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Spawar Low Temperture Stage

 Project Description

The objective of this project is to produce a mechanical stand to house super conducting  microchips for cryogenic testing.  The center of Cryogenic Exploration of Radio Frequency (CERF) at SPAWAR is in the process of testing and developing RF detecting microchips that operate at temperatures as low as 4 Kelvin (-452 Fahrenheit).  The current setup is very inefficient for this task, as it involves a significant amount time, effort, and expertise to set up each chip.  Our mission is to design a mounting bracket which will allow for easy and efficient microchip replacement, while still providing high thermal conduction and low electromagnetic interference.

The microchips currently used measure incoming electromagnetic signals that operate at the frequency of radio waves.  These tiny chips will soon enable the United States Navy to replace the gigantic parabolic antennae that are currently required to detect these signals.  This new high performance antenna design will also be standardized across the fleet, which will allow other naval engineers to design equipment around an established platform and consolidate when appropriate.

However these microchips operate at cryogenic temperatures and require a mounting and removal method that is appropriate for use on the naval fleet by naval technicians.  The design outlined in this report provides a thermally efficient, electromagnetic interference-free mounting bracket that allows for quick and easy installation and replacement of these microchips.

Like many other devices that were invented for the navy or the military, this product may one day be available for commercial use. These super conducting chips have may see a variety of applications in the future; from gathering radio signals for air traffic to satellite TV for use in the everyday household.  

The initial design set in place for our project involves a very improvised setup that needs to be replaced with a more functional device. The current designs for the chip uses thermal grease (Apiezon N), dental floss, and zip ties to bond and thermally connect the chip to an L-bracket made of aluminum oxide (alumina), which happens to be an excellent thermal conductor. From there, 10 connecting pads as well as 1 ground pad located on the chip are microscopically wire bonded to create a connection to a PCB board, which is then connected to coaxial cables that lead through the rest of the system.  These cables also must maintain excellent thermal contact to reduce the resistivity in the circuit and lower noise in the signal. This design while functional - lacks practicality since it involves an arduous process that is extremely difficult to maintain.

The goal of this project is to create a more practical way to make this connection between the chip and the cooling stage.  The idea is to implement a “plug and play” design, which would speed up the entire process while maintaining a strong thermal and electrical connection.

These are the minimal requirements that need to be met for the project.

·         The chip has to be electrically connected to the system well enough to capture the signal and transfer the it with minimal interference.

·         The chip has to be thermally connected to the system in such a way that it achieves the required 4K in a realistic time. 

·         The material that is chosen must be non-magnetic and non-metallic. 

·         The mass of the bracket should be as small as possible.  This is to make sure that the energy needed to cool the chip to the required 4K is minimal.

·         The chip must be oriented perpendicular to the induced magnetic field.  This orientation is done by having the chip facing up or down.

·         All circuitry must be shield up to 50GHz.  

·         The circuitry of the system must not add enough heat to the system preventing it from reaching the required 4K.

·         The chip must have a “plug and play” design.  This is to make sure that it is easy to install the chip with minimal time. This will also help keep the cost of training the maintainer personal down and reasonable.

During this project there are a couple of deliverable that need to be done for the project to be considered a success.  These are listed below:

·        All 3D model and assembly data files for the project.

·        Technical Drawings including 2D drawings of the 3D physical structure as well as layouts for internal metallization.

·        Intermediate designs that prove the possibility of the design.

·        All analysis done by the group, and a document containing justification for design decisions.