lines shown in FIG. 5, the individual sections perform flexural vibrations. None changes in the mechanism of these vibrations in a first approximation, i.e.
  • the thickness value d can be detemiined, for example, with the aid of an experiment set forth in the periodical AEU l5 (l96l), Issue No. 4, pages -180, equations (la) and (20a) of which are of interest. when the length of the mounting element is given and there is a )t/4 type coupling. The following applies:
  • E/p 5 l0cm/sec the speed of sound for longitudinal waves.
  • E is the modulus of elasticity.
  • p is the density of the material.
  • the symbol to is the angular frequency; i.e., w, 21rf,,, f being the center frequency of the filter.
  • lfl 0.3cm is selected, the following applies at a frequency: f, to /217 50 kHz d 0.035cm 4 in an entirely analogous manner, the corresponding formulas result for the relationships, for example, at 3M4 and 5M4 type coupling, i.e.
  • the mounting element consists, at least in its portion which is torsionally stressed, of a frame having approximately the following inner dimensions:
  • the width b is adapted to that of the resonators 2 or that of the transducer resonators l and I. In practice, b will be approximately 2mm. Thus the entire arrangement has suitable stability in addition to optimum decoupling.
  • the M4 long mounting elements 4 (FIG. 1). as more specifically shown in FIGS. 5 or 6, are to be provided using conventional principles employed for the construction of filters and the arrangement of the resonators l, l' and 2 thereon.
  • the mounting elements 4, as shown in FIG. 1, are of a common metal piece, are to be made, for example, by stamping, and are to be bent in such a manner that an integral body results. as shown in FIG. 7. This produces good stability during the first fabrication steps, and results in a stable. sturdy mounting arrangement.
  • This stability is particularly important since, after assembly of the parts of the filter shown in FIG. 1, or before welding on the coupling wires 3, the resonators 2 and the transducer resonators 1 32d I must be turned. Either because of their precise fabrication or as a result of a first prealignment before being welded to the mounting elements 4 they already have an approximately correct resonant frequency and band width. However, the. first welding step produces such stray phenomena that subsequent tuning, in the range of a few Hertz, is generally needed at this point. The magnetic fields produced as a result of electric welding, if such a technique is used, have an influence on the in herent frequency which must be eliminated by a demagnetization process.
  • the actual tuning process can be effected by grinding with a fine high-speed grinding disc or the like. It is best to grind the end of resonators and thus increase the frequency. This retains the characteristic impedance Z of the resonators l, l and 2 and thus also the degree of coupling between the adjacent resonators at a given cross section of the coupling wires 3.
  • the coupling between the resonators must be able to meet the requirements of filter theory, generally the coupling decreases from the outer to the inner resonator pairs by a factor of 2, or more. With a constant spacing 1 between the resonators and a constant cross section of the coupling wires 3, this can be accomplished only by varying the cross section of the resonators l, l and 2.
  • transducer resonator As shown in FIG. 8, Protrusions 9, as shown in FIG. 8, cause the total length of the transducer resonator l to become approximately equal to that of the resonators 2.
  • the shape of these protrusions is almost arbitrary.
  • the transducer resonator l is provided with similar protrusions.
  • the metallic portion of the transducer resonators l and l is provided, for exam ple, as an integral piece which has been machined to provide the protrusions 9, but these protrusions may also be welded on. The advantage is then that the weldedon protrusions need not necessarily be made of a temperature compensating material.
  • the length of the transducer resonators l and 1' may, however, also be selected to equal that of the intervening resonators 2, if at the same time the diameter of the transducer resonators l and l is increased. With the appropriate selection of length and diameter, tne inherent flexural resonant frequency remains substantially the same; however, the distance of the transducer resonators l and 1' from the adjacent resonators 2 must be reduced due to the decrease in coupling.
  • the adaptation of the length may also be effected by a slight curvature of coupling wires 13 fastened to the end surfaces of resonators l4 and 15, as shown in FIG. 9, or by a variation of the lengths of a first transducer resonator 17, as well as of intervening resonators l8 and a second transducer resonator (not shown), so that the filter has the approximate construction shown in FIG. 10, coupling wires 16 being essentially straight, but not parallel to one anodier.
  • FIG. ll shows another embodiment of an electromechanical filter constructed in accordance with the present invention. All of the resonators 1, l, and 2 are connected in succession by means of couplingelements 3, e.g. thin wires preferably connected to the resonator end faces. Nonadjacent ones of the resonators are coupled together by additional coupling wires 3'.
  • couplingelements 3 e.g. thin wires preferably connected to the resonator end faces.
  • Nonadjacent ones of the resonators are coupled together by additional coupling wires 3'.
  • An electromechanical filter having a signal input means and a signal output means comprising, in combination:
  • a first piezoelectrically acting transducer resonator having first and second end surfaces and serving as said input means.
  • a plurality of intervening resonators of the fiexural vibrating type each having first and second end surfaces, and a second piezoelectrically acting transducer resonator having first and second end surfaces and serving as said output means, said resonators being arranged substantially parallel to one another;
  • d is the thickness of the metal strips
  • l is the length of the metal strips
  • p is the density of the metal strips
  • E is the modulus of elesticity of the material of the metal strips.
  • a is a constant having a value selected from the group consisting of values of substantially 0.62; 0.1 and 0.046.
  • each of said resonators has a respective longitudinal axis, and wherein said coupling elements are arranged substantially parallel to one another and approximately at a right angle to said longitudinal axis of said resonators.
  • each of said metal strips is in the shape of a frame at least in that area which is subjected to torsion stresses.
  • each said frame has a respective opening having a height approximately equal to the length of each of said metal strips and having a width of between about one-third and one-half the length of each of said metal strips.
  • each said transducer resonator is each provided with a respective axially extending protrusion having a cross section smaller than the cross section of each said transducer resonator, said two coupling wires being connected to said protrusions.
  • each said resonator is substantially circular in radial cross section, the diameters of said transducer resonators being greater than the diameters of said intervening resonators.
  • each said resonator is substantially circular in radial cross section, said first transducer resonator. said intervening resonators and said second transducer resonator being arranged in succession, the lengths and diameters of said resonators increasing progressively from one resonator to the next.
  • a method of making an electromechanical filter comprising: providing a first transducer resonator.
  • each resonator having two end surfaces; fixing each resonator to a mounting element; fine tuning the resonators by mechanically removing material from at least one resonator after said step of fixing each resonator to a mounting element; and, after said step of fine tuning, fixing coupling wires to the resonator end surfaces.
  • a method of making an electromechanical filter comprising: providing a first transducer resonator, a plurality of intervening resonators and a second transducer resonator each resonator having two end surfaces; forming mounting elements as thin metal strips of material forming the edge portions of a common piece of metal so as to form the mounting elements as parts of a single piece of metal; fixing the resonators to the mounting elements; fixing coupling wires to the resonator end surfaces; and fine tuning the resonators by mechanically removing material from at least one resonator after said step of fixing each resonator to a mounting element.
  • a method as defined in claim 17, wherein the step of fixing the resonators is effected by spot welding, soldering, or cementing.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
US00283277A 1971-08-24 1972-08-24 Filter and method for its manufacture Expired - Lifetime US3808563A (en)

