The Faraday Enclosure Feedthrough (A3039)

© 2020 Jordan D. Kaufman, Open Source Instruments Inc. © 2020 Kevan Hashemi, Open Source Instruments Inc.

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Contents

Description
Versions
Design
Set-Up
Modifications
Development

Description

[07-OCT-20] The Faraday Enclosure Feedthrough (A3039) is any one of a family of connector assemblies that allow signals to pass in and out of Faraday enclosure without compromising the isolation the Faraday enclosure provides for our Subcutaneous Transmitter (SCT) system.

Each feedthrough system is comprised of two boards, either the (A303901A/B) on top and a base board A303902A/B. Each board has a network of vias appropriately spaced to block RF signal that could potentially interfere with DAQ. The base board is required to elevate the pins of the connectors and keep the integrity of the faraday enclosure. These two boards are connected electrically through pins that connect to the ground planes of both boards and to the BNC connectors as well as the faraday enclosure. This preserves the RF blocking of the faraday enclosure.


Figure 1: Faraday Canopy Feedthrough Boards. From left to right: A3039B, A3039A, and A3039C. Designed for use with the Flexible Mesh Canopy for IVC Rack (FE5A).

Versions

The table below lists the existing versions of the The Faraday Enclosure Feedthrough (A3039).

Version (Name) Connector Positions Comments
A3039A (8-8 Coaxial Feedthrough) Coaxial 8 For use with Loop Antenna (A3015C)
A3039B (8-8 Ethernet Feedthrough) Ethernet 8 For use with Animal Cage Camera (ACC)
A3039C (8-4 Coaxial Feedthrough) Coaxial 8-4 For use with Loop Antenna (A3015C)
Table: Versions of the Faraday Enclosure Feedthrough (A3039).

Design

S303901A: A303901A Schematic.
S303901B: A303901B Schematic.
S303901C: A303901C Schematic.
A303901A.zip: PCB for A3039A top, Gerber files and drawing.
A303902A.zip: PCB for A3039B top, Gerber files and drawing.
A303901B.zip: PCB for A3039B top, Gerber files and drawing.
A303902B.zip: PCB for A3039B top, Gerber files and drawing.
A303901C.zip: PCB for A3039B top, Gerber files and drawing.
A303902C.zip: PCB for A3039B top, Gerber files and drawing.

Set-Up

Installation for all feedthrough boards are identical. The surface in between the connectors of the A3039 feedthrough is taped with aluminum tape. It will have contact with the through-pins that electrically and mechanically connect both pieces of the boards. This ensures that all ground planes are connected electrically to the enclosure. Place it on the edge of the canopy so that one side of the connectors are in the enclosure and one side is out. During operation it is key that the canopy mesh is in contact with the aluminum tape on the A3039.

Modifications

[10-MAR-21] The BP2C+ are at risk of being in electrical contact with both the mesh and applied aluminum tape during installation. We will be covering them in clear DP270 Epoxy in order to insulate them electrically.

Development

[06-OCT-20] A303901A and A303902A BNC Feedthrough layouts were submitted for fabrication.

[01-NOV-20] A303901A and A303902A recieved and assembled. Once assembled the complete A3039A is taped with aluminum tape to base of Faraday Enclosure. Board ground and enclosure connected electrically and confirmed with DMM. The two pieces of A3039A are joined mechanically by small pins that are soldered to both the top and bottom boards. They are also grounded together through the same mechanism.

[15-NOV-20] A3039A was left on the floor in its installed state. One of the connectors was stepped on and the solder joints broke. There will need to be future design considerations as the board will be in a similarly installed position when it is shipped to customers. It is also difficult to connect and disconnect BNC cables.

[18-NOV-20] A3039B was submitted for fabrication, it is a RJ45 feedthrough board. The A3039B is comprised of the A303901B connector board and A303902B base board.

[1-DEC-20] A3039B was recieved and assembled using identical through-pin mechanism as the A3039A.

