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Interference Technology

For EMI / EMC Engineers

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Shielding

Design for Compliance Essentials

 

INTRODUCTION While unrealistic to discuss all aspects of product design in a single article, I’ll try to describe the most common design issues I find in the hundreds of client products I’ve had a chance to work on. These issues generally include PC board design, cables, shielding, and filtering. More detailed information may be found in the Reference section below. As … [Read more...]

Filter Installation Issues Pt. 3: Mounting and More

 

This article is the 3rd and final part of a three-part Filter Installation Issues series. Read Part 1: Input and Output Conductors here. Read Part 2: The Synergy of Filtering and Shielding here. There are now many suppliers of PCB-mounted shielding-cans that can be used with three-terminal filters, and they have many types that can be automatically assembled like any … [Read more...]

How to Specify Board-Level Shielding

 

The Purpose of Board Level Shields Board level shields (BLS) are generally small metallic shielded boxes mounted directly to PC board ground return layers. There are three primary purposes of board level shields: Isolation of sensitive circuitry from other noisy circuits on the board Trapping the emissions from noisy circuits on a board from propagating to the outside … [Read more...]

Filter Installation Issues Pt. 2: The Synergy of Filtering and Shielding

 

This article is part 2 of a three-part Filter Installation Issues series. Read Part 1: Input and Output Conductors here.  Some mains filter manufacturers only design and specify their filters to provide attenuation over the frequency range of the conducted emissions tests (typically up to 30MHz for commercial and industrial products), to keep costs low. Unfortunately, if … [Read more...]

Space Weather – Predicting EMC Effects of Solar Storms

 

When we think about weather, we know what it is. We feel it, worry about it, and talk about the heat, the moisture, the wind. Weather is dynamic, though mostly predictable because we can measure its conditions. We also know that the atmosphere involves large scale electrical activity. Cloud masses move above and below each other, generating enormous static-electricity … [Read more...]

Designing and Selecting Filters: The Importance of RF Reference

 

The Importance of the RF Reference The RF Reference is the node on a circuit’s schematic that we define as our reference voltage when designing an RF circuit or measuring its performance. For the most cost-effective EMC, all circuits (digital, analogue, switch-mode, etc.) should now be designed using RF techniques. It is common practice to call the RF Reference ‘earth’ or … [Read more...]

Use of Absorbers for Shielding

 

Background With the trending small size of electronic devices coupled with higher data speeds, there is a merging of the increasing physical closeness among components and the shrinking wavelengths associated with higher speeds. As wavelengths shrink, they approach the physical dimensions of components and devices, which result in increased “antenna effect” of noise. … [Read more...]

Cost-Effective Applications of EMI Gaskets

 

Introduction EMI gaskets are used extensively by the electrical/electronic industry to assist in complying with the various EMI radiated emission requirements. These requirements include compliance to DoD TEMPEST and EMI, and FCC and EU EMI test limits. As a rule of thumb the radiated emission TEMPEST requirements are about two orders of magnitude (40 dB) more stringent than … [Read more...]

Measuring Shielding Effectiveness with Two Near Field Probes

 

Introduction Sometimes you may find yourself needing to make a quick check on the shielding effectiveness (SE) of a material, such as plated plastic or shield gasket material. It’s possible to set up a quick measurement setup using near field probes by using a couple H-field (for magnetic field SE) or E-field (for E-field SE). You’ll also need a spectrum analyzer with … [Read more...]

Troubleshooting Radiated Emissions at the EMC Test Lab

 

Note: This is an excerpt from the book, EMI Troubleshooting Cookbook for Product Designers, by Patrick André and Kenneth Wyatt. See Reference 1. Introduction Radiated emissions are by far your highest risk when performing compliance testing at the test facility. With all the high-speed digital circuitry inside electronic products today, it becomes all too easy for harmonics … [Read more...]

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