People suffering from moderate to severe hearing loss can be treated with active middle ear implants. A new approach in this field is to implant an electromechanical transducer onto the round window membrane in order to improve coupling and be able to treat patients with middle-ear problems. In this paper the design study for a miniaturized displacement transducer (MDT) for the round window is presented. Based on a requirement analysis, the basic principle and analytical modeling of the actuator is shown. A parameter variation study results in an optimized actuator configuration that is able to generate an amplification of 110 dB SPL theoretically. As a next step this actuator has to be manufactured and tested.
In-stent restenosis is a frequent complication after stent implantation. This article investigates the design of a passive sensor system to be integrated into a stent for the detection of an in-stent restenosis by measuring the local pulse wave velocity (PWV). The proposed system uses two resonant circuits consisting of a capacitive pressure sensor and a coil as transponders. The pressure sensors are located at the proximal and distal end of the stent. An alternating external magnetic field with a constant frequency is applied such that the resonance frequencies of the transponders cross the excitation frequency when the pulse wave passes. The time delay between the resonances at the transponders can be captured to obtain the PWV. A model for the measurement system and a correlation between transponder design parameters and minimal resolvable time delay are derived. This correlation is based on the criterion that the 3 dB bandwidth of the transponder resonances may not overlap in the measurement time interval. This correlation can be used to design and analyze a transponder system for the proposed measurement system. In an experiment, in which the pressure sensors have been emulated by varactor diodes, it could be shown that the model is valid and that the criterion is suitable. Finally, the relevant design parameters of the transponders have been identified and their limitations investigated.
In-stent restenosis (ISR) is a frequent complication after stent implantation. Recently, a passive sensor system for integration into a stent has been presented, which is designed to detect an ISR early by measuring the local pulse wave velocity (PWV). This system is based on two pressure sensitive transponders, the resonance frequency of which hits the frequency of a magnetic field generated by an externally applied transceiver coil during a pulse cycle. This method is limited in applicability by the largest PWV it can measure. In this contribution a modified sensor system is investigated, which operates at two separate frequencies for each transponder. It has been shown that this modification solves the problem of limited PWV measurement range. Additionally, the previously developed model was shown to be valid for bifrequent operation. Furthermore, the influence of the system parameters on measurement precision have been investigated and verified in simulations.
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