Design Methodology and Innovative Device Concept for Acoustic Hearing Implants

Nowadays, hearing impaired people can be treated with a multitude of different devices and surgical interventions that are selected in function of the type and degree of hearing loss of the patient. These known therapies cover the major part of possible hearing losses except severe to profound mixed hearing loss. The present thesis results from an industrial project that aims to develop a dedicated hearing therapy that treats this kind of hearing loss based on direct acoustic cochlear stimulation (DACS). A semi-implantable investigational hearing device is used in a clinical trial with four patients to validate this novel therapy approach. The development of this investigational hearing implant presents a considerable challenge due to the numerous medical and engineering aspects that have to be considered. The conceptual design process is therefore of central importance because it incorporates all the relevant aspects and defines the future device characteristics and performances. Fundamental design aspects that are not considered at this early design stage can only be implemented with difficulties and increased efforts later on. This is the motivation to develop within the scope of this thesis a conceptual design methodology that supports and facilitates this essential design phase. A conceptual design methodology for acoustic hearing implants is therefore presented at the example of the DACS investigational device. The methodology consists of a four-step-procedure and a system diagram tool. The four steps of the procedure are: Step 1: determination and analysis of the human body functions that shall be emulated by the system Step 2: determination of the preliminary system architecture Step 3: determination of the user and system requirements Step 4: conceptual design The system diagram tool guides the engineer through all four steps and helps visualizing and structuring the system environments, functions, interfaces and, most important, all interactions between the system elements and environments. The diagram drawing rules ensure that all requirements coming from the environments are correctly linked with the concerned system functions and therefore ensure that the system meets all these requirements. Finally, the system diagram is a valuable tool for the conceptual design step. Because of the clearly represented system elements and interactions, it supports the development of integrated solutions. The output of the presented methodology is a design concept that cannot be directly quantified to assess the benefit of the methodology. Only once the resulting device is successfully verified against the system requirements and validated against the user requirements, it can be concluded that the underlying concept is adequate. The outcome of the clinical study shows that the four implanted patients benefit all from the DACS device, which is therefore well suited to treat severe to profound mixed hearing loss. This confirms that device meets the user requirements and implies that conceptual design methodology is adequate. The realized investigational device consists of an externally worn audio processor, a percutaneous connector, and an implantable actuator. The hermetically sealed balanced armature actuator provides a maximal equivalent sound pressure level of 125 dB over the frequency range between 100 Hz and 10'000 Hz with a limited 1-mW power supply. A lumped parameter model of the actuator dynamics and a finite element model of the electro-mechanic actuator are used for the detailed actuator design.

On the dependability of nanoscale circuits and systems

Milos Stanisavljevic

The invention of the integrated circuit and the manufacturing progress as well as continuing progress in the manufacturing process are the fundamental engines for the implementation of all technologies that support today's information society. The vast majority of microelectronic applications presented nowadays use the well-established CMOS process and fabrication technology which exhibit high reliability rates. The hypothesis of reliable components has mostly been taken in the development of electronic systems fabricated in the past four decades. The steady downscaling of CMOS technology has led to the development of devices with nanometer dimensions. For future nano-circuits, emerging nanodevices and their associated interconnects, the expected higher probabilities of failures, as well as the higher sensitivities to noise and variations, could make future chips prohibitively unreliable. The systems to be fabricated will be made of unreliable components and achieving 100% correctness will not be only extremely costly, but might be plainly impossible. The global picture is that reliability emerges as one of the most significant threats to the design of future integrated computing systems. Building reliable systems out of unreliable components will require increased cooperative involvement of the logic designers and architects, where high-level techniques will rely upon lower levels support based on novel modeling including component and system reliability as design parameters. An architecture suitable for circuit-level and gate-level redundant modules and exhibiting significant immunity to permanent and random failures, as well as unwanted fluctuation of the fabrication parameters is presented, which is based on a four-layer feed-forward topology, using averaging and thresholding as the core voter mechanisms. The architecture with both fixed and adaptable threshold is compared to triple and R-fold modular redundancy techniques, and its superiority is demonstrated based on numerical simulations as well as analytical developments. A chip implementation of the architecture is realized. Other applications of the architecture like delay variations minimization are identified and explored. A novel general method enabling introduction of fault-tolerance, and evaluation of circuit and architecture reliability is proposed. The method is based on the modeling of probability density functions (PDFs) of unreliable components and their subsequent evaluation for a given reliability architecture. PDF modeling, presented for the first in the context of realistic technology and arbitrary circuit size, is based on a cutting-edge reliability evaluation algorithm and offers scalability, speed and accuracy. Fault modeling has also been developed to support PDF modeling. In the second part of the thesis a new methodology that introduces reliability in existing design flows is proposed. The methodology consists of partitioning the whole system into reliability-optimal partitions and applying reliability evaluation and optimization at local and system level. System level reliability improvement of different fault-tolerant techniques is studied in depth. Optimal partition size analysis and redundancy optimization have been performed for the first time in the context of a large-scale system, showing that a target reliability can be achieved with low to moderate redundancy factors (R < 50) even for high defect densities (device failure rate up to 10-3). The optimal window of application of each fault-tolerant technique with respect to defect density is presented as a way to find the optimum design trade-off between the reliability and power/area. R-fold modular redundancy with distributed voting and averaging voter is selected as the most promising candidate for the implementation in trillion-transistor logic systems. Finally, a realistic circuit example of the methodology implementation is verified using simulations.

