Patent Description:
Piezoelectric transducers are well understood in the art to generate an electrical signal responsive to a mechanical movement or stress, or conversely, to generate a mechanical movement or stress responsive to an electrical signal. Piezomaterial, which provides the active layer of a typical piezo transducer, is generally manufactured using a casting process. In its native state, a typical cast piezoelectric material is composed of large numbers of microscopic electric dipoles which possess a random orientation, thereby rendering the overall polarization of the piezoelectric material at zero. When stressed, a piezoelectric material having a zero overall polarization will react to a mechanical force with only a very small response, and thereby with only a very weak piezoelectric effect. Consequently, in order to enhance the responsiveness of the piezoelectric sensitive material, the native dipoles of the material must be initially oriented in the direction of prospectively applied forces. This process of forcing the dipoles to orient in a uniform direction is called "polarizing".

Batch process polarizing is typically implemented by applying a very strong electrical field to the piezo materials in the prescribed direction for a sufficient time period. After the removal of the electric field, the majority of dipoles in the piezo electric material will remain in a particular orientation. As such, the process of polarizing piezoelectric materials is similar to the magnetization of magnetic material, wherein one applies a sufficiently large magnetic field to align the internal magnetic dipole moments of the magnetic material.

Batch process polarizing suffers from a significant drawback, at least in that only a single "batch" of piezo material is exposed to the polarizing process at a given time. That batch, once polarized, must be removed from the batch process, and then a new batch of piezo material is inserted into the polarizing process, exposed to the polarizing electric field, and removed from the process, and so on for each processed batch. Accordingly, batch processes increase production time, minimize throughput, and negatively impact cost efficiency due to the need to have a start time, end time, and down time before and during each batch process.

Piezoelectric transducers may be used in a variety of circumstances. For example, piezo sensors may be used for monitoring and actuation, such as for the monitoring of heartbeats, sleep quality, flow control, the providing of ultrasounds, healthcare aspects, temperature, force, vibration, hydration, balance, flow, and the like. Piezo sensors may also be used to provide human machine interfaces and interface haptic feedback, such as instead of capacitive touch technology, may be used to provide embedded haptic feedback, to provide virtual reality interfacing, to provide grip sensing, tactile sensing, pressure sensing, and the like. Piezo transducers may also allow for energy harvesting, such as to power bile implantable sensors, and may be used to provide autonomous sensors or to harvest energy to provide lighting, and may be used in conjunction with the Internet of things, to provide micro-power generation, self-powered medical devices, wireless sensor networks, accelerometer and gyroscopic sensors and harvesters, or may be used to replace batteries, and the like.

Piezo transducers may also be used in manufacturing settings, such as to provide machines, sensors, engineering retooling, grip monitoring, or to provide wearable sensors for manufacturing, and in many other manufacturing settings, in part due to the small, thin, flexible and durable nature of piezo transducers. Piezoelectrics may also provide enhancements to acoustics and audio technology, such as through the providing of thin film speakers and headphones, compact and flexible audio devices, high resolution ultrasound imaging ( such as may operate at <NUM> - <NUM>), microphones and acoustic sensors for control and voice recognition, autonomous audio sensors, and the like. Of course, all of the foregoing and myriad other technologies, such as prosthetics, may benefit from the use of piezoelectrics due to the thin, durable nature of piezo electrics, and the lack of necessity for a piezoelectric to receive external power. However, the level of usefulness of piezo electrics in all of the foregoing arenas is limited in the known art due to the inefficiency of manufacture of piezoelectronics which results, in part, because of the need for the aforementioned batch polarizing processes.

Therefore, the need exists for an apparatus, system and method of more efficiently manufacturing piezoelectrics.

Conventional systems and methods for manufacturing piezoelectrics are disclosed in <CIT>, <CIT> and <CIT>.

The invention provides a system and method for manufacturing piezoelectric transducers according to the independent claims <NUM> and <NUM>,.

The invention is illustrated by way of example and not limitation in the accompanying drawings, in which like references indicate similar elements, and in which:.

The figures and descriptions provided herein may have been simplified to illustrate aspects that are relevant for a clear understanding of the herein described devices, systems, and methods, while eliminating, for the purpose of clarity, other aspects that may be found in typical similar devices, systems, and methods. Those of ordinary skill may recognize that other elements and/or operations may be desirable and/or necessary to implement the devices, systems, and methods described herein. But because such elements and operations are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and operations may not be provided herein. However, the present invention is deemed to inherently include all such elements, variations, and modifications to the described aspects that would be known to those of ordinary skill in the art.

Although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the exemplary embodiments.

