Piezoelectric crystals are popular for passive sensors, such as accelerometers and acoustic emission sensors, due to their robustness and high sensitivity. These sensors are widespread in structural health monitoring among civil and industrial structures, but there is little application in high temperature environments (e.g. > 1000°C) due to the few materials that are capable of operating at elevated temperatures. Most piezoelectric materials suffer from a loss of electric properties above temperatures in the 500-700°C range, but rare earth oxyborate crystals, such as Yttrium calcium oxyborate (YCOB), retain their piezoelectric properties above 1000 °C. Our previous research demonstrated that YCOB can be used to detect transient lamb waves via Hsu-Nielsen tests, which replicate acoustic emission waves, up to 1000°C. In this paper, YCOB piezoelectric acoustic emission sensors were tested for their ability to detect crack progression at elevated temperatures. The sensor was fabricated using a YCOB single crystal and Inconel electrodes and wires. The sensor was mounted onto a stainless steel bar substrate, which was machined to include a pre-crack notch. A dynamic load was induced on the bar with a shaker in order to force the crack to advance along the thickness of the substrate. The obtained raw data was processed and analyzed in the frequency domain and compared to the Lamb wave modes that were evaluated in previous Hsu-Nielsen testing for the substrate.
A flexoelectric bridge-structured microphone using bulk barium strontium titanate (Ba<sub>0.65</sub>Sr<sub>0.3</sub>5TiO<sub>3</sub> or BST) ceramic was investigated in this study. The flexoelectric microphone was installed in an anechoic box and exposed to the sound pressure emitted from a loud speaker. Charge sensitivity of the flexoelectric microphone was measured and calibrated using a reference microphone. The 1.5 mm×768 μm×50 μm micro-machined bridge-structured flexoelectric microphone has a sensitivity of 0.92 pC/Pa, while its resonance frequency was calculated to be 98.67 kHz. The analytical and experimental results show that the flexoelectric microphone has both high sensitivity and broad bandwidth, indicating that flexoelectric microphones are potential candidates for many applications.
Various PZT/epoxy 1-3 composites were investigated for high power applications. “Hard” lead zirconate titanates (PZT4 and PZT8) were chosen for active piezoelectrics owing to their high mechanical quality factors, <i>Q<sub>m</sub></i>s, while the passive polymers were selected based on the desired properties for high power composites - low elastic loss, low elastic modulus and high thermal conductivity. 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 <i>Q<sub>m</sub></i>s with higher electromechanical coupling factors <i>k<sub>t</sub>: Qm</i> ~ 200 and <i>k<sub>t</sub></i> ~ 0.68 for PZT4 composites; Qm ~ 400 and <i>k<sub>t</sub></i> ~ 0.6 for PZT8 composites. The effects of high drive field on the behavior of 1-3 composites were further investigated by varying active and passive components. Improved high power characteristics of 1-3 piezoelectric composites were achieved by selection of optimized composite components, with enhanced electromechanical efficiency and thermal stability under high drive conditions.
Piezoelectric crystals have shown promising results as acoustic emission sensors, but are often hindered by the loss of electric properties above temperatures in the 500-700°C range. Yttrium calcium oxyborate, (YCOB), however, is a promising high temperature piezoelectric material due to its high resistivity at high temperatures and its relatively stable electromechanical and piezoelectric properties across a broad temperature range. In this paper, a piezoelectric
acoustic emission sensor was designed, fabricated, and tested for use in high temperature applications using a YCOB
single crystal. An acoustic wave was generated by a Hsu-Nielsen source on a stainless steel bar, which then propagated through the substrate into a furnace where the YCOB acoustic emission sensor is located. Charge output of the YCOB sensor was collected using a lock-in charge amplifier. The sensitivity of the YCOB sensor was found to have small to no degradation with increasing temperature up to 1000 °C. This oxyborate crystal showed the ability to detect zero order symmetric and antisymmetric modes, as well as distinguishable first order antisymmetric modes at elevated temperatures up to 1000 °C.
Piezoelectric devices have gained popularity due to their low complexity, low mass and low cost as compared with other
high temperature technologies. Despite these advantages, currently piezoelectric sensors for high temperatures are
limited by the temperature limits of piezoelectric materials and electrodes to under 1000°C. During this study, a sensor
capable of operating in temperatures up to 1250°C has been developed. The shear mode design is featured with low
profile and insensitive to mass-loading effects. Because current electrode materials cannot withstand temperatures above
1000°C for an extended period, an electrode-less design was implemented. This sensor prototype was tested at
temperatures ranging from room temperature to 1250°C in the frequency range of 100-300Hz, showing stable
performance. In addition, when tested for an extended dwelling time, the accelerometer demonstrated very stable
behavior once it reached a steady operation at 1250°C.
