Patent Publication Number: US-11651761-B2

Title: Ultrasonic transducers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/762,289 filed Mar. 22, 2018 entitled ULTRASONIC TRANSDUCERS, which is related to International Patent Application No. PCT/US2016/053328 filed Sep. 23, 2016 entitled ULTRASONIC TRANSDUCERS and claims benefit of the priority of U.S. Provisional Patent Application No. 62/222,916 filed Sep. 24, 2015 entitled ULTRASONIC TRANSDUCERS. 
    
    
     TECHNICAL FIELD 
     The present application relates generally to ultrasonic transducers, and more specifically to ultrasonic transducers that include perforated baseplates. 
     BACKGROUND 
     The physics of ultrasonic transducers generally involves a membrane film that is attracted to a surface, such as a surface of a baseplate, through the action of a variable electric field. The variable electric field can be produced by applying a voltage difference (e.g., an AC voltage) between a conductive surface of the membrane film and a conductive surface of the baseplate. For example, the baseplate may be made of a conductive material such as aluminum. The variable electric field produced between the conductive surfaces of the membrane film and the baseplate can create an electrical force of attraction that is approximately proportional to the square of the voltage between the conductive surfaces. Generally, a DC bias voltage (e.g., a few hundred volts) is applied between the conductive surfaces of the membrane film and the baseplate, onto which an AC voltage or drive signal can be added. 
     Prior ultrasonic transducer designs have typically employed a conductive aluminum baseplate and a metalized polymer membrane film. Such a baseplate can include a plurality of depressions (e.g., a series of grooves) in its surface that partially penetrate the baseplate. The depressions are configured to facilitate vibrational motion of the membrane film. Trapped or restricted air within these depressions can compress and expand as the membrane film moves, and act as an acoustic “spring” or compliance, which provides a restoring force against the membrane film, facilitating vibration. The configuration of the depressions, including their depth, spacing, shape, etc., combined with the material properties of the membrane film can determine the dynamics of the membrane film&#39;s vibrational motion. This design concept is employed in what are commonly known as Sell-type ultrasonic transducers, which have long been used in industry. 
     SUMMARY 
     In accordance with the present application, ultrasonic transducers are disclosed that include membrane films and perforated baseplates. In one aspect, an exemplary ultrasonic transducer includes at least one baseplate having a conductive surface with a plurality of apertures, openings, or perforations formed on or through the baseplate. The ultrasonic transducer further includes a membrane film having at least one conductive surface. The membrane film can be positioned adjacent or proximate to the apertures, openings, or perforations formed on or through the baseplate. By applying a voltage between the conductive surface of the membrane film and the conductive surface of the baseplate, an electrical force of attraction can be created between the membrane film and the baseplate. Varying this applied voltage can cause the membrane film to undergo vibrational motion. 
     In an exemplary aspect, the size and/or shape of the apertures, openings, or perforations formed on or through the baseplate can determine the frequency response of the ultrasonic transducer. The dimensions corresponding to the size and/or shape of the apertures, openings, or perforations can be varied so that different regions of the baseplate produce different frequency responses of the ultrasonic transducer, allowing the net bandwidth of the ultrasonic transducer to be increased, as desired. The dimensions of the size and/or shape of the apertures, openings, or perforations can be substantially the same, or production processes can be relied upon to provide some small variation(s) in the dimensions of the respective apertures, openings, or perforations. In a further exemplary aspect, the baseplate can have circular, elongated, slotted, square, oval, or any other suitable size, shape, and/or dimensions of the respective apertures, openings, or perforations formed on or through the baseplate. Unlike conventional ultrasonic transducer designs, there is no trapped air in a number of the disclosed ultrasonic transducer configurations, and therefore there is negligible acoustic compliance providing a restoring force to the membrane film. Rather, the bending stiffness of the membrane film provides for a substantial restoring force. When the membrane film is placed in contact with the baseplate, this bending stiffness is particularly well suited to provide a restoring force in the frequency range desired by the disclosed ultrasonic transducers. 
     Other features, functions, and aspects of the invention will be evident from the Detailed Description that follows. 
