Jörg Sorber

Multi-layer beam with variable stiffness based on electroactive polymers

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 beams 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.

Non-scanning measurement of local curvature with an ultrasound annular array

The paper studies a novel approach for measuring local object curvature radii without scanning. Instead of scanning, an ultrasound annular array is used, and the phase and amplitude differences on the different receiver rings, which contain the curvature information, are used to determine the object curvature radius. Two evaluation methods are compared: One method is based on changing the focus of the transducer, whereas the other one is based on measuring phase differences between several receiving channels.

Piezoresistive Chemosensoren auf der Basis von Hydrogelen (Piezoresistive Chemical Sensors Based on Hydrogels)

Abstract Hydrogele zeigen in Abhängigkeit von der sie umgebenden Flüssigkeit ein starkes Quellungsvermögen. Dies kann für die Schaffung chemischer Sensoren, z.B. für die Messung des pH-Wertes, ausgenutzt werden. Dafür lassen sich piezoresistive Sensoren nutzen, wobei das quellende Hydrogel zu einer Verformung der Silizium-Biegeplatte des Sensorchips führt. Es wurden die Ausgangsspannung in Abhängigkeit vom pH-Wert untersucht und die für eine hohe Signalreproduzierbarkeit erforderlichen Messbedingungen ermittelt.

EAP-Actuators with Improved Actuation Capabilities for Construction Elements with Controllable Stiffness

This contribution considers an actuator based on Electroactive Polymers (EAPs) which is used for constructional elements with controllable stiffness. The actuator consists of a Danfoss PolyPower EAP-foil and a supporting structure which applies the necessary pre-straining force to the foil. Usually, such structures have a constant spring stiffness which strongly limits the actuation range. The novel actuator shows a highly nonlinear spring stiffness for pre-straining the foil. Therefore, the pre-straining force is nearly constant all over the entire actuation range. This behavior can be used to double the possible actuation range. Such structures are suitable to be used in construction elements with variable stiffness. The contribution shows the basic function of this actuator and its capabilities for the application in new smart, self-sensing and self-controlling composite materials for lightweight constructions. The theoretical background of highly nonlinear spring stiffness is discussed and transferred to the developed structures. The theoretical calculations are based on analytic calculations and finite element analyses and are verified by experimental set-ups consisting of different actuators both with constant and highly nonlinear pre-straining spring constant.

Method for curvature measurements with ultrasound

The non-scanning measurement of the local curvature radius is a novel measurement method in ultrasound technology. The basic idea is to use the knowledge of the reflected sound field to characterize the reflector. This is realized by means of a focusing technique and the measurement of the sound field distribution on the receiver. The simulations show that in theory an accuracy of the radius measurement of up to 99% is possible with the suggested transducer configuration. The configuration enables the measurement of ball radii in the range of 10 mm. First measurements confirm the expected effects qualitatively.

Hydrogel-Based Sensor for a Rheochemical Characterization of Solutions

We propose a new type of on-line analytics system for biomedical and environmental monitoring. In order to provide the specific analyte detection, a chemical sensor with a functionalised hydrogel coating has been integrated together with a viscosity sensor in a miniaturized biocompatible rheochemical microsystem. The sensor has been calibrated and tested in aqueuos solutions of alcohol and salts of different concentration. The selective sensitivity of the polyelectrolyte block-copolymer coating to toxic transition-metal ions has been demonstrated.

Hydrogel-based Piezoresistive pH Sensors: Modeling, Simulation and Experimental Verification

This paper presents the investigations of a novel type of piezoresistive pH sensors exploiting the chemo- mechanical energy conversion due to PVA/PAA hydrogel swelling. The sensor structure consists of three parts including a commercial piezoresistive pressure sensor chip, a hydrogel layer, and a rigid grid. The sensor behaviour comprising membrane deflection, membrane stress and output voltage due to the hydrogel swelling has been calculated by finite element method using ANSYS software. It has also been determined experimentally and was compared with those obtained by simulation. A relatively good agreement between caculated and measured results could be achieved