Abstract
This paper describes the design, fabrication, and characterization of tightly focused (ƒ-number close to 1) high frequency needle-type transducers based on lead-free Na0.5Bi4.5Ti3.975Co0.025O15 (NBT-Co) piezo-ceramics. The NBT-Co ceramics, are fabricated through solid-state reactions, have a piezoelectric coefficient d33 of 32 pC/N, and an electromechanical coupling factor kt of 35.3%. The high Curie temperature (670 °C) indicates a wide working temperature range. Characterization results show a center frequency of 70.4 MHz and a −6 dB bandwidth of 52.7%. Lateral resolution of 29.8 μm was achieved by scanning a 10 μm tungsten wire target, and axial resolution of 20.8 μm was calculated from the full width at half maximum (FWHM) of the pulse length of the echo. This lead-free ultrasonic transducer has potential applications in high resolution biological imaging.
Highlights
Focused high frequency ultrasonic transducers have many clinical applications, ranging from imaging the skin and eye to small animal imaging, because of their improved image resolution [1,2,3,4]
The improvement of axial resolution is due to a reduction in wavelength, and pulse duration, for a fixed number of cycles per pulse
The improvement of on-focus lateral resolution is due to the small ƒ-number, defined as the ratio of the focal distance to the spatial dimension of the transducer, of the tightly focused transducer and the wavelength
Summary
Focused high frequency ultrasonic transducers have many clinical applications, ranging from imaging the skin and eye to small animal imaging, because of their improved image resolution [1,2,3,4]. Researchers have made many attempts, such as A- or B-site modification and grain orientation techniques, to overcome these shortcomings and improve the piezoelectric and ferroelectric properties of NBT ceramics [13,17,18]. In these studies, the B-site acceptor modification improved the piezoelectricity of NBT ceramics significantly [15]. The electrical and acoustic properties of the transducer were investigated in detail, which demonstrated the great potential of this lead-free transducer for application in high resolution biological and medical imaging
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