    
    
     
       BRIEF DESCRIPTION OF TIE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments described herein, and, together with the Detailed Description, explain these embodiments. In the drawings: 
         FIG.  1   a    is a block diagram of an exemplary parametric audio system, in which an exemplary ultrasonic transducer may be employed, in accordance with the present application; 
         FIG.  1   b    is an exploded perspective view of the ultrasonic transducer of  FIG.  1     a;    
         FIG.  2   a    is a cross-sectional view of an exemplary embodiment of the ultrasonic transducer of  FIGS.  1   a  and  1   b   , in which the ultrasonic transducer includes a membrane film and a perforated baseplate; 
         FIG.  2   b    is a cross-sectional view of an alternative embodiment of the ultrasonic transducer of  FIG.  2   a   , in which the perforated baseplate has flared apertures, openings, or perforations formed thereon or therethrough; 
         FIG.  3    is a cross-sectional view of a further exemplary embodiment of the ultrasonic transducer of  FIGS.  1   a  and  1   b   , in which the ultrasonic transducer includes a membrane film, a perforated baseplate, and a structure forming a plurality of chambers on a non-radiating side of the perforated baseplate; 
         FIG.  4    is a cross-sectional view of another exemplary embodiment of the ultrasonic transducer of  FIGS.  1   a  and  1   b   , in which the ultrasonic transducer includes a membrane film having a conductive surface, and a perforated baseplate, and the conductive surface of the membrane film is positioned adjacent or proximate to the perforated baseplate; 
         FIG.  5   a    is a cross-sectional view of still another exemplary embodiment of the ultrasonic transducer of  FIGS.  1   a  and  1   b   , in which the ultrasonic transducer includes a membrane film having two opposing conductive surfaces, and two perforated baseplates, and each conductive surface of the membrane film is positioned adjacent or proximate to a respective one of the perforated baseplates, thereby providing a two-way driving configuration of the ultrasonic transducer; 
         FIG.  5   b    is a cross-sectional view of an alternative embodiment of the ultrasonic transducer of  FIG.  5   a   , in which one side of the two-way driving configuration is made to terminate at one or more chambers in order to provide a one-way output configuration with increased output drive capability; and 
         FIG.  6    is a flow diagram of an exemplary method of manufacturing the ultrasonic transducer of  FIGS.  2   a    and  2   b.    
     
    
    
     DETAILED DESCRIPTION 
     The disclosures of U.S. patent application Ser. No. 15/762,289 filed Mar. 22, 2018 entitled ULTRASONIC TRANSDUCES, International Patent Application No. PCT/US2016/053328 filed Sep. 23, 2016 entitled ULTRASONIC TRANSDUCERS, and U.S. Provisional Patent Application No. 62/222,916 filed Sep. 24, 2015 entitled ULTRASONIC TRANSDUCERS, are hereby incorporated herein by reference in their entirety. 
     Ultrasonic transducers are disclosed that include membrane films and perforated baseplates. An exemplary ultrasonic transducer includes at least one baseplate having a conductive surface with a plurality of apertures, openings, or perforations formed on or through the baseplate. The ultrasonic transducer further includes a membrane film having at least one conductive surface. The membrane film can be positioned adjacent or proximate to the apertures, openings, or perforations formed on or through the baseplate. By applying a voltage between the conductive surface of the membrane film and the conductive surface of the baseplate, an electrical force of attraction can be created between the membrane film and the baseplate. Varying this applied voltage can cause the membrane film to undergo vibrational motion. The dimensions corresponding to the size and/or shape of the apertures, openings, or perforations formed on or through the baseplate can be varied so that different regions of the baseplate produce different frequency responses of the ultrasonic transducer, allowing the net bandwidth of the ultrasonic transducer to be advantageously increased. 
       FIG.  1   a    depicts an illustrative embodiment of an exemplary parametric audio system  100 , which includes an exemplary ultrasonic transducer  118 , in accordance with the present application. As shown in  FIG.  1   a   , the parametric audio system  100  can include a signal generator  102 , a matching filter  114 , driver circuitry  116 , and the ultrasonic transducer  118 . The signal generator  102  can include a plurality of audio sources  104 . 1 - 104 . n, a plurality of signal conditioners  106 . 1 - 106 . n, summing circuitry  108 , a modulator  110 , and a carrier generator  112 . In an exemplary mode of operation, the audio sources  104 . 1 - 104 . n  can generate a plurality of audio signals, respectively. The plurality of signal conditioners  106 . 1 - 106 . n can receive the plurality of audio signals, respectively, perform signal conditioning on the respective audio signals, and provide the conditioned audio signals to the summing circuitry  108 . For example, the plurality of signal conditioners  106 . 1 - 106 . n may each be configured to include nonlinear inversion circuitry for reducing or substantially eliminating unwanted distortion in any audio that may be reproduced from an output of the parametric audio system  100 . The plurality of signal conditioners  106 . 1 - 106 . n may each further include equalization circuitry, compression circuitry, or any other suitable signal conditioning circuitry. It is noted that such signal conditioning of the plurality of audio signals can alternatively be performed after the audio signals are summed by the summing circuitry  108 . 
