Abstract:
Systems and methods which improve the directivity of a transducer array by reducing electrical cross-talk between conductors connected to individual transducer array elements through the use of a plurality of interconnect circuits are shown. A plurality of signal transmission path circuits, such as circuit boards, flexible printed circuits, etc., are used to provide electrical power to and receive signals from transducer elements of a transducer array. Embodiments couple transducer elements to conductive traces of the signal transmission path circuits in a manner such that adjacent transducer elements are not connected to conductive traces on the same signal transmission path circuit. In some embodiments, a plurality of signal transmission path circuits are offset such that two identical signal transmission path circuits can be used to provide connectivity to array transducer elements using more widely spaced conductive traces, thus reducing electrical cross-talk effects.

Description:
TECHNICAL FIELD 
   The invention relates to ultrasonic transducers and in particular to ultrasonic transducer arrays comprising a plurality of flex circuit connectors to improve directivity. 
   BACKGROUND OF THE INVENTION 
   Ultrasonic systems transmit ultrasonic energy into a subject and receive reflected ultrasonic energy from the subject. Such ultrasonic systems can process received energy and generate an image for analysis by a user. Accordingly, ultrasonic systems are frequently used in medical diagnostic procedures to provide detailed images of internal organs and body structures. For example, the use of ultrasonic systems allows a surgeon to search for tumors, sparing patients the discomfort and inconvenience of invasive exploratory surgery. Ultrasonic systems are also familiar to many parents as the devices that provided the first pictures of their developing children in-utero. 
   Such ultrasonic systems generally include a transducer array with a number of individual transducer elements arranged in a predetermined geometry in one or two dimensions. Piezoelectric materials, generally of ceramic or polymeric material, convert between electrical energy and acoustic energy and are often used to form individual transducer elements. A multi-element transducer array is generally formed from a strip of such piezoelectric material, which is then cut to form a row or rows of individual transducer elements. 
   Ultrasonic systems that use transducer arrays with large numbers of individual transducer elements are generally desirable as providing a large viewing field, a large signal aperture, and/or to provide desired beam forming. Typically, as the density of individual transducer elements of a transducer array increases, so does the image quality produced by a system using that transducer array. However, as the density of the transducer array increases, the pitch of the transducer array, or the longitudinal distance of individual transducer elements, decreases. In conventional transducer arrays, a small transducer array pitch can result in undesirable interference between elements in the form of electrical and acoustic interactions, and image quality can suffer due to such cross-talk. Cross-talk can occur at the transducer and also in transmission circuitry contained in a transducer array head. As a transducer array becomes more dense, so too do connectors providing electrical connections to the transducer array, conductive circuits on printed circuit boards, and other transmission apparatus connected to the array. If the pitch between conductive circuits becomes too small, undesirable electrical cross-talk increases. 
   Various ultrasonic systems have employed transducer arrays wherein transducer elements are disposed in a two-dimensional configuration. That is, a plurality of transducer elements are disposed along the long or longitudinal axis of the transducer array and a plurality of transducer elements along the width or lateral axis of the transducer array. Such two-dimensional transducer arrays typically assume a configuration in which separate signal transmission path circuits are each coupled to a parallel set of transducer elements. To the inventors&#39; knowledge, such two-dimensional arrays have not been used to address the foregoing transducer element density issues or to provide improved directivity, but rather have been to provide a transducer array configuration adapted for use in particular situations. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed to systems and methods which improve the directivity of a transducer array by reducing electrical cross-talk between conductors connected to individual transducer array elements through the use of a plurality of interconnect circuits. Improved directivity transducer arrays allow ultrasonic systems to generate more detailed images of desired targets. 
   Certain embodiments of the present invention reduce the density of conductor traces electrically connected to transducer elements of a transducer array. A plurality of signal transmission path circuits, such as circuit boards, flexible printed circuits, etc., are used according to embodiments of the invention to provide electrical power to and receive signals from transducer elements, such as may comprise piezoelectric transducer elements, of a transducer array. The signal transmission path circuits comprise one or more conductive traces. Each conductive trace is coupled to one of the transducer array elements. In embodiments of the present invention, transducer elements are coupled to conductive traces in a manner such that adjacent transducer elements are not connected to conductive traces on the same signal transmission path circuit. 
   In some embodiments of the present invention, a plurality of signal transmission path circuits are offset in a direction that allows the first conductive trace on one circuit to connect to the first transducer element on an array. The offset is such that the first conductive trace on a second signal transmission path circuit connects to the second transducer element on an array. In this manner, two identical signal transmission path circuits can be used to provide connectivity to array transducer elements using more widely spaced conductive traces, thus reducing electrical cross-talk effects. 
   Embodiments of the present invention are advantageously used with one-dimensional transducer element arrays in a transducer head. A plurality of offset signal transmission path circuits is embedded in a matrix material. The matrix material has a precision surface (which can be flat, cylindrical, or other shape) for receiving the transducer element array. A manufacturing process also exposes conductive trace ends present on the signal transmission path circuits. These exposed ends form a two-dimensional staggered array, again allowing a low density conductive trace signal transmission path circuit to be used, reducing electrical cross-talk. 
