Patent Publication Number: US-2023161154-A1

Title: Ultrasound lens structure cleaner architecture and method using standing and traveling waves

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/064,645 filed on Oct. 7, 2020, which is also a continuation of U.S. patent application Ser. No. 15/395,665, filed on Dec. 30, 2016 (now U.S. Pat. No. 10,838,199 issued on Nov. 17, 2020), the contents of which are herein incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The preferred embodiments relate to various systems where debris or contaminants are to be removed from lens-related apparatus in the system, and more particularly to an ultrasound architecture and method in such a system. 
     A lens structure as used in this document is intended to include a lens, lens cover, or other surface through which a signal (e.g., light) may pass, and where the apparatus is exposed to potential contaminants that may reduce the likelihood of successful signal passage through the apparatus. As one prominent example, in the automotive industry, cameras are assuming an important role in both Driver-Assisted Systems (DAS) and automatic safety systems. This technology commonly first appeared in relatively expensive vehicles and has migrated to less expensive ones. Indeed, the National Highway Traffic Safety Administration (NHTSA) has mandated that all new cars must be outfitted with rear view cameras by 2018. Cameras are also now being incorporated into side view mirrors to assist drivers with lane changes and currently under consideration by at least one automobile manufacturer is the possible replacement of vehicle side view mirrors with side view cameras. Besides alleviating blind spots for the driver, front cameras integrated into the windshield provide Forward Collision Warning (FCW), Following Distance Indication (FDI), and Lane Departure Warnings (LDW). Of course, lens structures also may be used in other implementations, including, for example, outdoor surveillance cameras and lighting systems. 
     In the above context and others, and as the trend toward additional lens structures increase or become more ubiquitous, keeping the lens structure (e.g., lenses and lens covers) free of contaminants becomes a more prevalent need and is particularly important in safety-related applications. Further, the location, accessibility, or the user interest may prove inconvenient for manual cleaning of the lens, so that automated approaches may be desirable. As one prior art approach to this issue, several manufacturers have considered a miniature spray and wiper system. This design, however, requires (1) a small pump and nozzle; (2) a motorized wiper assembly; and (3) a running a hose from a fluid tank to the location of the nozzle, which may necessitate a run from the vehicle front where a fluid tank is typically located, to the vehicle back, at least for the rear view camera, which is typically located at the rear of the vehicle. As a result, this design is mechanically complex and potentially expensive. 
     Given the preceding, the present inventors seek to improve upon the prior art, as further detailed below. 
     BRIEF SUMMARY OF THE INVENTION 
     In a preferred embodiment, there is a lens structure system. The system comprises a lens structure and a multi-segmented transducer coupled to the lens structure. Each segment in the plurality of segments comprises a first conductor and a second conductor, wherein the first conductor and the second conductor are electrically coupled to the segment. The system also comprises circuitry for applying a voltage to selected segments in the plurality of segments, wherein the circuitry for applying a voltage comprises circuitry for applying a voltage with standing wave signals and circuitry for applying a voltage with traveling wave signals. 
     Numerous other inventive aspects are also disclosed and claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG.  1 A  illustrates a preferred embodiment system in a perspective exploded view. 
         FIG.  1 B  illustrates a top view of the ultrasonic transducer of  FIG.  1 A . 
         FIG.  1 C  illustrates the lens cover affixed atop the upper annular surface of an ultrasonic transducer. 
         FIGS.  2 A and  3 A  illustrate perspective views, and  FIGS.  2 B and  3 B  illustrate side views, of a membrane MEM and its mode shape diagrams of a first mode (0,1) shape. 
         FIGS.  4 A and  5 A  illustrate perspective views, and  FIGS.  4 B and  5 B  illustrate side views, of a membrane MEM and its mode shape diagrams of a second mode (1,1) shape. 
         FIG.  6    illustrates a top view of the two separate oscillating regions OR 1  and OR 2 , about line DL 1 , as achieved in  FIGS.  4 A and  4 B . 
         FIGS.  7 A and  8 A  illustrate perspective views, and  FIGS.  7 B and  8 B  illustrate top views, of a mode (2,1) shape. 
         FIG.  9    illustrates a preferred embodiment transducer and biasing conductors connected thereto. 
         FIG.  10    illustrates an example mechanical traveling wave graph implementing a (1,1) mode. 
         FIGS.  11  through  14    illustrate top views of example positions of the wave of  FIG.  10   . 
         FIG.  15    illustrates biasing signals to achieve a traveling wave (1,1) mode. 
         FIG.  16    illustrates using opposing polling areas and biasing signals to achieve a traveling wave (1,1) mode. 
         FIG.  17    illustrates a preferred embodiment method of operating the system of  FIGS.  1 A through  1 C . 
         FIG.  18    illustrates a schematic of an ultrasonic lens cleaning system including a four-segment transducer arrangement and a driver IC to provide phase transducer signals to generate either or both a standing and traveling wave to a lens. 
         FIG.  19    illustrates a preferred embodiment vehicle V with multiple implementations of the system of  FIGS.  1 A through  1 C . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIGS.  1 A through  1 C  illustrate various views of a lens structure cleaning system  10  according to a preferred embodiment.  FIG.  1 A  illustrates system  10  in a perspective exploded view, thereby separately illustrating a lens cover  12  that is to be coupled to an ultrasonic transducer  14 , that is, affixed in some manner (e.g., atop an upper annular surface, directly, or indirectly through an additional member(s)) of ultrasonic transducer  14  so that vibrations from ultrasonic transducer  14  may be transmitted either directly, or indirectly via any intermediate apparatus, to lens cover  12 .  FIG.  1 B  illustrates a top view of just ultrasonic transducer  14 , and  FIG.  1 C  illustrates lens cover  12  once affixed atop the upper annular surface of an ultrasonic transducer  14 , as may be achieved via various adhesives that may be selected by one skilled in the art. Various aspects of system  10  are further described below, with reference to all three of these figures, and additional features may be included in connection with system  10  (e.g., seals, housings, and the like), but such features are not described so as to focus the discussion on preferred embodiment aspects. 
     Lens cover  12  is intended to represent any type of lens structure as was introduced in the Background of The Invention section of this document. In the example of system  10 , lens cover  12  is a disc with a transparent center section  12   SC  (shown with a contrasting shading for distinction to the remainder) and an outer annular ring  12   AR  that surrounds transparent center section  12   SC . Thus, in general light in the visible spectrum may readily pass through transparent center section  12   SC , while it is otherwise blocked by outer annular ring  12   AR . In this manner, a preferred embodiment also may include a camera CM, and its respective lens, placed proximate to lens cover  12 , whereby generally light may pass through transparent center section  12   SC  so as to reach the camera lens, but the lens is otherwise protected by the additional surface provided by lens cover  12 . In many environments, transparent center section  12   SC  may become occluded by the presence of additional contaminating matter (e.g., dirt, water, other airborne constituents) so that light is partially or fully blocked from passing through that section, and the preferred embodiments endeavor to reduce or dispel such matter from the surface of lens cover  12 . 
     Transducer  14 , in a preferred embodiment, is formed from a cross-section of a cylindrical piezoelectric material, and preferably it has an outer diameter smaller than the outer diameter of lens cover  12 . By way of example, therefore, the outer diameter of transducer  14  may be 10 to 30 mm, while the larger outer diameter of lens cover  12  may be 12 to 35 mm. Thus, once assembled (e.g.,  FIG.  1 C ), the outer perimeter of lens cover  12  extends in some margin beyond the outer diameter of transducer  14 . As appreciated below, such a configuration may improve the effectiveness of standing and traveling waves transmitted from transducer  14  to lens cover  12 , thereby improving the ability to dispel contaminants from the surface of that lens cover. Transducer  14  is a segmented transducer, as defined by having plural circular sectors, each having a pair of conductors so as to apply a voltage to the sector. In the example illustrated, transducer  14  has four such segments (or sectors), shown in  FIG.  1 B  as S 1 , S 2 , S 3 , and S 4 , each consisting of approximately, or slightly less than, 90 degrees of the entire 360 degree circular cross-sectional perimeter of the transducer. Each segment S x  has an outer electrode SOE x  and an inner electrode SIE x , as may be achieved by silk-screening or otherwise attaching a thin conductive material to the respective outer and inner diameter of the piezoelectric material. As shown in a later  FIG.  9   , a preferred embodiment may include electrical connectors/wires connected to each of the illustrated electrodes, and a driver circuit for outputting signals to the conductors, whereby such signals are therefore applied, and alternated in amplitude, sign, and frequency, so as to achieve various preferred embodiment aspects further described below. 
     Given the preferred embodiment apparatus described above, transducer  14  may be excited with various signals so as to communicate vibrational forces into the abutted lens cover  12 . Such waves may be communicated in three different vibration modes, namely, radial mode at low frequencies (e.g., 44 kHz) and which are along the radii of the circular cross section of transducer  14 , axial mode at relative middle frequencies (e.g., 250 kHz), which are in the direction of the axis of the cylindrical transducer (i.e., vertical in  FIGS.  1 A- 1 C ), and a wall mode at higher frequencies (e.g., 2 MHz), which are modes that represent the radial motion of the wall thickness with respect to the outer wall of transducer  14 . In a preferred embodiment, axial mode vibrations are preferred, as they are likely to cause vibrations that are tangential from the surface of lens cover  12 , thereby providing a greater likelihood of dislodging certain contaminants (e.g., dust, water) from that surface. Note that frequency ranges of the various mode types may overlap. For example, high order radial modal frequencies will overlap with the axial modal frequencies, and high order axial modal frequencies will overlap with wall modal frequencies. However, in practice, this is not normally an issue because as mode orders increase, so does the modal damping. 