     The summing circuitry  108  can sum the conditioned audio signals, and provide a composite audio signal to the modulator  110 . Further, the carrier generator  112  can generate an ultrasonic carrier signal, and provide the ultrasonic carrier signal to the modulator  110 . The modulator  110  can then modulate the ultrasonic carrier signal with the composite audio signal. For example, the modulator  110  may be configured to perform amplitude modulation by multiplying the composite audio signal with the ultrasonic carrier signal, or any other suitable form of modulation for converting audio-band signal(s) to ultrasound. Having modulated the ultrasonic carrier signal with the composite audio signal, the modulator  110  can provide the modulated signal to the matching filter  114 . For example, the matching filter  114  may be configured to compensate for unwanted distortion resulting from a non-flat frequency response of the driver circuitry  116  and/or the ultrasonic transducer  118 . 
     The driver circuitry  116  can receive the modulated ultrasonic carrier signal from the matching filter  114 , and provide an amplified version of the modulated ultrasonic carrier signal to the ultrasonic transducer  118 , which can emit from its output at high intensity the amplified, modulated ultrasonic carrier signal as an ultrasonic beam. For example, the driver circuitry  116  may be configured to include one or more delay circuits (not shown) for applying a relative phase shift across frequencies and multiple output channels of the modulated ultrasonic carrier signal, sent to multiple transducers or transducer elements, in order to steer, focus, and/or shape the ultrasonic beam emitted by the ultrasonic transducer  118 . Once emitted from the output of the ultrasonic transducer  118 , the ultrasonic beam can be demodulated as it passes through the air or any other suitable propagation medium, due to nonlinear propagation characteristics of the air or other propagation medium. Having demodulated the ultrasonic beam upon its passage through the air or other propagation medium, audible sound can be produced. It is noted that the audible sound produced by way of such a nonlinear parametric process is approximately proportional to the square of the modulation envelope. 
       FIG.  1   b    depicts an exploded perspective view of the ultrasonic transducer  118  of  FIG.  1   a   . As shown in  FIG.  1   b   , the ultrasonic transducer  118  can include an exemplary vibrator layer  120  and an exemplary perforated baseplate  122 . The vibrator layer  120  can include a membrane film  130  having a conductive surface  128 . The perforated baseplate  122  can include a plurality of apertures, openings, or perforations  132  (e.g., circular apertures, openings, or perforations) formed thereon or therethrough. For example, the membrane film  130  may be implemented with a thin (e.g., about 0.2-100.0 μm (about 0.008-3.937 mil), typically about 8 μm (about 0.315 mil), in thickness) polyester, polyimide, polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) film, or any other suitable polymeric or non-polymeric film. Further, the conductive surface  128  of the membrane film  130  may be implemented with a coating of aluminum, gold, nickel, or any other suitable conductive material. In addition, the perforated baseplate  122  may be made of or coated with aluminum or any other suitable conductive material, and the plurality of apertures, openings, or perforations  132  formed on or through the perforated baseplate  122  may be circular, elongated, slotted, square, oval, or any other suitable shape. 
     As shown in  FIG.  1   b   , a DC bias voltage source  126  (e.g., 150 VDC) can be connected across the conductive surface  128  of the membrane film  130  and a conductive surface of the baseplate  122 . The DC bias voltage source  126  can increase the sensitivity and output capability of the ultrasonic transducer  118 , as well as reduce unwanted distortion in the ultrasonic beam emitted by the ultrasonic transducer  118 . In one embodiment, the membrane film  130  may have electret properties, allowing the vibrator layer  120  to function as a DC bias source in place of the DC bias voltage source  126 . It is noted that, in  FIG.  1   b   , the amplified, modulated ultrasonic carrier signal provided to the ultrasonic transducer  118  by the driver circuitry  116  is represented by a time-varying signal generated by an AC signal source  124 , which is connected with the DC bias voltage source  126  such that the voltage delivered to the ultrasonic transducer  118  is the sum of DC and AC components. 
