Ensuring adequate depth of i.v. anaesthesia by measuring propofol in breath gas could increase patient safety. Mass spectrometry, representing the reference standard of propofol breath gas measurements, is not feasible in routine clinical practice; hence, a photoacoustic sensor was developed. The photoacoustic sensor quantifies propofol concentration in gas via the sound waves emitted by propofol molecules excited by light of specific wavelength and frequency. We studied the performance of the new sensor in propofol test gas, gas sampling bags filled with breath gas from different patients, and performed real-time measurements in patients undergoing propofol anaesthesia in comparison to ion-molecule reaction mass spectrometry. In test gas, photoacoustic and mass spectrometry correlated with an R² of 0.9975 in a range from 2.5 to 60 ppb. In gas sampling bags, propofol could be detected with both methods. Bland-Altman analysis of propofol general anaesthesia over 18 h in 10 patients revealed a mean propofol difference of -0.02 ppb (standard deviation 3.31) between mass spectrometry and photoacoustic measurements in breath gas, ranging from 4 to 47 ppb. Photoacoustic measurement of propofol concentration in breath gas is feasible with high accuracy in clinical applications.

Acoustic emissions play a major role in the usability of many product categories. Therefore, mitigating the emitted sound directly at the source is paramount to improve usability and customer satisfaction. To reliably predict acoustic emissions, numerical methods such as the boundary element method (BEM) are employed, which allow for predicting, e.g., the acoustic emission into the free field. BEM algorithms need appropriate boundary conditions to couple the sound field with the structural motion of the vibrating body. In this contribution, firstly, an interpolation scheme is presented, which allows for appropriate interpolation of arbitrary velocity data to the computational grid of the BEM. Secondly, the free-field Helmholtz problem is solved with the open-source BEM software framework NiHu. The forward coupling between the device of interest and BEM is based on the surface normal velocities (i.e., a Neumann boundary condition). The BEM simulation results are validated using a previously established aeroacoustic benchmark problem. Furthermore, an application to a medical device (knee prosthesis frame) is presented. Furthermore, the radiated sound power is evaluated and contextualized with other low-cost approximations. Regarding the validation example, very good agreements are achieved between the measurements and BEM results, with a mean effective pressure level error of $0.63$ dB averaged across three microphone positions. Applying the workflow to a knee prosthesis frame, the simulation is capable of predicting the acoustic radiation to four microphone positions with a mean effective pressure level error of $1.52$ dB.

A simulation method relying on the finite and infinite element techniques and a post-processing routine is introduced in this paper for the calculation of self and mutual radiation impedances of horns and acoustical resonators. The proposed procedure can be applied for the evaluation of the frequency dependent coupling impedance matrix of an arbitrary number of ducts in an arbitrary geometrical arrangement. The resulting impedance matrix can be utilized in a one-dimensional low-frequency waveguide model in order to calculate the input impedance or admittance function of the system. The applicability and usefulness of the proposed methodology is demonstrated by multiple simulation cases.

A three-dimensional coupled vibroacoustic finite element model for physics-based simulations of the sound generation by mallet percussion instruments in the time domain is discussed in the present paper. The mechanical model takes the orthotropic material properties of the wooden sound bars and the nonlinear nature of the interaction force between the mallet head and the sound bar into account while the acoustical model considers radiation into an unbounded domain. A direct coupling of the sound bars, acoustical cavity resonators, and the excitation by a mallet is considered with exploiting the modal basis to reduce the number of degrees of freedom of the system. Both the mechanical and acoustical models are validated by comparing them to measurements performed on an Orff xylophone. A case study shows the capabilities of the coupled model, including the analysis of the energy balance, the effect of tuning the resonator, and the excitation of the torsional modes of the sound bar.