Ballistic, Electrolytic, and Electrostatic Electronics
by Lawrence Kamm

We are accustomed to think of electric currents as electrons moving inside conductors or semiconductors for transmitting power or information. There are other electric currents and voltages with uses other than for transmitting power or information. Streams of electrons or ions moving through empty space, sometimes with electrostatic or electromagnetic forces acting on them, are ballistic electric currents and occur in several devices. Electric currents flowing through liquid electrolytes have several different effects. Electric voltages generating corona discharge have uses. Electric voltages applied to piezoelectric materials have other useful effects. Here are 10 specific examples:

1. The old fashioned vacuum tube has a stream of electrons moving through a vacuum from cathode to plate accelerated or decelerated by electrostatic force from the grid.

2. The cathode ray tube, our TV or computer monitor, has streams of electrons electrostatically accelerated from cathodes to the screen with their paths deflected up/down and left/right either by electrostatic force from pairs of plates between which they pass or (more commonly) by magnetic fields generated by currents in control windings. When they hit the phosphors on the screen their kinetic energy excites the phosphors to emit light.

3. The Williams tube was an early computer memory, now obsolete, in which a CRT deposited electric charges corresponding to computer code on the inside of the screen.

4. Electron beam welding is done by bombarding metals in a vacuum with an electron stream. The kinetic energy of the electrons heats the metals. The benefits are concentrated heat and operation away from atmospheric gasses.

5. A proposed rocket propulsion emits a fast stream of electrons as rocket exhaust. The benefit is high specific impulse, i.e. ratio of momentum to mass, to reduce the mass of the rocket's fuel.

6. The mass spectrograph accelerates a stream of positive ions rather than electrons and deflects the stream with a magnetic field. Ions of different mass are deflected differently and are thereby identified. Very large mass spectrographs were one of the methods used in the Manhattan Project to separate uranium isotopes.

7. High voltages create corona discharges which charge dust particles in Cottrell precipitators and then attract those particles out of the air.

8. Program steered electron beams cause hardening of materials in rapid prototyping machines.

9. Electric currents in liquids produce electro-deposition in some cases and electro-erosion in others (EDM machining).

10. Electric voltages without conduction current drive piezo-electric crystals in clocks, linear actuators, and ultrasonic actuators for cleaning, sonar, and abrasion machining.

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