The military and defence sectors cover a whole universe of engineering and materials requirements. The vast majority of those needs are no different in type from those of other specific sectors, principally, aerospace, marine, transport, computing and communication, medical, textiles, energy, and all. (see other sections under: applications industries ). Very obviously however, there are requirements that set military and defence apart from other industries: Top of that list are:
a) Extremes – of operating conditions and qualities – for example, whilst commercial aircraft might typically experience forces of around 0-3 g or so, military aircraft generally need to handle several times that (9-10g), and guided missiles several times that again (30-100g ), and ballistic shells many times that (over 15000 g !); whatever civilian commercial systems do well, military systems must do better, much better.
b) Novelty – the military don’t just want the best features and the best materials available, they also want them before anyone else has them, most particularly ahead of any enemy. As such, the defence sector are often seen as vanguards of (often top secret), bleeding edge research and development effort. Release of such technology into civilian and commercial spheres invariably occurs some significant time later.
c) Adversariality – for every measure a counter-measure, for every attack a defence, for every weapon an amour, for every amour a weapon, for every concealment a detector, for every detector a concealment, and so on. Thus, this simple principle drives the rate and direction of the majority research and development in the sector; no more so than in materials science, and in the accelerated application of those new materials within engineered solutions, ultimately (ideally), to rapid deployment in the field.
Of course, there are many other drivers: cost – as always, availability – particularly in-the-field replacement parts etc, weight, durability, efficiency, and so on; the military versions of these needs, simply more acute, more extreme.
Key capability areas
Key capability areas for advanced materials and manufacturing in military and defence applications, feature:
– Extreme environments – durability, endurance, etc
– Remote controlled and autonomous vehicles and systems – on land, sea and air and space – for surveillance, defence, offence – includes robots
– Power and energy storage – esp batteries and energy scavenging – especially for remote sensors, and remote controlled and autonomous vehicles and systems
– Survivability – against environmental as well as intentional damage
– Sensor systems, and imaging systems – wide spectrum coverage, sensitivity, resolving power, etc – imaging systems using: acoustic in water (sonar), acoustic in air (munitions fire location, movement detection), radio/microwave (radar – various), terahertz/near-infra-red (see through thin soft materials), infrared (night/fog vision), optical (remote surveillance, adaptive optics, (wave-front sensors, etc)), x-ray (see through thick packaging) , muon (see through buildings/walls/ground) , radiological (nuke spotting, airborne/space-born Geiger counters) , magnetic (submarine hunting), electric (detect ground anomalies) , gravitational (sub hunting), chemical (sniff out IEDs, munitions, chemicals, etc).
Nanomaterials involve working at the nanoscale (< 100nm in at least one dimension), and are one of the most prolific areas of present day research. At this scale, increased relative surface area, as well as quantum effects, can change or enhance physical properties dramatically. Graphene is one of the best known examples – a 2D hexagonal lattice at the nanoscale, it is one of the strongest materials known and is also an excellent conductor of heat and electricity. Other key research at this scale is into the use of graphene nano-wires in advanced multi-spectral imaging systems, and, using graphene enhanced polymer composites to produce tougher lighter materials for structural engineering as well as protective amour. Also under development, 3D Graphene foam materials, utilising multi-wall graphene nanotubes, exhibit exceptional strength and ultra low density/low weight.
Future research is likely to see a host of other 2D nanomaterials such as silicine, germanene, phosphorine, and stanine, find their way into a range of products, with earliest adoption being most likely within the military, defence and aerospace industries. The first three of these (silicine, germanene, phosphorine) are particularly interesting, since in contrast to graphene, they are semiconductors, and this potentially avails us of nano-scale electronic circuits – for example, as so called ‘smart dust’. Using such a concept, we can conceive of massively distributed wireless sensor networks, or, indeed, perhaps swarms of semi-autonomous nanobots, each no bigger than a grain of sand, covering vast areas; such prospects are no longer confined to the realm of science fiction – possession of such technology could confer enormous military advantage, and a frightening one.
