The USA and the USSR were original signatories of the Limited Test Ban Treaty of 1963, prohibiting the majority of nuclear weapon detonation tests. Gagarin had made the first orbital flight a mere two years prior and the potential of space was of foremost consideration. The treaty specifically forbade detonation in space; however, this presented a new problem: how could compliance with this ban be monitored? The answer was found in project Vela. The USA constructed and launched six Vela Hotel class satellites equipped with X-ray, Neutron, and Gamma Ray detectors looking for illicit weapon detonations. No weapon signatures were ever found, but in 1967 Vela satellites began reporting bursts of Gamma Radiation of far greater magnitude than expected for even the largest nuclear detonation. It wasn't the Soviets. These bursts of Gamma Radiation matched no known nuclear weapon signature and their sources remained completely unknown. Vela craft continued to detect these Gamma Ray Bursts on occasion for the next decade but their cause remains elusive to this day.
Soviet spacecrafts Venera 11 and 12 were launched in 1978 with a primary objective of delivering landing craft to take pictures of the surface of Venus. The landers survived their descent but the lens caps on both failed to release and neither were able to take pictures. The orbiter craft fortunately had secondary objectives. They were also equipped with specialized Gamma ray detectors far more advanced than those found on the Vela Satellites. On March 5 1979, Venera 11 and 12 were struck by a tsunami of Gamma Radiation hundreds of times as powerful as ever recorded by the Vela Satellites. The radiation readings on the probes jumped from a normal 100 counts per second up to 200,000 in a mere fraction of that.
We now know that most of these anomalous Gamma Ray Bursts are the swan songs of stars going supernovae. We also know that the much larger 1979 signal resulted from something much rarer.
The source of this Gamma ray burst was determined to be a star that had gone supernova around 3000 BCE but it wasn’t the supernova itself that was being detected. It was what the remains of that star had become: a magnetar. A magnetar is one of the rarest astronomical objects known; Only twenty one have been confirmed to exist. They are by far the strongest magnets in the observable universe with field strengths between 1014 and 1016 Gauss. At times, the rotation of their crust and its magnetic field fall into misalignment resulting in a starquake. The tearing and repositioning of crust is analogous to an earthquake but with materials millions of times as dense and in a time scale less than a millionth of a second. These starquakes are responsible for much larger Gamma Ray Bursts such as were detected by the Venera craft.
Despite having a magnitude disparity of nearly sixteen orders, many of the same factors that make magnetars so very powerful are considerations that make for a better implantable permanent magnet. As we analyze the characteristics of magnets, magnetars will serve as our benchmark.
Magnetic Anistrophy and Maximizing Field Strength
A magnetic field is the result of either moving electric charges such as found within a solenoid, or by the intrinsic magnetic moments of a material. Electromagnetism is one of the fundamental forces and a complete explanation falls far outside the scope of this work. The important aspect that can be extrapolated regarding field strength of a permanent magnet is that field strength is the sum of the contributing magnetic moments. Not all magnetic moments are contributory. The ability for these moments within a substance to be aligned is determined by its Magnetic Anistrophy.
All substances have magnetic moments but the majority of these fields are canceled by opposing fields long before being detectable at the macroscopic level we inhabit. Objects with adequate Magnetic Anistrophy form a physical structure in which a high proportion of the magnetic moments prefer to align along a certain axis. Such is the case with magnetite. Magnetite is a mineral consisting of Iron and Oxygen that forms closely packed lattices. These lattices hold the iron in just such a way that the magnetic moments are aligned producing the strongest naturally formed magnetic mineral on Earth. These magnetite lodestones are the permanent magnets with which Archimedes purportedly pulled the nails from warships. A permanent magnet is a substance which exhibits significant Magnetic Anistrophy.
There are four commonly manufactured types of permanent magnet: Ferrite, Alnico, Samarium Cobalt, and Neodymium Iron Boron. Ferrite magnets are made from a ceramic compound which incorporates iron oxide. These magnets still fulfill many important roles due to a low price and the ease with which different shapes can be formed but Ferrite simply doesn't have the necessary field strength to be considered for an implant. The interesting aspect to note is that despite ceramic being noncontributory to the amplitude of magnetic moments, these magnets produce stronger fields than pure iron. The ceramic allows ferrite to better form the desirable internal alignment of moments and this anistrophy is more important than the intrinsic characteristics of the materials. This same effect is seen at much larger scales.
