An integrated three-dimensional sound-intensity probe

Abstract

The development of an integrated three dimensional sound intensity probe is discussed. Although a 3D sound-intensity probe exists, by integrating sensors into one chip the size can be reduced. A small sensor is preferable, because it enables the user to do measurements on small objects, very close to objects and with a minimum disturbance of the sound field. An investigation to particle velocity sensors is done. The results give insight in an optimum sensor configuration and the influence of some parameters. Following the design and fabrication of a 3D-particle velocity sensor is discussed. The expected direction of sensitivity did not match the observed direction perfectly and objects in the vicinity were responsible for this behavior. The deviation can be compensated for, either in signal processing or an adapted design. Furthermore a sound pressure sensitive device is developed. Instead of a membrane deflection principle a sound pressure –to- particle velocity transformer is used, and the particle velocity is measured. Integration of both sensor types on one chip can be achieved because the fabrication process is almost the same. Integrating the 3D particle velocity sensor with this sound pressure sensor results in a fully integrated three dimensional sound intensity sensor. Next, a sensor with four wires is developed, which has an improved self noise and a smaller size, enabling the development of an improved 3D sound intensity sensor. Instead of dicing chips from the wafer, a ‘break out’ design proves to be a good solution to separate the chips from the wafer. The use of a small connector is of great advantage over existing assembly methods. The integrated 3D sensor can be used to measure the sound field near (small) sound sources. In an experiment demonstrating this it is also demonstrated that measuring particle velocity near a sound source has advantages compared to measuring the sound pressure. Measuring sound intensity is normally done by a sound intensity analyzer. With the use of a small analyzer near the sensor a small sound intensity system is made, expandable to a large array.