Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications.
With the progression of high-power electric propulsion and high thrust-to-power propulsions system, thrust stand diagnostics require high-fidelity calibration systems that are accurate over a large-range of thrust levels. Multi-mode and variable I(sp) propulsion devices also require that a single stand be capable of measuring thrust from 10's of uNs to 100's of mNs. While the torsional thrust stand mechanic and diagnostics are capable of operating over such a large range, current pulsed calibration schemes are typically limited to a few orders of magnitude of dynamic range. In order to develop a stand with enough dynamic range, two separate calibration methods have been examined and compared to create a combined system. Electrostatic fin (ESF) and piezoelectric impact hammer (PIH) calibration systems were simultaneously tested on a large scale torsional thrust stand system. The use of the these two methods allowed the stand to be calibrated over four orders of magnitude, from 0.01 mNs to 750 mNs. The ESF system produced linear results within 0.52% from 0.01 mNs to 20 mNs, while the PIH system extended this calibration range from 10 mNs to 750 mNs with an error of 0.99%. The two calibration methods agreed within 4.51% over their overlapping range of 10-20 mNs.
In order to begin to evaluate and model the suitability of high temperature ceramic composites, such as AlN:Mo, as susceptor materials for power beaming applications, the electromagnetic, thermal, and mechanical properties of the material must be known at elevated temperatures. Work reported here focuses on the development of thermal property datasets for AlN:Mo composites ranging from 0.25% to 4.0% Mo by volume. To calculate thermal conductivity of the AlN:Mo composite series, specific heat capacity, thermal diffusivity, and density data were acquired. The calculated specific heat capacity, Cp, of the set of AlN:Mo composites was, on average, found to be approximately 803 J/kgK at 100 °C and to increase to approximately 1133 J/kgK at 1000 °C, with all values to be within +/- 32 J/kgK of the average at a given temperature. These calculated specific heat capacity values matched values derived from DSC measurements to within the expected error of the measurements. Measured thermal diffusivity, α, of the set of AlN:Mo composites was, on average, found to be approximately 3.93 x 10-1 cm2/s at 100 °C and to increase to approximately 9.80 x 10-2 cm2/s at 1000 °C, with all values within +/- 1.84 x 10-2 cm2/s of the average at a given temperature. Thermal conductivity, k, for the set of AlN:Mo composites was found to be approximately 108 W/mK at 100 °C and to decrease to approximately 38 W/mK at 1000 °C, with all values within +/- 5.3 W/mK of the average at a given temperature. Data trends show that increasing Mo content correlates to lower values of of Cp, α, and k at a given temperature.
Free-space measurement techniques can be contactless and are able to accommodate large, flat sheets of dielectric material, making them useful for characterization of hightemperature, millimeter-wave, window and radome candidate materials. As part of the present work, a high-temperature, W-band (75-110 GHz), free-space measurement system was developed and used to characterize complex dielectric properties of bulk material samples at temperatures ranging from 25 • C to 600 • C. Two test cases, polyvinyl chloride (PVC) and CoorsTek 92% alumina, were measured at 25 • C and found to have r values of 2.731 ± 0.005 and 8.061 ± 0.027 at 95 GHz, respectively. The 25 • C PVC sample was measured to have a r value of 0.032 ± 0.007. At 25 • C, the r value of the 92% alumina sample was below the uncertainty threshold achievable with the present free-space measurement apparatus and could only be bounded to <0.009. As the alumina sample was heated to 600 • C, r and r values increased to 8.501 ± 0.028 and 0.035 ± 0.008, respectively. The high-temperature behavior of the authors' 92% alumina ceramic was found to be similar to that previously documented for Sumitomo AKP-50 alumina over the 25 • C-600 • C temperature range. In addition to the 92% alumina sample, three commercially available ceramic substrates (zirconium oxide, boron nitride, and silicon nitride) were also characterized at temperatures ranging from 25 • C to 600 • C.
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