Microphone using simplified transducer

Abstract

A microphone includes a transducer element formed of a permanently charged, cellular ferroelectret film with electrodes on opposing surfaces. The transducer is mounted directly against a rigid support surface, eliminating the traditional air gap found in electret microphones. This configuration allows the microphone to withstand very high sound pressure levels without distortion. The support surface or housing is made of acoustically neutral material, such as polyurethane with Shore 90A hardness, to prevent tonal coloration caused by structural resonance. In one embodiment, the transducer structure is fabricated from a single sheet of ferroelectret film with printed electrodes on both sides, folded along perforated lines to create a compact, EMI-shielded unit. The design simplifies production by eliminating multi-layer laminations and reducing component count, while maintaining high signal fidelity. The microphone is especially suited for musical instruments and other high- SPL applications requiring accurate sound reproduction.

Description

MICROPHONE USING SIMPLIFIED TRANSDUCERCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to provisional application U.S. Serial No. 63 / 657,105, which is pending, which was filed June 6, 2024, and which is hereby incorporated by reference in its entirety for all purposes.FIELD OF THE INVENTION

[0002] This invention pertains to microphones, particularly designed for applications involving very high sound pressure levels (SPL). Such applications may include, but are not limited to, the capture of sound from musical instruments like saxophones, trumpets, and drums, as well as industrial, scientific, or environmental scenarios where extreme acoustic energy is present.BACKGROUND OF THE INVENTION

[0003] The field of audio technology, particularly in musical and industrial applications, continuously seeks advancements to enhance sound capture fidelity under demanding performance conditions. One critical challenge has been developing microphones capable of withstanding very high sound pressure levels (SPL) without compromising sound quality. This is especially relevant for musical instruments such as drums, brass, and guitar amplifiers, which can generate extreme SPLs that often exceed the performance limits of conventional microphones.

[0004] Traditional solutions typically involve dynamic microphones, which are mechanically robust but often lack the sensitivity and accuracy needed for faithful sound reproduction. Condenser microphones, on the other hand, offer higher fidelity but tend to suffer from distortion or overloading at high SPLs unless equipped with protective components such as pads, attenuators, or complex circuit designs. These additions increase system complexity, cost, and potential failure points.

[0005] Beyond musical applications, there is a growing need for microphones capable of operating under even more extreme SPL conditions. For instance, during rocket motor testing, sound pressure levels can reach up to 180 dB or more — levels that approach or exceed the threshold of pain and can damage conventional sensors. Accurate acoustic measurement in such environments is essential for data collection, safety analysis, and engineering validation.

[0006] During the launch of large rockets, SPLs may exceed 200 dB. Capturing such extreme acoustic energy requires highly specialized microphones and durablesensing elements that can withstand not only the sound intensity but also related environmental stresses such as vibration, pressure differentials, and thermal shock.

[0007] Similarly, jet engine testing routinely involves SPLs in the range of 140-160 dB. While less extreme than rocket launches, these levels still demand microphones with superior mechanical durability and acoustic performance. Reliable audio data in this context supports diagnostics, performance optimization, and noise compliance testing.

[0008] These examples underscore the need for robust microphones capable of accurate sound capture under very high SPL conditions. The transducer design described herein, incorporating cellular electret or ferroelectret materials, is particularly suited to such applications, offering a unique combination of durability, sensitivity, and fidelity even under the most challenging acoustic environments.

[0009] A key challenge in the use of ferro-electret cellular film in contact transducers lies in its manufacturing process. A significant drawback arises during reel-to-reel DC charging: as multiple film layers are wound together, charge accumulation across layers may cause electrical discharges between them. These discharges can result in regions with either insufficient or even opposite polarity charges, leading to severe quality issues. Such defects are difficult to detect before the electrodes are printed and the sheets are die-cut and crimped into individual transducers — by which point material and labor costs are already committed. Consequently, reel-to-reel charging failures can lead to substantial economic losses.

[0010] U.S. Patent No. 6,689,948 B2 and U.S. Patent No. 4,654,546 describe cellular or porous dielectric electret films and their use in acoustic transducers. These typically consist of biaxially oriented, foamed, permanently charged films — commonly based on polypropylene — containing lens-like gas bubbles (voids) that improve electromechanical conversion efficiency.

[0011] WO 96 / 06718 further discloses a pressure-inflation method for pre-foamed plastic films, enabling high degrees of swelling while maintaining a thin substrate. This technique increases the void volume ratio to 30-70% of the film’s thickness, enhancing the electromechanical response up to tenfold and significantly improving the signal-to-noise ratio.