Magnetars produce the brightest electromagnetic events in the universe but in terms of size they are actually quite small. They are an extremely rare form of neutron star which can have a radius as little as six miles while containing a mass many times that of our own humble sun. They arise when immense antecedent stars senesce. Destitute of nuclear fuel, temperatures in these elder stars can rise beyond 5 billion Kelvin and simpler atoms are fused into an iron core. Conditions such as these incite nearly unfathomable quantum mechanical effects. Iron photodisintegrates into alpha particles and is vented as relativistic jets fountaning into space while metallic hydrogen forms superconducting rivulets across the iron core like gossamer ribbons. At a certain density, the remaining outer atmosphere fractures from the core as a luminous burst of radiation that outshines entire galaxies. After this supernova, the iron core continues to collapse in on itself generating an enormous magnetic field. Under the exceedingly rare times that conditions are within just the right ranges, the newly birthed neutron star cools to its equilibrium configuration under the influence of this field arranging itself into the perfect internal alignment of a magnetar.
Manufacturing of magnets is a lot like this. A material with a ferrous constituent is heated above a crucial point called the curie temperature where the magnetic moments within can change direction freely. If allowed to cool the magnetic moments remain in disarray, but if cooled under the influence of a strong external magnetic field the moments align forming a strong permanent magnet. This process is called sintering. Anistrophy is produced through the manufacturing process and isn’t merely the result of constituent elements. Alnico magnets are created by sintering an alloy consisting of iron, aluminum, nickel, and cobalt. Sintered Alnico magnets have field strengths more than twice as strong as the best ferrite magnets. Furthermore, the curie temperature of Alnico is the highest of any magnet allowing for it to still be useful when heated until glowing red. Alnico is better than ferrite by far but still isn’t strong enough to be suitable for our purposes.
The prefix ferro from ferromagnetism is a misnomer. The etymology of Ferro has been traced back as far as the Etruscans whose economy was based on Iron commerce. The word ferrous is used colloquially to indicate the presence of Iron so one might assume that a ferromagnet by definition contains Iron. A broader definition for ferromagnet is that it’s a material that exhibits spontaneous magnetization. While both Alnico and Ferrite rely on Iron, new magnets were developed in the 1970s that replace Iron as the primary contributor of magnetic moments. These are the rare earth magnets.
Lanthanides such as Samarium and Neodymium can form crystalline internal structures that are more compact and align along a single axis far more readily than Iron. The downside is that these materials have a very low Curie temperature; below the normal ambient temperatures that humans prefer. This problem can be assuaged through the creation of alloys. Samarium Cobalt for example, replaces the Iron with Samarium resulting in the potential for a very high Anistrophy. The cobalt addition raises the Curie temperature to a laudable 800 C. Sintering this alloy produces a magnetic field almost five times stronger than produced by Ferrite. Samarium Cobalt magnets are within the range of strength to where they could be considered for implantation; however, they are very expensive to produce and the field strength produced has since been superseded by another rare-earth alloy magnet: Neodymium Iron Boron.
The strongest and thus most appropriate permanent magnet type is Neodymium Iron Boron. This shouldn’t be misunderstood as claiming that a more powerful field is always better. There are reasons that will be discussed later in the article for not exceeding a certain level of field strength but choosing Neodymium Iron Boron allows for a smaller magnet size; this in turn allows for a smaller and thinner implant which is less invasive, less likely to be rejected, and produces better results in terms of sensing the electromagnetic spectrum.
Amongst NdFeB magnets, there is a spectrum of grades available. The higher the grade, the stronger the magnet. The grade is determined by the number which follows the indicator “N.” This N number is the maximum energy product of the magnet using the unit Mega Gauss Oersted. This N scale is linear so an N42 would be twice as strong as an N21 grade magnet. The highest grade of NdFeB magnet commercially available is an N52.11.The strength of these N52 grade magnets is phenomenal. Consider that a four inch square with a depth of .5 inches can suspend over 300 pounds. If Archimedes had access to magnets of this grade the claim of pulling the nails from attacking seacraft would be rather believable.
