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摘要

An improved annular array sensor [10] that facilitates hermetic sealing and uses optimum acoustic matching layers is disclosed. The key to the performance improvement obtained in the present invention is the method of forming the annular elements [38,40] of the array. In one approach, the elements [38,40] are not quite separated from one another at the concave side [14] of the sensor shell [12]. A series of cuts [34] are made into a shell [12] of piezoelectric material from its convex side [16]. These cuts [34] are made almost entirely through the shell [12] so that a small amount of material [20] remains between the cut and the concave side [14]. After poling, the resulting ultrasonic sensor [10] has the basic electrical properties of a conventional sensor in which the cuts are made completely through the shell [12]. However, the continuous concave side [14] of the ultrasonic sensor [10] need not be sealed. A conductive coating [32] on the concave side [14] serves as a common ground for all the array elements [38,40]. In another embodiment, the concave side is grooved and plated with a conductive layer [60]. Then a series of thin-kerfed circular cuts [62] are made from the convex side [16] so that they intersect the relatively thick grooves [56]. The thick conducting layer [60) serves as both common ground and mechanical support structure. In the previous art, the conductive coating would be required to have good impedance matching properties, in addition to adequate conductivity. In either embodiment of the present invention, when an impedance matching layer [41] is selected for application to the concave side [14], no compromises need be made in its properties. Therefore the impedance match can be optimized, and the material used need not be an electrical conductor. To complete the sensor airay, individual electrical conductors [42] are connected to the annuli [40] and central disc [38], at the convex side [16]. An acoustically attenuating layer [41] may be used on the convex side [16].