Investigation of resolution and microphone size for measurements of airborne ultrasound

The growth of ultrasound technologies has entailed the presence of airborne ultrasound emissions in industry and public and private spaces. For occupational safety and health, procedural and technical recommendations are needed that allow measurements to be performed in the field within a short time and with little effort. This study aims to answer two research questions concerning the minimum spatial resolution and microphone size required to determine a spatial distribution of sound pressure levels with sufficient accuracy within a given measurement uncertainty. The investigation focused on high spatial resolution datasets of the airborne ultrasound field of an ultrasonic welding machine acquired using a laboratory measuring system. Based on these datasets, datasets with lower resolutions were generated and measurements with microphones of different sizes were simulated. Subsequently, four different methods of parameterization were applied to the datasets to characterize the airborne ultrasound field with respect to the structure and sound pressure levels. Comparing the parameters of datasets with high precision (high resolution and small microphone size) to those of datasets with reduced precision (lower resolution and larger microphone size) allowed a quantitative assessment of the influence of the reduction in precision. Corresponding recommendations on resolution and microphone size are given.