TY - CONF A1 - Hufschläger, Daniel A1 - Gaal, Mate A1 - Ahmadzadeh, Majid T1 - Simulation und Vermessung von thermoakustischen Schallquellen N2 - Zur Simulation des Schallfeldes von beliebig geformten konventionellen Schallquellen existieren viele Ansätze (EFIT, GPSS). Sie alle basieren auf der Annahme eines monochromatischen akustischen Signals, was meist eine gültige Annäherung darstellt. Allerdings sind bei thermoakustischen Quellen aufgrund ihrer Funktionsweise und der hohen Bandbreite viele der existierenden Ansätze nicht direkt anwendbar und können Beobachtungen bei der Vermessung von thermoakustischen Wandlern nicht vollständig abbilden und erklären. In diesem Beitrag wurde die bekannte Methode der generalisierten Punktquellensynthese (GPSS) für die Berechnung von Schallfeldern von thermoakustischen Schallquellen angewendet. Dabei gehen zahlreiche Parameter wie die Dicke und Geometrie der leitfähigen Schicht, Krümmung des Substrats, sowie die Signalform der Anregung in die Simulation ein. Neu an dem präsentierten Ansatz ist die Abweichung von der üblichen monochromatischen Annäherung und die Berücksichtigung der großen Bandbreite von thermoakustischen Wandlern. Für die Validierung der Simulationen wurden Schallfelder von Quellen mit bekannter Anregung und Geometrie breitbandig durch ein optisches Mikrofon vermessen. T2 - DGZfP Jahrestagung CY - Kassel, Germany DA - 23.05.2022 KW - Thermoacoustics KW - Sensor characterization KW - Simulation PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-549944 SP - 1 EP - 7 AN - OPUS4-54994 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Ahmadzadeh, Majid A1 - Weise, Matthias T1 - Focussed sound field of thermoacoustic transmitters N2 - The thermoacoustic effect offers a method for selectively exciting broadband and focused ultrasonic waves, which can be utilized in air-coupled ultrasonic testing of lightweight components that might otherwise sustain damage from liquid couplants. Thermoacoustic transmitters are composed of an electrically conductive layer deposited on an insulating substrate. When electrical pulses are applied, the conductive layer heats, briefly warming the adjacent air and inducing thermal expansion, which generates an acoustic wave. In testing applications, the thermoacoustic transmitter is positioned at the focal distance to the structure under examination, where the resolution of the resulting ultrasonic image is influenced by the focus diameter. To optimize imaging resolution, understanding the focusing characteristics of thermoacoustic transmitters is essential. In this study, thermoacoustic transmitters with an indium tin oxide (ITO) layer on a quartz glass substrate were developed. Geometrical parameters, including substrate curvature and conductive layer thickness, along with electrical excitation parameters, were systematically varied to investigate their impact on the sound field up to approximately 1 MHz. The results indicate that, among the parameters studied, substrate curvature exerts the most significant influence on the sound field. T2 - DAS-DAGA Tagung CY - Kopenhagen, Danmark DA - 17.03.2025 KW - Air-coupled ultrasound KW - Thermoacoustic transmitter KW - Focussed transducer PY - 2025 SP - 1 EP - 4 AN - OPUS4-63092 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Ahmadzadeh, Majid A1 - Weise, Matthias T1 - Air-coupled ultrasonic transmission using thermoacoustic transmitters and optical microphones N2 - Background, Motivation and Objective Air-coupled ultrasonic transducers are usually applied for testing of some lightweight components. To increase the bandwidth or air-coupled testing systems and thus increase their application range, thermoacoustic transducers can be paired with optical microphones in a transmission mode. Thermoacoustic transmitters are based on the thermal excitation of sound waves, while optical microphones are based on laser interferometry and Fabri-Pérot etalon. We studied the spectrum and the efficiency of the transmission of an air gap using a thermoacoustic transmitter and an optical microphone. Statement of Contribution/Methods Thermoacoustic transmitters with an electrically conductive layer of indium tin oxide (ITO) on a curved quartz glass substrate were developed. Their sound field was measured using a commercially available optical microphone Eta450 Ultra based on Fabri-Perot etalon. The curvature and the conductive layer thickness of the thermoacoustic transmitter were systematically varied to investigate their impact on the sound field and the spectrum of the measured signal for frequencies up to 1 MHz. The transmitters were excited using rectangular burst signals with a varied width. We examined the influence of all parameters on the focusing, spectrum, and sensitivity. The directivity of the microphone was evaluated as well. Results/Discussion The focusing of the sound fields of all transmitters most strongly depends on the curvature radius of the substrate. The spectrum recorded in the focus of each transducer has several maxima and minima, as shown in the left-hand diagram, which are mostly a consequence of the irregularities of the microphone spectrum. These irregularities are visible also in the directivity diagram on the right, which was recorded by rotating the microphone. The 20 dB bandwidth of the measurement system covers the range up to about 1 MHz, depending strongly on the width of the excitation pulse (left-hand diagram). This highlights a key advantage of thermoacoustic transmitters: their spectral characteristics can be controlled through the excitation conditions, offering a potentially broader range of applications compared to conventional air-coupled transmitters. One promising example is localized ultrasound spectroscopy based on the detection of local resonances. T2 - IEEE International Ultrasonic Symposium CY - Utrecht, The Netherlands DA - 15.09.2025 KW - Air-coupled ultrasound KW - Thermoacoustic transmitter KW - Sound field PY - 2025 SP - 1 EP - 4 AN - OPUS4-64541 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -