Magnetic Field Reduction

I work with RF engineers, but they won't tell me how to make a cell phone jammer. Something about it being illegal.....

Can you hear me now?

 

Obviously studies are rather inconclusive about the effects of EMF on humans. One major reason they are inconclusive is the extreme difficulty of finding controls that are not exposed to EMF.

Another problem is why so many people die of cancer. Seriously, 10,000 mechanisms all with .000001 probability of causing cancer in 60 years is a lot of cancer. Who can say if EMF is One, None, or a lot of these mechanisms.

If you understand the numbers (and I do) then drunk drivers are vastly more dangerous....but asking questions about EMF and how much a Prius generates is worthy of good answers and specific numbers.

 

Oh boy, don't even get me started ...

 

Oh, that was you on the floor??

 

I thought I was on the ceiling.

Tom

 

Fortunately, I'm a Pisces, and I had a tarot reading that said Pisces were less likely to be affected by EMF.

 

I'm pretty sure that wearing this would help with EMF exposure.

Visibility might be an issue though.

 

Please let us know what numbers you get and specifics of the setup that you measured them.

I sincerely doubt that Toyota has information available for release. It is easy to imagine that they have secrets to keep, but the reality is that any measurements made were not for human exposure info. They would have collected electronic interference data, which only true experts can use for making sure that static stays off the radios.

 

Tom

That's right, I was the one on the floor

 

Well, to put things in perspective, a hair dryer can produce 300 mG and a can opener can produce 600 mG

NJDEP-Radiation Protection Programs

A quick search on the net turns up a lot of freaky stuff, like ghost hunting. C'mon, now!

The consulting engineering firm Failure Analysis Associates, now called Exponent, conducted a few studies on EMF

Exponent- Electromagnetic Field (EMF) Exposure, Radiofrequency (RF) Exposure, and Cellular Phone Safety Studies

Is there a risk from Prius EMF exposure? Sure, nothing in life can possibly be zero risk. Is there EMF risk from having electric wires in a house? Sure. Is there EMF risk from using a computer. Yep. How about EMF risk from cell phone, and BlackBerry's? You bet

Am I going to lose sleep over it? Not likely

 

I used to design MRI scanners. You want to talk about EMF! I've spent more time in them than I care to admit.

Tom

 

But here you're just guessing that a thinner skull makes one more vulnerable to injury or disease. Without any scientific evidence, it's just that: a guess.

For all we know, thicker skulls could be more of a problem.

You can measure EMF, assuming decent equipment, and then say with certainty that one device has lower EMF than another. Beyond that, there's no solid evidence that the EMF is harmful. Less is probably better. How much is too much?

 

Say, were you the guy who put the 1/2 inch box end wrench on the table, scurried from the room, and started the scan? Or is that urban legend?

 

I was the development engineering manager for one of the top two medical imaging companies, so I can tell you a lot of stories. We had six scanners that belonged to us, and varied from a finished production unit used for training down to our development test bed that was mostly a pile of wires and loose parts. Some of the stories you have heard are apocryphal, but all happened in some form. Mostly the details have been confused with repeated retelling.

You need some background to understand the risks of a loose wrench. An MRI machine has a huge superconducting magnet that surrounds the patient. The magnet is a very large electromagnet with zero electrical resistance; not close to zero, actually zero. A hundred or so amps of electrical current are introduced into the magnet and then the coil ends are shorted together. Since the magnet has zero resistance, the current goes around forever, producing a strong static magnetic field at the expense of having to use superconducting materials and cryogenic cooling. The process of bringing it up to field is called ramping the magnet, because the current level ramps up over time. Normally a magnet is left ramped up. It only gets taken down for service or if a problem occurs. It makes sense to do this since no power is needed to keep the field going.

Three smaller electromagnetic coils are used to make a time-varying magnetic field. These three coils are arranged orthogonally, giving an X, Y, And Z field. They are called gradient coils. The gradient coils are not superconducting, and are driven by powerful amplifiers which are very similar to audio amplifiers (as an aside, most of the amplifiers were originally large PA amps, like those used by a rock band). The field produced by the gradient coils is strong, but no where near as strong as the static field from the main magnet. The gradient coils only operate during a scan.

Finally, there is a large RF transmitter and receiver which is connected to one or more antennas inside of the scanner. This is to bombard the patient with RF energy and excite protons in the patient's body. When the protons drop to a non-excited state, they retransmit energy as RF which is picked up by the RF receiver.

