One aspect of the present invention to provides an arrangement for producing an improved material that may be used as acoustic ribbons that overcome the disadvantages of the prior art.
Another aspect of the present invention provides polymer acoustic ribbons that have minimum mass and high sensitivity and with high signal conductivity coatings thereon.
Another aspect of the present invention provides polymer ribbon articles that may retain a geometric shape after being distorted.
In another aspect of the invention the sound sensor is usable as a wide bandwidth microphone having a frequency response approximately corresponding to that of the entire range of the human ear.
One embodiment of the present invention comprises a low mass, high conductivity, shape memory acoustic film material and a process utilized for the forming of an arrangement of polymer film acoustic ribbons, and the like, which ribbons are to be used in acoustic transducers including for example, ribbon microphones as fluid responsive moving sound sensors.
Another embodiment of the present invention comprises the method of designing and using such an arrangement to produce a fluid responsive sound sensor having particular mechanical, electrical and shape-memory characteristics that result in a durable yet light and low mass, highly sensitive fluid responsive sound sensor.
The processes of designing and fabricating practical ribbon structures begin with selecting a candidate material for fabricating sound responsive structures which may be, for example, a thin-film polyethylene terephthalate, or PET. The PET material may be supplied in roll or sheet form. The size selected may be about 3 inches wide, and the thickness selected may be about 2.5 microns, which is very thin, and light. PET is a high strength polymeric material that, during or after the foil ribbon manufacturing process, may be prepared with a layer of aluminum, gold, or other conductive metallic material as will be further taught herein.
Before the forming process can begin the polymer material must be cut into the desired shape. For a ribbon microphone application, where typically an elongated sound sensor is suspended between the poles of parallel magnets, the polymer material may be cut into rectangular strips. The preferred cutting method includes the use of a precision blade shear or a laser cutter. During the blade shearing process, the thin film polymer material may stick to the shear blade due to a static charge therewith. The polymer film also has a tendency to push away during the shearing process leaving the cut strip slightly tapered. To solve these problems, the material may be held for example, between two layers of waxed paper and adhesively taped along its leading edge with masking tape. This arrangement provides a static barrier and adds a temporary mass and rigidity to the polymer film, virtually eliminating the tendency for it to be pushed away during the shearing process.
Once the material is cut into the desired shape, in this example, a rectangle, a forming process may then be performed. The material may be thermally formed, or set, into the desired shape by placing the material between a pair of shaped steel dies, or forming dies. An identical repeating zig-zag or sawtooth pattern, for example, on the forming dies allows the two sides of the dies to mesh together with the material to be formed in between. With the two halves of the forming dies securing the material therebetween, the arrangement is ready to be thermally set.
A convenient method for heating the forming die assembly and polymer material is to place the articles, in a meshed state, into a preheated oven that is controlled by a thermostat. The forming die and polymer are then subjected to a suitable temperature over a period of time, and then removed from the oven and allowed to cool, when the polymer material will be found to have assumed the shape of the forming dies.
The material may be tested to determine its linear tensile strength and demonstrate that the PET material is about 8 times stronger than the thin aluminum material commonly used for ribbon microphone applications.
The material tensile, elongation and shape memory properties are important to the longevity and performance of acoustic ribbon elements. Because of the high strength, a polymeric ribbon element such as that made as taught herein is very desirable. This material when used as a ribbon element has the ability to resist wind blasts, high sound pressure levels, and electrical jolts such as those caused by the application of phantom power, without breaking or sagging. Phantom power is the 48 volt DC power supplied by mixing boards and microphone amplifiers used to power condenser type microphones. In some instances, the 48 volt DC power can be unintentionally routed to the ribbon microphone, which can then permanently distort and ruin the ribbon.
The excellent shape memory of preformed ribbons made from polyethylene terephthalate and other polymer and composite substrates allows them to retain their geometry and they can be extended to the point where the corrugations are flattened and readily returned, unstrained, to the original corrugated state. This material also has high strength which means the thickness of the material can be decreased to about 1.5 microns or less, thereby reducing the mass of the ribbon element which is also desirable because a lower mass ribbon is more responsive to incoming sound waves. Lower substrate and ribbon mass results in greater sensitivity and is desirable as it allows the faintest sounds to be converted into electrical energy. Having a low “substrate mass” may also be desirable in some instances where other high conductivity coatings with relatively greater mass than aluminum, such as gold and gold alloys for example, are used therewith.
Aluminization using direct evaporation of aluminum atoms upon the thin substrate material, applied evenly to one or both sides, has been found effective to produce a desired structure that is tough yet relatively low in mass, highly flexible and with good shape memory, and highly conductive, all of which are required for the successful sound-responsive ribbon-type element that may be used in a ribbon microphone or the like.
