From: ascen@world.std.com (Ascension Technology) Subject: Re: TECH: Tracking devices Date: Thu, 7 Mar 1996 18:23:34 GMT Organization: The World Public Access UNIX, Brookline, MA From: ascen@world.std.com (Ascension Technology) Stephane Morvan (smorvan@eng.clemson.edu) wrote: : From: Stephane Morvan : I'm trying to get some informations about tracking devices not subject : to magnetic interferences caused by metallic structures. I know that the : flock of birds can be shielded to prevent interferences and I would also : like to know up to what level interferences can be voided. : Thanks for any help, suggestions... The Flock of Birds does not use a physical shield to reduce metallic interference in it's tracking system. The method of magnetic signal transmitter and reception is designed to greatly reduce the distortion caused by 'eddy currents', one of the two main distortion factors for magnetic systems. In a study performed around Aluminum by an independent group for the Air Force, our DC based tracking system was 5-11 times less sensitive to the metal then a popular AC based tracking system. If your application requires metal in the working environment, then we recommend using stainless steel 300 series. (This type of steel is most often used in medical applications.) It requires a huge amount of it to distort our Flock system. Plastic and wood do not have any magnetic properties and are perfect for using around magnetic based trackers. A factor not often mentioned about magnetic trackers but is very important in understanding how distortion may affect them is: All magnetic based tracking systems assume a symmetric field around the transmitter. If the shape of the magnetic field is changed, this results in distortion. A good rule of thumb for ALL magnetic based tracking devices is: keep large amounts of metal further away from the transmitter (in ALL directions) then the furthest receiver. Please contact me directly at ascension@world.std.com for more details on this subject, or post here. Regards, Steve Work Technical Support Ascension Technology Corporation