Surface with varying electrical or magnetic properties

摘要

A substrate (2) has a surface on which is provided a modifying layer which is incomplete and has a distribution such as to provide a plurality of islands of said material and/or islands of substrate surface whereby the surface exhibits a modified electrical and/or magnetic property. As shown, substrate (2) is piezoelectric, and has a central electrode (9) and a peripheral electrode (10), between which are deposited a large number of electrically conductive dots having a dot density which decreases with distance from electrode (9). The construction acts as a sonar transducer over a relatively wide frequency range.