IL48094A - Electromechanical filter system - Google Patents

Description

Vat er The present invention relates to an filter Mechanical filters are frequently used to realise different functions in filter because of the advantages afforded by such in the frequency ranges for which they are over conventional filters having concentrated switching In the construction of mechanical filter assemblies it is convenient to support the coupled resonators in each filter in manner such that a stable construction is achieved which is insensitive to external and such that the resonators are not too greatly attenuated by the support means used since excessive attenuation in this respect would impair the oscillation quality of the filte A further requirement is that the coupling elements which connect the resonators should be connected thereto without this also applying when connection of the resonators and the coupling elements is effected before the filter system is assembled on the base plate used to supporting the Such filters are described in the Swiss Patent 491 in which filters the connection of the coupling elements to the resonators is achieved by providing the base plate with at least one recess in which one end of each of a plurality of like support elements is secured by a soldering material or a moulding In the case of electric circuitry containing a plurality of mechanical filters where space is limited and where the attainment of specific electrical values is desired it is often necessary to arrange the filters close to one another on a common base plate Since it is difficult to achieve a completely arrangement of the elements used to support the mechanical a part of the oscillation energy of a first filter is liable to pass via the support elements and the base plate into an adjacent filter so as to influence incoming and outgoing An object of the invention is to provide an improved electromechanical filter this invention consists in an mechanical filter assembly having a base at least two electromechanical filters each comprising a resonator which is mounted on a of said base plate through support pins received in recessed arranged in said said resonators being of the bending mode oscillation type and being arranged parallel to one another and linked together via a mechanical coupling element to form a mechanical filter wherein at least one of said comprises a synthetic resin material wherein the support pins received in the recess of said at least one is held in said recess by a hardenable material when is and has a higher mechanical attenuation factor than the synthetic resin material of said at least one conveniently the are arranged in spaces apart relationship on a carrier such as a circuit which is common to said The support pins are preferably metal pins of a very small Preferably the hardenable material is a moulding composition having a polyurethane or epoxide resin while the base plate or the arranged thereon comprise a The use of synthetic materials for the base plate or the affords the advantage whereby the supply wires for the supply and withdrawal of the magnetic energy do not require to be in the form of insulated as is usually the The invention will now be described in more reference to a number of embodiments thereby shown in the accompanying in 1 shows diagrammatical ly a filter assembly comprising two mechanical filters arranged a and shows diagrammatically a filter assembly comprising two mechanical filters arranged separately from one another on a common circuit The filter Fig 1 comprises two mechanical filters F2 which are arranged on a common base platel comprising a polycarbonate The filters Fl and F2 each comprise two mechanical resonators 2 and of the bending mode oxcillation one of which is adapted to transform mechanical oscillations into electrical oscillations via two vibrations being two wir coupling said The coupling wires are preferably arranged in regions of high oscillation amplitude in the exemplary embodiment adjacent the ends of the The resonators 2 and are in the form of cylindrical metal rods which are provided with flattened portions which extend in planes parallel to the longitudinal axes of the rods and which are aligned parallel to the horizontal plane of the base Oscillation excitation and oscillation tap off is effected by means of plates 4 and comprise an electrostrictive material and which are secured to the flattened portions of the resonators 2 and Each plate 4 is provided on the side thereof facing away from its respective resonator with a metallized surface which is connected to a thin wire leading to a supply wire 5 cast through the base plate A connection is connected to a support 6 and extends to a ection pin 7 which forms a continuation of the base plate When an voltage is connected between the supply wire 5 and the connection pin 7 of the resonator said resonator is excited to produce bending mode oscillations by the expansion and contraction of the plate by virtue of the transverse contraction when the bending natural frequency of said resonator is at least approximately in resonance with the frequency of the ected bending mode movement is transmitted via the coupling wires 3 to the adjacent resonator which thus likewise executes bending mode As a result of the piezoelectric effect obtained through the these bending mode oscillations give rise to an voltage between the metallized surface located on the face of the plate remote from the resonator and the resonator which can be between the supply wire and the connection pin For the support of each resonator 2 and there are provided two short metal pins 6 which are of very small thickness and each of which is secured at one end thereof in an oscillation mode of its respective The other end of each of said pins is received in a recess 8 and is held in place in said recess by a filler material In the shown in the filler material comprises a hardenable moulding resin having an epoxide base and when remain flexible and form a good joint with the support elements 6 of the resonators and with the base plate The moulding composition may comprise an epoxide resin having a bisphenol A with an epoxide value of a methylhexahydrophthalic anhydric and an acid ester produced from hexahydrophthalic anhydric acid and castor The good connection obtained between the moulding composition and the base plate is in to the microscopically rough surface structure of the which also possesses further advantages such as a relatively high mechanical a good temperature load capacity and sufficient resistance to The nature of the materials selected in the above respect is governed by the requirement for a higher mechanical attenuation factor of the filler material comparison to the base plate As a result of the higher mechanical attenuation factor of the moulding composition the mechanical oscillations which occur in the support elements 6 are attenuated to such an extent that the base platel absorbs only a small part of the oscillation After the subsequent attenuation in the base plate 1 and in the filler material located in the recess 8 of an adjacent only a negligible amount of residual oscillation energy is transmitted from the first filter to the adjacent The decoupling attained in this way enables even filters which exhibit considerably differing oscillation energy such as for signal receiving filters and signal transmitting filters to be arranged closely adjacent one another on a common base plate without the incoming signals being subjected to a disturbing influence by the signal transmitting These considerations also apply to arrangements in which more than two are arranged on one base In the filter assembly shown in the filters and F2 of the filter assembly shown in are arranged in spaced apart relationship on a common circuit board The references la and lb indicate of the base plate The la and lb assigned to respective filters are determined by the section in The filters Fl and in are provided with a screening hood and the spaced apart arrangement of the filters is favourable to avoid at least substantially the electric couplings between the filters which arise due to the closely adjacent arrangement of the filters in Furthermore in the arrangement of it is possible to keep the length of the supply lines to the filters iciently short to enable an optimal circuit arrangement to be always produced on the common circuit evei or different In the exemplary embodiment shown in the filler material and the base plate material have been selected in conformity with the exemplary embodiment of This produces a mechanism of the oscillation attenuation which is similar to that in the exemplary embodiment of although with the embodiment of the common circuit board is also included as an additional ation In accordance with particular the arrangement shown in can be combined with that in 1 or can be extended to form an arrangement having a plurality of filters on a circuit Similar conditions are achieved in the exemplary embodiment of 2 a plurality of individual filters are arranged on the continuous carrier plate in the form of a circuit board of for only one filter is supported in its base plate or its portion of the base plate by the moulding composition described with reference to insufficientOCRQuality