EPFL2009

Sensorless Position Control of Piezoelectric Ultrasonic Motors

Markus Flückiger

This dissertation considers mechatronic systems driven by piezoelectric ultrasonic motors (PUM). The focus is set on optimal system design and sensorless position control. Mechatronic industry faces the challenge to deliver ever more efficient and reliable products while being confronted to increasingly short time to market demands and economic constraints driven by competition. Although optimal design strategies are applied to master this challenge, they do not entirely respond to the given circumstances, as often only local criteria are optimised. In order to obtain a globally optimal solution, the many subfunctions of a mechatronic system and their models must be interrelated and evaluated concurrently from the very beginning of the design process. In this context PUM have been used increasingly during the last decade for various positioning applications in the field of mechatronic systems, laboratory equipment, and consumer electronics where their performances are superior to conventional electromechanical drive systems based on DC or BLDC motors. The position of the mobile component must be controlled. In some cases open-loop control is a solution, but more often than not sensors are used as feedback device in closed-loop control. Sensors are expensive, large in size and add fragile hardware to the device that compromises its reliability. Thus, not only the superior performance is not fully exploited but also the economical feasibility of the PUM drive system is jeopardised. Replacing sensors by advanced control techniques is an approach to these problems that is well established in the field of BLDC motors. Those sensorless control strategies are not directly transferrable, because of the fundamentally different working principles of PUM. Hence, the research of sensorless closed-loop position control techniques applicable to PUM and their validation with digitally controlled functional models is the very topic of this thesis. We propose a dedicated design methodology to this statement of the problem. A core model of the mechatronic system is conceived as general and simple as possible. It then develops for the different interrelated views reflecting the mechanical, electromechanical, drive electronic, sensorial and digital control functions of the global system. Each one becoming more specific and detailed in this process, the different views still enable mutual constraint adjustments and the dynamic integration of results from the other views during the design process. Starting with the stator of the PUM, a view describes the mechanical displacement. An electric equivalent model is written such that power input from the drive electronics is related to the mechanical energy transmitted to the mechanics. The resulting differential equations are solved by the finite element method (FEM). Position feedback configurations in the mobile part of the PUM are modelled analytically in order to be implemented in digital control and their electrical implications are updated to the stator model. In this way, sensors do not necessarily materialise physically any more, but are distributed among the mechanical configuration, the drive electronics and the digital controller. With respect to the sensor data, the controller is not simply receiving finalised data on the measured system parameter, but rather implements the sensor itself in software. Finally, the position detection performance obtained with the aforementioned design methodology was evaluated with the example of mechatronic locking devices actuated by custom-made as well as OEM motors. Functional models of motors, electronics and digital controllers were used to identify the limits of the proposed methods, and suggestions for further research were deduced. These results contribute to the development of robust sensorless position controllers for PUM.

EPFL2010

Development of a contactless capacitive immunosensor

Brice Perruche

In the present work, a label-free, contactless and capacitive immunosensor is developed using impedance spectroscopy, in the aim to perform low-cost immunoassays. Chapter 1 puts this work in perspective with some existing techniques, while a presentation of impedance theory used in this work is carried out in chapter 2. In Chapter 3, numerical simulations using a commercial finite element method software is carried out. The response of coplanar and face-to-face designs using an insulating layer is studied with respect to a frequency ranging from 100 Hz to 10 MHz . Two levels of capacitance were observed across the frequency range : the low frequency capacitance created by the insulating layer and the high frequency capacitance created by the solution. These capacitances depend on parameters like the solution conductivity, the distance between the electrodes, the electrodes width or the insulating layer thickness. A dimensionless parameter is defined to evaluate the quality of the geometry at high frequencies. Microchips using a coplanar design are developed in Chapter 4. They are composed of two silver electrodes drilled in a PET sheet by laser photoablation. The design of both holder and of the microchips is optimized to increase as much as possible the signal-to-noise ratio. Bovine Serum Albumin is detected by a variation of the channel conductivity. Chapter 5 introduces the design of a sensor using electrodes made of a mass market aluminium foil. The study of the frequency response of the electrodes led to the creation of a discrete analytical model. The electrodes are then mounted into a holder using a face-to-face or coplanar design. The system is characterized through the variation of several geometrical parameters (height of fluid in the reservoir, electrode surface area, solution conductivity, ...). The coplanar design is also optimized to be able to work in a holder equipped with a fluidic channel. Finally, the ability of the aluminium electrodes based sensor to monitor an adsorption is studied in Chapter 6. The resonance is used to detect the adsorption of proteins like BSA on the electrodes using coplanar and face-to-face designs. The adsorption is found to follow a Langmuir isotherm and an adsorption equilibrium constant is extracted. The second adsorbate layer is detected using a coplanar design, enabling the achievement of a immunoassay.

EPFL2011