The embodiments include piezoelectrics provided, in part, using a continuous manufactured printing. The piezoelectric transducers may be polarized using in-line polarizing, such as corona polarizing, by way of non-limiting example. The printed transducer may include three or more separate functional layers, including conductive layers, piezo active layers, and dielectric layers.

More particularly, the disclosed piezoelectric transducer may be comprised of an active piezo material (such as a polymer or other piezo material) layer that is sandwiched between two conductive layers. More particularly, and as referenced above, continuous corona polarizing may be used to activate the electro-active effect of the piezo material. This is in contrast to prior art embodiments, in which polarizing is done using high-voltage batch processes.

Corona discharge is a partial breakdown of air, typically at atmospheric pressure, that may be initiated by a discharge in an inhomogeneous electric field. Corona discharge may be used to polarize films of electro-materials, such as the disclosed piezo material, in order to enhance electronic properties, and is typically employed in opto electronics.

Although corona polarizing may be performed at room temperature, Corona polarizing at elevated temperatures may provide numerous advantages. For example, raising the temperature during polarizing may increase the mobility of electrons and molecules during the polarizing process, and the lowering of temperature from the elevated temperature to well below the transition temperature at a distinct breaking point may "freeze" electrons and molecules in the new orientation to be provided by the corona polarizing.

Piezoelectric films having optimized piezo properties may be continuously formed in the embodiments. Specifically, the piezo circuits in the embodiments may be printed on a substrate in a roll-to-roll fashion, and corona polarizing may be performed when the roll of printed material is exposed to a continuous electric field, such as in a heated or unheated environment. Accordingly, corona polarizing may be used to fabricate the printed piezoelectric transducers efficiently, continuously, and without the batch polarizing processes known in the art.

Of note, the polarizing employed in roll-to-roll processing may be used to create a specific and characteristic "D<NUM>" signature. A D<NUM> signature is an industry recognized descriptive piezoelectric performance parameter that quantifies the volume change when a piezo electric material is subject to an electric field, or the polarization of a piezo electric material upon application of a stress. This parameter obeys the equation d = p / σ, where p is polarization and σ is the stress factor.

Of note, the corona polarizing continuous electric field may be provided distinctly from the printing process, or may be provided as part of the printer or printing process. For example, one or more aspects of a 3D printer used in the piezo material printing process may be charged to form an anode, while another portion of the 3D printer, or the continuous printing substrate itself or the receiving surface on which the substrate "rolls" may be charged as a cathode, such that polarizing occurs to the printed material as it is laid onto the substrate.

Additionally and alternatively, the print material may be printed on a continuous substrate roll, such as by one or a series of printers, printing, different substances. As the print roll is printed, the roll may continuously pass through an electric field to perform a corona polarizing process in a continuous manner. As will be understood, either of the foregoing continuous corona processes may be performed at room temperature or at elevated temperature and, to the extent performed at elevated temperature, may include within the print process a substantially instantaneous drop in temperature in order to "freeze" the polarizing of the piezo material, as discussed above.

More particularly, the piezo material discussed throughout may be any printable piezo material known to those skilled in the art, such as polyvinylidene fluoride polymer (PVDF). For example, an fluro-polymer PVDF-TRFE based ink, such as ink formulated by Solvay, may provide the piezo material layer.

PVDF material may be deposited, such as on a conductive layer, such as a silver layer, as discussed herein, in a live print mode. Thereafter or prior to the foregoing prints, additional layers may be printed to form piezoelectrics, and the corona polarizing process may be performed at any stage once the piezo material has been printed. Alternatively, the disclosed embodiments may be operable using a previously printed roll of printed piezo, conductive, and dielectric material that is then rolled, such as in a roll-to-roll fashion, through the polarizing process. As discussed herein, the embodiments may include continuous, noncontact corona polarizing, although the skilled artisan will appreciate in light of the discussion herein that contact based or batch process polarizing may be similarly employed.

More particularly, PVDF may be used as a piezo material in the embodiments because it is printable, and is regarded as a tough material, a stable material, and hence provides distinct engineering advantages in the embodiments. For example, printed PVDF may withstand exposure to various harsh thermal, chemical, or ultraviolet conditions, such as may be necessary to print and polarize the disclosed piezoelectrics. That is, PVDF is of low weight, low thermal conductivity, high chemical resistance, high heat resistance, high mechanical strength, high abrasion resistance, low permeability, and provides various other material benefits that will be apparent to the skilled artisan.

