2.2. Fabrication
Since the piezoelectric patch operates in a lateral extension mode, the functional component has to be placed in the highest possible distance to the neutral axis of the casting. Hence tensile and compressive stresses can be detected in a wide range of frequencies [8]. To ensure the load transmission between casting good and piezoelectric component, module edges are firmly engaged with the casting matrix after the cavity filling and shrinkage on solidification. Contrary to the application with expanded metal parts [9] the present results are based on the application of Al99.5 sheets at the cavity surface. LTCC patches are placed on metal sheets via adhesive bonding. In the following step the support structure including the functional component is sited in the mold cavity using fixing pins as intermediate positioning system. Therefore a die casting mold with a simple prismatic geometry (178 x 178 x 3.5 mm³) is chosen. While the die is closing and the fixing pins are pulled out of the cavity expandable metal parts are compressed between the Al99.5 sheet and the cavity wall to guarantee the placing during the casting process. Detailed fabrication specifications are given by Rübner et al. [9]. The verification of the casting experiments is provided by x-ray analysis (ct-alpha big).