Marion Woytasik

Micro Blood Pressure Energy Harvester for Intracardiac Pacemaker

This paper presents the design, fabrication, and tests of a microspiral-shaped piezoelectric energy harvester and its associated microfabricated packaging that collects energy from ordinary blood pressure variations in the cardiac environment. This device could become a life-lasting, miniaturized energy source for active implantable medical devices such as leadless pacemakers. We present the concept and tested prototypes of 10 μm thin and ultra-flexible electrodeposited microbellows (6mm diameter, 21mm3 volume) as a new type of implant packaging. It enables direct blood pressure harvesting and permits a high efficiency of energy transfer to a transducer operating in quasi-static mode and hence adaptable and unaffected by frequent heartbeat frequency changes. Spiral-shaped piezoelectric transducers are introduced for their flexibility and large incoming mechanical energy. Non-trivial optimal electrodes placement and best spiral design parameters are studied and discussed. Three types of spiral prototypes (11mm3 volume each) with doubled-sided microstructured electrode patterns are presented and characterized. A power of 3 μJ/cm3/heartbeat and a transduction efficiency of 5.7×10-3 have been obtained for the best designs at 1.5Hz and we predict that twice as much could be obtained using similar design process and material. Through implementing smart adapted electronic circuits, a potential additional tenfold increase in power output could be achieved, which would be sufficient to power a leadless pacemaker.

Optimization and Microfabrication of High Performance Silicon-Based MEMS Microspeaker

A novel structure of electrodynamics microelectromechanical systems (MEMS) microspeaker designed for mobile electronics is proposed in this paper. The originality of the device lies on the use of a rigid silicon membrane suspended by highly flexible silicon springs, contrary to most MEMS and non-MEMS microspeakers, which use polymer diaphragms. Important rigidity of the membrane and high linearity of the magnetic actuation conferred outstanding sound quality. The design of the silicon springs enabled large out-of-plane displacement of the membrane, which improved the bass rendering and the acoustic intensity over the whole bandwidth. The low density of silicon material helped to reduce the mobile mass and thus improved the microspeaker efficiency. A prototype with a membrane diameter of 15 mm and a thickness of 20 μm is microfabricated and characterized. The silicon springs enabled out-of-plane displacement of more than 300 μm. Acoustic intensity of 80-dB SPL is measured at 10 cm with 500-mW input power. This sound pressure level is obtained at frequencies from 330 Hz up to 70 kHz. Thanks to the membrane backside microstructure, most of the membrane proper modes are shifted out of the audible bandwidth. The measured electroacoustic efficiency is almost three times better than that of conventional microspeakers.

Towards high fidelity high efficiency MEMS microspeakers

This paper presents simulations and microfabrication of different parts of high fidelity electrodynamic MEMS loudspeakers with high electroacoustic conversion efficiency. The originality of the structure lies on the use of rigid silicon membranes suspended by a whole set of silicon beams instead of flexible polymer membranes usually found in MEMS loudspeakers. The microspeaker structure includes a planar copper microcoil electroplated on the silicon membrane and permanent magnets bonded on the substrate. Microstructure of the silicon membrane was optimized using FEM simulations for providing both rigidity and lightness of the mobile part. The results presented on a deep RIE etched 15 mm diameter silicon membrane structured with 40 stiffening ribs and on a 30 µm thick microcoil with 35 turns experimentally show the feasibility of key stages required for manufacturing of MEMS microspeakers with outstanding properties.

Micromachined piezoelectric spirals and ultra-compliant packaging for blood pressure energy harvesters powering medical implants

This paper introduces a novel energy harvesting technique and an associated packaged device aimed at powering intracardiac active medical devices by scavenging energy from ordinary blood pressure variations. We present the innovative concept of a micro-bellows packaged implant that deforms due to cyclic blood pressure variations in the cardiac cavities. This bellows transmits stresses on a spiral-shaped piezoelectric transducer that converts mechanical deformations into electric energy. The particular shapes of the different components (bellows and spiral) are designed to dramatically increase the mechanical energy that is harvested. The miniature bellows design, fabrication through electrodeposition for high compliance and hermeticity, and experimental characterization are presented. The specific challenges that arise in spiral shapes piezoelectric harvesters working in bending mode are discussed and we present a method to predict the non-trivial optimal electrode placements for maximum efficiency. This design process is completed by an associated microfabrication method and three types of piezoelectric bimorph spiral samples with doubled-sided microstructured electrode patterns are presented. The experimental performances of these prototypes are confronted to numerical simulation. A power of 4.15 μW/cm3 at 1.5 Hz has been obtained for the best design and we predict that tens of micro-Watts per cubic centimeter could be obtained using similar design process and material.

Implanted, inductively-coupled, radiofrequency coils fabricated on flexible polymeric material: application to in vivo rat brain MRI at 7 T.

