Hartmann Oscillator

a gas-jet radiator of sonic and ultrasonic waves. The basic part of the oscillator is the nozzle, from which gas under a pressure p > 0.2 meganewtons per sq m (1.93 atmospheres) emerges at supersonic speed; in the process the gas jet creates compression and rarefaction waves. If a resonator is placed in this flow coaxially with the nozzle at a certain distance, sonic and ultrasonic waves are radiated. The frequency of the acoustic radiation is a function of the distance between the nozzle and the resonator and also of the size of the resonator. The most favorable conditions for radiation occur when the diameter of the nozzle’s output hole, the diameter of the resonator’s inlet, and the length of the inlet are all equal to each other.

Hartmann oscillators can radiate up to several dozen watts of acoustic power. If compressed air (from a tank or compressor) is blown through the nozzle, frequencies ranging from 5 or 6 kilohertz up to 120 kilohertz can be obtained. By using hydrogen in place of air, frequencies up to 500 kilohertz can be reached.

The Hartmann oscillator was named after its Danish inventor, J. Hartmann (1881-1951).