     Further to the preceding, also in the preferred embodiment, the vibrational forces are applied at excitation amplitudes and frequencies so as to transmit both standing and traveling waves, either in sequential or concurrent fashion, into the desirably chosen circular membrane shape of the abutted lens cover  12 . Thus, each type of wave is further detailed below, first with a discussion of standing waves and second with a discussion of traveling waves, with each applied to lens structure cleaning system  10 . 
     As is known in certain areas of physics, a standing wave is a stationary vibrational pattern created within a medium when two waves of the same frequency propagate through the medium in opposite directions. As a result, regions of minimum displacement (e.g., nodes) and regions of maximum displacement (e.g., anti-nodes) are created at fixed locations in the medium. As a result, the waves cause displacement along the medium (i.e., lens cover  12  in this instance), yet at the physical locations where wave interference occurs, there is little or no movement. Hence, in a circular membrane as exists in the preferred embodiment, where standing waves are so transmitted, the art defines certain mode shapes of the vibrational tendencies and movements of the surface being vibrated. Each mode shape is identified in the art by a convention of mode (d,c) shape, where d is the number of nodal diameters across the membrane surface, and c is the number of nodal circles at or within the perimeter of the circular membrane, where the term nodal (or node) refers to a point, line, or circle on the structure that has zero amplitude vibration, that is, it does not move, while the rest of the structure is vibrating. Various examples of mode shapes, by way of introduction and also in connection with preferred embodiments, are further explored below. 
     To further introduce mode shapes and various preferred embodiment aspects,  FIGS.  2 A and  3 A  illustrate perspective views, and  FIGS.  2 B and  3 B  illustrate side views, of a membrane MEM and its mode shape diagrams of a first mode (0,1) shape in a standing wave excitation that may be achieved by applying a voltage to the multiple-segmented transducer  14  of the preferred embodiment as if it were a single segmented transducer; such an effect may be achieved, therefore, by applying a first sine wave potential to all of its outer electrodes and a second sine wave potential, 180 degrees offset from the first sine wave (also achievable by 180 degree apart cosine potentials, instead of sine), to all of its inner electrodes, where both sine waves have a same first modal frequency. Alternatively, the effect may be achieved by applying a sine wave potential to all of the outer electrodes while connecting the inner electrodes to ground (or, vice versa, that is, grounding the outer electrodes and connecting the same sine wave to all inner electrodes). A modal frequency is one of the resonant frequencies for the system under consideration (i.e., here, lens cover  12 ), where the particular resonant frequency, among multiple resonant frequencies of the system, causes the shape of the respective mode. In this regard,  FIGS.  2 A,  2 B,  3 A, and  3 B , therefore, represent an instance where transducer  14  receives a voltage and first modal frequency, f m(0,1) , which creates mode (0,1) shape, also known as a “cupping” mode, as further detailed below. 
     The depictions of  FIGS.  2 A and  3 A  are generally representative of a perspective circular shape as shown by concentric circles between a center point and the outer perimeter. Radial lines are also shown, and if the shape were flat such lines would be straight. A curved radial line, however, suggests movement along the line. In this regard, therefore,  FIG.  2 A  is intended to illustrate a first extreme of the oscillatory movement of member MEM, where the surface bends upward (e.g., for reference, in a positive direction) with a maximum peak elevation at the center of the shape (also shown by light gray shading). The upward bend is also appreciated in the counterpart side view of  FIG.  2 B , which shows the mode surface as contrasted to a horizontal, or flat, reference line RL that is shown by a dashed line, and the maximum peak MxP is also indicated. In opposite fashion,  FIG.  3 A  is intended to illustrate a second extreme of the oscillatory movement of member MEM, where the surface bends downward (e.g., for reference, in a negative direction) also with a peak elevation at the center of the shape (also shown by dark gray shading). The downward bend is also appreciated in the counterpart side view of  FIG.  3 B , in which the minimum peak MnP is also indicated. 
     Given the illustrations of  FIGS.  2 A,  2 B,  3 A, and  3 B , note that the reference of a mode (0,1) indicates zero (i.e., d=0) nodal diameters and a single (i.e., c=1) nodal circle, the latter shown as D 1 . Note that the location of the nodal circle will depend on the conditions at the boundary of the membrane, where the illustrations assume that boundary is claimed; however, if the boundary were not claimed, the radial location of the nodal circle will change. In other words, as member MEM oscillates between the extreme positions shown in the Figures, a single circle, around the outside perimeter, does not vibrate. The vibrations inside nodal circle with diameter D 1 , therefore, will have some efficacy in removing contaminants that are on the surface of member MEM, but any matter that lands farther from the center and thus closer to the nodal circle with diameter D 1  may not experience sufficiently high acceleration to be removed. Further, material in high vibration zones may be pushed toward the nodal circles. Still further, and as appreciate later, a singular mode (0,1) has a limited area on membrane MEM that may reach a desirable amount of axial acceleration, thereby limiting the ability of the membrane to dispel contaminants 
     By way of an additional example,  FIGS.  4 A and  5 A  illustrate perspective views, and  FIGS.  4 B and  5 B  illustrate side views, of a membrane MEM and its mode shape diagrams of a second mode (1,1) shape in a standing wave excitation that may be achieved by applying a first sine wave to two adjacent segments (e.g., S 1 , S 2 ) of the multiple-segmented transducer  14 , while simultaneously applying the negative of that sine wave to the remaining two adjacent segments (e.g., S 3 , S 4 ), again therefore where one applied signal (e.g., sine wave) is 180 degrees out-of-phase with respect to the other. Note that the second mode (1,1) shape, as well as other standing wave mode shapes, may be achieved in other manners consistent with preferred embodiments, and for additional information in this regard the reader is invited to review U.S. patent application Ser. No. 15/225,212, filed Aug. 1, 2016, which is hereby incorporated fully herein by reference. The depictions of  FIGS.  4 A and  5 A  are again representative of a perspective circular shape as shown by concentric circles and radial lines, where  FIG.  4 A  is intended to illustrate a first extreme of the oscillation, and  FIG.  5 A  is intended to illustrate a second and opposite extreme of the oscillation. In the first extreme shown in  FIG.  4 A , and in the counterpart horizontal plot of  FIG.  4 B , membrane MEM has a maximum peak (i.e., positive) amplitude MxP in a first region on the right side of a nodal diameter line DL 1 , while at the same time membrane MEM also extends downward below the reference line RL and has a minimum peak (i.e., negative) amplitude MnP in a second region on the left side of nodal diameter line DL 1 . In the second extreme shown in  FIG.  5 A , and in the counterpart horizontal plot of  FIG.  5 B , membrane MEM has a maximum peak MxP on the left side of nodal diameter line DL 1 , while at the same time membrane MEM also extends downward below the reference line RL and has a minimum peak amplitude MnP on the right side of nodal diameter line DL 1 . As can be seen in these Figures, therefore, in mode (1,1) shape for a standing wave, membrane MEM again has a nodal circle around its outer perimeter. In addition, however, one diameter line DL 1  represents a nodal line, as oscillations occur left and right of that line, due to the voltage applied to opposing pairs of conductors/electrodes as introduced just above (or as achieved in other manners, again, for example with reference to the above-incorporated U.S. patent application Ser. No. 15/225,212). Thus, to further illustrate additional aspects below, the alternative oscillations about diameter line DL 1  also may be represented in a top view, as is shown in  FIG.  6   , which generally illustrates the two separate oscillating regions OR 1  and OR 2 , about line DL 1 . 
     By way of one additional example,  FIGS.  7 A and  8 A  illustrate perspective views, and  FIGS.  7 B and  8 B  illustrate top views, of a membrane MEM and its mode shape diagrams of a third mode (2,1) shape in a standing wave excitation that may be achieved by applying a first sine wave to two opposing segments (e.g., S 1 , S 3 ) of the multiple-segmented transducer  14 , while simultaneously applying the negative of that sine wave to the remaining two opposing segments (e.g., S 2 , S 4 ), again where one applied signal (e.g., sine wave) is 180 degrees out-of-phase with respect to the other. One skilled in the art will appreciate from earlier discussions that again the depictions of  FIGS.  7 A and  7 B  illustrate a first extreme of the oscillation, while  FIGS.  8 A and  8 B  illustrate a second and opposing extreme of the oscillation. In the top views of  FIGS.  7 B and  8 B , therefore, there are four oscillating regions OR 1  through OR 4 , also marked with either a “+” indication to designate a positive peak at a given time or a “−” indication to designate a negative peak at the given time. 
     The vibrational mode examples in the above-discussed Figures represent the lowest resonant frequencies of a circular plate system. They are also the most practical ones because they require the least amount of energy needed for excitation. Depending on the drive signal&#39;s frequency and the geometry of the electrodes, the actual vibration pattern can be one of the above-discussed mode shapes or a combination of them. In any case, they are standing waves. Moreover, having described various examples, they also may be characterized mathematically, as to generate a standing wave with the (d, 1) mode when d&gt;0, the circular transducer is divided into 2d channels of equal arc length and inputs are set as shown in the following Equation 1: 
         S   2k-1   =S   0  sin(ω 0   t ),  S   2k   =−S   0  sin(ω 0   t ),k=1,  . . . , d    Equation 1
 
