UHF - Abbreviation for "ultra high frequency.
ultrasonic - Signals that are just above the frequency range of human hearing of approximately 20 kHz.
uncharged - Material having atoms with the same number of electrons in orbit as the number of protons in the nucleus. Having no electrical charge.
unijunction transistor - Three terminal device that acts as a diode with its own internal voltage divider biasing circuit.
unity gain frequency - Frequency of operation for a device where the gain of the component drops to unity.