×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

# 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

# estimate axial field for disc shaped perm magn

 Forum Search FAQs Links MVPs

## estimate axial field for disc shaped perm magn

(OP)
I need a rough idea of the field strength and gradient as a function of axial distance for a disk shaped perm magnet. I found a formula on the internet (http://www.magnetsales.com/Design/DesignG.htm) that I don't think is right. Shouldn't the formula be corrected for the demagnetizing field ( Br*(1-Nd), where Br is the remanence and Nd the demagnetizing factor )?

I need to produce a 1Newton force at a distance of 4cm on an iron or permanent magnet object with a volume of 1.57*10^-8 meters^3. I would like the field source to be as small in size as possible. The field source should be less than a pound in weight. I don't think it's going to be possible. The formula I'm using for the force is  F = J*Volume*(dH/dx), where J is the polarization of the particle, and dH/dx is the field gradient.

Thanks for any suggestions

### RE: estimate axial field for disc shaped perm magn

The formula does not need correction.  The shape demagnetization factor is already considered in the permeance coefficient (which are used in the formulas for calculating external flux).

Your force requirements are quite challenging, particularly the 4cm distance specification.  The formular for force you are using is correct, but FEA would be more useful to determine if it is possible.  Even then it would take some time to calculate.

Are you looking for just one magnet or many?  I suggest you contact a vendor of permanent magnets to see if they can help you.

### RE: estimate axial field for disc shaped perm magn

your "iron or permanent magnet" is about equivalent to a  1500 ft cube and about 2.5 billion pounds-- unless you misplaced a decimal point... and one N will not be too effective to move an asteroid.

Most of the field is concemtrated in the vicinity of
the source magnet so I think about one ft is the maximum
what you have to take into consideration

Plesae read FAQ240-1032
My WEB: <http://geocities.com/nbucska/>

### RE: estimate axial field for disc shaped perm magn

Hello nbucksa:
The OP's stated the volume is 10e-8 (not 10e+8) cubic meters.  Admittedly, the minus sign on the exponent blends in with the ^ symbol.

### RE: estimate axial field for disc shaped perm magn

Sorry, I haven't seen it but this gives about 2.5 mm cube
which will be saturated when you reach a small fraction
of 1 N force -- so back to the drawing board.

Plesae read FAQ240-1032
My WEB: <http://geocities.com/nbucska/>

#### 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

#### Resources

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 partâ€™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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!

Already a member? Close this window and log in.