25 MHz ultrasonic transducers with lead- free piezoceramic, 1-3 PZT fiber-epoxy composite, and PVDF polymer active elements

Abstract

This paper presents the fabrication and characterization of single-element ultrasonic transducers whose active elements are made of lead-free piezoceramic, 1-3 PZT/polymer composite and PVDF film. The lead free piezoelectric KNNLT- LS(K(0.44)Na(0.52)Li(0.04))(Nb(0.84)Ta(0.10)S(0.06)b)O(3) powders and ceramics were prepared under controlled humidity and oxygen flow rate during sintering. Due to its moderate longitudinal piezoelectric charge coefficient (175 pC/N) and k(t) of 0.50, the KNN-LT-LS composition may be a good candidate for high frequency transducer applications. PZT fibers with 25 microm diameter formed by the viscose suspension spinning process were incorporated into epoxy to fabricate 1-3 composites with the averaged k(t) = 0.64 and d(33) = 400 pC/N. Using KNN-LS-LT ceramic, 1-3 PZT fiber composite, and PVDF film, 3 different unfocused single element transducers with center frequencies of 25 MHz were fabricated. The acoustic characterization of the transducers demonstrated that wideband and low insertion loss could be obtained employing KNN-LS-LT ceramic. The -6 dB bandwidth and insertion loss were 70% and -21 dB, respectively. In comparison, the insertion loss of the ceramic transducer was much smaller than those made with 1-3 composite and PVDF film. This was attributed to closer electrical impedance match to 50 ohm and higher thickness coupling coefficient of the ceramic transducer.

Lead-free piezoelectric materials and ultrasonic transducers for medical imaging

“…KNN-based transducers for medical imaging application were developed by Jadidian et al 55 The acoustic performance of a 25 MHz single element transducer with (K 0:44 Na 0:52 Li 0:04 )(Nb 0:84 Ta 0:10 Sb 0:06 )O 3 (abbreviated to KNN-LT-LS) active element was compared to a PZT fiber 1-3 composite transducer. The properties of KNNbased ceramics and 1-3 PZT composite are given in Table 6.…”

Lead-Free KNN-Based Piezoelectric Materials

“…The higher electronegativities of Ta 5+ and Sb 5+ compared to Nb 5+ increase covalency of the bonds and hence, the resultant Sp 3 hybridization of covalency over the ionic bond leads to further improvement in the piezoelectric properties of KNN-LT-LS. This composition has been shown to be a good candidate for high frequency transducer applications [19]. The MPB in KNN-LT ceramics was claimed to exist at about 5-6 mol% of LT (e r of 570, d 33~2 00 pC N À1 , and k p~3 6%) [20].…”

Microscale 1-3-Type (Na,K)NbO3-Based Pb-Free Piezocomposites for High-Frequency Ultrasonic Transducer Applications

“…Most importantly, the 1‐3 connectivity effectively enhances the electromechanical coupling coefficient in the thickness mode. Recently, high‐frequency ultrasonic transducers have been intensively studied to meet the need for imaging with improved resolution 3–8 . It is well‐known that in the thickness mode, the resonance frequency f r of a piezoelectric layer is inversely proportional to its thickness t .…”

“…Recently, high-frequency ultrasonic transducers have been intensively studied to meet the need for imaging with improved resolution. [3][4][5][6][7][8] It is well-known that in the thickness mode, the resonance frequency f r of a piezoelectric layer is inversely proportional to its thickness t. As a result, in the case of the 1-3 piezocomposites for high-frequency transducer applications, the piezoelectric layer must be lapped to a thickness thin enough to yield high-frequency resonances; in addition, better control and reduction of the spatial scale of piezoceramic rods in the composite is required to minimize lateral resonances.…”