Patent Publication Number: US-2018037329-A1

Title: Method and apparatus for inhibiting formation of and/or removing ice from aircraft components

Description:
RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 15/076,598, filed Mar. 21, 2016, which is a continuation of U.S. application Ser. No. 13/204,630, filed Aug. 5, 2011, all of which are incorporated in their entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to de-icing systems. More specifically, the invention relates to de-icing systems for use on the outer surface of an aircraft flight surface. 
     2. Discussion of the Related Art 
     Atmospheric icing occurs when water droplets in the atmosphere freeze on objects they contact. Atmospheric icing can lead to the buildup of ice on the exterior surfaces of an aircraft can cause significant changes in the aerodynamics of various flight surfaces. Such changes may enhance safety risks by altering airflow and increasing drag over the aircraft&#39;s lift and flight control surfaces. 
     Ice protection systems are commonly employed to deal with the problems of aircraft icing. Traditionally, de-icing systems rely on chemical or thermal means to prevent and/or remove ice formation/s. Additionally, some conventional de-icing systems create high-frequency (ultrasonic) transverse shear stress for delaminating ice layers on an isotropic structure. One such teaching is described in a publication by Jose L. Palacios, Edward C. Smith and Joseph L. Rose of Pennsylvania State University, entitled  Investigation of an Ultrasonic Ice Protection System for Helicopter Rotor Blades , (hereinafter “Palacios et al.”); copyright 2008 by the American Helicopter Society International, Inc., which is incorporated herein it its entirety. For example, Palacios et al. discloses the use of ultrasonic 28.5 kHz radial resonance disk actuators for inducing ultrasonic transverse shear stress for delaminating ice layers formed on a helicopter rotor blade. 
     Another method and apparatus for removing debris from a windshield or air foil is taught by U.S. Patent Application No. 2009/0120471 and U.S. Pat. Nos. 7,459,831 and 7,084,553, to Ludwiczak, all of which are incorporated herein by reference. Particularly, U.S. Application No. 2009/0120471 entitled Vibrating Debris Remover, discloses a device for attachment along the edge of a material, such as a car windshield or airfoil (such as an aircraft wing), including a vibration subunit that produces vibrating mechanical energy to remove solid debris from the surface of the material. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a system for an aircraft comprises: a component of the aircraft having a surface; a plurality of actuators each positioned proximate to a portion of the surface; and a control unit coupled to the plurality of actuators, the control unit configured to drive one or more of the plurality of actuators at one or more frequencies; wherein the plurality of actuators are each configured to introduce a displacement of the surface in three dimensions to inhibit a formation of ice on at least the portion of the surface and/or to break up existing ice formations on at least the portion of the surface. 
     In another embodiment, a method for use with an aircraft comprises: driving a plurality of actuators each positioned proximate to a portion of a surface of a component of the aircraft; and driving one or more of the plurality of actuators at one or more frequencies such that each of the plurality of actuators introduce a displacement of the surface in three dimensions to inhibit a formation of ice on at least the portion of the surface and/or to break up existing formations of the ice on at least the portion of the surface. 
     In another embodiment, a method for use in an aircraft comprises: determining that a condition is present, the condition indicating potential ice formation on a surface of an aircraft; driving a plurality of actuators in response to the determining step, the plurality of actuators proximate to a surface of the aircraft; transferring energy from the plurality of actuators to the surface to inhibit a formation of ice on at least a portion of the surface; determining that the condition is no longer present; and discontinuing the driving the plurality of actuators and the transferring the energy steps. 
     In another embodiment, a method for use in inhibiting ice formation on an aircraft, comprises: selectively driving a plurality of actuators in time in a sequence relative to each other, the plurality of actuators proximate to a surface of the aircraft and arranged in a pattern extending across at least a portion of the surface; transferring energy from the plurality of actuators to the surface to inhibit a formation of ice on at least a portion of the surface and to break up existing formations of the ice on the at least the portion of the surface. 
     In another embodiment, a method for use in inhibiting ice formation on an aircraft, comprises: driving a plurality of actuators at each of a plurality of predetermined frequencies within a predetermined time period, the plurality of actuators proximate to a surface of the aircraft; transferring energy from the plurality of actuators to the surface to inhibit a formation of ice on at least a portion of the surface and to break up existing formation of the ice on the at least the portion of the surface. 
     In yet another embodiment, a method for use with an ice inhibiting system for an aircraft comprises: identifying a host material and a shape of a surface of an aircraft, the surface to be exposed during flight of the aircraft; modeling the host material and the shape to determine resonant frequencies of the shape; coupling a plurality of actuators in proximity to at least a portion of the shape; driving the plurality of actuators at at least the resonant frequencies; measuring an impedance of the plurality of actuators as a function of frequency; selecting, based on the measuring, a plurality of resonant frequencies for use in driving the plurality of actuators during flight of the aircraft in order to inhibit a formation of ice on at least a portion of the surface and to break up existing formation of the ice on the at least the portion of the surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of several embodiments of the invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. 
         FIG. 1  is a block diagram depicting a de-icing system comprising a control system for coordinating actuation of one or more actuators in accordance with an embodiment of the invention; 
         FIG. 2  is a flowchart depicting a method for designing a component of an aircraft for use in removing existing ice and/or inhibiting the formation of ice on the component in accordance with an embodiment of the invention; 
         FIG. 3  is a flowchart depicting a method for inhibiting and/or removing ice from a component of an aircraft in accordance with yet another embodiment of the invention; 
         FIG. 4  is a perspective view of a component of an aircraft, shown with a plurality of actuators disposed on the inner surface in accordance with some embodiments of the invention; 
