Repulsion Device

Forcefields are energy-based barricades found in technologically advanced areas of the wasteland, such as the Mariposa Military Base, the underground base beneath the Cathedral or the Enclave's Raven Rock base in the Capital Wasteland.

Repulsion field
Pre-war repulsion fields are yellow-colored, while Enclave's post-war ones are blue. It is impossible to pass through a repulsion field without disabling it.

In Fallout and Fallout 2, yellow force fields may be temporarily disabled by utilizing the "Repair" command on the force field emitter.

In Fallout 3, repulsion fields can mostly be disabled using nearby terminals, which requires a Science check.

Pain field
It is possible to pass through this type of red-colored forcefield, but this will result in varying amounts of HP damage. Dogmeat is said to have succumb to death by attempting to pass through a force field in the mutant military base in The Vault Dweller's Memoirs.

Pulse field
A pulse field is an electromagnetic pulse grid which paralyses the circuits of every device crossing it, including T-51b Power Armors.

According to Lieutenant Morgan in the Anchorage Reclamation simulation, the Chinese use such a field to protect their base of operations in the quest Anchorage. It has to be disabled by the player so American T-51b units can advance to the Chinese command post.

When the player first gets to it, it's effectiveness is demonstrated by an American soldier running onto it, then he seemingly suffers a massive electrocution, collapses and evaporates just like people killed in the simulation, so it is probable that the field not only damages the armor, it kills the wearer as well.

A Chinese-controlled computer terminal reveals that the intelligence aquired by the Chinese regarding T-51b deployment was incorrect, as in the armor is being deployed ahead of schedule; for this exact reason, the sender of the decoded transmission heavily recommends the use of EM fields. Presumably the Chinese either knows the armor's schematics (and thus it's weaknesses) or they had previous experience regarding EM fields and an earlier Power Armor prototype.

Fallout 3
Repulsion Fields are encountered at 3 locations:
 * Raven Rock: These can be disabled by using a nearby terminal.
 * Around the Jefferson Memorial, only from The Waters of Life till Take It Back!. These are disabled by Liberty Prime.
 * At the Mobile Base Crawler. The following can be done with them by using the nearby repulsion field control panels:
 * Do Nothing: Nothing will happen.
 * Turn off the repulsion field: Requires 80 Science, and will completely turn the field off.
 * Set a timed charge: Requires 50 Explosives, this will blow the panel up and partially disable the field. If you then  walk through the field you will take damage.
 * Smash the Control Panel: this will destroy the panel, causing you to take damage and will partially disable the field. If you then walk through the shield you will take damage.

A pulse field appears in Fallout 3's Operation: Anchorage add-on, inside the Anchorage Reclamation simulation.