2015, Kiebert, Florian, König, Jörg, Kykal, Carsten, Schmidt, Hagen

Utilizing surface acoustic waves (SAW) to induce tailored fluid motion via the acoustic streaming requires detailed knowledge about the acoustic bulk wave excitation. For the first time, the Defocus Digital Particle Image Velocimetry is used to measure the fluid motion originating from a fluid loaded SAW-device. With this flow measurement technique, the acoustic streaming-induced fluid motion can be observed volumetrically, which is attractive not only for application, but also for simulation in order to gain deeper insights regarding three-dimensional acoustic effects.

2017, Collins, David J., Khoo, Bee Luan, Ma, Zhichao, Winkler, Andreas, Weser, Robert, Schmidt, Hagen, Han, Jongyoon, Ai, Ye

The authors regret that a citation to a relevant paper was missed. The following sentence and reference (ref. 1 shown below) should be added in the Introduction after the sentence ending "...of the applied flow rate.5,37": "For example, Lee et al. acoustically oscillate air/liquid interfaces using a ∼50 kHz piezoelectric transducer to produce acoustic streaming fields for size-based separation of cells and particles".1 The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

2024, Schulmeyer, Philipp, Weihnacht, Manfred, Schmidt, Hagen

Ice accumulation on infrastructure poses severe safety risks and economic losses, necessitating effective detection and monitoring solutions. This study introduces a novel approach employing surface acoustic wave (SAW) sensors, known for their small size, wireless operation, energy self-sufficiency, and retrofit capability. Utilizing a SAW dual-mode delay line device on a 64°-rotated Y-cut lithium niobate substrate, we demonstrate a solution for combined ice detection and temperature measurement. In addition to the shear-horizontal polarized leaky SAW, our findings reveal an electrically excitable Rayleigh-type wave in the X+90° direction on the same cut. Experimental results in a temperature chamber confirm capability for reliable differentiation between liquid water and ice loading and simultaneous temperature measurements. This research presents a promising advancement in addressing safety concerns and economic losses associated with ice accretion.

2023, Seifert, Marietta, Leszczynska, Barbara, Menzel, Siegfried B., Schmidt, Hagen, Gemming, Thomas

Self-sustained, wireless high-temperature stable sensors are developed, which are based on an aluminum alloy as the electrode metallization. Due to its cost-effectiveness accompanied by a high-temperature stability, this alloy substitutes and outperforms the commonly applied expensive Pt- and Ir-based metals. For the first time, a comprehensive structural, electrical and high-frequency characterization of these surface acoustic wave (SAW) sensors is shown. They are based on Catangasite (Ca3TaGa3Si2O14, CTGS) in combination with properly structured cover and barrier layers for the metallization. The frequency characteristics is determined up to 700 °C by ex situ and in situ methods. In addition, the morphology of the AlRu electrodes is analyzed after the thermal loadings and the temperature dependent sheet resistance is measured. The results reveal a reproducible and linear correlation between the applied temperature and the sheet resistance as well as the resonant frequency. In addition, hardly any degradation of the electrodes is detected after the thermal loadings. The observed high-temperature stability of the devices up to at least 700 °C demonstrates the large potential of the AlRu based SAW sensors as a cost-efficient alternative to expensive noble metal based sensors in industrial applications for the support of energy efficient operation.

2023, Seifert, Marietta, Leszczynska, Barbara, Weser, Robert, Menzel, Siegfried, Gemming, Thomas, Schmidt, Hagen

TiAl based surface acoustic wave (SAW) devices, which offer a promising cheap and easy to handle wireless sensor solution for intermediate high temperatures up to 600 °C, were prepared and investigated with respect to their durability. To obtain the devices, Ti/Al multilayers were deposited on high-temperature stable piezoelectric catangasite (CTGS) substrates and structured as electrodes via the lift-off technique. AlNO cover layers and barrier layers at the substrate site served as an oxidation protection. The devices were characterized regarding their electrical behavior by ex-situ measurements of their frequency characteristics after heat treatments up to 600 °C in air. In addition, long-term in situ measurements up to 570 °C were performed to analyze a possible drift of the resonant frequency in dependence on the temperature and time. Scanning electron microscopy of the surfaces of the devices and scanning transmission electron microscopy of cross sections of TiAl interdigital transducer electrode fingers and the contact pads were conducted to check the morphology of the electrode metallization and to reveal if degradation or oxidation processes occurred during the heat treatments. The results demonstrated a sufficient high-temperature stability of the TiAl based devices after a first conditioning of system. A linear dependence of the resonant frequency on the temperature of about −37 ppm/K was observed. In summary, the suitability of TiAl based SAW sensors for long-term application at intermediate temperatures was proven.

