A plurality of transducers is arranged successively on a common impedance matching layer of a resilient material. Each transducer comprises an elongated piezoelectric element having a width expansion vibrational mode, a pair of first and second electrodes attached to opposite surfaces of the element across its thickness and an elongated block of an impedance matching material disposed between the second electrode and the common impedance matching layer. The common impedance matching layer is bent to take the shape of an arch to conform to the surface of a frame structure which is convexed in the direction of propagation of ultrasonic energy. The piezoelectric elements are secured to the frame so that they bridge the parallel side members of the frame. The piezoelectric members are divided into a plurality of subgroups, each composed of successively arranged elements. The piezoelectric elements of a given subgroup are selected and energized during each clock interval for transmission of focused ultrasonic energy. The subgroup to be selected is shifted linearly to the next by at least one element in response to successive clock pulses. Becuase of the convex shape of the array, the transmitted energy is successively angulated to provide arc scan.