         FIG. 5  is a perspective view of a component of an aircraft with a plurality of actuators disposed on an inner surface in accordance with some embodiments of the invention; 
         FIG. 6  is a perspective view of a component of an aircraft with a plurality of actuators disposed on the inner surface in accordance with an embodiment of the invention; 
         FIG. 7  is yet another perspective view of a component of an aircraft with a plurality of actuators disposed on the inner surface in accordance with an embodiment of the invention; 
         FIG. 8  is a graph of impedance vs. frequency that depicts multiple resonant frequencies of a component of an aircraft according to some embodiments of the invention; 
         FIG. 9  is a side profile view of a component cross section, in accordance with some embodiments of the invention; 
         FIG. 10  is a schematic diagram of an actuator strip in accordance with an embodiment of the invention; 
         FIG. 11  is a graph depicting actuator power consumption with respect to frequency, in accordance with some embodiments of the invention; 
         FIG. 12  depicts a plurality of actuator devices grouped into zones, in accordance with some embodiments of the invention; and 
         FIG. 13  is a flowchart depicting a method for inhibiting and/or removing ice from a component of an aircraft in accordance with other embodiments of the invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the invention. 
     DETAILED DESCRIPTION 
     The following description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of exemplary embodiments. The scope of the invention should be determined with reference to the claims. 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
     Referring first to  FIG. 1 , a system  100  is shown for use in removing and/or inhibiting the accretion of ice on an aircraft component surface, according to some embodiments of the invention. Specifically, the system  100  comprises a control unit  102 , wherein the control unit  102  further comprises: a microcontroller  104 , a wave generator  106 , an amplifier  108  and a power source  110 . The system  100  further comprises a coupling  112 , actuators  114 , a component  120  and a sensor  122 . One of skill in the art would understand that, depending on the embodiment, the system  100  could comprise additional or fewer actuators than are depicted in  FIG. 1 . Additionally, the wave generator  106  may comprise one or more wave generators; similarly, the amplifier  108  may comprise one or more amplifier circuits and the sensor  122  may comprise one or more sensing devices. 
     In the illustrated embodiment, the control unit  102  is configured such that the microcontroller  104  is coupled to the wave generator  106 ; the wave generator  106  being coupled to the amplifier  108  and wherein the power source  110  is further coupled to the amplifier  108 . In some embodiments, the control unit  102  is coupled to the coupling  112  wherein the coupling  112  is further coupled to each of the actuators  114 . In some embodiments, each of the actuators  114  will be further coupled to the sensor  122 , wherein the sensor  122  is also coupled to the microcontroller  104  of the control unit  102 . In the illustrated embodiment, the one or more actuator/s  114  are mechanically disposed on (or proximate to) the component  120 . For example, in some embodiments the one or more actuator/s  114  are each positioned on or proximate to the component  120  in a manner corresponding to a curvature of the surface of the component  120 . In some embodiments, the one or more actuator/s  114  can be embedded within the component  120 . For example, the one or more actuator/s  114  may be embedded within multiple layers of a composite material forming the component  120 . 
     The coupling  112  may comprise essentially any mechanism by which electrical signaling may be transmitted from the control unit  102  to one or more of a plurality of the actuators  114 . For example, the coupling  112  may comprise, but is not limited to: wires, switches or electrical connectors etc. In some embodiments, communication between the control unit  102  and the coupling  112  and/or communication between the coupling  112  and the one or more actuator/s  114  may be achieved using a wireless signal. Additionally, in some embodiments, the control unit  102  will be designed so as to minimize the mass of the control unit  102 . 
     In some embodiments, the control unit  102  will be designed so as to minimize the control unit  102  weight or mass with respect to the size and/or output of a power supply. For example, the control unit  102  may be designed to minimize the ratio of the control unit mass to the mass of power source  110 . By way of example, the control unit  102  may be designed such that the control unit  102  is configured to provide power and the one or more of the plurality of actuators are configured to operate at a power to actuator-area ratio of no more than about 0.1 watts per square centimeter. In some embodiment, the total system power does not to exceed 2 kW per aircraft. In some embodiments, the power to actuator-area ratio will be approximately 0.03 watts per square centimeter. In some embodiments, the control unit  102  will weigh less than an absolute amount; by way of example, the control unit  102  may be constructed so as to not exceed a weight of 25 pounds. Furthermore, in some embodiments the control unit may be configured so as to not exceed a specific weight to power output ratio. For example, in some embodiments the control unit  102  may be configured to have a weight to power output ratio of less than 0.0125 lbs per watt. In some embodiments, the control unit  102  may be configured to have a weight to power output ratio of less than 0.01 lbs per watt. In some embodiments the control unit  102  may be configured to have a weight to power output ratio of less than 0.005 lbs per watt. 
     In some embodiments, each of the one or more actuator/s  114  may comprise one or more electrically driven spherical piezo-kinetic actuators. According to some embodiments the one or more actuator/s  114  may be flexible able to substantially conform to the curvature of a surface (e.g., a curvature of the component  120 ). 
     According to some embodiments, the component  120  may comprise an isotropic or composite material such as an alloy, carbon fiber, graphite, a polymer, a thermoplastic or a fiberglass, etc. For example, in some embodiments, the component  120  may comprise, but is not limited to, one or more aircraft components and/or flight surfaces such as an aircraft wing, an aircraft tail, an airfoil, an aircraft rudder, an aircraft control surface (such as a flap or elevator), a wind turbine blade, an engine intake surface, or a helicopter rotor blade, etc. By way of example, the one or more actuator/s  114  may be embedded within one or more layers of a composite material forming an aircraft component. For example, the one or more actuator/s  114  may be disposed proximate to (or embedded within) a composite leading edge of an aircraft component (such as an airplane wing or unmanned aerial vehicle airfoil or wing) with respect to a direction of flight of the aircraft. 