Despite the increasing popularity of magnet implants, there are only two shapes commonly chosen: discs for potency and cylinders for practicality. Because these implants function by displacement of the densely innervated fingertips, hands, and less often tragi, discs are the most common. A disc shape can be seated unobtrusively and yet provides a broad area of displacement in response to nearby fields. Cylinders are most often chosen for ease of implantation as an appropriately sized model can be implanted with use of an RFID injector. Many are intimidated with the idea of opening up and undermining their own flesh. The injection method is undeniably simpler and due to simplicity less likely to end in infection or rejection.
A cylinder implant does come with a significant downside. The field shape produced is less desirable and the total field strength is significantly reduced. One way to demonstrate this is by comparing the pull forces in relation to a magnets volume. 2x12mm Cylinder has a volume of 38 cubic mm and a pull force of 0.46 lb whereas a 1x3mm Disc has a volume of 7 cubic mm, and a pull force of .30 lb. The cylinder magnet has more than 5 times the volume of the disc but only provides just over a 50% increase to pull force. This doesn't mean that cylinder magnets aren't worth considering. The ability of a shape or design to elicit the maximum sensitivity to the electromagnetic might not end up being determined by any of these characteristics at all. I've spoken with a number of grinders that self-inserted cylinder shaped magnets that verbalize contentment with their implants.
Of course, the prevalence of disc and cylinder shaped implants has undeniably been influenced by availability. Custom manufacturing of magnets allows for novel shapes that produce better field characteristics. A disc magnet produces symmetrical field lines. This is unfortunate in that about half of the magnetic field is directed deep to the implant rather than aimed at the surface. There are a number of ways to change the shape of the field and in this section we’ll discuss magnet shapes that can produce field asymmetries. Arc magnets such as are used in brushless motors produce an asymmetrical field. The reason these are inappropriate as implants is that the shape is nearly the exact opposite of the contour of the body. The large outward facing arc creates a pocket which the body would struggle to fill and two pressure ridges that will inevitably break down skin. Sphere shaped magnets are an interesting shape in that they produce a symmetrical field but have particularly focused flux near each pole. Similar issues exist however in terms of using a sphere for an implant. A sphere under the skin produces a very undesirable pressure point. The answer to our pursuit for a beneficially asymmetrical field without detriment to the body is found with our friend the magnetar.
The mechanism by which neutron stars such as a magnetar's emit their periodic bursts of electromagnetic radiation is poorly understood. Some of the early attempts at explanation seemed to suggest the existence of monopolar magnets; this is clearly in violation of everything we understand about electromagnetism but no other explanation existed at the time that could explain the ejecting jets of plasma at relativistic speeds. This idea was quickly discredited but the emissions clearly required a field shape acutely focused towards a single point. One model shedding light on the process was suggested in the 2006 paper “The example of effective plasma acceleration in a magnetosphere.” The authors admit that their model doesn’t match the configurations we’ve observed for neutron stars, but they have identified at least one magnetic field configuration that could explain the patterns of emission. This configuration is that of a paraboloid.
A paraboloid is a shape commonly used to project or collect different forms of electromagnetic energy. For example, a satellite dish collects signals from a broad area and reflects it upon a small receiver positioned directly at the dish's focal point. A paraboloid magnet also projects its field towards a focus and doesn't necessitate the deep tight pocket such as found in an Arc. It's acceptable for the focus to be beyond the useful range of our field because our objective is simply to aim the flux outward. As of the writing of this article, a paraboloid magnet isn't available; however, it is an advancement that's being worked on.
