US2194539A - Piezoelectric crystal impedance element - Google Patents

Piezoelectric crystal impedance element Download PDF

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Publication number
US2194539A
US2194539A US228355A US22835538A US2194539A US 2194539 A US2194539 A US 2194539A US 228355 A US228355 A US 228355A US 22835538 A US22835538 A US 22835538A US 2194539 A US2194539 A US 2194539A
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United States
Prior art keywords
crystal
electrodes
impedance
portions
electrode
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Expired - Lifetime
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US228355A
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English (en)
Inventor
Joseph F Barry
Henry G Och
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AT&T Corp
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Bell Telephone Laboratories Inc
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Priority to US228355A priority Critical patent/US2194539A/en
Priority to GB19842/39A priority patent/GB530957A/en
Priority to FR858577D priority patent/FR858577A/fr
Application granted granted Critical
Publication of US2194539A publication Critical patent/US2194539A/en
Anticipated expiration legal-status Critical
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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 elements; Electromechanical resonators
    • H03H9/0023—Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns, or networks having balanced input and output
    • H03H9/0095—Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns, or networks having balanced input and output using bulk acoustic wave devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/542—Filters comprising resonators of piezoelectric or electrostrictive material including passive elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/56—Monolithic crystal filters
    • H03H9/566—Electric coupling means therefor
    • 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

