Ultraschallelement

An ultraschallelement is the smallest active unit of an ultrasound transducer. It is typically a thin piezoelectric plate or disk that converts electrical energy into mechanical vibrations to generate ultrasonic waves and, when used in receive mode, converts incoming mechanical vibrations back into electrical signals. The resonance of the element is determined by its thickness and the properties of the piezoelectric material.

Materials commonly used are piezoelectric ceramics such as lead zirconate titanate (PZT) and, in some cases, single-crystal materials like PMN-PT. The element is often bonded to a backing layer to damp unwanted ringing and to a matching layer to improve acoustic impedance matching with the surrounding medium. In medical imaging, elements are arranged into arrays (linear, curved, or phased), with kerfs between elements to isolate them.

Operating principle: When an alternating voltage at the element's resonance frequency is applied, the thickness mode oscillation radiates ultrasound into tissue; echoes are detected by the same element for pulse-echo imaging. In receive mode the element acts as a microphone, generating a voltage from mechanical stress of returning waves. The crystal frequency is chosen to suit the imaging band (typically 2–20 MHz in medical devices).

Design considerations include impedance matching, electromechanical coupling factor, bandwidth, and damping. The overall performance depends on element geometry, material properties, backing and matching layers, and electrical drive. Ultraschallelemente are essential building blocks of medical ultrasound probes, nondestructive testing transducers, and other ultrasonic devices.