Sylvain Druart

Miniaturized Wireless Sensing System for Real-Time Breath Activity Recording

A portable, non-invasive and easy to operate wireless system has been developed for monitoring the breathing activity of patient. The system is composed of a capacitive microsensor (airflow-humidity sensor) integrated on a silicon chip and of a Negative Temperature Coefficient thermistor; both are connected to a wireless network to allow efficient healthcare at home as well as in hospitals. The capacitive sensitive part of the microsensor is an array of interdigitated metallic electrodes covered by 100-nm-thick dense anodized aluminum oxide layer. The breath water vapor is adsorbed over the interdigitated electrodes and changes the sensor characteristic capacitance by up to two orders of magnitude. This modulated signal is then digitized and either stored in a memory or directly transmitted to a monitor through a short distance radio frequency (RF) link. Results show that the wireless platform can be powered by two AAA batteries and deployed in a mesh or star configuration as wireless sensor network. Full size of the microsensor is less than 1 cm2 and is conveniently implemented in a classical adhesive bandage or in nasal prongs. This microsystem is proposed for monitoring sleep-disordered breathing as well as breathing rhythm of athletes during effort.

Dew-Based Wireless Mini Module for Respiratory Rate Monitoring

Miniaturized humidity sensors combined with ZigBee transceiver and efficient data processing offer a powerful system for the monitoring of human breath. Every 10 ms, the expiration/inspiration phase is transmitted, allowing a medical diagnosis as efficient as required by the application. For the sensing system, a micro interdigitated capacitor, covered with a dense hydrophilic alumina layer, is connected to a capacitance-to-frequency circuit interface. A customized nasal canula-prototype embeds the microsystem underneath the patients nostrils while offering cabling until the belt-fixed radio transceiver. The fast data processing, executed in a mini notebook process unit, gives to the medical staff a live broadcast of the patients respiratory rate. In order to improve the size and the functionality of our sensing module, novel techniques for processing complementary metal oxide semiconductor (CMOS) in Silicon-on-Insulator (SOI) technology now allow for the construction of microsensors and CMOS circuits together on the same chip. These sensors consume extremely low power, of the order of 0.1 μW, present high sensitivity, occupy small chip area (1.25 mm2) and offer the prerequisite platform for a large variety of new sensors.

A Self-Oscillating System to Measure the Conductivity and the Permittivity of Liquids within a Single Triangular Signal

We present a methodology and a circuit to extract liquid resistance and capacitance simultaneously from the same output signal using interdigitated sensing electrodes. The principle consists in the generation of a current square wave and its application to the sensor to create a triangular output voltage which contains both the conductivity and permittivity parameters in a single periodic segment. This concept extends the Triangular Waveform Voltage (TWV) signal generation technique and is implemented by a system which consists in a closed-loop current-controlled oscillator and only requires DC power to, operate. The system interface is portable and only a small number of electrical components are used to generate the expected signal. Conductivities of saline NaCl and KCl solutions, being first calibrated by commercial equipment, are characterized by a system prototype. The results show excellent linearity and prove the repeatability of the measurements. Experiments on water-glycerol mixtures validate the proposed sensing approach to measure the permittivity and the conductivity simultaneously. We discussed and identified the sources of measurement errors as circuit parasitic capacitances, switching clock feedtrough, chage injection, bandwidth, charge injection, bandwidth, and control-current quality.

CMOS test circuit architecture for the extraction of fluid properties using interdigitated electrodes microsensors

Determining the electrical impedance of fluids is of interest in many applications such as the measurement of ionic concentration, the detection of dispersed particles or the humidity sensing. This paper shows a new test system for standard interdigitated electrodes microsensors using a single CMOS circuit that extracts the fluid impedance parameters. The system principle is to load the structure with constant current steps. The response is a voltage wave which contains the fluid resistance and the fluid capacitance in its shape. Simulations and PCB measurements prove the system ability to discriminate fluid resistive variations from fluid capacitive variations.

Fluid characterization by interdigitated electrodes sensors

The purpose of this paper is to present the concept of a complete fluid characterization microsystem. This system is composed of three parts. The first is a classical two-dimensional sensor using interdigitated (IDA) aluminum electrodes covered by anodized alumina. The second part is a CMOS digital circuit which is used to modulate the sensor topology. The work of the last part is to transduce the sensor useful signal in an oscillating voltage.

Wireless microsensors system for monitoring breathing activity

A portable, non-invasive and easy to operate wireless system has been developed for monitoring the breathing activity of patient. The system is composed of a capacitive microsensor (airflow-humidity sensor) integrated on a silicon chip and of a Negative Temperature Coefficient thermistor; both are coupled to a Radio Frequency wireless link. The sensitive part of the microsensor is an array of interdigitated metallic electrodes covered by 100 nm-thick dense anodized aluminum oxide layer. The breath water vapor is adsorbed over the interdigitated electrode and changes the sensor characteristic capacitance. This modulated signal is then digitized and either stored in a memory or directly transmitted to a monitor through the short distance RF link. Full size of the microsensor is less than 1 cm/sup 2/ and can be easily implemented in a classical adhesive bandage. This microsystem is proposed for monitoring sleep-disordered breathing as well as breathing rhythm of athletes during effort.

Impact of radiations on the electromechanical properties of materials and on the piezoresistive and capacitive transduction mechanisms used in microsystems

The impact of different types of radiation on the electromechanical properties of materials used in microfabrication and on the capacitive and piezoresistive transduction mechanisms of MEMS is investigated. MEMS technologies could revolutionize avionics, satellite and space applications provided that the stress conditions which can compromise the reliability of microsystems in these environments are well understood. Initial tests with MEMS revealed a vulnerability of some types of devices to radiation induced dielectric charging, a physical mechanism which also affects microelectronics, however integration of novel functional materials in microfabrication and the current trend to substitute SiO2 with high-k dielectrics in ICs pose new questions regarding reliability in radiation environments. The performance of MEMS devices with moving parts could also degrade due to radiation induced changes in the mechanical properties of the materials. It is thus necessary to investigate the effects of radiation on the properties of thin films used in microfabrication and here we report on tests with γ, high energy protons and fast neutrons radiation. Prototype SOI based MEMS magnetometers which were developed in UCL are also used as test vehicles to investigate radiation effects on the reliability of magnetically actuated and capacitively coupled MEMS.