       FIG.  2   a    depicts a partial cross-sectional view (e.g., partially across a cross-section C-C; see  FIG.  1   b   ) of an exemplary embodiment  200   a  (also referred to herein as the ultrasonic transducer  200   a ) of the ultrasonic transducer  118  of  FIGS.  1   a  and  1   b   . As shown in  FIG.  2   a   , the ultrasonic transducer  200   a  can include a membrane film  202   a  and a perforated baseplate  204   a . The perforated baseplate  204   a  can include a surface  210   a  with a plurality of apertures, openings, or perforations  212 . 1 - 212 . 2  formed thereon or therethrough. The membrane film  202   a  can have a conductive surface  206 . The non-conductive surface of the membrane film  202   a  opposite the conductive surface  206  can be placed adjacent to, proximate to, or directly against the surface  210   a  with the plurality of apertures, openings, or perforations  212 . 1 - 212 . 2  formed in the perforated baseplate  204   a . In one embodiment, the perforated baseplate  204   a  can be made of aluminum or any other suitable conductive material. In an alternative embodiment, the perforated baseplate  204   a  can be made of an insulating material (e.g., plastic) that has a conductive surface (e.g., a coating of conductive material such as aluminum, gold, or nickel). By applying a voltage between the conductive surface  206  of the membrane film  202   a  and the conductive surface of the perforated baseplate  204   a , an electrical force of attraction can be created between the membrane film  202   a  and the perforated baseplate  204   a . Varying this applied voltage can cause the membrane film  202   a  to undergo vibrational motion. 
     It is noted that the membrane film included in each of the ultrasonic transducers disclosed herein, such as the membrane film  202   a , can be under tension and have electret properties that provide an effect similar to a level of a DC bias voltage. Such tension on the membrane film  202   a  can be controlled for the purpose of adjusting the bending stiffness of the membrane film  202   a , as well as the restoring force of the membrane film  202   a  as it undergoes displacement during vibrational motion. Such tension can also be applied to the membrane film  202   a  by an external fixture (not shown) configured to impart a desired tension force to the membrane film  202   a , or by the application of a suitable force between the membrane film  202   a  and the baseplate  204   a . Such tension on the membrane film  202   a  can be uniform across the surface of the membrane film  202   a , or vary according to position on the membrane film surface. Moreover, the direction of the tension force can be directional or omnidirectional. 
     Unlike prior ultrasonic transducer designs that typically employ trapped or restricted air as the dominant determining factor of the vibration dynamics of an ultrasonic transducer, the vibration dynamics of the ultrasonic transducer  200   a  (see  FIG.  2   a   ) are chiefly determined by the bending stiffness of the membrane film  202   a , and/or the impedance of the apertures, openings, or perforations  212 . 1 - 212 . 2  formed on or through the perforated baseplate  204   a . In the case where the non-conductive surface of the membrane film  202   a  is placed directly against and in contact with the surface  210   a  of the perforated baseplate  204   a  (e.g., directly against and in contact with upper portions of the surface  210   a , such as an upper portion  215 ; see  FIG.  2   a   ), the distance from the center of the thickness of the membrane film  202   a  to the surface of the membrane film  202   a  in contact with the upper portion  215  is small, and the bending stiffness of the membrane film  202   a  at the location of contact with the upper portion  215  is high, resulting in a strong and consistent restoring force as the membrane film  202   a  bends and/or stretches during vibrational motion. In addition, because an electrical force of attraction is known to be inversely proportional to the distance between oppositely-charged electrodes, having the conductive surface  206  of the membrane film  202   a  (e.g., corresponding to a positively-charged electrode) and the conductive surface of the baseplate  204   a  (e.g., corresponding to a negatively-charged electrode) situated as close as possible, such as when the membrane film is in contact with the baseplate, can maximize both the electrical force of attraction and the restoring force, thereby maximizing the output of the ultrasonic transducer  200   a . Providing a structural curve or radius near the portions  214  and  215  allows for a very close spacing between the electrodes formed by the conductive surfaces of the baseplate  204   a  and the membrane film  202   a , resulting in a strong driving force while still allowing vibrational motion of the membrane film  202   a.    
