This work focuses on the development of novel strain gauges, which are suited for the operation in autonomous wireless condition monitoring systems. For this purpose, capacitive as well as highly resistive strain gauges were designed and fabricated. The Cand R-sensors were utilised in combination with demonstration circuits, which integrate the circuits for instrumentation, A/D-conversion and furthermore comprise a microcontroller with a wireless transceiver system, all on a small separate printed wiring board. The authors will also be able to present a small demonstration system in operation during the oral presentation.

This paper presents a novel capacitive strain gauge with interdigital electrodes, which was processed on polyimide and LCP (liquid crystal polymer) foil substrates. The metallization is deposited and patterned using thin-film technology with structure sizes down to 15 μm. We determined linear strain sensitivities for our sensor configuration and identified the most influencing parameters on the output signal by means of an analytical approach. Finite-element method (FEM) simulations of the strain gauge indicated the complex interaction of mechanical strains within the sensitive structure and their effect on the capacitance. The influence of geometry and material parameters on the strain sensitivity was investigated and optimized. We implemented thin films on 50 μm thick standard polymer foils by means of a temporary bonding process of the foils on carrier wafers. The characterization of the strain sensors after fabrication revealed the gauge factor as well as the cross sensitivities on temperatures up to 100 °C and relative humidity up to 100%. The gauge factor of a sensor with an electrode width of 45 μm and a clearance of 15 μm was −1.38 at a capacitance of 48 pF. Furthermore, we achieved a substantial reduction of the cross sensitivity against humidity from 1435 to 55 ppm %−1 RH when LCP was used for the sensor substrate and the encapsulation instead of polyimide. The gauge factor of a sensor half-bridge consisting of two orthogonal capacitors was 2.3 and the cross sensitivity on temperature was reduced to 240 ppm K−1. Finally, a sensor system was presented that utilizes a special instrumentation Integrated Circuit (IC). For this system, performance data comprising cross sensitivities and power consumption are given.

This investigation is aimed at the modeling of both the fabrication process and the reliability of press-fit interconnections on moulded interconnect devices (MID). These are multifunctional three-dimensional substrates, produced by thermoplastic injection moulding for large-series applications. The assembly process and subsequently the durability of press-fit interconnections has been modeled and proved with a finite element software. Especially, a simulation tool for process optimizations was created and applied. In order to obtain realistic results, a creep model for the investigated base material, a liquid-crystal polymer (LCP), was generated and verified by experiments. Required friction coefficients between metal pin and base material were determined by adapting simulations and experiments. Retention forces of pins pressed into substrate holes during as well after the assembly process, and after temperature loads were predicted by simulations. Additionally, the decreasing extraction forces over time due to creep in the thermoplastic base material have been predicted for different storage temperatures as well with finite element analyses. Following, the numerical results of the process and reliability modeling were verified by experiments. It is concluded that the behavior of the mechanical contact of the pin-substrate system, can be suitably described time- and temperature-dependent.

This paper demonstrates our approach for the design optimization of wireless torque sensor with FE simulation tools. Such a system comprises the SAW transducer, a torque transfer clip and the machine's shaft. The design process was based on construction, modelling and simulation. In order to optimise the performance, the SAW device, the bonding material and the clip were regarded.

In the case of structure-integrated sensors we regard transducers for mechanical properties like force, stress, or strain, which are mounted directly on a component. This allows much more compact solutions and reduced packaging effects compared to conventional packaging. Two main types exist. One is foil type like a strain gauge and the second is a chip-like element. Both concepts are investigated and their specifics will be further discussed. One of the principal aims of conventional packaging is to avoid mechanical stresses in a device as cross-sensitivities will affect sensitivity, offset and linearity. In the case regarded here it is the target to maximise the stress in a transducer as it is the characteristic property. Besides, sensitivity and offset must not be affected by the operating environment like temperature or humidity. As it is well-know from strain gauges, foil-type transducers are well-suited as they exhibit low inherent stiffness. Unfortunately conventional strain gauges will not be suited well for autonomous operation due to their low resistance and high power consumption. To that purpose we explored new concepts for thin-film based strain gauges. The characterisation of these sensors shows good potential for application in wireless sensing. Also assembly and packaging concepts for strain gauges with integrated circuits for instrumentation and wireless operation have been developed. In the case of chiptype transducers the principal questions of sensor mounting were investigated on SAW devices. Based on finite-element simulations different technologies for mounting chips were evaluated with respect to their influence on offset and sensitivity. Die attachment techniques like adhesive bonding, soldering, brazing, or glass bonding were regarded. Based on these results, proposals for assembly, packaging and interconnection are made. B5.1 Figure 1: Finite-element model of a structure-integrated wireless force sensor exhibiting the three principal areas of interest in this investigation.

