Patent Publication Number: US-2020282436-A1

Title: Multi-frequency reduction of fluid droplet

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 15/492,286 filed Apr. 20, 2017, which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/407,762 filed Oct. 13, 2016 and U.S. Provisional Patent Application Ser. No. 62/400,171 filed Sep. 27, 2016, the entireties of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     This relates generally to ultrasonics, and more particularly to multi-frequency reduction of a fluid droplet. 
     Unfortunately, the number of motor vehicle deaths appears to be increasing every year. This trend is caused by a variety of reasons, including an increase in the driving population. But more engineering effort is needed to reduce risk of death or serious injury in automobiles. In addition to avoiding risks to drivers and passengers, more robust obstacle and collision avoidance systems are required to reduce the high cost of damage to automobiles and other property due to collisions. 
     Fortunately, new technologies are becoming available that manufacturers can incorporate into new automobiles at a reasonable cost. Some promising technologies that may help to improve obstacle and collision avoidance systems are digital camera based surround view and camera monitoring systems. In some cases, cameras can increase safety by being mounted in locations that can give drivers access to alternative perspectives, which is otherwise diminished or unavailable to the driver&#39;s usual view through windows or mirrors. While mounting one or more cameras for alternative views can provide many advantages, some challenges may remain. 
     SUMMARY 
     A signal generator has a generator output. The signal generator is configured to generate first and second signals at the generator output. The first signal has a first frequency, and the second signal has a second frequency. Switching circuitry has a circuitry input and a circuitry output. The circuitry input is coupled to the generator output. The circuitry output is adapted to be coupled to an ultrasonic transducer mechanically coupled with a surface. The switching circuitry is configured to: provide the first signal to the ultrasonic transducer at the first frequency to reduce a fluid droplet on the surface from a first size to a second size; and provide the second signal to the ultrasonic transducer at the second frequency to reduce the fluid droplet from the second size to a third size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is partial block diagram of a system according to an embodiment including an apparatus that can expel fluid from a droplet on an optical surface using an ultrasonic transducer mechanically coupled to the optical surface. 
         FIG. 2  is a more detailed diagram of the system shown in  FIG. 1  according to an embodiment. 
         FIG. 3A  is a diagram of impedance versus frequency for an example ultrasonic transducer mechanically coupled to an example optical surface according to an embodiment. 
         FIG. 3B  is a diagram of example droplet size reduction versus frequency according to an embodiment. 
         FIGS. 4A-4F  show a flowchart representative of example machine readable instructions that may be executed to implement the example system to expel fluid from the droplet on the optical surface using the ultrasonic transducer mechanically coupled to the optical surface, according to an embodiment as shown in the example of  FIG. 1 . 
         FIG. 5  is a block diagram of an example processing platform capable of executing the machine readable instructions of  FIGS. 4A-4F  to implement the example system to expel fluid from the droplet on the optical surface using the ultrasonic transducer mechanically coupled to the optical surface, according to an embodiment as shown in the example of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     U.S. Pat. No. 10,384,239 is incorporated by reference in its entirety. 
       FIG. 1  is partial block diagram of a system  100  that can expel fluid from a droplet  102  on an optical surface  104  using an ultrasonic transducer  106  mechanically coupled to the optical surface  104 . For example, the ultrasonic transducer  106  can be a piezoelectric ultrasonic transducer  106  including a piezoelectric material (e.g., lead zirconate titanate PZT or niobium doped lead zirconate titanate PNZT.) The mechanical coupling of the ultrasonic transducer  106  with the optical surface  104  is representatively illustrated in the drawings by a dashed line box that encompasses the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . The fluid droplet  102  can be disposed on the optical surface  104  and can be coupled with the ultrasonic transducer  106  through the optical surface  104 . Accordingly, such coupling of the fluid droplet  102 , the ultrasonic transducer  106  and the optical surface  104  is representatively illustrated in the drawings by the dashed line box that encompasses the fluid droplet  102 , the ultrasonic transducer  106  and the optical surface  104 . In the example of  FIG. 1 , the ultrasonic transducer  106  mechanically coupled to the optical surface  104  and has a plurality of resonant frequency bands (e.g., first and second resonant frequency bands). 
     The example of  FIG. 1  shows a first amplifier  108   a  having a first output impedance  110   a . A first filter  112   a  (e.g., first filter network  112   a ) is tuned (e.g., by its corresponding filter component values) within the first resonant frequency band to facilitate matching the first output impedance  110   a  of the first amplifier  108   a  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  and to reduce by atomization the fluid droplet  102  from a first droplet size  102   a  to a second droplet size  102   b . A second filter  114   a  (e.g., second filter network  114   a ) is tuned (e.g., by its corresponding filter component values) within the second resonant frequency band to facilitate matching the first output impedance  110   a  of the first amplifier  108   a  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  and to reduce by atomization the fluid droplet  102  from the second droplet size  102   b  to a third droplet size  102   c . In the drawings: the first droplet size  102   a  is representatively illustrated using a dash-dot-dot-dash line style; the second droplet size  102   b  is representatively illustrated using a dash-dot-dash line style; and the third droplet size  102   c  is representatively illustrated using solid line style. 
     In the example of  FIG. 1 , the first filter  112   a  (e.g., first filter network  112   a ) can be tuned (e.g., by its corresponding filter component values) higher in frequency than the second filter  114   a  (e.g., second filter network  114   a .) Similarly, the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  can be higher in frequency than the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . In the example of  FIG. 1 , the first resonant frequency band to reduce the fluid droplet  102  from the first droplet size  102   a  to the second droplet size  102   b  is higher in frequency than the second resonant frequency band to reduce the fluid droplet  102  from the second droplet size  102   b  to the third droplet size. For example, the first filter  112   a  (e.g., first filter network  112   a ) can be tuned (e.g., by its corresponding filter component values) within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  to reduce by atomization the fluid droplet  102  from the first droplet size  102   a  to the second droplet size  102   b , and so as to be higher in frequency than the second filter  114   a  (e.g., second filter network  114   a ) tuned (e.g., by its corresponding filter component values) within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  to reduce by atomization the fluid droplet  102  from the second droplet size  102   b  to the third droplet size  102   c.    
     In the example of  FIG. 1 , a circuitry controller  116  can be coupled with an input  118   a ,  120   a  of the first amplifier  108   a  to generate a first signal at an input  122   a  of ultrasonic transducer  106 . The first signal at the input  122   a  of the ultrasonic transducer  106  includes a first frequency within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . In some examples, the first frequency of the first signal can be a first sweep of frequencies (e.g., a first frequency sweep) within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . Filter activation (and deactivation), as well as activation (and deactivation) of the ultrasonic transducer  106 , can be carried out by filter switching circuitry  124 , which is depicted in the drawings using stippled lines. For example, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the first filter  112   a  (e.g., first filter network  112   a ) to activate the first filter  112   a  (e.g. first filter network  112   a ) in response to a first control activation signal received from the circuitry controller  116  at an input  126  of the filter switching circuitry  124 . For example, the filter switching circuitry  124  can include a first filter switch controller  128  having a first low side switch control output  128   a  and a first high side switch control output  128   b . The first low side switch control output  128   a  of the first switch controller  128  can be coupled with a first low side switch  130   a  to control operation of the first low side switch  130   a , for example, operation between a conducting or closed state of the first low side switch  130   a  and a non-conducting or open state of the first low side switch  130   a . The first high side switch control output  128   b  can be coupled with a first high side switch  130   b  to control operation of the first high side switch  130   b , for example, operation between a conducting or closed state of the first high side switch  130   b  and a non-conducting or open state of the first high switch  130   b . As shown in the example of  FIG. 1 , the first low side switch  130   a  can be coupled between a ground reference and the first filter  112   a  (e.g., first filter network  112   a .) As shown in the example of  FIG. 1 , the first high side switch  130   b  can be coupled between the first filter  112   a  (e.g., first filter network  112   a ) and input  122   a  of the ultrasonic transducer  106 . 
     For example, first switch controller  128  can control both first low and high side switches  130   a ,  130   b  to be in a closed or conducting state, so as to activate the first filter  112   a  (e.g. first filter network  112   a ) in response to the first control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . For example, first switch controller  128  can control both first low and high side switches  130   a ,  130   b  to be in the open or non-conducting state, so as to deactivate the first filter  112   a  (e.g. first filter network  112   a ) in response to a first control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . 
     In the example of  FIG. 1 , the circuitry controller  116  can also be coupled with the input  118   a ,  120   a  of the first amplifier  108   a  to generate a second signal at the input  122   a  of ultrasonic transducer  106 . The second signal at the input  122   a  of the ultrasonic transducer  106  includes a second frequency within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . In some examples, the second frequency of the second signal can be a second sweep of frequencies (e.g., a second frequency sweep) within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . In the example of  FIG. 1 , the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the second filter  114   a  (e.g., second filter network  114   a ) to activate the second filter  114   a  (e.g. second filter network  114   a ) in response to a second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . For example, the filter switching circuitry  124  can include a second filter switch controller  138  having a second low side switch control output  138   a  and a second high side switch control output  138   b . The second low side switch control output  138   a  of the second switch controller  138  can be coupled with a second low side switch  140   a  to control operation of the second low side switch  140   a , for example, operation between a conducting or closed state of the second low side switch  140   a  and a non-conducting or open state of the second low side switch  140   a . The second high side switch control output  138   b  can be coupled with a second high side switch  140   b  to control operation of the second high side switch  140   b , for example, operation between a conducting or closed state of the second high side switch  140   b  and a non-conducting or open state of the second high switch  140   b . As shown in the example of  FIG. 1 , the second low side switch  140   a  can be coupled between a ground reference and the second filter  114   a  (e.g., second filter network  114   a .) As shown in the example of  FIG. 1 , the second high side switch  140   b  can be coupled between the second filter  114   a  (e.g., second filter network  114   a ) and input  122   a  of the ultrasonic transducer  106 . 
     For example, second switch controller  138  can control both second low and high side switches  140   a ,  140   b  to be in a closed or conducting state, so as to activate the second filter  114   a  (e.g. second filter network  114   a ) in response to the second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . For example, second switch controller  138  can control both second low and high side switches  140   a ,  140   b  to be in the open or non-conducting state, so as to deactivate the second filter  114   a  (e.g. second filter network  114   a ) in response to a second control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . 
     Also included in the example of  FIG. 1  is a second amplifier  108   b  having a second amplifier output impedance  110   b . The first additional filter  112   b  (e.g., first additional filter network  112   b ) is tuned (e.g., by its corresponding filter component values) within the first resonant frequency band to facilitate matching the second output impedance  110   b  of the second amplifier  108   b  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  and to reduce by atomization the fluid droplet  102  from a first droplet size  102   a  to a second droplet size  102   b . The second additional filter  114   b  (e.g., second additional filter network  114   b ) is tuned (e.g., by its corresponding filter component values) within the second resonant frequency band to facilitate matching the second output impedance  110   b  of the second amplifier  108   b  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  and to reduce by atomization the fluid droplet  102  from the second droplet size  102   b  to the third droplet size  102   c.    
     Also included in the example of  FIG. 1  are a pair of ultrasonic transducer couplers  142   a ,  142   b  (e.g., connectors  142   a ,  142   b ). For example, electrodes of ultrasonic transducer  106  can be soldered to wires, which can be attached to a circuit board via connectors  142   a ,  142   b . The pair of ultrasonic transducer couplers  142   a ,  142   b  can couple a bridge tied load including the ultrasonic transducer  106  between the first amplifier  108   a  and the second amplifier  108   b . For example, the pair of ultrasonic transducer couplers  142   a ,  142   b  can couple the ultrasonic transducer  106  between the first amplifier  108   a  and the second amplifier  108   b  as the bridge tied load  108   b . In addition to the first filter  112   a  (e.g. first filter network  112   a ), the example of  FIG. 1  includes a first additional filter  112   b  (e.g. first additional filter network  112   b .) The pair of ultrasonic transducer couplers  142   a ,  142   b  can couple the bridge tied load including the ultrasonic transducer  106  between the first filter  112   a  (e.g., first filter network  112   a ) and the first additional filter  112   b  (e.g., first additional filter network  112   b .) For example, the pair of ultrasonic transducer couplers  142   a ,  142   b  can couple the ultrasonic transducer  106  between the first filter  112   a  (e.g., first filter network  112   a ) and the first additional filter  112   b  (e.g., first additional filter network  112   b ) as the bridge tied load  106 . 
