| dc.description.abstract | Humans can localize a sound source with the help of three effects, Head Related Transfer Function (HRTF), Interaural Time Difference (ITD) and Interaural Level Difference (ILD). With help of these three effects humans can sense where in the space the signal is coming from. The space can be de- scribed by three planes: vertical-, horizontal- and median plane. Sound loc- alization is described by three dimensions: azimuth angle, elevation angle and distance or velocity detection for static or moving source. Diffraction of sound by human head is described by the diffraction formula. The sound is diffracted by the human head if the dimension of the head is smaller compared to 2λ/3. Sonar means Sound Navigation and Ranging, and has its roots from as early as the beginning of World War I. Sonar technology was actively used under World War I and World War II, and had an increase of interest among the scientists after this period. Sound is pressure perturbations that travels as a wave spreads spherically or cylindrically in the water by describing the decrease of the signal. Sound propagation is affected by absorption, re- fraction, reflection and scattering. There are three types of sonar equations described in this thesis, the active sonar equation for noise background, the active sonar equation for reverberation background and the passive sonar equation. In sonar the distance to the sound source is calculated by the travel time and the sound velocity of the incoming sound wave. Sound velocity in water is divided into four different regions and is temperature dependent. For circu- lar and spherical arrays, (just like the human head), the sound wave travels direct to the receiver as long as the elements has a "direct" path to the re- ceiver. Otherwise the sound signal is diffracted and travels along the sur- face of the transducer (with different sound velocity from as in water) until it has a "direct" path to the receiver. This has its limitations, and for some rotational angle on the transducer the sound wave is not possible to detect. This angle limitation depends on the normalized frequency μ = ka = 2πa/λ value. where a is radius of the circular transducer. In this thesis I m going to study at which rotational angle α the signal disappears when sending a sound signal pulse with frequency f = 100k H z and a normalized frequency μ = 25, and compare it with human listening. | eng |