[0012] The presence of gas-filled cells also provides an elastic structure, which distinguishes ferroelectret films from rigid piezoelectric materials. These voids enable microscopic thickness changes in response to dynamic pressure. As opposing charges across voids move closer or farther apart, mirror charges are induced in electrodes, generating output voltage proportional to the applied force. The swelledcore structure lowers the Young’s modulus, improving acoustic impedance matching — especially for air or soft-tissue contact — resulting in a more natural sound.

[0013] However, the practical implementation of these prior art methods faces serious limitations. In 6,689,948 B2, a manufacturing approach is described involving multiple lamination steps, screen printing, and die-cutting, with charged zones confined to one sheet end and connectors on the other. This increases both material complexity and labor costs. The process often requires two separate manufacturers — one for ferroelectret charging and lamination, the other for printing and die-cutting — making it commercially inefficient.

[0014] Printing electrodes directly onto biaxially oriented, swelled polypropylene film is also problematic. The material is highly fragile and tends to shrink under the curing temperatures (>80°C) needed for conductive inks like silver paste. This results in alignment issues between front and back electrodes, potentially causing edge shorts or interference. Additionally, the thinness of the film allows for wrinkling under electrode layers, which increases internal resistance and signal degradation between the sensing area and connector.

[0015] Another known shortcoming in prior art designs is bulkiness. The layered lamination results in thicker transducers, diminishing flexibility and acoustic responsiveness, especially when minimal sensor profile is desired.SUMMARY OF THE INVENTION

[0016] This invention introduces a novel air microphone specifically engineered for high SPL environments. It uniquely employs a permanently biased cellular ferroelectret film as the transducer element, offering exceptional resilience to extreme sound pressures. The innovative use of ferroelectret film enables accurate acoustic capture at very high SPLs without the need for additional damping mechanisms or protective circuits, while preserving the natural character and transient detail of the sound.

[0017] The introduction of this microphone represents a significant advancement in high-intensity audio capture, providing musicians, recording engineers, and researchers with a reliable tool for recording powerful sound sources with clarity and precision.

[0018] The object of the present invention is to overcome the drawbacks of prior-art microphones related to manufacturing complexity, inconsistent quality, high production costs, mechanical fragility during installation, and excessive weight that may influence the sound being picked up.

[0019] Another object of the invention is to enable the manufacture of microphones using a minimal number of materials and structural parts — specifically, avoiding the use of air gaps between electrodes, separate transducer components, and external wiring segments traditionally required for connecting the sensing element to a preamplifier.

[0020] A further objective is to provide a microphone transducer with a unitary, thin, and flexible construction that is durable during handling, resistant to electromagnetic interference (EMI), and capable of producing a high signal output even under extreme sound pressure levels.

[0021] The improved manufacturing method described herein enables the production of ultra-thin, lightweight, and conformable transducers in variable lengths, widths, and shapes. Electrodes are printed directly onto both sides of a single sheet of charged cellular ferroelectret film. This film is perforated or partially cut, allowing it to be folded into a mechanically stable and EMI-shielded configuration. The sensing electrodes in the active area continue uninterrupted toward the connection area, where crimped connectors are attached for direct integration with a preamplifier. The transducer may include an adhesive backing and, optionally, an additional mass layer to provide mechanical counterforce for optimal pressure coupling.

[0022] The fabrication process is streamlined and scalable, eliminating the need to handle multiple separate sheets, perform manual lamination steps, or involve multiple subcontractors for different stages of electrode printing, lamination, and cutting. As a result, the invention supports a significantly more efficient and economical method for producing high-performance transducers using charged, cellular, swelled ferroelectret films.

[0023] To alleviate the shortcoming in prior art designs of bulkiness, the present invention introduces a transducer and manufacturing method that eliminates many of these prior art limitations. It allows the use of internally charged, folded or laminated ferroelectret structures with simplified, low-cost, and scalable production — without the need for multi-stage lamination, external bias voltage, or fragile alignment processes.

[0024] In particular, this new structure utilizes a single sheet of charged ferroelectret film with conductive electrodes printed on both sides of the same substrate. The material is perforated or partially cut to enable folding along predetermined lines, allowing the sheet to be mechanically configured into a compact, layered transducer. This folded geometry creates a mechanically stable, electrically shielded structure that significantly improves EMI resistance, especially compared to earlier, unshielded open-face designs.

[0025] By integrating the electrodes onto a single film layer and folding it into position, the need for alignment across separate sheets is eliminated. This reduces both manufacturing complexity and the risk of misalignment-related defects. The resulting structure supports reliable signal transmission, consistent acoustic performance, and robust mechanical handling, while keeping the manufacturing process efficient and cost-effective.

