@inproceedings{9978,
  abstract     = {{Piezoelectric transducers are used in a wide range of applications. Reliability of these transducers is an important aspect in their application. Prognostics, which involve continuous monitoring of the health of technical systems and using this information to estimate the current health state and consequently predict the remaining useful lifetime (RUL), can be used to increase the reliability, safety, and availability of the transducers. This is achieved by utilizing the health state and RUL predictions to adaptively control the usage of the components or to schedule appropriate maintenance without interrupting operation. In this work, a prognostic approach utilizing self-sensing, where electric signals of a piezoelectric transducer are used as the condition monitoring data, is proposed. The approach involves training machine learning algorithms to model the degradation of the transducers through a health index and the use of the learned model to estimate the health index of similar transducers. The current health index is then used to estimate RUL of test components. The feasibility of the approach is demonstrated using piezoelectric bimorphs and the results show that the method is accurate in predicting the health index and RUL.}},
  author       = {{Kimotho, James Kuria and Sextro, Walter and Hemsel, Tobias}},
  booktitle    = {{IEEE Transactions on Reliability}},
  keywords     = {{Estimation of Remaining Useful Lifetime of Piezoelectric Transducers Based on Self-Sensing}},
  pages        = {{1 -- 10}},
  title        = {{{Estimation of Remaining Useful Lifetime of Piezoelectric Transducers Based on Self-Sensing}}},
  doi          = {{10.1109/TR.2017.2710260}},
  year         = {{2017}},
}

@inproceedings{6554,
  author       = {{Claes, Leander and Bause, Fabian and Rautenberg, Jens and Henning, Bernd}},
  booktitle    = {{Proceedings SENSOR 2015}},
  keywords     = {{piezoceramics, strip transducers, plate waveguide, dispersion diagram}},
  pages        = {{775--779}},
  title        = {{{Detection of ultrasonic plate waves using ceramic strip transducers}}},
  doi          = {{10.5162/sensor2015/P3.3}},
  year         = {{2015}},
}

@article{9874,
  author       = {{Hemsel, Tobias and Bornmann, Peter and Morita, Takeshi and Sondermann-Wölke, Christoph and Sextro, Walter}},
  issn         = {{0939-1533}},
  journal      = {{Archive of Applied Mechanics}},
  keywords     = {{Reliability, Ultrasonic power transducers, FMEA}},
  pages        = {{1--7}},
  publisher    = {{Springer Berlin Heidelberg}},
  title        = {{{Reliability analysis of ultrasonic power transducers}}},
  doi          = {{10.1007/s00419-014-0965-4}},
  year         = {{2014}},
}

@article{9878,
  abstract     = {{(K,Na)NbO3 ceramics have attracted much attention as lead-free piezoelectric materials with high piezoelectric properties. High-quality (K,Na)NbO3 ceramics can be sintered using KNbO3 and NaNbO3 powders synthesized by a hydrothermal method. In this study, to enhance the quality factor of the ceramics, high-power ultrasonic irradiation was employed during the hydrothermal method, which led to a reduction in the particle size of the resultant powders.}},
  author       = {{Isobe, G. and Maeda, Takafumi and Bornmann, Peter and Hemsel, Tobias and Morita, Takeshi}},
  issn         = {{0885-3010}},
  journal      = {{Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on}},
  keywords     = {{Q-factor, ceramics, crystal growth from solution, particle size, piezoelectric materials, potassium compounds, powders, sintering, sodium compounds, ultrasonic effects, (K0.48Na0.52)NbO3, KNbO3 powders, NaNbO3 powders, high-power ultrasonic irradiation, lead-free piezoelectric materials, lead-free piezoelectric powders, particle size reduction, piezoelectric properties, quality factor, sintered (K0.48Na0.52)NbO3 ceramics, sintering, ultrasonic-assisted hydrothermal method, Acoustics, Ceramics, Lead, Piezoelectric materials, Powders, Radiation effects, Transducers}},
  number       = {{2}},
  pages        = {{225--230}},
  title        = {{{Synthesis of lead-free piezoelectric powders by ultrasonic-assisted hydrothermal method and properties of sintered (K0.48Na0.52)NBO3 ceramics}}},
  doi          = {{10.1109/TUFFC.2014.6722608}},
  volume       = {{61}},
  year         = {{2014}},
}

@inproceedings{9783,
  abstract     = {{To optimize the ultrasound irradiation for cavitation based ultrasound applications like sonochemistry or ultrasound cleaning, the correlation between cavitation intensity and the resulting effect on the process is of interest. Furthermore, changing conditions like temperature and pressure result in varying acoustic properties of the liquid. That might necessitate an adaption of the ultrasound irradiation. To detect such changes during operation, process monitoring is desired. Labor intensive processes, that might be carried out for several hours, also require process monitoring to increase their reliability by detection of changes or malfunctions during operation. In some applications cavitation detection and monitoring can be achieved by the application of sensors in the sound field. Though the application of sensors is possible, this necessitates modifications on the system and the sensor might disturb the sound field. In other applications harsh, process conditions prohibit the application of sensors in the sound field. Therefore alternative techniques for cavitation detection and monitoring are desired. The applicability of an external microphone and a self-sensing ultrasound transducer for cavitation detection were experimentally investigated. Both methods were found to be suitable and easily applicable.}},
  author       = {{Bornmann, Peter and Hemsel, Tobias and Sextro, Walter and Maeda, Takafumi and Morita, Takeshi}},
  booktitle    = {{Ultrasonics Symposium (IUS), 2012 IEEE International}},
  issn         = {{1948-5719}},
  keywords     = {{cavitation, chemical reactors, microphones, process monitoring, reliability, ultrasonic applications, ultrasonic waves, acoustic properties, cavitation based ultrasound applications, cavitation intensity, change detection reliability, external microphone, malfunction detection reliability, nonperturbing cavitation detection, nonperturbing cavitation monitoring, process monitoring, self-sensing ultrasound transducer, sonochemical reactors, sonochemistry, ultrasound cleaning, ultrasound irradiation, Acoustics, Liquids, Monitoring, Sensors, Sonar equipment, Transducers, Ultrasonic imaging}},
  pages        = {{1141--1144}},
  title        = {{{Non-perturbing cavitation detection / monitoring in sonochemical reactors}}},
  doi          = {{10.1109/ULTSYM.2012.0284}},
  year         = {{2012}},
}