[5-DEC-20] A3039A and A3039B are used to take simultaneous video and EEG measurements using the video and neuroarchiver tools. This demonstrates that they work as feedthrows for use within a faraday enclosure.

[1-FEB-21] We decided on developing a 4-8 BNC Feedthrough A3039C. This circuit will allow us to shrink the size of the board to more easily fit inside the canopy with the IVC rack. It is easier to solder due to the size of the through hole pins on the BNC_V. Since it is a 4-8 one can connect 16 antenna to one octal data receiver.

[25-FEB-21] We have complete an array of tests inside the Faraday Canopy using the A3039A circuit. First we measured reception inside the enclosure with a varying number of MA1 absorbers. We turned on external interference by plugging in an antenna to the command transmitter. Then measured interference power with the canopy open and closed along with reception. The results are of this test are in the table below.

Number MA1 Xmitter 1 Reception Xmitter 2 Reception Interference Power Open Interference Power Closed
4 100.00% 100.00% -42.0dBm -68.5dBm
3 98.54% 99.86% -38.0dBm -61.0dBm
2 98.75% 99.23% -40.5dBm -59.5dBm
1 99.39% 99.73% -40.5dBm -59.0dBm
0 99.89% 100.00% -37.5dBm -52.0dBm
Table: Reception and Interference Power with Varying Number of MA1

[27-FEB-21 ]We ran another set of tests at higher controlled interference using a power boosted command transmitter. Again we varied the number of MA1 in the Faraday Canopy. We can see that at the higher interference values we start to have significant reductions in transmission. The interference power measurements were taken with the canopy opened in the front and closed.

Number MA1 Xmitter 1 Reception Xmitter 2 Reception Interference Power Open Interference Power Closed
4 92.52% 95.88% -24.5dBm -45.5dBm
3 97.82% 98.90% -19.5dBm -41.5dBm
2 92.75% 43.06% -17.0dBm -39.0dBm
1 91.37% 99.59% -22.0dBm -35.0dBm
0 76.01% 88.41% -22.0dBm -32.5dBm
Table: Reception and Interference Power with Varying Number of MA1

[1-MAR-21] We begin testing our (A3035) Implantable Inertial Sensor for Tufts University inside the faraday canopy. We use the coaxial feedthrough for these measurements. We measured transmission with all 4 MA1 absorbers in the enclosure and once with external interference and once without. The IIS is also submerged in water within a fish tank along with the antennas. The antenna is a hand turned 13mm loop of solid core wire. The exact power of the interference was not measured.

Interference Reception
No 98.62%
Yes 83.87%
Table: Reception with and without interference with the (A3035).

[5-MAR-21] We constructed one full A3039C, it was much faster to construct than the A3039A. One issue is that the BP2C+ combiner on the top of the board could potentially be grounded when alumnimum tape is applied. We will cover these in clear DP270 epoxy to insulate them from the alumnimum tape.

[10-MAR-21] We measured the power on one side of the splitter to the other of the A3039C. Using a Command Transmitter (A3029) and attenuators we were able to put -30dBm of RF power into one side of the A3039C. The output not being measured was always terminated with 50 Ohm terminator. The measurement error is +-.5 dBm

Device Input Power Output 1 Output 2
A3039C -30dBm -32.5dBm -33.5dBm
Mini-Circuits Power Splitter/Combiner -30dBm -33dBm -33dBm
Table: Versions of the Faraday Enclosure Feedthrough (A3039).

[10-MAR-21] We tested reception inside the enclosure using the A3039C at high intereference levels. We compared the performance of the A3039C to standard BNC T junctions. Again we used the command transmitter to transmit controlled interference to reduce the reception below our "robust" rate of 95%

Reception A3039C Reception BNC T
67.57% 80.00%
Table: Reception measurements from 4 antenna using A3039C and BNC T

[11-MAR-21] We covered the BP2C+ in DP270 clear epoxy, it cures and covers the surface as well as all of the pins thus insulating it circuit from the tape. Visible in figure 2 below are the connector through pins J18 J19... etc.


Figure 2: A3039C with DP270 Epoxy convering exposed surface mounted components.