Search

The contribution describes a new kind of multi-layer beam with a variable stiffness based on electroactive polymers (EAP). These structures are supposed to be components of new smart, self-sensing and -controlling composite materials for lightweight constructions. Dielectric Elastomer foils from Danfoss PolyPower are used to control the beam's stiffness. The basic idea is to change the area moment of inertia of bending beams. These beams are built up as multi-layer stacks of thin metal or PMMA plates. Its internal structure can be changed by the use of the electroactive polymers for controlling the area moment of inertia. So it is possible to strongly change the stiffness of bending beams up to two orders of magnitude. Thereby, the magnitude of varying the stiffness can be scaled by the number of layers and the number and type of electroactive polymer elements used within the bending beam. The mechanisms for controlling the area moment of inertia are described in detail. Modeling of the mechanical structure including the EAP uses a pseudo rigid-body model, a strain energy model as well as a finite element analysis. The theoretical calculations are verified by experiments. The prototype described here consists of two structural layers. First results show the feasibility of the proposed structure for mechanical components with stiffness control.

This paper gives a survey of both the design and essential properties of newly developed pyroelectric linear arrays made on the basis of lithium tantalate (LiTaO3). There are up to 256 pixels with a minimum pitch of 50 m. The detector is a hybrid arrangement of pyroelectric detector chip and 0.8 m CMOS read-out circuit in a hermetic metal housing. Thanks to the development of a new black coating technology the thermal resolution and the homogeneity of the spectral responsivity have been permanently improved. The absorption layer consists of a columnar NiCr thin film. It is deposited using a special GLAD technology in high vacuum. The band absorption coefficient in the wavelength range 1...15 m is about 0.9 for a layer with a thickness of about 1 m. The NiCr absorption layer has very low thermal mass and high temperature stability. It can be patterned by lift-off technology. The measurement results demonstrate the excellent homogeneity of the spectral responsivity and the improvement of the signal-to-noise ratio of the linear arrays.

Energy-autarkic sensor systems use energy from their environment for operation and data transfer. This needs both an efficient energy harvesting strategy and an appropriate energy storage management but also ultra-low-power technologies for sensors, signal processing, and wireless signal transfer. Binary Zero-Power Sensors (BIZEPS) are threshold switches which take the switching energy directly from the quantity to be measured. Hence, they deliver the switching states "ON" and "OFF" without any additional electrical energy.

Hydrogels are viscoelastic active materials. They consist of a polymer network with bound charges and a liquid phase with mobile anions and cations. In water based solutions these gels show large swelling capabilities under the influence of different possible stimulation types, such as chemical, electrical or thermal stimulation. In the present work a coupled chemo-electro-mechanical formulation for polyelectrolyte gels using the Finite Element Method (FEM) is applied. In addition to the three given fields, the dissociation reactions of the bound charges in the gel are considered. Thus, we are able to model and simulate pH-stimulation and to give the different ion concentrations, the electric potential and the mechanical displacement. Depending on the initial conditions and the dissociation ratio, different kinds of stimulation cycles can be simulated. Concluding, the developed model is applicable for chemical stimulation and can model both, hydrogel actuators and sensors.

With the rapid development of micro systems technology and microelectronics, smart electronic systems are emerging for the continuous surveillance of relevant parameters in the body and even for closed-loop systems with a sensor feedback to drug release systems. With respect to diabetes management, there is a critical societal need for a sensor that can be used to continuously measure a patient's blood glucose concentration twenty four hours a day on a long-term basis. In this work, thin films of "stimuli-responsive" or "smart" hydrogels were combined with microfabricated piezoresistive pressure transducers to obtain "chemomechanical sensors" that can serve as selective and versatile wireless biomedical sensors. The sensitivity of hydrogels with regard to the concentration of glucose in solutions with physiological pH, ionic strength and temperature was investigated in vitro. The response of the glucose-sensitive hydrogel was studied at different regimes of the glucose concentration change and at different temperatures. Sensor response time and accuracy with which a sensor can track gradual changes in glucose was estimated.