Concept and evaluation of an endaurally insertable middle-ear implant.

A concept for a partially implantable hearing device, for which the power supply and signal transmission are provided by an optical transmission path, is evaluated. The actuator is designed to fit into the round-window niche and to couple directly to the round-window membrane. Implantable hearing aids can be a suitable solution in the case of severe hearing loss, where conventional hearing aids often fail. However, the surgical effort for an implantation is comparatively high. Therefore, the objective of our work was to provide a hearing system which combines reliable coupling to the auditory system with an easy implantation technique. The actuator was designed as a piezoelectric thin-film cantilever. The optical transmission path was realised using an infrared light-emitting diode combined with an active receiver circuit. For a voltage of 1V, the unloaded actuator presents displacement amplitudes of 1µm up to a stimulus frequency of 25kHz and forces up to 0.2mN. Proportionally larger forces can be achieved by stacking single actuators. The overall transmission loss from the electrical input of the light-emitting diode driver to the mechanical output of the unloaded actuator was less than 25dB at 1kHz and maximum output.

Admittance matrix of a trapezoidal piezoelectric heterogeneous bimorph.

Bimorph structures are a standard method for transforming the high force of piezoelectric materials into a large deflection. In micro electromechanical systems (MEMS) applications, it is preferable to use structures consisting of a passive substrate (usually silicon) and one or more piezoelectric layers on the top. Such structures are called heterogeneous bimorphs or enakemesomorphs. In some MEMS applications- for example, for use as acoustic transducers-it is desirable to arrange such heterogeneous bimorphs in a circular shape, which results in trapezoidal cantilever structures. In this paper, an analytic dynamic description of such actuators is obtained. The resulting model is proved to be compatible with existing models for heterogeneous bimorphs with constant width. A comparison to a finite element analysis model of an exemplary layout shows divergences wholly within the same range as found for published models for constant-width structures.

Conditions for highly efficient and reproducible round-window stimulation in humans.

Round-window stimulation is a new clinical approach for the application of active middle-ear implants. To investigate factors influencing the efficiency of round-window stimulation, experiments in 6 human temporal bones were performed with different actuator geometries and coupling conditions. The experiments show that the amplitude ratio between stapes and round-window actuator vibration is most efficient when using a 1.0-mm diameter rod with a 30° inclined tip geometry and an attached silicone pad. In this case, the amplitude ratio is 0.34 for frequencies up to 1.5 kHz and 0.27 for frequencies up to 20 kHz, with a standard deviation of only 4-6 dB at most frequencies. The analysis of data presented here and in a companion paper suggests that control of proper round-window membrane pretension as well as the inclined tip geometry are the major requirements for maximal performance.

Modeling the eardrum as a string with distributed force.

In this paper, an analytical model of the tympanic membrane is introduced where the two-dimensional tympanic membrane is reduced to a one-dimensional string. It is intended to bridge the gap between lumped-element models and finite-element models. In contrast to known lumped-element models, the model takes the distributed effect of the sound field on the tympanic membrane into account. Compared to finite-element models, it retains the advantage of a low number of parameters. The model is adjusted to forward and reverse transfer functions of the guinea-pig middle ear. Although the fitting to experimental data is not perfect, important conclusions can be drawn. For instance, the model shows that the delay of surface waves on the tympanic membrane can be different from the signal transmission delay of the tympanic membrane. In a similar vein, the standing wave ratio on the tympanic membrane and within the ear canal can considerably differ. Further, the model shows that even in a low-loss tympanic membrane the effective area, which commonly is associated with the transformer ratio in a lumped-element and some hybrid circuit models, not only is frequency-dependent, but also different for forward and reverse transduction.

Upper bounds for energy harvesting in the region of the human head.

This paper investigates different approaches for supplying power to implantable hearing systems via energy harvesting. Because of the specific nature of the problem, only energy harvesting in the region of the human head is considered. Upper bounds as well as more conservative estimations for harvesting mechanical, thermal, and electromagnetic energy are presented and discussed.

Energy-consistent pseudopotentials for the 5d elements--benchmark calculations for oxides, nitrides, and Pt(2).

The performance of new relativistic energy-consistent pseudopotentials for the 5d elements, adjusted to atomic valence spectra from multiconfiguration Dirac-Hartree-Fock calculations (J. Chem. Phys. 2009, 130, 164108.), is examined in coupled cluster and multireference configuration interaction benchmark calculations for the diatomics HfO, TaO, WO, ReN, OsN, IrN, and Pt(2), with basis sets of up to quintuple-zeta quality. The final accuracy reached for the oxides and nitrides, with corrections for pseudopotential errors (contributions from 4f shell correlation, for example), is 0.3 pm for bond lengths and 17 cm(-1) (1.5%) for harmonic vibrational frequencies. The spectroscopic constants of the ground state of Pt(2) can be reproduced with deviations of 3 pm for the bond length and 1 cm(-1) for the vibrational frequency, without any correction for pseudopotential errors.

Development and assessment of a short-range meta-GGA functional.

Short-range DFT/long-range ab initio methods allow for a combination of the weak basis-set dependency of DFT with an accurate ab initio treatment of long-range effects like van der Waals interaction. In order to improve existing short-range LDA and GGA density functionals, we developed a TPSS-like short-range meta-GGA exchange-correlation functional and checked its performance in long-range CCSD(T) calculations for thermodynamical properties of the G2 set of molecules.

Local and density fitting approximations within the short-range/long-range hybrid scheme: application to large non-bonded complexes.

We introduce local and density fitting approximations into a hybrid approach which couples short-range density functionals with long-range wave-functions. The use of density fitting methods within the local-correlation approximation makes it possible to tackle bigger systems than without these methods, so that we are now able to treat systems of biological interest within the DFT/ab initio scheme. In first benchmark calculations, we apply it to the S22 database of Hobza and co-workers for binding energies of weakly bound molecular clusters.

Formation of ground-state vibrational wave packets in intense ultrashort laser pulses.

The formation of coherent vibrational wave packets in the electronic ground state of neutral molecules in intense ultrashort laser pulses and their subsequent detection by means of recently developed pump-probe experiments are discussed. The wave packet formation is due to the pronounced dependence of the strong-field ionization rate on the internuclear distance. This leads to a deformation of the initial wave function due to an internuclear-distance dependent depletion. The phenomenon is demonstrated with a time-dependent wave packet study for molecular hydrogen.

A short-range gradient-corrected density functional in long-range coupled-cluster calculations for rare gas dimers.

A previously proposed scheme for coupling short-range (sr) density functionals with wavefunction-based long-range (lr) ab initio methods has been extended by (a) developing a new gradient-corrected sr functional of the Perdew-Burke-Ernzerhof (PBE) type and (b) introducing coupled-cluster (CC) approaches (CC with single and double excitations (CCSD), and with additional perturbative triples (CCSD(T))) at the ab initio side. The results show that mixing-in of lr-ab initio correlation helps to remove deficiencies of currently used density functionals for the treatment of van-der-Waals interactions. Compared to full ab initio calculations, the basis set dependence is weaker so that the accuracy of the mixed results surpasses that of the ab initio ones for basis sets of triple-zeta quality.