[0026] A microphone comprising:- a transducer element formed of a permanently charged, cellular ferroelectret film having electrodes disposed on opposing sides thereof;- a rigid support surface positioned directly against the transducer element, such that no air gap exists between the film and the surface;- a housing enclosing the transducer and support surface, wherein the housing or the support surface is made from an acoustically neutral material having high internal damping, such as polyurethane with Shore 90A hardness; and- electrical contacts extending from the transducer to a signal conditioning circuit, wherein the transducer is configured to convert sound pressure directly into an electrical signal without external bias voltage.

[0027] The microphone according to item 1, wherein the electrodes are printed on both sides of a single sheet of ferroelectret film.

[0028] The microphone according to item 1 or 2, wherein the transducer element is folded along perforated or pre-cut lines to form a layered or EMI-shielded structure.

[0029] The microphone according to any of the preceding items, wherein the support surface comprises a polyurethane component such as RECATHAN® PUR MDI SH 90 A.

[0030] The microphone according to any of the preceding items, wherein the signal conditioning circuit includes a band-pass filter, a limiter, and / or a gain control stage.

[0031] The microphone according to any of the preceding items, further comprising an XLR connector and configured for phantom power supply.

[0032] The microphone according to any of the preceding items, wherein the support surface also serves as the mounting base for a printed circuit board.

[0033] The microphone according to any of the preceding items, wherein the transducer element is attached to the housing using adhesive and optionally provided with a mass element to enhance pressure coupling.

[0034] The microphone according to any of the preceding items, wherein the microphone is configured to operate under very high sound pressure levels exceeding 140 dB SPL without distortion.BRIEF DESCRIPTION OF DRAWINGS

[0035] The invention is described in more detail with the aid of examples by referring to the following drawings:

[0036] Fig. 1 A is an isometric top view of a microphone in accordance with one or more embodiments of the present invention.

[0037] Fig. 1 B is an isometric bottom view of a microphone in accordance with one or more embodiments of the present invention.

[0038] Fig. 2A is a microphone in accordance with one or more embodiments of the present invention.

[0039] Fig. 2B is a cross-sectional view of the microphone of Fig. 2A take at section A-A.

[0040] Fig. 3 is an exploded view of a microphone in accordance with one or more embodiments of the present invention.

[0041] Fig. 4A is a direct (top) view of the microphone's transducer element in Fig. 4C that is cut to its form and prepared for folding in accordance with one or more embodiments of the present invention.

[0042] Fig. 4B is an isometric view of a microphone's transducer element in a partly folded (folding have started) status in accordance with one or more embodiments of the present invention.

[0043] Fig. 4C is an isometric view of the microphone's transducer element of Fig. 4A and 4B, in folded status, yet without crimped contacts, in accordance with one or more embodiments.

[0044] Fig. 5 is an exploded view of layers of a microphone's transducer element.

[0045] Fig. 6 is a top view of a microphone's transducer element sheet with a plurality of printed signal electrodes for forming a plurality of microphone's transducers and a plurality of connectors, connectors having respective contact areas, printed on one side of a sheet in accordance with one or more embodiments of the present invention.

[0046] Fig. 7 is a plane view of a sheet with a plurality of printed ground electrodes for forming a plurality of contact microphone transducers and a plurality of connectors, connectors having respective contact areas, printed on opposite side of the sheet in Fig. 6, in accordance with one or more embodiments of the present invention.

[0047] Fig. 8 is a plane view of the die-cutting blade form, or laser-cutting form, for cutting five transducers of the invention from a sheet of ferroelectret film in accordance with one or more embodiments of the present invention.

[0048] Fig. 8 is an exploded view of a contact microphone transducer in accordance with one or more embodiments of the present invention.

[0049] Fig. 9 is a schematic diagram of a method of making a dielectric, swelled cellular electret film-based transducer in accordance with one or more embodiments of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0050] The following detailed description is of the best mode or modes of the invention presently contemplated. Such description is not intended to be understood in a limiting sense but to be an example of the invention presented solely for illustration thereof, and by reference to which, in connection with the following description and the accompanying drawings, one skilled in the art may be advised of the advantages and construction of the invention. In the various views of the drawings, reference characters designate like or similar parts.

[0051] All technical and scientific terms shall have the same meaning as commonly understood by one of ordinary skill in the art. Nonetheless, certain terms are defined herein to aid in the understanding of the disclosure; these definitions apply to all parts of speech of the term regardless of whether the term is defined explicitly as such.

[0052]

[0053] DEFINITIONS

[0054] All definitions are given in the singular but are similarly applicable in the plural.

[0055] The term "transducer" is used for a physical electromechanical element that converts sound waves through air and mechanical vibrations into an electrical signal. A transducer preferably comprises a cellular electret or ferroelectret material having a form factor suitable for a microphone intended for picking up sounds and vibrations, especially with regard to acoustic musical instruments and in the context of high sound pressure levels.

