Body-Scan Suits

With the composite successfully created, characterized, and proven, the next step of the project was to start building suits out of it and potentially test them under field conditions. Making such suits however required the successful solution to multiple problems.

First and foremost, the suit would have to be wearable. It would not be sufficient to encapsulate the diver in the new composite. The diver would also have to be able to move relatively comfortably and hopefully sufficiently freely while wearing the suit, so that the diver could swim. Neoprene suits solved this problem by using a relatively flexible material (bubbled neoprene) and by limiting the thickness of the material to 8mm or less. In contrast, our composite material is less flexible than bubbled neoprene of the same thickness. A simple demonstration of this fact is offered in the figure below.

The figure shows a sample (black, left hand) of 8mm neoprene cut out from a commercial Aqua Lung suit. To compare, a puck of composite material (white, right hand) is bent less but under greater force, showing less flexibility than the neoprene.

Since we want a suit made of our composite material, we needed to solve the problem in a different way. Historical analogs presented themselves in terms of late-medieval plate armor. To improve physical protection, late-medieval armorers made suits of sheet steel, here the steel plates were segmented to cover areas of the body with minimal or no bending, while areas of large bending were left uncovered by plate or covered by interlocking segments. See figure below for an example of high-medieval/renaissance full plate armor.

By analogy, we realized that we could build the composite suit by the same general principle of composite plates covering unbending or minimally bending areas of the human body. Because the suit’s goal was thermal protection rather than protection from physical blows, some of the details had to change, so the analogy was incomplete. Chiefly, the series of small interlocking plates to cover movable areas in armor were not practical for our diver suit, as the cold water would likely get in between those plates and cool the diver. So, we dispensed with those but retained the solid plates over most areas. The result was something akin to a Star Wars stormtrooper outfit as shown in the cartoon above. The bending areas would simply have to be left to flexible relatively thin neoprene instead. This overall strategy seemed to maximize the overall advantage in a reasonable tradeoff between protection and ergonomics.

Considering the expected stiffness of the composite plates, we had to achieve as close a fit as possible between the suit and its wearer. Late-medieval and Renaissance master armorers achieved that by painstakingly shaping metal sheets by hammer and anvil and cycles of reheating. We could not use the same approach for the composite. Instead, the composite had to be cast in its fitting form. To do so, we needed molds already shaped to fit the diver.

We found a solution based on 3D scans of the body of the diver. The process is outlined in the figure below.

The 3D scan (A) of the body of the diver was digitally segmented into shells (B) corresponding to different body areas of no bending or minimal bending. The segmentation generally followed the boundaries of the main muscle groups of basic anatomy. For simplicity, certain anatomic subgroups were united, if there was bending between them (e.g. pectoral and upper abdominal in E). The digital shells were copied in pairs distanced at around 7mm between the two shells (C) where the two halves were extended to complete matching sets of molds (D). The mold pairs were 3D printed in polycarbonate and used to cast corresponding pieces of composites (E ). The composite pieces were aligned onto the diver body and trimmed as needed to maximize fit and improve ergonomics.

We next had to solve a different problem. The composite segments needed to be attached to the diver. One idea was to have a thin neoprene suit as an undergarment or body mask. This would provide a mechanical scaffold for the composite segments, as well as provide some thermal protection at the exposed joints, places of significant bending, or boundaries between neighboring plates. The question was how to attach the composite to the neoprene.

We investigated multiple options of gluing, including neoprene glue and specialized silicone adhesives. Nothing worked satisfactorily. The reasons were that glue strength was not particularly high, while post-gluing bending was very successful at failing the bonding. Furthermore, the neoprene and the composite had very different chemical and physical properties. For example, the different stiffnesses meant that the same amount of bending would see the materials deform differently and thus fail the bonding. In addition, both glass and silicone are rather inert chemically, which means gluing to them is particularly challenging. Ultimately, we abandoned the chemical bonding approach.

Reasoning the chemical bonding would not work, we redirected to mechanical solutions. We noticed that gluing neoprene to neoprene was standard, while making pockets in this way was already a common practice. From these vantage points, we saw that the composite segments could be encapsulated mechanically in pockets of neoprene. This approach worked very well, producing our first composite suit named K1.

