IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, . 61, . 5, MAY 2014 792 0885–3010 © 2014 IEEE A Volumetric CMUT-Based Ultrasound Imaging System Simulator With Integrated Reception and μ-Beamforming Electronics Models Giulia Matrone, Member, IEEE, Alessandro S. Savoia, Member, IEEE, Marco Terenzi, Giosuè Caliano, Senior Member, IEEE, Fabio Quaglia, and Giovanni Magenes, Member, IEEE Abstract—In modern ultrasound imaging devices, two-di- mensional probes and electronic scanning allow volumetric im- aging of anatomical structures. When dealing with the design of such complex 3-D ultrasound (US) systems, as the number of transducers and channels dramatically increases, new chal- lenges concerning the integration of electronics and the imple- mentation of smart micro-beamforming strategies arise. Hence, the possibility to predict the behavior of the whole system is mandatory. In this paper, we propose and describe an advanced sim- ulation tool for ultrasound system modeling and simulation, which conjugates the US propagation and scattering, signal transduction, electronic signal conditioning, and beamforming in a single environment. In particular, we present the architec- ture and model of an existing 16-channel integrated receiver, which includes an amplification and micro-beamforming stage, and validate it by comparison with circuit simulations. The de- veloped model is then used in conjunction with the transducer and US field models to perform a system simulation, aimed at estimating the performance of an example 3-D US imag- ing system that uses a capacitive micromachined ultrasonic transducer (CMUT) 2-D phased-array coupled to the modeled reception front-end. Results of point spread function (PSF) calculations, as well as synthetic imaging of a virtual phantom, show that this tool is actually able to model the complete US image reconstruction process, and that it could be used to quickly provide valuable system-level feedback for an opti- mized tuning of electronic design parameters. I. I A  ultrasound (US)-based imaging systems at the state of the art allow 3-D real-time (4-D) visu- alization of moving anatomical structures [1], [2], thanks to two-dimensional phased arrays of piezoelectric trans- ducers and electronic volume scanning [3], [4]. In these systems, beam generation, focusing, and steering in both azimuth and elevation directions is entirely managed by the device electronics [5]; moreover, digital beamforming is implemented on dedicated very large scale integrated (VLSI) circuits [6]. This makes it possible to achieve high frame rates together with dynamic focusing and thus bet- ter image resolution and depth of field. The design of a volumetric imaging system still poses some challenges and critical technological aspects to be addressed, such as transducer fabrication, arrangement, and interconnection, the need for a high dynamic range and very-low-noise front-end reception circuitry, electron- ics size, power constraints, and higher frame rates for 4-D imaging (e.g., cardiac) applications. To enable 3-D real-time imaging and to achieve good performance from an acoustic point of view, in fact, the transducer array should be spatially sampled at less than one-half wave- length pitch (a fully populated array). Thus, the number of transducers and channels must be increased to the or- der of thousands, even for small apertures, which leads to practical wiring problems. Connecting all channels to the main system through coaxial cables, as traditional systems do, would definitely be unfeasible [7]. Moreover, the direct coupling between the transducer array elements and the cables severely reduces the SNR of the received signals. For these reasons, in modern US scanners, the trend toward miniaturization is leading to the integration of the electronics and some signal processing abilities directly within the probe handle and in close contact with the transducer array to enable 3-D imaging [5], [8]. This ten- dency can be further facilitated by MEMS-based capaci- tive micromachined ultrasonic transducer (CMUT) tech- nology [9]. CMUTs are very appealing because of their high compatibility with microelectronic technologies [10], which makes their employment (in certain applications) preferable to traditional piezoelectric technology [11]–[13]. A smart solution for addressing this challenge and par- tially solving wiring problems is to reduce the effective number of channels to be routed to the main imaging system, by implementing and integrating a first stage of beam-formation [called micro (μ)-beamforming] on a front-end application-specific integrated circuit (ASIC) placed inside the probe, close to the transducer array [14]– [17]. Basically, the μ-beamformer is in charge of delaying and summing the signals received by the transducers, af- ter being properly conditioned. μ-beamformers operate a fine realignment of the echoes received by each small sub- aperture inside the array (Fig. 1); then, at a higher level, the main beamformer combines these signals into a unique Manuscript received December 12, 2013; accepted February 19, 2014. G. Matrone and G. Magenes are with the Dipartimento di Ingegneria Industriale e dell’Informazione, Università degli Studi di Pavia, Pavia, Italy (e-mail: giulia.matrone@unipv.it). A. S. Savoia and G. Caliano are with the Dipartimento di Ingegneria, Università degli Studi Roma Tre, Rome, Italy. M. Terenzi and F. Quaglia are with STMicroelectronics, Cornaredo (Milan), Italy. DOI http://dx.doi.org/10.1109/TUFFC.2014.2971