Michael Heinrich

Integration of piezoelectric polymer transducers into microsystems for sensing applications

A polymer-based sensor for low frequency acceleration detection is fabricated by using microinjection molding technologies. Finite Element simulations and characterization of the sensing functionality are done. Due to an out-of-plane acceleration a force is applied to a seismic mass (length and width each 3.2 mm, thickness 1 mm), which leads to a deformation of a connected plate with dimensions of 1 mm × 1 mm × 50 μm. Thus, charge separation at the electrodes of integrated piezoelectric polyvinylidene fluoride (PVDF) copolymer sheets occur and can be measured as sensor signal. A charge sensitivity of 0.57 pC/g is determined which is in good agreement with the simulation results. A resonance frequency of 660 Hz was measured. Furthermore, the sensor concept as well as preparation technologies to assemble a compound structure containing piezoelectric layers and the system integration by micro injection molding are discussed. In addition, different bonding techniques for the assembly of the functional components are investigated and described.

Microinjection molding of polypropylene (PP) filled with MWCNT: Influence of processing parameters on the mechanical properties

Polypropylene composites with different contents of multiwalled carbon nanotubes (MWCNT) were microinjection molded to investigate the influence of melt temperature and injection velocity on the final mechanical properties. Therefore, samples of various MWCNT loadings from 1 wt% to 5 wt% were prepared by diluting commercial masterbatches. Microinjection molding was used to prepare micro tensile bars under different processing conditions. The nano composites expose mechanical properties significantly influenced by nanotube loading, injection velocity and melt temperature.

Initial Stress Behaviour of Micro Injection-Moulded Devices with Integrated Piezo-Fibre Composites

Based on an increasing demand for function integration in small components, micro injection moulding offers a highly productive solution to combine plastic structures with additional electronic and mechatronic features. Particularly two-component micro injection moulding allows embedding of active elements as well as the application of electric contacts in one process step by using insolating and conductive compounds, respectively. The study outlines major effects on the thermo-mechanical compatibility of active modules comprising several stacked piezo fibre composite beams. With regard to material properties, geometry of the module, machine set up and processing parameters a structural and strength analysis including process induced residual stress is used to predict favourable material combination and composite design.

Fiber-reinforced composite structures with embedded piezoelectric sensors

Embedding of piezoelectric materials into fiber-reinforced composites is constituted as promising technology to develop ultra-sensitive structural health monitoring functionalities, e. g. strain measurement or acoustic emission testing. Here, we present latest results of embedding piezoelectric polymer foils into fiber-reinforced composite structures. The applied processing technique allows the implementation of several piezoelectric transducers at different positions within the fiber-reinforced composite. For studying the functionality non-destructive impact testing and three-point bending experiments were carried out to characterize the composite. Exemplarily, the functionality of the embedded sensors is demonstrated by means of triggering an embedded light emitting diode which is switched on after the piezoelectric transducer sensed mechanical strain.