Development of an Acoustic Energy Density Probe Calibrator

An acoustic energy density probe is a sensor that uses multiple pressure transducers to measure acoustic energy density. Calibrating each pressure transducer an acoustic energy density probe at the same time is a difficult problem because the pressure transducers have a unique location and orientation. Two main issues arise that are involved in simultaneous calibration. The first issue is a uniform pressure issue. It arises from subjecting each microphone on the probe to the same known source at the same time because pressure is a function of distance and direction. The second issue is a seal issue. It arises from the probe/calibrator interface which must be sealed the same each time at each probe microphone. The probe of interest for this research is spherically shaped with four pressure transducers mounted in the sphere. A shaft used to connect the sphere to DSP hardware and house the transducer wires is mounted in the sphere. The axis of this shaft is the natural axis of the sphere. One microphone is mounted on the opposite side of the sphere as the shaft, and shares the same axis as the shaft. This microphone is known as the pole microphone. The other three transducers are located 68.75 ̊ off the axis of the probe shaft as measured form the pole microphone. These three side microphones are spaced equally around the sphere at 120 ̊ increments. All four microphones are oriented tangent to the surface of the sphere at their locations. The unique microphone locations are the source of the probe/calibrator interface issues. These probes were designed to be directionindependent. This means that the orientation of the probe relative to the direction of the sound field does not affect the probe’s ability to accurately measure acoustic energy density. In order for the probe to accurately measure acoustic energy density and be direction independent, each microphone must be accurately calibrated.