What environments would you need shielding for microelectronic devices?

Thread Starter

Netromello

Joined Oct 15, 2022
1
Hello there,
I’m an EE student with a project team developing a solar-powered car for competition. EMI from our in-vehicle radio, and even radio from outside the vehicle, has been causing our vehicle to accelerate full-throttle. We’re replacing our analog accelerometer with a digital encoder in hopes that will be enough to rid or mitigate the radio interference, but this has led me to another question.
There is little to no shielding on any of the boards. Most of the boards are placed in a box sitting on the dash of our vehicle, which wasn’t designed to be a shield. Few wires have any shielding on them, and as far as I understand, braided shielding does little for high frequency radiation.

My question is: At what environments would you need shielding for your electronics? Where PCB design and filters aren’t enough to protect against EMI? Would an on-the-road environment with the only prominent external EMI source being a nearby radio be enough to need shielding? And if you did need shielding, is it enough to simply shield one part of a system, like a sensor or PCB, a component and its wires, or does the entire system need to be shielded?
I think about desktop computer cases; as far as I’ve read, their cases have too many openings to act properly as a faraday cage, so they’re essentially bare boards with no shielding, yet they seem to handle EMI well without it. But they’re probably not in environments that would have a lot of strong EMI sources

Additionally, any recommendations on intro books to EMI and EMI protection/design tips if they exist would be greatly appreciated!
 

drjohsmith

Joined Dec 13, 2021
541
Hello there,
I’m an EE student with a project team developing a solar-powered car for competition. EMI from our in-vehicle radio, and even radio from outside the vehicle, has been causing our vehicle to accelerate full-throttle. We’re replacing our analog accelerometer with a digital encoder in hopes that will be enough to rid or mitigate the radio interference, but this has led me to another question.
There is little to no shielding on any of the boards. Most of the boards are placed in a box sitting on the dash of our vehicle, which wasn’t designed to be a shield. Few wires have any shielding on them, and as far as I understand, braided shielding does little for high frequency radiation.

My question is: At what environments would you need shielding for your electronics? Where PCB design and filters aren’t enough to protect against EMI? Would an on-the-road environment with the only prominent external EMI source being a nearby radio be enough to need shielding? And if you did need shielding, is it enough to simply shield one part of a system, like a sensor or PCB, a component and its wires, or does the entire system need to be shielded?
I think about desktop computer cases; as far as I’ve read, their cases have too many openings to act properly as a faraday cage, so they’re essentially bare boards with no shielding, yet they seem to handle EMI well without it. But they’re probably not in environments that would have a lot of strong EMI sources

Additionally, any recommendations on intro books to EMI and EMI protection/design tips if they exist would be greatly appreciated!
Have a look here
https://learnemc.com/emc-resources

EMC / EMI / ESD is a large and "impossible" topic

One can do 99.9 % correct, and that 0.1% will cause you infinite problems

One "just" has to design conservatively , and constantly think about cause and effect of what you do ,

BIG generalisation here:
Try to design things not to be sensitive to interference,
differential is better than single ended,
digital is better than low voltage analogue

design protocols on a processor to be resistant to interference
e.g. instead of looking for "a pulse" , make it a set of coded pulses,
use partiy or better error checking / encoding on all links,

The power supplies are a good cause of many problems , especially on mobile gear,
you need filtering on power lines at the board level,
 

KeithWalker

Joined Jul 10, 2017
2,609
You also need to ensure that each electronic module or device is connected to the battery ground by its own conductor to avoid interference caused by ground loops.
 

nsaspook

Joined Aug 27, 2009
10,676
First, work on eliminating the source(s). that's usually more effective and easier than shielding every possible interference access point. Motor controllers, inverters, power supplies are the usual RFI/EMI suspects.
 

LowQCab

Joined Nov 6, 2012
2,627
Another aspect to consider is the specific Antenna-Design that You are using for 2-way-Comms.

Understanding how RF Frequencies are radiated from an Antenna,
and also radiated from the Coax-Cable between the Transmitter and the Antenna,
can, many times allow You to mitigate any RFI problems.

The best setup is to build the Transmitter and Antenna as a single self-contained-unit,
with an Antenna-Design that is as Directional as is Practical for your application,
which is mounted as far away from everything, and as high as possible,
with only Shielded Data/Voice, and Power-Wiring, running to the Transmitter/Antenna-Combination,
and with NO Coaxial-Cable running between the Transmitter and the Antenna.

Usually, the "Base-Station" can utilize a much more sophisticated Antenna.
This will reduce the amount of RF-Power required, on both ends, for reliable Comms.

A "Bi-Cone" Antenna-Design is probably the best suited to the situation.
.
.
.
 

MisterBill2

Joined Jan 23, 2018
13,712
Shielding is needed with all signals whose amplitude matters, and whose generator source impedance is greater than zero. THis is the very broad explanation,and all of the terms that I used need to be qualified with a lot more details.
 
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