Combined with high-field MRI scanners, small implanted coils allow for high resolution imaging with locally improved SNR, as compared to external coils. Small flexible implantable coils dedicated to in vivo MRI of the rat brain at 7 T were developed. Based on the Multi-turn Transmission Line Resonator design, they were fabricated with a Teflon substrate using copper micromolding process and a specific metal-polymer adhesion treatment. The implanted coils were made biocompatible by PolyDimethylSiloxane (PDMS) encapsulation. The use of low loss tangent material achieves low dielectric losses within the substrate and the use of the PDMS layer reduces the parasitic coupling with the surrounding media. An implanted coil was implemented in a 7 T MRI system using inductive coupling and a dedicated external pick-up coil for signal transmission. In vivo images of the rat brain acquired with in plane resolution of (150 μm)(2) thanks to the implanted coil revealed high SNR near the coil, allowing for the visualization of fine cerebral structures.

Multilayer out-of-plane overlap electrostatic energy harvesting structure actuated by blood pressure for powering intra-cardiac implants

We present an innovative multilayer out-of-plane electrostatic energy harvesting device conceived in view of scavenging energy from regular blood pressure in the heart. This concept involves the use of a deformable packaging for the implant in order to transmit the blood pressure to the electrostatic transducer. As shown in previous work, this is possible by using thin metal micro-bellows structure, providing long term hermeticity and high flexibility. The design of the electrostatic device has overcome several challenges such as the very low frequency of the mechanical excitation (1 to 2 Hz) and the small available room in the medical implant. Analytical and numerical models have been used to maximize the capacitance variation, and hence to optimize the energy conversion. We have theoretically shown that a 25-layer transducer with 6-mm diameter and 1-mm thickness could harvest at least 20 mJ per heart beat in the left ventricle under a maximum voltage of 75 V. These results show that the proposed concept is promising and could power the next generation of leadless pacemakers.

Planar Microcoil Optimization of MEMS Electrodynamic Microspeakers

A method for optimizing the planar microcoil of MEMS electrodynamic microspeakers with the aim of maximizing the electroacoustic efficiency is presented. The proposed approach is based on a mixed-model using both analytical models and finite element method (FEM). FEM simulation was used for computing the spatial distribution of the magnetic field created by the permanent magnets, making thus possible to analyze any geometry of permanent magnets. Different configurations of magnets were considered, and for each the planar copper microcoil was optimized while taking into account the technological constraints due to the microfabrication process, the associated electronics and the targeted acoustic power emission. The results showed that the proposed method predicts the force factor in very good agreement with experimental measurements carried out on the micromachined device. Moreover, according to the electro-mechano-acoustic model, these results showed that the optimized microcoil associated to the best magnet configuration increases the electroacoustic efficiency by more than 200% compared to conventional microspeakers.

Design of a 3D multilayer out-of-plane overlap electrostatic energy harvesting MEMS for medical implant applications

This paper presents an innovative inertial electrostatic energy harvester for powering active medical devices implanted in the heart by scavenging the heart beat vibrations. The design of the electrostatic device has to overcome several challenges related to the very low frequencies of the mechanical excitation, the need for high reliability and more than ten years durability. Analytical and numerical modelling of the electrostatic device was carried out to maximize the capacitance variation, in order to maximize the energy conversion capability of the device. Optimization of the spring shape has been performed using numerical modelling to minimize the stress concentration in the flexible parts of the MEMS structure. Finally, based on a behavioral model including the electronic interface, we estimated that the device will be able to harvest about 10 μW average power in pulsed mode with 20 V DC output voltage for the electronic interface and 20 Hz resonant frequency, corresponding to 74 μW/cm3 power density.

Energy harvesting devices as long lasting power sources for the next generation pacemakers

This paper presents devices for harvesting energy from regular blood pressure variation in heart cavities. Specific challenges of this concept are analyzed. First, a very flexible and hermetic packaging solution is proposed. Then, piezoelectric and electrostatic transducers are conceived and optimized for the pacemaker application. According to our simulations and experiments, the proposed devices should provide the targeted electrical energy of 10 μJ per heartbeat in real environment.

Electrodynamic MEMS: Application to Mobile Phone Loudspeakers

This paper presents an electrodynamic MEMS for mobile phone loudspeaker applications. The whole structure of the loudspeaker is a new conception to reach higher performances than in existing devices: a linear behavior to ensure a high acoustic fidelity and a high efficiency to increase the power autonomy. So, the motor is ironless, constituted of permanent magnet only. Several electrodynamic structures are presented and studied with analytical formulations of the magnetic field. The emissive part is a plane silicon surface, very rigid and light, the suspension is achieved by silicon beams, which are not sensitive to mechanical fatigue, the electroplated copper coil is thick and requires a specialist technique to be deposited. The moving part displacements are in a range far larger than in existing MEMS (600 μ m). The trends for dimensioning the structure are investigated and prototypes realized and tested, with NdFeB ring magnets. As a result, the 70 dB SPL at 10 cm bandwidth reaches up to 100 kHz, and the behavior is particularly linear.