With that quick overview, here is what happens when you walk into an MRI scanner bay with a wrench: It's not starting the scan that is the problem, it's having anything ferris near the main magnet. Normally the magnet is ramped up, so as soon as you get too close, the wrench gets yanked from your hand or pulled off the cart and goes flying through the air toward the magnet. If your unlucky, the wrench will fly through the bore of the magnet, come out the other side, slow down, and fly back at you. It can whip back and forth through the magnet like it's on a spring. Eventually it will end up stuck to or into the magnet, if it hasn't already stuck into something else, like your eye. We were very careful about ferris materials near the magnets.

We did have one episode where a fire alarm was tripped and the local fire department responded. One of the fire fighters entered a suite wearing a Scott Air Pack, which is basically a SCUBA tank, and was pulled off his feet and pinned to the magnet. We had to quench the magnet to get him off.

Speaking of quenching magnets, that brings up another story. With six high powered magnets in the building, much of the area was filled with a fairly strong static field. As I'm sure you know, magnetic fields do weird things to CRTs, but monitors have built-in degaussing circuits to compensate for stray fields. All of the engineers working in the back part of the building were subject to these fields, so all of their monitors had degaussed to compensate for the static field. When one of the magnets would quench, it would instantly change the magnetic field, so all of the monitors would look like mood rings, displaying a rainbow of colors. You could hear chorus of groans burst forth spontaneously when that happened. A few muttered curses, followed by everyone hitting their degauss buttons. Not long after that, the magnet would ramp up, and the whole process would repeat.

None of the radiation in an MRI scanner is ionizing, but it is powerful. You can easily boil a bucket of water with the RF transmitter, and the high-field magnets are so strong they induce electrical currents inside your head whenever you turn or otherwise cut the field lines. The induced currents can be seen as flashes of light in your field of vision. It's kind of creepy.

One of my favorite tricks was to take a large coin, such as a half dollar, and set it on its side inside the scanner. U.S. coins are non-ferris, so there was no magnetic attraction, but moving a conductor through a magnetic field induces a voltage, and a solid piece of metal is essentially an infinite series of loops, so moving the coin induces a current which generates a magnetic field that resists the movement. It feels like you are trying to move the coin through a thick liquid. So I would set a coin on its side and say: "Watch what happens when I let go of this." The coin would try to fall over, but the magnetic fields resisted the effort. Having electrical resistance, part of the energy would be dissipated as heat, so the opposing field slowly looses the battle and the coin gently drops over onto its side. The whole thing looks like slow motion. It takes about six seconds for one to fall over, depending on the coin and the field of the magnet.

Credit cards were always a problem. We used to leave our wallets in our desks. It was a morning ritual: come in, take off your coat, and take out your wallet. One trip into a test suite with your wallet and all of the credit cards were done. Same thing with mechanical watches. That was good for a few curse words too.

One last little bit of trivia: we kept the main magnet coils at about eight degrees, Kelvin. That's frigging cold. You can't imagine the banshee wail liquid helium makes when you boil off a bunch of it through a vent line.

Tom

 

Ah, I love it when you talk dirty. We're in different fields, but essentially the same line of work. I probably could have put my Calculus to better use in your department though

Never got to play with liquid He. Have used liquid N a lot. Was on a couple of projects where Liquid O2 was around. I have a lot of respect for supercold liquids, witnessed a tragic eye injury.

 

I once heard that the many amps of current in the superconducting magnet was started by just using a 9V battery. Is this true?

 

I was wincing at the reactions you got for your questions. Here's why. Last month I was running Electromagnetic Vunerability testing on an aircraft at a military base. These test are to ensure that an aircraft flying by a TV or radio tower does not have something bad happen. One of the sensible requirements is that a health and safety crew come out and measure all the fields that the pilot is exposed to while running these tests. Now by calculation, the pilot should not be exposed to levels beyound the legal limit, but these tests prove that this is the case. It does not matter whether the biological effects are fully understood to establish limits and ensure that they are met. That you want to know what the actual fields are is quite reasonable...and the only way to know is measure.

It is a seperate debate of what the numbers mean once you have them. If you do make some measurements, please post them. The technical types here can definitely make use of them. Additionally, you may be in a position to show that the Prius might be a better car than what is expected.