     In practice, the system  100  functions to inhibit and/or prevent the deposit of ice and/or functions to remove existing ice, from the component  120 , by vibration of the component  120  accomplished with the actuation of one or more of the actuator/s  114 . Actuation of one or more of the actuator/s  114  may be controlled by the control unit  102  via signaling received via the coupling  112 . By way of example, the wave generator  106  can generate a signal at a desired frequency for use in vibrating the one or more actuator/s  114  causing actuation of the component  120 . More specifically, when the signal of wave generator  106  is received by the amplifier  108  (and amplified using power source  110 ), the resulting amplified signal is then input to the coupling  112  and then received by the one or more actuator/s  114 . In some embodiments, receipt of a periodic signal by the one or more actuator/s  114  will result in actuation of the one or more actuator/s  114  causing a transfer of mechanical energy into the component  120 . In some embodiments, this transfer of mechanical energy provides a displacement of a portion of the component in three dimensions which inhibits the formation of ice (or other debris) and/or breaks up and removes existing ice formed on the portion of the component surface. 
     In accordance with some embodiments, the one or more actuator/s  114  will be disposed on the component  120  (e.g., the leading edge of an airfoil/aircraft wing with respect to a direction of flight). Upon receipt of signaling from the coupling  112 , the one or more actuator/s  114  will be actuated at a frequency determined by the wave generator  106 , resulting in a transfer of vibrational mechanical energy, in three dimensions (e.g., x, y and z directions), into the surface of the component  120 . By way of example, the one or more actuator/s  114  can be positioned relative to the component  120  such that actuation of the one or more actuator/s  114  will cause in-plane, out-of plate bending to occur in the surface of the component  120  (i.e., deformations in three dimensions including transverse and longitudinal directions). 
     In some embodiments, the actuation of the one or more actuator/s  114  may be used to at least partially inhibit the formation of ice on a surface of the component  120  (e.g., an aircraft wing) and/or for use in removing ice that has already deposited on the surface of the component  120 . As would be appreciated by one of skill in the art, ice is only one form of debris for which embodiments the invention may be used; however, accretions other types of debris (such as, but not limited to, dirt and oil) may also be removed and/or inhibited using some embodiments of the invention. Additionally, as would be appreciated by one of skill in the art, some methods and applications of embodiments of the invention may be applied to a component or surface that is not part of an aircraft. 
     In some embodiments, the actuation frequency of the one or more actuator/s  114  will be controlled by the microcontroller  104  based on feedback received from the sensor  122 . That is, the control unit  102  can be configured such that the control unit  102  is coupled to at least one sensor (such as the sensor  122  of  FIG. 1 ) and configured to switch a driving frequency of the one or more actuator/s  114  based on signaling received from the sensor  122 . Alternatively, in some embodiments the control unit  102  may be configured to drive the one or more actuator/s  114  automatically (and independent of) signaling received from the sensor  122 . 
     By way of example, the sensor  122  may sense/detect the operational or resonant frequency along one or more location/s of the component  120 . This measured resonant frequency of the component  120  may then be used by the microcontroller  104  to tune the frequency of the signal generated by the wave generator  106 . In turn, the control unit  102  will actuate the one or more actuator/s  114  at a frequency at, or near, the resonant/operational frequency of the component  120  (at or near their respective locations). The operational or resonant frequency of a position along the component  120  may be affected by many factors, including but not limited to the mass, composition and/or the geometry/shape of the component  120 . 
     Additionally, in some embodiments, at least one sensor (e.g., the sensor  122 ) will be coupled to one or more actuators (e.g., the one or more actuator/s  114 ) and configured to sense an impedance of the one or more actuator/s  114  when the actuator is being driven by the control unit  102 . Similarly, in some embodiments, the control unit  102  can be configured to drive the one or more actuator/s  114  at a predetermined power consumption rate such that the actuators do not exceed the predetermined power threshold. By way of example the one or more actuator/s  114  may be driven in such a manner so as not to exceed a specific power to surface area ratio. 
     In some embodiments, actuation of the one or more actuator/s  114  at the resonant frequency of the component  120  will more effectively remove and/or prevent the formation of ice on the surface of the component  120 , than would actuation at other, non-resonant, frequencies. In some embodiments, actuation of the one or more actuator/s  114  will be effective for removing ice deposits/preventing ice formation on the component  120  surface when actuated at lower frequencies, for example, between 1 Hz and 1 kHz. In some embodiments, actuation of the one or more actuator/s  114  will be effective for removing ice deposits/preventing ice formation on the component  120  when actuated at a frequency between 10 Hz and 500 Hz. In some embodiments, actuation of the one or more actuator/s  114  will be effective for removing ice deposits/preventing ice formation on the component  120  when actuated at between 55 Hz and 235 Hz. In some embodiments, actuation of the component  120  surface in the lower frequency ranges will not only reduce power consumption (relative to actuation at high frequencies) but will more effectively displace the component  120  surface, effectively removing and preventing the accretion of ice (or other debris). Thus, in some forms, lower mass or weight components can be provided relative to higher frequency systems. 
     Referring next to  FIG. 2 , a flowchart is shown that depicts a method for designing a component of an aircraft for use in removing existing ice and/or inhibiting the formation of ice on the component, in accordance with one embodiment of the invention. This method will be described with occasional reference to the de-icing system depicted by  FIG. 1 ; however, it is to be understood that the method  200  is not limited to the depicted system of  FIG. 1 , or any other system. 
