MTL Annual Report

The Capacitive Micromachined Ultrasound Transducer (CMUT) is an alternative to traditional piezoelectric transducers. The CMUT technology provides an opportunity for highly integrated ultrasound-imaging system solutions because of its CMOS compatibility, ease of large array fabrication, and improved bandwidth and sensitivity performance ^[1].

Figure 1: The architecture of a 3D ultrasound imaging system with CMUT devices.

This project aims to provide a highly flexible platform for 3D ultrasound imaging. Figure 1 presents the system architecture. The CMUT device is flip-chip bonded to the supporting electronic circuits, which eliminates the cables that are usually required by traditional systems between the piezoelectric transducers and circuits. As a result, the channel count of the imaging system is increased and the capacitive loading due to cables is greatly reduced. The transmitters in the system are reconfigurable to implement Tx Beamforming; the analog front-end receivers and the DSP perform various Rx Beamforming algorithms from the received echo waveforms.

The transmitters generate high-voltage electric pulses to drive the CMUT device. The pulse magnitude should be as large as the process allows, with programmable pulse frequency at 1~10MHz and pulse duration at about 0.5~20us. In order to further increase the transmitted signal power within the transducer bandwidth, transmitter pulse-shaping is desirable. Direct waveform synthesis ^[2] or PWM modulation ^[3] are possible realizations of the transmitter pulse-shaping.

We will implement a 2D ultrasound-imaging system based on a 1D transducer and corresponding electronics as the first step. Afterwards, a 3D ultrasound-imaging system using 2D transducers will be investigated.

1. O. Oralkan, “Acoustical Imaging Using Capacitive Micromachined Ultrasonic Transducer Arrays: Devices, Circuits, and systems,” Ph.D. dissertation, Stanford University, Palo Alto, CA, 2004. [↩]
2. P. Mercier, D. Daly, and A. Chandrakasan, “An Energy-Efficient All-Digital UWB Transmitter Employing Dual Capacitively-Coupled Pulse-Shaping Drivers,” IEEE Journal of Solid-State Circuits, vol. 44, no. 6, June 2009. [↩]
3. A. Dancy and A. Chandrakasan, “A Reconfigurable Dual Output Low Power Digital PWM Power Converter,” ISLPED 98, August 10-12, 1998 [↩]