     where, ω 0  is the resonant frequency of the (d, 1) mode. For the case when d=0, only one channel is needed. 
       FIG.  9    again illustrates transducer  12  in the same general manner as depicted in  FIG.  1 B , although in  FIG.  9    the illustration is rotated for sake of reference. Further, conductors are shown connected to each respective pair of a respective outer electrode SOE x  and a segment inner electrode SIE x , and system  10  is also shown to include a driver circuit  10   D  for providing voltage signals to the illustrated conductors, where each voltage output from circuit  10   D  is shown as two signals, so as to suggest the polarity of any signal can be reversed, in order to obtain additional signal and responsive wave options, as understood later. Thus, a potential is defined between each paired set of conductors. For example, the voltage between outer electrode SOE 1  and inner electrode SIE 1  is defined as ν S1 , and note the (+) and (−) conventions are used to define a polarity for sake of reference, but as detailed below not to suggest that the outer electrode is always positive with respect to its inner counterpart. To further illustrate this convention, therefore, a voltage of +1V applied to ν S1  is intended to suggest that the one volt is positive to outer electrode SOE 1  relative to inner electrode SIE 1 , while a voltage of −1V applied to ν S1  is intended to suggest that the one volt is negative to outer electrode SOE 1  relative to inner electrode SIE 1 . In any event, therefore, driver circuit  10   D  may apply any of the illustrated voltages ν S1 , ν S2 , ν S3 , and ν S4 . For example, a sine wave at a modal resonant frequency f m(1,1)  may be applied to one pair of conductors/electrodes, with a 180 degree opposite phase sine wave at the same resonant frequency f m(1,1)  applied to an opposing pair of conductors/electrodes. Thus, in a preferred embodiment, a first phase of the sine wave is applied to ν S1 , while a second phase of the sine wave, 180 degrees apart from the first phase, is applied to ν S3 ; at the same time, no voltage is applied to ν S2  or ν S4 . Alternatively to achieve the same mode (1,1), a sine wave at a modal resonant frequency f m(1,1)  may be applied to two adjacent conductors (and their respective electrodes), with a 180 degree opposite phase sine wave at the same resonant frequency f m(1,1)  applied to an opposing pair of adjacent conductors (and their respective electrodes). Thus, in a preferred embodiment, a first phase of the sine wave is applied to ν S1  and ν S2 , while a second phase of the sine wave, 180 degrees apart from the first phase, is applied to ν S3  and ν 4 . 
     It is therefore recognized in connection with the above that certain modes achievable by transducer  14 , if driven with applied voltages to various segments will result in symmetric mode shapes. For example the (0,1) shape has a single outer nodal circle with diameter D 1  at its perimeter, and inside that perimeter the flexing is circularly symmetric as shown by the comparable concentric circles with radii inside that outer nodal circle, and the greatest amount of displacement is achieved closer to the membrane center. As another example, the (1,1) shape also has an outer nodal circle at its perimeter, but instead of extreme flexing at the center achieved by the (0,1) shape, peaks are achieved off center but at two different regions; however, a nodal diameter line is created, along which there is no displacement. As still another example, the (2,1) shape creates peaks off center and at four different regions; however, two nodal diameter lines are created, along which there is no displacement. In all events, therefore, either the drop off in displacement at increased radial lengths of the (0,1) shape, or the additional nodal diameters of the (1,1) and (2,1) shape, demonstrate that such shapes may be less likely to expel certain contaminants from lens cover  12  in locations where there is little vibration, that is, it may tend to accumulate contaminants in nodal circles or diameters. The preferred embodiments include additional modes of operation, therefore, so as to achieve improved results over these considerations, as further explored below. 
     In another aspect of a preferred embodiment, and to overcome the limitations noted above with respect to contaminants accruing at nodal points, circles, or lines, a preferred embodiment further combines both standing and traveling waves in system  10 , either time multiplexed or concurrently, as will now be further explored. Specifically, a traveling wave has a wave front that moves as a periodic wave across a surface and therefore, apart from the outer perimeter of the lens cover and arguably the center point of the surface around which the wave rotates, has no other stationary point, as compared to various standing waves which, as demonstrated above, can have one or more points, lines, or circles that are stationary, despite movement elsewhere on the surface. Moreover, the same system  10  described above with respect to standing waves also may readily be biased, via driver circuit  10   D , so as to also achieve mechanical traveling waves. By way of introduction, various such traveling waves may be achieved by biasing adjacent ones of the four segments with signals that are 90 degrees apart. The relationship is described mathematically below according to the following Equations 2 through 5: 
         S   4k-3   =S   0  sin(ω 0   t )   Equation 2
 