     The method  200  begins with step  202  which entails identifying the component and material. In some embodiments, identification of the component and material will include identifying the surface shape and/or composition of the component. Identification of the component may further involve identifying the shape and/or temperature of an aircraft surface structure that is (or will be) exposed during flight of the aircraft. In some embodiments, the component will comprise the leading edge of an aircraft component with respect to a direction of flight, e.g., the leading edge of an aircraft wing etc. 
     In step  204 , the component is modeled and the resonant frequencies of the component are determined. In some embodiments, the resonant frequencies of the component may be determined using one or more sensors, for example similar to the sensor  122  described above with respect to  FIG. 1 . In one embodiment, the model of the component is used to determine the resonant frequency of the surface of the component, which may be a function of one or more variables including, but not limited to, the shape/geometry of the component&#39;s surface and/or the material composition of the component etc. 
     As would be appreciated by one of skill in the art, there may be several ways to model a component and/or component surface in order to determine one or more resonant frequencies. For example, in some embodiments, the approximate resonance of a component and/or component surface may be determined by attaching one or more actuators to the component/component surface and performing a vibrational analysis (e.g., using Finite Element Analysis) to determine one or more resonance frequencies of the component and/or component surface. 
     In some embodiments, resonance frequencies of a component and/or component surface may be determined using a sensor (e.g., the sensor  122  as discussed above in the system  100  of  FIG. 1 ) for running a constant impedance analysis in the desired frequency zones. By way of example, sensors (such as the sensor/s  122 ) may be attached to the component and used to determine the impedance of the component as the frequency is operated at between 1 Hz and 1 kHz. In some embodiments, the sensors attached to the component and/or component surface may perform constant impedance analysis of the component and/or component surface as the one or more actuators are actuated at one or more frequencies of actuation between 10 Hz and 500 Hz. In some embodiments, the sensors attached to the component may perform constant impedance analysis of the component and/or component surface as the one or more actuators are actuated at one or more frequencies of actuation between 55 Hz and 235 Hz. 
     In some embodiments, the structural resonance of a component and/or component surface may be determined using one or more actuators and/or accelerometers and actuator resonance may be determined using an impedance measurement. However, as would be appreciated by one of skill in the art, the component resonance will change when one or more actuators are coupled to the component surface. 
     In step  206 , one or more actuators are attached to the component. In some embodiments, the actuators will be attached an inner surface of the component. For example, the component may comprise an inner facing portion (e.g., an airfoil like such as an aircraft wing) and the actuators may be attached to either the outer facing or inner facing surfaces of the air foil. However, in some embodiments, the actuators will be attached to the inner facing surfaces at regularly spaced intervals and/or one or more actuators may be positioned within a composite material, as will be discussed in further detail below. 
     Furthermore, in some embodiments the actuators will be mechanically disposed on a surface of the component such that actuation of the actuators will mechanically displace the component in an out-of-plane (three-dimensional) motion without causing structural damage to the component. By way of example, the actuators may be disposed on the component such that actuation will cause a three dimensional force to be transferred to the surface of the component. 
     One or more actuators (e.g., the one or more actuators  114  of  FIG. 1 ) may be disposed on the component in essentially any arrangement, depending on embodiment. In some embodiments, a plurality of actuators may be arranged on the component in a pattern extending across at least a portion of the component&#39;s surface. As will be discussed in further detail below with respect to  FIG. 12 , in some embodiments, a plurality of actuators may be arranged in a plurality of zones on the component, wherein each zone corresponds to a respective region of the component&#39;s surface. 
     In step  208 , the one or more determined resonant frequencies of the component (as determined in step  204 ) are tested by actuating the actuators attached in step  206 , as will be discussed in further detail with respect to  FIG. 8 , below. In some embodiments, the relative resonant frequencies of the component will vary by location on the component. Thus, in some embodiments, each actuator will be actuated at (or near) the frequencies corresponding to the resonant frequencies of the component at that respective actuator&#39;s position on the component. 
     In step  210 , one or more of the actuators will be actuated (driven) to remove existing ice from the component and/or to inhibit the accretion of new ice deposits on the component. In some embodiments, this is done to verify that the device will actually work before put into operational use. In practice, the actuators may be actuated/driven for essentially any duration of time and in any pattern; however, in some embodiments the actuators will be actuated for a duration ranging between 0.001 seconds and 10 seconds, e.g., in the interest of minimizing power consumption. In some embodiments, the actuators will be actuated at one or more frequencies of actuation between 1 Hz and 1 kHz. In some embodiments, the actuators will be actuated at one or more frequencies of actuation between 10 Hz and 500 Hz. In some embodiments, the actuators will be actuated at one or more frequencies of actuation between 55 Hz and 235 Hz. 
       FIG. 3  is a flowchart depicting a method  300  for inhibiting and/or removing ice from a component of an aircraft in accordance with yet another embodiment of the invention. Although, this method will be described with occasional reference to the de-icing system (e.g., the system  100  depicted in  FIG. 1 ), but it should be understood that the disclosed method is not limited to the system  100 , or any other system. 
     The method  300  of  FIG. 3  begins with determining icing conditions, as depicted in step  302 . In some embodiments, the determination of icing conditions is made with respect to the icing conditions on an outer facing surface of the component. In some embodiments, this determination may be made using one or more sensors such as the sensors  122  depicted in  FIG. 1 . Furthermore, icing conditions may be determined using a variety of other sensors; by way of example, this determination may be based on, but is not limited to, information received from one or more temperature, altitude, humidity, wind speed and/or moisture sensors etc. 