Whilst methods for the basic synthesis of such nanomaterials, are becoming increasingly well developed, two major challenges remain: 1) atomic and molecular control of the structure of nanomaterials, and 2) control and definition of the placement of such materials in bulk, for industrial applications. Another area of concern, that must be addressed, is the toxicity of many of these substances, not only to humans, but also potentially to the planet.
Metamaterials are synthetic composite materials, that exhibit properties and behaviours not normally found in nature. At the nanoscale, they interact in unusual ways with (usually) electromagnetic energy waves passing through or across them. One well known application of such materials is in so called ‘cloaking’ applications, which have been a perennial and keen interest of the military.
Cloaking need not only be optical/vision based of course, but at different frequencies, cloaking aircraft, ships, tanks against against radar detection is attracting a great deal of research and development; cloaking against terahertz and xray imaging is also an important objective; and whilst utilising very different types of (acoustic) metamaterial, cloaking against sonar detection is already well established area of research and development. Alongside new metamaterials themselves, this area of research has also given rise to new theoretical paradigms, most importantly perhaps, the study of transformation optics, together with new concepts and new novel devices such as (variable) gradient index lenses (GRIN lenses), acoustic diodes, to name but a few of many. Intriguingly, transformation optics opens up the possibility of imaging things smaller than the wavelength of light, and this has a great number of potentially useful applications in, for example, detecting toxic gases and even airborne pathogens from a distance.
Currently many such applications are considered to be at a low technological readiness level (TRL), although they are advancing increasingly fast. High readiness level advanced metamaterial applications also exist; in particular, the use of metamaterials in antenna arrays for synthetic aperture radar is becoming well established – providing for smaller size, higher power, better directivity; also, infrared spectrum metamaterials for thermal management in satellites – maximising thermal radiation of waste heat, whilst simultaneously rejecting heat from incident sunlight.
Materials for Energy
The use of new materials in energy storage and generation is also of key interest to military organisations, who absolutely rely on advanced electronics and communications equipment in the field, and have increasingly critical energy requirements with the greater adoption of remote controlled and autonomous robotic vehicles in the field. Novel battery technology, alternative energy sources such as (flexible) photovoltaics, hydrogen fuel cells and energy harvesting, are all very hot topics. These are discussed in greater detail in the section on energy ( see : energy ) . Needless to say, the military wants what everyone else now wants, just better and sooner – ie: higher energy density, lighter weight, lower environmental impact and toxicity, lower cost.
Bio-inspired or biomimetic materials are synthetic materials that mimic materials found in nature. Examples include photonic materials that mimic photosyntheses, super-hydrophobic (water repellent) surface coatings that mimic for example lotus leaves and that find uses in coatings on military equipment; and functionally graded materials that mimic for example (hardness graded) squid beaks, that find applications in amour plating and machine bearings . Many materials that support self-assembly and self organisation also fall into this category, especially as those implementing sensor arrays.
One very wide application area is in medical and health related technologies, such as wound dressings and tissue engineering using functional polymers and flexible electronics, drug delivery systems using nanobots, and prosthetics of all sorts using a wide variety of materials and approaches, including artificial muscles and embedded sensor arrays – plus many more. Applications mirror those of the civilian health sectors (see separate section: medical and healthcare), but again, have even more demanded of them in military settings.
Research and development in this field need must span multiple scientific disciplines, and faces additional challenges when attempting to move developments out of the lab and into products manufacturable at scale.
Multi-functional materials, including also many adaptive materials, provide additional functionality beyond their primary purpose. For example, structural materials that also provide power generation, adaptive camouflage, self healing, sensor or actuator arrays. Possible combinations are manifold and some applications are considerably more mature than others.
Shape Metal Alloys (SMAs) are one such example, the most common of which are currently based on NiTi alloys. SMAs revert their physical shape upon the action of stimulus, typically thermal – which tends to provide relatively slow response times. Faster response times are obtained using thin-film approaches, and magnetic fields as the stimulus, and latterly SMA wires embedded in composite structures have shown great potential in generating greater strength, speed, and force.
Structural composite materials are another area of rapid development. For example damage monitoring of structural components using embedded optical fibres and ceramic piezo-materials.
Polychromic, chromogenic, and halochromic materials that change colour due to external influences, are also being actively researched for camouflage and smart textiles. (see separate section: textiles ).