Calculations of the Sound Scattering of Hyperbolic Frequency Modulated Chirped Pulses from Fluid-filled Spherical Shell Sonar Targets

摘要

The theory of the sound pressure scattered from a fluid-filled spherical shell immersed in a second fluid is developed for the case of ensonification with hyperbolic frequency modulated chirped pulses. Hyperbolic frequency modulation is also known as 'linear period modulation' and 'logarithmic phase modulation'. The theory is used to calculate the target strength of a stainless steel shell filled with a mixture of Freon-113(trade mark) and ethanol, and immersed in sea water. The sensitivity of the target strength to pulse centre frequency, pulse bandwidth, pulse length and fluid temperature is examined and significant sensitivity is found in some cases, especially for temperature. The signal reflected by the target is shown as a function of time, and the results of correlating the return with a replica of the transmitted signal are also shown. Comparison is made with a solid stainless steel sphere and air-filled spherical shells, and similar parameter sensitivity is found, with the exception that their target strengths are insensitive to temperature.