Thermal expansion coefficients of high-purity AlN, sapphire, and silicon were calculated from the data obtained with precision high-temperature x-ray lattice parameter measurements. The mean thermal expansion coefficients obtained in the range 20–800°C are α⊥ = 5.3 × 10−6/°C and α∥ = 4.2 × 10−6/°C for AlN, α⊥ = 7.3 × 10−6/°C and α∥ = 8.1 × 10−6/°C for α-Al2O3, and α = 3.6 × 10−6/°C for Si.

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Single-crystal layers of AlN have been grown on sapphire substrates between 1000 and 1100 °C by vapor-phase reaction of aluminum chlorides with ammonia. The purity, color, crystallinity, growth morphology, and electrical resistivity of the epitaxial layers have been investigated. Infrared specular reflection measurements showed the presence of an appreciable strain at the AIN-sapphire epitaxy interface. Optical absorption data strongly suggest the AlN is a direct band-gap material with a value of about 6.2 eV at room temperature.

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A magnetorheological elastomer (MRE-based semi-active (SA) vibration isolator is developed and tested in real-time with a SA controller, illustrating the feasibility of MRE-based isolators. While several researchers have applied MREs to tunable vibration absorbers (TVAs), little work has been done using MREs in primary isolation systems. Further, in cases where TVAs were developed, few SA controllers were implemented in proof of concept experiments. This article presents a magnetically biased MRE-based vibration isolator, which enables the device to have a fail-safe operation in the event of a power failure. To test the effectiveness of the MRE isolator, a SA controller is developed to minimize the payload velocity. A comparison by simulation of variable modulus and damping systems is also presented. Finally, experimental results are given, showing that the MRE isolator and SA controller system reduce resonances and payload velocities by 16-30% when compared to passive systems.

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In this paper, we introduce the analytical framework of the modeling dynamic characteristics of a soft artificial muscle actuator for aquatic propulsor applications. The artificial muscle used for this underwater application is an ionic polymer-metal composite (IPMC) which can generate bending motion in aquatic environments. The inputs of the model are the voltages applied to multiple IPMCs, and the output can be either the shape of the actuators or the thrust force generated from the interaction between dynamic actuator motions and surrounding water. In order to determine the relationship between the input voltages and the bending moments, the simplified RC model is used, and the mechanical beam theory is used for the bending motion of IPMC actuators. Also, the hydrodynamic forces exerted on an actuator as it moves relative to the surrounding medium or water are added to the equations of motion to study the effect of actuator bending on the thrust force generation. The proposed method can be used for modeling the general bending type artificial muscle actuator in a single or segmented form operating in the water. The segmented design has more flexibility in controlling the shape of the actuator when compared with the single form, especially in generating undulatory waves. Considering an inherent nature of large deformations in the IPMC actuator, a large deflection beam model has been developed and integrated with the electrical RC model and hydrodynamic forces to develop the state space model of the actuator system. The model was validated against existing experimental data.