Abstract
High resolution ultrasonic imaging requires high frequency wide band ultrasonic transducers, which produce short pulses and highly focused beam. However, currently the frequency of ultrasonic transducers is limited to below 100 MHz, mainly because of the challenge in precise control of fabrication parameters. This paper reports the design, fabrication, and characterization of sensitive broadband lithium niobate (LiNbO3) single element ultrasonic transducers in the range of 100–300 MHz, as well as their applications in high resolution imaging. All transducers were built for an f-number close to 1.0, which was achieved by press-focusing the piezoelectric layer into a spherical curvature. Characterization results demonstrated their high sensitivity and a −6 dB bandwidth greater than 40%. Resolutions better than 6.4 μm in the lateral direction and 6.2 μm in the axial direction were achieved by scanning a 4 μm tungsten wire target. Ultrasonic biomicroscopy images of zebrafish eyes were obtained with these transducers which demonstrate the feasibility of high resolution imaging with a performance comparable to optical resolution.
Highlights
As one of the most important and well established tools, ultrasound imaging provides noninvasive valuable diagnostic information, especially in the form of cross-sectional images of soft tissues[1,2,3,4]
The photographs of the completed press-focused ultrahigh frequency LiNbO3 transducers were presented at bottom of Fig. 1
This study reports the design, fabrication, and characterization of LiNbO3 ultrahigh frequency, broadband, high sensitivity and small f-number transducers
Summary
As one of the most important and well established tools, ultrasound imaging provides noninvasive valuable diagnostic information, especially in the form of cross-sectional images of soft tissues[1,2,3,4]. Conventional ultrasonic imaging system typically works at frequencies below 100 MHz, which provides tens of microns to millimeter spatial resolution[5,6,7]. The lateral resolution at the focal point is determined by the product of wavelength and the f-number, (the ratio of the focal distance to the transducer aperture). To achieve high lateral resolution and adequate sensitivity, a highly focused, low f-number transducer design was implemented. The high frequency, low f-number imaging yields improved spatial resolution at the focal point at the expense of imaging depth[1,9,13]. We report the design, fabrication, and characterization of press-focused LiNbO3 transducers at frequencies of 100–300 MHz. The high resolution imaging capability of the transducers was demonstrated by scanning a zebrafish eye. The fine structures of the eye were discernible with these ultrahigh frequency transducers
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