Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Mechanical EMI shielding - 168 Mhz

Mechanical EMI shielding - 168 Mhz

Mechanical EMI shielding - 168 Mhz

I need to filter ~180 Mhz and lower emissions from an infrared transmitter while minimizing the amount of IR loss. What is the formula for determining the maximum aperture size that will still block a given wavelength or frequency? Is this formula usable to determine mesh size? Our short term solution is a fine wire mesh, but I need to determine the mesh size. Thanks in advance.

RE: Mechanical EMI shielding - 168 Mhz

If you can afford the size, you may use a resonant cavity.
You may reduce the size of the cavity by using an -- IR xparent -- dielectric with high "e".


RE: Mechanical EMI shielding - 168 Mhz

Per AFDH-1 the cutoff frequency for a rectangualr waveguide is fc=5900/W,
W largest dim of port in inches and fc cutoff in Mhz.  Approximate attenuation
at 10*fc will be A=27.3*T/W, T in inches (port thickness), A in dB.

RE: Mechanical EMI shielding - 168 Mhz

The formulas in the preceding post are ok - but the waveguide is in cutoff for frequencies below the cutoff frequency and the attenuation formula applies to frequencies below the cutoff frequency, fc. There is little attenuation for frequencies above the cutoff. Consequently the attenuation at 10*fc is not A=27.3*T/W; however, this formula does give the attenuation for 0.1*fc.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close