Testing for EMI (electromagnetic interference) is a critical step in product design due to FCC and CE regulations. In this article, we will look at MuRooms; modular metal rooms that significantly reduce outside EMI sources for testing and experimentation purposes.

EMC (electromagnetic compatibility) testing is a critical step in modern electronics product design. It is critical in design, from mobile devices to aerospace, to ensure device functionality, regardless of the types of EMI present.

EMC testing is also often compulsory for products to meet certain regulatory standards, especially when designing for applications that require RF functionality across any part of the electromagnetic spectrum, such as Wi-Fi or Bluetooth.

Actually getting a product to pass EMC regulations, however, can be challenging and is almost always a costly expense. This is why you should consider EMC compliance and EMI countermeasures early in your design.

 

SpaceX's ship, Crew Dragon, in an anechoic chamber for EMI testing. Image courtesy of Elon Musk

 

Luckily, resources for successful EMC testing continue to grow in type and number. The first line of defense, of course, is to use best design practices for EMC, such as the use of differential signals and stitching via. These tactics, however,  are no guarantees and even the most carefully engineered product can emit RF signals which violate emission laws.

Here's some food for thought on how to handle the prospect of EMC testing in a design. 

 

Pre-Certified Components

While using pre-certified hardware doesn't guarantee that a device will be compliant with standards, it's often a step in the right direction. Many companies offer pre-certified components to help designers get their products to market faster. 

There are many pre-certified components and modules available, ranging from FCC certification to specific certifications for specific standards such as ZigBee or Thread.

For example, Silicon Labs just released a new Wi-Fi portfolio with pre-certified options. Some companies release pre-FCC-certified development kits, such as Digi International's Xbee3 embedded systems, including modems and connectivity modules. u-blox offers global pre-certification for devices in their NINA family of Wi-Fi and Bluetooth modules, including their NINA-W10.

 

The new Wi-Fi module family released by Silicon Labs. Image courtesy of Silicon Labs

 

Texas Instruments has a portfolio of pre-certified products, along with a handy whitepaper on how pre-certified components can help designers work with the "black magic" of RF. 

If you'd like to see a pre-certified module in action, check out our article on using a GT-tronics module to add BLE5 to a project

Even with pre-certification, however, EMC testing is necessary to ensure compliance.

 

Pre-Compliance In-House EMC Testing

While large corporations can often afford the cost of retesting products smaller business may not have the budget for more than a few tests.

DIY EMC testing is not going to be as in-depth as a certified test house, but it can definitely be used as a method for minimizing the chance of mistakes. Such DIY testing can be done using testing rigs and comparatively inexpensive spectrum analyzers that can give engineers an idea of how noisy their products are.

 

Spectrum analyzers can be critical tools in EMC testing

 

But such testing may be difficult if not done in a low-EMI environment such as those found in test-houses. This is why many companies contract out to EMC testing services for help. 

 

EMC Testing Services and EMI Shielding

EMC testing services are designed to help companies that don't have in-house resources for testing. Many of these companies have an anechoic chamber for full isolation and control when testing for electromagnetic environmental effects.

 

An anechoic chamber at the Acoustics Research Centre of the University of Salford, UK. Image courtesy of Daniel Wong-McSweeney [CC BY 4.0]

 

E3 testing can include any number of factors, such as electrical surge and electrostatic discharge (ESD). It's important to keep in mind that these tests may only test a product once, regardless if it passes or fails. This means that any designs which come back having failed need to be redesigned and then retested, which can become costly in terms of both budgets and manpower.

Some facilities instead build EMI-shielded spaces for EMC testing. These labs are sometimes used in sensitive testing applications, such as electron microscopy. In recent news, Magnetic Shield Corp. announced that their modular metallic chamber rooms, known as MuRooms, have been installed at the Materials Research Lab at the University of Illinois (UOI) Champaign-Urbana. The rooms are made using a proprietary alloy known as MuMetal, an unoriented soft magnetic nickel-iron alloy that has a high permeability and as such is very effective for shielding against electromagnetic waves.

Due to its ability to readily absorb EMI, it is commonly found in low-intensity magnetic fields with frequencies around 100kHz. The MuRooms are capable of reducing the earth's magnetic field by 125 times, the internal field magnitude is 0.4μT, and ambient magnetic fields between 0-500Hz are reduced to 20nT.

 

MuRooms EMI shielding for sensitive electronics and testing

 

While this use of EMI shielding is for research, the same concept can be applied to EMC pre-testing for device design. Depending on a company's EMC testing needs, modular labs like these could be built in-house, allowing for future adjustment and positioning of rooms that would otherwise not be possible.

 


 

EMC testing is critical and EMI from the natural environment can be a real pain. Test houses can be very expensive especially when testing multiple products so any DIY testing that can be done should probably be done.

 

Comments

1 Comment


  • timfoo 2019-01-31

    A point to note, an anechoic chambers used for acoustics measurements/testing has nothing or very little to do with EMC measurements/testing.