[0056] "Electret," "cellular electret," or, in accordance with one or more embodiments of the present invention, "ferroelectret," refers to a dielectric material that has an essentially permanent electrical polarization. "Ferroelectret" is sometimes spelled "ferro-electret," and such spelling should be considered reasonably similar for the purposes of this invention. Ferroelectret refers to an electret having a cellular or foam-like structure, often consisting of polymer films with voids or air-filled cavities. This structure is crucial for their electromechanical properties, achieved by injecting and trapping charges within their voids, creating a permanent dipole moment.

[0057] The terms "dielectric swelled cellular electret film" or "pressure inflated prefoamed cellular electret film" are employed herein to denote a foamed plastic product, as described in WO publication 96 / 06718 or its equivalent U.S. Patent No. 5,955,014 A, which is permanently charged under a strong electric field, achieved through the injection of electric charge into the material. U.S. Patent No. 5,955,014 A is hereby incorporated by reference in its entirety for all purposes.

[0058] In contrast, the term "dielectric cellular electret film" is employed herein to denote electromechanical films of a generally cellular nature possessing a permanent electric charge without pressure or high-pressure expansion.

[0059]

[0060] MICROPHONE OF PRESENT INNOVATION

[0061] Fig. 1 A is an isometric top view, and Fig. 1 B is an isometric bottom view of a microphone in accordance with one or more embodiments of the present invention.

[0062] Fig. 2B is a cross-sectional view of the microphone of Fig. 2A take at section A-A in accordance with one or more embodiments of the present invention.

[0063] Referring to Figs. 1 A and 1 B, in accordance with one or more embodiments of the present invention, a microphone 100 is presented. It has a body made of a rather thick, for example 2.5 mm thick and 80 mm diameter aluminium tube (101). One end of the tube has a metal mesh (102), as is usual in microphones. The other end has a back plate (103). In its center, a 3 / 8" rivet nut (105) is used to fix the microphone to a stand. On the side of the plate (103) is an XLR connector (104) for outputting the signal.

[0064] The body (101) could also be made of die-cast light alloy, be CNC-routed from billet aluminium, or be CNC-machined from RECATHAN® PUR MDI SH 90 A 07OMM polyurethane rod, or any other material with comparable mechanical and acoustic properties. While aluminium offers structural strength, it can also introduce subtle resonant coloration due to its metallic nature, especially in applications requiring high-fidelity sound capture.

[0065] This coloration may, in certain use cases, become particularly noticeable in this invention due to the unique transducer configuration: the sensing element is mounted directly against a heavy, rigid support surface, without the traditional air gap typically found in electret microphones. As a result, any structural resonance from the housing material can mechanically couple into the transducer and influence the recorded sound.

[0066] This effect is especially critical when capturing musical instruments, where tonal purity and transparency are paramount. In such cases, the housing material must not introduce any coloration of its own.

[0067] To address this, the invention utilizes dense but acoustically neutral materials, such as polyurethane with Shore 90A hardness. Materials like RECATHAN® offer sufficient rigidity to maintain structural integrity while also exhibiting excellent internal damping characteristics, effectively suppressing housing resonance. This ensures that the microphone body remains acoustically transparent, preserving the natural tonal balance of the sound source.

[0068] In applications where tonal coloration is less critical — such as voice capture or industrial monitoring — traditional materials like aluminium may still be suitable.

[0069] Referring to Fig. 2, a cross-sectional view is presented, and in Fig. 3, an exploded view is shown. These illustrate how the microphone's transducer element 204, made of cellular electret film, is mounted directly against an opposing force plate 203. This plate may be made from, for example, 3 mm thick steel, but is preferably fabricated from an acoustically neutral material, such as polyurethane with Shore 90A hardness. The purpose of this plate is to provide mechanical counterforce for the transducer, enabling accurate detection of pressure changes without introducing structural coloration into the sound.

[0070] The force plate can be of varying thickness and made from other suitable materials, including engineering plastics or even wood, depending on the desired acoustic profile. In some embodiments, the opposing force plate 203 may also function as or be integrated with the printed circuit board 207, upon which the preamplifier and signal conditioning components are mounted.

[0071] Located beneath the opposing force plate is the printed circuit board assembly (PCBA) 207, which houses the signal processing electronics. The electronics are typically powered by standard 48V phantom power supplied via the XLR connector. Alternatively, the microphone may contain a rechargeable battery housed within the enclosure.