     The first filter  112   a  (e.g., first filter network  112   a ) and the first additional filter  112   b  (e.g., first additional filter network  112   b ) can be included in a first balanced filter  112   a ,  112   b . The pair of ultrasonic transducer couplers  142   a ,  142   b  can be coupled between the first filter  112   a  (e.g., first filter network  112   a ) and the first additional filter  112   b  (e.g., first additional filter network  112   b ) in the first balanced filter  112   a ,  112   b  including the first filter  112   a  (e.g., first filter network  112   a ) and the first additional filter  112   b  (e.g., first additional filter network  112   b .) 
     The first balanced filter  112   a ,  112   b  may be desired for its quality factor relative to quality factor of the first filter (e.g. first filter network  112   a ) alone. For example, the first filter network  112   a  can have a first filter network quality factor. The first balanced filter  112   a ,  112   b  including the first filter network  112   a  and the first additional filter network  112   b  can have a first balanced filter quality factor. The first balanced filter quality factor of the first balanced filter  112   a ,  112   b  can be greater than the first filter network quality factor of the first filter network  112   a.    
     The first filter  112   a  can be matched pair tuned with the first additional filter  112   b  within the first resonant frequency band to facilitate matching the first output impedance  110   a  of the first amplifier  108   a  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  and to reduce by atomization the fluid droplet  102  from the first droplet size  102   a  to the second droplet size  102   b.    
     Similarly, in addition to the second filter  114   a  (e.g. second filter network  114   a ), the example of  FIG. 1  includes a second additional filter  114   b  (e.g. second additional filter network  112   b .) The pair of ultrasonic transducer couplers  142   a ,  142   b  can couple the bridge tied load including the ultrasonic transducer  106  between the second filter  114   a  (e.g., second filter network  114   a ) and the second additional filter  114   b  (e.g., second additional filter network  114   b .) For example, the pair of ultrasonic transducer couplers  142   a ,  142   b  can couple the ultrasonic transducer  106  between the second filter  114   a  (e.g., second filter network  114   a ) and the second additional filter  114   b  (e.g., second additional filter network  114   b ) as the bridge tied load  106 . 
     The second filter  114   a  (e.g., second filter network  114   a ) and the second additional filter  114   b  (e.g., second additional filter network  114   b ) can be included in a second balanced filter  114   a ,  114   b . The pair of ultrasonic transducer couplers  142   a ,  142   b  can be coupled between the second filter  114   a  (e.g., second filter network  114   a ) and the second additional filter  114   b  (e.g., second additional filter network  114   b ) in the second balanced filter  114   a ,  114   b  including the second filter  114   a , (e.g., second filter network  114   a ) and the second additional filter  114   b  (e.g., second additional filter network  114   b .) 
     Similar to what was discussed with respect to the first balanced filter  112   a ,  112   b , the second balanced filter  114   a ,  114   b  may be desired for its quality factor relative to quality factor of the second filter (e.g. second filter network  114   a ) alone. For example, the second filter network  114   a  can have a second filter network quality factor. The second balanced filter  114   a ,  114   b  including the second filter network  114   a  and the second additional filter network  114   b  can have a second balanced filter quality factor. The second balanced filter quality factor of the second balanced filter  114   a ,  114   b  can be greater than the second filter network quality factor of the second filter network  114   a.    
     The second filter  114   a  can be matched pair tuned with the second additional filter  114   b  within the second resonant frequency band to facilitate matching the first output impedance  110   a  of the first amplifier  108   a  with impedance of the ultrasonic transducer  106  mechanically coupled to the surface  104  and to reduce by atomization the fluid droplet from the second droplet size  102   b  to the third droplet size  102   c.    
     In the example of  FIG. 1 , the circuitry controller  116  can be coupled with an additional input  118   b ,  120   b  of the second amplifier  108   b  to generate a first additional signal at an additional input  122   b  of ultrasonic transducer  106 . The first additional signal at the additional input  122   b  of the ultrasonic transducer  106  includes the first frequency within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . For example, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the first additional filter  112   b  (e.g., first additional filter network  112   b ) to activate the first additional filter  112   b  (e.g. first additional filter network  112   b ) in response to the first control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . For example, the first filter switch controller  128  of the filter switching circuitry  124  can include having a first additional low side switch control output  128   c  and a first additional high side switch control output  128   d . The first additional low side switch control output  128   c  of the first switch controller  128  can be coupled with a first additional low side switch  150   a  to control operation of the first additional low side switch  150   a , for example, operation between a conducting or closed state of the first additional low side switch  150   a  and a non-conducting or open state of the first additional low side switch  150   a . The first additional high side switch control output  128   d  can be coupled with a first additional high side switch  150   b  to control operation of the first additional high side switch  150   b , for example, operation between a conducting or closed state of the first additional high side switch  150   b  and a non-conducting or open state of the first additional high switch  150   b . As shown in the example of  FIG. 1 , the first additional low side switch  150   a  can be coupled between the ground reference and the first additional filter  112   b  (e.g., first additional filter network  112   b .) As shown in the example of  FIG. 1 , the first additional high side switch  150   b  can be coupled between the first additional filter  112   b  (e.g., first additional filter network  112   b ) and additional input  122   b  of the ultrasonic transducer  106 . 
     For example, first switch controller  128  can control both the first additional low side switch  150   a  and the first additional high side switch  150   b  to be in a closed or conducting state, so as to activate the first additional filter  112   b  (e.g. first additional filter network  112   b ) in response to the first control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . At the same time, the first switch controller  128  can also control both first low and high side switches  130   a ,  130   b  to be in the closed or conducting state, so as to activate the first filter  112   a  (e.g. first filter network  112   a ) in response to the first control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . Accordingly, in response to the first control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 , the first switch controller  128  can activate both the first filter  112   a  (e.g. first filter network  112   a ) and the first additional filter  112   b  (e.g. first additional filter network  112   b .) Moreover, since the first balanced filter  112   a ,  112   b  can include both the first filter  112   a  (e.g., first filter network  112   a ) and the first additional filter network  112   b  (e.g. first additional filter network  112   b ), in response to the first control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 , the first switch controller  128  can activate the first balanced filter  112   a ,  112   b.    
     For example, first switch controller  128  can control both the first additional low side switch  150   a  and the first additional high side switch  150   b  to be in an open or non-conducting state, so as to deactivate the first additional filter  112   b  (e.g. first additional filter network  112   b ) in response to the first control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . At the same time, the first switch controller  128  can also control both first low and high side switches  130   a ,  130   b  to be in the open or non-conducting state, so as to deactivate the first filter  112   a  (e.g. first filter network  112   a ) in response to the first control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . Accordingly, in response to the first control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 , the first switch controller  128  can deactivate both the first filter  112   a  (e.g. first filter network  112   a ) and the first additional filter  112   b  (e.g. first additional filter network  112   b .) Moreover, since the first balanced filter  112   a ,  112   b  can include both the first filter  112   a  (e.g., first filter network  112   a ) and the first additional filter network  112   b  (e.g. first additional filter network  112   b ), in response to the first control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 , the first switch controller  128  can deactivate the first balanced filter  112   a ,  112   b.    
     In the example of  FIG. 1 , the circuitry controller  116  can also be coupled with the additional input  118   b ,  120   b  of the second amplifier  108   b  to generate a second additional signal at the additional input  122   b  of ultrasonic transducer  106 . The second additional signal at the additional input  122   b  of the ultrasonic transducer  106  includes the second frequency within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . For example, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the second additional filter  114   b  (e.g., second additional filter network  114   b ) to activate the second additional filter  114   b  (e.g. second additional filter network  114   b ) in response to the second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . For example, the second filter switch controller  138  of the filter switching circuitry  124  can include a second additional low side switch control output  138   c  and a second additional high side switch control output  138   d . The second additional low side switch control output  138   c  of the second switch controller  138  can be coupled with a second additional low side switch  160   a  to control operation of the second additional low side switch  160   a , for example, operation between a conducting or closed state of the second additional low side switch  160   a  and a non-conducting or open state of the second additional low side switch  160   a . The second high side switch control output  138   d  can be coupled with a second additional high side switch  160   b  to control operation of the second additional high side switch  160   b , for example, operation between a conducting or closed state of the second additional high side switch  160   b  and a non-conducting or open state of the second additional high switch  160   b.    
     As shown in the example of  FIG. 1 , the second additional low side switch  160   a  can be coupled between the ground reference and the second additional filter  114   b  (e.g., second additional filter network  114   b .) As shown in the example of  FIG. 1 , the second additional high side switch  160   b  can be coupled between the second additional filter  114   b  (e.g., second additional filter network  114   b ) and additional input  122   b  of the ultrasonic transducer  106 . For example, second switch controller  138  can control both the second additional low side switch  160   a  and the second additional high side switch  160   b  to be in a closed or conducting state, so as to activate the second additional filter  114   b  (e.g. second additional filter network  114   b ) in response to the second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . At the same time, the second switch controller  138  can also control both second low and high side switches  140   a ,  140   b  to be in the closed or conducting state, so as to activate the second filter  114   a  (e.g. second filter network  112   b ) in response to the second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . Accordingly, in response to the second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 , the second switch controller  138  can activate both the second filter  114   a  (e.g. second filter network  114   a ) and the second additional filter  114   b  (e.g. second additional filter network  114   b .) Moreover, since the second balanced filter  114   a ,  114   b  can include both the second filter  114   a  (e.g., second filter network  112   a ) and the second additional filter network  114   b  (e.g. second additional filter network  114   b ), in response to the second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 , the second switch controller  138  can activate the second balanced filter  114   a ,  114   b.    
     For example, second switch controller  138  can control both the second additional low side switch  160   a  and the second additional high side switch  160   b  to be in an open or non-conducting state, so as to deactivate the second additional filter  114   b  (e.g. second additional filter network  114   b ) in response to the second control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . At the same time, the second switch controller  138  can also control both second low and high side switches  140   a ,  140   b  to be in the open or non-conducting state, so as to deactivate the second filter  114   a  (e.g. second filter network  114   b ) in response to the second control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . Accordingly, in response to the second control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 , the second switch controller  138  can deactivate both the second filter  114   a  (e.g. second filter network  114   a ) and the second additional filter  114   b  (e.g. second additional filter network  114   b .) Moreover, since the second balanced filter  114   a ,  114   b  can include both the second filter  114   a  (e.g., second filter network  114   a ) and the second additional filter network  114   b  (e.g. second additional filter network  114   b ), in response to the second control deactivation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 , the second switch controller  138  can deactivate the second balanced filter  114   a ,  114   b.    
     As shown in the example of  FIG. 1 , the optical surface  104  can be oriented within a gravitational field so that a component of the gravitational field that is tangential to the surface  104  (e.g., as depicted for by downward arrow tangential to surface  104 ) operates upon the fluid droplet  102 . This orientation can be achieved, for example, while activating the ultrasonic transducer  106  that is mechanically coupled to the optical surface  104  to expel fluid of the fluid droplet  102  from the optical surface. For example, the foregoing orienting of the optical surface  104  can be orienting the optical surface  104  within the gravitational field so that the component of the gravitational field that is tangential to the optical surface  104  is greater than a component of the gravitation field that is normal into the optical surface  104 . 
     As mentioned previously, in the example of  FIG. 1  filter activation (and deactivation), as well as activation (and deactivation) of the ultrasonic transducer  106 , can be carried out by filter switching circuitry  124 , which is depicted in the drawings using stippled lines. For example, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the first filter  112   a  (e.g., first filter network  112   a ) to activate the first filter  112   a  (e.g. first filter network  112   a ) in response to a first control activation signal received from the circuitry controller  116  at an input  126  of the filter switching circuitry  124 . Similarly, at the same time, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the first additional filter  112   b  (e.g., first additional filter network  112   b ) to activate the first additional filter  112   b  (e.g. first additional filter network  112   b ) in response to the first control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . 
     As shown in the example of  FIG. 1 , the circuitry controller  116  can be coupled with the input  118   a ,  120   a  of the first amplifier  108   a  to generate the first signal at the input  122   a  of ultrasonic transducer  106 . Similarly, at the same time, the circuitry controller  116  can be coupled with the additional input  118   b ,  120   b  of the second amplifier  108   b  to generate the first additional signal at the additional input  122   b  of ultrasonic transducer  106 . The first signal at the input  122   a  of the ultrasonic transducer  106  includes the first frequency within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . Similarly, as already discussed, the first additional signal at the additional input  122   b  of the ultrasonic transducer  106  likewise can include the first frequency within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . The first signal and the first additional signal can be antiphase (e.g., one-hundred-and-eighty degrees out of phase) with one another. 
