US2091250A - Wave filter - Google Patents

Wave filter Download PDF

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Publication number
US2091250A
US2091250A US35918A US3591835A US2091250A US 2091250 A US2091250 A US 2091250A US 35918 A US35918 A US 35918A US 3591835 A US3591835 A US 3591835A US 2091250 A US2091250 A US 2091250A
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United States
Prior art keywords
impedance
rod
tanh
mechanical
terminals
Prior art date
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Expired - Lifetime
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US35918A
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English (en)
Inventor
Ralph B Blackman
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AT&T Corp
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Bell Telephone Laboratories Inc
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Publication date
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US35918A priority Critical patent/US2091250A/en
Priority to FR815901D priority patent/FR815901A/fr
Priority to DE1936I0055741 priority patent/DE687871C/de
Application granted granted Critical
Publication of US2091250A publication Critical patent/US2091250A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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

Definitions

  • This invention relates to impedance elements for use in wave filters and more particularly to impedance elements of the electromechanical type in which a mechanical vibrator coupled to an electrical circuit produces a reaction therein by virtue of its coupling thereto.
  • the principal object of the invention is to improve the efiiciency and the frequency characteristics of electromechanical vibrators intended for operation at relatively high frequencies, for example the frequencies of carrier telephony. Another object is to improve and simplify the construction of mechanical vibratory systems having relatively complex resonance characteristics.
  • Fig, 1 is a view partly in section of one embodiment of the electromechanical impedance element of the invention
  • Fig. 2 is a diagrammatic representation showing how two of the impedance elements of Fig. 1 may be utilized in a wave filter of the lattice type;
  • Fig. 3 shows reactance characteristics to which reference is made in explaining the invention
  • Fig. 4 shows diagrammatically the reactance characteristics of the branches of the lattice network of Fig. 2;
  • Fig. 5 is a diagram of a typical attenuation characteristic obtainable with the filter of Fig. 2.
  • Fig. 1 shows, partly in section, one embodiment of the electromechanical impedance element of the invention in which the mechanical vibrator ll comprises a central portion [2 and two symmetrical end portions I3 having a cross-sectional area difiering from that of the central portion.
  • the cross-sections of these portions of the vibrator may be round or of any other convenient shape, and their areas and the lengths of the sections are proportioned to produce desired resonance characteristics.
  • the vibrator is preferably made of non-magnetic material having 2. low dissipation constant, such, for example, as brass, aluminum or glass.
  • the vibrator is longitudinally symmetrical about a central plane by the line [4, l4 and when driven in the manner explained below it will have a nodal region coinciding with this plane of symmetry.
  • the vibrator is preferably supported at or near this nodal region. As shown in the figure, this may be done by means of a flange [5 which may be made an integral part of the mid-section 12. The flange may be clamped between the two parts l6 and i! of the outer casing, or supported in any other suitable manner.
  • the vibrator is set into vibration by means of two similar electromagnetic drives, one being located at each end.
  • Each of these drives comprises a magnetic armature l8, secured to the end of the vibrator, a permanent magnet I 9, two pole-pieces 20 and 2
  • the assembly is enclosed within the housing M and the lead wires to the coils are introduced through the insulating bushings 41.
  • Fig. 2 is a schematic diagram showing how two electromechanical impedances 2'! and 28 of the type described above may be connected between a pair of input terminals 29 and 3D, and a pair of output terminals 3
  • the impedance 21 has terminals 33, 34, 35 and 3G
  • the impedance 28 has terminals 31, 38, 39 and 40, corresponding, respectively, to terminals 23, 25, 24 and 26 shown in Fig. 1.
  • Each of the impedances is shown within a dotted enclosure, in the interest of clarity.
  • are connected between terminals 29 and 3
  • terminals 40 and 38 of the impedance 28 are connected between terminals 29 and 32, and terminals 31 and 39 between terminals 3! and 30 to form the diagonal branches of the lattice network.
  • C1 may be connected, respectively, in series with the terminals 35 and 36 and a second pair of equal capacitances C2, C2 may be connected in series with the terminals 31 and 38 in order to improve the transmission characteristics of the filter, as explained hereinafter.
  • the nature of the impedance characteristic obtainable with this type of electromechanical impedance element will now be considered.
  • the mechanical input impedance Z of a rod of nonuniform cross--section, such as the vibrator ll, when the driving forces at the two ends are in phase opposition is the same as that of a rod of the length of one of the end sections l3 connected in tandem with a rod of half the length of the mid-section E2, the latter being fixed at its distant end. If the vibrator is driven from one end only, a standing wave is set up thereon, and in general the central plane will be in motion.
  • the vibrator may be considered to be fixed at its center.
  • the impedance will be the same as that of a mechanical transmission line consisting of a section equal in length to the end section l3 in series with a second section of half the length of the central section if,
  • Equation (33) given on page 113 of Sheas Transmission Networks and Wave Filters, published by D. Van Nostrand Company,'the input impedance of such a system may be expressed as Z -I- K1 tanh P1 K +z, tanh P (1) in which K1 and Pr are the characteristic impedance and transfer constant, respectively, of an end section it, and Zr is the terminating impedance of the end section.
  • K1 and Pr are the characteristic impedance and transfer constant, respectively, of an end section it
  • Zr is the terminating impedance of the end section.
  • the characteristic impedance K and the transfer constant P of a rod assuming that the elastic waves are propa" gated with a plane wave front normal to the axis, may be found from the following express1ons:
