Angelika Hackner

Solid-State Gas Sensors: Sensor System Challenges in the Civil Security Domain

The detection of military high explosives and illicit drugs presents problems of paramount importance in the fields of counter terrorism and criminal investigation. Effectively dealing with such threats requires hand-portable, mobile and affordable instruments. The paper shows that solid-state gas sensors can contribute to the development of such instruments provided the sensors are incorporated into integrated sensor systems, which acquire the target substances in the form of particle residue from suspect objects and which process the collected residue through a sequence of particle sampling, solid-vapor conversion, vapor detection and signal treatment steps. Considering sensor systems with metal oxide gas sensors at the backend, it is demonstrated that significant gains in sensitivity, selectivity and speed of response can be attained when the threat substances are sampled in particle as opposed to vapor form.

Oxygen detection system consisting of a millimeter wave Fabry-Pérot resonator and an integrated SiGe front-end

Oxygen shows significant absorption lines in the millimeter wave spectrum. Resonators are widely used to achieve a strong absorption even with a short absorption paths length for concentration measurements. A sensor system based on a Fabry-Pérot resonator for oxygen measurements at ambient pressure is presented here. The Fabry-Pérot resonator consists of two metal mirrors with a diameter of 50 mm. For purpose of oxygen detection the resonator covers a frequency range between 55 GHz and 65 GHz with a resonant peak density between 1 GHz and 1.5 GHz, depending on the mirror distance, and a quality factor of approximately 7000. To achieve a compact sensor system the concept envisages two integrated transceiver circuits directly coupling to coaxial ports in the metal mirrors of the resonator. The integrated SiGe front-end addresses a frequency band from 50 GHz to 75 GHz. They are realized as heterodyne structures with integrated directional couplers, thus it is possible to measure scattering parameters. For first oxygen concentration measurements, the resonator sample was coupled to a commercially available Vector Network Analyzer. The cavity was filled with oxygen concentrations of 0% vol. and 20% vol. at ambient pressure and temperature resulting in a significant change of the quality factor for frequencies close to the oxygen absorption line at 60.6 GHz. The sensor does not contain hot components. This is an advantage compared to other oxygen sensors, like electrochemical or metal-oxide sensors.

Multi-Parameter Monitoring System für Hydraulische Flüssigkeiten

Zusammenfassung Es wird ein miniaturisiertes Messsystem für hydraulische Flüssigkeiten vorgestellt. Das System besteht aus zwei Teilen: (i) einem opto-chemischen Sensor, der die Stärke und die energetische Lage der O-H Absorption in der Umgebung von 3500 cm−1 detektiert, und (ii) einem Partikelsensor, der auf einem Lichtschrankenprinzip beruht. Der erste Sensor misst den Wasser- und den Säuregehalt und der zweite die Anzahl fester Teilchen in der Flüssigkeit. Abstract A miniaturised sensor system for aviation hydraulic fluids is presented. The system consists of an optochemical sensor and a particle sensor. The optochemical sensor detects the form of the O-H absorption feature around 3500 cm−1 to reveal the water and acid contamination in the fluid. The particle sensor uses a light barrier principle to derive its particle contamination number.

Self-Test Procedures for Gas Sensors Embedded in Microreactor Systems

Metal oxide (MOX) gas sensors sensitively respond to a wide variety of combustible, explosive and poisonous gases. However, due to the lack of a built-in self-test capability, MOX gas sensors have not yet been able to penetrate safety-critical applications. In the present work we report on gas sensing experiments performed on MOX gas sensors embedded in ceramic micro-reaction chambers. With the help of an external micro-pump, such systems can be operated in a periodic manner alternating between flow and no-flow conditions, thus allowing repetitive measurements of the sensor resistances under clean air, R0, and under gas exposure, Rgas, to be obtained, even under field conditions. With these pairs of resistance values, eventual drifts in the sensor baseline resistance can be detected and drift-corrected values of the relative resistance response Resp=(R0−Rgas)/R0 can be determined. Residual poisoning-induced changes in the relative resistance response can be detected by reference to humidity measurements taken with room-temperature-operated capacitive humidity sensors which are insensitive to the poisoning processes operative on heated MOX gas sensors.

Surface ionization based gas detection

Surface ionization (SI) is a form of gas detection which utilizes just as the well-established resistive response gas detection the interaction of adsorbed gas molecules and metal oxide or also noble metal surfaces. In contrast to the conventional resistive response detection the SI gas detection features a high amine gas selectivity. This work deals with the SI response mechanism and with the main characteristics of SI gas detection.