     The circuitry controller  116  can begin ramping up the amplitude of the first signal at the ultrasonic transducer  106  from a predetermined initial amplitude level of the first signal to a predetermined full amplitude level of the first signal. At the same time, in a similarly way, circuitry controller  116  can also begin ramping up the amplitude of the first additional signal at the ultrasonic transducer  106  from a predetermined initial amplitude level of the first additional signal to a predetermined full amplitude level of the first additional signal. 
     For example, respective amplitudes of the first signal and the first additional signal can be ramped up (e.g., increased) by the circuitry controller  116  from their respective predetermined initial amplitude levels to their respective predetermined full amplitude levels at a predetermined ramp up rate. For example, the circuitry controller  116  can begin ramping up (e.g., increasing) respective amplitudes of the first signal and the first additional signal at the predetermined ramp up rate. The circuitry controller  116  can continue ramping up respective amplitudes of the first signal and the first additional signal at the predetermined ramp up rate, by increasing respective amplitudes of the first signal and first additional signal, while respective predetermined full amplitude levels of the first signal and the first additional signal have not yet been reached. Because the circuitry controller  116  can control and/or increase and/or set the respective amplitudes of the first signal and first additional signal, the circuitry controller  116  can determine that ramping up of the first signal and the first additional signal is finished. For example, as the circuitry controller  116  is finishing ramping up, the circuitry controller  116  can control and/or increase and/or set the respective amplitudes of the first signal and first additional signal to their respective predetermined full amplitude levels. For example, after the circuitry controller  116  controls and/or increases and/or sets the respective amplitudes of the first signal and first additional signal to their respective predetermined full amplitude levels, the circuitry controller  116  can determine that ramping up (e.g. increasing amplitude of the first signal and first additional signal) is finished. 
     In another example of ramping up, an amplitude sensor  162  can include an analog differential amplifier that can differentially sense voltage across the input  122   a  and the additional input  122   b  of the ultrasonic transducer  106 . The voltage differentially sensed by the analog differential amplifier across the input  122   a  and the additional input  122   b  of the ultrasonic transducer  106  is indicative of respective amplitudes of the first signal and the first additional signal in antiphase with one another. The first signal and the first additional signal can be ramped up by the circuitry controller  116  from their respective predetermined initial amplitude levels to their respective predetermined full amplitude levels at a predetermined ramp up rate. For example, the circuitry controller  116  can begin ramping up the first signal and the first additional signal at the predetermined ramp up rate. The circuitry controller  116  can continue ramping up the first signal and the first additional signal at the predetermined ramp up rate, by increasing respective amplitudes of the first signal and first additional signal, while respective predetermined full amplitude levels of the first signal and the first additional signal have not yet been reached. For example, as the circuitry controller  116  is finishing ramping up, the circuitry controller  116  can use the analog differential amplifier in differentially sensing the voltage across the input  122   a  and the additional input  122   b  of the ultrasonic transducer. This measurement can be the first sensed amplitude  164   a  and can be indicative of respective amplitudes of the first signal and the first additional signal in antiphase with one another. In this example, the amplitude comparator  166  can compare the first sensed amplitude  164   a  to the ascending target amplitude  168   a , for example, to determine whether the first sensed amplitude  164   a  satisfies the ascending target amplitude  168   a  for the first signal and the first additional signal. For example, when the amplitude comparator  166  determines that the first sensed amplitude  164   a  is below the ascending target amplitude  168   a , the amplitude comparator  166  can determine that the first sensed amplitude  164   a  does not satisfy the ascending target amplitude  168   a  for the first signal and the first additional signal. The circuitry controller  116  can adjust to increase respective amplitudes of the first signal and the first additional signal based on the first sensed amplitude  164   a . For example, the circuitry controller  116  can adjust to increase amplitude of the first signal and the first additional signal based on the amplitude comparator  166  determining that the first sensed amplitude  164   a  does not satisfy the ascending target amplitude  168   a . The ascending target amplitude  168   a  can be based on the respective predetermined full amplitude levels of the first signal and the first additional signal, so that the circuitry controller  116  can adjust to increase respective amplitudes of the first signal and the first additional signal to the predetermined full amplitude levels. 
     The circuitry controller  116  can then use the analog differential amplifier in differentially sensing the voltage across the input  122   a  and the additional input  122   b  of the ultrasonic transducer, so as to determine a second sensed amplitude  170   a  of the first signal and the first additional signal. The amplitude comparator  166  can compare the second sensed amplitude  170   a  of the first signal and the first additional signal to the ascending target amplitude  168   a , for example, to determine whether the second sensed amplitude  170   a  of the first signal and the first additional signal satisfies the ascending target amplitude  168   a . For example, when the amplitude comparator  166  determines that the second sensed amplitude  170   a  of the first signal and the first additional signal meets, or for example exceeds the ascending target amplitude  168   a , the amplitude comparator  166  can determine that the second sensed amplitude  170   a  of the first signal and the first additional signal satisfies the ascending target amplitude  168   a . For example, when the amplitude comparator  166  determines that the second sensed amplitude  170   a  of the first signal and the first additional signal satisfies the ascending target amplitude  168   a , the circuitry controller  116  can determine that increasing the amplitude of the first signal and the first additional signal is finished. For example, since the ascending target amplitude  168   a  can be based on the respective predetermined full amplitude levels of first signal and the first additional signal, the circuitry controller  116  can determine that respective amplitudes of the first signal and the first additional signal have been increased to reach the predetermined full amplitude levels of first signal and the first additional signal. This comparison can determine that ramping up, and increasing the amplitude of the first signal and first additional signal, is finished. Similarly, in case of overshooting the ascending target amplitude  168   a , the circuitry controller  116  can then use the analog differential amplifier in differentially sensing the voltage across the input  122   a  and the additional input  122   b  of the ultrasonic transducer, so as to determine decreasing the amplitude of the first signal and the first additional signal to match the ascending target amplitude  168   a.    
     Ramping up the respective amplitudes of the first signal and the first additional signal, as just discussed in various prior examples, can facilitate activating the ultrasonic transducer  106  at the first frequency within the first resonant frequency band of the ultrasonic transducer. For example, by coupling the first signal and the first additional signal, the fluid droplet  102  can be reduced by atomization from the first droplet size  102   a  to the second droplet size  102   b . Thereafter, the circuitry controller  116  can begin limiting the first signal and the first additional signal by ramping down the respective amplitudes of the first signal and the first additional signal at ultrasonic transducer from the respective predetermined full amplitude levels of the first signal and the first additional signal to the respective predetermined reduced levels of the first signal and the first additional signal. 
     For example, respective amplitudes of the first signal and the first additional signal can be ramped down (e.g., decreased) by the circuitry controller  116  from their respective predetermined full amplitude levels to their respective predetermined reduced amplitude levels at a predetermined ramp down rate. For example, the circuitry controller  116  can begin ramping down (e.g., decreasing) respective amplitudes of the first signal and the first additional signal at the predetermined ramp down rate. The circuitry controller  116  can continue ramping down respective amplitudes of the first signal and the first additional signal at the predetermined ramp down rate, by decreasing respective amplitudes of the first signal and first additional signal, while respective predetermined reduced amplitude levels of the first signal and the first additional signal have not yet been reached. Because the circuitry controller  116  can control and/or decrease and/or set the respective amplitudes of the first signal and first additional signal, the circuitry controller  116  can determine that ramping down of the first signal and the first additional is finished. For example, as the circuitry controller  116  is finishing ramping down, the circuitry controller  116  can control and/or decrease and/or set the respective amplitudes of the first signal and first additional signal to their respective predetermined reduced amplitude levels. For example, after the circuitry controller  116  controls and/or decreases and/or sets the respective amplitudes of the first signal and first additional signal to their respective predetermined reduced amplitude levels, the circuitry controller  116  can determine that ramping down (e.g. decreasing amplitude of the first signal and first additional signal) is finished. 
     In another example of ramping down, the amplitude sensor  162  can include an analog differential amplifier that can differentially sense voltage across the input  122   a  and the additional input  122   b  of the ultrasonic transducer  106 . The voltage differentially sensed by the analog differential amplifier across the input  122   a  and the additional input  122   b  of the ultrasonic transducer  106  is indicative of the respective amplitudes of the first signal and the first additional signal in antiphase with one another. The first signal and the first additional signal can be ramped down by the circuitry controller  116  from their respective predetermined full amplitude levels to their respective predetermined reduced amplitude levels at a predetermined ramp down rate. For example, the circuitry controller  116  can begin ramping down the first signal and the first additional signal at the predetermined ramp down rate. The circuitry controller  116  can continue ramping down the first signal and the first additional signal at the predetermined ramp down rate, by decreasing respective amplitudes of the first signal and first additional signal, while respective predetermined reduced amplitude levels of the first signal and the first additional signal have not yet been reached. For example, as the circuitry controller  116  is finishing ramping down, the circuitry controller  116  can use the analog differential amplifier in differentially sensing the voltage across the input  122   a  and the additional input  122   b  of the ultrasonic transducer. This measurement can be the first sensed amplitude  164   a  and can be indicative of respective amplitudes of the first signal and the first additional signal in antiphase with one another. In this example, the amplitude comparator  166  can compare the first sensed amplitude  164   a  to the descending target amplitude  168   a , for example, to determine whether the first sensed amplitude  164   a  satisfies the descending target amplitude  168   a  for the first signal and the first additional signal. For example, when the amplitude comparator  166  determines that the first sensed amplitude  164   a  is above the descending target amplitude  168   a , the amplitude comparator  166  can determine that the first sensed amplitude  164   a  does not satisfy the descending target amplitude  168   a  for the first signal and the first additional signal. The circuitry controller  116  can adjust to decrease respective amplitudes of the first signal and the first additional signal based on the first sensed amplitude  164   a . For example, the circuitry controller  116  can adjust to decrease amplitude of the first signal and the first additional signal based on the amplitude comparator  166  determining that the first sensed amplitude  164   a  does not satisfy the descending target amplitude  168   a . The descending target amplitude  168   a  can be based on the respective predetermined reduced amplitude levels of the first signal and the first additional signal, so that the circuitry controller  116  can adjust to decrease respective amplitudes of the first signal and the first additional signal to the predetermined reduced amplitude levels. 
     The circuitry controller  116  can then use the analog differential amplifier in differentially sensing the voltage across the input  122   a  and the additional input  122   b  of the ultrasonic transducer, so as to determine a second sensed amplitude  170   a  of the first signal and the first additional signal. The amplitude comparator  166  can compare the second sensed amplitude  170   a  of the first signal and the first additional signal to the descending target amplitude  168   a , for example, to determine whether the second sensed amplitude  170   a  of the first signal and the first additional signal satisfies the descending target amplitude  168   a . For example, when the amplitude comparator  166  determines that the second sensed amplitude  170   a  of the first signal and the first additional signal meets, or, for example, is below the descending target amplitude  168   a , the amplitude comparator  166  can determine that the second sensed amplitude  170   a  of the first signal and the first additional signal satisfies the descending target amplitude  168   a . For example, when the amplitude comparator  166  determines that the second sensed amplitude  170   a  of the first signal and the first additional signal satisfies the descending target amplitude  168   a , the circuitry controller  116  can determine that decreasing the amplitude of the first signal and the first additional signal is finished. For example, since the descending target amplitude  168   a  can be based on the respective predetermined reduced amplitude levels of first signal and the first additional signal, the circuitry controller  116  can determine that respective amplitudes of the first signal and the first additional signal have been decreased to reach the predetermined reduced amplitude levels of first signal and the first additional signal. This comparison can determine that ramping down, and decreasing the amplitude of the first signal and first additional signal, is finished. Similarly, in case of overshooting the descending target amplitude  168   b , the circuitry controller  116  can then use the analog differential amplifier in differentially sensing the voltage across the input  122   a  and the additional input  122   b  of the ultrasonic transducer, so as to determine increasing the amplitude of the first signal and the first additional signal to match the descending target amplitude  168   b.    
