Rayette Ann Fisher

A comparative study of central and distributed MPPT architectures for megawatt utility and large scale commercial photovoltaic plants

In this paper different distributed PV architectures are studied from an energy yield perspective. These distributed architectures are applied to massively paralleled thin film plants employing high voltage PV modules, mc-Si plants with long series strings of low voltage modules and plants with medium voltage thin film modules in order to evaluate the effectiveness of the distributed architecture in each case. The effects of partial shading, module mismatch and cable losses are quantified in order to obtain the energy yield for each of the architectures under study. The results of this trade-off study are used to quantify the benefits of a distributed architecture as well as determine the optimal location of the dc/dc converters that perform the MPPT function.

Reconfigurable arrays for portable ultrasound

A collaborative effort is aimed at the development of reconfigurable array technology. The goal is to enable innovative medical ultrasound imagers ideally suited for portable ultrasound and applications such as remote emergency medicine and combat casualty care. Success depends on developing several technologies, the first of which is capacitive micromachined ultrasound transducers (cMUTs). The monolithic nature of cMUTs facilitates close connection with microelectronics. Thus a second technology under development is a switch matrix application specific integrated circuit (ASIC) that will enable the changing of interconnect between cMUT cells. The reconfigurable array concept arises from this ability to dynamically combine cMUT cells to form ideal apertures for a given imaging target (e.g. annular and phased apertures of various ring widths) and to move these apertures across the reconfigurable array plane [1-4]. Two central hypotheses are being tested: (1) the reconfigurable array can acquire acoustic pulse-echo data in a manner equivalent or superior to today’s 1D piezoceramic arrays (2) reconfigurable array technology will enable highly portable ultrasound platforms. Keywords-reconfigurable; annular; array; cMUT; ASIC; switch matrix; dynamic; phased; real-time

Multi-row linear cMUT array using cMUTs and multiplexing electronics

A large area reconfigurable imaging array for research purposes is being developed with co-integrated cMUTs and control electronics. The goal is a 2.5cm 2D tileable module with ≫16,000 transducer sub-elements spaced at a pitch of 185um in X and Y dimensions. As a prototype demonstration of some of the goals of this effort, a multi-row linear array using cMUTs and external multiplexing electronics was designed and fabricated. In this paper the challenges of trenched cMUT attach to a laminate interposer as part of a tileable module will be discussed. The architecture of the tileable module build-up for manufacturability, reliability, acoustic planarity, and reduced spacing between tiles and cMUT chips will also be addressed. Finally, a first prototype will be shown and experimental acoustic results with the new cMUT-based probe will be presented.

5F-2 Packaging and Design of Reconfigurable Arrays for Volumetric Imaging

Recent advances in capacitive micromachined ultrasound transducers (cMUTs), piezoceramic acoustic stack design, and transducer-to-electronics integration are enabling the fabrication of highly integrated reconfigurable ultrasound arrays. Reconfigurability in this context refers to the ability to reorganize the array elements in any configuration deemed desirable. Attractive configurations are an annular array, which can be translated electronically along a 2D array surface, or a phased array whose element orientation and pitch can be varied to optimize an image [1-6]. Further, annular array configurations make possible 3D-stacked miniaturized systems by reducing channel count, system size, and power consumption. In addition to such benefits, the annular array also provides dynamic axisymmetric focusing for excellent image quality. Several methods of integration have been explored to realize stacked transducer arrays with low channel count. Key components of the design include advanced interconnect such as through silicon vias in cMUTs and z-axis backing stacks, switch matrix application specific integrated circuits (ASICs), and high density multi-layer flex.

Hybrid beamforming and steering with reconfigurable arrays

Reconfigurable arrays offer an advantage over traditional ultrasound arrays because of their flexibility in channel selection. To improve ultrasound beamforming and coverage through beam steering, we propose a hybrid beamforming technique to elongate the depth of focus of transmit beams and a method of element selection that improves steering capabilities that take advantage of array reconflgurability using annular rings. A local minimization technique to optimize the hybrid aperture is discussed in this paper. The chosen hybrid apertures covering four focal zones result in improved range in depth of focus when compared with pure spherical beams via point spread functions (PSF) and lesion signal-tonoise ratio (LSNR) calculations. Improvements were statistically significant at focal depth extremes. Our method of beam steering utilizing a quantized phase delay selection to minimize delay errors indicated better performance by removing an artifact present with traditional ringed element selection.