     In step  304 , one or more actuators are driven (actuated) according to parameters defining a mode of operation to remove existing ice and/or to inhibit the formation of ice on the surface of the component. Actuation of the actuator results in a displacement of the surface in three dimensions to inhibit a formation of ice on at least the portion of the surface and/or to break up existing ice formations on at least the portion of the surface. In some embodiments, the actuators will be driven at one or more frequencies of actuation between 1 Hz and 1 kHz. In some embodiments, the actuators will be driven at one or more frequencies of actuation between 10 Hz and 500 Hz. In some embodiments, the actuators will be driven at one or more frequencies of actuation between 55 Hz and 235 Hz. 
     In some embodiments, the mode of operation will be controlled by a control unit such as the control unit  102  illustrated in the block diagram of  FIG. 1  (above). By way of example, the control unit  102  may receive, from one or more sensor devices, an indication that ice has formed on a component such as the component  120  depicted in  FIG. 1 . Receipt of a positive ice formation indication may originate from one or more sensors, such as the sensor  122  depicted in  FIG. 1 , or alternatively, may originate from one or more sensor/s and or indication means external to (and not depicted by) the system  100  of  FIG. 1 . 
     Alternatively, in some embodiments one or more sensors may be used to indicate the existence of conditions under which the likelihood of ice formations would be increased. By way of example, one or more sensor/s may detect conditions (e.g., altitude, temperature and or humidity) under which ice accretions may form. Given such an indication, one or more of the actuator/s  114  can be actuated to at least partially inhibit or prevent ice formation. By way of example, the control unit  102  of the system  100  of  FIG. 1  may receive an indication that ice has already formed, or is likely to form, on a surface of the component  120 . Based on this indication, the control unit  102  can drive the one or more actuators  114  via coupling  112 . 
     In some embodiments, actuation of the actuators (e.g., the one or more actuators  114  as depicted in  FIG. 1 ) may occur simultaneously. In other embodiments, the microcontroller  104  may control the actuation of different actuators such that the actuators are actuated according to a pattern. For example, the microcontroller may activate the one or more actuators  114 , so that actuation occurs in stages e.g., in essentially any “sweeping” pattern, depending on actuator arrangement. 
     In some embodiments, wherein the plurality of actuators are arranged on the component in a plurality of zones, the control unit (e.g., the control unit  102  of FIG.  1 ) may be configured to selectively drive the plurality of actuators of each of the plurality of zones in time relative to the others of the plurality of zones. 
     Furthermore, in some embodiments, the frequency of the output signal generated by the wave generator  106  may be varied in order to cause a corresponding variation in the frequency of actuation e.g., in the one or more actuators  114 . Thus, a control unit (e.g., the control unit  102  of  FIG. 1 ) may be used to vary the speed of actuation (i.e., to control frequency “sweeping”) of one or more of the plurality of actuators, such as the one or more actuators  114  of  FIG. 1 . 
     Additionally, actuation of the one or more actuators on the component may occur simultaneously or may be performed in phases such that some actuators are activated at different time intervals and for different durations of time with respect to other of the actuators. In some embodiments, actuation of individual actuators will occur in stages, so as to “sweep” the surface of the component. For example, driving frequencies may be adjusted based on impedance measurements from one or more sensors, such as the sensors  122  discussed above with respect to  FIG. 1 . Additionally, in some embodiments the control unit (e.g., the control unit  102  of  FIG. 1 ) may drive actuation of two or more of the plurality of actuators in time, in a sequence relative to each other, such that actuation of the actuators occurs in a specific pattern. 
     In some embodiments, wherein the plurality of actuators are arranged by zones, actuation may be driven on a zone by zone basis. For example, the control unit may be configured to selectively (and simultaneously) drive a plurality of actuators wherein the actuators are grouped into different zones (corresponding to different regions on the component) such that the actuators of each of the plurality of zones are driven sequentially in time relative to the actuators of the other zones. 
     In some embodiments, a control unit (e.g., the control unit  102  of  FIG. 1 ) may be configured to control actuation of one or more of the actuators at one or more predetermined frequencies. For example, the control can be configured to selectively drive one or more of the actuators at a plurality of predetermined frequencies within a predetermined time period, or may be configured to “sweep” over a range of frequencies. For example, a control unit (such as the control unit  102  of  FIG. 1 ) may be configured to selectively drive two or more of the plurality of actuators in time in a sequence relative to each other, the two or more of the plurality of actuators arranged in a pattern extending from one portion of the surface in a linear sweep to another portion of the surface. 
     In optional step  306 , the control unit parameters affecting actuation frequency and actuation pattern/location may be adjusted based on one or more sensed conditions. By way of example, one or more sensors (e.g., the sensor  122  as depicted in  FIG. 1 ) may send signals back to the control unit related to present or changing conditions of the component. For example, driving frequencies may be adjusted based on impedance measurements from the sensors  122 . 
     In some embodiments, the resonant frequencies of the component may change as the component is acted upon by outside forces (e.g., wind, water, thermal expansion/compression, etc.). For example, the sensed conditions of the component may pertain to whether or not ice accretions are built up on a surface of the component and actuation parameters may be adjusted based on the amount of ice buildup or on the basis of other factors such as temperature, humidity, wind speed, moisture level, pressure and/or the geometric characteristics and/or shape of the component, etc. In some embodiments, adjusted parameters will enable the control unit to actuate one or more actuators in a manner that is more effective for the removal of ice, or prevention of ice formation, on the component (e.g., actuation at the component&#39;s resonant frequency). After one or more actuators have been actuated to remove and/or inhibit the formation of ice on the component, the method proceeds to step  308 . 
