Alumina/epoxy nanocomposite matching layers for high-frequency ultrasound transducer application
ABSTRACT Mismatch of acoustic impedance at the interface between a piezoelectric transducer and the medium to be probed will substantially reduce the amount of ultrasound energy being transmitted into the medium. Therefore, matching layer is a critical component of an ultrasonic transducer. A spin-coating process was used to fabricate alumina/polymer nanocomposite films with alumina volume fractions ranging from 14 to 32%. The particle size of alumina is in the range of 10 to 40 nm. The thicknesses of the matching layer can be controlled by the spinning speed and the concentration of solution. Acoustic impedances of these nanocomposite matching layers are in the range of 2.8 to 5.1 MRayls with different alumina contents, which meet the matching layer requirement. The attenuation of a nanocomposite matching layer with smooth surface is about 15 dB/mm at 40 MHz. The pulse-echo spectrum and frequency spectrum of a high-frequency transducer using this nanocomposite matching layer are reported.
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ABSTRACT: The acoustic properties of passive materials for ultrasonic transducers have been measured at room temperature in the frequency range from 25 to 65 MHz using ultrasonic spectroscopy. These materials include alumina/EPO-TEK 301 composites and tungsten/EPO-TEK 301 composites. Experimental results showed that the acoustic impedance of the composites monotonically increased with the volume fraction of the particle filler, which is in agreement with the Denavey model. The attenuation, however, peaked between 7 and 9% volume fraction of particle filler. For comparison, several other passive materials were also fabricated and measured. The results suggest that materials that possess a higher attenuation also appear to have a larger velocity dispersion.IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/2001; 48(1):78-84. · 1.82 Impact Factor
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ABSTRACT: The visualisation of living tissues at microscopic resolution is attracting attention in several fields. In medicine, the goals are to image healthy and diseased tissue with the aim of providing information previously only available from biopsy samples. In basic biology, the goal may be to image biological models of human disease or to conduct longitudinal studies of small-animal development. High-frequency ultrasonic imaging (ultrasound biomicroscopy) offers unique advantages for these applications. In this paper, the development of ultrasound biomicroscopy is reviewed. Aspects of transducer development, systems design and tissue properties are presented to provide a foundation for medical and biological applications. The majority of applications appear to be developing in the 40-60-MHz frequency range, where resolution on the order of 50 microm can be achieved. Doppler processing in this frequency range is beginning to emerge and some examples of current achievements will be highlighted. The current state of the art is reviewed for medical applications in ophthalmology, intravascular ultrasound, dermatology, and cartilage imaging. Ultrasound biomicroscopic studies of mouse embryonic development and tumour biology are presented. Speculation on the continuing evolution of ultrasound biomicroscopy will be discussed.Ultrasound in Medicine & Biology 02/2000; 26(1):1-27. · 2.46 Impact Factor
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ABSTRACT: This paper discusses the design, fabrication, and testing of sensitive broadband lithium niobate (LiNbO3) single-element ultrasonic transducers in the 20-80 MHz frequency range. Transducers of varying dimensions were built for an f# range of 2.0-3.1. The desired focal depths were achieved by either casting an acoustic lens on the transducer face or press-focusing the piezoelectric into a spherical curvature. For designs that required electrical impedance matching, a low impedance transmission line coaxial cable was used. All transducers were tested in a pulse-echo arrangement, whereby the center frequency, bandwidth, insertion loss, and focal depth were measured. Several transducers were fabricated with center frequencies in the 20-80 MHz range with the measured -6 dB bandwidths and two-way insertion loss values ranging from 57 to 74% and 9.6 to 21.3 dB, respectively. Both transducer focusing techniques proved successful in producing highly sensitive, high-frequency, single-element, ultrasonic-imaging transducers. In vivo and in vitro ultrasonic backscatter microscope (UBM) images of human eyes were obtained with the 50 MHz transducers. The high sensitivity of these devices could possibly allow for an increase in depth of penetration, higher image signal-to-noise ratio (SNR), and improved image contrast at high frequencies when compared to previously reported results.IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 12/2003; 50(11):1548-57. · 1.82 Impact Factor