With the size reduction of satellites, the need for miniaturized propulsion systems is increasing. This has led to research funding for the miniaturization of chemical and electric propulsion by NASA and the Air Force Office of Scientific Research (AFOSR). Miniaturized electric propulsion research has been an active area of interest recently. Electric propulsion systems are interesting candidates for miniaturization due to efficiency and the reduction in onboard propellant and the ability to apply existing techniques in electronic fabrication. A miniature electrostatic thruster is being developed in LTCC at Boise State University. The thruster is composed of an antenna to create the plasma, a cylinder to contain the plasma and grids to extract the plasma beam at high velocity. In this work, the development of the inductively coupled plasma (ICP) antenna in LTCC will be presented. This antenna is fabricated using DuPont's 951 Low Temperature Co-fired Ceramic (LTCC). A Direct Write is used to apply silver paste for the spiral ICP antenna. Using LTCC allows for the antenna to be embedded in the device under a thin sheet of LTCC dielectric, which protects the antenna from ion back bombardment during operation. This thin sheet is the seventh layer of the total device, with the ICP antenna one layer below the top. The design of the antenna is based on the research done by J. Hopwood. This paper discusses the fabrication and performance of the ICP antennas in LTCC. These ICP antennas are operated at pressures from 10 mTorr to 1 Torr with radio frequencies (RF) of 500 MHz to 1 GHz to inductively couple with low pressure argon to produce plasma. The performance of the antennas will be verified with data showing the start and stop power of the plasma at various pressures and an electric field map of the RF field above the antenna.
Miniaturized propulsion systems are of particular interest in the development of the newer generation of nano-satellites.These small satellites require a low-thrust propulsion system that is highly efficient in the use of propellant. Currently an electric propulsion device is being developed using the unique capabilities of Low Temperature Co-fired Ceramic (LTCC) materials to fit this purpose. In addition to being a stable, vacuum compatible material with high temperature capability, LTCC is a high permittivity material, with Er=7.8 and a loss tangent of 0.006 1 . The antenna design implements an Inductively Coupled Plasma (lCP) source 2 using a spiral antenna embedded in the LTCC. The antenna's spiral is fabricated in silver paste using a direct-write tool, and is in total 11 cm long and 1 cm in diameter. It is being analyzed for effectiveness in the range of 450MHz-IGHz; the high permittivity causes the length of the antenna's spiral to be approximately one electrical wavelength long with respect to the operating frequency. This gives the antenna interesting characteristics within the 450MHz-l GHz range due to interference patterns generated by the relatively large length of the conductor and its spiraling pattern. As part of this project an analysis of the antenna characteristics and plasma coupling is being done using the COM SOL Multiphysics modeling software 3 along with COMSOL's RF and Plasma Modules. The simulation results will be compared with the experimental results for the antenna and thruster assembly including antenna electric field patterns, plasma start power versus frequency and pressure, and plasma density measurements. 1. DuPont. (2010)."DuPont Green Tape low temperature co fired ceramic (LTCC) materials," Available: www2.dupo nt.comlMCM/en _US/products/green _tape _ltcc.html 2. F. Iza and J. Hopwood, " Influence of operating frequency and coupling coefficient on the efficiency of micro fabricated inductively coupled plasma sources," Plasma Sources
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