  • This invention relates to piezoelectric crystalsand more particularly to crystals adapted-for use as impedance elements in electrical circuits.
  • the principal object of the invention is to increase the impedance of a piezoelectric crystal element by any desired factor.
  • Other objects are to reduce the required thickness and the cost of high impedance crystals.
  • a piezoelectric crystal is provided with a pair of electrodes and an alternating electromotive force is impressed upon the electrodes the crystal will constitute an electrical impedance the magnitude of which at any given frequency is dependent upon the electrostatic capacitance between the electrodes and the piezoelectric and elastic constants of the crystal.
  • this impedance is directly proportional to the thickness of the crystal.
  • the impedance of a given crystal element is increased by any desired factor by dividing or subdividing the electrodes and interconnecting these divisions in such a way that different portions of the crystal are connected in series or in seriesparallel combinations.
  • a comparativelythin crystal may be made to provide a high impedance, and the crystal may be easily mounted without resort to special arrangements.
  • the magnitude of the impedance may be readily adjusted simply by changing the relative proportions of the electrodes.
  • the invention is applicable to crystal elements of any piezoelectric material adapted to vibrate either in the iiexural mode or in the longitudinal mode at the fundamental frequency or a harmonic frequency.
  • the electrodes may be further divided so that a single crystal element will provide two impedances.
  • a wave filter circuit is shown which employs the crystal as an impedance element.
  • 1 shows a piezoelectric crystal element with its associated electrodes
  • Fig. 2 represents the equivalent electrical circuit for the crystal element of Fig. 1;
  • P18. 3 shows how the electrodes of Fig. 1 may be divided and portions of the crystal interconnected in series to increase the impedance
  • Fig. 4 shows diagrammatically the connection of the diiferent portions of the crystal of Fig. 3;
  • Fig. 5 shows a series-parallel connection for the electrodes of Fig. 3;
  • Fig. 6 shows diagrammatically the connection of the various portions of the crystal of Fig. 5;
  • Fig. 7 shows a preferred electrode arrangement when the connections are as shown in Fig. 5;
  • Fig. 8 shows the development of one mode of carrying out the connections of Fig. 7;
  • Fig. 9 shows the electrodes of Fig. 8 divided along the center line in order to provide two impedances
  • Fig. 10 shows a layout for electrodes so arranged that electrical connection may be made through supports placed at a'nodal point
  • FIG. 11 shows diagrammatically the circuit for a crystal having the electrodes shown in Fig. 10;
  • Fig. 12 shows a crystal having two electrodes on each side adapted to vibrate at a harmonic frequency
  • Fig. 13 shows how the electrodes of the harmonic crystal of Fig. 12 may be subdivided to increase the impedance
  • Fig. 14 shows a lattice-type wave filter which uses a high impedance crystal having divided electrodes in accordance with the'invention.
  • Fig. 1 is an elevation of a piezoelectric crystal element I, with its associated electrodes 2 and 3 provided with electrical terminals 6 and 5.
  • the crystal element maybe cut from any piezoelectric material such, for example, as quartz, and is preferably in the form of a rectangular plate having any desired orientation with respect to the principal axes of the mother crystal;
  • the electrodes are associated with the two major faces and are preferably metallic coatings applied directly to the surface of the crystal.
  • the crystal element When an alternating electromotive force is applied to the terminals 4 and 5 the crystal element will offer an impedance which may be represented by the equivalent electrical circuit of Fig. 2 comprising a capacitance Co shunted by a resonant arm consisting of an inductance L in series with a second capacitance C.
  • the capacitance Cc represents the electrostatic capacitance between the two electrodes 2, 3, and the values of L and C depend upon the piezoelectric and elastic constants of the crystal.
  • the impedance of the crystal element is'increased to any desired extent by dividing the electrodes and electrically interconnecting the divisions.
  • the electrode 2 may be divided into three parts designated by their areas A, B and C.
  • the other electrode 3 is divided into corresponding portions A, B and C.
  • the lines of division may be either longitudinal or transverse with respect to the face of the crystal. Fig. 3, therefore, may be taken as representing tions or" the crystal of Fig. 3 with divided electrodes will be, respectively,
  • the total inipedance is the sum of the impedances or the various portions, as indicated diagrammatically in Fig. i.
  • the total impedance Z1 is therefore M M M 214 (1) If the areas A, B and C are equal, each will be approximately equal to %M: and the total in pedance wfll he M M M 21 e 34:92 2
  • the minimum resultant impedance is obtained when all of the electrodes are equal in area.
  • the minimum resultant impedance may be decreased by connecting the portions of the crystal in a series-parallel arrangement, as shown in Fig. 5 where the central portion is connected in parallel with a branch consisting of the two outer portions in series.
  • the circuit is shown diagrammatically in Fig. 6.
  • the impedance Z2 of this arrangement is given approximately by the expression If all of the areas are equal the impedance is approximately M M M 1 1 1 z -M -M M Other values of- Z2 ranging between Z and 92 may be provided by making the areas unequal. If
  • the impedance is approximately o] co
  • the approximate Formula 6 can safely be used in making calculations provided the ratio of B to M is small compared to unity. if this ratio is less than one-fifth, the error introduced in the calculated impedance Z2 by the use of the approximate formula will be less than h per cent.
  • the two electrodes A and r?) are connected together electrically, and likewise the electrodes B and C' are connected.
  • These electrodes may, ther fore, be replaced, respectively, by single electrodes such as D and E as shown in Fig. '7.
  • the crystal 9 is vibrating in the longitudinal mode there will be a node of motion near the center, and the crystal is preferably supported at this point.
  • the two supports and 7, located at this nodal region, are provided for this purpose. If the supports are of conducting material the terminals may be connected thereto, as shown.
  • the leads to the. terminals t and 5 may be connected directly to the electrodes D and E by means of soft solder, for example. 1
  • Fig.8 shows the development oi one mode of interconnecting theelectrodes C and A" of Fig. 5.
