Gosh, TN isn't declining as I thought. Your challenge seems to place in a research lab. When I ran into ssuch problems and the solution proposals grew until I couldn't decide which one to test (as usual you are expected to do the job over a night and with no money) then I use go back and ask myself if there might be another concept. Background noise is a plague and many a time nearly impossible to eliminate. Therefore I wonder if not the cheaapest and fastest way is to modify the noise source. B&O had a similar issue with their studio recorders. They eliminated the problem by encapsulate the motor in my-metal. The S/N lowered by one magnitude. Just a thought. Labbing with various resistiviity stuff can be expensive a case.../Inge On 9 August 2016 at 17:11, Carl Van Wormer <[log in to unmask]> wrote: > The longer story is (feel free to ignore this if you don't care about the > background details): > > My short term goal is to set up an experiment to see if a shield of > intermediate resistance will address my present condition. We all know > that the major cause or problems is . . . solutions. > > The inherited problem system is used to transfer power (5W-10W) during > Phase 1 of operation, and to transfer acoustic signals (Piezo pickup, 10kHz > to 1MHz) daring Phase 2 of operation. The 100 turn, 15mm diameter coils > were mounted inside of ferrite cup-cores with a gap between the 2 halves of > the cores. One core-half was mounted in a fixed aluminum housing, while > the other was mounted in an aluminum housing at the end of a rotating shaft > (on axis) with a gap between the cores of about 1mm. > > I came in to solve a noise pickup problem on the received acoustic signal > which was caused by a VFD motor speed controller. The symptoms could be > simulated on the bench by connecting a 3kHz, 5V signal generator square > wave to the rotating housing. In the classic “fix it, but don’t change > hardly anything” request, I found that I could shield the receiving coil > (inside the core) with some copper foil tape (leaving a gap to avoid the > “shorted turn” effect). This eliminated the effect of the capacitive > coupling on my test bench. During the implementation phase, I found that > we still had some noise that was traced to the capacitive coupling on the > rotating (source) side. Since the coils were not differential (one end of > each was connected to local ground), the asymmetrical coupling signal > caused a current to flow in the transmitting coil that magnetically coupled > to the receiving coil. Adding a shield to the rotating coil addressed that > noise injection method. The system was pronounced “Good.” > > We have found that the Phase 1 power transfer efficiency is reduced in the > shielded systems. Eddy current losses in the shield seem to be the cause, > so I’m looking for ways to reduce those losses in my environment. Raising > the resistance of the shield material seems to be a simple solution, as > long as the resistance is low enough to provide effective shielding. > Unfortunately, I’ve been unable to find some easy to acquire samples of > various resistive sheets to play with. I was hoping to do some easy > experiments to see if my resistive based shielding approach stands up to my > first set of experiments before I started the process of defining a > material to be used. I’ve found some conductive ABS filament ( > http://www.makergeeks.com/coabs3dfi10.html) that might work if I can find > somebody to print a plate and a method to electrically connect to it, but I > don’t know a local friend with a 3-d printer. > > I’m still hoping for the sample kit of sheets of various resistivity > materials, but I haven’t found the right page in the Digi-Key catalog . . . > > Thanks for any suggestions, > Carl > > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. > Sent: Tuesday, August 09, 2016 5:55 AM > To: [log in to unmask] > Subject: Re: [TN] looking for medium resistance material > > There is just about every type of material with just the right properties > you are looking for available as a 3d printing medium. > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner > Sent: Tuesday, August 09, 2016 12:44 AM > To: [log in to unmask] > Subject: Re: [TN] looking for medium resistance material > > Very kind of you Inge, but this is not really my cup of tea these days. I > am aware that there are a number of suppliers of carbon based inks and > these can be tailored to produce desired sheet resistivity ranges. That > sort of thing is widely used on flex circuits and additive (printed > electronics) circuitry. I would think internet searching should bring up a > good candidate list of suppliers in a few iterations . There is cross over > here to ESD protection products, so that would be a good search area also. > > --- > Regards > > > Mike > > www.chrisfennerfund.org > www.facebook.com/chrisfennerfund/ > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord > Sent: Sunday, August 7, 2016 10:37 AM > To: [log in to unmask] > Subject: Re: [TN] looking for medium resistance material > > Carl, > when I was active I used to contact SemiAlloys. I needed certain > resistivity in lids for resistivity pulsed current seam welding of small > packages for missiles. We produced about 50,000 pcs from SemiAlloys with > He/Kr10 exp -10 with succcess. Mike Fenner has more to say , I think.. > They are extremly nice to cooperate with. Mike as well, despite he is > english. > > Semi Alloys Inc > > 888 S Columbus Ave > > Mount Vernon, NY 10550 > > (914) 664-8318) > > > > Good Luck / Inge > > > On 7 August 2016 at 05:40, Carl Van Wormer <[log in to unmask]> > wrote: > > > I usually want my physical structural resistances to be as low as > > possible > > (conductors) or as high as possible (insulators). Now I need an > > intermediate resistance, probably in the range of 100 to 1000 Ohms per > > square. The application will be an electrostatic shield in an > > alternating field, hopefully balancing magnetic heating losses against > > capacitive shielding effectiveness. > > I have never seen these materials offered from any of my normal > > sources, but I’m sure that there is something out there that will > > work. It could be sheet materials, paints, or slightly conductive > > epoxies, or something else I haven’t thought of. Since there is a > > very wide experience base on this site, I’m asking here first. > > Any suggestions will be appreciated. > > > > Thanks, > > Carl > > > > > > > > > > Carl B. Van Wormer, P.E., AE7GD > > Senior Hardware Engineer > > Cipher Engineering LLC > > 21195 NW Evergreen Pkwy Ste 209 > > Hillsboro, OR 97124-7167 > > 503-617-7447x303 > > [log in to unmask]<mailto:[log in to unmask]> > > http://cipherengineering.com<http://cipherengineering.com/> > > > > This message may contain confidential and/or proprietary information, > > and is intended for the person/entity to whom it was originally > > addressed. Any use by others is strictly prohibited. If I sent this > > to you by mistake, please be nice and delete it, and then tell me of > > my mistake so I can send it to the right person. > > > > > > >