Piezoelectric materials are the most favourite materials to generate ultrasound in the present. A body of piezoelectric material oscillates, when an alternating voltage is applied. The alternating voltage can induce different mechanical oscillation modes. The technically mostly used mode is the thickness mode, then the frequency of the oscillating body is proportional to its thickness. For most technical applications the piezoelectric ceramics are the most important materials and amongst these the lead-titanate-zirconate ceramics, briefly called PZT. These ceramics can be produced economically and have very good piezoelectric specifications. The traditional application of ultrasound in medical diagnosis includes frequencies to 10 MHz. The development of ultrasound for diagnosis in ophthalmology, dermatology and vascular walls goes to frequencies up to 100 MHz. A increase in frequency will increase the spatial resolution. To generate a frequency of 100 MHz, a PZT ceramic has to be 20 µm thick. Thin ceramic layers of this thickness can not be produced by common mechanical machining. By this reason screen printing techniques are developed to produce thin piezoelectric ceramic layers. The project group “Active Materials” is also working in this field of technical development.

A further method to produce thin piezoelectric layers is the physical vapour deposition of thin zinc oxide layers. This material has significant lower piezoelectric specifications than PZT, but it can be integrated in micro systemic processes with physical vapour deposition. With zinc oxide layers frequencies to 2 GHz can be generated. By etching technique and additional mechanical machining it is possible to produce several hundred ultrasound transducers with lenses on the opposite on a silicon wafer.

The group Piezosystems & Manufacturing Technology develops and manufactures customer-specific and standardized 1-3 piezocomposits in the frequency range from 50 kHz to 5 MHz (in special cases up to 20 MHz).

The constant quality of the composites is warranted by using high-precison CNC structuring techniques and a detailled and completely documented mechanical resp. piezoelectrical quality assurance.

The development of ultrasound in medical diagnosis goes to higher frequencies. As presented in “Piezoelectric Materials” this development demands new processes to produce high frequency oscillators. The transfer of energy from the ultrasound transducer into the body to be examined and back to the transducer can be significantly improved by a matching layer. However this matching layer has to be adapted to the demands of the high frequency ultrasound. A solution is offered by nano technology. In cooperation with the Leibniz-Institute für Neue Materialien, INM, a new matching layer with adjustable acoustical impedance was developed. By the content of nano particles in a polymer matrix the acoustical impedance can be adjusted to values between 4 MRayl and 7 MRayl.