  • the dot-and-dash lines 8 and 9 indicate, respectively, the center line of the upper face of the crystal plate l and the center line of the lower face. of edges of the crystal and the lines l2, l3 represent the opposite pair of edges.
  • the dotted lines Ell, H represent one the strips of plating M and I5 which extend along two impedances each of the electrodes may be subdivided along the center line into two equal parts as shown in Fig. 9.
  • the electrode D is thus split into the halves D1 and D2, and the electrodes A, C and E are divided, respectively, into the parts A1, A's, C1, C2 and E1, E2.
  • the terminals 1, 5 are replaced by the two sets of terminals 15, H and i8, RS.
  • Sucha crystal may be used, for example, in a wave filter oi the type shown in Fig. 14 and described hereinafter.
  • the crystal may now be supported at its center and contacts made through the supports to the extensions F and F.
  • the electrode C is connected to the electrodes 3'1 and B: by the side strips 20 and 2
  • the electrode A is connected to the electrodes B1 and B2 by the strips 22 and 23.
  • all of the electrodes may be further subdivided along the center lines 8 and 9, in the same manner as shown in Fig. 9, to provide two impedances.
  • Fig. 10 the portion of the crystal between the two overlapping electrodes F and F is connected in parallel with an arm consisting of the other three portions of the crystal in series, as shown in Fig. 11.
  • the values of the four component impedances are indicated in the figure and the total impedance Z; between terminals 4 and 5 is given approximately by the formula M M M M z m o r
  • Fig. 12 shows a crystal element I with electrodes on each side divided transversely to form the equal electrodes G, H, J and K. If the electrodes J and K on the same side are connected together and an alternating electromotive force is applied at terminals 4 and 5, the crystal will vibrate at the first harmonic, which is approximately twice the fundamental frequency.
  • each electrode is further divided into the equal portions G1, G2, H1, H2, J1, J1 and K1, K2 and these are interconnected as shown in Fig. 13, the original impedance of the crystal will be increased by a factor of four.
  • the two adjacent electrodes J: and K1 may, of course, be replaced by a single electrode. Obviously other ratios of impedance may be obtained by changing the relative sizes of the electrodes, as I explained above in connection with other figures.
  • each electrode may be divided into more than two parts, and these may be connected in series or in series-parallel combinations to obtain any desired impedance ratio. Furthermore, the
  • electrodes of crystals having 3,4 or (Q+l) pairs of electrodes and adapted to vibrate at the sec- 0nd, third or Qth harmonic may be subdivided in a similar manner to obtain the desired impedance.
  • Fig. 14 shows how the high impedance crystal element of the invention may be used in a wave filter.
  • the filter is of the symmetrical lattice type and comprises two equal line impedance branches and two equal diagonal impedance branches connected between a pair of input terminals 24, 25 and a pair of output terminals 26, 21. Included in the line branches are the two equal piezoelectric crystal impedances 28, 28, and in the diagonal branches the two equal crystal impedances 30, 3
  • the two impedances 28 and 29 may be furnished by a single crystal with the electrode layout shown in Fig. 9.
  • the connections to the termiother two equal impedances 30 and Si may be supplied by individual crystal elements or by a second single crystal having electrodes as shown in Fig. 9.
  • the terminals l6, l1, l8 and I9 correspond, respectively, to the terminals l6, l1, l8 and I9 and the connections are made as shown.
  • the filter circuit is completed by the addition of two equal variable capacitances 32, 33 in the line branches and four equal series innals l8, i1, i8 andIS are made as shown.
  • the filter may be trode on the opposite side, means for making electrical connections to said two overlapping electrodes, and means for interconnecting the remaining electrodes.
  • An impedance element in accordance with claim 1 in which means are provided for supporting said'crystal at said overlapping portions of said two electrodes.
  • A11 impedance element comprising a piezoelectric crystal having two opoositeiy disposed electrode surfaces, two electrodes associated with one of said surfaces, two other electrodes associated with the other of said surfaces, two of said elecrodes on opposite sides having overlapping portions, each of said'two electrodes also being opposed to the other electrode on the opposite side, means for making electrical connections to said two overlapping electrodes, and an electrical connection between the remaining electrodes.
  • An impedance element comprising a piezoelectric crystal having two oppositely disposed electrode surfaces three electrodes associated with one of said surfaces, three other electrodes associated with the other of. said surfaces, two of said electrodes on opposite sides having overlapping portions, each of said two electrodes also being opposed to another electrode on the opposite side, means for making electrical connections to said two overlapping electrodes, and
  • An impedance element comprising a piezoelectric crystal, a plurality of pairs of oppositely disposed electrodes associated, res ectively, with a plurality of diiferent portions of said crystal, and means for connecting one of said portions in parallel with a combination comprising a plurality of the remaining portions in series.
  • An impedance element comprising a pieaoelectric crystal, three pairs or" oppositely disposed electrodes associated, respectively, with three difierent portions of said crystal, and means for connecting one of said portions in parallel with a combination comprising the remaining portions in series.
  • a piezoelectric device comprising a piezo electric crystal and associated electrodes so interconnected that in adjacent parts of said crystal the electrostatic field is of opposite direction whereby said crystal is adapted to vibrate at a harmonic frequency, a plurality of pairs of oppositely disposed electrodes associated with one of said parts, and means for connecting in series the portions of the crystal associated with said plurality of. pairs of electrodes.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
US228355A 1938-09-03 1938-09-03 Piezoelectric crystal impedance element Expired - Lifetime US2194539A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US228355A US2194539A (en) 1938-09-03 1938-09-03 Piezoelectric crystal impedance element
GB19842/39A GB530957A (en) 1938-09-03 1939-07-07 Piezoelectric crystal impedance element
FR858577D FR858577A (fr) 1938-09-03 1939-08-02 éléments d'impédance à cristaux piézo-électriques

