Through-Ice Acoustic Communication for Ocean Worlds Exploration.

Subsurface exploration of ice-covered planets and moons presents communications challenges because of the need to communicate through kilometers of ice. The objective of this task is to develop the capability to wirelessly communicate through kilometers of ice and thus complement the potentially failure-prone tethers deployed behind an ice-penetrating probe on Ocean Worlds. In this paper, the preliminary work on the development of wireless deep-ice communication is presented and discussed. The communication test and acoustic attenuation measurements in ice have been made by embedding acoustic transceivers in glacial ice at the Matanuska Glacier, Anchorage, Alaska. Field test results show that acoustic communication is viable through ice, demonstrating the transmission of data and image files in the 13-18 kHz band over 100 m. The results suggest that communication over many kilometers of ice thickness could be feasible by employing reduced transmitting frequencies around 1 kHz, though future work is needed to better constrain the likely acoustic attenuation properties through a refrozen borehole.

Piezoelectric energy harvesting in internal fluid flow.

We consider piezoelectric flow energy harvesting in an internal flow environment with the ultimate goal powering systems such as sensors in deep oil well applications. Fluid motion is coupled to structural vibration via a cantilever beam placed in a converging-diverging flow channel. Two designs were considered for the electromechanical coupling: first; the cantilever itself is a piezoelectric bimorph; second; the cantilever is mounted on a pair of flextensional actuators. We experimentally investigated varying the geometry of the flow passage and the flow rate. Experimental results revealed that the power generated from both designs was similar; producing as much as 20 mW at a flow rate of 20 L/min. The bimorph designs were prone to failure at the extremes of flow rates tested. Finite element analysis (FEA) showed fatigue failure was imminent due to stress concentrations near the bimorph's clamped region; and that robustness could be improved with a stepped-joint mounting design. A similar FEA model showed the flextensional-based harvester had a resonant frequency of around 375 Hz and an electromechanical coupling of 0.23 between the cantilever and flextensional actuators in a vacuum. These values; along with the power levels demonstrated; are significant steps toward building a system design that can eventually deliver power in the Watts range to devices down within a well.

High temperature, high power piezoelectric composite transducers.

Piezoelectric composites are a class of functional materials consisting of piezoelectric active materials and non-piezoelectric passive polymers, mechanically attached together to form different connectivities. These composites have several advantages compared to conventional piezoelectric ceramics and polymers, including improved electromechanical properties, mechanical flexibility and the ability to tailor properties by using several different connectivity patterns. These advantages have led to the improvement of overall transducer performance, such as transducer sensitivity and bandwidth, resulting in rapid implementation of piezoelectric composites in medical imaging ultrasounds and other acoustic transducers. Recently, new piezoelectric composite transducers have been developed with optimized composite components that have improved thermal stability and mechanical quality factors, making them promising candidates for high temperature, high power transducer applications, such as therapeutic ultrasound, high power ultrasonic wirebonding, high temperature non-destructive testing, and downhole energy harvesting. This paper will present recent developments of piezoelectric composite technology for high temperature and high power applications. The concerns and limitations of using piezoelectric composites will also be discussed, and the expected future research directions will be outlined.

1-3 piezoelectric composites for high temperature transducer applications.

High temperature Pb(Zr,Ti)O3 /epoxy 1-3 composites were fabricated using the dice and fill method. The epoxy filler was modified with glass spheres in order to improve the thermal reliability of the composites at elevated temperatures. Temperature dependent dielectric and electromechanical properties of the composites were measured after aging at 250°C with different dwelling times. Obvious cracks were observed and the electrodes were damaged in the composite with unmodified epoxy after 200 hours, leading to the failure of the composite. In contrast, composites with >12 vol% glass sphere loaded epoxies were found to exhibit minimal electrical property variation after aging for 500 hours, with dielectric permittivity, piezoelectric coefficient and electromechanical coupling being on the order of 940, 310pC/N and 57%, respectively. This is due to the improved thermal expansion behavior of the modified filler.

Influence of Domain Size on the Scaling Effects in Pb(Mg1/3Nb2/3)O3-PbTiO3 Ferroelectric Crystals.

The property degradation observed in thin Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT) crystals is believed to relate to large domains and subsequent clamping induced by surface-boundary. In this work, the properties were investigated as function of domain size, using controlled poling. The degraded piezoelectric and dielectric properties of thin PMN-PT were found to increase significantly, by decreasing domain size. Furthermore, the fine domain structure was found to be stable at 3kV/cm after 7.0×10(5) negative-pulse cycles, hence, enabling PMN-PT crystals for high-frequency (>20 MHz) ultrasound-transducers.

Recent Developments on High Curie Temperature PIN-PMN-PT Ferroelectric Crystals.

Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) ferroelectric crystals attracted extensive attentions in last couple years, due to their higher usage temperatures range (> 30°C) and coercive fields (~5kV/cm), meanwhile maintaining similar electromechanical couplings (k(33)> 90%) and piezoelectric coefficients (d(33)~1500pC/N), when compared to their binary counterpart Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3). In this article, we reviewed recent developments on the PIN-PMN-PT single crystals, including the Bridgman crystal growth, dielectric, electromechanical, piezoelectric and ferroelectric behaviors as function of temperature and dc bias. Mechanical quality factor Q was studied as function of orientation and phase. Of particular interest is the dynamic strain, which related to the Q and d(33), was found to be improved when compared to binary system, exhibiting the potential usage of PIN-PMN-PT in high power application. Furthermore, PIN-PMN-PT crystals exhibit improved thickness dependent properties, due to their small domain size, being on the order of 1µm. Finally, the manganese acceptor dopant in the ternary crystals was investigated and discussed briefly in this paper.