         S   4k-2   =S   0  cos(ω 0   t )   Equation 3
 
         S   4k-1   =S   0  sin(ω 0   t )   Equation 4
 
         S   4k   =−S   0  cos(ω 0   t ), k=1,  . . . , N    Equation 5
 
     where, ω 0  is the resonant frequency of the [N,1] standing wave. 
     Implementation of the preceding into system  10  will generate a traveling wave for the (d, 1) mode, whereby the traveling wave front will rotate around the longitudinal axis  12   AX  of the circular lens cover  12  (or other membrane or plate). The direction of rotation can be reversed by reversing the polarity of the inputs in any one set and keeping the other set unchanged. Various implementation details are examples are explored below. 
       FIG.  10    illustrates an example mechanical traveling wave graph  20  implementing a (1,1) mode traveling wave excitation in system  10  of  FIGS.  1 A through  1 C , and  FIGS.  11  through  14    illustrate the traveling wave rotating around the center axis  12   AX  of lens  12 . The mode designations in these examples are for circular traveling waves (d,c) modes having, at an instantaneous point in time where the wave can per perceived as not moving, d nodal diameters and c nodal circles (including the boundary), where d&gt;0 and c&gt;0. In other words, such nodes are points or lines on the lens structure that are momentarily at rest in a time instant, but the traveling wave excitation causes the nodes to rotate about the lens center axis  12   AX . In the example of  FIG.  10   , the traveling wave rotates in a clockwise direction  22  when viewed from above and relative to axis  20   AX . In this (1,1) mode example, moreover, a single node diameter  24  extends in the indicated X-Y plane about the Z direction axis  20   AX . Thus,  FIG.  10    illustrates a traveling wave excitation of a planar lens  12  (not shown in  FIG.  10   ) that is understood to be positioned in the X-Y plane, and the excitation causes Z-direction of motion across the lens surface with a positive Z-direction displacement maxima  26  and a negative Z-direction displacement minima  28 .  FIGS.  11  through  14    provide simplified views of the traveling wave rotating in the direction  22  (i.e., clockwise) at different points in time, with  FIG.  11    illustrating an initial example position of the maxima  26  and the minima  28  with the intervening single node diameter  24  extending in the X direction at Y=0 between the positive and negative lobes associated with the maximum and minimal points  26  and  28 . At the time represented in  FIG.  12   , the mechanical vibration by the transducer segments S 1  through S 4  rotates the positions of the lobes and the points  26  and  28  in the clockwise direction  22  by approximately 30 degrees.  FIGS.  13  and  14    respectively illustrate further rotation in the direction  22  by additional 30 degree increments, where the node diameter  24  is positioned in the Y-direction in  FIG.  14    at X=0. In operation, the phase shifted sinusoidal excitation of the transducer segments S 1  through S 4  causes a continuous rotation of the traveling wave pattern about the Z-direction lens axis. As seen in  FIGS.  11  through  14   , the node diameter  24  rotates or travels, in contrast to standing wave excitation techniques in which the node diameter remains stationary. Accordingly, the  FIG.  9    driver circuit  10   D  advantageously provides traveling wave excitation in which the surface area of the lens along is vibrated and thus cleaned. 
     The traveling wave excitation can be mathematically represented. The displacement of a circular lens  12  or other circular plate can be represented by the following Equation 6: 
     
       
         
           
             
               
                 
                   
                     
                       
                         W 
                         
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                     = 
                     
                       
                         [ 
                         
                           
                             
                               J 
                               n 
                             
                             ( 
                             
                               
                                 β 
                                 
                                   n 
                                   ⁢ 
                                   m 
                                 
                               
                               ⁢ 
                               r 
                             
                             ) 
                           
                           - 
                           
                             
                               
                                 
                                   J 
                                   n 
                                 
                                 ( 
                                 
                                   
                                     β 
                                     nm 
                                   
                                   ⁢ 
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                                 ) 
                               
                               
                                 
                                   I 
                                   n 
                                 
                                 ( 
                                 
                                   
                                     β 
                                     nm 
                                   
                                   ⁢ 
                                   R 
                                 
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                             ⁢ 
                             
                               
                                 I 
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                               ( 
                               
                                 
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                       [ 
                       
                         
                           
                             
                               sin 
                               ⁢ 
                               n 
                               ⁢ 
                               θ 
                             
                           
                         
                         
                           
                             
                               cos 
                               ⁢ 
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                   , 
                 
               
               
                 
                   Equation 
                   ⁢ 
                       
                   6 
                 
               
             
           
         
       
     
     Where J n  is the nth Bessel function, I n  is the modified Bessel function of the first kind, and n and m are mode index numbers, n=0,1,2 . . . , m=1,2,3, . . . The natural mode frequencies are given by the following Equation 7: 
     
       
         
           
             
               
                 
                   
                     ω 
                     
                       n 
                       ⁢ 
                       m 
                     
                   
                   = 
                   
                     
                       
                         λ 
                         
                           n 
                           ⁢ 
                           m 
                         
                         2 
                       
                       
                         R 
                         2 
                       
                     
                     ⁢ 
                     
                       
                         D 
                         
                           ρ 
                           ⁢ 
                           T 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                       
                   7 
                 
               
             
           
         
       
     
     where R is the radius of the circular plate, T is its thickness, λ nm  is a root to Bessel function equations, D is the lens material stiffness (determined by Young&#39;s modulus, Poisson&#39;s ratio, etc.), and ρ is the lens material density, thereby defining the following Equation 8: 
     
       
         
           
             
               
                 
                   
                     
                       R 
                       
                         n 
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                     ( 
                     r 
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                   = 
                   
                     [ 
                     
                       
                         
                           J 
                           n 
                         
                         ( 
                         
                           
                             β 
                             
                               n 
                               ⁢ 
                               m 
                             
                           
                           ⁢ 
                           r 
                         
                         ) 
                       
                       - 
                       
                         
                           
                             
                               J 
                               n 
                             
                             ( 
                             
                               
                                 β 
                                 nm 
                               
                               ⁢ 
                               R 
                             
                             ) 
                           
