The present invention relates to amplifying and tuning piezoelectric sonic and ultrasonic while dealing with heat dissipation and focusing the energy at a desired location and/or direction. For example, the invention relates to increasing the energy directed at a desired location from piezoelectric devices when operated in open air.
One aspect of the invention is directed towards addressing transfer of energy in open air, from piezoelectric devices, in a desired direction and/or to a desired location has several limitations. These limitations include; lack of heat dissipation, inherent power capability of the devise and directional control especially when multiple devices are used. Due to these limitations, open air applications are severally limited in many areas where otherwise the efficiency of piezoelectric devices could provide many benefits. Listed below are some of these areas that this invention will facilitate: Ultrasonic cleaning; currently ultrasonic cleaning is accomplished in a liquid medium because the liquid transfers the energy much more efficiently than open air and the liquid also acts as a heat sink to dissipate the thermal energy. With this invention thermal cleaning can be accomplished in open air. Long distance echo location such as sonar: currently long distance echo location such as sonar can only be efficiently accomplished in a liquid medium such as water. With this invention, the energy directed at a target in open air can be increased to allow echo location at far greater distances; deterrent to human or animal encroachment: currently the use of sonic or ultrasonic as a deterrent to encroachment is limited by the amount of energy directed at the target. This invention increases the amount of energy directed at a target when using piezoelectric devices.
One aspect of the invention increases the amount of energy transmitted to a target and/or in a given direction, produced by piezoelectric devices. This aspect of the invention resolves several problems with increasing the amount of energy produced by piezoelectric devices. By sandwiching the piezoelectric devices between metal plates the problem of heat dissipation is resolved. By sizing the metal plates such that the plates have a resonance at the desired frequency of the device, the amount of energy transmitted is increased and more efficiently radiates the heat produced. By stacking the sandwiched devices as shown in
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.
The detailed description of the drawings particularly refers to the accompanying figures in which:
The embodiments of the invention described herein are not intended to be exhaustive or to limit the invention to precise forms disclosed. Rather, the embodiments selected for description have been chosen to enable one skilled in the art to practice the invention.
Referring initially to
One aspect of the invention provides a directional transmission of sonic energy 25 that depending on the application can be focused at infinity, to a point forward of the assembly, or in a fan beam forward of the assembly depending on the shape of the heat conductive plates (e.g., metal plates). In the example provided herein, round plates are used with parabolic contours (not shown) of increasing diameter (e.g., see
Variables affecting resonance of heat conductive plates, including metal plates, include the speed of sound in the metal, its thickness and its diameter or length and width if not circular. The speed of sound in aluminum and stainless steel are extremely close so that calculations of resonances for either produce nearly the same thicknesses and diameters, whereas for other metals such as copper, silver, etc. yield dimensions different enough to have to be calculated separately. For this example the calculations are for aluminum or stainless steel.
(Resonant) Frequency=((t=thickness of the material)*A)/(diameter2) where A=(the speed of sound in the material)*(a proportionality constant) or f=(t*A)/d2. For the unit dimensions in cm and frequency in hertz and the material being stainless steel or aluminum, A=791,815.5. The following table 1 illustrates calculated thickness and diameter measurements for a resonance of 10 KHz with aluminum or stainless steel.
Plates disposed between piezoelectric devices can be made of metal or other materials which are sonically or ultrasonically compatible with creating the effects described above. Heat and sonically/ultrasonically conductive plates, e.g., discs of steel or aluminum, can be formed or cut slightly larger than calculated as described above and then trimmed to tune the plates after the piezoelectric devices are bonded to it. Such fabrication steps can include activating the piezoelectric devices and then machining or forming the plates in order to achieve a maximum desired effect as described above. Note that references herein to the terms “sonic” and “ultrasonic” are used interchangeably herein however, it is understood that ultrasonic includes references to frequencies above human hearing ranges (e.g., above 25 kHz), sonic references include frequencies within an average human hearing range, and subsonic includes references to frequencies below an average human hearing range.
