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Yayın Subarray delta-sigma beamforming for ultrasonic imaging(IEEE, 2002) Bilge, Hasan Şakir; Karaman, MustafaWe present a beamforming architecture based on subarray processing with non-uniform oversampling 1-bit delta-sigma (??) modulation. The subarray processing combines conventional phased array and synthetic aperture approaches to form a large aperture using small subarrays thus reduces active channel count. ??-based beamforming improves the efficiency of front-end processing further: oversampling permits precise delaying and single bit data processing simplifies beamforming operation. To reduce the number of firings we use a low beam density associated with the subarray size, and then increase the beam density by lateral interpolation prior to coherent beam summation. Our experimental test results show that the proposed scheme provides high-resolution beamforming while simplifying the front-end.Yayın A lumped circuit model for the radiation impedance of a 2D CMUT array element(IEEE, 2005) Bozkurt, Ayhan; Karaman, MustafaElements of a 2D array used for 3D acoustic imaging have dimensions smaller than half of the acoustic wavelength due to the Nyquist criteria for spatial sampling. Therefore, analyses involving circuit models for the array elements have to account for the reactive part of the radiation impedance of the array element. In this paper, we introduce a lumped circuit model for the complex radiation impedance of a 2D CMUT array element. Using the finite element method (FEM) we first show that the radiation impedance of the array element is identical to that of a plane piston transducer of comparable dimensions. Then, we show that the complex radiation impedance of the 2D array element can be represented by a simple resonant circuit placed parallel to the real radiation impedance in the Mason's equivalent circuit. The component values of the reactive lumped elements forming the resonant circuit were determined by fitting the impedance of overall equivalent circuit to the FEM results using the Nelder-Mead minimization algorithm.
