Electronics Protection - June/July 2012 - (Page 10)

Feature Ferrite Testing Reveals Significant Performance Variations Blake Roberts, FerriShield Ferrite Product Manager Leader Tech, Inc. In an ideal EMC design, ferrites are not needed. They add cost, a part number to the BOM, and a non appealing aesthetic look to the cable. However, ideal designs rarely exist, and due to the shortened design cycles of most markets, products and suppliers making individual components, ferrites are often needed to pass EMC. It is quite often that each component is compliant by itself but when assembled in the final unit, the proximity of the components allow for EMI to create a new non-compliant landscape. This is why ferrites are being used more and more frequently. When a ferrite must be used there are tools to consider in selecting the appropriate ferrite: 1. Select the appropriate size core 2. Select the appropriate frequency specific material 3. Select a high quality supplier with the highest attenuation material possible Quite often, an engineering approach is not taken when choosing a ferrite. Below is a very common chain of events when selecting a ferrite core for an application. Typical Design Steps of a Ferrite Application 1. Final Assembly is completed (at least for one unit) 2. Unit is sent for final compliance testing 3. Unit fails the EMC test 4. EMC engineer goes to available sample kit display in lab and selects the best mechanical fit for the cable 5. A process of elimination is used on various sizes until the unit passes 6. The supplier’s part number is recorded and added to the BOM. Often this process adds a ferrite that is too large or the completely wrong composition for the application. The process is not built to identify the most optimum part for the application but a quick resolution to go to market. Once the larger part is on the BOM, hard tools are created for over-molding the ferrite (that is also too large and costly). So, the quick decision at the lab has now been followed by a more costly over-mold, higher component price due to increased amount of raw material and added shipping due to increased weight. Why? Because the wrong size ferrite was not present in the lab when the problem was found. In another example of a ferrite application, a ferrite core is selected, tested and found to work. The problem area is 600 MHz and at the lab a high frequency core was selected. 600 MHz is a frequency where a broadband material or a high frequency core will give significant attenuation. So since there was not a broadband core of the same size in the sample kit, the engineer selects the high frequency material. The presence and amount of Nickel (Ni) is what drives the high frequency attenuation in the high frequency ferrite material. Generally the high frequency material has double the amount of Ni in the composition and drives the raw material price up. So by selecting the wrong material, an added cost has now turned into a non optimized cost component of the BOM. While it is important to use the appropriate size and material, it is equally important to understand permeability and its effects on the impendance attenuation over broadband frequencies. Permeability is an often overlooked factor since most ferrite suppliers only publish impedance data. Recent empirical testing of FerriShield Ferrites shows that there 10 is a notable increase in Ohms of impedance when compared to the exact same competitive alternative. Over the past few years, as the commodity price for raw materials including Ni, Cu and Zn have become unstable, many ferrite manufactures initiated a product formulation change to maintain competitive market pricing. This composition shift not only provided a NET lower cost for the manufacturer but it also resulted in a lower perm material. The effects of permeability on a ferrite core can dramatically reduce a part’s impedance in higher frequencies (10 MHz and above). (See chart below) Due to this industry-wide shift in raw material formulation and manufacturing processes, many RFI/EMI ferrites on the market are delivering lower than expected performance across a wide-band frequency range. This variance is an important design consideration for most commercial, military and consumer electronics manufacturers in order to meet Class B radiated emissions standards. To compensate for the lower performance, a larger and heavier ferrite must be specified to attain the same level of suppression that was once provided by the smaller and higher perm ferrite core. These physical characteristics typically conflict with target engineering and market demands for smaller, lighter-weight electronic devices. In today’s marketplace with the dramatic increase in specialized sub-cons that provide a single component to the electronics package, most radiated emission problems are realized after the product is assembled and ready for market. In many instances, a component does not demonstrate an EMI problem when isolated but when assembled in close proximity to other devices, EMI compliance and signal integrity problems become apparent. Also, as technology changes and legacy platforms are enhanced with add-on features such as faster clock speeds, thumb drive readers and additional USB ports, the once-compliant legacy product becomes a landscape for EMI problems. During the later stages of design and manufacturing, ferrites are typically the most prudent solution for eliminating the interference issue and maintain the shortest time to market. For the purposes of testing the effects of industry-wide ferrite material formulation changes, LeaderTech engineers selected one of the Company’s most popular FerriShield 28 Material Ferrites with a true 850 permeability. Competitive ferrite samples that exhibited the exact dimensions (outside diameter, inside diameter and length) as well as published permeability were procured for testing. All ferrites in the sample group were analyzed on the same test wire using an Agilent 4396B RF Network/Spectrum/Impedance June/July 2012 www.ElectronicsProtectionMagazine.com http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - June/July 2012

Electronics Protection - June/July 2012
FLIR T-series Cameras Introduce Thermal Image Enhancement Technology
Renewable Raw Materials - The Future of Plastic Enclosures
Global Electronic Enclosure Resins and Markets
Ferrite Testing Reveals Significant Performance Variations
Packaging Solutions for Critical Electronics Protection in Challenging Environments
Fluid Submersion Technology for Green Data Center Cooling
TRTL BOT Unveils KidSafe Case for iPhone 4 and 4S
Curtiss-Wright Controls Defense Solution Releases New D2D ATR 3U OpenVPX Chassis
Stulz Introduces CyberRow Data Center Cooling Solution
Abbott Technologies Offers New Sealed Power Supply
New Engineered Multi-Cavity Shielding Solution
Gore Enhances Product Performance with new of Screw-in Vents
Industry News
Calendar of Events

Electronics Protection - June/July 2012