     As just discussed in the various prior examples, the circuitry controller  116  can limit the first signal and the first additional signal by ramping down the respective amplitudes of the first signal and the first additional signal at ultrasonic transducer from the respective predetermined full amplitude levels of the first signal and the first additional signal to the respective predetermined reduced levels of the first signal and the first additional signal. Thereafter, the circuitry controller  116  can begin determining when to deactivate the first filter  112   a  (and the first additional filter  112   b ) and the ultrasonic transducer  106  based on sensing a first current transient of the ultrasonic transducer  106 . As shown for example in  FIG. 1 , an ultrasonic transducer current sensor  172  can be coupled to the ultrasonic transducer  106  to sense current transients, for example, to sense the first current transient of the ultrasonic transducer. For example, the ultrasonic transducer current sensor  172  can include an AC level detector. For example, the AC level detector can include a rectifier followed by a low-pass filter. In another example, the AC level detector can take a maximum value over a time window which is at least one electrical period long. 
     The ultrasonic transducer current sensor  172  can sense current, for example, to determine a first current sensing  174  of a first current transient of the ultrasonic transducer  106 . For example, the circuitry controller  116  can include a current transient comparator  176  to compare the first current sensing  174  of the first current transient of the ultrasonic transducer  106  to a current transient threshold  178 , for example, to determine whether the first current sensing  174  of the first current transient of the ultrasonic transducer  106  satisfies the current transient threshold  178 . For example, when the current transient comparator  176  determines that the first current sensing  174  of the first current transient of the ultrasonic transducer  106  is above the current transient threshold  178 , the current transient comparator  176  can determine that the first current sensing  174  of the first current transient of the ultrasonic transducer  106  does not satisfy the current transient threshold  178 . The circuitry controller  116  can delay deactivating the first filter  112   a  (and the first additional filter  112   b ) and delay deactivating the ultrasonic transducer  106  based on the ultrasonic transducer current sensor  172  sensing the first current transient of the ultrasonic transducer  106 . For example, the circuitry controller  116  can delay deactivating the first filter  112   a  (and the first additional filter  112   b ) and delay deactivating the ultrasonic transducer  106  based on the current transient comparator  176  determining that the first current sensing  174  of the first current transient of the ultrasonic transducer  106  does not satisfy the current transient threshold  178 . The current transient threshold  178  can be based on a predetermined reduced current transient of the ultrasonic transducer  106 , so that the circuitry controller  116  can delay until the current of the ultrasonic transducer  106  reaches the predetermined reduced current transient of the ultrasonic transducer  106 . The predetermined reduced current transient of the ultrasonic transducer  106  can be a zero current transient, or a near zero current transient. 
     The circuitry controller  116  can also determine whether delaying the deactivation of the first filter  112   a  (and the first additional filter  112   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. The ultrasonic transducer current sensor  172  that can sense current of the ultrasonic transducer  106 , for example, can determine a second current sensing  180  of the first current transient of the ultrasonic transducer  106 . The current transient comparator  176  can compare the second current sensing  180  of the first current transient of the ultrasonic transducer  106  to the current transient threshold  178 , for example, to determine whether the second current sensing  180  of the first current transient of the ultrasonic transducer  106  satisfies the current transient threshold  178 . For example, when the current transient comparator  176  determines that the second current sensing  180  of the first current transient of the ultrasonic transducer  106  meets, or for example is lower than the current transient threshold  178 , the current transient comparator  176  can determine that the second current sensing  180  of the first current transient of the ultrasonic transducer  106  satisfies the current transient threshold  178 . For example, when the current transient comparator  176  determines that second current sensing  180  of the first current transient of the ultrasonic transducer  106  satisfies the current transient threshold  178 , the circuitry controller  116  can determine that delaying the deactivation of the first filter  112   a  (and the first additional filter  112   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. For example, since the current transient threshold  178  can be based on the predetermined reduced current transient, the circuitry controller  116  can determine that the first current transient of the ultrasonic transducer  106  has been reduced to reach the predetermined reduced current transient, and so can determine that delaying the deactivation of the first filter  112   a  (and the first additional filter  112   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. 
     In the examples just discussed, ultrasonic transducer current sensor  172  can be employed in determining whether delaying the deactivation of the first filter  112   a  (and the first additional filter  112   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. However, in simpler examples, ultrasonic transducer current sensor  172  may not be needed. In a simpler example, circuitry controller  116  can determine that delaying the deactivation of the first filter  112   a  (and the first additional filter  112   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished by using timer  182 . For example, timer  182  can determine when a predetermined prior time period has elapsed, prior to deactivating the first filter  112   a  (and the first additional filter  112   b ) and deactivating the ultrasonic transducer  106 . The predetermined prior time period can be selected to provide sufficient time for the current transient to die down to a sufficiently reduced current transient level. 
     For example, after finishing ramping down the respective amplitudes of the first signal and the first additional signal, the circuitry controller  116  can start timer  182  to measure elapsed time. After the timer  182  determines that the predetermined prior time period has elapsed, the circuitry controller  116  can determine to deactivate the first filter  112   a  (and the first additional filter  112   b ) and deactivate the ultrasonic transducer  106 . After the timer  182  determines that the predetermined prior time period has elapsed, the circuitry controller  116  can determine that delaying the deactivation of the first filter  112   a  (and the first additional filter  112   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. 
     After the circuitry controller  116  determines that delaying the deactivation of the first filter  112   a  (and the first additional filter  112   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished, the circuitry controller  116  can control the filter switching circuitry  124  to deactivate the first filter  112   a  (and the first additional filter  112   b ) and deactivate the ultrasonic transducer  106 . Further, the circuitry controller  116  can use, for example, timer  182  to delay a predetermined period of time after deactivating the first filter  112   a  (and the first additional filter  112   b ) and deactivating the ultrasonic transducer  106 . Additionally, after delaying the predetermined period of time after deactivating the first filter  112   a  (and the first additional filter  112   b ) and deactivating the ultrasonic transducer  106 , the circuitry controller can then activate the second filter  114   a  (and the second additional filter  114   b ) and activate the ultrasonic transducer  106 . 
     For example, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the second filter  114   a  (e.g., second filter network  114   a ) to activate the second filter  114   a  (e.g. second filter network  114   a ) in response to the second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . Similarly, at the same time, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the second additional filter  114   b  (e.g., second additional filter network  114   b ) to activate the second additional filter  114   b  (e.g. second additional filter network  114   b ) in response to the second control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . 
     As shown in the example of  FIG. 1 , the circuitry controller  116  can be coupled with the input  118   a ,  120   a  of the first amplifier  108   a  to generate the second signal at the input  122   a  of ultrasonic transducer  106 . Similarly, at the same time, the circuitry controller  116  can be coupled with the additional input  118   b ,  120   b  of the second amplifier  108   b  to generate the second additional signal at the additional input  122   b  of ultrasonic transducer  106 . The second signal at the input  122   a  of the ultrasonic transducer  106  includes the second frequency within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . Similarly, as already discussed, the second additional signal at the additional input  122   b  of the ultrasonic transducer  106  likewise can include the second frequency within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . The second signal and the second additional signal can be antiphase (e.g., one-hundred-and-eighty degrees out of phase) with one another. 
     The circuitry controller  116  can begin ramping up the amplitude of the second signal at the ultrasonic transducer  106  from a predetermined initial amplitude level of the second signal to a predetermined full amplitude level of the second signal. At the same time, in a similarly way, circuitry controller  116  can also begin ramping up the amplitude of the second additional signal at the ultrasonic transducer  106  from a predetermined initial amplitude level of the second additional signal to a predetermined full amplitude level of the second additional signal. 
     While various examples of ramping up the amplitude of the first signal and the first additional signal have already been discussed in detail previously herein, amplitude of the second signal and the second additional signal can be ramped up by the circuitry controller  116  in similar ways. Accordingly, application of these previously discussed ramping up examples to ramping up the amplitude of the second signal and the second additional signal is not discussed in detail here. Instead, the reader is directed to the previously discussed ramping up examples, and directed to apply the previously discussed ramping up examples to ramping up the amplitude of the second signal and the second additional signal. 
     Ramping up the respective amplitudes of the second signal and the second additional signal, as just discussed, can facilitate activating the ultrasonic transducer at the second frequency within the second resonant frequency band of the ultrasonic transducer, for example, by coupling the second signal and the second additional signal to reduce the fluid droplet  102  by atomization from the second droplet size  102   b  to the third droplet size  102   c . Thereafter, the circuitry controller  116  can begin limiting the second signal and the second additional signal by ramping down the respective amplitudes of the second signal and the second additional signal at ultrasonic transducer from the respective predetermined full amplitude levels of the second signal and the second additional signal to the respective predetermined reduced levels of the second signal and the second additional signal. 
     While various examples of ramping down amplitude of the first signal and the first additional signal have already been discussed in detail previously herein, amplitude of the second signal and the second additional signal can be ramped down by the circuitry controller  116  in similar ways. Accordingly, application of these previously discussed ramping down examples to ramping down amplitude of the second signal and the second additional signal is not discussed in detail here. Instead, the reader is directed to the previously discussed ramping down examples, and directed to apply the previously discussed ramping down examples to ramping down amplitude of the second signal and the second additional signal. 
     As just discussed, the circuitry controller  116  can limit the second signal and the second additional signal by ramping down the respective amplitudes of the second signal and the second additional signal at ultrasonic transducer from the respective predetermined full amplitude levels of the second signal and the second additional signal to the respective predetermined reduced levels of the second signal and the second additional signal. Thereafter, the circuitry controller  116  can begin determining when to deactivate the second filter  114   a  (and the second additional filter  114   b ) and the ultrasonic transducer  106  based on sensing a second current transient of the ultrasonic transducer  106 . As shown for example in  FIG. 1 , the ultrasonic transducer current sensor  172  can be coupled to the ultrasonic transducer  106  to sense current transients, for example, to sense the second current transient of the ultrasonic transducer. 
     The ultrasonic transducer current sensor  172  can sense current, for example, to determine a first current sensing  174  of the second current transient of the ultrasonic transducer  106 . For example, the circuitry controller  116  can include a current transient comparator  176  to compare the first current sensing  174  of the second current transient of the ultrasonic transducer  106  to the current transient threshold  178 , for example, to determine whether the first current sensing  174  of the second current transient of the ultrasonic transducer  106  satisfies the current transient threshold  178 . For example, when the current transient comparator  176  determines that the first current sensing  174  of the second current transient of the ultrasonic transducer  106  is above the current transient threshold  178 , the current transient comparator  176  can determine that the first current sensing  174  of the second current transient of the ultrasonic transducer  106  does not satisfy the current transient threshold  178 . The circuitry controller  116  can delay deactivating the second filter  114   a  (and the second additional filter  114   b ) and delay deactivating the ultrasonic transducer  106  based on the ultrasonic transducer current sensor  172  sensing the second current transient of the ultrasonic transducer  106 . For example, the circuitry controller  116  can delay deactivating the second filter  114   a  (and the second additional filter  114   b ) and delay deactivating the ultrasonic transducer  106  based on the current transient comparator  176  determining that the first current sensing  174  of the second current transient of the ultrasonic transducer  106  does not satisfy the current transient threshold  178 . The current transient threshold  178  can be based on the predetermined reduced current transient of the ultrasonic transducer  106 , so that the circuitry controller  116  can delay until the current of the ultrasonic transducer  106  reaches the predetermined reduced current transient of the ultrasonic transducer  106 . As already mentioned, the predetermined reduced current transient of the ultrasonic transducer  106  can be the zero current transient, or the near zero current transient. 
     The circuitry controller  116  can also determine whether delaying the deactivation of the second filter  114   a  (and the second additional filter  114   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. The ultrasonic transducer current sensor  172  that can sense current of the ultrasonic transducer  106 , for example, can determine a second current sensing  180  of the second current transient of the ultrasonic transducer  106 . The current transient comparator  176  can compare the second current sensing  180  of the second current transient of the ultrasonic transducer  106  to the current transient threshold  178 , for example, to determine whether the second current sensing  180  of the second current transient of the ultrasonic transducer  106  satisfies the current transient threshold  178 . For example, when the current transient comparator  176  determines that the second current sensing  180  of the second current transient of the ultrasonic transducer  106  meets, or, for example, is lower than the current transient threshold  178 , the current transient comparator  176  can determine that the second current sensing  180  of the second current transient of the ultrasonic transducer  106  satisfies the current transient threshold  178 . For example, when the current transient comparator  176  determines that the second current sensing  180  of the second current transient of the ultrasonic transducer  106  satisfies the current transient threshold  178 , the circuitry controller  116  can determine that delaying the deactivation of the second filter  114   a  (and the second additional filter  114   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. For example, since the current transient threshold  178  can be based on the predetermined reduced current transient, the circuitry controller  116  can determine that the second current transient of the ultrasonic transducer  106  has been reduced to reach the predetermined reduced current transient, and so can determine that delaying the deactivation of the second filter  114   a  (and the second additional filter  114   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. 
