A novel beamformer for circular sonar arrays
A new Beamformer (BF) technique using Linear Deltamodulation (DM) on the spatially sampled circular array sensor signals is presented. In this method, the FIR-type of beam-former implementation for circular arrays results in an extremely simplified hardware which does away with multipliers and retains basically adders. Thus, the immediate problem of large word-size is considerably resolved. The DM-type of BF by virtue of the implementation, provides an additional advantage of beam-space interpolation. Various aspects of array gain, sidelobes and noise performance are dealt with the help of simulation studies. Hardware structures both for fixed and programmable beamformer coefficients are also proposed which bring out the potential of this technique for compact sonar systems.
Effects of Signal Quantization on the Performance of Multichannel Processing Systems
This paper determines the effects of amplitude quantizing on the performance of conventional or optimum multichannel space, time signal‐processing systems, with emphasis on underwater acoustic applications. The system output signal‐to‐disturbance ratio is chosen as the performance criterion. The selection of proper analog‐to‐digital conversion parameters is influenced both by the characteristics of the system and the characteristics of external fields in which the system is operating. The external disturbance is assumed to consist of sonar self‐noise, which included ambient sea noise and noise generated by nearfield noise sources, plane‐wave interference, reverberation, or, in general, any combination of these. Through the use of representative assumptions on the statistical properties of external fields in space and time domain, some useful criteria for selecting the parameters of quantization are derived.
Right coronary artery stenosis associated with tricuspid valve ring annuloplasty
A 70-year-old man with severe symptomatic functional mitral valve regurgitation underwent successful mitral valve repair combined with tricuspid valve ring annuloplasty. Pre-operative coronary angiography (CAG) showed no significant stenosis. One-and-a-half years later, the patient presented with an acute exacerbation of heart failure. Repeat CAG demonstrated tight stenosis in the right coronary artery (RCA) with arterial kinking that corresponded to the same point as the stenosis where the RCA is the closest to the tricuspid valve ring. The new lesion probably occurred as a consequence of the tricuspid valve ring annuloplasty.