                           
                             
                               I 
                               n 
                             
                             ( 
                             
                               
                                 β 
                                 nm 
                               
                               ⁢ 
                               R 
                             
                             ) 
                           
                         
                         ⁢ 
                         
                           
                             I 
                             n 
                           
                           ( 
                           
                             
                               β 
                               
                                 n 
                                 ⁢ 
                                 m 
                               
                             
                             ⁢ 
                             r 
                           
                           ) 
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                       
                   8 
                 
               
             
           
         
       
     
     Equation 6 can be simplified as shown in the following Equation 9: 
     
       
         
           
             
               
                 
                   
                     
                       W 
                       
                         n 
                         , 
                         m 
                       
                     
                     ( 
                     
                       r 
                       , 
                       θ 
                     
                     ) 
                   
                   = 
                   
                     
                       
                         R 
                         
                           n 
                           , 
                           m 
                         
                       
                       ( 
                       r 
                       ) 
                     
                     [ 
                     
                       
                         
                           
                             sin 
                             ⁢ 
                             n 
                             ⁢ 
                             θ 
                           
                         
                       
                       
                         
                           
                             cos 
                             ⁢ 
                             n 
                             ⁢ 
                             θ 
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                       
                   9 
                 
               
             
           
         
       
     
     Solutions for W to a forced response at a resonant frequency ω are given by the following Equations 10 through 12: 
         W   1 ( r,θ,t )= AR   n,m ( r )cos  n θ cos ω t    Equation 10
 
         W   2 ( r,θ,t )= BR   n,m ( r )sin  n θ sin (ω t +α)   Equation 11
 
         W   3   =W   1   +W   2    Equation 12
 
     Rearranging W 3  yields the following Equation 13: 
         W   3 ( r,θ,t )=½  R   n,m ( r )[( A+B  cos α)cos( nθ−ωt )+( A−B  cos α)cos( nθ+ωt )+2 B  sin α sin  n θ cos ω t]   Equation 13
 
     Setting α=0, and A=B, the above can be rewritten as the following Equation 14: 
         W   3 ( r,θ,t )= AR   n,m ( r )cos( nθ−ωt )   Equation 14
 
     Equation 14 defines a traveling wave with angular speed ω/n in a positive direction θ. By letting A=−B, the direction is reversed to the negative θ direction. The transducer segments S 1  through S 4  in this example form a circular ring shape so that the light can go through the lens  12  in the center along the direction of the axis  12   AX . 
     From the above, one skilled in the art should appreciate that system  10 , providing a transducer  14  with four channels or segments, can provide various mode shapes for both standing and traveling waves that are imposed on lens  12 . Indeed, recall in connection with  FIGS.  4 A and  5 A  (and  4 B and  5 B), that a standing wave (1,1) shape may be actuated by driver circuit  10   D  applying a first sine wave to two adjacent segments (e.g., S 1 , S 2 ) of the multiple-segmented transducer  14 , while simultaneously applying the negative of that sine wave to the remaining two adjacent segments (e.g., S 3 , S 4 ), again therefore where one applied signal (e.g., sine wave) is 180 degrees out-of-phase with respect to the other. Referring to the diagram of  FIG.  9   , however, note that likewise a traveling wave (1,1) shape may be actuated by driver circuit  10   D  applying 90 degree out of phase signals to each respective segment in the four segments of the multiple-segmented transducer  14 , as shown in the following Table 1: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Segment 
                 Voltage 
                 signal 
               
               
                   
                   
               
             
            
               
                   
                 S 1   
                 v S1   
                 sin ωt 
               
               
                   
                 S 2   
                 v S2   
                 cos ωt 
               
               
                   
                 S 3   
                 v S3   
                 −sin ωt 
               
               
                   
                 S 4   
                 v S4   
                 −cos ωt 
               
               
                   
                   
               
            
           
         
       
