The Biefeld–Brown effect is an electrical occurrence first observed by inventor Thomas Townsend Brown in the 1920s. This effect happens when high voltage is applied to the electrodes of an unevenly shaped capacitor, creating a pushing force that moves toward the smaller electrode. Brown thought this force might be related to anti-gravity and called it electrogravitics, a term that combines electricity and gravity. Later experiments in vacuum chambers could not reproduce Brown's results. Scientists later found that the force measured was likely caused by corona wind, which occurs during electrical discharges.

Overview

The Biefeld–Brown effect is often believed to create an ionic wind that moves surrounding neutral particles. This effect occurs when high voltage is applied to an asymmetric capacitor, which has two electrodes of unequal size. When the capacitor is charged to very high electrical potentials, a force is created that pushes the negative electrode away from the positive electrode.

Using an asymmetric capacitor, where the negative electrode is larger than the positive electrode, allows more thrust to be generated in the direction from the area with less electrical charge to the area with more electrical charge. These capacitors are called Asymmetrical Capacitor Thrusters (ACT). These devices are used in ionocrafts and lifters, which create thrust in the air using electrical power. They do not require fuel or moving parts to operate.

History

The "Biefeld–Brown effect" was the name given to a discovery made by Thomas Townsend Brown during the 1920s while he was still in high school. Brown was experimenting with X-ray tubes, and when he applied a strong electrical charge to a Coolidge tube placed on a scale, he noticed that the tube's weight changed depending on its position. This suggested there was a force acting on it. Brown believed this force might be related to gravity and designed a system to create motion using this idea. On April 15, 1927, he applied for a patent called "Method of Producing Force or Motion," which described using electricity to control gravity and create movement. In 1929, he wrote an article for the magazine Science and Invention that explained his work. The article also described a device called the "gravitator," which Brown claimed could move without using electricity, gears, or wheels, instead relying on a concept he called "electro-gravitation." He also said that unevenly shaped capacitors could create fields that interacted with Earth's gravity and imagined future uses like moving ships and spacecraft.

At some point, this effect was also called the "Biefeld–Brown effect," likely to link it to Paul Alfred Biefeld, a physics professor at Denison University. Brown studied at Denison for a year but left before completing his education. There is little evidence that he worked with Biefeld, and Denison University has no records of such experiments or a connection between Brown and Biefeld.

In 1960, Brown filed another patent titled "Electrokinetic Apparatus," where he used the term "electrokinesis" to describe the Biefeld–Brown effect, connecting it to the study of how electricity affects fluids. He also believed the effect could produce an anti-gravity force, which he called "electrogravitics." However, there is little proof to support his claims about anti-gravity. In 1965, he filed a patent stating that uneven capacitors could create force even in a vacuum, but no experiments have confirmed this.

In 1988, R. L. Talley tested electrodes similar to Brown’s in a low-pressure environment and found no thrust. However, he did observe force during electrical breakdown. In 2004, Tajmar tested the same setup in a vacuum and found no movement, suggesting the Biefeld–Brown effect is actually a known phenomenon called "corona wind."

Effect analysis

The effect is generally believed to depend on corona discharge, a process that allows air molecules to become charged near sharp points or edges. Typically, two electrodes are used, with a high voltage between them. The voltage can range from a few thousand volts up to millions of volts. One electrode is small or sharp, while the other is larger and smoother. The most effective distance between the electrodes occurs when the electric field is about 10 kV/cm. This is just below the voltage at which air usually breaks down between two sharp points, a condition known as the saturated corona current. This creates a strong electric field around the smaller, positively charged electrode. Ionization occurs near this electrode, meaning electrons are pulled from the atoms in the surrounding air by the electrode's charge.

This leaves a group of positively charged ions in the air, which are attracted to the larger, negatively charged electrode by Coulomb's law. At the larger electrode, the ions lose their charge. This process creates an opposing force on the smaller electrode. This effect can be used for propulsion (such as in EHD thrusters), fluid pumps, and EHD cooling systems. The speed achieved by these systems is limited by the momentum of the ionized air, which is reduced when ions collide with neutral air molecules. A theoretical explanation of this force has been proposed (see the external links provided).

This effect works regardless of the polarity of the electrodes. The smaller electrode can be either positive or negative, while the larger electrode must have the opposite charge. In some experiments, it is reported that the thrust produced is slightly stronger when the smaller electrode is positively charged. This may be due to differences in the energy required to create ions and the energy released when ions form, depending on the air's composition.

As air pressure decreases, several factors reduce the force and momentum available. Fewer air molecules are present near the ionizing electrode, which reduces the number of ions created. At the same time, fewer collisions occur between ions and neutral air molecules. Whether this increases or decreases the maximum momentum of the ionized air is not usually measured. However, the force acting on the electrodes decreases until the system enters the glow discharge region. The reduction in force is also linked to the lower breakdown voltage of air at lower pressures, which requires a smaller voltage between the electrodes. This reduces the force described by Coulomb's law.

In the glow discharge region, air becomes a conductor. Although the voltage and current travel nearly as fast as light, the movement of the conductors is almost nonexistent. This results in a Coulomb force and momentum change so small that they are effectively zero.

Below the glow discharge region, the breakdown voltage increases again, while the number of potential ions decreases, and the chance of collisions is lower. Experiments have shown both the presence and absence of force at very low pressures. It is likely that successful experiments used very high voltages, which increased the chance of ionizing the limited number of air molecules and produced greater force per ion. However, the force observed in these cases is usually smaller compared to experiments conducted at normal air pressure.