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DE2142332A DE2142332C2 (de) 1971-08-24 1971-08-24 Mechanisches Filter und Verfahren zur Herstellung des Filters

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US3808563A true US3808563A (en) 1974-04-30

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US (1) US3808563A (ja)
JP (1) JPS4830841A (ja)
DE (1) DE2142332C2 (ja)
FR (1) FR2151391A5 (ja)
GB (1) GB1394289A (ja)
IL (1) IL40139A (ja)
IT (1) IT963927B (ja)
SE (1) SE382726B (ja)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3931600A (en) * 1973-06-11 1976-01-06 Kokusai Electric Co., Ltd. Mechanical filter
US3952387A (en) * 1973-07-03 1976-04-27 Tokyo Shibaura Electric Co., Ltd. Method of manufacturing an ultrasonic probe
US4184132A (en) * 1977-07-01 1980-01-15 Societe Anonyme De Telecommunications Electromechanical filters

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5528021Y2 (ja) * 1973-08-04 1980-07-04
JPS5645223Y2 (ja) * 1975-04-19 1981-10-22
JPS53105032A (en) * 1977-02-25 1978-09-12 Hazama Gumi Method of excavating subbase using high pressure water jet
DE2729839C3 (de) * 1977-07-01 1981-03-26 Siemens AG, 1000 Berlin und 8000 München Trägerfrequentes Nachrichtenübertragungssystem mit Vormodulation

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2647949A (en) * 1949-10-27 1953-08-04 Rca Corp Adjustable tuning for mechanical resonators
US2845697A (en) * 1957-03-11 1958-08-05 Zenith Radio Corp Method of manufacturing a longitudinal mode mechanical vibrator
US2870521A (en) * 1955-02-24 1959-01-27 Gulton Ind Inc Method of adjusting the resonant frequency of a vibrating system
US3086182A (en) * 1957-12-12 1963-04-16 Telefunken Gmbh Mechanical frequency filters
DE1541975A1 (de) * 1967-05-12 1969-12-11 Siemens Ag Elektromechanisches Bandfilter
US3717828A (en) * 1971-04-07 1973-02-20 N Arleevskaya Multisection electromechanical band pass filter with resonators and transducers mechanically connected together and to the filter baseplate

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1100834B (de) * 1957-04-06 1961-03-02 Telefunken Gmbh Mechanisches Frequenzfilter
CH491545A (de) * 1968-05-29 1970-05-31 Siemens Ag Elektromechanisches Filter

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2647949A (en) * 1949-10-27 1953-08-04 Rca Corp Adjustable tuning for mechanical resonators
US2870521A (en) * 1955-02-24 1959-01-27 Gulton Ind Inc Method of adjusting the resonant frequency of a vibrating system
US2845697A (en) * 1957-03-11 1958-08-05 Zenith Radio Corp Method of manufacturing a longitudinal mode mechanical vibrator
US3086182A (en) * 1957-12-12 1963-04-16 Telefunken Gmbh Mechanical frequency filters
DE1541975A1 (de) * 1967-05-12 1969-12-11 Siemens Ag Elektromechanisches Bandfilter
US3717828A (en) * 1971-04-07 1973-02-20 N Arleevskaya Multisection electromechanical band pass filter with resonators and transducers mechanically connected together and to the filter baseplate

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3931600A (en) * 1973-06-11 1976-01-06 Kokusai Electric Co., Ltd. Mechanical filter
US3952387A (en) * 1973-07-03 1976-04-27 Tokyo Shibaura Electric Co., Ltd. Method of manufacturing an ultrasonic probe
US4184132A (en) * 1977-07-01 1980-01-15 Societe Anonyme De Telecommunications Electromechanical filters

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DE2142332C2 (de) 1983-07-14
DE2142332A1 (de) 1973-03-01
IL40139A (en) 1975-06-25
IT963927B (it) 1974-01-21
JPS4830841A (ja) 1973-04-23
GB1394289A (en) 1975-05-14
SE382726B (sv) 1976-02-09
FR2151391A5 (ja) 1973-04-13
IL40139A0 (en) 1972-10-29

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