Direct Laser 3D Printing of Refractory Materials.

Direct laser 3D printing of refractory materials such as silicon carbide (SiC), tungsten (W), and tantalum hafnium carbide (TaHfC) have been systematically investigated. High relative density has been achieved for SiC, SiC/Al, W, and W/TaHfC. High density SiC structures and W thin wall were also fabricated. By mixing the metal powders (e.g. Al or W) with ceramic powder such as SiC or TaHfC, a metal/ceramic matrix is formed during the direct laser melting process to tailor the mechanical properties.

Thickness Dependent Properties of Relaxor-PbTiO(3) Ferroelectrics for Ultrasonic Transducers.

The electrical properties of Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT) based polycrystalline ceramics and single crystals were investigated as a function of scale ranging from 500 microns to 30 microns. Fine-grained PMN-PT ceramics exhibited comparable dielectric and piezoelectric properties to their coarse-grained counterpart in the low frequency range (<10 MHz), but offered greater mechanical strength and improved property stability with decreasing thickness, corresponding to higher operating frequencies (>40 MHz). For PMN-PT single crystals, however, the dielectric and electromechanical properties degraded with decreasing thickness, while ternary Pb(In(1/2)Nb(1/2))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) exhibited minimal size dependent behavior. The origin of property degradation of PMN-PT crystals was further studied by investigating the dielectric permittivity at high temperatures, and domain observations using optical polarized light microscopy. The results demonstrated that the thickness dependent properties of relaxor-PT ferroelectrics are closely related to the domain size with respect to the associated macroscopic scale of the samples.

Design of low-loss 1-3 piezoelectric composites for high-power transducer applications.

Lead zirconate titanate (PZT)/polymer 1-3 composites have improved electromechanical properties compared with monolithic counterparts, but possess a low mechanical quality factor, limiting their use in high-power transducer applications. The goal of this work was to improve the mechanical quality factor of 1-3 PZT/polymer composites by optimizing the polymer materials. Theoretical analysis and modeling were performed for optimum composite design and various polymers were prepared and characterized. 1-3 piezocomposites were constructed and their electromechanical properties were experimentally determined. The results demonstrated that the composites with high-thermal-conductivity polymers generally have degraded electromechanical properties with significantly decreased mechanical quality factors, whereas the composites filled with low-loss and low-moduli polymers were found to have higher mechanical quality factors with higher electromechanical coupling factors: Q(m) ~ 200 and k(t) ~ 0.68 for PZT4 composites; Q(m) ~ 400 and k(t) ~ 0.6 for PZT8 composites. The improved mechanical quality factor of 1-3 piezocomposites may offer improved performance and thermal stability of transducers under high-drive operation.

Scaling effects of relaxor-PbTiO(3) crystals and composites for high frequency ultrasound.

The dielectric and piezoelectric properties of Pb(Mg(13)Nb(23))O(3)-PbTiO(3) (PMN-PT) and Pb(In(12)Nb(12))O(3)-Pb(Mg(13)Nb(23))O(3)-PbTiO(3) (PIN-PMN-PT) ferroelectric single crystals were investigated as a function of thicknessscale in monolithic and piezoelectricpolymer 1-3 composites. For the case of PMN-PT single crystals, the dielectric (epsilon33Tepsilon0) and electromechanical properties (k(33)) were found to significantly decrease with decreasing thickness (500-40 mum), while minimal thickness dependency was observed for PIN-PMN-PT single crystals. Temperature dependent dielectric behavior of the crystals suggested that the observed thickness dependence in PMN-PT was strongly related to their relatively large domain size (>10-20 mum). As anticipated, 1-3 composite comprised of PIN-PMN-PT crystals exhibited superior properties to that of PMN-PT composite at high frequencies (>20 MHz). However, the observed couplings, being on the order of 80%, were disappointedly low when compared to their monolithic counterparts, the result of surface damage introduced during the dicing process, as evidenced by the broadened [002] peaks in the x-ray diffraction pattern.

Characterization of hard piezoelectric lead-free ceramics.

K4CuNb8O23 doped K(0.45)Na(0.55)NbO3(KNNKCN) ferroelectric ceramics were found to exhibit asymmetrical polarization hysteresis loops, related to the development of an internal bias field. The internal bias field is believed to be the result of defect dipoles of acceptor ions and oxygen vacancies, which lead to piezoelectric "hardening" effect, by stabilizing and pinning of the domain wall motion. The dielectric loss for the hard lead-free piezoelectric ceramic was found to be 0.6%, with mechanical quality factors Q on the order of >1500. Furthermore, the piezoelectric properties were found to decrease and the coercive field increased, when compared with the undoped material, exhibiting a typical characteristic of "hard" behavior. The temperature usage range was limited by the polymorphic phase transition temperature, being 188 degrees C. The full set of material constants was determined for the KNN-KCN materials. Compared with conventional hard PZT ceramics, the lead-free possessed lower dielectric and piezoelectric properties; however, comparable values of mechanical Q, dielectric loss, and coercive fields were obtained, making acceptor modified KNN based lead-free piezoelectric material promising for high-power applications, where leadfree materials are desirable.