This paper deals with the analysis of different beam shapes for piezoelectric energy harvesters. The theory is based on the well-established Rayleigh-Ritz method for piezoelectric compound structures. It is validated by experiments with triangular-shaped and rectangular-shaped beams. It turns out that triangular-shaped beams are more effective than rectangular-shaped ones in terms of curvature homogeneity independent of the proof mass. This effect is opposed by the adverse mass distribution and the increased stiffness of triangular-shaped beams. Therefore, the overall efficiency is only weakly influenced by the beam shape. Nevertheless triangular-shaped beams drastically outperform rectangular ones in terms of tolerable excitation amplitude and maximum output power.

A piezoelectric energy converter is presented, whose resonance frequency can be tuned by applying mechanical stress to its structure. The converter consists of a piezo-polymer cantilever beam with two additional thin arms, which are used to apply an axial preload to the tip of the beam. The compressive or tensile prestress applied through the arms leads to a shift of the beam's resonance frequency. Experiments with this structure indicate a high potential: the resonance frequency of a harvester to which a compressive preload was applied could be altered from 380 Hz to 292 Hz. In another experiment, a harvester with stiffened arms was tuned from 440 Hz to 460 Hz by applying a tensile preload. In combination with automatic control of the applied force, this type of structure could be used to enhance the performance of energy harvesters in vibrating environments with occasional shifts of the vibrational frequency.

This paper presents an electromagnetic vibration scavenger that exhibits a tunable eigenfrequency. By applying a static electrical field the eigenfrequency can be shifted. This feature is originated from exploiting the elastostriction of the utilized piezoelectric bimorph suspension. It is demonstrated that in the tuning operation mode more than 50 μW are scavenged continuously across the feasible frequency range of 20 Hz.

Polymeric structures with integrated, functional microelectrical mechanical systems (MEMS) elements are increasingly important in various applications such as biomedical systems or wearable smart devices. These applications require highly flexible and elastic polymers with good conductivity, which can be embedded into a matrix that undergoes large deformations. Conductive polydimethylsiloxane (PDMS) is a suitable candidate but is still challenging to fabricate. Conductivity is achieved by filling a nonconductive PDMS matrix with conductive particles. In this work, we present an approach that uses new mixing techniques to fabricate conductive PDMS with different fillers such as carbon black, silver particles, and multiwalled carbon nanotubes. Additionally, the electrical properties of all three composites are examined under continuous mechanical stress. Furthermore, we present a novel, low-cost, simple three-step molding process that transfers a micro patterned silicon master into a polystyrene (PS) polytetrafluoroethylene (PTFE) replica with improved release features. This PS/PTFE mold is used for subsequent structuring of conductive PDMS with high accuracy. The non sticking characteristics enable the fabrication of delicate structures using a very soft PDMS, which is usually hard to release from conventional molds. Moreover, the process can also be applied to polyurethanes and various other material combinations.

A novel design of a piezoelectric silicon micropump is proposed, which provides a constant flow rate over a wide backpressure range of up to 30 kPa. This highly appreciable feature is based on a new serial arrangement of two active valves and relies on both an appropriate electrical actuation sequence of the piezo-actuators and an immanent limitation of the membrane deflection by the valve seats. The design is optimized for the low flow regime ranging from 0.1 to 50 µl min−1. A detailed lumped-parameter model is derived in order to reveal the physics behind this pumping principle and to identify the optimum control scheme. For the fabrication of our device, a comparably simple and robust 2-wafer process is utilized. A thorough experimental investigation demonstrates the high performance of the micropump. The backpressure independence of the flow rate enables high-resolution volumetric dosing within the aforementioned flow range. The stroke volume and hence the resolution of the micropump is adjustable via the upstroke voltage of the actuator between 50 and 200 nl. Depending on this setting typical actuation frequencies range from 0.05 to 5 Hz and the flow rate scales proportional to the frequency within that frequency range.