High temperature sensors play a significant role in aerospace, automotive and energy industries. In this paper, a shearmode
piezoelectric accelerometer using YCa<sub>4</sub>O(BO<sub>3</sub>)<sub>3</sub> single crystals (YCOB) was designed and fabricated for high
temperature sensing applications. The prototype sensor was tested at the temperature ranging from room temperature to
1000°C. The sensitivity of the sensor was found to be 1.9±04 pC/g throughout the tested frequency and temperature
range. Moreover, YCOB piezoelectric accelerometers remained stable performance at 1000°C for a dwell time of three
The current NASA Decadal mission planning effort has identified Venus as a significant scientific target for a
surface in-situ sampling/analyzing mission. The Venus environment represents several extremes including high
temperature (460°C), high pressure (~9 MPa), and potentially corrosive (condensed sulfuric acid droplets that adhere to
surfaces during entry) environments. This technology challenge requires new rock sampling tools for these extreme
conditions. Piezoelectric materials can potentially operate over a wide temperature range. Single crystals, like LiNbO3,
have a Curie temperature that is higher than 1000°C and the piezoelectric ceramics Bismuth Titanate higher than 600°C.
A study of the feasibility of producing piezoelectric drills that can operate in the temperature range up to 500°C was
conducted. The study includes the high temperature properties investigations of engineering materials and piezoelectric
ceramics with different formulas and doping. The drilling performances of a prototype Ultrasonic/Sonic Drill/Corer
(USDC) using high temperate piezoelectric ceramics and single crystal were tested at temperature up to 500°C. The
detailed results of our study and a discussion of the future work on performance improvements are presented in this
In this paper low voltage single crystal actuators were investigated using thin PMN-PT plates for applications requiring low voltage, large strain, low profile and/or actuation at cryogenic temperatures. Firstly, single crystal thickness effect on piezoelectric properties was studied by investigating the relationship between electromechanical coupling coefficient of PMN-PT crystals and the crystal thickness. It was found that electromechanical coupling coefficient (k<sub>t</sub>) of 50 μm, 75 μm and 100 μm PMN-PT single crystal thin plates are 0.5, 0.51, and 0.55, respectively, which are slightly lower than that of bulk single crystal (0.6). A couple of single crystal actuators were then assembled using crystal plates with thickness of 150-200 μm. These actuators were characterized by measuring strain vs. electric field at room temperature and cryogenic temperatures. A 3 mm x 3 mm x 19 mm single crystal stack actuator showed a 21 μm stroke at room temperature under 150 V, and a 10 μm stroke at 60 K under 200 V. A 5 mm x 5 mm x 12 mm single crystal actuator showed 13.5 μm stroke at room temperature under 150 V, and 6 μm stroke at 77 K under 150 V. These low voltage actuators hold promising for space precise positioning and adaptive structures and cryogenic SEM, SPM and STM applications.
An electroactive polymer (EAP)-ceramic hybrid actuation system (HYBAS) was developed recently at NASA Langley Research Center. This paper focuses on the effect of the bending stiffness of the EAP component on the performance of a HYBAS, in which the actuation of the EAP element can match the theoretical prediction at various length/thickness ratios for a constant elastic modulus of the EAP component. The effects on the bending stiffness of the elastic modulus and length/thickness ratio of the EAP component were studied. A critical bending stiffness to keep the actuation of the EAP element suitable for a rigid beam theory-based modeling was found for electron irradiated P(VDF-TrFE) copolymer. For example, the agreement of experimental data and theoretical modeling for a HYBAS with the length/thickness ratio of EAP element at 375 times is demonstrated. However, the beam based theoretical modeling becomes invalid (i.e., the profile of the HYBAS movement does not follow the prediction of theoretical modeling) when the bending stiffness is lower than a critical value.
(1-x)BiScO<sub>3-x</sub>PbTiO<sub>3</sub> (BSPT) polycrystalline material with a morphotropic phase boundary (MPB) composition (x=0.64) exhibits a high Curie temperature (T<sub>C</sub>) about 450°C and good piezoelectric properties with d<sub>33</sub> values around 460pC/N. Manganese (Mn) modified BSPT was utilized in order to increase the electric resistivity and RC time constant. At 450°C, BSPT66-Mn ceramic exhibited a resistivity of 3x10<sup>7</sup> Ohm.cm and RC value of 0.08s, respectively, significantly higher than the values for undoped BSPT and commercial PZT5 materials. The manganese additive shifts T<sub>C</sub> of BSPT materials to lower temperatures, which were found to be 442°C and 462°C for modified BSPT64 and BSPT66, respectively. The piezoelectric behavior for the modified BSPT material was found to deteriorate slightly owing to the hardening effect of manganese, but showed superior temperature stability and enhanced resistivity. The detailed temperature dependent properties were studied in this work and compared to commercial PZT5 materials. The complete set of materials constants, including the elastic s<sub>ij</sub>, c<sub>ij</sub>, piezoelectric d<sub>ij</sub>, e<sub>ij</sub>, g<sub>ij</sub>, h<sub>ij</sub>, dielectric and electromechanical k<sub>ij</sub> values were determined using resonance technique and derived from the experimental data.
A hybrid actuation system (HYBAS) utilizing advantages of a combination of electromechanical responses of an electroative polymer (EAP), an electrostrictive copolymer, and an electroactive ceramic single crystal, PZN-PT single crystal, has been developed. The system employs the contribution of the actuation elements cooperatively and exhibits a significantly enhanced electromechanical performance compared to the performances of the device made of each constituting material, the electroactive polymer or the ceramic single crystal, individually. The theoretical modeling of the performances of the HYBAS is in good agreement with experimental observation. The consistence between the theoretical modeling and experimental test make the design concept an effective route for the development of high performance actuating devices for many applications. The theoretical modeling, fabrication of the HYBAS and the initial experimental results will be presented and discussed.