Asta Kärkkäinen

Significance of Nanotechnology for Future Wireless Devices and Communications

This paper reviews the expected wide and profound impact of nanotechnology for future wireless devices and communication technologies.

SIMULATION OF THE TRANSFER FUNCTION FOR A HEAD-AND-TORSO MODEL OVER THE ENTIRE AUDIBLE FREQUENCY RANGE

In this study, a method for simulating the transfer function of a head-and-torso model over the entire audible frequency range is introduced. The simulation method uses the ultra-weak variational formulation (UWVF) which is a finite element type method tailored for wave problems. In particular, the UWVF uses plane wave basis functions which better approximate the oscillatory field than a polynomial basis used in the standard finite element methods (FEM). This leads to reduction in the computational complexity at the high frequencies which, accompanied with parallel computing, extends the feasible frequency range of the UWVF method. The accuracy of the new simulation tool is investigated using a simple spherical geometry after which the method used for preliminary HRTF simulations in the geometry of a widely used head-and-torso mannequin.

Simulation of the head-related transfer functions using cloud computing

Due to the complexity of measurements for obtaining individual head-related transfer functions (HRTFs), numerical simulations offer an attractive alternative for generating large HRTF data bases. In this study, HRTFs are simulated using a fast multipole boundary element method (BEM). The BEM is well suited for the HRTF simulations. Namely, only the surface of the model geometry is discretized which simplifies the pre-processing compared to other full-wave simulation methods (such as finite element and finite difference methods). The BEM is formulated in frequency domain and the model is solved separately for each frequency. Since a large number of frequencies is needed in wide-band HRTF simulations, the BEM simulation greatly benefits from distributed (or parallel) computing. That is, a single computing unit takes care of a single frequency. In this study, a distributed BEM using cloud computing is introduced. Simulations are computed in a public cloud (Amazon EC2) using a realistic head and torso geometry (3D laser scanned geometry of Bruel & Kjaer HATS 4128 mannequin). The frequency range of the simulations is from 20 to 20000 Hz. The feasibility of cloud computing for simulating HRTFs is examined and first analysis results for the simulated HRTFs are shown.

Simulations of head‐related transfer functions in wideband acoustics

Head‐related transfer functions (HRTFs) have been simulated in three dimensions for a head‐and‐torso model for the entire audio frequency range, from 20 Hz to 20 kHz. As opposed to data acquired through measurements, the results derived from computer simulations are free from the effects of noise and imperfections in the electro‐acoustic chain. In addition, the spatial resolution can easily be made better than in any practical experiment. The simulations have been performed using an ultraweak variational formulation method for solving Helmholtz equation. The numerical method with its parallel computing capability is efficient, enabling numerical calculations of large physical systems, e.g., of size 0.4×0.5×0.8 m, at high frequencies. The method uses plane‐wave basis functions instead of polynomial basis as in standard finite‐element methods (FEM), resulting in the need of much sparser volume mesh than in FEM. For HRTF calculations, a so‐called perfectly matched layer has been utilized and the solutions ar...