     In step  308  the removal of icing conditions is determined. The removal of icing determination may be made by one or more sensors (e.g., the sensor  122  as depicted in  FIG. 1 ). Alternatively, in some embodiments, the determination of de-icing may be made with other sensors or detection means not depicted in the system  100  of  FIG. 1 . For example, at known altitudes and temperatures, icing conditions may not be known to occur, however icing conditions may be determined by altimeter and/or temperature data from other parts of the aircraft. Upon, determining that ice has been adequately removed from the component, the method  300  proceeds to step  310  wherein the driving of the one or more actuators is terminated. 
       FIG. 4  illustrates a component  400  comprising an inner surface  402 , an outer surface  404  and a plurality of actuator strips  406 . In some embodiments, one or more of the plurality of actuator strips  406  will be disposed on the component&#39;s inner surface  402 . In some embodiments, the actuator strips  406  will be comprised of a flexible material that will be capable of substantially conforming to a curved surface, such as the curved surface of an aircraft component. For example, in some embodiments, the actuator strips  405  may comprise a Macro Fiber Composite such as part number M8557P1 made by Smart Material Corporation of Sarasota, Fla. (see also_http://www.smart-material.com/MFC-product-main.html, which is incorporated herein by reference). 
     Although  FIG. 4  illustrates three (shown) actuator strips  406  at regularly spaced intervals, there may be essentially any number of actuator strips which may be arranged on (or proximate to) the component&#39;s inner surface  402  in virtually any pattern. For example,  FIG. 6  illustrates a component  400  with (six shown) actuator strips  406  disposed on the inner surface  402  of the component  400 . 
     In some embodiments the actuator/s and/or actuator strip/s will be spaced in such a manner so as to provide optimal performance and reliability while still minimizing the number of actuators required. Furthermore, the spacing of one or more actuators and/or actuator strips may be unique to each component, depending on how the component behaves at each resonance mode. 
     In some embodiments, each of the plurality of actuator strips will comprise one or more actuators. As discussed above, the component  400  may be composed of an isotropic or composite material; however, in some embodiments the component  400  will form an airfoil, such as the leading edge of an aircraft component with respect to the an aircraft direction of flight (e.g., the leading edge of an aircraft wing). However in alternative embodiments, the component  400  may form essentially any aircraft component or structure including, but not limited to: an aircraft tail, an aircraft rudder, an aircraft control surface such as a flap or an elevator, a wind turbine blade, a helicopter rotor blade and/or a refrigeration coil cooling fin etc. 
     In practice, when one or more of the plurality of actuators is driven within one or more of the actuator strips  406 , a force will be exerted in three dimensions relative to the surface plane of the component  400 . For example, when one or more of the actuator strips  406  are actuated, a force will be imparted upon the inner surface  402  of the component  400  causing a mechanical displacement in the component  400  in three dimensions (i.e., transverse and longitudinal directions). 
       FIG. 5  illustrates a component  400  comprising an inner surface  402 . The component  400  further includes six actuator strips  504  disposed at regular intervals on the inner surface  402  of the component  400 , according to some embodiments of the invention. However, in some embodiments, a greater (or lesser) number of actuators may be disposed on the outer surface of the component and may be positioned in virtually any pattern or arrangement. For example,  FIG. 7  illustrates a component  400  comprising twelve actuator strips  504  disposed on an inner surface  402  of the component  400 . 
     Referring next to  FIG. 8 , which illustrates a graph  800  of impedance vs. frequency is shown depicting resonance points (i.e., modes)  802 ,  804 ,  806  and  808  of a component, over varying frequencies (x-axis). The impedance is in units of decibel Volts (dBV). An input signal  810  applied to the component is shown and the resulting impedance output signal  812  is displayed. The peaks of the output signal  812  are the points of lowest relative impedance such that each peak corresponds to a resonant frequency of the component. By way of example, the output signal  812  illustrates that the component has a first resonance point  802  at a frequency of about 78 Hz; a second resonance point  804  at a frequency of about 201 Hz; a third resonance point  806  at a frequency of about 207 Hz; and a fourth resonance point  808  at a frequency of about 235 Hz. 
     In practice, once the resonant frequencies have been determined, one or more actuators may then be driven at, or near, a determined resonance frequency of the component in order to cause maximal in-plane, out-of-plane bending/deformation, resulting in at least the partial removal of ice accretions and/or at least partially inhibiting the formation of new ice on the surface of the component. 
       FIG. 9  illustrates a cross-sectional side-perspective view of a component  400  together with actuator strips  504  disposed on the inner surface of the component  400 . As discussed above, when the one or more of the actuator strips  504  are driven (actuated), a three dimensional bending/deformation will result in the surface of the component  400 . In some embodiments each strip could contain only a single actuator element; however, in some embodiments, each of the actuator strips will contain a plurality of actuators. For example,  FIG. 10  illustrates a single actuator strip  1000  connected to a driving power source  1002  and a plurality of (fourteen total) actuators  114 . 
     Although the plurality of actuators  114  depicted in  FIG. 10  totals fourteen, a greater or lesser number of actuators may be disposed in a single actuator strip. As illustrated, the plurality of actuators  1004  are connected, in parallel, to the power source  1002 . 
     In practice, each actuator element of the plurality of actuators  1004  may be modeled as an RC circuit; thus, in some embodiments of the invention the plurality of actuators may be modeled as a capacitive element. 
       FIG. 11  illustrates a graph  1100  of the power consumption in watts (y-axis) of one or more actuator elements with respect to frequency (x-axis). For example, the graph  1100  depicts the power consumption with respect to frequency of a single actuator element driven at 1.5 kV  1102 ; a single actuator element driven at 4 kV  1104 ; four actuator elements driven simultaneously at 1.5 kV  1106 ; four actuator elements driven simultaneously at 4 kV  1108 ; six actuator elements driven simultaneously at 1.5 kV  1110 ; and six actuator elements driven simultaneously at 4 kV  1112 . The power consumption at a given frequency (illustrated in the lines of  FIG. 11 ) can be appreciated by those of skill in the art, through the relationship between a sine wave input and the impedance (Z) of a component according to Equation (1): 
     