[0072] The electronics may include a limiter and / or compressor, and band-pass filtering to shape the frequency response for different applications. Adjustable high- pass and low-pass filters and gain controls can be implemented using DIP switches or similar means. Additionally, wireless signal transmission can be supported in certain versions of the device, expanding the range of potential use cases.

[0073] It can be seen that the force plate 203 is equipped with studs 210 and, in the illustrated embodiment, is suspended using rubber bands 205 to reduce handlingnoise, a technique commonly employed in traditional microphone shock-mount systems. These rubber bands are attached to a surrounding support ring 206, which includes studs 211 for tensioning and securing the suspension.

[0074] However, due to the use of acoustically neutral materials — such as polyurethane with Shore 90A hardness — for the force plate or housing, the structure itself provides effective damping of mechanical vibrations. As a result, the use of rubber band suspension may no longer be necessary in many embodiments. This simplification reduces the number of components, lowers manufacturing cost, and enhances mechanical robustness without compromising audio quality.

[0075] Additionally, the force plate 203 includes a central hole 209, through which the electrical contact lead (Fig. 4c - 406) from the transducer 204 are routed to the printed circuit board assembly 207, enabling connection to the preamplifier circuitry mounted beneath.

[0076] Referring to Fig. 4A, 4B, and 4C.

[0077] Fig. 4C is an isometric view of the transducer 204 of Figs. 1 A, 1 B, 2a, 2B, and 3, in completely folded status, in accordance with one or more embodiments of the present invention.

[0078] Fig. 4B is the same but in a partly folded status.

[0079] Fig. 4A is a top view, from the signal electrode side, of the transducer of Fig.4C (before any folding step) in accordance with one or more embodiments of the present invention.

[0080] In that order, Fig. 4A - 4B - 4C shows the transducer before and after various folding stages, from beginning to completion. To begin, begin being a cut form. Fig. 4A is a transducer after a prior manufacturing step, that being laser or die-cutting. Fig. 4C is a transducer after a prior manufacturing step 4B. Fig. 4C is completely folded, ready for crimping contacts and attaching their housing. In Fig. 4B, the protective paper 410 from the adhesive 409 has already been removed.

[0081] The transducer signals are preferably transmitted via transmission traces 405a and 405b to a preamplifier on the circuit board 207. Two connectors, such as a 2,54 mm Crimpflex ™ version from Nicomatic ®, are to be crimped to the traces' ends 407. One connector is for signal trace, and one is for ground electrodes on the opposite sides of the signal electrodes (403a, 403b, 403c).

[0082] Transducer 204 may have any suitable shape, form, or form factor, but preferably, it is designed to be round. A suitable diameter is 50 mm, but it can be less or more, depending on the final application and characteristic preferences. It consistsof the shape of transducer 204 and the shape of connector 406. However, other shapes may also be suitable for various reasons, not least for commercial purposes.

[0083] The transducer is attached to force plate 203, preferably using a 50-micron acrylic adhesive. Such an adhesive is made, for example, by 3M®.

[0084] Herein, a contact microphone's transducer 204 i.e. converts sound waves and vibrations into electrical signals. Due to its cellular nature, sensitivity to thickness changes, and very good impedance matching with air, the swelled cellular ferroelectret material-based transducer is very good for the application.

[0085] Continuing refer to Fig. 4A, 4B, 4C, and in addition to Fig. 5. Fig. 5 is an exploded view of the microphone's transducer in accordance with one or more embodiments of the present invention.

[0086] Transducer element 204 comprises a unitary ferroelectret film 504 for its entire area. Thus, advantageously, transducer 204 is realized as a unitary, flexible, and laminated structure that extends seamlessly from sounds and vibrations, picking areas 403a, 403b, and 403c through a connector area 406, including contact area 407.

[0087] Transducer 204 is advantageously formed as a dual structure with a first side 403a and a second side formed of portions 403b and 403c. There are two perforations, 402a and 403b, to fold portions 403b and 403c against 403a. Portions 403a, 403b, 403c, and traces 405a and 405b of each of transducer 204, are disposed on same each side 403a, 403b and joined by the manufacturing process to form the respective transducer 204, connector 406, and contact area 407.

[0088] Advantageously, transducer 204 does not require a mechanically separate transducer and distinct wiring between the transducer and one or more connectors for connecting to a preamplifier since it will be formed by printing electrodes on substrate 151a, formed by laminating thin dielectric films, for example polyester, on a preferably swelled, voided ferro-electret film.

[0089] Transducer 204 comprises signal pickup (transducer) areas 403a, 403b, and 403c, divided along fold lines 402a and 402b. The first signal acquisition area 403a, a second signal acquisition area 403b, and a third signal acquisition area 403c are connected via narrow traces 404 crossing (passing) fold lines 402a, 402b. Sensing areas 403b and 403c continue to trace 405a and 405b to connect to the preamplifier on circuit board 207. Transducer 204's final shape may be any suitable for its final purpose, but it preferably is almost round.