     The size and/or shape of the apertures, openings, or perforations  212 . 1 - 212 . 2  can be specified to determine the frequency response of the ultrasonic transducer  200   a . The dimensions corresponding to the size and/or shape of the apertures, openings, or perforations  212 . 1 - 212 . 2  can also be varied within one ultrasonic transducer assembly, so that different regions of the perforated baseplate  204   a  can produce different frequency responses of the ultrasonic transducer  200   a , and the net bandwidth of the ultrasonic transducer  200   a  can be increased, as desired. The dimensions of the size and/or shape of the apertures, openings, or perforations  212 . 1 - 212 . 2  can be substantially the same, or production processes can be relied upon to provide some small variation(s) in the dimensions of the respective apertures, openings, or perforations  212 . 1 - 212 . 2 . The apertures, openings, or perforations  212 . 1 - 212 . 2  can be any suitable size, shape, and/or configuration. For example, the apertures, openings, or perforations  212 . 1 - 212 . 2  may be circular, elongated, slotted, square, oval, or any other suitable shape. Such apertures, openings, or perforations formed on or through the perforated baseplate  204   a  may also be flared like acoustic horns in order to provide increased output levels.  FIG.  2   b    depicts an ultrasonic transducer  200   b  that includes at least one such flared aperture, opening, or perforation  112 . 3 , which is formed in a surface  210   b  of a perforated baseplate  204   b . The ultrasonic transducer  200   b  can further include a membrane film  202   b , which can be placed adjacent or proximate to the flared apertures, openings, or perforations (e.g., the flared aperture, opening, or perforation  112 . 3 ) formed in the perforated baseplate  204   b.    
     The apertures, openings, or perforations  212 . 1 - 212 . 2  of the perforated baseplate  204   a  can be formed using any suitable molding, forming, or punching process, resulting in the formation of a plurality of dimples (e.g., a dimple  213 ; see  FIG.  2   a   ) in the surface  210   a  of the perforated baseplate  204   a . As shown in  FIG.  2   a   , the dimple  213  can have a shallow sloping portion  214  that is essentially tangent to the upper portion  215  (see  FIG.  2   a   ) of the surface  210   a  near the membrane film  202   a . For example, each upper portion  215  may correspond to a portion of the surface  210   a  of the perforated baseplate  204   a  that was not deformed by the punching process, and may therefore be at least partially flat. The dimple  213  can also have a wall portion  216  with an increased slope. The shallow sloping portion  214  of the dimple  213  can smoothly transition to the wall portion  216  with the increased slope, which terminates at the aperture, opening, or perforation  212 . 1 . The radius of curvature, r (see  FIG.  2   a   ), of the dimple  213  can be relatively large, for example, about 203.2 μm (8 mil), 1270 μm (50 mil), 2540 μm (100 mil), 5080 μm (200 mil), or any other suitable radius of curvature. The punching process used to form the apertures, openings, or perforations  212 . 1 - 212 . 2  can employ standard punches and/or perforating machines, creating the plurality of dimples (e.g., the dimple  213 ) on one side of the baseplate  204   a  as the punches move through the baseplate material. Once the baseplate  204   a  is cut by the punches, a plurality of metal-edged holes (apertures, openings, perforations) may remain on the opposite side of the perforated baseplate  204   a . In one embodiment, the membrane film  202   a  can be placed directly against the upper portions of the surface  210   a  (e.g., the upper portion  215 ) on the smoother side of the perforated baseplate  204   a  in order to provide an increased force on the membrane film  202   a , as well as provide for an increased ruggedness of the overall ultrasonic transducer design. 
     It is noted that the electrical force of attraction created between the membrane film  202   a  and the perforated baseplate  204   a  is inversely proportional to the distance between the membrane film  202   a  and the shallow sloping portion  214  of the dimple  213 . Because the distance between the membrane film  202   a  and the shallow sloping portion  214  is kept small at a location near the upper portion  215 , the electrical force of attraction between the membrane film  202   a  and the perforated baseplate  204   a  is increased at such locations, and is the source of essentially all of the vibrational motion of the membrane film  202   a.    