2016, Schmidt, Hagen

Im Rahmen des Projekts wurden Funktionsprinzipien der Akustoelektronik, d.h. der akustischen Oberflächen- und Volumenwellen-Technik (surface acoustic waves: SAW, bulk acoustic waves: BAW) für die Nutzung zur Fluidaktorik in Laboranalysensystemen untersucht und weiterentwickelt. Angestrebt wurden vor allem kostengünstige und applikationsangepasste mikroakustische Lösungen. Hierzu wurden die Grundlagen verschiedener mikroakustischer Fluid-Manipulationen, wie Mischen/Homogenisieren, Erwärmen und Zerstäuben, für einen effizienten Einsatz in kommerziellen Anwendungen aufbereitet. Dies umfasste auch die Entwicklung von innovativen und kosteneffizienten Technologien zur flüssigkeitsdichten Verkapselung der Fluid-Mikroaktoren sowie Systemdesign, Aufbau, Charakterisierung und Optimierung derartiger Baugruppen für den Einsatz in unterschiedlichen Labor- und Analysengeräten. Es wurden mehrere Technologien auf ihre mikroakustische Tauglichkeit untersucht und Verkapselungsmaterialien charakterisiert, darunter silikatische Gläser und organische Polymere Auf der Geräteseite wurden ein Mischstab für den Einsatz in Autosamplern sowie eine optische Messzelle mit Mischfunktion als geeignete Anwendungen identifiziert. Mit den ausgewählten Verkapselungstechnologien ausgestattete mikroakustische Aktoren konnten erfolgreich gemeinsam mit den Projektpartnern im Rahmen von Demonstrationssystemen realisiert und getestet werden.

2021, Suhak, Yuriy, Fritze, Holger, Sotnikov, Andrei, Schmidt, Hagen, Johnson, Ward L.

Temperature-dependent acoustic loss Q−1 is studied in partially disordered langasite (LGS, La3Ga5SiO14) and ordered catangasite (CTGS, Ca3TaGa3Si2O14) crystals and compared with previously reported CTGS and langatate (LGT, La3Ga5.5Ta0.5O14) data. Two independent techniques, a contactless tone-burst excitation technique and contacting resonant piezoelectric spectroscopy, are used in this study. Contributions to the measured Q−1(T) are determined through fitting to physics-based functions, and the extracted fit parameters, including the activation energies of the processes, are discussed. It is shown that losses in LGS and CTGS are caused by a superposition of several mechanisms, including intrinsic phonon–phonon loss, point-defect relaxations, and conductivity-related relaxations.

2019, Suhak, Yuriy, Johnson, Ward L., Sotnikov, Andrei, Schmidt, Hagen, Fritze, Holger

Transport mechanisms in structurally ordered piezoelectric Ca3TaGa3Si2O14 (CTGS) single crystals are studied in the temperature range of 1000-1300 °C by application of the isotope 18O as a tracer and subsequent analysis of diffusion profiles of this isotope using secondary ion mass spectrometry (SIMS). Determined oxygen self-diffusion coefficients enable calculation of oxygen ion contribution to the total conductivity, which is shown to be small. Since very low contributions of the cations have to be expected, the total conductivity must be dominated by electron transport. Ion and electron conductivities are governed by different mechanisms with activation energies (1.9±0.1) eV and (1.2±0.07) eV, respectively. Further, the electromechanical losses are studied as a function of temperature by means of impedance spectroscopy on samples with electrodes and a contactless tone-burst excitation technique. At temperatures above 650 °C the conductivity-related losses are dominant. Finally, the operation of CTGS resonators is demonstrated at cryogenic temperatures and materials piezoelectric strain constants are determined from 4.2 K to room temperature. Copyright © Materials Research Society 2019.

2012, Schmidt, Hagen

[no abstract available]