Marianne Vandecasteele

Power-efficient readout circuit for miniaturized electronic nose

A hybrid combination of piezoelectric MEMS resonators and CMOS oscillator readout circuit forms the necessary ingredients of a new generation of electronic nose (e-nose) devices that, owing to their form factor and power consumption, enable a range of novel applications. This paper presents a hybrid low-power, high-resolution e nose system, including the necessary digital interface. An integrated readout was designed for the tracking of resonant frequency shift due to a change in the VOC environment concentration. It interfaces a piezo-actuated functionalized doubly clamped beam resonator that combines low actuation power (μW), high VOC sensitivity but low quality factor in air, large parasitic capacitance and multiple resonance modes. The sensor characteristics translate into a challenging readout design, as high gain-bandwidth product versus low power and low noise are required for optimal detection resolution.

Power-Efficient Oscillator-Based Readout Circuit for Multichannel Resonant Volatile Sensors

This work presents a multichannel electronic nose system that enables a range of novel applications owing to high sensitivity, low form factor and low power consumption. Each channel is based on a combination of doubly-clamped piezoelectric MEMS resonators and CMOS oscillator-based readout designed in TSMC 0.25 μm technology. Using “application specific” polymer coatings, the individual resonators can be tuned to detect mixtures of volatile organic compounds (VOCs). This system achieves ppm-level theoretical limit of detection for ethanol which paves the way towards a broad range of applications such as personalized health and environment air quality.

Piezoelectric transduction of flexural modes in pre-stressed microbeam resonators

This paper reports on the optimization of the design of piezoelectric transducer elements integrated on doubly-clamped microbeam resonators utilized as (bio)chemical sensors. We report and emphasize the often forgotten influence of membrane stresses on defining the dimensions and optimal position of the piezoelectric transducer elements. The study takes into account stress induced structural changes and provides models for the equivalent motional parameters of resonators with particular shapes of the transducers matching the flexural modes of vibration. The above is analyzed theoretically using numerical models and is confirmed by impedance measurements and optical measurements of fabricated doubly-clamped beam resonators. We propose various transducer designs and highlight the advantages of using higher order vibration modes by implementing specially designed mode matching transducer elements. It is concluded that the paper describes and highlights the importance of accounting for the membrane stresses to optimize the resonator performance and the low power in electronic feedback of resonating sensing systems.

Congestive heart failure patient monitoring using wearable Bio-impedance sensor technology.

A new technique to monitor the fluid status of congestive heart failure (CHF) patients in the hospital is proposed and verified in a clinical trial with 8 patients. A wearable Bio-impedance (BioZ) sensor allows a continuous localized measurement which can be complement clinical tools in the hospital. Thanks to the multi-parametric approach and correlation analysis with clinical reference, BioZ is successfully shown as a promising parameter for continuous and wearable CHF patient monitoring application.

Towards a low‐power miniaturized micromechanical electronic nose

An electronic nose based on an array of vibrating doubly clamped beams is proposed. These very high aspect ratio (length/thickness) suspended resonators can be individually functionalized by applying polymer coatings by an inkjet printing approach. The absorption of volatile compounds induces a swelling of the polymers that results in axial stress formation and a shift of the resonance frequency. Furthermore, integrated piezoelectric transducers are used for both actuating the resonators, as well as monitoring their resonance frequency in an oscillator loop. This allows for detection at ppm‐level concentrations of low‐molecular weight volatiles.