     In the examples just discussed, ultrasonic transducer current sensor  172  can be employed in determining whether delaying the deactivation of the second filter  114   a  (and the second additional filter  114   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. However, in simpler examples, ultrasonic transducer current sensor  172  may not be needed. In a simpler example, circuitry controller  116  can determine that delaying the deactivation of the second filter  114   a  (and the second additional filter  114   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished by using timer  182 . For example, timer  182  can determine when a predetermined prior time period has elapsed, prior to deactivating the second filter  114   a  (and the second additional filter  114   b ) and deactivating the ultrasonic transducer  106 . The predetermined prior time period can be selected to provide sufficient time for the current transient to die down to a sufficiently reduced current transient level. 
     For example, after finishing ramping down the respective amplitudes of the second signal and the second additional signal, the circuitry controller  116  can start timer  182  to measure elapsed time. After the timer  182  determines that the predetermined prior time period has elapsed, the circuitry controller  116  can determine to deactivate the second filter  114   a  (and the second additional filter  114   b ) and deactivate the ultrasonic transducer  106 . After the timer  182  determines that the predetermined prior time period has elapsed, the circuitry controller  116  can determine that delaying the deactivation of the second filter  114   a  (and the second additional filter  114   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished. 
     After the circuitry controller  116  determines that delaying the deactivation of the second filter  114   a  (and the second additional filter  114   b ) and delaying the deactivation of the ultrasonic transducer  106  is finished, the circuitry controller  116  can control the filter switching circuitry to deactivate the second filter  114   a  (and the second additional filter  114   b ) and deactivate the ultrasonic transducer  106 . Further, the circuitry controller  116  can use, for example, timer  182  to delay the predetermined period of time after deactivating the second filter  114   a  (and the second additional filter  114   b ) and deactivating the ultrasonic transducer  106 . Additionally, after delaying the predetermined period of time after deactivating the second filter  114   a  (and the second additional filter  114   b ) and deactivating the ultrasonic transducer  106 , a cycle controller  184  of the circuitry controller  116  can determine whether to repeat a cycle by once again initiating activation of first filter  112   a  (and first additional filter  112   b ) and activation of the ultrasonic transducer  106 , or instead end the cycle, based for example on a user control input to the cycle controller to end the cycle. 
     While the foregoing discussions have described ramping up and ramping down of the first and first additional signals and the second and second additional signals,  FIG. 1  further shows clamp diodes  186   a ,  186   b ,  186   c ,  186   d  and transient voltage suppressor (TVS) diodes  188   a ,  188   b ,  188   c ,  188   d  for protecting circuitry in case current is unexpectedly interrupted. As shown in the example of  FIG. 1 , a first parallel combination of clamp diode and transient voltage suppressor diode  186   a ,  188   a  can be coupled between the first filter  112   a  and a ground reference. Similarly, a second parallel combination of clamp diode and transient voltage suppressor diode  186   b ,  188   b  can be coupled between the first additional filter  112   b  and the ground reference. Additionally, a third parallel combination of clamp diode and transient voltage suppressor diode  186   c ,  188   c  can be coupled between the second filter  114   a  and the ground reference. A fourth parallel combination of clamp diode and transient voltage suppressor diode  186   d ,  188   d  can be coupled between the second additional filter  114   b  and the ground reference. 
       FIG. 2  is a more detailed diagram of the system shown in  FIG. 1  according to an embodiment. Like example system  100  shown in  FIG. 1 , example system  200  shown in  FIG. 2  can expel fluid from a droplet  102  on an optical surface  104  using an ultrasonic transducer  106  mechanically coupled to the optical surface  104 . As shown in greater detail in the example of  FIG. 2 , first amplifier  108   a  can include a first pair of series coupled transistors  202   a ,  204   a  coupled between a DC voltage rail and a ground reference. Respective control gates of the first pair of transistors  202   a ,  204   a  can be coupled as the input  118   a ,  120   a  of the first amplifier  108   a . The first and second filter networks  112   a ,  114   a  can be coupled to receive an output of the first amplifier  108   a  at a series coupling node  206   a  between first and second ones of the first pair of series coupled transistors  202   a ,  204   a.    
     Similarly, as shown in greater detail in the example of  FIG. 2 , the second amplifier  108   b  can include a second pair of series coupled transistors  202   b ,  204   b  coupled between the DC voltage rail and the ground reference. Respective control gates of the second pair of transistors  202   b ,  204   b  can be coupled as the input  118   b ,  120   b  of the second amplifier  108   b . The first and second additional filter networks  112   b ,  114   b  can be coupled to receive an output of the second amplifier  108   b  at a series coupling node  206   b  between first and second ones of the second pair of series coupled transistors  202   b ,  204   b.    
     The first filter network  112   a  can include a series coupled inductor  208   a  coupled in series with the output of the first amplifier  108   a  at the series coupling node  206   a  between first and second ones of the first pair of series coupled transistors  202   a ,  204   a . The first filter network  112   a  can also include a capacitor  210   a  coupled in series with the inductor  208   a.    
     Similarly, second filter network  114   a  can include a series coupled inductor  212   a  coupled in series with the output of the first amplifier  108   a  at the series coupling node  206   a  between first and second ones of the first pair of series coupled transistors  202   a ,  204   a . The second filter network  114   a  can also include a capacitor  214   a  coupled in series with the inductor  212   a.    
     The first additional filter network  112   b  can include a series coupled inductor  208   b  coupled in series with the output of the second amplifier  108   b  at the series coupling node  206   b  between first and second ones of the second pair of series coupled transistors  202   b ,  204   b . The first additional filter network  112   b  can also include a capacitor  210   b  coupled in series with the inductor  208   b.    
     Similarly, second additional filter network  114   b  can include a series coupled inductor  212   b  coupled in series with the output of the second amplifier  108   b  at the series coupling node  206   b  between first and second ones of the second pair of series coupled transistors  202   b ,  204   b . The second additional filter network  114   b  can also include a capacitor  214   b  coupled in series with the inductor  212   b.    
     The first additional filter network  112   b  can be tuned (e.g., by its corresponding filter component values) in a similar way using the same or similar component values as the first filter network  112   a  can be tuned (e.g., by its corresponding filter component values). For example, the series coupled inductor  208   a  of the first filter network  112   a  can have an inductance L 1  that is the same or similar as the inductance L 1  of the series coupled inductor  208   b  of the first additional filter network  112   b . Further, the series coupled capacitor  210   a  of the first filter network  112   a  can have a capacitance C 1  that is the same or similar as the capacitance C 1  of the series coupled capacitor  210   b  of the first additional filter network  112   b.    
     Similarly, the second additional filter network  114   b  can be tuned (e.g., by its corresponding filter component values) in a similar way using the same or similar component values as the second filter network  114   a  can be tuned (e.g., by its corresponding filter component values). For example, the series coupled inductor  212   a  of the second filter network  114   a  can have an inductance L 2  that is the same or similar as the inductance L 2  of the series coupled inductor  212   b  of the second additional filter network  114   b . Further, the series coupled capacitor  214   a  of the second filter network  114   a  can have a capacitance C 2  that is the same or similar as the capacitance C 2  of the series coupled capacitor  214   b  of the second additional filter network  114   b.    
     As shown in the example of  FIG. 2 , the first filter network  112   a  and the first additional filter network  112   b  are tuned by their corresponding filter component values (e.g., series inductance L 1  and series capacitance C 1 ) within the first resonant frequency band to facilitate matching the respective first and second output impedance of the first and second amplifiers  108   a ,  108   b  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  and to reduce by atomization the fluid droplet  102  from the first droplet size  102   a  to the second droplet size  102   b . The second filter network  114   a  and the second additional filter network  114   b  are tuned by their corresponding filter component values (e.g., series inductance L 2  and series capacitance C 2 ) within the second resonant frequency band to facilitate matching the first and second output impedances of the first and second amplifiers  108   a ,  108   b  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104  and to reduce by atomization the fluid droplet  102  from the second droplet size  102   b  to the third droplet size  102   c.    
     In the example of  FIG. 2 , the first filter network  112   a  and the first additional filter network  112   b  can be tuned to the first frequency by their corresponding filter component values (e.g., series inductance L 1  and series capacitance C 1 ) to be higher in frequency than the second filter network  114   a  and the second additional filter network  114   b  as tuned to the second frequency by their corresponding filter component values (e.g., series inductance L 2  and series capacitance C 2 ). 
     Although  FIG. 2  shows example greater details of the first and second amplifier  108   a ,  108   b  than what is shown in  FIG. 1 , the example of  FIG. 2  is similar to the example of  FIG. 1  as already discussed in detail previously herein. Further, although  FIG. 2  shows example greater details of the first and first additional filter networks  112   a ,  112   b  and shows example greater details of the second and second additional filter networks  114   a ,  114   b , the example of  FIG. 2  is similar to the example of  FIG. 1  as already discussed in detail previously herein. Accordingly,  FIG. 2  is not further discussed here, and the reader directed instead to the previous discussion of  FIG. 1  for discussion of those elements that are similar to both the example of  FIG. 1  and the example of  FIG. 2 . 
     The examples of  FIGS. 1 and 2  show filter switching circuitry to switch the first and first additional filter networks  112   a ,  112   b  with the second and second additional filter networks  114   a ,  114   b . In another example, the forgoing can be extended to include the filter switching circuitry to switch a third and third additional filter network (not shown in  FIGS. 1 and 2 ). The filter switching circuitry coupled between the circuitry controller and the third filter network (and between the circuitry controller and the third additional filter network) to activate the third filter (and to activate the third additional filter) in response to a third control signal from the circuitry controller. The third and third additional filter network can be tuned within a third resonant frequency band to facilitate matching the first output impedance of the first amplifier with impedance of the ultrasonic transducer mechanically coupled to the surface and to reduce the fluid droplet by atomization. The circuitry controller can be coupled with the input of the first amplifier to generate a third signal at the input of the ultrasonic transducer, the third signal including a third frequency within the third resonant frequency band of the ultrasonic transducer mechanically coupled to the surface. 
     Just discussed was switching circuitry to switch the first and first additional filter networks, with the second and second additional filter networks and with the third and third additional filter networks. In yet another example, this architecture can be extended even further to include the filter switching circuitry to switch a fourth and fourth additional filter network (not shown in  FIGS. 1 and 2 ). The filter switching circuitry coupled between the circuitry controller and the fourth filter network (and between the circuitry controller and the fourth additional filter network) to activate the fourth filter (and to activate the fourth additional filter) in response to a fourth control signal from the circuitry controller. The fourth and fourth additional filter network can be tuned within a fourth resonant frequency band to facilitate matching the first output impedance of the first amplifier with impedance of the ultrasonic transducer mechanically coupled to the surface and to reduce the fluid droplet by atomization. The circuitry controller can be coupled with the input of the first amplifier to generate a fourth signal at the input of the ultrasonic transducer, the fourth signal including a fourth frequency within the fourth resonant frequency band of the ultrasonic transducer mechanically coupled to the surface. 
     The forgoing examples can be extended even further, to further examples including the switching circuitry to switch activation of fifth, sixth, and so on, filter networks, up to an arbitrary number Nth filter network, and up to an arbitrary number Nth resonant frequency band. 
     The foregoing examples are directed to a plurality of filters tuned within respective resonant frequency bands of the ultrasonic transducer mechanically coupled to the surface. More broadly, the ultrasonic transducer mechanically coupled to the surface can have a plurality of resonant frequency bands, and a filter can cover the plurality of resonant frequency bands. For example, the filter can be the plurality of filters tuned within respective resonant frequency bands of the ultrasonic transducer mechanically coupled to the surface. As another example, the filter can be a single filter covering the plurality of resonant frequency bands. 
