Spectroscopic properties of Er3+-doped antimony oxide glass

International audienceSpectroscopic properties of Er3+ ions have been studied in the 60Sb2O3-20WO3-19Na2O-1Bi2O3 (SWNB) glasses doped with 0.25 and 0.50 mol% Er2O3 respectively. The Judd-Ofelt parameters measured from the absorption spectra have been used to calculate the radiative life-time (τr) and the stimulated emission cross section. The low phonon energy, a reduced quenching effect and a high quantum efficiency of 90% for the 1.53 μm expected laser emission into pumping at 980 nm are in favor of promising material laser application

Digitally Assisted Analog: An Anti-Clipping Function for Class-D Audio Amplifier

International audienceThis paper presents a new speaker protection scheme for Class-D audio amplifiers, which acts by limiting the amount of clipping below a specified level. It is associated with a gain modulation algorithm to maintain the best tradeoff between audio quality and sound level. The proposed approach works for a large range of frequencies, independently of the power supply voltage and load impedance. Thanks to listening and model-based psycho-acoustical evaluations, this solution is found to be more effective than existing solutions such as soft clipping or analog limiters. It can be easily integrated into a Class-D amplifier targeted for mobile applications because the sensing and gain modulation use a small area (a few % of the amplifier IC) and an extra-low current consumption (<1% of the amplifier's idle current)

Comparison Between Voltage and Current Driving Methods of a Micro-Speaker

International audienceSince its inception, most of audio amplifier controls the loudspeaker in voltage. But previous studies highlighted the importance of the speaker control in current. These studies have been done only with large size loudspeakers (bass or midrange speakers) and this is certainly not transposable for the type of loudspeaker in interest i.e. micro-speaker. First of all, this paper describes a model of loudspeaker (voltage driven and also current driven) represented by a comprehensive set of data based on a minimal number of measurements. Simulation results based on these models are presented using single frequency signals such as multi-frequencies signals to compare the two driven methods. At this level of modelling, simulation results show that, contrary to the woofer applications, current driving of micro-speaker does not affect significantly in terms of harmonic distortions, intermodulation distortions and transient behaviour. Abstract Since its inception, most of audio amplifier controls the loudspeaker in voltage. But previous studies highlighted the importance of the speaker control in cur-rent. These studies have been done only with large size loudspeakers (bass or midrange speakers) and this is certainly not transposable for the type of loud-speaker in interest i.e. micro-speaker. First of all, this paper describes a model of loudspeaker (voltage driven and also current driven) represented by a com-prehensive set of data based on a minimal number of measurements. Simulation results based on these models are presented using single frequency signals such as multi-frequencies signals to compare the two driven methods. At this level of modelling, simulation results show that, contrary to the woofer applications, current driving of micro-speaker does not affect significantly in terms of har-monic distortions, intermodulation distortions and transient behaviour

High fidelity microelectromechanical system electrodynamic micro-speaker characterization

International audienceThis paper deals with the heterogeneous characterization of a microelectromechanical system (MEMS) electrodynamic micro-speaker. This MEMS micro-speaker consists of an optimized silicon structure based on a very light but very stiff membrane. The mobile part is suspended using soft suspension beams, also made of silicon, which enable large out-of-plane displacement. The electromagnetic motor is composed of a micro-assembly permanent ring magnet and of a deposit mobile planar coil fixed on the top of the silicon membrane. Previous publications have presented the MEMS as theoretically able to produce high fidelity and high efficiency over a wide bandwidth. The present study intends to validate the electrical, the mechanical, and the acoustic performance improvements. The characterization of the microfabricated micro-speaker showed that the electric impedance is flat over the entire audio bandwidth. Some results validates the performance improvements in terms of audio quality as compared to state of the art of the MEMS micro-speakers, such as the high out-of-plane membrane displacement over ±400 μm, the 80 dBSPL sound pressure level at 10 cm, the 2% maximal distortion level, and the useful bandwidth from 335 Hz to cutoff frequency

A longitudinal traveling wave piezoelectric transformer

International audienc

A transverse traveling wave piezoelectric transformer

International audiencePiezoelectric transformers can be a promising candidate in isolated power converters to replace magnetic ones as they present high quality factor, high voltage gain and low electromagnetic compatibility issues. Herein a new topology of traveling wave piezoelectric transformer (TWPT) is proposed. Unlike conventional piezoelectric transformers, the proposed transformer uses progressive waves to carry out the electromechanical conversion. The main asset of the structure is the obtaining of a polyphase system of voltage at the output. Thus, associated with an appropriate converter circuit topology, it enables any kind of AC-DC or AC-AC power conversion. The proposed piezoelectric transformer consists in a multi-electrode ring architecture and uses transverse wave, i.e. the deformation is orthogonal to the propagation direction, to perform the electro-mechanical coupling. Furthermore an analytical modelling is exposed to describe the electro-mechanical behaviour of the transformer. The technique allows to obtain an admittance matrix that completely characterizes the coupling between all the electrodes and that can be used to simulate the transformer in electronic circuit software. With this model it is possible to predict numerically the voltages, currents, displacements and stresses in the piezoelectric transformer over time as a function of the geometrical and physical parameters of the materials in early design stage and it allows a co-design between the piezoelectric transformer and its power electronics circuitry. Finally, a prototype of the TWPT with four phase output voltage is presented to experimentally validate this new concept

High Fidelity MEMS Electrodynamic Micro-Speaker Characterization

International audienceThis paper deals with the heterogeneous characterization of a MEMS electrodynamic micro-speaker. This MEMS micro-speaker consists of an optimized silicon structure based on a very light but very stiff membrane. The mobile part is suspended using soft suspension beams, also made of silicon, which enable large out-of-plane displacement. The electromagnetic motor is composed of a micro-assembly permanent ring magnet and of a deposit mobile planar coil fixed on the top of the silicon membrane. Previous publications have presented the MEMS as theoretically able to produce high fidelity and high efficiency over a wide bandwidth. The present study intends to validate the electrical, the mechanical and the acoustic performance improvements. The characterization of the microfabricated micro-speaker showed that the electric impedance is flat over the entire audio bandwidth. Some results validates the performance improvements in terms of audio quality as compared to state of the art of the MEMS micro-speakers, such as the high out-of-plane membrane displacement over ±400 µm, the 80 dB SPL sound pressure level at 10 cm, the 2 % maximal distortion level, and the useful bandwidth from 335 Hz to cutoff frequency

Stability of symmetrical comb-drive actuator

18th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications 4–7 December 2018, Daytona Beach, Florida, USAInternational audienceThis paper reports the study, design, and simulation of a symmetrical comb-drive actuator. The approach for definition of the potential energy of the system is proposed. The electrical parameters of the comb-drive actuator are defined in COMSOL Multiphysics® software. Depending on an actuation voltage and an initial design it can form system with one, two, and three stable states. We show that the equilibrium at x = 0 is more stable for the comb-drive actuator with positive overlap than for device with the gap of the same value. The proposed approach will be used for design of the symmetrical actuator, which forms the output of the recently proposed contactless four-terminal MEMS element for capacitive adiabatic logic based on silicon MEMS technology