       
         
           
             Z 
             = 
             
               
                 1 
                 
                   2 
                    
                   π 
                    
                   
                       
                   
                    
                   f 
                 
               
                
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   n 
                 
                  
                 
                     
                 
                  
                 
                   C 
                   i 
                 
               
             
           
         
       
     
     where Z=impedance (ohms) of the component, f=frequency (Hz) and C=capacitance of the actuator (farads). Furthermore, as would be appreciated by those of skill in the art, the peak power (Ppk) of a component can then be calculated using Equation (2): 
     
       
         
           
             
               P 
               pk 
             
             = 
             
               
                 V 
                 2 
               
               Z 
             
           
         
       
     
     where P pk =peak power (watts); Z=the impedance calculated in Equation 1 (ohms) and V=the maximum positive voltage (volts). Finally, the RMS power can be calculated using Equation (3): 
     
       
         
           
             
               P 
               rms 
             
             = 
             
               
                 1 
                 
                   2 
                 
               
                
               
                 P 
                 pk 
               
             
           
         
       
     
     where P rms =power (watts) and P pk =peak power from Equation 2 (watts). In some embodiments, the voltage of the input signal is known and the impedance is measured, such that the peak and rms power can be calculated using Equations (2) and (3). The power illustrated in  FIG. 11  is the rms power, P rms . 
     Although one or more actuator elements may be driven in essentially any pattern in a wide range of frequencies, in some embodiments actuators will be driven in a manner that most effectively removes and/or inhibits ice accretion while also minimizing the number of actuators required and the amount of power consumed consumption. In some embodiments, actuation of one or more actuator/s (e.g., the actuators  114  of  FIG. 1 , above) will be effective for removing ice deposits/preventing ice formation on a component surface when actuated at one or more frequencies, for example, between 1 Hz and 1 kHz. In some embodiments, actuation of the one or more actuator/s  114  will be effective for removing ice deposits/preventing ice formation on the component  120  when actuated at one or more frequencies between 10 Hz and 500 Hz. In some embodiments, actuation of the one or more actuator/s  114  will be effective for removing ice deposits/preventing ice formation on the component  120  when actuated at one or more frequencies between 55 Hz and 2435 Hz. 
     Referring next to  FIG. 12 , which illustrates a component surface  1200 , an airfoil center line  1205 , a plurality of individual actuators  114  arranged in a total of six zones  1220 ,  1230 ,  1240 ,  1250 ,  1260  and  1270 . Although  FIG. 12  illustrates the division of the individual actuators  114  into six zones ( 1220 ,  1230 ,  1240 ,  1250 ,  1260  and  1270 ), one of skill in the art would appreciate that one or more zones may be arranged to include any (or all of) the individual actuators  114  and that the zones may be arranged in essentially any pattern or design on the component surface  1200 . For example, the individual actuators  114  could be separated into different zones with respect to the airfoil center line  1205 . Additionally, one or more zones may be arranged to include two or more of the individual actuators  114 , irrespective of whether or not the two or more actuators are adjacently located on the component surface  1200 . 
     In practice, a control unit (not shown) can be configured to drive actuation of the actuators of any particular zone at a specific time and/or over a constant or varying frequency range. For example, a control unit (e.g., the control unit  102  as depicted in  FIG. 1 ) may be configured to selectively drive each actuator for a time period of between about 0.001 seconds to 10 seconds. In another example, the control unit may be configured to selectively drive each actuator for a time period corresponding to between about 1 to 10 periods of a sinusoidal, triangle, square, and pulse wave of a driving frequency. 
     By way of further example, a control unit (e.g., the control unit  102  as depicted in  FIG. 1 ) may drive zone activation such that the actuators are driven in a “sweeping” motion from left to right across the component surface  1200 . For example, the control unit  102  may drive the individual actuators  114  of zone  1220 , and then successively drive the individual actuators  114  of remaining zones  1230 ,  1240 ,  1250 ,  1260  and  1270 . In some embodiments, actuation of the individual actuators  114  associated with a particular zone may overlap in time with actuation of the individual actuators  114  of a different zone. In some embodiments, the actuation of the individual actuators  114  of a particular zone will not overlap in time with the actuation of the individual actuators  114  of another zone. 
     In some embodiments, actuation of individual zones may occur in a pattern that skips one or more adjacent zones. For example the control unit  102  may successively drive the individual actuators  114  of zones  1220 ,  1240 ,  1260  and then successively drive the individual actuators  114  of remaining zones  1230 ,  1250 ,  1260  and  1270 . By way of another example, the control unit  102  may successively drive the individual actuators  114  of zones  1240 ,  1230  and  1220  while simultaneously and successively driving the individual actuators  114  of zones  1250 ,  1260  and  1270 . As such, the control unit may be configured to selectively drive at least two adjacent actuators of the plurality of actuators at sequential times. Alternatively the control unit may be configured to sequentially drive at least two non-adjacent ones of the plurality of actuators at sequential times. 
     In some embodiments, the control unit  102  will be configured to drive the actuation of the individual actuators  114  associated with different zones at an essentially constant frequency. By way of example, the control unit may be configured to drive each zone at one or more frequencies corresponding to one or more determined resonance frequencies of a proximately located component. 
     In some embodiments, the control unit may be configured to drive different zones at different frequencies or to drive actuation over a range of frequencies with respect to a unit of time. By way of further example, a control unit may be configured to drive the individual actuators  114  of zones  1220 ,  1230  and  1240  at a first frequency corresponding to a first mode/resonance frequency of the component, wherein the individual actuators  114  associated with the zones  1250 ,  1260  and  1270  will be driven at a second mode/resonance frequency of the component. 