     It is further noted that the ultrasonic transducer  200   a  (see  FIG.  2   a   ) can direct and radiate its output energy from either side (or both sides) of the perforated baseplate  204   a , i.e., from the smoother side of the perforated baseplate  204   a  with the upper portions of the surface  210   a  (e.g., the upper portion  215 ), or from the opposite side of the perforated baseplate  204   a  with the plurality of metal-edged holes (e.g., forming the plurality of apertures, openings, or perforations  212 . 1 ,  212 . 2 ). The non-radiating side of the perforated baseplate  204   a  can be left open, or can be made to terminate at one or more chambers (e.g., one or more chambers  320 . 1 - 320 . 2 ; see  FIG.  3   ), which can be either empty or filled with any suitable acoustic absorbing material. Further, one or more acoustic elements can be implemented on the non-radiating side of the perforated baseplate  204   a  in order to reinforce the output of the ultrasonic transducer  200   a . Such chambers (e.g., the chambers  320 . 1 - 320 . 2 ; see  FIG.  3   ) can be implemented as trapped air chambers, such as resonant cavities having dimensions that optimally redirect and/or reflect output energy from the non-radiating side of the perforated baseplate  204   a  back to the radiating side of the perforated baseplate  204   a  opposite the respective chambers. If the ultrasonic transducer  200   a  is configured to direct and radiate its output energy from the side of the perforated baseplate  204   a  with the plurality of metal (or other suitable strong material)-edged holes, then the use of an additional layer (e.g., a screen) for protecting the relatively fragile membrane film  202   a  can be avoided, so long as the plurality of apertures, openings, or perforations  212 . 1 ,  212 . 2  are kept small. In such a configuration, the perforated backplate  204   a  not only imparts force to the membrane film  202   a , but also serves to protect the membrane film  202   a  from damage. Such a configuration can also simplify the assembly of the ultrasonic transducer  200   a , as well as reduce its cost. 
       FIG.  3    depicts a partial cross-sectional view of a further exemplary embodiment  300  (also referred to herein as the ultrasonic transducer  300 ) of the ultrasonic transducer  118  of FIGS.,  1   a  and  1   b . As shown in  FIG.  3   , the ultrasonic transducer  300  includes a membrane film  302  and a perforated baseplate  304 . The perforated baseplate  304  includes a surface  310  with a plurality of apertures, openings, or perforations  312 . 1 - 312 . 2  formed thereon or therethrough. The membrane film  302  can have a conductive surface  306 , and can be placed adjacent or proximate to the apertures, openings, or perforations  312 . 1 - 312 . 2  formed on or through the perforated baseplate  304 . By applying a voltage between the conductive surface  306  of the membrane film  302  and a conductive surface of the perforated baseplate  304 , an electrical force of attraction can be created between the membrane film  302  and the perforated baseplate  304 . Varying this applied voltage can cause the membrane film  302  to undergo vibrational motion. 
     The ultrasonic transducer  300  of  FIG.  3    can further include a structure  318  that forms the plurality of closed chambers  320 . 1 - 320 . 2  for absorbing, redirecting, and/or reflecting output energy from the non-radiating side of the perforated baseplate  304  back to the radiating side of the perforated baseplate  304  opposite the respective chambers  320 . 1 - 320 . 2 . The plurality of chambers  320 . 1 - 320 . 2  can also provide an acoustic compliance to enhance vibration dynamics of the membrane film  302 . For example, the structure  318  forming the plurality of chambers  320 . 1 - 320 . 2  may be made from any suitable conductive material, or any suitable non-conductive material, which, for example, may be molded from plastic or any other suitable material. Further, the plurality of chambers  320 . 1 - 320 . 2  may be configured to be in registration or aligned with the plurality of apertures, openings, or perforations  312 . 1 - 312 . 2 , respectively, or a single chamber may be configured to align with several such apertures, openings, or perforations. 
     It is noted that the curved structure of the respective chambers  320 . 1 - 320 . 2  (see, e.g., a curved structural portion  330 ), as well as the curved structure of the surface  310  of the perforated baseplate  304  (see, e.g., a curved structural portion  340 ) can be configured to allow for substantially free movement of the membrane film  302  between the structure  318  and the perforated baseplate  304  while it undergoes vibrational motion. In an alternative embodiment, the perforated baseplate  304  can be made of any suitable non-conductive material (e.g., plastic), and the structure  318  can be made of any suitable conductive material (e.g., aluminum), allowing the conductive surface  306  of the membrane film  302  to be placed directly against the perforated baseplate  304 . In another embodiment, an ultrasonic transducer  400  (see  FIG.  4   ) can be provided that includes a perforated baseplate  404  made of any suitable conductive material (e.g., aluminum), and a membrane film  402  having a conductive surface  406 , which can be placed directly against the perforated baseplate  404  so long as a thin insulating coating (e.g., a polymer, oxide) is applied to either the conductive surface  406  of the membrane film  402  or a surface  410  of the perforated baseplate  404  facing and at least partially making contact with the conductive surface  406  of the membrane film  402 . Such a thin insulating coating allows the generation of an electrical field, and thus an electrical force, but prevents a short circuit. In an alternative embodiment, the membrane film  402  and the perforated baseplate  404  can be separated from one another by an air gap. 