[0090] In accordance with one or more embodiments of the present invention, as shown in Fig. 4B, one or more margins 411 are disposed between an edge of atransducer 204 and signal electrode area 401. Therein, one or more margins 411 are preferably about 1 mm to prevent 50 Hz / 60 Hz electromagnetic noise (hum) from entering the picked signal for amplification.

[0091] Referring now to Fig. 5, it is an exploded view of a transducer during manufacturing in accordance with one or more embodiments of the present invention.

[0092] T ransducer 204 comprises a plurality of layers. Outer layer 501 , which comprises a protective paper layer 501a (to be removed before folding) and an adhesive 501b, more specifically, an adhesive layer 501b on the first side 501 and adhesive layer 503b on the opposite side 503 with protective paper layer 503a are applied in step 665 (Fig. 9).

[0093] Transducer 204 is disposed of two electrodes, signal (505) and ground (506), printed on opposite sides of the cellular electret film 504. Cellular, preferably swelled electret film 504, for example, made of PP, is made printable by laminating very thin PET layers, preferably about 23 microns, due to their good availability and still being thin enough not to reduce much of signal strength on both sides of it.

[0094] A ground electrode 506 is disposed on the bottom side of the electret film 504, and optionally also protective graphite layer 507 is disposed facing ground electrode 506.

[0095] Adhesive layers 501b and 503b are preferably between 20 and 100 microns thick. However, in accordance with one or more embodiments of the present invention, the thickness of the adhesive 50 microns is a very good choice because of its good availability.

[0096] Since the electrodes are printed directly onto the PET layers, the adhesive thickness does not reduce signal strength and increase noise, as has been the case with prior art ferroelectret pickups, as explained in patents such as U.S. Pat. No. 6,242,683 and U.S. Pat. No. 6,336,367.

[0097]

[0098] METHOD OF MANUFACTURING DIELECTRIC SWELLED CELLULAR ELECTRET FILM-BASED PICKUP

[0099] Fig. 9 is a schematic diagram of method 600 of making a dielectric swelled cellular electret film-based transducer 204 in accordance with one or more embodiments of the present invention. This transducer is particularly suited for use as a microphone transducer.

[0100] In the first step 605, a biaxially oriented polypropylene ("PP") film is manufactured for this purpose and used as a PP electret film for transducer 204.

[0101] The method of manufacturing of PP electret film is disclosed, for example, in U.S. Patent No. 4,654,546, which is hereby incorporated by reference in its entirety for all purposes. Alternately, PP electret film for transducer 104 is purchased, acquired, or provided as necessary by a user or other person associated with method 600. Therein, PP electret film will first be in roll form.

[0102] In a subsequent step 610a, the PP film is subjected to AC corona treatment. The AC corona treatment is necessary to make one or more PP film surfaces beneficial for lamination with PET layers in a subsequent step. The AC corona treatment improves the adhesive bonding of the PET layers and the PP film, i.e., the PP film surface.

[0103] In step 610b, which, while preferably performed at the same time as step 610a, is not required to be performed at the same time as step 610b, the PET layers are also subjected to an AC corona treatment on one or more sides of the PET layers, or preferably on both sides of the PET layer, for improved adhesion between the swelled PP film and the silver paste.

[0104] In subsequent step 615, directed broadly to swelling, the material’s later (after step 625) sensitivity (pC / N) is enhanced by undergoing swelling after AC charging and before DC charging. This is explained in WO publication 96 / 06718 or its equivalent U.S. Patent No. 5,955,014. U.S. Patent No. 5,955,014 is hereby incorporated by reference in its entirety for all purposes.

[0105] During the swelling of step 615, the PP film's thickness is increased by increasing the height of cavities. Advantageously, the weight remains the same, but the thickness increases. This gives more sensitivity when charged for having a permanent electric charge.

[0106] As previously taught, as the thickness changes, the opposite charges on the opposite sides of the voids either draw closer together or move farther apart, generating so-called mirror charges across the electrodes positioned above the cellular electret film. Consequently, this produces a measurable electrical output voltage proportional to the force change.

[0107] The charged material PP electret film holds positive and negative charges on opposite sides. Thus, signal electrodes are usually printed on the positive side and ground on the negative side, but these can also be arranged in opposite manners.

[0108] Due to the elastic swelled cellular core, Young's modulus of cellular electret film transducer 204 is significantly reduced. This leads to improved impedance matching, particularly with air, as opposed to hard piezoelectric materials.

