Showing papers by "Amin Nikoozadeh published in 2016"

Ex Vivo HIFU Experiments Using a $32 \times 32$ -Element CMUT Array

Abstract: High-intensity focused ultrasound (HIFU) has been used as noninvasive treatment for various diseases. For these therapeutic applications, capacitive micromachined ultrasonic transducers (CMUTs) have advantages that make them potentially preferred transducers over traditional piezoelectric transducers. In this paper, we present the design and the fabrication process of an $8 \times 8$ -mm $^{2}~32 \times 32$ -element 2-D CMUT array for HIFU applications. To reduce the system complexity for addressing the 1024 transducer elements, we propose to group the CMUT array elements into eight HIFU channels based on the phase delay from the CMUT element to the targeted focal point. Designed to focus at an 8-mm depth with a 5-MHz exciting frequency, this grouping scheme was realized using a custom application-specific integrated circuit. With a 40-V dc bias and a 60-V peak-to-peak ac excitation, the surface pressure was measured 1.2 MPa peak-to-peak and stayed stable for a long enough time to create a lesion. With this dc and ac voltage combination, the measured peak-to-peak output pressure at the focus was 8.5 MPa, which is expected to generate a lesion in a minute according to the temperature simulation. The following ex vivo tissue experiments successfully demonstrated its capability to make lesions in both bovine muscle and liver tissue.

Lamb Wave Multitouch Ultrasonic Touchscreen

Abstract: Touchscreen sensors are widely used in many devices such as smart phones, tablets, and laptops with diverse applications. We present the design, analysis, and implementation of an ultrasonic touchscreen system that utilizes the interaction of transient Lamb waves with objects in contact with the screen. It attempts to improve on the existing ultrasound technologies, with the potential of addressing some of the weaknesses of the dominant technologies, such as the capacitive or resistive ones. Compared with the existing ultrasonic and acoustic modalities, among other advantages, it provides the capability of detecting several simultaneous touch points and also a more robust performance. The localization algorithm, given the hardware design, can detect several touch points with a very limited number of measurements (one or two). This in turn can significantly reduce the manufacturing cost.

Capsule ultrasound device: Further developments

Abstract: We are developing a capsule ultrasound (CUS) device - a pill with the capability to scan the gastrointestinal (GI) tract through ultrasound. In this paper, we discuss the design and fabrication of the main components of the CUS device including the CMUT array, front-end electronics, and the wireless transmitter. We demonstrate a successfully fabricated 128-element CMUT array with polydimethylsiloxane (PDMS)-filled trenches and show their input impedance in air. The front-end electronics, measuring 6 mm by 6 mm and the high-data rate wireless transmitter, measuring 1 mm by 1.76 mm, have been fabricated. Our preliminary power analysis indicates that our total power consumption is less than 20 mW for the CUS device. Our future work involves integrating these core components for imaging experiments.

Fully integrated 2D CMUT ring arrays for endoscopic ultrasound

Abstract: Ultrasound has become more prevalent as a medical tool for real-time volumetric imaging. Sparse 2D CMUT ring arrays generate high resolution volumetric images with fewer elements than a fully populated 2D array, allow for integration with electronics in an endoscope form factor, and provide a central lumen for simultaneous use of additional diagnostic and therapeutic tools, such as HIFU or photoacoustic fibers, without increasing the overall package size. We have previously fabricated QuadRing capacitive micromachined ultrasound transducers (CMUTs). Each of the four independent, concentric rings in the array contains 128 elements and operates at a different center frequency. In this work, we use one of the four concentric rings at 4MHz for a fully integrated endoscope assembly. Custom charge-amplifier ASICs were used in these assemblies rather than transimpedance amplifiers, reducing the noise figure of the system. The CMUT arrays are flip chip bonded to a custom 8-leg flexible PCB (flex) that provides electrical connections between the CMUT array, ASICs, and Verasonics imaging system. The flip chip bonded assembly is integrated with a custom 3D printed tip that encases and mechanically supports the assembly, and provides a convenient built-in reference for the passivation layer. Additionally, one flex version flips the CMUT bias, grounding the top electrode without additional circuitry by level-shifting the IC supplies. This feature is particularly desirable for clinical applications, as it shields the patient from the CMUT bias voltage. This new 128-element forward-facing CMUT endoscope has been used for real-time 3D imaging on the bench and expands the toolkit beyond previous work in several ways: high quality images are obtained using a relatively sparse array; new ASICs have shown improvements in SNR; and the array size has enabled use of new 3D-printed, highly customizable assembly tools. We have validated operation with a grounded CMUT top electrode, a critical step towards clinical use. Furthermore, a large lumen increases the breadth of tools that can be used in conjunction with the imaging array.