     With regard to the various configurations of the ultrasonic transducers  118  (see FIGS.,  1   a  and  1   b ),  200   a  (see  FIG.  2   a   ),  200   b  (see  FIG.  2   b   ),  300  (see  FIG.  3   ), and  400  (see  FIG.  4   ) described herein, the electrical force created from a variable electric field produced by applying a voltage difference (e.g., an AC voltage) between the membrane film and the perforated baseplate of each ultrasonic transducer is primarily attractive, i.e., the electrical force operates to move the membrane film in a direction toward the perforated baseplate. Using a DC bias voltage under normal driving conditions, the “pull” of such a force created from the variable electric field can be either increased or decreased, but, typically, the pull of the force does not go negative. Moreover, the restoring force is mainly derived from the stiffness of the membrane film of the respective ultrasonic transducer. 
     Based on the various ultrasonic transducer configurations described herein, it is possible to provide a two-way driving configuration of an ultrasonic transducer. A cross-sectional view of such a two-way driving configuration is illustrated in  FIG.  5   a   , which depicts an exemplary ultrasonic transducer  500   a  that includes a membrane film  502   a , a first perforated baseplate  504   a , and a second perforated baseplate  514   a . As shown in  FIG.  5   a   , the membrane film  502   a  has conductive surfaces  506 . 1 ,  506 . 2  on its opposing sides. The first perforated baseplate  504   a  includes a surface  510   a  with a plurality of apertures, openings, or perforations  512 . 1 ,  512 . 2  formed thereon or therethrough. Likewise, the second perforated baseplate  514   a  includes a surface  516  with a plurality of apertures, openings, or perforations  518 . 1 ,  518 . 2  formed thereon or therethrough. The conductive surface  506 . 1  of the membrane film  502   a  is disposed against the surface  516  of the second perforated baseplate  514   a , and the conductive surface  506 . 2  of the membrane film  502   a  is disposed against the surface  510   a  of the first baseplate  504   a . The first and second perforated baseplates  504   a ,  514   a  can each be made of a conductive material such as aluminum and coated with a thin insulating material (e.g., a polymer, oxide). By applying a voltage difference (e.g., an AC voltage) between the conductive surface  506 . 2  of the membrane film  502   a  and a conductive surface of the first perforated baseplate  504   a , and applying another voltage difference (e.g., an AC voltage), typically with opposite phase and/or polarity, between the conductive surface  506 . 1  of the membrane film  502   a  and a conductive surface of the second perforated baseplate  514   a , the membrane film  502   a  can be made to move alternately in a first direction toward the first perforated baseplate  504   a  and in a second direction toward the second perforated baseplate  514   a . As a result, the output capability of the ultrasonic transducer  500   a  in the two-way driving configuration can be increased up to at least two times the output capability of conventional ultrasonic transducers in known one-way driving configurations. 
     While the membrane film  502   a  of the ultrasonic transducer  500   a  is disclosed herein as having two conductive surfaces  506 . 1 ,  506 . 2  on its opposing sides, the ultrasonic transducer  500   a  may alternatively be configured to include a membrane film with a conductive surface on just one of its sides. Such an alternative configuration would avoid the need for an insulating coating on one of the baseplates  504   a ,  514   a . Electrically driving such ultrasonic transducers in the two-way driving configuration can be performed using any suitable combination of AC and DC voltages relative to the conductive surface(s) of the membrane film and the conductive surface(s) of the baseplate(s). Because an electrical force can be generated from voltage differences, each non-moveable conductive surface of a baseplate can have a varying voltage relative to a corresponding conductive surface on a moveable membrane film in order to produce vibrational motion. Such vibrational motion of the membrane film can be increased or magnified by applying a DC bias voltage relative to the respective conductive surfaces of the membrane film and the baseplate. Moreover, the membrane film or an insulating coating on the baseplate(s) can have electret properties, and can be used to replace or augment the applied DC bias voltage. 