     In the foregoing examples, a plurality of signals can be generated having respective frequencies within respective resonant frequency bands of the ultrasonic transducer  106  mechanically coupled to the surface  104 . The ultrasonic transducer  106  can be activated at the respective frequencies within the respective resonant frequency bands using the plurality of signals. Multistage reducing of the fluid droplet  102  by atomization can be carried out in response to activating the ultrasonic transducer  106  using the plurality of signals at the respective frequencies within the respective resonant frequency bands. The plurality of signals can have respective frequency sweeps within respective resonant frequency bands of the ultrasonic transducer  106  mechanically coupled to the surface  104 . Generating the plurality of signals can include generating the first signal having the first frequency within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the surface  104 . Generating the plurality of signals can also include generating the second signal having the second frequency within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the surface  104 . Activating the ultrasonic transducer  106  can include activating the ultrasonic transducer at the first frequency within the first resonant frequency band using the first signal. Activating the ultrasonic transducer  106  can also include activating the ultrasonic transducer at the second frequency within the second resonant frequency band using the second signal. The multistage reducing of the fluid droplet  102  can include a first stage, reducing the fluid droplet  102  from the first droplet size  102   a  to the second droplet size  102   b  in response to activating the ultrasonic sonic transducer  106  using the first signal at the first frequency within the first resonant frequency band. The multistage reducing of the fluid droplet  102  can also include a second stage, reducing the fluid droplet from the second size  102   b  to the third size  102   c  in response to activating the ultrasonic transducer  106  using the second signal at the second frequency within the second resonant frequency band. 
       FIG. 3A  is a diagram  300   a  of impedance (Ohms in decibels) versus frequency (logarithmic scale in kilohertz) for an example ultrasonic transducer mechanically coupled to an example optical surface according to an embodiment.  FIG. 3A  shows the example first frequency  302  of an example three-hundred kilohertz for the example ultrasonic transducer mechanically coupled to the example optical surface. The example first frequency  302  of the example three-hundred kilohertz can correspond to a first nominal resonance frequency of a first low impedance resonance extremity  302  in the diagram of  FIG. 3A  at the first frequency  302  of the example ultrasonic transducer mechanically coupled to the example optical surface. The example first frequency  302  of the example three-hundred kilohertz can correspond to the first nominal resonance frequency of the first low impedance resonance extremity  302  that is centered within a first resonance band “302band”. More broadly, the first frequency  302  is within a first resonance band “302band”. The first resonance band is defined herein as extending in frequency to plus and minus ten percent of the first nominal resonance frequency of the first low impedance resonance extremity for the ultrasonic transducer mechanically coupled to the optical surface. For example, with the example first frequency of the example three-hundred kilohertz, the first resonance band extends in frequency to plus and minus ten percent of the first nominal resonance frequency of three-hundred kilohertz (e.g. the first resonance band extends in frequency to plus and minus thirty kilohertz from the three-hundred kilohertz, or the first resonance band extends in frequency from two-hundred-and-seventy kilohertz to three-hundred-and-thirty kilohertz). 
     Further,  FIG. 3A  shows the example second frequency  304  of an example twenty-six kilohertz for the example ultrasonic transducer mechanically coupled to the example optical surface. The example second frequency  304  of the example twenty-six kilohertz corresponds to a second nominal resonance frequency of a second low impedance resonance extremity  304  in the diagram of  FIG. 3A  at the second frequency  304  of the example ultrasonic transducer mechanically coupled to the example optical surface. The example second frequency  304  of the example twenty-six kilohertz corresponds to the second nominal resonance frequency of the second low impedance resonance extremity  304  that is centered within a second resonance band “304band”. More broadly, the second frequency  302  is within a second resonance band “304band”. The second resonance band is defined herein as extending in frequency to plus and minus ten percent of the second nominal resonance frequency of the second low impedance resonance extremity for the ultrasonic transducer mechanically coupled to the optical surface. For example, with the example second frequency of the example twenty-six kilohertz, the second resonance band extends in frequency to plus and minus ten percent of the second nominal resonance frequency of twenty-six kilohertz (e.g. the second resonance band extends in frequency to plus and minus two and six-tenths kilohertz from the twenty-six kilohertz, or the second resonance band extends in frequency from twenty-three-and-four-tenths kilohertz to twenty-eight-and-six-tenths kilohertz). 
       FIG. 3B  is a diagram  300   b  of example droplet size reduction versus frequency according to an embodiment. The example of  FIG. 3B  shows the example first frequency  302  of the example three-hundred kilohertz for the example ultrasonic transducer mechanically coupled to the example optical surface. As shown in the example of  FIG. 3B , the example first frequency  302  of the example three-hundred kilohertz can reduce the droplet from the first droplet size  306  (e.g., reduce from ten millimeters in droplet diameter) to the second droplet size  308  (e.g., reduce to four millimeters in droplet diameter). This example can be a first expelling mode. 
     Further, the example of  FIG. 3B  shows the example second frequency  304  of the example twenty-six kilohertz for the example ultrasonic transducer mechanically coupled to the example optical surface. As shown in the example of  FIG. 3B , the example second frequency  304  of the example twenty-six kilohertz can reduce the droplet from the second droplet size  308  (e.g., reduce from four millimeters in droplet diameter) to the third droplet size  310  (e.g., reduce to eight-tenths of a millimeter in droplet diameter). This example can be a second expelling mode. 
     While example manners of implementing the example systems  100 ,  200  that can expel fluid from a droplet  102  on an optical surface  104  using an ultrasonic transducer  106  mechanically coupled to the optical surface  104  of  FIGS. 1 and 2 , one or more of the elements, processes and/or devices illustrated in  FIGS. 1 and 2  may be combined, divided, re-arranged, omitted, eliminated and/or implemented in any other way. 
     Further, the example systems  100 ,  200 , example ultrasonic transducer  106 , example first amplifier  108   a , example second amplifier  108   b , example first amplifier impedance  110   a , example second amplifier impedance  110   b , example first filter network  112   a , example first additional filter network  112   b , example second filter network  114   a , example second filter network  114   b , example circuitry controller  116 , example first amplifier inputs  118   a ,  120   a , example second amplifier inputs  118   b ,  120   b , example input of ultrasonic transducer  122   a , example additional input of ultrasonic transducer  122   b , example filter switching circuitry  124 , example input  126  of the filter switching circuitry, example first filter switch control  128 , example first low side switch control output  128   a , example first high side switch control output  128   b , example first additional low side switch control output  128   c , example first additional high side switch control output  128   d , example first low side switch  130   a , example first high side switch  130   b , example second filter switch control  138 , example second low side switch control output  138   a , example second high side switch control output  138   b , example second additional low side switch control output  138   c , example second additional high side switch control output  138   d , example second low side switch  140   a , example second high side switch  140   b , example ultrasonic transducer couplers  142   a ,  142   b , example first additional low side switch  150   a , example first additional high side switch  150   b , example second additional low side switch  160   a , example second additional high side switch  160   b , example amplitude sensor  162 , example first sensed amplitude  164   a , example first additional sensed amplitude  164   b , example amplitude comparator  166 , example ascending target amplitude  168   a , example descending target amplitude  168   b , example second sensed amplitude  170   a , example second additional sensed amplitude  170   b , example ultrasonic transducer current sensor  172 , example first current sensing  174 , example current transit comparator  176 , example current transient threshold  178 , example second current sensing  180 , example timer  182 , example cycle controller  184 , example clamp diodes  186   a ,  186   b ,  186   c ,  186   d , example transient voltage suppressor (TVS) diodes  188   a ,  188   b ,  188   c ,  188   d , example first transistor pair  202   a ,  204   a , example second transistor pair  202   b ,  204   b , example outputs of series coupling nodes  206   a ,  206   b , example series coupled inductors  208   a ,  208   b ,  212   a ,  212   b , and example series coupled capacitors  210   a ,  210   b ,  214   a ,  214   b , as shown in the examples of  FIGS. 1 and 2  may be implemented by hardware, software, firmware and/or any combination of hardware, software and/or firmware, and may be implemented by one or more analog or digital circuit(s), logic circuits, programmable processor(s), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)). 
     Further still, the example systems  100 ,  200 , example fluid droplet  102 , example first droplet size  102   a , example second droplet size  102   b , example third droplet size  102   c , example optical surface  104 , example ultrasonic transducer  106 , example first amplifier  108   a , example second amplifier  108   b , example first amplifier impedance  110   a , example second amplifier impedance  110   b , example first filter network  112   a , example first additional filter network  112   b , example second filter network  114   a , example second filter network  114   b , example circuitry controller  116 , example first amplifier inputs  118   a ,  120   a , example second amplifier inputs  118   b ,  120   b , example input of ultrasonic transducer  122   a , example additional input of ultrasonic transducer  122   b , example filter switching circuitry  124 , example input  126  of the filter switching circuitry, example first filter switch control  128 , example first low side switch control output  128   a , example first high side switch control output  128   b , example first additional low side switch control output  128   c , example first additional high side switch control output  128   d , example first low side switch  130   a , example first high side switch  130   b , example second filter switch control  138 , example second low side switch control output  138   a , example second high side switch control output  138   b , example second additional low side switch control output  138   c , example second additional high side switch control output  138   d , example second low side switch  140   a , example second high side switch  140   b , example ultrasonic transducer couplers  142   a ,  142   b , example first additional low side switch  150   a , example first additional high side switch  150   b , example second additional low side switch  160   a , example second additional high side switch  160   b , example amplitude sensor  162 , example first sensed amplitude  164   a , example first additional sensed amplitude  164   b , example amplitude comparator  166 , example ascending target amplitude  168   a , example descending target amplitude  168   b , example second sensed amplitude  170   a , example second additional sensed amplitude  170   b , example ultrasonic transducer current sensor  172 , example first current sensing  174 , example current transit comparator  176 , example current transient threshold  178 , example second current sensing  180 , example timer  182 , example cycle controller  184 , example clamp diodes  186   a ,  186   b ,  186   c ,  186   d , example transient voltage suppressor (TVS) diodes  188   a ,  188   b ,  188   c ,  188   d , example first transistor pair  202   a ,  204   a , example second transistor pair  202   b ,  204   b , example outputs of series coupling nodes  206   a ,  206   b , example series coupled inductors  208   a ,  208   b ,  212   a ,  212   b , and example series coupled capacitors  210   a ,  210   b ,  214   a ,  214   b , as shown in the examples of  FIGS. 1 and 2 , may include one or more elements, processes and/or devices in addition to, or instead of, those illustrated in  FIGS. 1 and 2 , and/or may include more than one of any or all of the illustrated elements, processes and devices. 
     When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the example systems  100 ,  200 , example ultrasonic transducer  106 , example first amplifier  108   a , example second amplifier  108   b , example first amplifier impedance  110   a , example second amplifier impedance  110   b , example first filter network  112   a , example first additional filter network  112   b , example second filter network  114   a , example second filter network  114   b , example circuitry controller  116 , example first amplifier input  118   a ,  120   a , example second amplifier input  118   b ,  120   b , example input of ultrasonic transducer  122   a , example additional input of ultrasonic transducer  122   b , example filter switching circuitry  124 , example input  126  of the filter switching circuitry, example first filter switch control  128 , example first low side switch control output  128   a , example first high side switch control output  128   b , example first additional low side switch control output  128   c , example first additional high side switch control output  128   d , example first low side switch  130   a , example first high side switch  130   b , example second filter switch control  138 , example second low side switch control output  138   a , example second high side switch control output  138   b , example second additional low side switch control output  138   c , example second additional high side switch control output  138   d , example second low side switch  140   a , example second high side switch  140   b , example ultrasonic transducer couplers  142   a ,  142   b , example first additional low side switch  150   a , example first additional high side switch  150   b , example second additional low side switch  160   a , example second additional high side switch  160   b , example amplitude sensor  162 , example first sensed amplitude  164   a , example first additional sensed amplitude  164   b , example amplitude comparator  166 , example ascending target amplitude  168   a , example descending target amplitude  168   b , example second sensed amplitude  170   a , example second additional sensed amplitude  170   b , example ultrasonic transducer current sensor  172 , example first current sensing  174 , example current transit comparator  176 , example current transient threshold  178 , example second current sensing  180 , example timer  182 , example cycle controller  184 , example clamp diodes  186   a ,  186   b ,  186   c ,  186   d , example transient voltage suppressor (TVS) diodes  188   a ,  188   b ,  188   c ,  188   d , example first transistor pair  202   a ,  204   a , example second transistor pair  202   b ,  204   b , example outputs of series coupling nodes  206   a ,  206   b , example series coupled inductors  208   a ,  208   b ,  212   a ,  212   b , and example series coupled capacitors  210   a ,  210   b ,  214   a ,  214   b , as shown in the examples of  FIGS. 1 and 2  is/are hereby expressly defined to include a tangible computer readable storage device or storage disk such as a memory, a digital versatile disk (DVD), a compact disk (CD), a Blu-ray disk, etc. storing the software and/or firmware. 
