Understanding EMI
Interference to an electronic circuit caused by conducted or radiated electromagnetic radiation, or EMI, is a growing challenge of the electrification era. The proliferation of electronic devices in the world has caused EMI to become a relevant concern. Although all electronics emit magnetic and electrical energy, if this energy unintentionally interacts with another device and causes it to malfunction, then it is considered interference.
Most EMI is caused by frequencies that fall between 1 kHz and 10 GHz. The wavelength of 60Hz “power mains” is 5,000 km — the approximate distance from New York to Los Angeles. The wavelength of a 2.45GHz microwave oven is 12.2 cm or 4.8 inches.
λ = Wavelength in meters (m)
c = Speed of light. Constant of 299,792,458 meters/second
f = Frequency in Hertz (Hz)
| f |
~ λ |
| 10 kHz |
30 km (18.60 mi) |
| 100 kHz |
3 km (1.86 mi) |
| 1 MHz |
300 m (983 ft) |
| 30 MHz |
10 m (32.80 ft) |
E-Fields |
| 100 MHz |
3 m (9.83 ft) |
E-Fields |
| 1 GHz |
30 cm (11.80 in) |
E-Fields |
| 10 GHz |
3 cm (1.18 in) |
E-Fields |
E-Fields come from digital components such as printed circuit boards (PCBs), radio, cell phones, radar transmissions.
- Frequency (f) — the number of completed cycles of a periodic process per unit time (seconds).
- Unit of Measure — Hertz or Hz (cycles/second)
- Wavelength (λ lambda) — the distance between two points of corresponding phase in consecutive cycles.
- Unit of Measure — meters
EMI Shielding
When an electromagnetic wave is travelling in space and hits an electrically conductive object, the following will happen:
- The wave will reflect
- The wave will be absorbed
- A secondary wave will be created
- A combination of above
Shielding Effectiveness (S.E.), sometimes called attenuation or isolation, is measured in decibels (dB). Decibels are used to express the ratio between two amounts of energy, E1 and E2.
Quantitative EMI Shielding Values
| Shielding Effectiveness |
Attenuation Ratio |
Leakage Through Shield |
| dB |
|
% |
| 20 |
10:1 |
10 |
| 40 |
100:1 |
1.0 |
| 60 |
1,000:1 |
0.1 |
| 80 |
10,000:1 |
0.01 |
| 100 |
100,000:1 |
0.001 |
| 120 |
1,000,000:1 |
0.0001 |
The main goal of an EMI shielding solution is to seal an electrical device enclosure to prevent transmission of electromagnetic interference by isolating it from its surroundings. A conductive enclosure used to block electrostatic fields is also known as a Faraday cage (shown here). The amount of EMI shielding needed depends upon the material used, its thickness, the size of the shielded volume, and the frequency of the fields of interest and the size, shape, and orientation of apertures in a shield to an incident electromagnetic field.
EMI Shielding Solutions
At Zatkoff Seals & Packings, we offer a variety of Parker Chomerics EMI shielding products, including an extensive selection of EMI gaskets, shielded windows, shielded honeycomb air vents, cable shielding products, grounding solutions, shielding laminates, and metal foil tapes. We also offer conductive adhesives, coatings, sealants, greases and inks, as well as conductive plastics. Learn more about our EMI shielding materials and capabilities here.
Additionally, we combine different EMI shielding and thermal management materials to create integrated solutions for your application. Reduce the number of single parts in assemblies, devices, and systems to make installation and maintenance more efficient.