   The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
       FIG. 1  is a block diagram of an ultrasonic diagnostic instrument and transducer array according to an embodiment of the present invention; 
       FIG. 2  is an illustration of a transducer assembly having a transducer array and flexible circuits adapted according to an embodiment of the invention; 
       FIG. 3  is an illustration of a backing block comprising a one-dimensional curved transducer array and flexible circuits adapted according to an embodiment of the present invention; 
       FIG. 4  shows a conventional backing block formed with a single flexible circuit and a one-dimensional array of exposed conductive traces; 
       FIGS. 5   a - 5   c  are illustrations of backing blocks according to embodiments of the present invention; and 
       FIG. 6  is a graph showing the directivity of an embodiment of the present invention compared to a conventional transducer array. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a block diagram of an ultrasonic diagnostic instrument  100  in which embodiments of the present invention may be employed. Ultrasonic transducer array  102  generates ultrasonic sound waves and receives reflected ultrasonic sound waves. Transducer array  102  comprises a number of individual transducer elements that varies depending on the desired application. In a preferred embodiment, a transducer array is a flat linear array similar to transducer array  102  shown in  FIG. 1 . However, in other embodiments, a transducer array may be curved, non-linear, or other configuration. Transducer array  102  comprises a one-dimensional array. That is, transducer array  102  comprises a plurality of transducer elements disposed along the long or longitudinal axis of the transducer array and one transducer element along the width or lateral axis of the transducer array (it being appreciated that a two-dimensional array would, in contrast, comprises a plurality of transducer elements disposed along the long or longitudinal axis of the transducer array and a plurality of transducer elements along the width or lateral axis of the transducer array). 
   Beamforming comprising in some embodiments ultrasonic wave generation and echo signal processing is accomplished by beamformer circuitry  104  which interfaces with the transducer  102 . Signal information from beamformer circuitry  104  is received by signal processor  106  which processes the signal information. Signal processor  106  drives display  108  thereby producing visible information used by a user. Power supply  110  provides electrical power used by components of ultrasonic diagnostic instrument  100 . Preferred embodiments of the present invention use a battery for power supply  110 . 
     FIG. 2  is an illustration of a transducer array used in a hand-held transducer assembly adapted according to an embodiment of the present invention. Transducer assembly  200  is comprised of a body  206 . Signal cable  201  enters body  206  at one end and is routed into the interior of body  206 . Transducer assembly further comprises a linear piezoelectric transducer array  207  comprising a number of individual transducer elements  202 . In certain embodiments of the present invention, curved transducer arrays may be used. In a preferred embodiment of the present invention, transducer array  207  comprises 128 transducer elements. However, in other embodiments of the invention, different quantities of transducer elements  202  are present. Individual transducer elements  202  are electrical coupled to conductive traces  204  on one of two flexible printed circuits (FPCs)  203  such that adjacent transducer elements  202  are connected to a conductive trace  204  on a different one of FPCs  203 . While many of the embodiments of the present invention described herein are shown with FPCs, standard printed circuit boards, flexible circuits or other media for providing the appropriate signal can also be used with certain embodiments. 
   Returning to  FIG. 2 , each FPC  203  is connected to a separate cable bundle  205  which merges into signal cable  201 . While this embodiment of the present invention utilizes two FPCs to divide electrical connections to transducer elements  202 , more FPCs can be used to further divide the electrical connections to transducer elements. Transducer assembly  200  further comprises two dowel pins  208  attached to body  206 . Holes in FPCs  203  (not shown) are sized to receive tooling features (in this embodiment, dowel pins  208 ) which project through the holes to accurately position FPCs  203  in a desired position relative to each other. 
     FIG. 3  is an illustration of a backing block  300  comprising a one-dimensional curved transducer array  302  coupled to offset FPCs  301 ,  304  according to an embodiment of the present invention. Offset FPCs are separated vertically and offset by the pitch of the array along the long or longitudinal axis of the transducer array. The short or lateral axis of a transducer array is generally along the width of a transducer element of the transducer array. 
   While this embodiment uses a curved transducer array  302 , in other embodiments, transducer array  302  can assume other forms, such as, for example, a linear form. In this embodiment, a first FPC  301  is used to couple conductive traces  305  to individual transducer elements  303  located in transducer array  302 . Conductive traces  305  from first FPC  301  are coupled alternatingly to non-adjacent transducer elements  303 . A second FPC  304  has conductive traces  307  coupled to non-adjacent transducer elements  303  that are not already connected to first FPC  301 . FPCs are generally formed from a flexible sheet of nonconductive material such as Kapton. Conductive traces  301  are then formed on the nonconductive material using techniques such as etching, photolithography, or electroplating. Conductive traces  301  are themselves formed of conductive material such as, for example, copper. 
