Shields and Force Fields
A common sight in many science fiction series and movies, the shield generator is a device which creates a non-physical barrier in order to protect “whatever is inside” from “whatever is outside” of the shield. In practice, a shield is meant to protect against all sorts of radiation, weapons fire, and explosions, or to prevent access to a certain area. We differentiate between a shield, which envelops an object, and a force field, which is separates two or more objects.
Shields
A shield is an ellipsoid barrier that protects the content enveloped by the barrier. How the shield is generated is described below; for now, we focus on the properties of the shield. Objects that interact with the exterior of the shield introduce a stress on the shield. The spherical shape of the shield mitigates the applied outside force by distributing it over the shield as whole. In contrast, a force applied from the inside of the shield easily punches through the shield. This allows starships to fire their weapons while the shield is active. However, part of the energy of the weapons is absorbed by the shield, 1) reducing the net power of the weapon and 2) damaging the shield. To prevent this from happening, an additional emitter is activated that destructively interferes with the shield locally to create a temporal aperture through which the weapon may pass. One might be tempted to think that this principle can be used to render the shield inoperable from the outside as well. However, the interfering source needs to transmit along with the original shield signal, because outside signals are reflected. Therefore, the shield can only be disrupted from the inside.
> Reflective and deflective shielding
For starship shields, we differentiate between reflective shielding and deflective shielding. Reflective shields act like a mirror, reflecting incoming objects at more or less the same angle at which they hit the shield. Deflective shields act more like a cushion, deflecting incoming objects antiparallel to the ship’s velocity. So, generally, along its bow. The deflector shield absorbs more of the object’s energy, while reflector shields are exposed to more stress. Absorbing energy is more favourable when the object’s energy density is not too high. Therefore, deflector shields are used to keep the ship safe from cosmic rays, solar winds, and interstellar dust particles, while reflector shields are used to defend against weapons fire and extreme conditions. The ship’s deflectors get their name from this.
> Inverse shielding
From the way shields are generated (see below), it is inherently impossible to contain an object by surrounding it with a shield. Containing an object is also called ‘inverse shielding’, because it does the opposite of what a normal shield does. To achieve inverse shielding, the shield must be generated from outside the object. To get a 4π solid-angle cover, the shield needs to be projected from at least 4 directions. To engulf the object in a spherical shape, a concave mirror can be employed in the shield projector to alter the positions along the shield grid at which constructive interference occurs.
To increase the effectiveness of the shield, and to protect it from outside influences, inverse shielding can be combined with regular shielding. The emitter beams from the inverse-shield generator are reflected by the regular shield and can be tuned to constructively interfere with itself. The net result is that this reinforces the shield. Now, the object is shielded from both inside and outside influences. It must be noted, however, that the inverse shield can be disrupted from the outside, in the same manner as the regular shield allows own weapons fire to pass. The disrupting party would need the know the exact shield frequencies and interference positions.
Force Fields
The most notable difference between a force field and a shield comes from its geometry: a shield is spherical, but a force field is planar. Because a force field is a (finite) plane, it is difficult to generate it using a point source, like is done with shields. Therefore, it is often opted to generate a force field within a fixed frame. It can then be used to shield one room from another. Because the field is projected inside a frame, the field is equally impenetrable from both sides. The generating frame is protected by the fringe field around the edges. The figure to the right illustrates this in a sideview. This should prevent damage to the force field generators when the force field is exposed to e.g. an explosion. The point source approach is in practice only feasible when projecting the force field onto an existing wall. This can be useful when that wall needs to be reinforced. Such a force field can be used to prevent structural collapse, for example.
> Shuttle bay force fields
In shuttle bays, a low-power force field is used to maintain atmosphere in the shuttle bay when the bay doors are opened. To allow shuttles to pass through, they emit an interfering dispersion field. This works because the power of the force field is low. Because of symmetry, this allows shuttles to both exit and enter the shuttle bay. Flying through the force field creates a drag on the shuttle. To prevent shuttles from passing through, the power of the field needs to be increased to at least the level when the drag force exceeds the shuttle’s engine power.
Shield generator
The shield generator emits radiation at different wavelengths which interfere constructively only at the set distance where the shield is meant to be created. In this way, an electromagnetic ‘bubble’ is created that reflects short wavelength EM-waves as well as charged particles. The reflection is effective even up to the point where the electrons and protons inside atoms are reflected. As a result, all matter and hazardous radiation is reflected and prevented from harming the contents of the shield.