     One of skill in the art should appreciate that zone activation may occur in virtually any pattern with virtually any combination of activation durations. However, in some embodiments the zone boundaries, zone activation sequence (and duration) and zone actuation frequency variation will be controlled in such a manner so as to effectively remove and/or inhibit the formation of ice on the component surface while minimizing power consumption and total actuator count. As would be appreciated by one of skill in the art, generally less power will be consumed when actuating one or more actuators at lower frequencies, as opposed to actuating the same actuators at high frequencies (e.g., ultrasonic frequencies). Furthermore, as would also be appreciated by those of skill in the art, actuation of one or more actuators at (or near) the resonant frequencies of a component surface will induce greater displacement in the component surface, per unit of power, relative to actuation at non-resonant frequencies of the component surface. Additionally, as would be further appreciated by one of skill in the art, in some embodiments, driving actuation of one or more zones successively in time will consume less power than driving actuation of all actuators simultaneously; thus, the ability to control actuation by zone will yield greater control over the power output that need be expended, and will potentially reduce the size of the power supply necessary to carry out some embodiments since less power will be required at any given point in time. 
       FIG. 13  illustrates a flowchart depicting a method for inhibiting and/or removing ice from a component of an aircraft in accordance with other embodiments of the invention. The method  1300  begins with determining icing conditions, as depicted in step  302 . In some embodiments, the determination of icing conditions is made with respect to the icing conditions on an outer facing surface of the component. In some embodiments, this determination may be made using one or more sensors such as the sensors  122  depicted in  FIG. 1 . Furthermore, icing conditions may be determined using a variety of other sensors; by way of example, this determination may be based on, but is not limited to, information received from one or more temperature, altitude, humidity, wind speed and/or moisture sensors etc. In some embodiments, the icing conditions of a surface of the component may be based, at least in part, on a measured impedance of a surface of the component. 
     Steps  1320 ,  1330 ,  1340  and  1350  provide embodiments of example methods of driving actuators; for example, they provide examples of step  304  of  FIG. 3 . 
     The method  1300  proceeds to optional step  1320  which involves driving one or more of a plurality of actuators at a constant resonant frequency. As would be understood by one of skill in the art, a component may have multiple modes/resonant frequencies. In some embodiments, one or more of a plurality of actuators will be driven at the same frequency corresponding to the same mode/resonance frequency of a component. In some embodiments one or more of a plurality of actuators will be driven at different frequencies wherein each actuation frequency corresponds to a different mode (yet a resonance frequency) of the component. Additionally, one or more of a plurality of actuators may be driven at a resonant frequency wherein the resonant frequency corresponds to a resonant frequency of the component proximate to that respective actuator. Alternatively, in some embodiments of the invention, one or more of a plurality of actuators may be driven at a non-resonant frequency or near a resonant frequency. 
     In optional step  1330 , one or more of a plurality of actuators will be driven while sweeping across a dimension of the surface (e.g., a surface of the component). As discussed above with respect to  FIG. 12 , a plurality of actuators may be driven at either different or overlapping times in a “sweeping” manner, across one or more surfaces or components. 
     In optional step  1340 , one or more of a plurality of actuators will be driven while sweeping the driving frequencies of at least one actuator. In some embodiments, the actuation frequency of an actuator, or a plurality of actuators, may be required in response to changing resonance conditions of the component. For example, a component, such as an aircraft wing surface, may be subject to changing environmental conditions during flight. As would be appreciated by one of skill in the art, the resonance properties of the component (aircraft wing) may vary due to factors such as temperature, altitude, moisture and the affect of ice accretions etc. In response to changing resonance conditions, in some embodiments it may be advantageous to vary (sweep) the driving frequency of one (or more) actuators to correspond to a new or changing resonance frequency of the component. 
     Additionally, in some embodiments, due to power consumption factors, it may be advantageous to change the driving frequency of one or more actuators to either reduce (or increase) net power consumption. 
     In optional step  1350 , a plurality of actuators are driven on a zone-by-zone basis. As discussed above with respect to  FIG. 12 , each actuation device may be included into essentially any group of actuation devices (i.e., included in any zone). In some embodiments, due to power consumption (or other concerns), it may be advantageous to activate zones by location rather than activating all actuation devices simultaneously. As would be appreciated by one of skill in the art, zone actuation may occur in essentially any pattern in any timing scheme and with any duration. However, in some embodiments, zone activation will occur so as to achieve balance between efficiently removing and/or inhibiting ice accretions on a component while minimizing power consumption. 
     In optional step  1360 , a determination/sensing of icing conditions is made. In some embodiments, this determination will be made with respect to the icing conditions on an outer facing surface of a component. In some embodiments, this determination may be made using one or more sensors such as the sensors  122  depicted in  FIG. 1 . Furthermore, icing conditions may be determined using a variety of other sensors; by way of example, this determination may be based on, but is not limited to, information received from one or more temperature, altitude, humidity, wind speed, impedance and/or moisture sensors etc. In some embodiments, the icing conditions of a surface of the component may be based, at least in part, on a measured impedance of a surface of the component. Based on the determined conditions, the driving mode and/or driving frequency of one or more actuators and/or actuation zones may be adjusted. By way of example, driving mode/frequency may be adjusted into any of the modes described in steps  1320 ,  1330 ,  1340  or  1350  described above. 
     In step  308 , a determination will be made regarding the removal of icing conditions. This determination may pertain to the removal of prior accreted ice, or may be made with respect to the likelihood of new ice formations, for example based on one or more factors, including but not limited to: temperature, altitude, humidity, wind speed, impedance and/or moisture etc. In some embodiments, once a removal of ice from the component is verified, the method  1300  will proceed to step  310  wherein the driving of the one or more of the plurality of actuators is terminated. 
     The described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. As such, the following descriptions are not to be taken in a limiting sense, but are made merely for the purpose of describing the general principles and exemplary embodiments of the instant invention. The scope of the invention should be determined with reference to the claims.