     
     In still other preferred embodiments, note that variations may be used to achieve traveling wave patterns, including, for example, where only positive waveforms are available, for instance based on limitations from a signal wave generator. In one such instance, 90 degree phase shifts between adjacent ones of four segments may be achieved by reversing polarity. Thus, as a first example,  FIG.  15    illustrates a preferred embodiment biasing in such an instance, so as to once again achieve a traveling wave (1,1) mode. Hence, in  FIG.  16    and contrasting segment S 2  to segment S 3 , segment S 2  is biased in the positive direction by the conventions of  FIG.  9    and with a cosine wave, while segment S 3 , is biased in the negative direction by the conventions of  FIG.  9    and with a sine wave. Thus, a 90 degree phase shift is achieved as between these segments, as further maintained between those segments and the remaining segments S 1  and S 4  which are biased as also shown in  FIG.  15   . Alternatively, in a second example,  FIG.  16    illustrates a preferred embodiment biasing that combines with the polling areas of the transducer segments as oriented so that the directionality of dipoles in one region (e.g., piezoelectric material) align so that when a voltage is applied thereto, the behavior of the dipoles aligned in that direction is opposite of that in a second region in which the dipoles are aligned in the opposite direction.  FIG.  16    illustrates a preferred embodiment biasing in this latter instance, where the indication of “+” or “−” on a segment is intended to designate the directionality of dipoles in that segment. Thus, note that the dipoles of segments S 1  and S 3  are reversed, so that while each outer conductor in those two segments receives the signal sin ωt, the mechanical effect is 180 degrees out of phase due to the reversed polling direction of those two differing segments. Similar observations can be made with respect to the dipoles of segments S 2  and S 4  as reversed with respect to one another, so that while each outer conductor in those two segments receives the signal cos ωt, the mechanical effect is 180 degrees out of phase due to the reversed polling direction of those two differing segments. Lastly, note that additional preferred embodiments may be implemented by extending the four channel concepts described herein to higher modes using a transducer with more channels (preferably in multiples of four segments, i.e., 8 segments, 12 segments, and so forth). Further in this regard, the reader is invited to review co-owned U.S. patent application Ser. No. 15/186,944, filed Jun. 20, 2016, which is hereby incorporated fully herein by reference. 
       FIG.  17    illustrates a preferred embodiment method  30  of operating system  10 . By way of introduction, method  30  may be controlled driver circuit  10   D , which can include, or cooperate with, a processor, controller, or other circuit or device, as may be hardwired or programmed by concepts according to one skilled in the art, and an example of which is shown later in  FIG.  18   . As further introduction, such control advances method  30  so as to apply transducer voltages to selective ones (or all) of the conductors/electrodes of system  10 , so as to alternate between different mode shapes created in lens cover  12 , via standing and traveling waves applied to it from transducer  14 . In combination, therefore, the standing and traveling waves increase the ability to accelerate the surface of lens cover  12  so as to achieve a desirably sufficient amount of acceleration coverage across a majority of the area of the cover. As a result, the accelerated movement of the lens cover increases the chances of dispelling portions of any contaminants along a majority of the area of the cover. Additional details follow. 
     Method  30  commences with a start step  32 , which may be initiated by various apparatus or events, when it is desired to start an attempt to remove particulate from lens cover  12  by vibrating it via transducer  14 . For example, where lens cover  12  is part of an automotive application as was introduced earlier and further explored later, start step  32  may be user actuated, such as by an operator of the automobile, or a processor can initiate the step in response to a condition, such as at system start-up, or after the passage of time, or response from a sensor or upon detection of some other event, such as rain, that might cause some matter (e.g., water) to come in contact with the exterior of lens cover  12 . As another example, when lens cover  12  is part of a remote lens system (e.g., surveillance camera), step  22  may occur at some fixed time interval, or in response to signaling from another device, such as in response to environmental conditions or as part of an Internet-of-Things communication. In any event, once step  32  is enabled, method  30  has begun, after which method  30  continues from step  32  to step  34 . 
     In step  34 , a mode counter md is initialized to a value of one. As will become evident below, mode counter md increments, and thereby provides a count, up to a total number of modes TLM that are shaped onto lens cover  12 , by transducer  14 , in cyclic and alternating fashion, so as to attempt to remove contaminants from lens cover  12 . Next, method  30  continues from step  34  to step  36 . 
     In step  36 , voltage is applied to a set of selective ones or all of the electrodes of transducer  14 , via the respective conductors connected to those electrodes, so as to achieve a mode, indicated as MODE[md], meaning according to the index provided by counter md. Thus, for a first occurrence of step  36 , a first mode (i.e., MODEM) is effected by applying the necessary voltage signals to a first set of electrodes so as to accomplish that mode. For example, consider the first mode to be the application of the mode (0,1) standing shape, discussed earlier in connection with  FIGS.  2 A,  3 A,  2 B, and  3 B . To achieve this mode, all outer electrodes SOE x  receive a voltage of a first sine wave, while all inner electrodes SIE x  receive a voltage of a second sine wave of the same sample amplitude as the first sine wave, but with the two waves phase offset by 180 degrees; moreover, both sine waves are applied with a frequency f m(0,1) , which is the resonant frequency of system  10  required to achieve the mode (0,1) shape. Note also that step  36  applies the signals to the selected set of conductor/electrodes for a number indicated as MC cycles, that is, for a duration of input sign waves equal to MC periods or cycles. The value of MC may be selected by various considerations. For example, MC may be based on a pre-programmed value or on a feedback signal (e.g., modal resonance frequency which will return to a baseline value as contaminant mass is ejected from the surface), or from information from a camera system from which it can be determined if a sufficiently clear image is obtained through the lens. After the MC cycles at the current MODE[md] have been achieved, method  30  continues from step  36  to step  38 . 
     In step  38 , a condition is evaluated to determine whether the mode counter and has reached a total number of modes TLM that are desired to be shaped onto lens cover  12 , by transducer  14 . If and is less than TLM, then method  30  advances from step  38  to step  40 , whereas if and equals TLM, then method  30  advances from step  38  to step  42 . In step  40 , the mode counter and is incremented and the flow returns to step  36 . In a repeat of step  36 , therefore, an additional set of selective ones or all of the electrodes of transducer  14  receive a voltage so as to achieve a next mode, indicated as MODE[md], which in the case of a first repetition of step  26  will be the second mode, that is, MODE[2]; however, further in the preferred embodiment, the additional mode may be another instance of a standing wave, or alternatively it may be a traveling wave. For example, consider the second mode to be the application of the mode (1,1) traveling shape, discussed earlier in connection with  FIGS.  10  through  14   . To achieve this mode, recall that the signals from Table 1 may be applied, whereby four different phases, across 360 degrees, are applied equally spaced among the four different transducer segments. Again, step  36  applies these signals to the selected set of conductor/electrodes for MC cycles, after which method  30  again continues from step  36  to step  38 . 
     Step  38  has been described earlier, as it evaluates the condition of whether the mode counter and has reached a total number of modes TLM that are desired to be shaped onto lens cover  12 , by transducer  14 . Given the sequencing now described, and the potential looping from step  38  not being satisfied and returning to step  36  one or more times for the application of respective additional modes, note that TLM may be set to any number with a corresponding indication of each MODE[md] to be applied for each incidence of step  36 , until the condition of step  38  is satisfied and method  30  continues to step  42 . 
     In step  42 , a condition is evaluated to determine whether a sufficient duration of cycles has been applied by the preceding occurrence(s) of step  36 . To appreciate this step, recall that each incidence of step  36  excites transducer  14  to apply either a standing or traveling wave mode shape to lens cover  12 , for a total of MC cycles per step  36  incidence. Each of these MC cycles, therefore, endeavors to clear contaminants from the surface of lens cover  12 . Depending on the number of cycles per step  36  incidence, and the number of step  36  occurrences, it may be desirable to repeat the occurrence(s) of step  36  for all TLM modes MODE[md] one or more additional times, in an ongoing effort to clear contaminants from the surface of lens cover  12 . Thus, the step  42  condition may use duration (or some other measure) as a basis to evaluate whether to repeat the occurrence(s) of step  36  for all modes MODE[md]. If such a repetition is desired, method  30  returns from step  42  to step  34 , whereas if step  42  is satisfied, then method  30  ends in step  44 . While method  30 , therefore, concludes with step  44 , it may be subsequently re-started by returning to step  32 , by one of the actions as mentioned earlier with respect to that step. 
     Given the preceding, one skilled in the art will appreciate that in each of the multiple different modes, one area of lens cover  12  will achieve a maximum or peak acceleration, while various other areas of the lens cover will achieve some lesser percentage of that peak. In an effort to achieve the greatest likelihood of dispelling contaminants, therefore, a greater percentage of peak acceleration across a greater area of lens cover  12  is likely to be desirable. Thus, one criterion to evaluate the cleaning performance is to check the acceleration distribution values on the lens surface. The acceleration values on the lens surface can be calculated through Finite Element Modeling (FEM) simulation or through measurements from Laser Doppler Vibrometer (LDV). The obtained values can then be compared against a prescribed threshold, e.g., 50% of the peak acceleration value, to determine the lens area that exceeds the threshold. The area above the chosen threshold will be referred to as ‘active area.’ The active area achieved by different excitation methods can be compared, as is shown in Table 2, which is compares the active area achieved by (0,1) standing wave, (1,1) traveling wave, and the combination of the two based on FEM simulation. To simplify the comparison, the values of the active area as a percentage of the total area are listed. Note that the peak value used to calculate the threshold is the largest value that can be obtained by (0,1) standing wave and (1,1) traveling wave (and in this example, the largest value is achieved by (0,1) standing wave). 
                             TABLE 2                          Lens area exceeds threshold (% of lens area)                                         [0, 1] standing                   and [1, 1]       Threshold (% of   [0, 1] mode   [1, 1] mode   traveling wave       peak value)   standing wave   traveling wave   combined                                     25%   55.0%   81.3%   84.0%       50%   2.6%   30.8%   30.9%       75%   1.1%    6.0%   6.7%       90%   0.5%     0%   0.5%                    
From Table 2, one skilled in the art will appreciate that on average the traveling wave yields larger active area. However, the largest acceleration value (found in the center of lens  12 ) comes from the standing wave excitation. The combination of both excitations yields better coverage of both center and off-center lens area.
 
