Showing papers by "Arif Sanli Ergun published in 2004"

Forward-viewing CMUT arrays for medical imaging

Abstract: This paper reports the design and testing of forward-viewing annular arrays fabricated using capacitive micromachined ultrasonic transducer (CMUT) technology. Recent research studies have shown that CMUTs have broad frequency bandwidth and high-transduction efficiency. One- and two-dimensional CMUT arrays of various sizes already have been fabricated, and their viability for medical imaging applications has been demonstrated. We fabricated 64-element, forward-viewing annular arrays using the standard CMUT fabrication process and carried out experiments to measure the operating frequency, bandwidth, and transmit/receive efficiency of the array elements. The annular array elements, designed for imaging applications in the 20 MHz range, had a resonance frequency of 13.5 MHz in air. The immersion pulse-echo data collected from a plane reflector showed that the devices operate in the 5-26 MHz range with a fractional bandwidth of 135%. The output pressure at the surface of the transducer was measured to be 24 kPa/V. These values translate into a dynamic range of 131.5 dB for 1-V excitation in 1-Hz bandwidth with a commercial low noise receiving circuitry. The designed, forward-viewing annular CMUT array is suitable for mounting on the front surface of a cylindrical catheter probe and can provide Doppler information for measurement of blood flow and guiding information for navigation through blood vessels in intravascular ultrasound imaging.

High-frequency CMUT arrays for high-resolution medical imaging

Abstract: The paper describes high-frequency 1D CMUT arrays designed and fabricated for use in electronically scanned high-resolution ultrasonic imaging systems. Two different designs of 64-element linear CMUT arrays are presented. A single element in each array is connected to a single-channel custom front-end integrated circuit for pulse-echo operation. The first design has a resonant frequency of 43 MHz in air, and operates at 30 MHz in immersion. The second design exhibits a resonant frequency of 60 MHz in air, and operates at 45 MHz in immersion. Experimental results are compared to simulation results obtained from the equivalent circuit model and nonlinear dynamic finite element analysis; a good agreement is observed between these results. The paper also briefly discusses the effects of the area fill factor on the frequency characteristics of CMUTs, which reveals that the transducer active area should be maximized to obtain a wideband response at high frequencies.

Optimized membrane configuration improves CMUT performance

Abstract: The performance of a capacitive micromachined ultrasonic transducer (CMUT) was improved by optimizing its membrane configuration. CMUTs with three different membrane configurations: square, rectangular and tent, were designed and fabricated using a process based on the wafer-bonding technique. Paired tests showed that improved transmission (TX) and reception (RX) efficiencies were achieved by using tent or rectangular membranes instead of square membranes. The improvements were 46% and 44% in TX and 43% and 65% in RX, respectively.

Capacitive micromachined ultrasonic transducers (CMUTs) with isolation posts

Abstract: We report on a capacitive micromachined ultrasonic transducer (CMUT) featuring isolation posts (PostCMUT) to solve a device reliability problem caused by charging during fabrication and operation, and to extend the device operation range beyond collapse voltage. The PostCMUTs were fabricated using a newly developed process based on the wafer-bonding technique. Paired tests showed the superior reliability characteristics of the PostCMUT design compared to those of earlier CMUT designs. The PostCMUTs showed no hysteresis during membrane-post contact.

Integrated ultrasonic imaging systems based on CMUT arrays: recent progress

Abstract: The paper describes the development of an ultrasonic imaging system based on a two-dimensional capacitive micromachined ultrasonic transducer (CMUT) array. The transducer array and front-end electronics are designed to fit in a 5-mm endoscopic channel. A custom-designed integrated circuit, which comprises the front-end electronics, is connected with the transducer elements via through-wafer interconnects and flip-chip bonding. FPGA-based signal-processing hardware provides real-time three-dimensional imaging. The imaging system is being developed to demonstrate a means of integrating the front-end electronics with the transducer array and to provide a clinically useful technology. Integration of the electronics can improve signal-to-noise ratio, reduce the number of cables connecting the imaging probe to a separate processing unit, and provide a means of connecting electronics to large two-dimensional transducer arrays. The paper describes the imaging system architecture and the progress we have made on implementing each of its components: a 16/spl times/16 CMUT array; custom-designed integrated circuits; a flip-chip bonding technique; signal-processing hardware.

CMUT ring arrays for forward-looking intravascular imaging

Abstract: The paper describes an annular CMUT ring array designed and fabricated for the tip of a catheter used for forward-looking intravascular imaging. A 64-element, 2-mm average diameter array was fabricated as an experimental prototype. A single element in the array is connected to a single-channel custom front-end integrated circuit for pulse-echo operation. In conventional operation, the transducer operates at around 10 MHz. In the collapsed regime, the operating frequency shifts to 25 MHz and the received echo amplitude is tripled. The SNR is measured as 23 dB in a 50-MHz measurement bandwidth for an echo signal from a plane reflector at 1.5 mm. We also performed a nonlinear dynamic transient finite element analysis for the transducer, and found these results to be in good agreement with experimental measurements, both for conventional and collapsed operation.

Dynamic FEM analysis of multiple cMUT cells in immersion [capacitive micromachined ultrasonic transducers]

Abstract: This paper reports on the accurate modeling of immersion capacitive micromachined ultrasonic transducers (cMUTs) using a time-domain, nonlinear FEM package. A cMUT device consists of many cells. In this paper, a square membrane was used as the unit cell to cover the transducer area by periodic replication on the surface. The FEM calculations were used to analyze the nonlinear operation regimes of the cMUT. Nonlinear operation regimes (collapsed and collapse-snapback) provided higher acoustic output pressures than the conventional operation. The FEM calculations were compared to transmit experiment results performed with a hydrophone, and good agreement was observed.

Micromachined Ultrasonic Transducers and Their use for 2D and 3D Imaging

Abstract: Capacitive micromachined ultrasonic transducers (cMUTs) have proven to have remarkable features such as wide bandwidth and high sensitivity allowing the implementation of systems with wide dynamic range. This paper will review the theory and implementation of CMUTs that enable performance that is superior to piezoelectric transducers. In particular, the paper will discuss one-dimensional and two-dimensional arrays, broad frequency of operation (10 kHz to 50 MHz), and high coupling coefficient (k T 2 value as high as 0.85), and the use of these arrays in imaging applications.