Alternative embodiments can include structures made of actuator materials which are capable of changing their shape, e.g., curvature, parabolic shape or effective diameter, based on application of electric, heat, mechanical forces, or other stimuli in order to adjust the focus or shape of the sonic or ultrasonic waves being transited through the plates. For example, the plates can be formed in layers which can slide in relation to each other to increase radius or length and width. For example, a shape memory alloy can be used in one or more plates. Shape memory alloys used herein can include copper-aluminum-nickel, and nickel-titanium (NiTi) alloys but such shape memory alloys can also be created by alloying zinc, copper, gold and iron. Electromechanical materials used herein can include metals, ceramics and carbon/carbon composite materials as well as piezoelectric and electrostrictive materials. Plates can be constructed of piezoelectric bimorphs can be configured in series and parallel. Bimorphs can be constructed of two piezoelectric plates that are bonded with their polarity in opposite directions. Under electric field one piezoelectric layer contracts in the thickness direction while the other expands. Due to the contraction and expansion in the thickness direction one layer expands along the length and the other contracts inducing bending of the bonded layers. Unimorphs are similar in configuration to bimorphs with the difference that one of the layers in passive. Under expansion in the poling direction the strain in the plane perpendicular to the poling direction undergoes a contraction such that strain occurs only on the active layer (piezoelectric or electrostrictive material) leading to a bending of the whole device. Such devices can be used to induce relatively large deflections and the amplitude increases with the lateral dimensions. Flextensional actuators, which sometimes are also known as the Moonie and Cymbal structures, use end-caps to convert transverse to longitudinal strain. Another approach used to increase the strain that can be induced with a piezoelectric material for a given field is to drive the material at its resonance frequency. Such materials can also be used to alter the interaction of sonic or ultrasonic waves passing through the plates. In general for any mechanical system it can be shown that at resonance the strain is amplified by a factor called the mechanical Q. Other embodiments can involve placing one or more actuators in mechanical coupling with a plate to induce a mechanical deflection or change in a plate's shape. Another embodiment could use piezeo, piezoelectric, piezoceramic, cryogenic shape materials, electroactive polymers or polymer-metal composites as actuator materials or other types of electromechanically active materials which change shape, volume, modulus, or some other mechanical property in response to some kind of controllable signal.
Another embodiment can include rotational coupling of the plates with the piezoelectric devices to rotate the devices and plates relative to each other while also deflecting or altering the shape of the plates in order to further provide for variable tuning of the sonic or ultrasonic structures as well as outputs, waveforms, focus points, etc.
Another embodiment can include having an acoustic lens formed within or adjacent to one or more of said plates in order to alter waveforms of sonic or ultrasonic waves passing through the plates.
Another embodiment can include a thermally conductive bonding material which bonds the plates to the piezoelectric devices. This conductive bonding material can be selected based on different refractory or other interactive effects with sonic or ultrasonic waves which pass through the material to further tune the combined wavefront of sonic or ultrasonic waves which are passing through the plates and piezoelectric devices. Different adhesives or bonding materials can be used between each different piezoelectric device in order to further alter a waveform passing through such bonding material.
Another embodiment can include injection of liquid or semiliquid material into cavities formed in the plates which alter or refract the shape of a waveform passing through the plates. Another embodiment can have mechanical substitution or rotation into or out of a stack of piezeoelectric devices which change the focus of a waveform of sonic or ultrasonic energy as such energy passes through the plates which are rotated into the assembly. Such an assembly could have a system which mechanically grips or couples with a plate, removes it from the stack, and then inserts a different plate which provides a different focus or wave front effect in order to alter energy propagation and wavefronts which are generated and focused as predetermined locations. An assembly can have a carrier or holder which holds the plates in position with a locking or unlocking mechanism which secures the plates in position until such a time a plate is selected for substitution.
Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the spirit and scope of the invention as described and defined in the following claims.
The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/676,569, filed Jul. 27, 2012, entitled “APPARATUS AND METHODS OF TUNING AND AMPLIFYING PIEZOELECTRIC SONIC AND ULTRASONIC OUTPUTS”, the disclosure of which is expressly incorporated by reference herein.
The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used and licensed by or for the United States Government for any governmental purpose without payment of any royalties thereon.
Number | Date | Country | |
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61676569 | Jul 2012 | US |