[0109] In a subsequent step, 620 is directed broadly to lamination, following the swelling, to prevent shrinkage during subsequent silver paste curing, preferably a 23- micron-thin polyester (PET) layer, but can be thinner or slightly thicker, is laminated onto both sides of the electret film in a reel-to-reel process preferably using the wet gluing method. The PET is preferred to be heat treated to prevent its shrinking during silver paste curing.

[0110] Advantageously, the thin PET film on both sides of the core’s cellular PP film enables the direct printing of transducer signal and ground electrodes, resulting in a laminate where the cellular, swelled ferroelectret film forms the core. Herein, the core is the material in the laminate that gets charged in a high DC field where discharges occur in the core’s lens like gas bubbles (cavities) during DC charging.

[0111] Advantageously, a thin PET layer of 10-20 microns does not significantly increase thickness. The excessive thickness of PET layers in the laminate would decrease the sensitivity of the achieved electromechanical films, i.e., the charge output from sound and vibrations. Herein, in accordance with one or more embodiments of the invention, an excessive thickness of a PET layer is defined as 23 microns. In accordance with one or more embodiments of the invention, an excessive thickness of a PET layer is defined as 30 microns or more. That is, advantageously, in accordance with one or more embodiments of the present invention, the thickness is kept at a minimum.

[0112] In step 620, instead of polyester (PET) many other plastics can be used. Therein, polyamide is a substitute. However, PET is the most cost-effective and more cost-effective than polyamide; it is easily available and has excellent purpose- directed properties. Purpose-directed properties are defined herein as being the property of being heat treatable for becoming non-shrinking and the property of having, after corona treatment, good adhesion with silver paste.

[0113] Utilizing a very thin wet adhesive in a reel-to-reel lamination process, with an end thickness of 10-20 microns after curing, helps minimize overall thickness and weight and achieve the best properties for a contact microphone transducer. Advantageously, the thinner PET with adhesive layers between later explained electrodes and the core’s cellular PP film yields higher output, as the thicker the entire structure between signal and ground electrodes, the lower the output of such ferroelectrics.

[0114] The laminated (PET-PP-PET) structure, with the PET being heat treated beforehand, does not shrink during the approximately 80°C curing required for the silver paste and graphite layers needed for electrodes, as explained later. Preferably,such a laminated structure facilitates creating a structure where electrodes printed on both side surfaces can be perfectly aligned before cutting into individual pickups.

[0115] Following the lamination process of step 620, in step 625, the obtained PET- PP-PET material, i.e. , laminate 504, is charged at a very high DC voltage, typically in the range of 20-25 kV, against resistive material.

[0116] In accordance with one or more embodiments of the present invention, the cellular ferroelectret film is charged in step 625 after it is laminated with PET films. The sequence of step 620, followed by step 625, helps prevent discharges when a charged material is rolled into an end-roll in the final phase of reel-to-reel charging. Charging this laminated material in sheets is also possible, but it is slower, resulting in increased manufacturing costs. Step 625 of charging must be completed before printing the electrodes in step 650.

[0117] When the laminated (PET-PP-PET) ferroelectret material is charged, it is preferably cut into smaller sheets 151a in step 630 of broadly cutting. In accordance with one or more embodiments of the present invention, five transducers 204 will be available for cutting from one sheet after screen printing the electrodes in step 650.

[0118] Referring to Fig. 6 and Fig. 7. After cutting onto smaller sheet 151a in step 630 to obtain the preferred quantity of transducers, the sheet is prepared for high- precision printing in step 640 by making one or more alignment holes 153 in sheet 151a. Hole cutting in the sheets can be done by laser cutting or die cutting.

[0119] After obtaining sheet 151 a, if not already present, one or more alignment holes 153 are made through sheet 151a to prevent unintended displacement of sheet 151a during printing of signal electrodes 505 or ground electrodes 506 or proper alignment during printing of the electrodes 158, 154.

[0120] After sheets 151a are obtained and alignment holes 153 are made, signal electrodes 505 are arranged, preferably screen-printing with silver paste in step 650 (Fig. 6). Inkjet printing could be possible as well, but screen printing is a well-tested method. One embodiment's film for printing screen is shown in Fig. 7. Five individual transducers are obtained using it.

[0121] Referring to Fig. 7 and 8, after step 650 (Fig 6), ground electrodes 506 are screen-printed, preferably with silver paste in step 655 (Fig. 6) on the opposite side of sheet 151a. In one embodiment of the invention, a screenprinting film is shown in Fig. 8. Then, after curing the silver paste 506, in step 655, the same design is printed with graphite as a graphite layer 507. Since graphite serves as the outer face of the final product, this protection is preferred for durability. Silver could also be protected from oxidation and silver migration by using printed or cast lacquer or a very thinplastic film with adhesive. Graphite possesses excellent resistance to handling and abrasion, and unlike silver, it does not oxidize or migrate. Instead of printing graphite for silver paste protection, a very thin glued plastic sheet or printed insulation could also be used.

