Data processing: artificial intelligence – Machine learning – Genetic algorithm and genetic programming system
Reexamination Certificate
1999-04-20
2002-08-13
Davis, George B. (Department: 2122)
Data processing: artificial intelligence
Machine learning
Genetic algorithm and genetic programming system
C342S373000
Reexamination Certificate
active
06434539
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for determining waveform factors for forming transmitting and receiving beams for an array of transmitting or receiving elements in an acoustic system for imaging in non-homogenous or non-uniform mediums and, in particular, wherein the number of waveform delays required to form the optimal transmitting or receiving beams is greater than the number of signal channels for providing the waveforms to the transmitting elements or collecting from the receiving elements.
BACKGROUND OF THE INVENTION
There are many acoustic imaging systems that require the controlled, directional transmission or reception of sound energy in non-homogenous or non-uniform mediums and in frequency ranges extending from the ultrasonic frequencies and through the audible frequencies to the sub-audible frequencies. Examples of such could range from ultrasonic medical imaging systems to geological imaging or profiling systems and are characterized in that the medium or environment in which the imaging or profiling is to be performed is non-homogenous or non-uniform. That is, the mediums through which such systems form transmitting and receiving beams are non-homogenous, being comprised of layers or bodies or masses of differing materials, and as a consequence have transmission characteristics that vary significantly and non-uniformly from point to point through the medium. For example, ultrasonic medical imaging systems are required to form imaging transmission or receiving beams in the human body, which is a complex structure formed of bone, muscle, fluids and other tissues. Geological imaging and profiling systems are likewise required to form imaging receiving beams in a medium formed of layers and masses of different rocks, soils and liquids typically having widely varying transmission characteristics. In contrast, air acoustic systems, sonar systems and radar systems operate in mediums that are relatively homogenous and uniform. That is, the mediums in which they operate, such as air or water, are comprised of the same substance throughout and, as a consequence and although the transmission characteristics of the air or water may vary noticeably from point to point, have relatively uniform transmission characteristics compared to the human body or geological structures. It will therefore be apparent that the beamforming requirements imposed on acoustic systems for operating in non-homogenous and non-uniform mediums, hereafter referred to as non-homogenous
on-uniform acoustic systems, are often more stringent than those imposed on systems operating in homogenous or uniform mediums. For example, non-homogenous
on-uniform acoustic imaging systems are frequently required to form transmitting or receiving beams that “look around, through or between” the components of complex structures made of substances having widely varying characteristics.
One common technique for the controlled, directional transmission or reception of acoustic energy in non-homogenous
on-uniform acoustic imaging systems is the use of arrays of acoustic transmitting and receiving elements, which are often referred to as “phased arrays”. In this method, the elements of an array, which are generally but not necessarily identical units, are arranged in a predetermined two or three dimensional geometric relationship and the directional pattern or patterns of transmission or reception of the array, often referred to as “beams”, are determined by the combination of the patterns of transmission or reception of the individual elements of the array. In particular, the directions and shapes of the beams are determined by the transmission and reception patterns of the individual elements, the geometric relationship between the elements and the phase relationships among the signals used to drive the elements or received from the elements. Of these, the geometric arrangement of the elements and the characteristics of the elements are generally fixed and the phase relationships among the signals driving or received from the elements are typically controlled to form and direct the “beams” of the array.
It is well understood that a phased array in a non-homogenous
on-uniform acoustic imaging system can form a transmitting or receiving beam of a desired pattern or shape and can direct the beam in an arbitrary direction by appropriate selection and control of the phase relationships among the transmitted or received signals. In a typical phased array non-homogenous
on-uniform acoustic imaging system, the selection and control of the phase relationships among the signals is accomplished by selection and control of time delays through the signal channels through which driving signals are provided to the array elements or the received signals are received from the array elements. It is commonly understood that if each element is provided with its own independent signal channel these delays can be chosen optimally to provide the best possible beam, subject to the physical constraints of the geometry of the array, the number and characteristic of the array elements and the signal waveforms. This result can also be achieved where the number of available signal channels is greater than the number of array elements, or when the geometry of the array is symmetric with respect to the desired beam or beams so that the number of required unique delays is reduced to less than the number of signal channels and so that, for example, one channel can be used for more than one array element.
It is a commonly occurring problem, however, that the number of required delays is greater than the number of available signal channels and it is then necessary for at least some of the array elements to share one or more of the channels, that is, to be grouped or wired together and connected to a channel. In such instances, each such group of array elements connected from a single signal channel operates as a single array element and it is often difficult to obtain the optimum beam or beams from the array, or even a close approximation of the optimum beams. It is possible in theory, however, to obtain a beam or beams that are close to the optimum beam or beams if the Nyquist criterion for spatial sampling can be satisfied by the array and if appropriate groupings of the array elements and corresponding signal channel delay times can be determined and implemented in a realizable system.
In general, the methods of the prior art for determining groupings of acoustic array elements and sets of signal channel delay times have attempted to find the array element groupings and channel delay times that provide beams that match, as closely as possible, the beams formed in the optimum situation wherein the number of available signal channels is equal to the number of array elements. In those instances wherein the optimum required delays fall into localized clusters of values such that the number of such clusters of values is equal to or less than the number of available signal channels, a reasonable solution is to choose a delay time for each channel that is equal to the center, or average, of a corresponding cluster of delay time values and, thereby, the corresponding group of array elements. In general, however, the set of optimum delay time values will be irregularly scattered between some minimum value and some maximum value and the selection of a set of delay times that optimally approximates the optimum delay time values is unobvious and difficult, at best.
One method that has been used to find a set of delay times that acceptably approximate the optimum delay time values has been to find a set of delay times that minimizes the sum of the squares of the differences between each optimum delay time value and the closest delay of the set of approximate delay times. Determining such a set is a non-linear problem, however, since small changes in the delay times selected to represent the optimum delay time values may cause a change in the correspondence between any given optimum delay time value and the delay ti
Gaidos John A.
Hogan William
Woodsum Harvey C.
Booker Kelvin
Davis George B.
Davis & Bujold P.L.L.C.
Sonetech Corporation
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