Many kinds of powerful devices are used in war or for civil purposes.
It would be called a "bomb" when the release of energy is very sudden
and linked to the detonation of some explosive. Like for example:
- Simple blast devices, like grenades, that produce a shock wave.
- Flash bombs that blind the enemy for a short while.
- Smoke bombs, that produce a sudden massive amount of smoke. Most
commonly they are phosphor bombs (not to be confused with phosphor
bombs used to mutilate and inflict cruel and lasting wounds).
- Schrapnel devices, that project pieces of metal all around. A
modern version being the claymore, just metal spheres spread over a
layer of high explosive. A gun would be a pricision one-schrapnel
device.
- EMP bombs (electromagnetic pulse). They contain an electric
magnet,
through which a high current is driven, creating a strong magnetic
field. The magnet is exploded by high explosives and the magnetic
field spreads around as an electromagnetic shock wave, destroying
electronic
devices.
- Rock penetration bombs. They arrive on the target at such a high
speed that the pressure of their nose melts any rock or concrete. The
bomb penetrates the rock like if it was hard butter. It ultimately
explodes deep underground.
- Cutting bombs. A fuse of high explosive is paste in the
shape of the hole that must be cut away in a door or wall.
- Metal plastifying bombs. Either their pressure molds a metal
plate to the shape of a shell and propels it at high speed, or the
metal is pressed to a rod that extends forward at hypersonic speed
due to the pinch effect.
Can a bomb play an audio signal? The idea would be a long
explosive fuse whose diameter varies along the length. The variations
of the diameter are comparable to the oscillations of the groove in a
recorded audio disc. The explosion front speeding along the fuse, would
produce a variating pressure on the surrounding air, like the needle of
the disc player reads the record.
For example the fuse would unroll from a parachute and then would be
lit from the bottom.
What can such an explosive device be
used for?
- The first idea was to
broadcast "surrender!" loud out above an enemy army. Whatever the
message broadcast, the force of it should have a strong psychological
effect. It should be hearable deep inside bunkers.
- A less sympathetic usage would be the generation of simple tones,
whose
frequencies would be aimed at structures, devices or people. That would
for example allow to burst open precise objects, whose resonance
frequency is known. It would allow to knock out people with less
overall damage.
The difficulty lays in the audio frequency that can be
attained.
A few kHz are needed to reproduce a human voice. Frequencies in the
order of 10 to 100 Hz are typical to make structures resonate or cause
physiological or psychological effects.
I read that a block of TNT of 500 kg would produce a positive pressure
pulse af about 20 ms. Allowing another 20 ms for an optimal negative
pulse, this yields a period of 40 ms hence a frequency of 25 Hz. That
would be for packs of 500 kg of TNT placed along a fuse and the target
being aside of the fuse and far from it. A typical quantity of
explosive for this application would rather be less than a gram.
Asuming that the volume of the sphere of hot explosion gas is
proportional to the mass of explosive, the duration of the blast is
proportional to the radius of the sphere and the radius is proportional
to the cubic root of the volume, then a reduction of mass of 500 kg
down to 0.1 gram yields an increase in frequency of 170 times. Then 25
Hz
x
170 yields 4250 Hz. This makes the system seem possible (don't trust
but verify).
