Phonon attenuation in the GHz regime : Measurements and simulations with a visco-elastic material model

Aluminum and PMMA thin film samples are investigated regarding their mechanical properties like speed of sound and attenuation. Aluminum is often used as a transducer layer for pump probe laser measurements and different PMMA types have a large importance in the nanoimprinting technique. The measurements are performed on a short pulse laser pump probe setup, where bulk wave packets in the GHz regime are excited and detected using near infrared laser pulses of less than 100 fs duration. This contact-free and non-destructive measurement method is explained. In order to extract the attenuation precisely from the measurements, the entire experimental setup is simulated numerically: The heat distribution and the thermo-elastic wave excitation caused by the laser pulse, the mechanical wave propagation, and the photo-acoustic detection. By means of the visco-elastic modeling of the wave propagation, the simulations are fitted to the measurements by tuning the attenuation parameters in the numerical model. In this way it is possible to extract the attenuation from the measurements. First, two different types of Aluminum on a sapphire substrate are analyzed: Electron beam evaporated Aluminum and sputtered Aluminum, respectively. The thicknesses of the Aluminum films are in the range of 300 nm. It turns out that the attenuation is much higher in the sputtered Aluminum film. Afterwards, PMMA thin films used for nanoimprinting with thicknesses between 300 and 600 nm are analyzed. The PMMA thin films are spincoated onto a Silicon wafer and covered with an Aluminum transducer layer. The very good agreement between the measurements and simulations of the stacked samples allows a reliable determination of the attenuation in the PMMA films in the GHz regime

Phonon attenuation in the GHz regime : Measurements and simulations with a visco-elastic material model

Aluminum and PMMA thin film samples are investigated regarding their mechanical properties like speed of sound and attenuation. Aluminum is often used as a transducer layer for pump probe laser measurements and different PMMA types have a large importance in the nanoimprinting technique. The measurements are performed on a short pulse laser pump probe setup, where bulk wave packets in the GHz regime are excited and detected using near infrared laser pulses of less than 100 fs duration. This contact-free and non-destructive measurement method is explained. In order to extract the attenuation precisely from the measurements, the entire experimental setup is simulated numerically: The heat distribution and the thermo-elastic wave excitation caused by the laser pulse, the mechanical wave propagation, and the photo-acoustic detection. By means of the visco-elastic modeling of the wave propagation, the simulations are fitted to the measurements by tuning the attenuation parameters in the numerical model. In this way it is possible to extract the attenuation from the measurements. First, two different types of Aluminum on a sapphire substrate are analyzed: Electron beam evaporated Aluminum and sputtered Aluminum, respectively. The thicknesses of the Aluminum films are in the range of 300 nm. It turns out that the attenuation is much higher in the sputtered Aluminum film. Afterwards, PMMA thin films used for nanoimprinting with thicknesses between 300 and 600 nm are analyzed. The PMMA thin films are spincoated onto a Silicon wafer and covered with an Aluminum transducer layer. The very good agreement between the measurements and simulations of the stacked samples allows a reliable determination of the attenuation in the PMMA films in the GHz regime

Acoustic Compressibility of Caenorhabditis elegans

The acoustic compressibility of Caenorhabditis elegans is a necessary parameter for further understanding the underlying physics of acoustic manipulation techniques of this widely used model organism in biological sciences. In this work, numerical simulations were combined with experimental trajectory velocimetry of L1 C. elegans larvae to estimate the acoustic compressibility of C. elegans. A method based on bulk acoustic wave acoustophoresis was used for trajectory velocimetry experiments in a microfluidic channel. The model-based data analysis took into account the different sizes and shapes of L1 C. elegans larvae (255 ± 26 μm in length and 15 ± 2 μm in diameter). Moreover, the top and bottom walls of the microfluidic channel were considered in the hydrodynamic drag coefficient calculations, for both the C. elegans and the calibration particles. The hydrodynamic interaction between the specimen and the channel walls was further minimized by acoustically levitating the C. elegans and the particles to the middle of the measurement channel. Our data suggest an acoustic compressibility κCe of 430 TPa-1 with an uncertainty range of ±20 TPa-1 for C. elegans, a much lower value than what was previously reported for adult C. elegans using static methods. Our estimated compressibility is consistent with the relative volume fraction of lipids and proteins that would mainly make up for the body of C. elegans. This work is a departing point for practical engineering and design criteria for integrated acoustofluidic devices for biological applications.status: publishe