     It is noted that one side of the ultrasonic transducer  500   a  in the two-way driving configuration can be made to terminate at one or more chambers (e.g., one or more chambers  520 . 1 ,  520 . 2 ; see  FIG.  5   b   ) in order to provide an ultrasonic transducer  500   b  (see  FIG.  5   b   ) in a one-way output configuration with increased output drive capability. A cross-sectional view of the ultrasonic transducer  500   b  in the one-way output configuration is illustrated in  FIG.  5   b   , which depicts a membrane film  502   b , a perforated baseplate  504   b , and a structure  514   b  that forms the plurality of chambers  520 . 1 - 520 . 2  for absorbing, redirecting, and/or reflecting output energy from a non-radiating side of the ultrasonic transducer  500   b  to a radiating side of the ultrasonic transducer  500   b , or by acting as an acoustic compliance to provide a restoring force. As shown in  FIG.  5   b   , the membrane film  502   b  has conductive surfaces  506 . 3 ,  506 . 4  on its opposing sides. The perforated baseplate  504   b  includes a surface  510   b  with a plurality of apertures, openings, or perforations  512 . 3 ,  512 . 4  formed thereon or therethrough. The conductive surface  506 . 3  of the membrane film  502   b  is disposed against the surface of the structure  514   b , and the conductive surface  506 . 4  of the membrane film  502   b  is disposed against the surface  510   b  of the baseplate  504   b . For example, the structure  514   b  forming the plurality of chambers  520 . 1 - 520 . 2  may be made from any suitable conductive material, or any suitable non-conductive material, which, for example, may be molded from plastic or any other suitable malleable material. Further, the plurality of chambers  520 . 1 - 520 . 2  may be configured to be in registration or aligned with the plurality of apertures, openings, or perforations  512 . 3 - 512 . 4 , respectively. During operation of the ultrasonic transducer  500   b , output energy resulting from the membrane film  502   b  being made to move in a direction toward the structure  514   b  can be redirected and/or reflected, by action of the plurality of chambers  520 . 1 - 520 . 2 , toward the respective apertures, openings, or perforations  512 . 3 ,  512 . 4  in the perforated baseplate  504   b , thereby increasing the output drive capability of the ultrasonic transducer  500   b  beyond what was heretofore achievable in conventional ultrasonic transducers in known one-way driving configurations. 
     It is noted that a DC bias voltage can be employed to magnify the electrical force of attraction causing the membrane film  502   a  to move in the first direction toward the first perforated baseplate  504   a , as well as the electrical force of attraction causing the membrane film  502   a  to move in the second direction toward the second perforated baseplate  514   a . Further, the apertures, openings, or perforations  512 . 1 ,  512 . 2 ,  518 . 1 ,  518 . 2  (see  FIG.  5   a   ) can each be circular, elongated, slotted, oval, or any other suitable shape for maximizing the performance of the ultrasonic transducer  500   a . In one embodiment, some or all of the apertures, openings, or perforations  512 . 1 ,  512 . 2 ,  518 . 1 ,  518 . 2  can be flared like acoustic horns. In addition, the thin insulating material coating the respective first and second perforated baseplates  504   a ,  514   a  can be implemented as either a thin polymer such as Mylar, urethane, acrylic, or any other suitable polymer, or an oxide such as iron oxide, aluminum oxide, or any other suitable oxide. It is further noted that the ultrasonic transducer designs described herein can be used in parametric array loudspeaker systems or any other suitable systems and/or applications that employ sonic and/or ultrasonic transducers, for transmission and/or reception. Such ultrasonic transducer designs can be segmented for use with a phased array, or multiple discrete elements can be used in one ultrasonic transducer assembly for ruggedness and assembly convenience. 
     An exemplary method of manufacturing an ultrasonic transducer that includes a conductive baseplate and a membrane film is described herein with reference to  FIG.  6   . As depicted in block  602 , in a punching process, a plurality of apertures, openings, or perforations are formed on or through the conductive baseplate, causing a plurality of dimples to be formed in the conductive baseplate adjacent to and between at least some of the plurality of apertures, openings, or perforations. As depicted in block  604 , a surface of the membrane film is coated with a conductive material. As depicted in block  606 , a non-conductive surface of the membrane film opposite the surface coated with the conductive material is placed directly against upper portions of the conductive baseplate adjacent or proximate to the plurality of dimples in order to increase the electrical force of attraction between the membrane film and the conductive baseplate, as well as increase the ruggedness of the ultrasonic transducer. As depicted in block  608 , at least some of the plurality of apertures, openings, or perforations are flared like acoustic horns in order to increase an output level of the ultrasonic transducer. 
     It will be appreciated by those of ordinary skill in the art that modifications to and variations of the above-described ultrasonic transducers may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited except as by the scope and spirit of the appended claims.