       FIG.  18    illustrates ultrasonic lens cleaning system  10  in greater detail, including driver circuit (e.g., integrated circuit)  10   D  and an even number NS of transducer segments, where in the example illustrates NS=4, thereby providing segments S 1  through S 4  to clean a lens  12 . The illustrated embodiments include an even number NS transducer segments or elements that are mechanically coupled, directly or indirectly, to the lens  12 , where NS is an even integer greater than or equal to 4. The individual transducer segments S x  in this example are radially spaced from a center axis  12   AX  of the circular lens  12  and the electrodes (see, e.g.,  FIG.  1 B ) are angularly spaced from one another around a periphery of the lens  12 . As detailed further below, driver circuit  10   D  provides phase shifted oscillating signals AS and AC to the electrodes of the transducer segments S x  to generate a standing or mechanical traveling wave to vibrate the lens  12  for improved ultrasonic cleaning The disclosed driver circuit  10   D , system  10 , and methods provide improved lens cleaning solutions. 
     Driver circuit  10   D  in this example is a driver integrated circuit powered by a battery or other power source  104 .  FIG.  18    shows a camera lens assembly including the ultrasonic lens cleaning system  10 . The lens assembly includes the transducer segments S 1  through S 4  forming a cylindrical or “ring” configuration which is mechanically coupled to vibrate a lens  12 . Lens  12  may be as shown in  FIGS.  1 A- 1 C , or may have other shapes or configurations (e.g., fisheye, single transparent surface, and the like). 
     Driver circuit  10   D  receives input power from a power supply or power source  104 , such as a battery providing a battery voltage signal VB with respect to a reference node, such as a ground node GND in one example. Driver circuit  10   D  includes a terminal  106  (e.g., an IC pin or pad) to receive the battery voltage signal VB from the power supply  104 , as well as a ground terminal  108  for connection to GND. Driver circuit  10   D  includes a power management circuit  110  that receives the battery voltage signal VB and provides one or more supply voltages (not shown) to power the internal circuitry of driver circuit  10   D . In addition, driver circuit  10   D  includes terminals  112 - 1 ,  112 - 2 ,  112 - 3 , . . . ,  112 -NS and  114 - 1 ,  114 - 2 ,  114 - 3 , . . . ,  114 -NS for connection of multiplexer signal outputs to the lead wires  142 - 1 ,  142 - 2 ,  142 - 3 , . . . ,  142 -NS and  144 - 1 ,  144 - 2 ,  144 - 3 , . . . ,  144 -NS to deliver driver signals to the transducer segments  102 . 
     Driver circuit  10   D  provides a set of phase shifted oscillating signals to cause the transducer segments to vibrate lens  12  to facilitate or promote cleaning of the lens  12  through provision of mechanical traveling waves that rotate around the lens axis  12   AX . In one example, driver circuit  10   D  provides phase shifted sinusoidal ultrasonic drive signals to actuate the transducer segments and cause transducer  14  to mechanically vibrate lens  12  using ultrasonic waves to remove dirt and/or water from the surface of lens  12 . Non-sinusoidal oscillating signals can be provided, for example, square waves, pulse-width modulated waveforms, triangular waveforms or other waveform shapes. Mechanical oscillation or motion of lens  12  at ultrasonic waves of a frequency at or close to the system resonant frequencies can facilitate energy efficient removal of water, dirt and/or debris from lens  12 . In one example, driver circuit  10   D  delivers phase shifted oscillating drive signals to the transducer segments at or near a resonant frequency of the mechanical assembly. A fixed driver signal frequency can be used, or the frequency may be adapted by driver circuit  10   D  to accommodate changes over time or different frequencies can be used for cleaning different types of debris from lens  12 . Driver circuit  10   D  in one example tracks changes in the resonant mechanical frequency of an associated lens system, and provides a closed loop system to use this information to maintain cleaning performance over time and in varying environmental conditions. 
     Driver circuit  10   D  includes a signal generator  130  and a phase shift circuit  132 , along with first and second amplifiers  134 - 1  (AMP 1) and  134 - 2  (AMP 2) to generate and provide phase shifted oscillating signals AS and AC to the transducer segments to generate a standing wave across, or a mechanical traveling wave rotating around the center axis  12   AX  of, the lens  12 . Any suitable amplifier circuitry  134  can be used, for example, a power op amp circuit designed to accommodate the frequency bandwidth of the signals VS provided by the signal generator  130  and the output signal requirements to properly drive a given transducer segment. The signal generator circuit  130  generates a first output signal VS that oscillates at a non-zero frequency ω. In some examples, the frequency ω is ultrasonic, such as about 20 kHz or more, although not a strict requirement of all implementations of the presently disclosed examples. In certain examples, the signal generator  130  is an analog circuit capable of providing an oscillating output signal VS of any suitable waveform shape in a range of frequencies, for example from 1 kHz through 3 MHz, and can provide the signal VS that concurrently includes multiple frequency components in order to excite the driven transducers at multiple frequencies concurrently. In one example, the signal generator circuit  130  is a pulse width modulated circuit to provide a square wave output signal voltage waveform VS. In other examples, the signal generator  116  provides sinusoidal output voltage signals. In other examples, triangle, saw tooth, or other wave shapes or combinations thereof can be provided by the signal generator  130 . 
     The phase shift circuit  132  receives the first output signal VS and generates a second output signal VC that oscillates at the non-zero frequency ω. The second output signal VC is phase shifted from the first output signal VS by a non-zero angle. In one example, the signal generator circuit  130  generates a sinusoidal first output signal VS represented as VS=K*sin(ωt) and the phase shift circuit  132  provides the second output signal VC=K*cos(ωt) shifted by 90 degrees from the first output signal VS. The first amplifier  134 - 1  includes an input to receive the first output signal VS, and a first amplifier output  136  to generate a first amplified signal AS based on the first output signal VS. The second amplifier  134 - 2  includes an input to receive the second output signal VC, and a second amplifier output  138  to generate a second amplified signal AC based on the first output signal VC. 
     Driver circuit  10   D  interfaces with the transducer segments by connection to the IC terminals grouped as driver signal output terminal pairs  112 ,  114  individually associated with a corresponding one of the transducer segments  102 . The individual driver signal output terminal pairs include a first output terminal  112  that can be coupled to a first side conductor (e.g., outer side) of a corresponding transducer segment, and a second output terminal  114  that can be coupled to a second side conductor (e.g., inner side) of the corresponding transducer segment. Driver circuit  10   D  may include extra output terminal pairs  112  and  114  to allow configuration of the IC to drive different numbers of transducer segments  102  for different applications, such as NS=2, 4, 8, 16, etc. Driver circuit  10   D  also includes a routing circuit  140  that delivers the first amplified signal AS to a first set of the output terminals  112 ,  114  and delivers the second amplified signal AC to a second set of the output terminals  112 ,  114  to generate standing wave or a mechanical traveling wave to vibrate lens  12 . 
     The routing circuit  140  can be a fixed interconnection system to route the signals AS and AC to specific output terminals  112 ,  114 . In other examples, a configurable routing circuit  140  can be used to allow reconfiguration of driver circuit  10   D  for different applications. In the example of  FIG.  18   , the routing circuit  140  includes an integer number NS multiplexers  141 - 1 ,  141 - 2 ,  141 - 3 , . . . ,  141 -NS. The individual multiplexers  141  corresponding to one of the transducer segments. The individual multiplexers  141  in various examples include two or more multiplexer inputs. In the example of  FIG.  18   , a first multiplexer input of the individual multiplexers  141  is coupled with the first amplifier output  136  to receive the signal AS, and a second multiplexer input is coupled with the second amplifier output  136  to receive the second amplified signal AC. The individual multiplexers  141  have first and second outputs, including a first multiplexer output  142  coupled to deliver a first multiplexer output signal SO to a first conductor (e.g., outer) side of the corresponding transducer segment  102 . A second multiplexer output  144  is coupled to deliver a second multiplexer output signal SI to a second conductor (e.g., inner) side of the corresponding transducer segment. The multiplexers  141 - 1  through  141 -NS provide corresponding outer and inner signals SO- 1 , SO- 2 , SO- 3 , . . . , SO-NS and SI- 1 , SI- 2 , SI- 3 , . . . , SI-NS to the respective transducer segments  102 - 1 ,  102 - 2 ,  102 - 3 , . . . ,  102 -NS as shown in  FIG.  18   . 
     A select input of the individual multiplexers  141  receives a select signal to select among the inputs. In  FIG.  18   , two select inputs receive select signals P and SC, respectively. In this example, the P input signals P- 1 , P- 2 , P- 3 , . . . , P-NS are used to select a polarity for the corresponding transducer segment and the SC inputs SC- 1 , SC- 2 , SC- 3 , . . . , SC-NS select between the amplified sine signal AS and the phase shifted, amplified cosine signal AC. The individual multiplexers  141  operate according to the corresponding received select signals P and SC to provide a selected oscillating signal AS or AC to one of the inner and outer conductors of the corresponding transducer segments. The other conductor of the associated transducer segment may be coupled to a reference voltage, such as the constant voltage signal GND, or to the other oscillating signal. 
     The routing circuit  140  in  FIG.  18    includes a lookup table  126  (LUT) to provide the select signals P and SC to the multiplexers  141  according to one or more configuration inputs. In certain examples, driver circuit  10   D  includes at least one configuration input terminal  116 ,  118  to allow configuration by an external circuit, such as a host circuit  120 . Driver circuit  10   D  includes four terminals  116  to receive a binary coded input NS to specify the number of output multiplexers to be used to drive NS transducer segments. Three input terminals  118  are provided to receive a binary coded ND signal designating the number of nodal diameters for the resulting traveling wave. The NS inputs provide the NS signal via lines  122  to the lookup table  126 , and the ND inputs provide the ND signal via lines  124  to the lookup table  126 . 
     The LUT  126  in one example is encoded to provide the P and SC signals to configure the multiplexers  140  according to the host-specified NS and ND values to operate the transducer segments to generate a standing or traveling wave to clean lens  12 . The multiplexers  141  in  FIG.  18    allow selection from the sine wave AS or the cosine wave AC based on the P and SC signals from the lookup table  126 . In other examples, the individual multiplexers  141  include a third multiplexer input coupled with a reference voltage, such as GND. This configuration allows selective interconnection of specific ones of the outer and/or inner conductors with the amplified sinewave signal AS, the amplified cosine signal AC or the reference voltage GND according to the P and SC signals to establish a mechanical traveling wave excitation of lens  12 . In this regard, driver circuit  10   D  is configurable by the host circuit  120  to implement a variety of different configurations based on the number of transducer segments (NS) and the number of nodal diameters (ND). The configuration of the multiplexers  141  provides the polarity and the selection of sine or cosine waveforms for the electrode or electrical connection of each side of the transducer segments. In the case of piezoelectric transducer segments, the segments vibrate when a periodic electrical signal is applied, in order to separate debris from the mechanically coupled lens  12 . The entire lens assembly will typically have one or more resonant frequencies determined by the mechanical properties of all the components and the boundary conditions, and the signal generator circuit  130  in certain examples provides the sinewave VS at a frequency ω at or near one of the resonant points for effective, efficient cleaning 
     In one example, the lookup table  126  provides the multiplexer select signals to configure the polarity (P) and sine/cosine signal (SC) provided by the individual multiplexers  141 . The following Table 3 shows an example of these control signals, where AS and AC are sine and cosine amplitude inputs, P and SC are control signal bits. SO and SI are inner and output signal outputs from the multiplexers  141 , which are determined by the traveling wave pattern to be excited for lens cleaning. This example can be used for a four-segment system such as those described herein. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 P 
                 SC 
                 SO 
                 SI 
               
