Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R19/00—Electrostatic transducers
  • H04R19/01—Electrostatic transducers characterised by the use of electrets
• • 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
  • B06B1/0292—Electrostatic transducers, e.g. electret-type

Definitions

• Electrets are materials that can store electrical charges over a long period of time.
• Electrets eg in the form of polymer films, but also inorganic electrets such as Si0 2
• Electrets can be electrically charged by a variety of methods (corona processes, electron beams, contact charging, ).
• corona processes, electron beams, contact charging, When charging charge carriers are injected into portions of the electret or charge separation in the electret caused, whereby the electret becomes the carrier of an electric field.
• Charged electrets can be used in a variety of electronic components,
• Electrets are contacted and charged with electrodes on at least one side to form an electret structure.
• G.M. Sessler Ed.
• Electrets Vol. 1, 3rd Edition, Laplacian Press, Morgan Hili, CA, 1999
• G.M. Sessler Electrets: recent developments, Journal of Electrostatics, Vol. 51-52, pp. 137-145, 2001.
• a challenge for technically deployable electret structures is the stability of charge separation in the electret for long periods of time, ideally several years or decades for application-relevant ones
• Ambient conditions e.g., elevated temperatures of, for example, up to 85 ° C
• elevated temperatures e.g., up to 85 ° C
• piezoelectrics porous electret films that internally store the charges on pore surfaces have been intensively researched as piezoelectric material ("Piezoelectrics"), as described, for example, in M. Paajanen, J. Lekkala, K. Kirjavainen, ElectroMechanical Film (EM Fi).
• EM Fi ElectroMechanical Film
• charge storage such as Teflon FEP, PTFE and PFA, and therefore can be used even at higher temperatures for a long time.
• porous electret foils pieoelectrons
• charge carriers only have to travel over relatively short distances in order to meet and recombine with an oppositely charged charge carrier.
• electrets with very high charge stability are required.
• suitable materials and pretreatment methods electrets can be achieved which have good charge stability at room temperature and elevated Temperatures and which can potentially be used for the above applications.
• electrets that are suitable for use under such harsh conditions there are only a few options for choosing electrets that are suitable for use under such harsh conditions
• DE 44 21 859 C2 shows a filter for cleaning gases with an electret and the electret at least partially surrounding layers of a porous dielectric.
• the porous dielectric is made of a foam, in particular of an open-cell or open-cell foam.
• the electret is as a thin layer or plate of a polymer, such. As polytetrafluoroethylene, formed and is polarized by thermal treatment.
• DE 2 232 264 shows an electret structure, which consists of two thin dielectric films, between which an ionized air layer is introduced.
• This electret structure can be used as an ultrasonic transducer.
• the invention describes a novel structure of an electret structure and a method for producing such an electret structure, in which the disadvantages of the prior art are avoided.
• the migration of charge carriers after the electrical charge is through the
• Structure according to the invention difficult and thus ensures a high charge stability.
• an electret structure comprising an electrically conductive support, a first electret layer and a porous dielectric layer interposed between the support and the electret layer is arranged.
• the electrically conductive carrier preferably forms the electrode of the electret structure according to the invention.
• the invention is based on the idea of using the porous dielectric layer to separate the charged first electret layer from the back electrode.
• Dielectric layer between the electret and electrode is thereby significantly increased.
• the structure of the invention offers the advantage of a stronger spatial separation of positive and negative charges, since the porous layer itself is charged. This significantly reduces the risk of loss of charge due to recombination of charge carriers within the charged electret layer.
• Electroacoustic transducers which use an electret structure according to the invention are preferably constructed in such a way that the electret structure itself does not oscillate, but instead builds up an electric field, so that the generation or the detection of sound waves follows the known principle of the art
• a porous dielectric is applied to an electrically conductive carrier which forms the electrode.
• porous polymers such as porous Teflon (eg PTFE, PFA, FEP, AF etc.), but also other materials with dielectric properties, for example porous ceramics, can be used for this purpose.
• the porous, dielectric layer thus formed may preferably be metallized on its side facing the carrier or the electrode. As a result, a good electrical connection is advantageously achieved and / or a
• porous, dielectric layer comprises porous Teflon
• aluminum for the metallization of the porous, dielectric layer, which has both the electrical connection of the porous
• an electret material is applied to the porous dielectric layer, for example by laminating a film of teflon (e.g., PTFE, PFA, FEP, AF, etc.) forming the first electret layer in which
• teflon e.g., PTFE, PFA, FEP, AF, etc.
• Charge carriers are introduced by charging the film.
• the outer material e.g., Teflon
• the outer material may be dropped as a wet solution and then dried.
• the entire electret structure is sealed off to the side.
• This can be realized, for example, in that the upper electret layer at the edge of the structure extends to the support and is joined to it (e.g., glued or laminated).
• Alternative seals are possible, e.g. by applying an adhesive, the side of the electret structure or a ring around the electret structure.
