A swept frequency method for measuring the magnetic permeability of thin films for frequencies up to 2 GHz with a resolution at 1 GHz of 4 . 1 pm in permeance is described. It is based on the measurement of impedance of a strip loop loaded with the sample under test. The method employs a commercial impedance or network analyzer, is simple, and suitable for permeability measurements of thin magnetic films which are used in recording heads and microwave components.

The relation between electrical breakdown and mechanical properties in soft polymeric materials is of particular interest for multiple applications, such as smart and flexible materials. In the literature, this relation is commonly investigated by variation of temperature, which indirectly causes a change in mechanical properties, but it also affects other factors that may influence the electrical breakdown, such as conductivity. Here, we present experiments that are performed at a constant temperature, on blends of chemically identical tri-block thermoplastic elastomers with different stiffnesses. Stress-strain measurements proved that continuous variation in mechanical properties could be obtained, here a range of 94 -316 kPa was found. Breakdown measurements found that the breakdown field increases with Youngs modulus. The results were compared to several theories in literature, however, only the recently proposed theory of [5] was found to explain the observations adequately.

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Dielectric elastomer actuators (DEA) are a class of eletro-active polymers with promising properties for a number of applications, however, such actuators are prone to failure. One of the leading failure mechanisms is the electrical breakdown. It is already well-known that the electro-mechanical actuation properties of DEA are strongly influenced by the mechanical properties of the elastomer and compliant electrodes. It was recently suggested that also the electrical breakdown in such soft materials is influenced by the mechanical properties of the elastomer. Here, we present stress-strain measurements obtained on two tri-block thermoplastic elastomers (SEBS 500040 and SEBS 500120, poly-styrene-ethylene-butadiene-styrene), with resulting large differences in mechanical properties, and compare them to measurements on the commonly used VHB 4910. Materials were prepared by either direct heat-pressing of the raw material, or by dissolving in toluene, centrifuging and drop-casting. Experiments showed that materials prepared with identical processing steps showed a difference in stiffness of about 20%, where centrifuged and drop-casted films were seen to be softer than heat-pressed films. Electric breakdown measurements showed that for identically processed materials, the stiffness seemed to be a strong indicator of the electrical breakdown strength. It was therefore found that processing leads to differences in both stiffness and electrical breakdown strength. However, unexpectedly, the softer drop-cast films had a much higher breakdown strength than the heatpressed films. We attribute this effect to impurities still present in the heat-pressed films, since these were not purified by centrifuging.

Dielectric elastomer actuators (DEA) based on Maxwell-stress induced deformation are considered for many potential applications where high actuation strain and energy are required. However, the high electric field and voltage required to drive them limits some of the applications. The high driving field could be lowered by developing composite materials with high-electromechanical response. In this study, a sub-percolative approach for increasing the electromechanical response has been investigated. Composites with conductive carbon black (CB) particles introduced into a soft rubber matrix poly-(styrene-co-ethylene-co-butylene-co-styrene) (SEBS) were prepared by a drop-casting method. The resulting composites were characterized by dielectric spectroscopy, tensile tests, and for electric breakdown strength. The results showed a substantial increase of the relative permittivity at low volume percentages, thereby preserving the mechanical properties of the base soft polymer material. Young's modulus was found to increase with content of CB, however, due to the low volume percentages used, the composites still retain relatively low stiffness, as it is required to achieve high actuation strain. A serious drawback of the approach is the large decrease of the composite electric breakdown strength, due to the local enhancement in the electric field, such that breakdown events will occur at a lower macroscopic electric field.