@inproceedings{9785,
  abstract     = {{Hydrothermal method enables to synthesize high quality piezoelectric materials. To shorten the reaction time and to get higher quality materials, we propose an ultrasonic irradiation to the solution during the hydrothermal method. We named it ultrasonic assisted hydrothermal method (UAHTM). We have synthesized lead-free piezoelectric material and PZT thin film and the effect of UAHTM have been confirmed. In this study, we tried to improve UAHTM. First, to generate powerful and stable ultrasonic irradiation at high temperature on UAHTM, we developed a new transducer using LiNbO3 single crystal. Second, to prevent contamination to the materials, A Teflon cover on the tip of transducer was attached.}},
  author       = {{Isobe, Gaku and Ageba, Ryo and Maeda, Takafumi and Bornmann, Peter and Hemsel, Tobias and Morita, Takeshi}},
  booktitle    = {{AIP Conference Proceedings}},
  editor       = {{B. J. Linde, Bogumil and Paczkowski, Jacek and Ponikwicki, Nikodem}},
  keywords     = {{contamination, lead compounds, piezoelectric materials, piezoelectric thin films, piezoelectric transducers, ultrasonic effects}},
  number       = {{1}},
  pages        = {{569--572}},
  publisher    = {{AIP}},
  title        = {{{Synthesis of piezoelectric materials by ultrasonic assisted hydrothermal method}}},
  doi          = {{10.1063/1.3703251}},
  volume       = {{1433}},
  year         = {{2012}},
}

@inproceedings{9788,
  abstract     = {{A hydrothermal method utilizes a crystallization process in the solution so that the pure and high-quality powders can be realized. Sintering from the hydrothermal KNbO3 and NaNbO3 powders, a high-dense lead-free piezoelectric (K,Na)NbO3 ceramics could be obtained (density: 98.8\%). Concerning about the g33 constant, high value as large as commercial PZT ceramics was measured. Therefore, the hydrothermal (K,Na)NbO3 ceramics is usable for the sensors and the energy harvesting devices. To demonstrate the (K,Na)NbO3 ceramics, a hydrophone sensor was fabricated and evaluated.}},
  author       = {{Maeda, Takafumi and Bornmann, Peter and Hemsel, Tobias and Morita, Takeshi}},
  booktitle    = {{Ultrasonics Symposium (IUS), 2012 IEEE International}},
  issn         = {{1948-5719}},
  keywords     = {{crystallisation, hydrophones, piezoceramics, potassium compounds, powder technology, powders, sensors, sintering, sodium compounds, (K0.48Na0.52)NbO3, KNbO3 powder, NaNbO3 powder, crystallization, energy harvesting devices, g33 constant, hydrophone sensor, hydrothermal lead-free (K0.48Na0.52)NbO3 ceramics, hydrothermal method, piezoelectric applications, sintering, Materials, Transducers}},
  pages        = {{194--195}},
  title        = {{{Piezoelectric applications of hydrothermal lead-free (K0.48Na0.52)NbO3 ceramics}}},
  doi          = {{10.1109/ULTSYM.2012.0048}},
  year         = {{2012}},
}

@inproceedings{9568,
  abstract     = {{A simple pre-stress estimate method of Langevin transducers is studied. The measurement setup consists of a capacitor, an impedance converter and a voltmeter. Based on the piezoelectric equation and the basic circuit theory, the mathematical expression between the pre-stress and the voltage across the capacitor is derived. The pre-stress level can then be calculated out of the measurement of the capacitor voltage. In order to evaluate the precision of this method, a force washer is used to measure the pre-stress of the Langevin transducer. The result shows the pre-stress level obtained from this method is 30-40\% higher than the pre-stress level measured by the force washer. This method is simple and can be used to estimate the pre-stress of various Langevin transducers. The precision of this method can be raised if d33 is identified under different pre-stress levels.}},
  author       = {{Bo, Fu and Ting, Li and Hemsel, Tobias}},
  booktitle    = {{Piezoelectricity, Acoustic Waves, and Device Applications, 2008. SPAWDA 2008. Symposium on}},
  keywords     = {{capacitors, impedance convertors, piezoelectric transducers, stress analysis, Langevin transducers, basic circuit theory, capacitor, impedance converter, piezoelectric equation, pre-stress estimating method, voltmeter, Capacitors, Educational institutions, Equations, Force measurement, Impedance measurement, Manufacturing, Mechatronics, Piezoelectric transducers, Voltage, Voltmeters, Langevin transducer, capacitor, piezoelectric element, pre-stress}},
  pages        = {{324--327}},
  title        = {{{A simple pre-stress estimating method of langevin transducers}}},
  doi          = {{10.1109/SPAWDA.2008.4775801}},
  year         = {{2008}},
}