A non-conventional acoustic transduction method using fluidic laminar proportional amplifiers

Abstract

Pressure sensing using fluidic laminar proportional amplifiers (LPAs) was developed at Harry Diamond Laboratories in the late 1970s and was applied to acoustic detection and amplification. LPAs use a partially constrained laminar jet of low-pressure air as the sensing medium, which is deflected by the incoming acoustic signal. LPA geometries enable pressure gain by focusing incoming pressure fluctuations at the jet’s nozzle exit, thereby applying leverage to create jet deflection over its short transit toward a splitter. With no input signal, the jet is not deflected and downstream pressures on both sides of the splitter are equal. A differential input signal of magnitude one, referenced to ambient pressure balancing the opposite side of the jet, produces an differential output signal of magnitude ten. This amplified signal can be differentially fed into the inputs on both sides of the next LPA for additional gain. By cascading LPAs together, very small signals can be amplified a large amount. Originally, a DC pressure amplifier, LPAs have exceptional infrasound response, and excellent sensitivity since there is no mass or stiffness associated with a diaphragm, and is matched to the environment. Standard microphones at the output ports can take advantage of increased sensitivity and gain.