The shape of the magnet itself isn't the only determinant of the field shape. The direction of anistrophy is created during the sintering process. Disc shaped magnets for example can be purchased with either a radial or diametric axis of magnetization. By and large, implants are magnetized axially. This is optimal for a disc as the field lines extend primarily deep and superficial to a magnet. For a cylinder, diametrical magnetization results in the potential for a considerable amount of torque. In the presence of a magnetic field the cylinder will inevitably spin. While unlikely to cause acute injury, this spinning isn't conducive to close association with nervous tissue. The body will respond to a moving object such as this beneath the skin by encapsulating it with epithelial tissue much as how calluses on well used areas of skin. There are other interesting directions of magnetization that can be produced such as radial magnetization in a ring magnet; however, these provide no benefit in terms of implants.
Due to the immense gravity of a magnetar, its shape is theorized to be a sphere more perfect than any man could produce but the axis of rotation isn't necessarily the same as the axis of magnetization. Consider that the earth spins at just over 1000 miles an hour resulting in a flattening of the poles into an ellipsoid shape. Magnetars spin at closer to 900,000 miles per hour. A thick iron surface overlays fluidic neutron matter with a density second only to black holes. Fluctuations in the movement of this fluid can shift the local gravity causing the surface to bulge outward in the grip of angular momentum. At this point, the surface is in opposition to the magnetic field. The iron surface is torn asunder and magnetic flux converges and spills from the site of least insulation. Mere milliseconds pass before gravity collapses all back as it should be, but the Gamma Ray Burst continues forth into the dark space between galaxies.
An appropriately sized and shaped piece of Iron can serve as an insulator against magnetic fields or as a means to focus them regardless of whether we're discussing permanent magnets or magnetars. A backplating of ferrous material such as Iron or Steel is amongst the simplest ways to shape a field. The effect is much like that provided by the older Alnico horseshoe shaped magnets. The U shape of the Alnico magnets allow both poles of the magnet to adhere to a ferrous material effectively doubling its pull strength. A proper backing on a neodymium magnet will focus flux on the opposite side of a magnet. Even better than a mere backing is an entire “cup” of ferrous material which leaves only desired surface of the magnet exposed. The total Gauss as measured at the exposed surface can be as much as double what it would be without the surrounding cup. As promising as this sounds, the benefit is rather minor. The size of the backplating determines the increase in Gauss. A larger plate that is below magnetic saturation may indeed double the Gauss but a smaller plate will only redirect the flux to the extent of saturation. Any further flux passes through the magnet as waste.
This is a great phenomenon for large companies looking for economical solutions but for an implant it's better to simply get a larger magnet. Although Gauss measured at the surface is increased by a backplate, the flux rapidly loops back towards the plate which makes for a field that extends a shorter distance. When dealing with ferrous coatings and backplating, it's more appropriate to think of the magnet system as a circuit. As such, there are many factors to consider. For example, the most common coating placed on rare-earth magnets is Nickel, which is effective at preventing the oxidation that bare neodymium is so prone to. Nickel also serve to some degree as a magnetic Faraday cage. The effect is minimal in larger magnets but in a 3mm X 1mm disc, the total Gauss yielded is detectable. Future magnetic implants may incorporate a thin layer of ferrous material around the majority of the magnet. This isn't currently available but research and testing is being performed.
Magnet size is of course another factor warranting considerable attention. It may be obvious that a larger magnet is more powerful but the increase in magnetic field strength isn't necessarily proportional to the increase in volume. I'm sorry to have to tell you that you'll find no magnetar stories here as size has little meaning when dealing with such extremes of power; the real focus becomes density. Regarding permanent magnets, size is important but must be analyzed in context of its shape. I'll begin with the claim that the optimal size of disc magnet for implant is 3mm X 1mm and I'll explain why along the way. We'll begin by comparing the effects of small size changes away from our 3mm X 1mm disc.
|Thickness||Diameter||Gauss||Pull Force||Volume in Cubic mm|
As diameter is increased, the volume increases linearly.
The results of the graphs above may initially seem skewed. As one can see, doubling the thickness of the magnet doubles the volume and the pull strength. Increasing the diameter though doesn't follow the same trend. By extending the diameter out to 4mm, we have a 78.8% increase in volume but only a 50 percent increase in pull strength. An increase of diameter provides diminishing returns. Furthermore, Neodymium Iron Boron is notoriously brittle. Some strength is provided by the coating chosen but anything larger than a 1mm thin broad disc is likely to shatter.
