JPH07193896A - Ultrasonic wave converter array - Google Patents

Abstract

PURPOSE: To reduce the number of converter elements by increasing the (x) coordinate of the central point of a converter element outward between the central points of adjacent converter elements so as to keep the definite integral of a function f(x) over (x) is constant. CONSTITUTION: A row (i) and a column (j) of an MXN matrix located in an orthogonal coordinate system provided with an origin S, (x) and (y) axes are formed by the converter element Tij. The row (i) is extended in the (x) direction and the column (j) is extended in the (y) direction. Intervals between the centers of the adjacent converter elements, e.g. (Mij and Mij+1), (Mij+1 and Mij+2), and (Mij+2 and Mij+3) monotonically increases outward. Consequently, a function f(x) for the row (i) and a function g(y) for the column (j) may be selected such that they are, respectively an even function with respect to the center S of, symmetry i.e., f(x)=f(-x) and g(y)=g(-y), and decreases strictly monotonously with the increase in the absolute values |x| and |y|.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to ultrasonic transducer arrays.

[0002]

2. Description of the Related Art In medical ultrasonic diagnostic technology, a cavity region of a human body is irradiated with an ultrasonic pulse, and a reflected ultrasonic echo pulse corresponds to a two-dimensional (2D) section passing through the human body by a signal processing unit. An ultrasonic image is formed. For the transmission and reception of ultrasonic pulses, heretofore mainly one-dimensional (1D), particularly linear arrays of piezoelectric transducer elements driven with a predetermined phase delay by an electronic control unit have been used. There is. A linear array driven by such a phase delay transmits and receives ultrasonic radiation that is swingable and focusable in a plane defined by the normal to the array surface and the longitudinal axis of the array. can do. The sway angle for ultrasonic radiation measured relative to the normal is generally greater for smaller transducer elements. Transducer element spacing is an additional diffraction pattern (side lobe)
In order to avoid the
At an ultrasonic frequency of MHz it is about 0.2 mm. On the other hand, a certain minimum length of the linear array is required in order to achieve sufficient ultrasound amplitude and precise focusing of the radiation. With both of these requirements of maximum spacing of transducer elements and minimum length of the array, the minimum number of transducer elements for the array is, for example, 64, which should not be exceeded.

Apart from 1D arrays, also known are two-dimensional (2D) arrays, in particular matrix-shaped ultrasonic transducer arrays, which consist of individual generally rectangular transducer elements. Matrix transducer arrays are described, for example, in German Patent C-3437862 and corresponding U.S. Pat.
4683396 or German Patent Application Publication No.A-37337
No. 76 and corresponding US Pat. No. 4,801,835. If the transducer elements of the matrix array are now driven with a corresponding predetermined phase delay, they can be swung and focused in two angular directions instead of just one, unlike linear arrays. Ultrasonic radiation can be generated and detected. Higher image resolution is thus achieved. In order to be able to pass by ultrasonic radiation a sufficiently large spatial angular range, a square array, ie N =
At M and 3.5 MHz test frequency, for example, a maximum mutual spacing of about 0.2 mm and about 20 × 20 mm ²
The minimum area (aperture) condition of the 2D array of the above must be satisfied. Thereby, for example, 64x64
A minimum number of transducer elements, which can be = 4096, is also needed for 2D arrays.

With such a large number of transducer elements and the need for small dimensions, problems arise in the manufacture and connection of the transducer elements and a large number due to the transmission of control and image signals. The problem of requiring control and data lines arises. Therefore, what is needed is a way to reduce the number of transducer elements without significantly degrading the emission characteristics of the 2D array.

"American Institute of Electrical and Electronics Engineers, Ultrasonic Ferroelectronics and Frequency Control," Vol. 38, No. 4
No. 3, July 1991, pp. 320-333, an ultrasonic transducer matrix having a typical 10.times.10 mm square aperture and square equidistant transducer elements for an electrocardiogram is known. . Sidelobes are practically completely suppressed in the emission characteristics of this converter matrix because the spacing of the converter elements is less than half a wavelength. Starting from this embodiment of the ultrasonic transducer matrix, two possibilities are known in which the number of transducer elements can be reduced. In the first possibility, the transducer elements located at the corners of the matrix are removed so that a transducer array with circular openings with diameters corresponding to the length of the sides of the original square is produced. The spacing of the transducer elements is then unchanged, so that the side lobes are further suppressed. However, the main lobe is slightly wider. The second possibility consists in removing the transducer elements from the matrix array by statistical selection. This increases the average spacing of the transducer elements, and the strength of the main lobe increases with the decrease in the number of transducer elements remaining in the array.