               
                   
                   
               
             
            
               
                   
                 0 
                 0 
                 AS 
                 GND 
               
               
                   
                 1 
                 0 
                 GND 
                 AS 
               
               
                   
                 0 
                 1 
                 AC 
                 GND 
               
               
                   
                 1 
                 1 
                 GND 
                 AC 
               
               
                   
                   
               
            
           
         
       
     
     One example of the contents of the lookup table  126  is shown in Table 4 for a 16-segment system, where NS represents the number of segments and ND represents the number of nodal diameters. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 NS 
                 ND 
                 P 
                 SC 
               
               
                   
                   
               
             
            
               
                   
                 16 
                 1 
                 0000 0000 1111 1111 
                 1111 0000 1111 0000 
               
               
                   
                 16 
                 2 
                 0000 1111 0000 1111 
                 0011 0011 0011 0011 
               
               
                   
                 16 
                 4 
                 0011 0011 0011 0011 
                 0101 0101 0101 0101 
               
               
                   
                   
               
            
           
         
       
     
       FIG.  19    illustrates a preferred embodiment vehicle V with system  10  implemented in numerous locations relative to the vehicle V. For example, a forward facing camera may be installed as part of a system  10  in a mount located behind the windshield W of vehicle V. As another example, a respective rearward facing camera may be installed as part of a system  10  in each of the vehicle side mirror locations SMR, either in addition to or in lieu of an actual side mirror. As a final example, another rearward facing camera may be installed near or at the rear of the vehicle V, so as to assist with backup technology. Each system  10  communicates with a processor P, such as a controller, microcontroller, or the like, located either under the hood or inside the interior of the vehicle, where such communication as may be connected by some type of conductors, including a vehicle network system. In any event, each system  10  is operable to capture light signals as images, for various types of processing and/or display. Moreover, as described above, each such camera has a lens structure (e.g., lens, lens cover), and associated therewith is a transducer that is operable according to method  20  so as to reduce any contaminants on the surface of the lens structure. 
     From the above, the preferred embodiments are shown to provide an ultrasound lens structure cleaner and architecture method, either as a standalone unit or as part of a larger preferred embodiment system (e.g., a vehicle; surveillance camera; lighting system). Such preferred embodiments provide numerous benefits. For example, greater vibration coverage of the lens structure surface is achieved with a combination of waves providing both high transverse amplitudes and rotational patterns. As another example, greater acceleration coverage is achieved of the lens structure surface. As still another example, note that strains may be developed in multiple directions, rather than just the axial direction, to promote cracking of dried materials. More particularly, besides high transverse acceleration (orthogonal to the surface), lateral strain can be developed, which may be important for cracking dried contaminants Thus, strain may be imposed on the lens surface in both the radial and tangential directions. Thus, whereas due to the circular nature of the mode shape, strain is only applied in the radial but not in the tangential direction, the preferred embodiment may apply strain additionally in the tangential direction, whereby contaminants can be even more effectively removed. Moreover, asymmetric modes (e.g., mode (1,1) shape) will apply strain in both directions, leading to more effective cracking. As still another benefit, a straightforward driver circuit may drive system  10 . Still further, the preferred embodiments are implemented without vibration or resonance frequency matching issues. In view of the above, therefore, the inventive scope is far reaching, and while various alternatives have been provided according to the disclosed embodiments, still others are contemplated and yet others can ascertained by one skilled in the art. Given the preceding, therefore, one skilled in the art should further appreciate that while some embodiments have been described in detail, various substitutions, modifications or alterations can be made to the descriptions set forth above without departing from the inventive scope, as is defined by the following claims.