Emile Martincic

Analytical and Finite-Element Modeling of Localized-Mass Sensitivity of Thin-Film Bulk Acoustic-Wave Resonators (FBAR)

Analytical and finite-element models of a localized-mass sensor fabricated with thin-film bulk acoustic wave resonator (FBAR) are reported. While our group demonstrated FBAR-based localized-mass sensors, no previous modeling of these sensors is found in the literature. The finite-element model (FEM) defines the boundary conditions and performs parametric analysis of the sensors mass loading, whereas the analytical approach takes advantage on a modified Masons model to describe the transmission-line circuit of the sensor. The sensitivity of the resonance frequency to location and size of mass deposition has been studied. Both the experimental and modeled responsivities exhibit a nonlinear dependence on the location and size of the localized-mass.

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.

Polymer-based flexible capacitive pressure sensor for non-invasive medical monitoring applications

In this paper, the design, the fabrication and the electromechanical characterization of polymer-based flexible pressure sensor are presented. This kind of sensors is developed for the non-invasive monitoring of pressure/force distributions that is required in many medical applications such as the monitoring of plantar pressures or chronic venous disorder treatments. The sensors considered in this paper are of a capacitive type. They are composed of two millimetric copper electrodes, separated by polydimethylsiloxane (PDMS) dielectric layers and deposited on a Kapton substrate. A study of the deformation of PDMS thin films under normal stress is carried out by finite element computations as well as experiments. This study points out a sensor design optimization parameter, the form ratio of the indented PDMS layer, which is used to design and fabricate capacitive micro-sensors samples. Preliminary electromechanical characterizations of realized sensor samples validate the approach. Under a 10 N normal stress, the sensitivity of 9 square mm sensors varies from 3% up to 17% in capacitive change, according to the chosen form ratio of the used PDMS layer.

Analytical and finite-element modeling of a localized-mass sensor

Analytical and finite-element models of a localized-mass sensor fabricated with thin-film bulk acoustic wave resonator (FBAR) are reported. A Masonpsilas model-based analytical approach to understand the non-linear behavior of the sensor is introduced. On the other hand, careful finite-element analysis (FEA) of the sensor is carried out for different mass-loading configurations. Based on both modeling and experimental results, the non-linear behavior of the localized-mass sensorpsilas responsivity is confirmed.

Mechanical Characterization of PDMS Films for the Optimization of Polymer Based Flexible Capacitive Pressure Microsensors

This paper reports on the optimization of flexible PDMS-based normal pressure capacitive microsensors dedicated to wearable applications. The operating principle and the fabrication process of such microsensors are presented. Then, the deformations under local pressure of PDMS thin films of thicknesses ranging from 100 μm to 10 mm are studied by means of numerical simulations in order to foresee the sensitivity of the considered microsensors. The study points out that, for a given PDMS type, the sensor form ratio plays a major role in its sensitivity. Indeed, for a given PDMS film, the expected capacitance change under a 10 N load applied on a 1.7 mm radius electrode varies from a few percent to almost 40% according to the initial PDMS film thickness. These observations are validated by experimental characterizations carried out on PDMS film samples of various thicknesses (10 μm to 10 mm) and on actual microsensors. Further computations enable generalized sensor design rules to be highlighted. Considering practical limitations in the fabrication and in the implementation of the actual microsensors, design rules based on computed form ratio optimization lead to the elaboration of flexible pressure microsensors exhibiting a sensitivity which reaches up to .

Integration of commercial microspeakers in an acoustic absorbing liner

In this work, the fabrication of an acoustic sound absorbing surface (i.e. liner) made of commercial Visaton™ K16 microspeakers is presented. The acoustic liner is made of a circular surface composed of a 10 cm diameter fix support with 7 embedded microspeakers covering 8.5% of th overall surface. Different electrical connections of the microspeakers using no added electronic circuit are tested and the obtained absorption coefficient is 0.2 close to the natural resonance frequency of the microspeakers. A Negative Impedance Converter is used to electrically compensate the losses occurring in the acoustic liner. The maximum sound absorption is raised to 0.31 using the NIC again close to the natural resonance frequency of the microspeakers with a 7 microspeakers configuration covering 8.5% of the wall surface. The back cavity of the microspeakers is found to slightly move the maximum absorption peak but not to modify the maximum absorption. The influence of the microspeakers density is measured in open circuit configuration. The surface covered by the microspeakers ranges from 2.85% up to 12.35% of the wall surface. The maximum sound absorption ranges then from 0.1 to 0.34.

High acoustic performance MEMS microspeaker

In this paper, a theoretical approach for the electrodynamic motor optimization has been presented. The analytical simulations of the electroacoustic efficiency were validated with an experimental measurements were we have seen a very good agreement. The same assembled device was characterized in an anechoic chamber, where we have detected an SPL around 80 dB for 0.5 W.

Acoustic vs electric power response of a high-performance MEMS microspeaker

This paper presents the characterization of the acoustic performance of an electrodynamic MEMS microspeaker and the influence of magnets position, which allows halving device size while intensifying the force factor. This work is based on the previously reported MEMS microspeaker dedicated to handheld electronics. A vacuum-formed seal has been designed and applied to enhance acoustic performance at low frequencies. The efficiency of the electroacoustic conversion is increased by a factor 5-10 compared to conventional microspeakers and low harmonic distortions were observed. Measurements of the acoustic power versus electrical input power were carried out in an anechoic room within the hearing range.

High resolution micro-Pirani pressure sensor gauge with transient response processing

A micro-Pirani pressure sensor, which consists of a pressure dependent thermo-resistance gauge, is traditionally exploited using a steady state resistance measurement. Any signal variation occurs over a constant voltage bias due to the initial resistance of the device which affects the sensors sensitivity. Our work shows for the first time an experimental investigation of a micro-Pirani gauge based on its dynamic behavior when heated by a current step. Such processing magnifies the pressure dependence of the gauges signal by eliminating the initial resistance influences on the measurement. Furthermore, a first order low pass filter step response identification of the experimental transient signal strongly reduces the thermal noise influence on the measurement. The heating step, the recording of the time dependent signal and its post-processing can be easily achieved by a small-size controller. The proposed system provides a substantial enhancement of the micro-Pirani pressure sensor performance.