This investigation is aimed at the stability of press-fit interconnections for MID. Moulded Interconnect Devices (MID) are 3-dimensional substrates produced by thermoplastic injection moulding for large-series applications. The assembly process of press-fit interconnections has been correctly modelled with a FE-Software. With this model the behaviour of the mechanical contact pressure, which decreases due to creep in the thermoplastic base material, could be described. Especially, the modelling is a tool to optimize pin and hole geometries. In order to obtain realistic results, the creep law parameters for the applied base material, a liquid-crystal polymer (LCP), was fitted to experimental. The required coefficients of friction were determined by adapting the simulations to the experiments. The time-dependent retention force between a pin and the substrate directly after assembly or after temperature loads could be predicted with finite element analyses, which was used as reliability criterion.

This paper focuses on the mechanical properties of polydimethylsiloxane (PDMS) relevant for microelectromechanical system (MEMS) applications. In view of the limited amount of published data, we analyzed the two products most commonly used in MEMS, namely RTV 615 from Bayer Silicones and Sylgard 184 from Dow Corning. With regard to mechanical properties, we focused on the dependence of the elastic modulus on the thinner concentration, temperature and strain rate. In addition, creep and thermal aging were analyzed. We conclude that the isotropic and constant elastic modulus has strong dependence on the hardening conditions. At high hardening temperatures and long hardening time, RTV 615 displays an elastic modulus of 1.91 MPa and Sylgard 184 of 2.60 MPa in a range up to 40% strain.

sensor is described. The geometry of the device, the behaviour of the packaging materials as well as the packaging process are regarded using this method. The complex material behaviour of adhesives and moulding compounds was investigated. The results show, that for modelling the influence of the packaging on the sensor performance correctly, the nonlinear temperature- and time-dependent material behaviour has to be taken into account. Differences of the coefficients of thermal expansion of the packaging materials lead to thermo-mechanical stress in the package. Due to the time-dependent material properties, this results in a change of the offset and the sensitivity of the sensor over time and may lead to a sensor working outside its specification. The piezoresistive and piezo-Hall coefficients of semiconductor Hall plates were measured, thereby the stress- and temperature-dependency of the Hall plates were determined. According to the results, package-induced stresses lead to a change of the offset voltage up to 60% full-scale while the sensitivity changes by plusmn4 %

This paper presents a new concept of low degree-of-freedom deformable mirrors. The application of the mirror is the focusing of a laser beam, featuring a variable focal length. The deformation shape, which is in this case a circular parabolic and an elliptical parabolic respectively, is achieved by a local variation of the mirror's thickness. The paper explains the analytical treating of the mirror's thickness distribution as well as an iterative approximation procedure using FEM simulation. The mirrors were fabricated using hot embossing and injection molding technology. The molds required are made from steel whereas the structuring is done by conventional milling. The fabricated mirrors were coated with a reflective gold layer. For deformation measurements a functional demonstrator consisting of the coated mirror, assembly plates and an electromagnetic actuator was produced. The deformation of the mirror was measured using a 3D coordinate measuring machine. The optical function was characterized by a CCD laser measurement setup. Deviation between the measured and the optimal deformation function was sufficiently small. The spot size of the focused laser beam was up to 470 mu m whereas the focal length could be varied in a range of 250 mm to 1000 mm. Due to the use of polymeric material, the long time behavior in respect of creep was researched using FEM simulations as well as endurance tests.