  • A represents the cross-sectional area
  • p is the density of the material
  • E is Youngs modulus of elasticity
  • l is the length of the line and denotes the frequency multiplied by Z-rr.
  • the impedance Zr is given by the equation in which K2 and P2 are the characteristic impedance and transfer constant, respectively, of half of the mid-section l2.
  • Equation (2) is obtained by setting up an expression for the input impedance of the mid-section, similar in form to equation (1), and substituting therein the value of which, when numerator and denominator are divided by tanh P1, leads to the expression K Kg 2 tanh P tanh P 1 2 tanh P tanh P
  • the impedance Z may be considered to be made up of the series connection of two impedances Z1 and Z2 corresponding to the two terms on the right-hand side of Equation (4). The first of these two impedances, corresponding to the first term, is
  • K K tanh P tanh Pg (5) 1 K1 K2 tanh P tanh Pg which will be recognized as the impedance of two open-circuited, uniform transmission lines connected in parallel.
  • a transmission line is periodically resonant at some frequency f and at every odd multiple thereof, and is anti-resonant at zero frequency and every even multiple of f.
  • the two lines in parallel have the same transfer constants, that is, when P1: P2, the critical frequencies of one will coincide with those of the other, and the combined impedance will be of the same form as the impedance of one alone.
  • Such an impedance characteristic is shown by the dotted curve 9.2 of Fig. 3 for the frequency range from zero to 3
  • the impedance Z2, corresponding to the second term, is
  • the mechanical impedance Z of the vibrator l I which, as explained above, may be considered to be made up of the two series impedances Z1 and Z2, will therefore be the algebraic sum of the two curves 42 and 43, and will be of the form shown by the solid line curve 44 of Fig. 3, having anti-resonances at the frequencies zero, 1, 2f and 3 and resonances at the frequencies f1, f2 and f3.
  • the armature [8, considered as a lumped mass, will not change the lccation of the anti-resonances but will cause each resonance to occur at a somewhat lower frequency.
  • the magnetic field surrounding the armature exerts a force of attraction which increases more and more rapidly as the armature approaches the pole-pieces and is in effect a negative stiffness which willfurther lower each resonance frequency.
  • the electrical impedance of the system at this point will be just the inverse of the mechanical impedance described above, resonances occurring where anti-resonances are located in the mechanical impedance, and vice versa. In this connection reference is made to United States Patent No.
  • Curve 45 may represent, for example, the impedance of the element 2'! of Fig. 2, in combina- 40 tion with the capacitances Cl.
  • a second electromechanical impedance, such as 28 of Fig. 2, with its associated capacitances C2 may be designed to have resonances at the frequencies f5, f7 and f9, and anti-resonances at the frequencies zero, 4.3 ft and fa, as shown by the dotted curve 46 of Fig. 4.
  • Two such impedances may be arranged, as explained above in connection with Fig. 2, to form a lattice type band-pass wave filter.
  • the transmission band will be located between the fre- 5 quencies f4 and f9 where the two reactances are of opposite sign, and peaks of attenuation Will occur at the frequencies ha and hi where the two curves cross each other.
  • the transmission characteristic is shown diagrammatically by Fig. 5. Other attenuation peaks, not shown, may be located either above or below the transmission band.
  • an electromechanical impedance comprising, as a mechanical vibratory element, a rod of elastic material longitudinally symmetrical about its middle section, the material of said rod having a low dissipation constant and said rod comprising a plurality of portions of different cross-sectional areas the lengths and cross-sections of which are proportioned to produce a plurality of mechanical resonances located within the transmission band of said filter at frequencies unharmonically related to each other and relatively close together in order to broaden said band and increase the discrimination, means for supporting said rod at its middle section, similar electromagnetic driving means disposed at each end of said rod and adapted to produce longitudinal mechanical waves in said rod in response to oscillatory electric currents, and circuit connections between said driving means whereby the mechanical forces impressed on the opposite ends of said rod are equal in magnitude and opposite in phase.
  • an electromechanical impedance in accordance with claim 1 in which the electromagnetic driving means are adapted to produce longitudinal compressional waves in the driven rod.
  • an electromechanical impedance in accordance with claim 1 in which the mechanical vibratory element comprises a rod of non-magnetic material and magnetic armatures at each end of said rod, said armatures forming part of the said electromagnetic driving means and being disposed to produce longitudinal compressional waves in said rod.
  • an electromechanical impedance comprising, as a mechanical vibratory element, a rod of non-magnetic elastic material longitudinally symmetrical about its middle section, said rod comprising a plurality of portions of difierent cross-sectional areas the lengths and cross-sections of which are proportioned to produce a plurality of mechanical resonances located within the transmission band of said filters at frequencies unharmonically related to each other and relatively close together in order to broaden said band and increase the discrimination, means for supporting said red at its middle section, similar electromagnetic driving means disposed at each end of said rod and adapted to produce longitudinal mechanical waves in said rod in response to oscillatory electric currents, and circuit connections whereby said driving means are adapted to impress forces of opposite phase on said rod.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
  • Apparatuses For Generation Of Mechanical Vibrations (AREA)
US35918A 1935-08-13 1935-08-13 Wave filter Expired - Lifetime US2091250A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US35918A US2091250A (en) 1935-08-13 1935-08-13 Wave filter
FR815901D FR815901A (fr) 1935-08-13 1936-08-03 Filtres d'ondes électro-mécaniques
DE1936I0055741 DE687871C (de) 1935-08-13 1936-08-14 Elektromechanische Impedanz fuer Wellenfilter

