Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1990-11-19
1993-01-26
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310367, H01L 4108
Patent
active
051824850
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an ultrasonic transducer comprising at least one row of ultrasonic elements, in which transverse side edges of consecutive elements extend obliquely with respect to the lateral centre axis of the row.
Such an ultrasonic transducer comprising a row of ultrasonic elements, hereinafter to be called the "array", is known from U.S. Pat. No. 4,425,525. When such arrays are used for examination with the aid of ultrasonic vibrations, for example medical examination, it is a problem that each of the elements in the array delivers, when driven, a pressure pattern which has a main lobe and a number of side lobes. Said side lobes are not only present when the pressure pattern is examined parallel to the longitudinal axis of the array, the lateral axis, but also in the direction perpendicular thereto, the transverse direction. Said side lobes may have a relatively high intensity with respect to the main lobe and seriously hamper the interpretation of an ultrasonic echo image obtained with the aid of the array.
In the known array, it is proposed to give each of the subelements the shape of a diamond, the ends of the diamond, viewed along the transverse axis of each of the elements, being flattened off. With the aid of elements shaped in this way, in which the width of each element, viewed from the lateral centre axis of the array towards the two longitudinal side edges thereof, thus gradually decreases, a pressure pattern whose side lobes are appreciably suppressed is obtained in the transverse direction of the array. A drawback of the known array is, however, that the side lobes of the pressure pattern, viewed in the lateral direction, are not suppressed at all. In an array of ultrasonic elements, such side lobes result in interference of the side lobes of adjacent elements, as a result of which so-called "grating lobes" are produced which may affect the pressure pattern very disadvantageously because such grating lobes may, under certain circumstances, be as intense as the main lobe. It is a technique known per se to suppress such grating lobes to a certain degree by dividing up the elements by saw cuts into subelements ("sub-dicing"), a specific ratio between the width of the saw cuts and the width of the subelements being chosen for the best possible suppression of the grating lobes with this technique. In order to obtain a better suppression of the grating lobes, it is desirable to deal with the cause thereof, the presence of side lobes in the pressure pattern of each of the elements.
The invention offers a solution for achieving this by providing an ultrasonic transducer of the type mentioned in which the total extension (2a) of each of the ultrasonic elements (14b, 14c, 14d) in the lateral direction is greater than the distance (p) between the central points of the consecutive elements on the lateral centre axis (x) of the row.
As a result of the measure according to the invention, it has proved possible, as will be explained in more detail below, to suppress the side lobes in the pressure pattern both in the transverse direction and also in the lateral direction so that said side lobes, and in particular the grating lobes which are produced therefrom by interference, do not affect the analysis of the ultrasonic echo image disadvantageously.
It is pointed out that it is known from German Patent Specification 3,304,666 to suppress the side lobes of the elements of an ultrasonic transducer. For this purpose, in the longitudinal direction of the array, towards the two ends of the array, elements are used which are gradually ever less intensely polarized, as a result of which the elements in the centre of the array make the greatest contribution to the beam. This solution is, however, cumbersome because elements having a mutually differing degree of polarization have to be used.
The invention will be explained in more detail below on the basis of an exemplary embodiment with reference to the drawing. In the latter:
FIG. 1 shows a diagrammatic view in perspective of a known ultrasonic array;
F
REFERENCES:
patent: 4242912 (1981-01-01), Burckhardt et al.
patent: 4425525 (1984-01-01), Smith et al.
B.V. Optische Industrie "De Oude Delft"
Budd Mark O.
Marn Louis E.
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