   In this embodiment first FPC  301  and second FPC  304  are nearly identical. To manufacture backing block  300  in one embodiment, first FPC  301  and second FPC  304  are positioned in a mold with an offset along the long axis of the transducer array as described above. In other embodiments, FPCs may not be identical and may comprise additional features or structures not present in the other FPC. The offset FPCs are then encased with a matrix material forming backing block  300 . The formed backing block may be cured and/or processed to form a desired shape or to expose electrical connections. Once electrical connections are exposed, transducer elements  303  can be positioned on the exposed electrical connections. Cables or other electrical transmission components may be attached at connector end  308  of backing block  300  in certain embodiments of the present invention. The reduced number of traces on each FPC provides not only advantageous imaging performance and directivity, but also allows for connecting cables to be split or otherwise formed in bundles that allows the formation of transducer assemblies in shapes not easily obtained with conventional systems. For example, two smaller cable bundles used in certain embodiments of the present invention can allow a transducer assembly to have more flexibility and/or a narrower cross-section. 
   While the embodiment of the present invention shown in  FIG. 3  comprises a transducer array with ten transducer elements, in other embodiments, more or fewer transducer elements are present. In a preferred embodiment, 128 individual transducer elements are present. 
   Also, FPCs may comprise material that is used to shield conductive traces  305 ,  307  from interference (crosstalk). In certain embodiments, grounding conductive material such as copper is affixed to the side of an FPC not occupied by conductive traces. The grounding material can be placed on only one side of an FPC or can also extend around the FPC, thereby shielding conductive traces  305 ,  307  from interference on all sides. The grounding material is positioned to shield conductive traces  305 ,  307  while not presenting a profile that will generate an acoustic signal while the array is operating. 
     FIG. 4  shows a conventional backing block  400  with one row of exposed conductive traces  401  in a curved transducer assembly. As earlier mentioned, in other embodiments a flat linear transducer assembly or other transducer configuration may be used. Exposed conductive traces  401  are part of a single FPC  402  embedded in a matrix material forming backing block  400 . Individual transducer array elements (not shown) may be attached to surface  403 , a precision surface on backing block  400  with a single exposed conductive trace  401  contacting each individual transducer array element. 
     FIGS. 5   a  and  5   b  are illustrations of backing blocks according to embodiments of the present invention.  FIG. 5   a  shows backing block  500  comprising two FPCs  501 ,  502  embedded in a matrix material. The FPCs are offset in both a vertical plane and in a plane formed by a long axis of the transducer array, and are offset along the long axis by the pitch of the transducer array. In other embodiments of the present invention, the offsets of FPCs may be different. The matrix material has been processed to form groove  504  with two rows of exposed conductive traces  503 . Individual transducer array elements (not shown) may be inserted in a one-dimensional array in groove  504 . Individual transducer array elements thus inserted each contact a single exposed conductive trace. Adjacent individual transducer array elements contact exposed conductive traces that are positioned on different FPCs. For example, a transducer array element placed on the first transducer element at the front of the illustration contacts an exposed conductive trace of FPC  501 . A transducer array element placed in the position adjacent to the first would contact an exposed conductive trace of FPC  502 . Additional transducer elements placed would continue to alternate between contacting exposed conductive traces of different FPCs. In this way, conductive traces are alternatingly connected electrically to individual transducer elements. 
     FIG. 5   b  shows backing block  500  comprising three FPCs  501 ,  502 , and  505  embedded in a matrix material. As with the two FPC backing block shown in  FIG. 5   a , groove  504  has three rows of exposed conductive traces  503  that contact individual transducer array elements (not shown) inserted in groove  504 . In the illustrated embodiment, inserted individual transducer array elements alternate between the three FPCs. For example, a transducer array element placed on the first transducer element at the front of the illustration contacts an exposed conductive trace of FPC  501 . A transducer array element placed in the position adjacent to the first would contact an exposed conductive trace of FPC  502 . And a third transducer array element placed in the next position would contact an exposed conductive trace of FPC  505 . This pattern repeats for additional transducer array elements added to groove  504 . Other embodiments of the present invention may have backing blocks comprising more than three FPCs.  FIG. 5   c  is a flat linear version of the embodiment shown in  FIG. 5   b.    
   Improved directivity of transducer arrays according to embodiments of the present invention is noted compared to conventional transducer arrays.  FIG. 6  shows a exemplary graph illustrating the results of a directivity test comparing a conventional one-dimensional linear array with a single FPC similar to the one shown in  FIG. 4  to the one-dimensional linear array with a dual FPC similar to the one shown in  FIG. 5   a . The dual FPC transducer array configuration according to an embodiment of the present invention had a measured acceptance angle (at a −3 dB cutoff) of approximately 38 degrees compared to a measured acceptance angle of 29 degrees for the conventional transducer array. This represents an increase of approximately 30 percent for an embodiment of the present invention compared to a conventional transducer array. In other embodiments, greater or lesser increases in directivity may be found depending on factors such as number of FPCs used, array type, array size, transducer element pitch, operating frequency, etc. 
   Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.