[0122] Fig. 6 is a plane view of a plurality of transducers' 204 signal electrodes 505 and a plurality of connector traces 405 having respective contact areas 701 printed on one side of a sheet 151a in accordance with one or more embodiments of the present invention.

[0123] Fig. 7 is a plane view of a plurality of transducer 204 ground electrodes 506, and connector traces 508 having respective contact areas 509 printed on one side of a sheet 151a in accordance with one or more embodiments of the present invention.

[0124] In step 650, signal electrodes 505 comprising transducers 204 and a plurality of connector traces 405 having respective contact areas 509 are directly printed on sheet 151a using sheet printing utilizing alignment holes 153 for precise alignment of sheet 151a.

[0125] Instead of sheet printing, signal electrodes can be screen-printed reel-to-reel on laminated PET-PP-PET electret film. However, sheet printing has a higher accuracy than reel-to-reel printing where accuracy is more difficult to obtain.

[0126] Both printed layers are printed exactly in the correct place using alignment holes 153.

[0127] After printing signal and ground electrodes, adhesive sheets with protective papers are applied. The signal side is completely covered with adhesive, and later, in step 670, the transducer is folded so that signal electrodes remain inside. In practice, only half of the whole area needs adhesive. The adhesive is also added on the ground electrode side. There, it is needed on the final folded transducer only in area 408 (Ref Fig. 4G).

[0128] In step 665, sheet 151a is cut to individual transducers 204. This can be achieved through die-cutting or laser cutting. Preferably, alignment holes 153 are utilized to more accurately make the cuts.

[0129] Referring to Fig. 4B and Fig. 4G, an innovative new method is to use perforations (402a, 402b) that enable folding the transducer like origami in the final state before crimping contacts. In the described embodiment of the innovation, trying to achieve a round shape, two perforations (402a, 402b) are crosswise. Depending on preferences, it is possible to have only longitudinal or only crosswise perforation, or both kinds, to enable folding and form a shield against EMI (electromagnetic interference, the 50 or 60 Hz hum). In this method, the transducer area always hastwo layers of electroactive material and a complete shield in which signal strength and shielding are optimized for highly efficient production.

[0130] Fig. 4A represents a transducer to become like in Fig. 4C. Fig. 4B shows it during folding. At this point, the protective paper (409) covering the adhesive layer has already been removed. In the innovative pickup production method, the perforations obtained during cutting facilitate the final folding process to create completed transducers ready for attaching connectors.

[0131] It is evident to those skilled in the art that various embodiments of the invention are not limited to the examples outlined above, but rather can be modified within the scope of the claims provided below. The form (shape) can be selected based on the requirements of each specific case; there can be multiple transducer areas, and the shape of the area can vary beyond a rectangular form in the top view. These transducers have versatile applications, including their use as transducers in musical instruments.

[0132] While the invention has been described in conjunction with specific embodiments, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description.

Claims

Claims1. A microphone comprising: a transducer element formed of a permanently charged, cellular ferroelectret film having electrodes disposed on opposing sides thereof; a rigid support surface positioned directly against the transducer element, such that no air gap exists between the film and the surface; a housing enclosing the transducer and support surface, wherein the housing or the support surface is made from an acoustically neutral material having high internal damping, such as polyurethane with Shore 90A hardness; and a plurality of electrical contacts extending from the transducer to a signal conditioning circuit, wherein the transducer is configured to convert sound pressure directly into an electrical signal without external bias voltage.

2. The microphone according to claim 1, wherein the electrodes are printed on both sides of a single sheet of ferroelectret film.

3. The microphone according to claim 1, wherein the transducer element is folded along perforated or pre-cut lines to form a layered or EMI-shielded structure.

4. The microphone according to claim 1, wherein the support surface comprises a polyurethane component such as RECATHAN® PUR MDI SH 90 A.

5. The microphone according to claim 1 wherein the signal conditioning circuit includes a band-pass filter, a limiter, and / or a gain control stage.

6. The microphone according to claim 1, further comprising an XLR connector and configured for phantom power supply.

7. The microphone according to claim 1, wherein the support surface also serves as the mounting base for a printed circuit board.

8. The microphone according to claim 1, wherein the transducer element is attached to the housing using adhesive and optionally provided with a mass element to enhance pressure coupling.

9. The microphone according to claim 1, wherein the microphone is configured to operate under very high sound pressure levels exceeding 140 dB SPL without distortion.

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