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US35918A US2091250A (en) 1935-08-13 1935-08-13 Wave filter

Publications (1)

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US2091250A true US2091250A (en) 1937-08-31

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Country Status (3)

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US (1) US2091250A (fr)
DE (1) DE687871C (fr)
FR (1) FR815901A (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2552139A (en) * 1948-06-17 1951-05-08 Philco Corp Electrical system
US2571019A (en) * 1948-04-30 1951-10-09 Rca Corp Electrical coupling system for magnetostrictive elements
US2578452A (en) * 1949-05-14 1951-12-11 Rca Corp Mechanical filter
US2599068A (en) * 1950-10-31 1952-06-03 Rca Corp Adjacent channel rejection by magneto-striction
US2647948A (en) * 1949-03-30 1953-08-04 Rca Corp Electromechanical filter
US2652543A (en) * 1948-12-14 1953-09-15 Motorola Inc Electromechanical filter
US2904701A (en) * 1957-06-07 1959-09-15 Stirling A Colgate Electrical generator and driving engine unitary therewith

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1261248B (de) * 1963-09-13 1968-02-15 Siemens Ag Elektromechanisches Bandpassfilter
DE1275216B (de) * 1965-03-16 1968-08-14 Siemens Ag Elektromechanisches Filter

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2571019A (en) * 1948-04-30 1951-10-09 Rca Corp Electrical coupling system for magnetostrictive elements
US2552139A (en) * 1948-06-17 1951-05-08 Philco Corp Electrical system
US2652543A (en) * 1948-12-14 1953-09-15 Motorola Inc Electromechanical filter
US2647948A (en) * 1949-03-30 1953-08-04 Rca Corp Electromechanical filter
US2578452A (en) * 1949-05-14 1951-12-11 Rca Corp Mechanical filter
US2599068A (en) * 1950-10-31 1952-06-03 Rca Corp Adjacent channel rejection by magneto-striction
US2904701A (en) * 1957-06-07 1959-09-15 Stirling A Colgate Electrical generator and driving engine unitary therewith

Also Published As

Publication number Publication date
FR815901A (fr) 1937-07-26
DE687871C (de) 1940-02-07

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