From US Pat. No. 2,928,068, a pressure wave converter with a ceramic block is known. The electrodes are arranged on opposite sides of the ceramic block such that there are different piezoelectrically activated areas between the electrodes. The polarization degree in this range decreases outward from the center of the ceramic block.

[0007] "Journal of the Auscultical Society of America"
Acoustical Society of America ", Vol. 49, No. 5 (Part 2), May 1971, pp. 1668-1669, an ultrasonic transducer having a solid crystal block is known. Due to the special electrode arrangement, a Gaussian distribution with a maximum in the center of the crystal block of the amplitude of the emitted ultrasonic radiation is generated in the crystal block.

From German Patent No. C-3334090 and corresponding US Pat. No. 4,518,889 is known an ultrasonic transducer array with rod-shaped parallel arranged transducer elements. The spacing of the transducer elements increases outward on either side of the center point or centerline so that the acoustic wave response of the effective surface of the array, and thus also the polarization, decreases with a Gaussian function with increasing distance from the center point or centerline To do.

From US Pat. No. 2837728, an ultrasonic transducer array is known which has an equal number of transducer elements that are evenly electrically excited. The spacing of the transducer elements increases from the centerline as the axis of symmetry in the matrix array and from the center point in the circular array according to the mathematical rule spacing = K · sec (n · θ). Where K is a constant, θ is a constant angle of about 10 °, and n is the number of transducer elements calculated from the center point or centerline.

[0010]

The object of the present invention is to reduce the number of transducer elements compared to an array having an equal area and an equidistant arrangement of transducer elements, while at the same time the radiation characteristics being reduced. It is to provide an ultrasonic transducer array that has not been significantly degraded.

[0011]

This problem is solved according to the invention by the characterizing part of claim 1. Each line (x
The spacing of the transducer elements in the (direction) is (a) an even function with respect to the center of symmetry (S) with coordinates x = 0 and y = 0, and a function f in the x-direction that monotonically falls toward both sides.
(X) is defined and (b) the transducer element T in each row
The x-coordinate of the center point Mij of ij is chosen such that the definite integral of the function f (x) with respect to x is at least approximately constant between the center points Mij and Mij + 1 of the adjacent transducer elements Tij and Tij + 1. It increases monotonically outward according to the rule of being.

This means that if xij is the x-coordinate of the center point Mij of the transducer element Tij, and xij + 1 is the x-coordinate of the center point Mij + 1 of the transducer element Tij + 1.

[Equation 1] Can be represented as Definite integral

[Equation 2] Is the graph of the horizontal axis (x axis) and the function f (x), and x = x
It corresponds to the area between ij and both straight lines defined by x = xij + 1. The ultrasonic transducer array may be a linear array with only one row or a two-dimensional, especially matrix-like array with multiple rows.

In this case, the invention makes it possible for the sensitivity of the array to be increased at its edges without significantly degrading the emission characteristics, ie, by significantly increasing the side lobes, due to the change in the center point spacing of the transducer elements according to the invention. It is based on the recognition that it can be reduced without significantly widening the main lobe.

In the two-dimensional array embodiment, preferably:
The spacing between adjacent transducer elements in each column (y-direction) also increases monotonically outward according to a rule equal to that in the row, with a corresponding function g (y) for the column. That is, if yij is the y coordinate of the center point Mij of the transducer element Tij, and yij + 1 is the y coordinate of the center point Mij + 1 of the transducer element Tij + 1,

[Equation 3] Is.

The functions f (x) and / or g (y) are preferably trigonometric functions, Hanning-, Hamm.
ing-, Riesz-, De la-Vall-Pu
issin-, Tukey-, Bohman-, Poi
sson-, Hanning-Poisson-, Ca
uchy-, Gauss-, Doph-Chebysh
ev-, Kaiser-Bessel-, Barilo
n-Femes-, Exact-Blackman-,
Blackman-, Minimum-3-Sample
e-Blackman-Harris- or Mini
um-4-Sample-Blackman-Har
A ris-function is provided. These functions are known within the framework of theoretical studies of harmonic spectrum analysis by the discrete Fourier transform applied to signal recognition (“Proceedings of di-E-E”). the IEEE) "Volume 66, Issue 1, 19
See pp. 51-83, July 1978). The Fourier transform of these functions has a distinctive main lobe and relatively small side lobes. This characteristic is used for the radiation characteristic in this advantageous embodiment according to the invention.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an embodiment of a matrix ultrasonic transducer array. This figure is an overview of a portion of the central area around the center of symmetry S of such a transducer matrix. The transducer elements are labeled Tij,
It also preferably has a square shape. Transducer element Tij
Forms the row i and the column j of an M × N matrix located at the origin S = (0,0) and a right-angle (x, y) coordinate meter with x-axis and y-axis (where 1 ≦ i ≦ M
And 1 ≦ j ≦ N). Row i extends in the x direction and column j extends in the y direction. The ultrasonic transducer matrix may be square (ie the number M of rows equals the number N of columns) or rectangular (ie the number M of rows is different from the number N of columns). . The spacing between the center points of adjacent transducer elements, for example Mij and Mij + 1, Mij + 1 and Mij + 2 and Mij + 2 and Mij + 3, is always increasing outwards. Therefore the function f (x) for row i
And an even function with respect to the center of symmetry S, ie, f (x) = f (−x), as a function g (y) for column j
Or g (y) = g (-y), and absolute value | x |
Alternatively, a function is selected that decreases strictly monotonically with increasing | y |. Thereby these functions f (x) and g
(Y) disappears at the maximum value ± xmax or ± ymax that can be set in this embodiment, that is, f (xmax)
= F (-xmax) = 0 or g (ymax) = g (-yma
x) = 0, a window function. The window function edges ± xmax or ± ymax may be located at positive or negative function values.