The figure above shows the K1 suit constructed by encapsulating the composite pieces in external pockets. The pockets were completely and permanently sealed by gluing the top thin neoprene on all four sides to the thin neoprene suit. Thus, no chemical bonding was required between the composite and the neoprene. This technique proved highly successful.

The K1 suit was field-tested by direct comparison with a commercial neoprene suit. For this purpose, two divers dived together at the same time in Monterey Bay, one wearing the K1 and the other wearing a 7mm commercial neoprene suit. Both divers wore watertight automated dataloggers (one inside the suit and one outside it). The loggers logged temperature and pressure at 1 second intervals automatically. After the dives, the data was uploaded in a computer for analysis.

The figure above shows the experimental results of the field test of the K1 suit versus a commercial 7mm neoprene suit. The left graph shows the temperature difference between the two dataloggers (internal minus external), for each of the divers (K-suit in blue and 7mm neoprene in orange). The difference of the difference is shown as well (delta, gray). The right graph shows the corresponding depth data, calculated from the logged pressure data.

The experimental results showed that the K1 suit outperformed the 7mm suit by about 4 degC in terms of thermal protection.

In addition, the K1 diver reported that the ergonomics of the suit was essentially the same as a 3mm neoprene suit, and thus much better than the ergonomics of a 7mm suit. The reason for that was that the effective flexibility was determined by the flexibility of each suit at the joints. The 7mm being significantly thicker than the 3mm of the K1 thus offered much more resistance to the motions of the diver.

The K1 was an excellent first step in the suit evolution, but we wanted further improvements. We chose to make those improvements in two different directions. First, we wanted further thermal protection, so the segment thickness needed to be increased. Second, we wanted to test the sonic protection offered by such a suit. Third, we wanted to make the suit neutrally buoyant, to improve the ergonomics of mass distribution for the diver, as well as decrease the high positive buoyancy experienced with the K1.

The solution to all three requirements was constructed by adding an extra layer of solid ceramic microspheres encapsulated in silicone at maximal volumetric percentage. For this purpose, the new suit was made by recasting the same pieces in hollow glass encapsulated in silicone, and separately casting a relatively thin layer of flat composite made of solid ceramic microspheres encapsulated in silicone, then putting the two layers together by glue and duct tape as needed. The result was thicker plates, whose ceramic layer faced outward. The figure below shows an example of this double plate.

This arrangement also solved the sonic protection requirement, as the outer layer made of ceramics had higher effective density and thus was more reflective to incoming mechanical waves in the water. The physical basis for this was that reflection was dependent on the density mismatch between the material and the water. Higher mismatch should produce more reflection.

The same arrangement of the two layers also produced an effective overall density close to the density of water, i.e. neutrally buoyant, since the solid ceramic microspheres had about twice the density of water, while the hollow glass microspheres had effective density of about one tenth that of the water.

Using these double plates, the K2 suit was assembled by the same external-pocket method as the K1. The figure below shows photos of the K2.

The resulting suit was field-tested in the same away as before, by diving in pairs in Monterey Bay and using automated dataloggers to log pressure and temperature.

The figures below show the results of the field test of the K2 against a commercial 5mm neoprene suit. The top figure shows the temperature difference between the inside logger and outside logger, for each suit, and the corresponding depth, versus time. The bottom figure shows the difference of the difference of K2 vs the 5mm. The K2 was about 5 degC warmer than the 5mm at depth.

In another field test, the K2 was compared to a 7mm neoprene suit. The results are shown below.

The results indicate that the K2 outperformed the 7mm by about 1degC. This is surprising, since the K1 outperformed another 7mm suit by 4degC. The K2 diver also reported problems with leakage of water into the suit from the area around the neck. This is part of the likely explanation for the subdued thermal performance.

In addition, the K2 diver reused the molds made to fit the K1 diver, to save time and expense. The tradeoff was that the pieces offered a less good fit to the K2 diver, which might have resulted into more space available between the suit and the body of the diver. As a result, more water would accumulate in the wetsuit and thus together with a neck leak contribute to excessive cooling of the diver.

This experience showed us that additional factors such as fit quality, sealing quality, and ease of manufacture were just as important for the overall performance of the suit as its basic design of segmented composites. We therefore set out to resolve these issues.