Claims (7)

1. An electromechanical filter assembly having a base plate, at least two electromechanical filters each comprising a resonator which is mounted on a sub-zone of said base plate through support pins received in recessed arranged in said sub-zones, said resonators bei'ng. of the bending mode oscillation type and being arranged parallel to one another and linked together via a mechanical coupling element to form a mechanical, multi-stage filter circuit, wherein at least one of said sub-zones comprises a synthetic resin material and wherein the support pins received in the recess of said at least one sub-zone is held in said recess by a hnrdenable material which, when hard, is flexible and has a higher mechanical attenuation factor than the /synthetic resin material of said at least one sub-zone.

2. An assembly as claimed in Claim 1 or Claim 2, wherein said at least one sub-zone comprises a glass- fibre-reinforced polycarbonate and wherein said hardenable material is a moulding composition. having polyurethane or epoxide resin base.

3. An assembly as claimed in Claim 2, wherein said ! carrier plate is a circuit board.

4. An assembly as claimed in Claim 1 or Claim 2, wherein said at least one sub-zone comprises a glass-fibre-reinforced polycarbonate material, and wherein said .hardenable material is a moulding composition having a- polyurethane or epoxide resin base.

5. An assembly as claimed in any one of the proceeding claims, wherein said base plate (1) is of continuous configuration.

6. An assembly as claimed on Claim 5, wherein said base plate comprises a glass-fibre-reinforced polycarbonate material.

7. An electromechanical filter assembly subs tantial 1 as herein before . described with reference to, and as illustrated in, the drawings forming part of this Specification.