As referenced, the piezomaterial may be printed onto one or more other layers, which may form or be printed atop a substrate. More specifically, the conductive, piezo, and dielectric layers discussed herein may be printed onto one or more substrates, such as a polyethylene terephthalate substrate (PET) or Mylar substrate, of any of various thicknesses, such as PET having a thickness in the range of <NUM> to <NUM> (<NUM> mils to <NUM> mils). Such print processes will readily allow for the continuous polling process disclosed throughout.

The embodiments disclosed throughout may be printed and polarized using a roll-to-roll type coating and printing technique, which decreases production time, augments throughput, and enhances cost efficiency in the manufacture of piezoelectric transducers. Such a complete roll-to-roll (R2R) fabrication of piezoelectric transducers allows for continuous exposure of the roll in an in-line, noncontact polarizing process, such as a corona polarizing process. Thereby, the embodiments may drastically reduce the manufacturing time of discrete piezo electric sensors, at least by eliminating the need for human intervention at process stages, and eliminating the need for polling of the piezoelectrics in batches. The aforementioned improved manufacturing more readily enables penetration of piezoelectric sensors into the various market segments discussed herein, at least because of the avoidance of piezoelectrics having prohibitive manufacturing costs.

<FIG> illustrates an exemplary piezo electric transducer <NUM> printed on a substrate roll <NUM> in accordance with the embodiments. As illustrated, a bottom electrode of conductive ink <NUM> is printed and receives, printed thereupon, one or more piezo layers <NUM>, such as a PVDF layer, by way of nonlimiting example. Printed atop the conductive layer is a top electrode <NUM>, which results in the finished printed sensor shown in <FIG>.

<FIG> illustrates an alternative embodiment in which piezoelectronic circuits <NUM> include multiple piezo layers which may be printed using the disclosed processes. In the illustration, a first conductive electrode <NUM><NUM> is printed on a substrate <NUM>, and printed thereupon is printed a first piezo layer <NUM>, PVDF layer <NUM>. This PVDF layer <NUM><NUM> then receives thereupon a printed conductive electrode <NUM><NUM>, which has printed thereupon a dielectric <NUM>, i.e., substantially nonconductive, layer of a printable dielectric ink, as will be understood to the skilled artisan. Thereafter, conductive electrode <NUM><NUM> is layered upon the dielectric layer <NUM>, PVDF layer <NUM><NUM> is layered upon conductive electrode <NUM><NUM>, and conductive electrode <NUM><NUM> is printed atop PVDF layer <NUM><NUM>. This results in dual piezo sensors 200a, 200b that may be kept electrically distinct, or which may be electrically connected, in certain circumstances, based on the presence of the dielectric layer between conductive electrode <NUM> and conductive electrode <NUM>. The skilled artisan will appreciate that other piezo material layers may be used in the embodiments-that is, PVDF layers are used in the foregoing discussions by way of non-limiting example only.

<FIG> is a manufacturing system <NUM> diagram. In the illustration, the piezoelectric circuits <NUM> of <FIG> and <FIG> are continuously printed, via a series of manufacturing prints <NUM>, onto a continuous substrate roll <NUM>. As illustrated, as the roll <NUM> is continuously rolled, at least from at least start roller 330a to at least an end roller 330b, through a polarizing electric field <NUM>. In the illustration, the polarizing process <NUM> is performed at ambient temperature <NUM>, although, as referenced throughout, the polarizing process may be performed in the presence of an elevated temperature <NUM>. In an elevated temperature embodiment, also included in the continuous print example illustrated may be a low(er) temperature chamber or pseudo-chamber employed as a cooler <NUM> to cool the roll after polarizing, in which the temperature of the piezomaterial may be drastically decreased in a relatively short time frame, such that the polarizing of the piezomaterial is "frozen".

Claim 1:
A system for manufacturing piezoelectrics, comprising:
at least a first roller (330a) and an end roller (330b);
a continuously advancing printable substrate roll (<NUM>, <NUM>, <NUM>) extending at least from the first roller (330a) to the end roller (330b) as the first and end roller turn;
at least one printer (<NUM>) configured to print piezoelectric material (<NUM>, <NUM>) onto the continuously advancing substrate roll (<NUM>, <NUM>, <NUM>) to form a plurality of the piezoelectrics; and
an electric field generator configured to generate an electric field (<NUM>) at ambient temperature (<NUM>) or at above-ambient temperature (<NUM>);
wherein the electric field generator is configured to polarize the piezoelectric material (<NUM>, <NUM>) as the continuously advancing substrate roll (<NUM>, <NUM>, <NUM>) is rolled from the first roller (330a) to the end roller (330b);
characterized in the system further comprising a cooler (<NUM>) configured to drive the ambient (<NUM>) or above-ambient temperature (<NUM>) to below-ambient temperature substantially immediately following the electric field generation.