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.
Tactile perception of different types of tissue is important in order for surgeons to perform procedures correctly and
safely. This is especially true in minimally invasive surgery (MIS) where the surgeon must be able to locate the target
tissue without a direct line of sight or direct finger touch. In this study, tissue characterization using an acoustic wave
tactile sensor array was investigated. This type of tactile sensor array can detect the acoustic impedance change of target
materials. Abnormal tissues can have different Young’s moduli and shear moduli caused by composition change
compared to those of healthy tissues. This also leads to a difference in acoustic impedance which can be detected using
our sensor array. The array was fabricated using a face-shear mode PMN-PT piezoelectric resonator which is highly
sensitive to acoustic impedance load. Gelatin and water mixtures with weight concentration of 5 wt % - 30 wt % were
prepared as tissue phantoms. The shear modulus of each phantom was measured using bulk face-shear mode crystal
resonators, and it was found that shear modulus change from 120 kPa to 430 kPa resulted on 30 % electrical impedance
shift from the resonator. Imaging display of elastic properties of prepared phantoms was also tested using the fabricated
sensor array. The proposed tissue characterization technique is promising for the development of effective surgical
procedures in minimally invasive surgery.
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 YCa4O(BO3)3 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