The gas sensor research presented here has a focus on the measurement of the composition of natural gas and gases from sustainable resources, such as biogas. For efficient and safe combustion, new sensor systems need to be developed to measure the composition of these new gases. In general about 6 gas components need to be measured to determine the caloric value and the combustion properties of these gas mixtures. The concentration levels of the relevant components are relatively high, and the emphasis of this research work is therefore on selectivity and avoidance of cross contamination. For this reason and because of their limited stability, chemical sensors are not considered. The sensors in this work are based on physical interaction with the gas. One single sensing principle is insufficient for identification of all components in the natural gas and a microsystem for measuring three different physical properties of the gas components are proposed in this work: thermal conductivity, optical and photo-acoustic infrared absorption.

This paper presents a readout circuit for a carbon dioxide (CO ₂ ) sensor that measures the CO ₂ -dependent thermal time constant of a hot-wire transducer. The readout circuit periodically heats up the transducer and uses a phase-domain ΔΣ modulator to digitize the phase shift of the resulting temperature transients. A single resistive transducer is used both as a heater and as a temperature sensor, thus greatly simplifying its fabrication. To extract the transducer's resistance, and hence its temperature, in the presence of large heating currents, a pair of transducers is configured as a differentially driven bridge. The transducers and the readout circuit have been implemented in a standard 0.16-μm CMOS technology, with an active area of 0.3 and 3.14 mm ² , respectively. The sensor consumes 6.8 mW from a 1.8-V supply, of which 6.3 mW is dissipated in the transducers. A resolution of 94-ppm CO ₂ is achieved in a 1.8-s measurement time, which corresponds to an energy consumption of 12 mJ per measurement, >10× less than prior CO ₂ sensors in CMOS technology.

The heart rate is a vital indicator of the health state of an individual. By continuously monitoring it, the fitness and health of the cardiovascular system of a user can be analyzed and impending problematic health episodes could be addressed better. Existing techniques to measure heart rate, such as ECG or PPG, are either uncomfortable for the user, are not low-power or sensitive to motion artifacts. Infrared thermography is a non-contact technique with improved user comfort and low power consumption. In this work we have analyzed, built and tested a novel system that uses infrared differential thermometry to detect the heart rate in the auricle. The sensor system was fitted into a commercial headphone since this work is a first step into integration of the system in a Bluetooth headset. To our knowledge, there has been no previous work on the detection of the heart rate signal in the ear using infrared thermometry. Positive results have been obtained after extraction of the frequency features of the bioheat transfer signal on test persons in rest.

In this research fluorescent optochemical pH probes for the detection of ischaemia have been investigated. Myocardial ischaemia is the most prominent risk during heart surgery. During open heart surgery the heart is temporarily arrested and, since there no blood flowing, oxygen supply and removal of waste products is stopped and heart cells can be damaged. In this paper we propose a novel method to monitor the condition of the heart by placing optochemical pH sensors on several strategic places around the heart during surgery. Low cost opto-chemical pH sensors, using a HPTS (8-hydroxy-1,3,6-pyrene trisulfonic acid trisodium salt) fluorescent dye encapsulated in a thin bio-compatible hydrogel layer, were investigated for this application. Our research started with an extensive optical characterization of several types of hydrogel layers at different pH levels. Secondly a reflection probe prototype using several of these layers was designed, built and tested. Dual wavelength excitation and ratiometric detection of the fluorescent signals was used to detect the pH level. Typical output signals of 35% to 53% per pH in the range from 6.5-8.0 pH have been measured and a response time of typically 400 seconds was obtained for the prototypes. Finally based on our measurements on the HPTS layers and the reflection probe we propose an improved type of pH probe for the detection of ischaemia during open heart surgery.

A color sensor based on the wavelength dependent response of reverse-biased photodiodes in silicon has been integrated with bipolar readout circuits. An integrated chroma amplifier has been realised to provide a color output signal determined by the ratio between photocurrents and a luminance amplifier to supply an output current proportional to the logarithm of the photocurrent, using translinear circuits.