Everyone hello, I haven't posted anything for a while, I was studying for qualification exams and I didn't want to tempt "fate" by posting on the
forum. Now, though we have some time, my most recent efforts have been directed towards a reduction of "brain reading scans". Such technology does
exist as described in the link below:
The paper used fMRI data to reconstruct images, such technology uses powerful magnets to align molecules within the blood, it may also be possible to
reconstruct images using EEG:
EEG is an older technology than MRI and has less spatial resolution. Though, the specific form of the technology shown in the wikipedia article
requires probes to touch the skin, it may be possible to obtain an EEG or EEG-like signal from an array of antennas. The reason is that the brain
produces radio waves from DC to 100 Hz, these are extremely low frequency compared to AM (KiloHz), FM(MegaHz), Cell Phone (GigaHz).
The reason why I focus on EEG is that it is passive, meaning the brain generates the radio waves and all that one needs is an array of antennas and
probably much processing (DSP) to detect and make use of them, which can be easily hidden. Other thought reconstruction techniques may require large
magnetic fields and large equipment, which is easily detectable.
So the question may arise, how can we stop such signals from our brains to the antennas?
This is related to the "tin foil hat" phenomena:
Though the concept of a metal "blocking" radio frequencies, is not incorrect, more thought is needed to make it truly functional. Also, there are
clearly some issues regarding style and subtlety. First, we need to be more specific, very rarely does the strength of an EM field go from something
to nothing, what is more common is an EM field weakening or attenuating as it passes through materials. Since there are different levels of
attenuation, we may ask, how do we quantify this?
The amount of attenuation depends on the type of material, thickness of the material, and the frequency of the EM wave. In order to be completely
specific we must refer to some textbooks. One of the most well known textbooks in Electromagnetism is:
Classical Electrodynamics by John David Jackson
Reading the reviews, the book is both famous and infamous
, it is widely used throughout the United States in graduate physics programs from MIT
to UC Berkeley. It is famous for both for it's depth and breadth of material in electromagnetism and it is infamous for the difficulty of its
homework problems. What concerns us is a description of fields at the surface and within a conductor. In the 3rd edition of "Jackson" page 354, eqns
8.8 - 8.10 we find a series of equations that describe the behavior of an EM field within a conductor. What concerns us is the skin depth:
If we look at the most widely used form:
One can see that the skin depth depends on the type of material and the frequency, take note of aluminum, the skin depth of aluminum for frequencies
0-100 Hz is 100 mm
that is 10 cm of material, so we see that a tin foil cap would have attenuated the desired frequencies very little. In order
to significantly attenuate frequencies of 0-100 Hz we would look for a metal that has the lowest resistivity and the highest relative permeability.
There are several choices, 1+mm of Mu Metal, 2+mm of Electrical Steel aka transformer steel,1+cm of steel 410, etc. Strangely enough steel 410 is
sometimes used to make salad or mixing bowls, so stacking a series of salad bowls would work. It may also help if the metal is grounded. It also helps
if the mu metal isn't bent too much as it loses some of it's ability to significantly reduce low frequency signals.
Even if we make a hat of 1+mm of mumetal we would still have problems. Since low frequency waves have such large skin depths for most materials, it
may be reasonable to conclude that it may be possible to pick up EEG signals from any portion of the head and body. Simply covering the top of one's
head with a mu metal helmet may not shield the signals emitted from the face, eyes, the lower rear of one's head, and possibly the rest of one's
body. In this case one one have to wear something akin to a suit or armor like the knights of old, in that case it is best simply to construct an
enclosure, like a room.
In public though a hat or cap made of 1+mm mumetal may be sufficient, wearing exposed aluminum or mumetal on the head is not recommended, it draws
negative attention, and with enough snarky comments eventually the person will stop wearing it. It has to be done subtly and with style, a little
pizzazz may help.