Increasing the thickness of the magnet though does show a proportional increase in field strength. I considered increasing the dimensions to 3mm X 2mm such as provided by the leading magnet implant distributor. The reason I began with a preference for a 1mm depth has to do with how well it fits under the skin without acting as a pressure point but I'd be willing to give these advantages up for a magnet with twice the performance. Unfortunately, the 3mm X 2mm magnet doesn't live up to the “twice as good” I'd hoped for. In terms of pull strength and Gauss at the surface of the magnet, the 2mm is twice as strong; a promising start. But analyzing field strength at various distances showed little substantial gain. Both magnets have a field strength below what's palpable at a point between 0.7 and 0.8 inches. The 1mm model seems to dip below utility at 0.76 inches and the 2mm lasts to around 0.79. The increase in useful field is negligible. Some might argue that the increase of maximum lifting power of 0.6 would make the increase in size worthwhile despite having nearly no gain in total field size. The reality is actually the opposite.
Studies performed in the early eighties demonstrated that as little as 35mmhg can cause pressure ulcers over a time frame of 8 hours. This level of pressure can prevent capillary refill. A pressure of 70mmhg over 2 hour can cause pathological changes to canine skin as this exceeds the pressure needed to occlude veins. A pressure of 500mmhg can cause pressure sores and muscle damage in pigs within 1 hour through a combination of arterial occlusion and some local tissue damage. It makes sense to analyze how much pressure can be generated by our 3mm X 1mm magnet. A 3mm disc has an area of 0.01 in2. which is exposed to a maximum 0.3lbs of pressure in the form of a metal object being attracted to the magnet unit. This equates to 30lbs of pressure per square inch or 1551 mmhg. These numbers are useful to help us approximate how much pressure our skin can withstand without damage but no solid conclusion can be drawn. Based on these numbers, I suppose that a 3mm X 1mm Neodymium Iron Boron could safely carry its maximum load for as long as twenty minutes without worry of skin damage occurring. If a person places another magnet over the implant, this safe time would likely be less than ten minutes. Doubling the strength of the magnet by increasing the thickness to 2mm doesn't increase the functionality of the implant, it limits it as it provides no increase in range, no increase in ability to sense the electromagnetic spectrum, and it decreases the allowable contact time with a ferrous object.
For those of you who already have a 2mm X 3mm disc magnet implanted, your in luck. SFM has performed testing on the leading suppliers 2mm X 3mm silicone coated magnet and found a Gauss rating of 1850 from the surface of silicone and once cut open to expose the surface of the magnet is rated at 3500 Gauss , far lower than the calculated 5837 that an N52 of that size should exhibit. An implant must be assessed according to it's whole size. Thus, a rating of 1850 Gauss at surface is closer to the field one would expect from an Alnico magnet rather than Neodymium Iron Boron. On the other hand, I've known grinders who state they can pick up objects weighing more than would be expected from the units we tested. We very well might have been sent a number of flawed units. If this is the case, it's advisable for those with these implants to be cautious as to how long they allow contact in order to prevent injury.
Searching online will demonstrate the plethora of different magnets. There are so many shapes, materials, and features available. The vast majority are completely unsuitable though in that while getting a Neodymium magnet is easy; getting a magnet appropriately coated in a biologically inert material is far more difficult and effective bio-proofing should be your number one consideration. There's more to this process than slicing open a hole and dropping in a specimen of foreign rare-earth metal. As we all know, the human body is quicker to wage war on foreigners than an American President.
There are scores of biocompatible materials. We have hips of titanium with hydroxylapatite surfaces adhering to bone. Nylon catheters feed us through perforations in the abdomen while Latex tubes in the urethra collect waste. Silicone wraps sexual organs when having intercourse or collects menstrual fluid when not. Teflon coats both pacemakers and artificial heart valves serving plumbers and electricians alike. Despite the variety, finding a coating appropriate for our application is rather difficult as Neodymium Iron Boron has one major downside: its very low Curie temperature.
