TY  - JOUR
A1  - Daschewski, Maxim
A1  - Kreutzbruck, M.
A1  - Prager, J.
T1  - Influence of thermodynamic properties of a thermo-acoustic emitter on the efficiency of thermal airborne ultrasound generation
JF  - Ultrasonics
N2  - In this work we experimentally verify the theoretical prediction of the recently published Energy Density Fluctuation Model (EDF-model) of thermo-acoustic sound generation. Particularly, we investigate experimentally the influence of thermal inertia of an electrically conductive film on the efficiency of thermal airborne ultrasound generation predicted by the EDF-model. Unlike widely used theories, the EDF-model predicts that the thermal inertia of the electrically conductive film is a frequency-dependent parameter. Its influence grows non-linearly with the increase of excitation frequency and reduces the efficiency of the ultrasound generation. Thus, this parameter is the major limiting factor for the efficient thermal airborne ultrasound generation in the MHz-range. To verify this theoretical prediction experimentally, five thermo-acoustic emitter samples consisting of Indium-Tin-Oxide (ITO) coatings of different thicknesses (from 65 nm to 1.44 mu m) on quartz glass substrates were tested for airborne ultrasound generation in a frequency range from 10 kHz to 800 kHz. For the measurement of thermally generated sound pressures a laser Doppler vibrometer combined with a 12 mu m thin polyethylene foil was used as the sound pressure detector. All tested thermo-acoustic emitter samples showed a resonance-free frequency response in the entire tested frequency range. The thermal inertia of the heat producing film acts as a low-pass filter and reduces the generated sound pressure with the increasing excitation frequency and the ITO film thickness. The difference of generated sound pressure levels for samples with 65 nm and 1.44 mu m thickness is in the order of about 6 dB at 50 kHz and of about 12 dB at 500 kHz. A comparison of sound pressure levels measured experimentally and those predicted by the EDF-model shows for all tested emitter samples a relative error of less than +/- 6%. Thus, experimental results confirm the prediction of the EDF-model and show that the model can be applied for design and optimization of thermo-acoustic airborne ultrasound emitters.
KW  - Thermophone
KW  - Thermo-acoustic effect
KW  - Thermal sound generation
KW  - Resonance-free ultrasound emitter
KW  - Thermal inertia
Y1  - 2015
U6  - https://doi.org/10.1016/j.ultras.2015.06.008
SN  - 0041-624X
SN  - 1874-9968
VL  - 63
SP  - 16
EP  - 22
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Daschewski, Maxim
A1  - Kreutzbruck, Marc
A1  - Prager, Jens
A1  - Dohse, Elmar
A1  - Gaal, Mate
A1  - Harrer, Andrea
T1  - Resonance-free measuring and excitation of ultrasound
JF  - Technisches Messen : tm ; Plattform für Methoden, Systeme und Anwendungen der Messtechnik
N2  - In this contribution we present innovative methods for broadband and resonance-free sensing and emitting of ultrasound. The sensing method uses a polyethylene foil and a laser vibrometer as a broadband and resonance-free sound receiver. In general, this method enables absolute measurement of sound particle velocity and sound pressure in arbitrary, laser beam transparent liquids and gases with known density and sound velocity. The resonance-free emitting method is based on the electro-thermo-acoustic principle and enables, contrary to conventional ultrasound transducers, generation of arbitrary shaped acoustic signals without resonances and post-oscillations.
KW  - Ultrasound
KW  - transfer function
KW  - characterization of ultrasonic measurement systems
KW  - thermo-acoustic ultrasound emitter
Y1  - 2015
U6  - https://doi.org/10.1515/teme-2014-0020
SN  - 0171-8096
VL  - 82
IS  - 3
SP  - 156
EP  - 166
PB  - De Gruyter
CY  - Berlin
ER  -