Visitors of two public exhibitions A and B are equipped with compasses.
Exhibition A:
I want to guide these visitors along a certain path throughout the exhibition by "overriding" the earth magnetic field so that they can follow there compasses "north" along the path. The path where this deviation should work on is no wider than 1.5 meters. This deviation can be turned on and off by a switch (thus can not be accomplished by permanent magnets).
Exhibition B:
I want to notify the visitors of events by generating a short magnetic pulse that will shortly deviate their compasses. This should work over a ground circle area of at least 1 meter radius.
Update 13th April:
The direction of deviation is not of importance.
Annotation:
Update 13th April:
The path will guide the visitor along a rectangular playing area of about 20mx20m. Due to the nature of the installations, the only options to install hardware are the sides and the floor (max. height 20mm).
Assumptions:
- Local earth magnetic field strength is below 65 uT.
- There are no other electromagnetic influences.
- Height of compasses above ground are 2 meters maximum.
Research so far:
I built a small solenoid magnet with about 400 windings, 4.8V and iron core. Although getting up to 1400 uT at the magnet itself, it rapidly drops in the distance (between ~1/r^2 and ~1/r^3) to a level where it cannot be distinguished from the earth magnetic field; reaching 70uT as soon as 20cm.
In order to reach compasses in 2 meters height (200cm distance, 20cm*10) I would have to amplify the strength by a factor of 1000 (10^3, because of 1/r^3) in case I assume a Dipole (Wikipedia). I doubt this can be accomplished with my small self-built magnet.
What would be the most cost- and time-efficient way to accomplish exhibition A and B?
In particular I'm interested in:
- how to simulate such an environment on a computer,
- what kind of magnet type/layout is suitable,
- can this be accomplished with off-the-shelf equipment,
- are there any dangers for the visitors.
I'm happy to provide more details if needed.
Best Answer
There are probably easier ways to do this than using real compasses. You can still make things which are 'compass like" in appearance. Infrared would be amongst the easiest. RF would also work.
But ...
A large coil which fits the path shape should do what you want. Large diameter is the key to large distance. If you want to cover an area of about 1 metre you could have a 1 metre diameter or edge coil either on / in the floor or above their heads. Magnetic field will be proportional to amp turns. More turns = less Amps needed for a given field strength.
Best result would be from a coil above and below or either side BUT you will get usable results with a single coil. Two coi;s allow you to achieve a uniform field across the space concerned. Searching for Helmholtz coil will give you many ideas - but there are other types that are suitable.
Wikipedia Helmholtz Coil
More here ....... and here
Pictures galore - all linked to web pages.
Wow .........
It is widely acknowledged that the fields generated by such arrangements are safe for living creatures, even using substantially more current than you will need. BUT you will always find people who are suspicious of such equipment.