Magnetic Field Strength

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ed downey

ed downey

Senior Member
Location
Missouri
I Was Wondering If Karl Riley Or Anyone Else Could Help Me With This Problem.

I Have A MRI That Is Existing And We Are Adding An Addition To The Hospital. There Is A Window In The MRI Room That Is On The 2nd Floor And We Are Adding The Addition Right Outside The Window.

If We Put A Piece Of Steel Up Over The Window (Approximately 36"x 48") And The Magnetic Flux Density Is Known To Be 5 Guass At The Window. What Is The Force In Foot-Pounds Or Newtons On The Sheet Of Steel. And What Is The Formula For Figuring This?

Thanks For Any Help On This Matter.

-Ed
 
hbiss

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Re: Magnetic Field Strength

I suggest that you contact the MRI machine manufacturer with what you plan to do. They are the ones that built the thing and should have requirements for adjacent rooms and materials.
 
K

karl riley

Senior Member
Re: Magnetic Field Strength

I note that he field strength you mentioned was 5 gauss (not mg, or mG, which is milligauss). Also, this is a DC field, not AC.

I don't know where foot pounds or force comes in to this. Reasons? I am not following this part.

There are shielding companies that deal with magnetic shielding. The one I have worked with is Amuneal, and I think amuneal.com will get you there, or else search. But the usual problem is AC field shielding, so if the literature on their web site does not deal with DC fields, question them by email.

Usually they need you to state what gauss or milligauss level the client requires.

Karl
 
K

karl riley

Senior Member
Re: Magnetic Field Strength

Ed, I did a double take on the force question. I am so used to AC fields. You mean the magnetic attractive force exerted on the steel plate, right? I think it would be negligible at 5 gauss. This is just an opinion based on the fact that the earth's field averages 0.6 gauss, so that 5 gauss is less than 9 times that strength.

Considering the fact that the 0.6 gauss field is barely enough to turn a freely suspended magnetized compass needle, if you multiply that by 9 it is still a tiny force.

I would put "magnetism" in search and see what you come up with.

Karl
 
ed downey

ed downey

Senior Member
Location
Missouri
Re: Magnetic Field Strength

Well I Finally Got A Hold Of The Manufacturer Of The MRI (A German Company) And They Stated That The Force On The Steel Plate Would Be Somewhere Around 50 Newtons (11.24 Foot Pounds).

I Have Now Forwarded This Information To The Structural Engineer So That He Can Take This Into Account While Designing The Attachment Of The Steel Plate Over The Window.

Thanks For Your Help.
-Ed
 
charlie b

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Magnetic Field Strength

Let me clarify the units of measure. The 50 Newtons of force is equivalent to 11.24 pounds (not "foot-pounds") of force. The term ?foot-pounds? applies either to energy (the amount of energy needed to push a one pound weight across one foot of distance) or to torque (the amount of torque generated by a force of one pound acting at a distance of one foot from the center of rotation).
 
K

karl riley

Senior Member
Re: Magnetic Field Strength

So I guess the 11 pounds will be pulling on the window steel, not pushing? But then wind exerts a lot more than 11 pounds, I would think.

Karl
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
Re: Magnetic Field Strength

why do you want to put a steel plate where the window was?
Click to expand...
I have to double that question?
as steel could retransmit the field and act like an armature. but aluminum wouldn't, nor would lead. of course at that amount of field strength I'm not sure but I think aluminum would act as a shield too. and not have the effect of steel.
Of course I'm out of my field. :D LOL :D
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: Magnetic Field Strength

I will take a guess that the steel plate is to protect patients from the construction activities, not to protect the construction workers from the magnetic field.

mri-pallet.jpg
In this photograph, you can see a fully loaded pallet jack that has been sucked into the bore of an MRI system.
Click to expand...
More MRI Flying Objects

Those where not so bad, but a six year old boy was killed by an oxygen tank that got pulled into the MRI machine he was in.

News Story

[ August 19, 2003, 05:51 AM: Message edited by: iwire ]
 
ed downey

ed downey

Senior Member
Location
Missouri
Re: Magnetic Field Strength

Iwire,

You Are Exactly Right SInce The New Construction Is Directly Outside The Window Which Will Be Covered With The Steel Plate And We Do Not Want Any Small Items Being Attracted To The MRI While It Is In Use. We Have Also Posted Signs And Informed Every New Worker To The Site (During Their Safety Orientation) That If You Have A Pacemaker You Cannot Work In This Area.
-Ed
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: Magnetic Field Strength

Originally posted by hurk27:
I could imagine a box of 16D's emptying through the window at the speed of a bullet?
Click to expand...
Bad enough, I was thinking of the steel workers swinging beams into place and the beams start pointing towards the window like a compass. :D

I can not help thinking of Wile E. Coyote "Super Genius" and his large Acme magnet dragging ocean liners, the Eiffel Tower, rockets, satellites and anything else metal into his cave.

wile_mag.jpg


I would love to have free reign of an MRI machine to experiment with.

[ August 20, 2003, 04:08 PM: Message edited by: iwire ]
 
K

karl riley

Senior Member
Re: Magnetic Field Strength

Why does the mention of a magnetic field bring out the joker in us?

Hurk, steel will concentrate the static magnetic field to some extent and hence reduce its expansion in space. I do not think lead or aluminum will have any effect at all on the static field.

For an AC field, aluminum does reduce it due to induced eddy currents absorbing energy, but lead is still a dud. You are thinking perhaps of radioactivity, which lead will absorb.

Karl
 
K

karl riley

Senior Member
Re: Magnetic Field Strength

Ed,
somehow your message got lost so I am replying here: to measure DC fields at low levels, or any levels, go to meda.com/
They have a great selection. I have the uMag-01.

Karl
 
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