The Biefeld–Brown effect is an electrical effect that produces an ionic wind that transfers its momentum to surrounding neutral particles, first discovered by Paul Alfred Biefeld (Germany) and Thomas Townsend Brown (USA). The effect is more widely referred to as electrohydrodynamics (EHD) or sometimes electro-fluid-dynamics, a counterpart to the well-known magnetohydrodynamics. Extensive research was performed during the 1950s and 1960s on the use of this electric propulsion effect during the publicized era of the United States gravity control propulsion research (1955 - 1974). Top secret experiments into the effect were also conducted in France 1955-1958 by Thomas Townsend Brown and SNCASO called Project Montgolfier.[1] During 1964, Major Alexander Procofieff de Seversky published much of his related work in U.S. Patent 3,130,945, and with the aim to forestall any possible misunderstanding about these devices, termed these flying machines as ionocraft. In the following years, many promising concepts were abandoned due to technological limitations. The effect has only recently become of interest again and such flying devices are now known as EHD thrusters. Simple single-stage versions lifted by this effect are sometimes also called lifters.
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The effect is generally believed to rely on corona discharge, which allows air molecules to become ionized near sharp points and edges. Usually, two electrodes are used with a high voltage between them, ranging from a few kilovolts and up to megavolt levels, where one electrode is small or sharp, and the other larger and smoother. The most effective distance between electrodes occurs at an electric potential gradient of about 10 kV/cm, which is just below the nominal breakdown voltage of air between two sharp points, at a current density level usually referred to as the saturated corona current condition. This creates a high field gradient around the smaller, positively charged electrode. Around this electrode, ionization occurs, that is, electrons are stripped from the atoms in the surrounding medium; they are literally pulled right off by the electrode's charge.
This leaves a cloud of positively charged ions in the medium, which are attracted to the negative smooth electrode by Coulomb's Law, where they are neutralized again. This produces an equally scaled opposing force in the lower electrode. This effect can be used for propulsion (see EHD thruster), fluid pumps and recently also in EHD cooling systems. The velocity achievable by such setups is limited by the momentum achievable by the ionized air, which is reduced by ion impact with neutral air. A theoretical derivation of this force has been proposed (see the external links below).
However, this effect works using either polarity for the electrodes: the small or thin electrode can be either positive or negative, and the larger electrode must have the opposite polarity.[2] On many experimental sites it is reported that the thrust effect of a lifter is actually a bit stronger when the small electrode is the positive one.[3] This is possibly an effect of the differences between the ionization energy and electron affinity energy of the constituent parts of air; thus the ease of which ions are created at the 'sharp' electrode.
As air pressure is removed from the system, several effects combine to reduce the force and momentum available to the system. The number of air molecules around the ionizing electrode is reduced, decreasing the quantity of ionized particles. At the same time, the number of impacts between ionized and neutral particles is reduced. Whether this increases or decreases the maximum momentum of the ionized air is not typically measured, although the force acting upon the electrodes reduces, until the glow discharge region is entered. The reduction in force is also a product of the reducing breakdown voltage of air, as a lower potential must be applied between the electrodes, thereby reducing the force dictated by Coulomb's Law.
During the glow discharge region, the air becomes a conductor. Though the applied voltage and current will propagate at nearly the speed of light, the movement of the conductors themselves is almost negligible. This leads to a Coulomb force and change of momentum so small as to be zero.
Below the glow discharge region, the breakdown voltage increases again, whilst the number of potential ions decreases, and the chance of impact lowers. Experiments have been conducted and found to both prove and disprove a force at very low pressure. It is likely that the reason for this is that at very low pressures, only experiments which used very large voltages produced positive results, as a product of a greater chance of ionization of the extremely limited number of available air molecules, and a greater force from each ion from Coulomb's Law; experiments which used lower voltages have a lower chance of ionization and a lower force per ion. Common to positive results is that the force observed is small in comparison to experiments conducted at standard pressure. This is likely to be the result of the massively reduced number of ions produced by the experiment, although this could also be interpreted to be a different force entirely.
Further experimentation is necessary to validate the new theory as opposed to the solution provided by Coulomb's Law.
An article by Martin Tajmar (see below, or a summary) describes an experiment designed to test the possibility that this effect may need some other effect than ion winds for its explanation. No such effect was found, to the limit of experimental accuracy. In particular, no thrust could be observed in a vacuum. A similar device was tested in a vacuum in an episode of the Mythbusters with the same result.
Critics and supporters alike have called throughout the years for vacuum experiments, in order to eliminate ion wind contributions from the devices. While there have been a handful of such experiments, most notably the efforts of Dr. R.L. Talley in the late 1980s and early 1990s, there is still a great deal of discrepancy over whether the effect is directly related to gravity or not, mainly because it isn't predicted by conventional electrostatics or general relativity.[4]
T. T. Brown was granted a number of patents on his discovery:
Historically numerous patents have been granted for various applications of the effect, from electrostatic dust precipitation, to air ionizers, and also for flight. A particularly notable patent — U.S. Patent 3,120,363 — was granted to G.E. Hagen in 1964, for apparatus more or less identical to the later so called 'lifter' devices. Other ionic US patents of interest: 2022465, 2182751, 2282401, 2295152, 2460175, 2636664, 2765975, 3071705, 3177654, 3223038, 3120363, 3130945