One embodiment of the invention comprises a ribbon microphone that accommodates the entire range of human hearing, both in frequency response and also in dynamic range including high sound pressure levels exceeding safe hearing limits but within recordable limits using the improved microphone and ribbon assembly. Such sound pressure levels start below about 10 dB, which is at the lowest threshold of natural hearing, and extend to above 150 dB, which is well above a safe sound level for humans, but within normal operating range of the ribbon microphone assembly as taught herein.
Another aspect of the invention includes a fluid coupled sound sensor having a corrugated ribbon-like form comprised of layers of conductive and nonconductive materials, the nonconductive materials having a thickness of about 3 microns or less and the conductive coating having a thickness of at least 100 nanometers, with a total weight of about 0.004 grams per square inch or less. The structure is produced whereby the conductive and nonconductive materials work in unison to produce a highly flexible, shape memory, highly sound responsive component, and whereby said sound responsive component comprises the ribbon in a ribbon microphone assembly having an acoustic responsivity of about 2 Hz to about 20 KHz.
Further, the ribbon structure is effective to return to a corrugated shape after extension to a flat shape, as encountered during wind blasts, for example, thereby overcoming limitations in the prior art, while maintaining sensitive sound responsivity over the acoustic range of human hearing.
One embodiment of the invention thus comprises a fluid coupled sound-sensor having a corrugated ribbon-like form comprised of layers of conductive and nonconductive materials, the nonconductive materials having a thickness of about 3 microns or less and the conductive layer having a thickness of at least 100 nanometers, with a total weight of about 0.004 grams per square inch or less, whereby the conductive and nonconductive materials work in unison to produce a highly flexible, shape memory, sound-responsive component, and whereby the sound responsive component comprises a ribbon in a ribbon microphone assembly having an acoustic responsivity of about 20 Hz to about 20 KHz. The conductive layer may be comprised of aluminum. The non-conductive layer may be comprised of a polymer. The corrugated ribbon-like form is cyclable from said corrugated form to a flat form and back to a corrugated form.
Another embodiment of the invention comprises a geometrically shaped acoustic ribbon comprised of layers with one layer being a highly elastic shape memory material and at least one additional layer of highly conductive material, wherein the combination of the layers produces high elongation and toughness characteristics while maintaining low mass and high conductivity of said acoustic ribbon.
Another embodiment of the invention comprises a method of manufacturing a coated, geometrically shaped, shape memory acoustic ribbon with an elastic polymeric substrate material with a second highly conductive layer and weighing no more than 0.004 grams per square inch and comprising: forming a sized, elongated, coated or coat-able polymeric substrate film between a pair of opposed, geometrically shaped dies; pinching the dies about the polymeric substrate film to form an assembly; heating said dies and said pinched die and polymeric film assembly to a temperature of about 300 degrees F. for a period of about 15 minutes to set said elongated film into a predetermined geometric pattern; cooling the assembly; removing the film from the dies; and if not pre-coated with a conductive coating, coating the geometrically formed, set, elongated film with a conductive coating. The polymeric film may be comprised of polyethylene terephthalate. The coating may be comprised of a metal selected from the group comprises of: aluminum, gold, silver, nitinol, copper-zinc-aluminum and copper-aluminum-nickel. The method may include perforating the polymeric film with a plurality of spaced apart holes to minimize the mass thereof. The method may include applying a coating of wetting material to the film prior to the pinching of the film between the dies. The wetting material may be comprised of isopropyl alcohol.
Another embodiment of the invention includes an acoustic ribbon for use in a flux frame of an acoustic ribbon microphone, comprising: an elongated polymeric substrate coated with a conductive coating; an arrangement of holes spaced along the substrate through the conductive coating and the substrate. The conductive coating may be comprised of nickel titanium. The conductive coating may be comprised of a compound selected from the group comprised of aluminum, copper, zinc or nickel. The elongated polymeric substrate may be comprised of a zig-zag geometric shape.
Another embodiment of the invention includes an elongated acoustic ribbon for microphones, the ribbon being comprised of a polymer substrate and a first conductive layer of metal coated on a first side of the substrate, the acoustic ribbon having a total weight no greater than 0.004 grams per square inch. The substrate may consist of Polyethylene Terephthalate. The substrate may be coated by a second conductive layer of metal on a second side thereof. The elongated acoustic ribbon for microphones may reside unstrained, in a zig-zag shape in cross section. The elongated acoustic ribbon may be comprised of a “shape-memory” microphone element. The second conductive layer of metal may be comprised of metal of a different thickness than the first conductive layer. The second conductive layer of metal may be comprised of a different conductive metal than the first conductive layer.
