Micromachining of High Quality PMN-31%PT Single Crystals for High-Frequency (>20 MHz) Ultrasonic Array Transducer Applications

Micromachining of High-Quality PMN-PT/Epoxy 1-3 Composite for High-Frequency (>30 MHz) Ultrasonic Transducer Applications

Fabricating PMN-PT composites, the core component of high-frequency (> 30 MHz) transducers, remains challenging due to their poor machinability and ultrasmall kerfs. This urgent problem is significantly impeding the development of PMN-PT ultrasonic transducers for use in clinical research, biomedical sciences, and nondestructive testing (NDT). In this study, high-quality PMN-0.3PT/epoxy 1-3 composites at 30 and 50 MHz were manufactured using a modified picosecond (1.5 ps) laser technique. Their performance was thoroughly analyzed, which was comparable to that with low-stress dry plasma etching. There were fewer microcracks around PMN-PT pillars. The minimum kerf was less than [Formula: see text], and the highest aspect ratio was larger than 7.5. The microdomain morphology and hysteresis loops of PMN-PT pillars further confirmed that composites still maintained excellent piezoelectric performance and suffered fewer damages during laser cutting. The characterization results exhibited a large electromechanical coupling (>0.77), a high dielectric constant (>1600), and a relatively low acoustic impedance (< 17 Mrayls). The ultrasonic transducers with center frequencies of 30 and 50 MHz were designed and prototyped to validate the performance of composites. The transducers showed broad bandwidth (>80%), high two-way insertion loss (IL) (>-23 dB), and imaging resolution superior to [Formula: see text]. Finally, the C-scan experiments of IC chips were also used to further illustrate the applicability of transducers. These encouraging results further demonstrated that ultrafast laser technology will bring more accessible and affordable methods for fabricating high-frequency PMN-PT composite transducers with excellent performance.

Increasing Performances of 1-3 Piezocomposite Ultrasonic Transducer by Alternating Current Poling Method

Ultrasonic transducers are the basic core component of diagnostic imaging devices, wherein the piezoelectric materials are the active element of transducers. Recent studies showed that the alternating current poling (ACP) method could develop the properties of piezocomposites, which had great potential to improve transducer performance. Herein, transducers (f_c = 3 MHz) made of DCP and ACP 1-3 piezocomposites (prepared by PZT-5H ceramics and PMN-PT single crystals) were fabricated. The effect of the ACP method on the bandwidth and insertion loss (sensitivity) was explored. The results indicate that the ACP method can significantly enhance the bandwidth and slightly increase the insertion loss of transducers. Particularly, a superhigh bandwidth of 142.8% was achieved in the transducer of ACP 1-3 PMN-PT single crystal combined with suitable matching and backing layers. This bandwidth is higher than that of all reported transducers with similar center frequency. Moreover, the optimization mechanism of transducer performance by the ACP method was discussed. The obtained results suggested that the ACP is an effective and convenient technology to improve transducer performances, especially for the bandwidth.

Fabrication of microgrooves in PMN-PT using femtosecond laser irradiation and acid etching

A simple method of fabricating Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) deep grooves with high aspect ratios using an 800-nm femtosecond laser with chemical-selective etching is demonstrated. The 567-µm-deep grooves with aspect ratios of approximately 35 were obtained with no cracks or thermal affected zone. The morphologies and chemical compositions of grooves were analyzed by a scanning electron microscope with an energy dispersive x-ray spectrometer. The formation mechanism of PMN-PT grooves is attributed to the chemical reactions of hydrochloric acid (HCl) and laser-induced structural changes (LISCs). PMN-PT in LISC became amorphous or mixtures of metal oxide from crystal and all the compounds could react with concentrated HCl and form soluble matter, leaving no precipitation. Furthermore, influences of laser irradiation parameters on depths and aspect ratios of grooves are studied.

Fluorinated Polyethylene Propylene Ferroelectrets with an Air-Filled Concentric Tunnel Structure: Preparation, Characterization, and Application in Energy Harvesting

Fluorinated polyethylene propylene (FEP) bipolar ferroelectret films with a specifically designed concentric tunnel structure were prepared by means of rigid-template based thermoplastic molding and contact polarization. The properties of the fabricated films, including the piezoelectric response, mechanical property, and thermal stability, were characterized, and two kinds of energy harvesters based on such ferroelectret films, working in 33- and 31-modes respectively, were investigated. The results show that the FEP films exhibit significant longitudinal and radial piezoelectric activities, as well as superior thermal stability. A quasi-static piezoelectric d₃₃ coefficient of up to 5300 pC/N was achieved for the FEP films, and a radial piezoelectric sensitivity of 40,000 pC/N was obtained in a circular film sample with a diameter of 30 mm. Such films were thermally stable at 120 °C after a reduction of 35%. Two types of vibrational energy harvesters working in 33-mode and 31-mode were subsequently designed. The results show that a power output of up to 1 mW was achieved in an energy harvester working in 33-mode at a resonance frequency of 210 Hz, referring to a seismic mass of 33.4 g and an acceleration of 1 g (g is the gravity of the earth). For a device working in 31-mode, a power output of 15 μW was obtained at a relatively low resonance frequency of 26 Hz and a light seismic mass of 1.9 g. Therefore, such concentric tunnel FEP ferroelectric films provide flexible options for designing vibrational energy harvesters working either in 33-mode or 31-mode to adapt to application environments.