Feedforward Harmonic Suppression for Noise Control of Piezoelectric Synthetic Jet Actuators 2023-01-1042

Piezoelectric Synthetic Jet Actuators (PSJAs) are a class of pulsatile flow generation devices that promises to improve upon steady forced cooling methods in air flow generation, surface cleaning and heat transfer applications. Their acoustic emissions and vibrations, an intrinsic by-product of their operation, needs to be mitigated for applications in noise-sensitive contexts. Already used for in aerodynamic control [1], thrust vectoring [2], spray control [3], and heat transfer [4, 5], they are being considered for sensor lens cleaning in automobiles. In this study, the sound generation mechanisms of PSJAs were investigated. Driven with a single frequency sinusoidal input, PSJAs produce undesirable emissions at harmonic frequencies within the frequency range of speech communication. The sound pressure levels of these emissions may exceed allowable levels standard in industry. Previous attempts at noise control include passive strategies, such as, nozzle design [6, 7], enclosure design [8], and mufflers [4]. Active strategies, such as out-of-phase actuator pairs [9, 10], and signal modulation have also been considered. These strategies provide baseline noise reduction, but further reduction is possible by specifically targeting prominent frequencies in the emissions. This study found that feedforward active control, achieved through input harmonic tuning, resulted in significant drops in the loudness of the radiated sound with minimal effect on flow through performance. Individual harmonics are directly fed into the driving signal through the addition of phase-shifted amplitude-adjusted harmonic signals. Acoustic emissions from some harmonics could be reduced to background levels using this method. This method could be developed into ad hoc input tuning which will enable long-term applications of the device.