• a further, second electret layer between the back electrode and the porous dielectric.
• the metallization of the porous, dielectric layer is omitted in this case.
• the side of the second electret layer facing the carrier or the return electrode can be metallized.
• This optional structure can be advantageously chosen if the metallization of the porous dielectric and / or the connection of the porous dielectric to the carrier cause problems due to the material properties.
• the charge carriers migrate slowly from the surface (or from the volume) of the upper electret layer in the direction of the electrode. In structures known from the prior art with electrets which are applied directly to electrodes, the charge carriers become the electrode after some time
• the charge carriers from the electret when they have reached the underside of the charged electret layer, reach the porous dielectric.
• inventive structure has a very high charge stability.
• the inventive method for producing such an electret structure accordingly comprises the following steps: a) Provision of an electrically conductive carrier, in particular one
• a Teflon film on the porous dielectric layer d) electrically charging the nonporous electret, whereby the first
• Electret layer is formed.
• the sequence of method steps b) and c) is not defined in the context of the invention. It is also possible according to the invention to first apply the porous dielectric layer to the electret material (step c)), for example by lamination, and then to apply the composite of the porous dielectric layer and the electret material to the carrier (step b).
• the electrical charging of the film in step d) can be carried out, for example, by a corona process, electron beams or contact charging.
• the electrically charged sandwich structure before use in a component in a further process step f) are additionally pre-aged, for example by aging at a temperature at which a high mobility of the charge carriers is given in the electret.
• This temperature depends on the materials chosen.
• Mobile charge carriers migrate rapidly under these conditions until they reach positions within the electret where they have high energy stability (so-called traps), or until they reach the electret-air interface at the transition from the electret to the porous dielectric where they immobilize be as described above.
• the electret structure according to the invention is suitable, for example, for use in a sound transducer for environmental sensor technology (eg environment detection in FIG.
• Figure 1 illustrates an electr et structure according to a first embodiment of the invention.
• Figure 2 illustrates an electret structure according to a second embodiment of the invention
• FIG. 1 shows schematically a section through an electret structure 1 according to a first exemplary embodiment of the invention.
• the electret structure 1 comprises a metallic carrier 10, which forms the electrode of the electret structure 1.
• An electrically charged Teflon film forms the first electret layer 30.
• a layer 20 of a porous, dielectric material e.g. a ceramic, a polymer or porous Teflon, so that the sandwich structure according to the invention results.
• the porous, dielectric layer 20 thus comprises a solid dielectric 22 with, for example, differently sized pores 24. Between the porous, dielectric layer 20 and the carrier 10 is in this
• Carrier facing surface 42 is provided with a metal coating 45.
• the first electret layer has charge carriers 50, in this example with negative electrical charge. Compensating charges 55 with negative electrical charge.
• the electret structure 1 can be used for example in sound transducers.
• Dielectric 22 touch can occur a transfer of charge carriers and take place a further migration of charge carriers.
• the electret 30 will abut a pore 24, ie an air-filled cavity. A transgression of the charge carriers 50 into the air of the pore 24 takes place not happening.
• the charge carriers 50 are immobilized in the dielectric 22 at the boundary between the electret 30 and the air of the pore 24 and remain stably bound in the electret layer 30 over long periods of time.
• the electret layer 30 extends laterally as far as the carrier 10 and is glued or laminated there. Thereby, a circumferential seal 35 is realized around the electret structure 1, which improves the life under severe environmental conditions.
• FIG. 2 schematically shows a section through an electret structure 1 according to a second exemplary embodiment of the invention. The operation is essentially the same as that in connection with FIG. 1
• no second electret layer is provided between the porous, dielectric layer 20 and the carrier 10.
• the surface 25 of the porous, dielectric layer 20 facing the carrier 10 has a metallization layer 45, which serves directly for connecting the porous, dielectric layer 20 to the carrier 10.
• Adhesive material is provided which prevents the penetration of moisture and dirt into the porous dielectric layer 20.
• the electret structure 1 according to the invention, since charge carriers are effectively immobilized at interfaces between the electret layer and pores of the porous, dielectric layer 20 and recombination with oppositely polarized charge carriers is prevented.
• further intermediate layers such as an electret layer 40 and / or a metallization layer 45, the connection of the porous, dielectric layer 20 to the carrier 10, which preferably forms the back electrode of the electret structure 1, for each selected material can be additionally optimized.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)

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• 2013
  • 2013-10-17 DE DE201310221140 patent/DE102013221140A1/de not_active Withdrawn
• 2014
  • 2014-08-19 CN CN201480056804.1A patent/CN105659627A/zh active Pending
  • 2014-08-19 EP EP14753067.9A patent/EP3058760A1/de not_active Withdrawn
  • 2014-08-19 WO PCT/EP2014/067623 patent/WO2015055336A1/de active Application Filing

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