Explosively formed jets (EFJ) and fragments and self-forging penetrators (SFP) are used for precision strike against targets such as armored vehicles and reinforced structures. Current technology uses chemical explosive energy to form the jets and fragments [rocket propelled grenades]. This is highly inefficient and requires precise machining of the metal liners from which the fragments and jets are formed. The Magneto Hydrodynamic Explosive Munition (MAHEM) program offers the potential for higher efficiency, greater control, and the ability to generate and accurately time multiple jets and fragments from a single charge.
The MAHEM program will demonstrate compressed magnetic flux generator (CMFG)-driven magneto hydrodynamically formed metal jets and SFP with significantly improved performance over EFJ. Generating multiple jets or fragments from a single explosive is difficult, and the timing of the multiple jets or fragments cannot be controlled. MAHEM offers the potential for multiple targeted warheads with a much higher EFJ velocity, than conventional EFJ/SFP. This will increase lethality precision. MAHEM could also be packaged into a missile, projectile or other platform, and delivered close to target for final engagement.
Explosive warheads have worked in pretty much the same way since Henry Shrapnel's 1784 artillery shell, which was designed to explode and throw out musket balls in all directions. The shaped charge was a 20th century refinement in which the force of the explosion blasted a hollow metal cone into an armor-piercing jet, enabling low-velocity weapons like the bazooka to knock out heavy tanks. Then came the Explosively Formed Projectile. Here, the explosion folds metal into an aerodynamic slug that is less penetrating than a shaped charge but able to do more damage against lightly-armored targets. (It's a larger mass at a lower velocity, and makes a bigger hole.)
MAHEM is different because it combines explosives with electricity. It works in three stages. The first is an electronically modified explosion. The explosion creates an expanding fireball; applying an electrical current to the fireball increases the velocity and pressure of the blast, getting more bang from the same ingredients.
In the second stage, the power of the explosion is converted into electricity. This builds on previous work into "explosively driven flux compression generators" that convert explosive power into an electromagnetic pulse. In MAHEM, a ceramic material produces an intense electric current as the shockwave hits it, in a process known as electromagnetic braking. In contrast to a normal explosion, in which most of the energy is wasted, the makers claim the MAHEM has "superb energy conversion efficiency."
Other explosively driven flux compression generators are designed to produce a high-energy electromagnetic pulse to destroy electronics. In MAHEM, the electrical energy is used to accelerate metal, as with a railgun. Depending on the intended target and how it is triggered, MAHEM can fire shrapnel, an armor-piercing jet, or an explosively formed projectile. And because of its high efficiency, MAHEM can accelerate a projectile to higher speed, or accelerate a greater weight, than existing warheads. It also has more controlled precision; the makers claim it can project multiple jets.
Contracts and SBIRs indicate MAHEM progress
Adjustable dial-a-yield warhead that could be set to any blast level as needed.
A shoulder-launched bunker-buster that was completed last year.
SBIR - Electromagnetic Explosive Warhead (EMEW) for Scalable Lethal and Nonlethal Effects
Another is a contract for a "Novel Light-weight Warhead for Breaching and Destroying Hardened Structures"— a shoulder-launched bunker-buster that was completed last year.
The latest version is the Electromagnetic Explosive Warhead (EMEW), a MAHEM warhead for the US Army's Organic Precision Munitions program, which includes portable lethal drones. EMEW provides "augmented explosion, selectable fragmentation, and controlled blast." The pattern and direction of the effects can be controlled, or it can produce blast only with no fragments, like a giant stun grenade, for "non-lethal effects."
A scientific paper from China entitled "Physical Modeling of Magneto Hydrodynamic Explosive Munition and Detonation Control" from the journal Applied Mechanics and Materials. The paper was written by a team at the "ministerial key laboratory" at the Nanjing University of Science and Technology, and is a detailed theoretical breakdown of how MAHEM works. It includes block diagrams of the electronics, the complex "kinematics differential equations of kill element" that indicates how it accelerates metal projectiles, and details of the ferroelectric ceramics in the flux generator. This is more information than you can get from any US source, and appears to be based on the reverse-engineering MAHEM by a team with a very detailed knowledge of magnetohydrodynamics and munitions.
The Chinese paper was published in 2013 and refers to several other theoretical studies, but only limited experimental work. Unless there is other, undisclosed practical side to the work, China is still several years behind the US in developing this type of warhead.
SOURCES -Popular Mechanics, DARPA, SBIR