Another embodiment of the invention comprises an elongated shape memory acoustic microphone ribbon element assembly, consisting of: an elongated shape memory polymeric substrate; and a conductive coating arranged on the substrate, wherein the ribbon element assembly weighs no more than 0.004 grams per square inch. The conductive coating may comprise carbon nanotubes. The substrate may have a predetermined shaped formed thereon. The coating may be arranged on both a first and a second side of the substrate. The substrate may be comprised of Polyethylene Terephthalate. The coating may be comprised of a metal. The coating may be comprised of aluminum. The assembly preferably has dimensions of about: length 3.4″ and 0.145″ wide and 2.5 microns thick, and weighs about 0.002 grams. The substrate may be perforated. The coating may be perforated.
The objects and advantages of the present invention will become more apparent when viewed in conjunction with the following drawings in which:
Referring now to the drawings in detail, and particularly to
The process begins with the selection of a suitable polymeric material, for example, a thin film polyethylene terephthalate 10. This material is supplied in roll and sheet form and the material size selected is 3 inches wide and the thickness is 2.5 microns. This polymeric material is, during or after the foil ribbon manufacturing process, coated with a layer of aluminum, gold, or other conductive material.
Before the forming process can begin the polymer material 10 must be cut into the desired shape as represented in
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The second method for placement of the film material 10 between the dies 18 and 20 is represented in
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The combination of the polymer substrate 64 and the conductive coating(s) 62 and/or 66 for an acoustic ribbon 60 of the present invention should be limited in weight and/or mass per unit area to that of a single component acoustic aluminum ribbon of the prior art. Such a prior art acoustic aluminum ribbon have dimensions for example, of 3.4″×0.145″×2.5 microns and may weigh 0.002 grams. A strip of thin film polyethylene terephthalate that measures 3.4″×0.145″×2.5 microns weighs about 0.001 grams. This permits 0.001 grams of aluminum metal to be added as a coating to the polymer substrate while maintaining a similar mass compared to prior art ribbons. Thus, a conductive coating (of for example, aluminum of up to 0.001 grams per 3″ length) may be added to the polymer substrate as inclusive of the present invention. Such conductive coating (of aluminum) may be added to the substrate 64 in single layers, multiple layers or combinations of thicknesses to one or both sides of that substrate 64.
Referring back to
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An advantage of the polyethylene terephthalate film is that it will not become brittle with age under normal conditions because it contains no plasticizers. Another advantage is that it offers good shape retention. Once cooled after the formation of the corrugation of the film, the structure retains its geometry as seen in
Referring back to
A ribbon microphone built with an aluminum ribbon as described in the prior art can be used in a bidirectional configuration allowing it to receive and process sound levels from multiple directions. It also can be used in a broad frequency range from 30 Hz to 20 KHz. The polymer composite ribbon of the present invention exhibits broad response from 20 Hz to 20 KHz, unlike ribbon tweeters or loudspeakers made from aluminum and or polymers, contrasted graphically in
Referring back to
Once prepared, each ribbon is extended under moderate tension in the axial direction as demonstrated in
By contrast, the polymer composite ribbon 30 when also extended so that the corrugations become flat or nearly so can be observed to return to its original length when released, as demonstrated in
The process of forming a conductive, shape memory ribbon 30 may also be performed in reverse, by providing a conductive substrate first such as an aluminum ribbon used in ribbon microphones, and then depositing a settable polymer onto the conductive substrate through vapor deposition. Such polymeric vapor deposition may be performed in a controlled chamber with heat, gases, ultraviolet curing lamps and polymer vaporization capabilities which may include plastic films such as thermoplastics like PET, PEEK, Kapton or Parylene, or carbon deposition of nanotubes and films. The polymeric vapor may be effective to conform to a preformed ribbon, further aiding the shape retention qualities, and may be enhanced by the application of fibrous substances, particles, and at various thicknesses at different locations. Alternatives also include lamination processes or any process of providing combined physical properties, with the object to provide the elongation and toughness characteristics, while maintaining low mass and high conductivity, all required to produce a successful sound sensor ribbon microphone arrangement which is one object of the present invention.
One embodiment of the present invention relates to microphone elements which are responsive to minute acoustic vibration of fluids such as air over the frequency and amplitude range of human hearing, yet which are tough and resistant to various damaging forces, and a method for manufacturing thin film acoustic ribbons particularly for ribbon microphones, and is a continuation-in-part of our U.S. patent application Ser. No. 11/242,611 filed Oct. 3, 2005 now U.S. Pat. No. 7,894,619 and Ser. No. 11/242,612 filed Oct. 3, 2005, now U.S. Pat. No. 7,900,337 which were based on Provisional patent application Ser. No. 60/620,934 filled 21 Oct. 2004, each of which are incorporated herein by reference in their entirety.
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