2B-1 Solutions for Reconfigurable Arrays in Ultrasound

A reconfigurable array may involve a relatively large 2D array of transducer sub-elements and a layer of electronics which uses switches to connect certain sub-elements together, to a single system channel [Fischer et al., 2005 and Thomenius et al., 2005]. An annular array pattern, consisting of ring-shaped element groups, may be electronically scanned, or stepped, across the surface of such a reconfigurable array. The array could use 20 to 32 system channels and provide image quality comparable to a 128 channel linear array [Hazard et al., 2003 amd Dietz et al., 1979], This paper discusses some of the unique challenges and solutions pertaining to reconfigurable two-dimensional ultrasound arrays. Size constraints of the electronics result in some non-ideal aspects to the switch array; namely, there are constraints on the distribution of system channel access points across the array, and that these switches have a certain on-resistance which introduces non-ideal signal propagation delays. Some solutions will be discussed in this paper which aim to reduce the effect of these non-ideal constraints, and may suggest certain design tradeoffs which can be made in the design of future reconfigurable switch arrays

Reconfigurable mosaic annular arrays

Mosaic annular arrays (MAA) based on reconfigurable array (RA) transducer electronics assemblies are presented as a potential solution for future highly integrated ultrasonic transducer subsystems. Advantages of MAAs include excellent beam quality and depth of field resulting from superior elevational focus compared with 1-D electronically scanned arrays, as well as potentially reduced cost, size, and power consumption resulting from the use of a limited number of beamforming channels for processing a large number of subelements. Specific design tradeoffs for these highly integrated arrays are discussed in terms of array specifications for center frequency, element pitch, and electronic switch-on resistance. Large-area RAs essentially function as RC delay lines. Efficient architectures which take into account RC delay effects are presented. Architectures for integration of the transducer and electronics layers of large-area array implementations are reviewed.

Packaging and modular assembly of large-area and fine-pitch 2-D ultrasonic transducer arrays

A promising transducer architecture for largearea arrays employs 2-D capacitive micromachined ultrasound transducer (CMUT) devices with backside trench-frame pillar interconnects. Reconfigurable array (RA) application-specified integrated circuits (ASICs) can provide efficient interfacing between these high-element-count transducer arrays and standard ultrasound systems. Standard electronic assembly techniques such as flip-chip and ball grid array (BGA) attachment, along with organic laminate substrate carriers, can be leveraged to create large-area arrays composed of tiled modules of CMUT chips and interface ASICs. A large-scale, fully populated and integrated 2-D CMUT array with 32 by 192 elements was developed and demonstrates the feasibility of these techniques to yield future large-area arrays. This study demonstrates a flexible and reliable integration approach by successfully combining a simple under-bump metallization (UBM) process and a stacked CMUT/interposer/ASIC module architecture. The results show high shear strength of the UBM (26.5 g for 70-μm balls), high interconnect yield, and excellent CMUT resonance uniformity (s = 0.02 MHz). A multi-row linear array was constructed using the new CMUT/interposer/ASIC process using acoustically active trench-frame CMUT devices and mechanical/ nonfunctional Si backside ASICs. Imaging results with the completed probe assembly demonstrate a functioning device based on the modular assembly architecture.

Optimization of beams with nonspherical extended depths of focus for reconfigurable 2D arrays

The flexibility of reconfigurable 2D arrays allows us to utilize various beamforming techniques with a limited number of channels. We investigated a different beamforming technique incorporating spherical and axicon focusing to attain an extended range of focus in the transmit beam. In this paper, we develop and optimize this hybrid beamforming technique for balance between range and image quality. A local minimization technique is discussed and four apertures chosen to cover a 4.5 cm depth for breast imaging were compared to pure spherical beams via PSF and CNR calculations. Improvements were statistically significant at focal depth extremes.