The Curie temperature is that point where the magnetic moments of a substance are able to rotate and move freely. If an implant is heated above 100 C it loses a considerable amount of strength. Further heating to 310 C and the unit will cease to be magnetic. It will not regain strength upon cooling. It can be remagnetized if one locates a facility able and willing to do this. The units must be arranged in the same direction they faced during sintering for the remagnetization to provide similar performance. If heated much higher than the Curie point, the units can be rendered both irreversibly and irrecoverably damaged. The alloy itself has changed and no amount of external field can cause remagnetization.
PTFE, more commonly known by the trade name Teflon is one option for biocoating. It was one of the earliest materials identified as safe for implantation. It's still used extensively in grafts to repair blood vessels. One can even buy non-stick cookware repair kits and while using it to coat an implant would be ill advised, the directions on these sprays reveals the shortcoming of all such products: Bake at 500°. Teflon application generally requires temperatures that will destroy a magnet. Variants of PTFE have been developed that can be applied at much lower temperatures but there is another reason Teflon is inappropriate. It has a Young's Modulus of 0.5 GPa and a yield strength of 23 MPa. This means it's slightly more difficult to tear than an equally sized sheet of aluminum foil. If applied thickly enough, PTFE is an excellent biocompatible coating. I've never seen someone tear a sheet of 3mm thick aluminum with their hands; however, magnetic field strength diminishes rapidly with distance which necessitates a very thin coating.
We've discussed magnetars in detail and yet haven't gotten around to discussing how powerful it is magnetically. This is best demonstrated through comparison. The smallest magnetic field commonly detected is that of the human brain with a strength of 1.0 X 10-8 Gauss. This is four orders of magnitude below Earth's magnetic field of 3.1 X 10-4 Gauss. The weakest of Ferrite magnets have a field strength at surface that measures as low as 0.05 Gauss although as discussed previously modern ferrite is often considerably stronger. Neodymium Iron Boron magnets are three orders of magnitude stronger than this with a rating around 1.25 X 104 Gauss. Most MRI machines only produce a field about twice as strong as this at 3 x 104 Gauss. The strongest man made magnetic field was produced using conventional explosives that compressed an already impressively strong electromagnetic coil. This experiment by the Russian Federal Nuclear center produced a field strength of 28 X 106. At this point, we run out of intermediate examples. There simply isn't anything, even amongst astronomical phenomena, that compares to the massive power of a magnetar at 1.0 X 1015 Gauss. If a magnetar was located the same distance from Earth as the Moon the effect of this magnetic field would wipe the information from all the credit cards on earth. This is a bit anticlimactic isn't it?
Despite how powerful a magnetar's field might be the nature of magnetism is such that a rapid decline of field strength occurs with distance. This is why a very thin coating on our magnetic implants is of such importance. Adding even a millimeter of coating can cut the strength and palpable range of an implant in half.
This requirement for thinness is why silicone is a poor choice as a coating. Silicone has a Young's Modulus between 0.001 and 0.05 GPa and a yield strength of 2.4 MPa. Because it's such a weak material a coating less than 1mm would be worthless. Silicone tears easily and responds poorly to fatigue. Breast implants made with this material are notorious for rupturing with even the newest models exhibiting a failure rate as high as 33 percent. Keep in mind that is not the silicone gel within that is the issue but rather the silicone bag in which it rests. Earlier models on average began leaking by year ten and ruptured by year 13. Discontentment with silicone is one of the divides between the grinder world and the body modification world. Body modification artists really are responsible for pioneering magnet implants. As such, they designed the early implants using a material that they're familiar with. Silicone can be shaped into nearly any shape of interest and so has been used for decades as when implanted beneath the skin it results in totally aesthetic changes of bodily form. Solid silicone serves this purpose well but leaves a lot to be desired in terms of sequestering a moderately toxic metal. Grinders have approached the design of implants without a bias towards any particular substance and the most prevalent coating found in grinders' implants is a substance called Parylene C.
