Are Cordless Wristbands Suitable for the Electronics Industry?
Cordless wristbands theoretically utilize corona discharge to dissipate some static electricity. Corona discharge, also known as tip discharge, refers to the discharge of static electricity from the tip of a charged conductor (typically requiring a voltage exceeding 1500V) to the air. However, the required voltage for dissipating static electricity in cordless wristbands is too high, making them unsuitable for the electronics industry, as few electronic components can withstand voltages exceeding 1500V.
Corona Discharge
Corona discharge is a localized, self-sustaining discharge of a gaseous medium in a non-uniform electric field. It is the most common form of gas discharge. Near a pointed electrode with a large radius of curvature, the local electric field strength exceeds the ionization field strength of the gas, causing ionization and excitation, resulting in corona discharge. When corona occurs, a bright light can be seen around the electrode, accompanied by a hissing sound. Corona discharge can be a relatively stable form of discharge or an early stage in the breakdown process of a non-uniform electric field gap.
The formation mechanism of corona discharge varies depending on the polarity of the tip electrode, primarily due to differences in the accumulation and distribution of space charge during corona discharge. Under DC voltage, both negative and positive corona discharges accumulate space charge near the tip electrode. In a negative corona discharge, after electrons undergo collisional ionization, they are driven away from the tip electrode, forming negative ions, while positive ions accumulate near the electrode surface. As the electric field intensifies, positive ions are drawn into the electrode, resulting in a pulsed corona current, while negative ions diffuse into the interstitial space. This process repeats itself, initiating another cycle of ionization and charged particle movement. This cycle continues, resulting in numerous pulsed corona currents. This phenomenon was discovered by G.W. Tritcher in 1938 and is known as the Tritcher pulse. If the voltage continues to increase, the pulse frequency and amplitude of the corona current increase, transforming into a negative glow discharge. Further voltage increases result in a negative streamer discharge, also known as a feather discharge or brush discharge due to its shape. When negative streamer discharge continues to develop to the opposite electrode, it leads to spark discharge, causing the entire gap to break down. Positive corona discharge also presents positive ions near the tip electrode, but these are continuously repelled into the gap space, while electrons are attracted into the electrode, similarly forming a repetitive pulsed corona current. As the voltage continues to rise, streamer discharge occurs, which can lead to gap breakdown.
The discharge process of AC corona at power frequency is basically the same as that of DC positive and negative corona during the positive and negative half-cycles. The power frequency corona current is in phase with the voltage, reflecting corona power loss. In engineering applications, the relationship between the applied voltage and the amount of corona charge is often used to represent corona characteristics, known as the volt-coulomb characteristic of corona. In reality, surface conditions of the conductor, such as damage, raindrops, and deposits, can easily cause corona discharge.
Corona discharge has various impacts in the field of engineering technology. Corona discharge on high-voltage and ultra-high-voltage transmission line conductors in power systems can cause corona power loss, radio interference, television interference, and noise interference. When designing circuits, sufficient conductor cross-sectional area should be selected, or split conductors should be used to reduce the surface electric field of the conductors to avoid corona discharge. For high-voltage electrical equipment, corona discharge will gradually damage the insulation performance of the equipment. Under certain conditions, the space charge of corona discharge can also increase the gap breakdown strength. When lightning or switching overvoltage occurs in the line, the overvoltage amplitude can be weakened due to corona loss. Corona discharge can be used for electrostatic dust removal, sewage treatment, air purification, etc. Corona discharge of sharp objects such as trees on the ground under the influence of the earth's electric field is an important link in atmospheric electrical balance. Corona discharge on water droplets splashed on the ocean surface can promote the generation of organic matter in the ocean and may also be one of the effective discharge forms for pre-synthesis of amino acids in the ancient atmosphere of the earth. Corona discharge is a technically significant research topic for different applications.