Preferably both functions f and g are equal. That is, f (z) = g (z) for the real independent variable z.

The center of symmetry S coincides with the center point Mij of the transducer element Tij in the illustrated embodiment, but may be located outside the individual transducer element.

From the above rules for the spacing of the center points Mij of the transducer elements Tij, at least the number of columns j is greater than 3 and preferably greater than the number M of rows i.

The spacings between the center points Mij of the transducer elements Tij are only outlined and can also be experimentally slightly corrected later.

[Brief description of drawings]

FIG. 1 is a schematic view of a portion of the central area around the center of symmetry of an embodiment of a matrix ultrasonic transducer array according to the present invention.

[Explanation of symbols]

 Tij transducer element Mij center point S symmetry center i row j column

 ─────────────────────────────────────────────────── ————————————————————————————————————————————————————————————————————————— Germany 91052 Erlangen Memerciyutraße 39

Claims (4)

[Claims] 1. Adjacent transducers in an ultrasonic transducer array having at least one row (i) extending in the x direction and columns (j) extending in the y direction of the transducer elements (Tij). The spacing between the center points (Mij and Mij + 1) of the elements (Tij and Tij + 1) is in each row (i): a) an even function with respect to the center of symmetry (S) with coordinates x = 0 and y = 0, and A function f (x) in the x direction that monotonically decreases toward both sides is defined. B) The center point (Mi) of the transducer elements (Tij) in each row (i).
j) has x-coordinates of adjacent transducer elements (Tij and Tij
Characterized by monotonically increasing outwards according to the rule that the definite integral of the function f (x) with respect to x between the center points (Mij and Mij + 1) of +1) is chosen to be at least approximately constant. And ultrasonic transducer array. 2. The function f (x) is a trigonometric function, Hannin.
g-, Hamming-, Riesz-, De la-
Val-Puissin-, Tukey-, Bohm
an-, Poisson-, Hanning-Pois
son-, Cauchy-, Gauss-, Doph-
Chebyshev-, Kaiser-Bessel
-, Barillon-Femes-, Exact-Bl
ackman-, Blackman-, Minimum
-3-Sample-Blackman-Harris
-Or Minimum-4-Sample-Blac
The ultrasonic transducer array of claim 1, wherein the ultrasonic transducer array is selected from the group of kman-Harris-functions. 3. Adjacent transducer elements (Tij or Tij +
The distance between the center points (Mij and Mij + 1) of 1) is also an even function with respect to the center of symmetry (S) in each column (j), and a function in the y direction that monotonically decreases toward both sides. g (y) is defined, b) the center point (Mi) of the transducer elements (Tij) in each row (i)
j) has the y coordinate of adjacent transducer elements (Tij and Tij
Monotonically according to the rule that the definite integral of the function g (y) with respect to y between the center points (Mij and Mij + 1) of +1) is chosen to be at least approximately constant for each column (j). The number increases outwardly.
Or the ultrasonic transducer array described in 2. 4. The function g (y) is a trigonometric function, Hannin.
g-, Hamming-, Riesz-, De la-
Val-Puissin-, Tukey-, Bohm
an-, Poisson-, Hanning-Pois
son-, Cauchy-, Gauss-, Doph-
Chebyshev-, Kaiser-Bessel
-, Barillon-Femes-, Exact-Bl
ackman-, Blackman-, Minimum
-3-Sample-Blackman-Harris
-Or Minimum-4-Sample-Blac
An ultrasonic transducer array as claimed in claim 3, characterized in that it is selected from the group of kman-Harris-functions.