This brings us to V&P Scientific. V&P is a company which produces coated stir rods for chemistry application. They are significantly more capable than the preceding Teflon coated models as they use neodymium rather than Alnico or Samarium Cobalt. They can do this because they use Parylene which is applied via vapor deposition in a vacuum chamber. High temperatures aren't required so the temperature limit is circumvented. Its Young's modulus is 2.8 GPa and it has a yield strength of 55.2 MPa, significantly better than Teflon or Silicone. For a period of time, the most commonly chosen magnet for implant by grinders was the V&P scientific VP782N-3 magnet. This model was only available in sets of 100 at a price upwards of $250. This did wonders in terms of drawing the grinders together as a community as a number of group buys were made. This was an important first collaboration; however these magnets are not optimal as implants. Parylene is a biologically stable corrosion resistant coating which can be applied in layers as thin as a couple of microns. Therein lies the shortcoming. Though these coatings are as thin as might be desired, they are also somewhat brittle. While perfect for many applications, they also provide little resistance to mechanical stresses such as those we place on our fingertips daily. Thicker coatings aren't an option either. The organization I work with, Science for the Masses, ordered a run of multiple deposition Parylene coated magnets against the advisement of the coating companies and as advised it resulted in a coating which easily peels away from the magnet surface. Were the coating to chip or peel after implantation rejection is inevitable. Mind you there have been many successful implants using either Silicone or Parylene; however, when implanting an object under the skin it's only reasonable to seek a coating with better properties than either of these materials can provide.
When I first became interested in magnet implants, I devised a method to overcome the limitations of Parylene consisting of a durable biosafe resin coating. I still have one of these implants as of the writing of this article but the added resin material is approximately 1mm thick. While far more resilient than the silicone models being sold it still suffers the loss of strength associated with a thick coating, and I no longer advise this method. A number of other DIY style coatings have been used in the past. These range from resins that are so difficult to obtain that they are of nearly occult status to people advising the use of Sugru and hot glue guns. Needless to say, not a single one has been found with characteristics preferable to the materials already discussed.
There is another material which does fulfill all of our requirements with but one shortcoming. This is Titanium Nitride. TiN has a Young's modulus between 350 and 600 GPa and a yield strength of around 400 MPa. This is two orders of magnitude greater than the best material discussed previously. Where Parylene failed because of brittleness, a TiN coated magnet requires a hammer to break integrity. TiN also exhibits significantly lower bioreactivity than any of the other materials that have been used. It's preferred in orthopedic implants related to it non-reactivity in the body as well as for the coating of machine tools such as drill bits due to its incredible resistance to wear. TiN can be applied via a few different methods. The most common are physical vapor deposition and chemical vapor deposition. Both of these methods require very high temperatures far outside the range allowable for Neodymium Iron Boron. However, if one searches long enough and hard enough there are alternative methods available which can provide a TiN coating at an adequately low temperature.
The nearest Spiral Galaxy to our own Milky Way is the Andromeda Galaxy, also known by its Meissier designation as M31. It was the first extragalactic object humans have ever been aware of. In 1917, a supernova was observed from M31 and and it was noted that the intensity of light was ten magnitudes fainter than supernova observed in other regions of sky. This was the first evidence that rather than a nebula within our own galaxy, M31 might be a galaxy in its own right. It was Edward Hubble at the Mount Wilson Observatory in the mountains above Los Angeles who finally proved this conclusively through measurement of distance. 75 years later, a short duration hard spectrum Gamma Ray Burst was detected from M31 more than 2.5 million light years away: the signature of a magnetar from another Galaxy entirely. When body modification artists began implanting magnets to sense the electromagnetic spectrum it opened up an entirely new aspect of the world to be sensed. The newest magnet implant produced in a collaboration between SFM and Dangerous Things extends this further in terms of both detectable range safety and as an implantable device. As such it is worthy of its name: the M31. The M31 is a 3mm X 1mm Neodymium Iron Boron Disc magnet with a flux loss-less coating of Titanium Nitride. Admittedly the name is actually referential to the size of the device itself. It's a magnet that's 3mm X 1mm, but I rather like the redaction. Point being that regardless of what it's named or why, in terms of range, strength, durability, and biocompatibility it is by far the best magnet implant available and is the only magnet augment worthy of consideration.