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US228355A US2194539A (en) 1938-09-03 1938-09-03 Piezoelectric crystal impedance element

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2653547A (en) * 1947-03-01 1953-09-29 Borg Warner Hydrodynamic coupling
US2763050A (en) * 1950-01-06 1956-09-18 Bell Telephone Labor Inc Crystal unit inductance adjustment
US3437848A (en) * 1964-09-24 1969-04-08 Telefunken Patent Piezoelectric plate filter
US3748503A (en) * 1970-09-11 1973-07-24 Braun Ag Piezo electric motor
US4129799A (en) * 1975-12-24 1978-12-12 Sri International Phase reversal ultrasonic zone plate transducer
US4365182A (en) * 1980-10-14 1982-12-21 The United States Of America As Represented By The Secretary Of The Army Method of fabricating acceleration resistant crystal resonators and acceleration resistant crystal resonators so formed
US4608510A (en) * 1981-01-15 1986-08-26 Asulab S.A. - ESA 55 Piezoelectric micro-resonateur
US5294898A (en) * 1992-01-29 1994-03-15 Motorola, Inc. Wide bandwidth bandpass filter comprising parallel connected piezoelectric resonators
US5371430A (en) * 1991-02-12 1994-12-06 Fujitsu Limited Piezoelectric transformer producing an output A.C. voltage with reduced distortion

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2653547A (en) * 1947-03-01 1953-09-29 Borg Warner Hydrodynamic coupling
US2763050A (en) * 1950-01-06 1956-09-18 Bell Telephone Labor Inc Crystal unit inductance adjustment
US3437848A (en) * 1964-09-24 1969-04-08 Telefunken Patent Piezoelectric plate filter
US3748503A (en) * 1970-09-11 1973-07-24 Braun Ag Piezo electric motor
US4129799A (en) * 1975-12-24 1978-12-12 Sri International Phase reversal ultrasonic zone plate transducer
US4365182A (en) * 1980-10-14 1982-12-21 The United States Of America As Represented By The Secretary Of The Army Method of fabricating acceleration resistant crystal resonators and acceleration resistant crystal resonators so formed
US4608510A (en) * 1981-01-15 1986-08-26 Asulab S.A. - ESA 55 Piezoelectric micro-resonateur
US5371430A (en) * 1991-02-12 1994-12-06 Fujitsu Limited Piezoelectric transformer producing an output A.C. voltage with reduced distortion
US5294898A (en) * 1992-01-29 1994-03-15 Motorola, Inc. Wide bandwidth bandpass filter comprising parallel connected piezoelectric resonators

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Publication number Publication date
FR858577A (fr) 1940-11-28
GB530957A (en) 1940-12-24

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