       FIGS. 4A-4F  show a flowchart representative of example machine readable instructions that may be executed to implement the example system  100  to expel fluid of the fluid droplet  102  from the optical surface  104  using the ultrasonic transducer  106  mechanically coupled to the optical surface  104 , according to an embodiment as shown in the example of  FIG. 1 . In this example, the machine readable instructions comprise a program for execution by a processor such as the processor  512  shown in the example processor platform  500  discussed below in connection with  FIG. 5 . The program may be embodied in software stored on a tangible computer readable storage medium such as a CD-ROM, a floppy disk, a hard drive, a digital versatile disk (DVD), a Blu-ray disk, or a memory (e.g., FLASH memory) associated with the processor  512 , but the entire program and/or parts thereof could alternatively be executed by a device other than the processor  512  and/or embodied in firmware or dedicated hardware. Further, although the example program is described with reference to the flowchart illustrated in  FIGS. 4A-4F , many other methods of implementing the example system  100  to expel fluid of the fluid droplet  102  from the optical surface  104  using the ultrasonic transducer  106  mechanically coupled to the optical surface  104  of this disclosure may alternatively be used. For example, the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, or combined. As used herein, when the phrase “at least” is used as the transition term in a preamble of a claim, it is open-ended in the same manner as the term “comprising” is open ended. Comprising and all other variants of “comprise” are expressly defined to be open-ended terms. Including and all other variants of “include” are also defined to be open-ended terms. In contrast, the term consisting and/or other forms of consist are defined to be close-ended terms. 
     As mentioned above, the example processes of  FIGS. 4A-4F  may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a tangible computer readable storage medium such as a hard disk drive, a FLASH memory, a read-only memory (ROM), a compact disk (CD), a digital versatile disk (DVD), a cache, a random-access memory (RAM) and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term tangible computer readable storage medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, “tangible computer readable storage medium” and “tangible machine readable storage medium” are used interchangeably. Additionally or alternatively, the example processes of  FIGS. 4A-4F  may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a non-transitory computer and/or machine readable medium such as a hard disk drive, a FLASH memory, a read-only memory, a compact disk, a digital versatile disk, a cache, a random-access memory and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term non-transitory computer readable medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. 
     A process flow  400  of  FIGS. 4A-4F  can begin at block  402 . At block  402 , the optical surface can be oriented within a gravitational field so that a component of the gravitational field that is tangential to the surface operates upon the fluid droplet. For example, as shown in the example of  FIG. 1 , the optical surface  104  can be oriented within a gravitational field so that a component of the gravitational field that is tangential to the surface  104  (e.g., as depicted for by downward arrow tangential to surface  104 ) operates upon the fluid droplet  102 . This orientation can be achieved, for example, while activating the ultrasonic transducer  106  that is mechanically coupled to the optical surface  104  to expel fluid of the fluid droplet  102  from the optical surface. For example, the foregoing orienting of the optical surface  104  can be orienting the optical surface  104  within the gravitational field so that the component of the gravitational field that is tangential to the optical surface  104  is greater than a component of the gravitation field that is normal into the optical surface  104 . 
     Next, as shown in example of  FIG. 4A , at block  404  the first filter (and the first additional filter) tuned within the first resonant frequency band can be activated to facilitate impedance matching of the first amplifier (and the second amplifier) with impedance of the ultrasonic transducer. As shown for example in  FIG. 1 , the first filter  112   a  (e.g., first filter network  112   a ) is tuned (e.g., by its corresponding filter component values) within the first resonant frequency band to facilitate matching the first output impedance  110   a  of the first amplifier  108   a  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . Similarly, as shown for example in  FIG. 1 , the first additional filter  112   b  (e.g., first additional filter network  112   b ) is tuned (e.g., by its corresponding filter component values) within the first resonant frequency band to facilitate matching the second output impedance  110   b  of the second amplifier  108   b  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . In the example of  FIG. 1 , filter activation (and deactivation), as well as activation (and deactivation) of the ultrasonic transducer  106 , can be carried out by filter switching circuitry  124 , which is depicted in the drawings using stippled lines. For example, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the first filter  112   a  (e.g., first filter network  112   a ) to activate the first filter  112   a  (e.g. first filter network  112   a ) in response to a first control activation signal received from the circuitry controller  116  at an input  126  of the filter switching circuitry  124 . Similarly, at the same time, the filter switching circuitry  124  can be coupled between the circuitry controller  116  and the first additional filter  112   b  (e.g., first additional filter network  112   b ) to activate the first additional filter  112   b  (e.g. first additional filter network  112   b ) in response to the first control activation signal received from the circuitry controller  116  at the input  126  of the filter switching circuitry  124 . 
     Next, as shown in example of  FIG. 4A , at block  406  the first signal (and the first additional signal) including the first frequency within the first resonant frequency band of the ultrasonic transducer can be generated. For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can be coupled with the input  118   a ,  120   a  of the first amplifier  108   a  to generate the first signal at the input  122   a  of ultrasonic transducer  106 . Similarly, at the same time, the circuitry controller  116  can be coupled with the additional input  118   b ,  120   b  of the second amplifier  108   b  to generate the first additional signal at the additional input  122   b  of ultrasonic transducer  106 . The first signal at the input  122   a  of the ultrasonic transducer  106  includes the first frequency within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . Similarly, the first additional signal at the additional input  122   b  of the ultrasonic transducer  106  likewise can include the first frequency within the first resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . 
     Next, as shown in the example of  FIG. 4A , at block  408  a ramping up of the amplitude of the first signal (and of the first additional signal) at ultrasonic transducer can begin from the predetermined initial amplitude level of first signal (and of the first additional signal) to the predetermined full amplitude level of first signal (and of the first additional signal). For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can begin ramping up the amplitude of the first signal at the ultrasonic transducer  106  from a predetermined initial amplitude level of the first signal to a predetermined full amplitude level of the first signal. At the same time, in a similarly way, circuitry controller  116  can also begin ramping up the amplitude of the first additional signal at the ultrasonic transducer  106  from a predetermined initial amplitude level of the first additional signal to a predetermined full amplitude level of the first additional signal. For example, respective amplitudes of the first signal and the first additional signal can be ramped up (e.g., increased) by the circuitry controller  116  from their respective predetermined initial amplitude levels to their respective predetermined full amplitude levels at a predetermined ramp up rate. 
     Next, as shown in the example of  FIG. 4A , at block  410  an amplitude of the first signal can be sensed (and an amplitude of the first additional signal can be sensed). For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can include an amplitude sensor  162  that can sense amplitude of the first signal, for example, to determine a first sensed amplitude  164   a  of the first signal and the first additional signal. 
     Next, as shown in the example of  FIG. 4A , at block  412  an amplitude of the first signal and the first additional signal can be adjusted (e.g., increased) based on the sensed amplitude of the first signal and the first additional signal. Next, as shown in the example of  FIG. 4A , at decision block  414  it is determined whether adjusting the amplitude of the first signal is finished (and whether adjusting the amplitude of the first additional signal is finished). For example, at decision block  414  it is determined whether the ramping up adjustment to increase amplitude of the first signal is finished (and whether the ramping up adjustment to increase amplitude of the first additional signal is finished). If it is determined by the circuitry controller that adjusting the amplitude of the first signal is not finished, for example ramping up adjustment is not finished (and, for example, that adjusting the amplitude of the first additional signal is not finished, for example, ramping up is not finished), then flow of execution can be redirected to block  410  to sense amplitude of the first signal (and, for example, to sense amplitude of the first additional signal and the first additional signal). However, if it is determined by the circuitry controller that the adjusting the amplitude of the first signal is finished for example, ramping up is finished (and, for example, that the adjusting the amplitude of the first additional signal is finished, for example, ramping up is finished), then flow of execution can be directed to block  416  of  FIG. 4B . 
     Next, as shown in the example of  FIG. 4B , at block  416  the ultrasonic transducer is activated at the first frequency within the first resonant frequency band of the ultrasonic transducer by coupling the first signal (and the first additional signal) with the ultrasonic transducer. At block  418 , the activated ultrasonic transducer can expel fluid from the fluid droplet to reduce the fluid droplet by atomization from the first droplet size to the second droplet size. For example, as shown in the example of  FIG. 1 , the ultrasonic transducer  106  can be activated at the first frequency within the first resonant frequency band of the ultrasonic transducer  106 , for example, by coupling the first signal and the first additional signal to reduce the fluid droplet  102  by atomization from the first droplet size  102   a  to the second droplet size  102   b.    
     Next, as shown in the example of  FIG. 4B , at block  420  the limiting of the first signal (and limiting of the first additional signal) by ramping down the amplitude of first signal (and by ramping down the first additional signal) at the ultrasonic transducer can begin. For example, respective amplitudes of the first signal and the first additional signal can be ramped down (e.g., decreased) by the circuitry controller from their respective predetermined full amplitude levels to their respective predetermined reduced amplitude levels at a predetermined ramp down rate. For example, such limiting can include ramping down from the predetermined full amplitude level of the first signal to the predetermined reduced level of the first signal, and can include ramping down from the predetermined full amplitude level of the first additional signal to the predetermined reduced level of the first additional signal. At block  422  the amplitude of first signal can be sensed (and the amplitude of the first additional signal can be sensed). For example, as shown in the example of  FIG. 1 , the amplitude sensor  162  can sense amplitude of the first signal and the first additional signal, for example, to determine the first sensed amplitude  164   a  of the first signal and the first additional signal when the first signal and the first additional signal are being limited and/or reduced. 
     As shown in the example of  FIG. 4B , at block  424  amplitude of the first signal can be adjusted (e.g., decreased) based on sensed amplitude of first signal and the first additional signal. At decision block  426  it is determined by the circuitry controller whether adjusting the amplitude of the first signal is finished (and whether adjusting the amplitude of the first additional signal is finished). For example, at decision block  426  it is determined whether the ramping down adjustment to decrease amplitude of the first signal is finished (and whether the ramping down adjustment to decrease amplitude of the first additional signal is finished). If it is determined that adjusting the amplitude of the first signal is not finished, for example ramping down adjustment is not finished (and, for example, that adjusting the amplitude of the first additional signal is not finished, for example, ramping down is not finished), then flow of execution can be redirected to block  422  to sense amplitude of the first signal (and, for example, to sense amplitude of the first additional signal). However, if it is determined by the circuitry controller that adjusting the amplitude of the first signal is finished for example, ramping down is finished (and, for example, that adjusting the amplitude of the first additional signal is finished, for example, ramping down is finished), then flow of execution can be directed to block  428  of  FIG. 4C . 
     As shown in the example of  FIG. 4C , at block  428  determining when to deactivate first filter (and deactivate the first additional filter) and deactivate the ultrasonic transducer based on sensing the first current transient of ultrasonic transducer can begin. At block  430  the first current transient of ultrasonic transducer can be sensed. At block  432 , delay the deactivation of the first filter (and deactivation of the first additional filter) and deactivation of the ultrasonic transducer can be based on the sensed first current transient of ultrasonic transducer. For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can begin determining when to deactivate the first filter  112   a  (and the first additional filter  112   b ) and the ultrasonic transducer  106  based on sensing the first current transient of the ultrasonic transducer  106 . As shown for example in  FIG. 1 , the ultrasonic transducer current sensor  172  can be coupled to the ultrasonic transducer  106  to sense current transients, for example, to sense the first current transient of the ultrasonic transducer. 
     As shown in  FIG. 4C , at decision block  434  it can be determined by the circuitry controller whether delaying deactivation of the first filter (and deactivation of the first additional filter) and deactivation of the ultrasonic transducer based on the sensed first current transient of the ultrasonic transducer is finished. If it is determined that delaying such deactivation is not finished, then flow of execution can be redirected to block  430  to sense amplitude of the first current transient of the ultrasonic transducer. However, if it is determined by the circuitry controller that delaying such deactivation is finished, then flow of execution can be directed to block  436  of  FIG. 4C . At block  436  of  FIG. 4C , the first filter and the first additional filter and the ultrasonic transducer are deactivated, when delaying such deactivation is finished. 
     Next, after deactivating the first filter (and the first additional filter) and the ultrasonic transducer, as shown in the example of  FIG. 4C , at block  438  there can be a delay of a predetermined period of time. For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can use, for example, timer  182  to delay the predetermined period of time after deactivating the first filter  112   a  (and the first additional filter  112   b ) and deactivating the ultrasonic transducer  106 . 
