Laser-based primary calibration for microbarometers

In previous work, the National Center for Physical Acoustics at the University of Mississippi designed and built a large chamber for secondary (referenced) calibration of microbarometers. Sandia National Laboratories (SNL) then refined and implemented this chamber at their Facility for Acceptance, Calibration, and Testing (FACT) site. These large chambers incorporate moving coil loudspeakers capable of operating in receive and transmit modes, and in more recent work, Penn State University (PSU) and SNL used these loudspeakers to implement a reciprocity-based primary (non-referenced) calibration technique. Unfortunately, while this technique has been shown to have suitable uncertainty above 0.05 Hz, uncertainty increases rapidly below this frequency. Due to this, the authors are investigating a new chamber-based calibration technique that may provide better results within the 0.01–0.05 Hz band. This method uses a laser-based sensor to monitor loudspeaker displacement, in combination with a model of the acoustic chamber, to estimate the acoustic pressure at a sensor under test. The use of these two calibration methods may enable primary calibration over the full band of interest (0.01–10.0 Hz) and lend credence to each method. This talk will discuss low-band calibration challenges, the laser-based method, and calibration results.