     Next, as shown in the example of  FIG. 4D , at block  440  the second filter (and the second additional filter) tuned within the second resonant frequency band can be activated to facilitate impedance matching of the first amplifier (and the second amplifier) with impedance of the ultrasonic transducer. As shown for example in  FIG. 1 , the second filter  114   a  (e.g., second filter network  114   a ) is tuned (e.g., by its corresponding filter component values) within the second resonant frequency band to facilitate matching the first output impedance  110   a  of the first amplifier  108   a  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . Similarly, as shown for example in  FIG. 1 , the second additional filter  114   b  (e.g., second additional filter network  114   b ) is tuned (e.g., by its corresponding filter component values) within the second resonant frequency band to facilitate matching the second output impedance  110   b  of the second amplifier  108   b  with impedance of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . 
     Next, as shown in example of  FIG. 4D , at block  442  the second signal (and the second additional signal) including the second frequency within the second resonant frequency band of the ultrasonic transducer can be generated. For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can be coupled with the input  118   a ,  120   a  of the first amplifier  108   a  to generate the second signal at the input  122   a  of ultrasonic transducer  106 . Similarly, at the same time, the circuitry controller  116  can be coupled with the additional input  118   b ,  120   b  of the second amplifier  108   b  to generate the second additional signal at the additional input  122   b  of ultrasonic transducer  106 . The second signal at the input  122   a  of the ultrasonic transducer  106  includes the second frequency within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . Similarly, the second additional signal at the additional input  122   b  of the ultrasonic transducer  106  likewise can include the second frequency within the second resonant frequency band of the ultrasonic transducer  106  mechanically coupled to the optical surface  104 . 
     Next, as shown in the example of  FIG. 4D , at block  444  a ramping up of the amplitude of the second signal (and of the second additional signal) at ultrasonic transducer can begin from the predetermined initial amplitude level of second signal (and of the second additional signal) to the predetermined full amplitude level of second signal (and of the second additional signal). For example, respective amplitudes of the second signal and the second additional signal can be ramped up (e.g., increased) by the circuitry controller from their respective predetermined initial amplitude levels to their respective predetermined full amplitude levels at a predetermined ramp up rate. For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can begin ramping up the amplitude of the second signal at the ultrasonic transducer  106  from a predetermined initial amplitude level of the second signal to a predetermined full amplitude level of the second signal. At the same time, in a similarly way, circuitry controller  116  can also begin ramping up the amplitude of the second additional signal at the ultrasonic transducer  106  from a predetermined initial amplitude level of the second additional signal to a predetermined full amplitude level of the second additional signal. 
     Next, as shown in the example of  FIG. 4D , at block  446  an amplitude of the second signal can be sensed (and an amplitude of the second additional signal can be sensed). For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can include an amplitude sensor  162  that can sense amplitude of the second signal and the second additional signal. 
     Next, as shown in the example of  FIG. 4D , at block  448  the amplitude of the second signal and the second additional signal can be adjusted (e.g., increased) based on the sensed amplitude of the second signal and the second additional signal. Next, as shown in the example of  FIG. 4D , at decision block  450  it is determined by the circuitry controller whether the adjusting the amplitude of the second signal is finished (and whether the adjusting the amplitude of the second additional signal is finished). For example, at decision block  450  it is determined whether the ramping up adjustment to increase amplitude of the second signal is finished (and whether the ramping up adjustment to increase amplitude of the second additional signal is finished). If it is determined that the adjusting the amplitude of the second signal and the second additional signal is not finished, for example ramping up adjustment is not finished, then flow of execution can be redirected to block  446  to sense amplitude of the second signal (and, for example, to sense amplitude of the second additional signal). However, if it is determined by the circuitry controller that the adjusting the amplitude of the second signal is finished for example, ramping up is finished (and, for example, that the adjusting amplitude of the second additional signal is finished, for example, ramping up is finished), then flow of execution can be directed to block  452  of  FIG. 4E . 
     Next, as shown in the example of  FIG. 4E , at block  452  the ultrasonic transducer is activated at the second frequency within the second resonant frequency band of the ultrasonic transducer by coupling the second signal (and the second additional signal) with the ultrasonic transducer. At block  454 , the activated ultrasonic transducer can expel fluid from the droplet to reduce the droplet by atomization from the second droplet size to the third droplet size. For example, as shown in the example of  FIG. 1 , the ultrasonic transducer  106  can be activated at the second frequency within the second resonant frequency band of the ultrasonic transducer  106 , for example, by coupling the second signal and the second additional signal to reduce the fluid droplet  102  by atomization from the second droplet size  102   b  to the third droplet size  102   c.    
     Next, as shown in the example of  FIG. 4E , at block  456  the limiting of the second signal (and limiting of the second additional signal) by ramping down the amplitude of second signal (and by ramping down the second additional signal) at the ultrasonic transducer can begin. For example, respective amplitudes of the second signal and the second additional signal can be ramped down (e.g., decreased) by the circuitry controller from their respective predetermined full amplitude levels to their respective predetermined reduced amplitude levels at a predetermined ramp down rate. For example, such limiting can include ramping down from the predetermined full amplitude level of the second signal to the predetermined reduced level of the second signal, and can include ramping down from the predetermined full amplitude level of the second additional signal to the predetermined reduced level of the second additional signal. At block  458  the amplitude of second signal can be sensed (and the amplitude of the second additional signal can be sensed). As shown in the example of  FIG. 4E , at block  460  amplitude of the second signal can be adjusted based on sensed amplitude of second signal, and similarly, amplitude of the second additional signal can be adjusted based on sensed amplitude of second additional signal. 
     As shown in the example of  FIG. 4E , at decision block  462  it is determined by the circuitry controller whether the adjusting the amplitude of the second signal is finished (and whether the adjusting amplitude of the second additional signal is finished). For example, at decision block  462  it is determined by the circuitry controller whether the ramping down adjustment to decrease amplitude of the second signal is finished (and whether the ramping down adjustment to decrease amplitude of the second additional signal is finished). If it is determined by the circuitry controller that the adjusting amplitude of the second signal is not finished, for example ramping down adjustment is not finished (and, for example, that the adjusting amplitude of the second additional signal is not finished, for example, ramping down is not finished), then flow of execution can be redirected to block  458  to sense amplitude of the second signal (and, for example, to sense amplitude of the second additional signal). However, if it is determined by the circuitry controller that the adjusting amplitude of the second signal is finished for example, ramping down is finished (and, for example, that the adjusting amplitude of the second additional signal is finished, for example, ramping down is finished), then flow of execution can be directed to block  464  of  FIG. 4F . 
     As shown in the example of  FIG. 4F , at block  464  determining when to deactivate second filter (and deactivate the second additional filter) and deactivate the ultrasonic transducer based on sensing the second current transient of ultrasonic transducer can begin. At block  466  the second current transient of ultrasonic transducer can be sensed. At block  468 , delay in deactivating the second filter (and deactivating the second additional filter) and deactivating the ultrasonic transducer can be based on the sensed second current transient of ultrasonic transducer. For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can begin determining when to deactivate the second filter  114   a  (and the second additional filter  114   b ) and the ultrasonic transducer  106  based on sensing the second current transient of the ultrasonic transducer  106 . As shown for example in  FIG. 1 , the ultrasonic transducer current sensor  172  can be coupled to the ultrasonic transducer  106  to sense current transients, for example, to sense the second current transient of the ultrasonic transducer. 
     As shown in  FIG. 4F , at decision block  470  it can be determined by the circuitry controller whether delaying deactivation of the second filter (and deactivation of the second additional filter) and deactivation of the ultrasonic transducer based on the sensed second current transient of the ultrasonic transducer is finished. If it is determined by the circuitry controller that delaying such deactivation is not finished, then flow of execution can be redirected to block  466  to sense amplitude of the second current transient of the ultrasonic transducer. However, if it is determined by the circuitry controller that delaying such deactivation is finished, then flow of execution can be directed to block  472  of  FIG. 4F . At block  472  of  FIG. 4F , the second filter and the second additional filter and the ultrasonic transducer are deactivated, when delaying such deactivation is finished. 
     Next, after deactivating the second filter (and the second additional filter) and the ultrasonic transducer, as shown in the example of  FIG. 4F , at block  474  there can be a delay of a predetermined period of time. For example, as shown in the example of  FIG. 1 , the circuitry controller  116  can use, for example, timer  182  to delay the predetermined period of time after deactivating the second filter  114   a  (and the second additional filter  114   b ) and deactivating the ultrasonic transducer  106 . 
     Next, as shown in the example of  FIG. 4F , at decision block  476  it is determined whether to end the cycle of expelling fluid from the optical surface. For example, if a control input registered at a time determines that the cycle is not to end at that time, then flow execution transfers to block  404  shown in  FIG. 4A . However, if a control input registered at that time determines that the cycle is to end at that time, then after block  476 , the example method  400  can end. 
       FIG. 5  is a block diagram of an example processing platform capable of executing the machine readable instructions of  FIGS. 4A-4F  to implement the example system to expel fluid from the droplet on the optical surface using the ultrasonic transducer mechanically coupled to the optical surface, according to an embodiment as shown in the example of FIG.  1 . 
     The processor platform  500  can be, for example, a server, a personal computer, a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), a personal digital assistant (PDA), an Internet appliance, a DVD player, a CD player, a digital video recorder, a Blu-ray player, a gaming console, a personal video recorder, a set top box, or any other type of computing device. 
     The processor platform  500  of the illustrated example includes a processor  512 . The processor  512  of the illustrated example is hardware. For example, the processor  512  can be implemented by one or more integrated circuits, logic circuits, microprocessors or controllers from any desired family or manufacturer. The hardware of processor  512  can be virtualized using virtualization such as Virtual Machines and/or containers. The processor  512  can implement example circuitry controller  116 , including example amplitude sensor  162 , example first sensed amplitude  164   a , example first additional sensed amplitude  164   b , example amplitude comparator  166 , example ascending target amplitude  168   a , example descending target amplitude  168   b , example second sensed amplitude  170   a , example second additional sensed amplitude  170   b , example ultrasonic transducer current sensor  172 , example first current sensing  174 , example current transient comparator  176 , example current transient threshold  178 , example second current sensing  180 , example timer  182  and example cycle controller  184 . The processor  512  can also implement example filter switching circuitry  124  including example first filter switch controller  128  and second filter switch controller  138 . The processor  512 , in implementing circuitry controller  116 , can generate the first signal (and first additional signal) having the first frequency and can generate the second signal (and second additional signal) having the second frequency using methods such as pulse-width modulation (PWM) or direct digital synthesis (DDS). 
     The processor  512  of the illustrated example includes a local memory  513  (e.g., a cache). The processor  512  of the illustrated example is in communication with a main memory including a volatile memory  514  and a non-volatile memory  516  via a bus  518 . The volatile memory  514  may be implemented by Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM) and/or any other type of random access memory device. The non-volatile memory  516  may be implemented by FLASH memory and/or any other desired type of memory device. Access to the main memory  514 ,  516  is controlled by a memory controller. 
     The processor platform  500  of the illustrated example also includes an interface circuit  520 . The interface circuit  520  may be implemented by any type of interface standard, such as an Ethernet interface, a universal serial bus (USB), and/or a PCI express interface. 
     In the illustrated example, one or more input devices  522  are connected to the interface circuit  520 . The input device(s)  522  permit(s) a user to enter data and commands into the processor  512 . The input device(s) can be implemented by, for example, an audio sensor, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, isopoint and/or a voice recognition system. 
     One or more output devices  524  are also connected to the interface circuit  520  of the illustrated example. The output devices  524  can be implemented, for example, by display devices (e.g., a light emitting diode (LED), an organic light emitting diode (OLED), a liquid crystal display (LCD), a cathode ray tube display (CRT), a touchscreen, a tactile output device, a printer and/or speakers). The interface circuit  520  of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip or a graphics driver processor. 
     The interface circuit  520  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem and/or network interface card to facilitate exchange of data with external machines (e.g., computing devices of any kind) via a network  526  (e.g., an Ethernet connection, a digital subscriber line (DSL), a telephone line, coaxial cable, a cellular telephone system, etc.). 
     The processor platform  500  of the illustrated example also includes one or more mass storage devices  528  for storing software and/or data. Examples of such mass storage devices  528  include floppy disk drives, hard drive disks, compact disk drives, Blu-ray disk drives, RAID systems, and digital versatile disk (DVD) drives. 
     The coded instructions  532  of  FIG. 5  may be stored in the mass storage device  528 , in the volatile memory  514 , in the non-volatile memory  516 , and/or on a removable tangible computer readable storage medium such as a CD or DVD. 
     Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.