Discontinuously operated MOX sensors for low power applications

Metal oxide semiconductor sensors are limited by their low selectivity, high power consumption and temporal drift. This paper proposes a novel discontinuous temperature modulation operation mode characterized by ondemand measurements and periodic warmup cycles.The performance of two sets of FIS SB-500-12 sensors, one group continuously operated and the other group discontinuously operated, was compared in a scenario of carbon monoxide detection at low concentrations for five consecutive days. Results showed that the discontinuous operating mode moderately increased the prediction error and the limit of detection but was advantageous in terms of energy savings (up to 60% with respect to the continuous temperature modulation mode) .Postprint (author's final draft

Towards Internet of Things for event-driven low-power gas sensing using carbon nanotubes

One of most important applications of sensing devices under the Internet of Things paradigm is air quality monitoring, which is particularly useful in urban and industrial environments where air pollution is an increasing public health problem. As these sensing systems are usually battery-powered and gas sensors are power-hungry, energy-efficient design and power management are required to extend the device's lifetime. In this paper, we present a two-stage concept where a novel low-power carbon nanotube is used as a gas detector for an energy-consuming metal-oxide (MOX) semiconductor gas sensor. We propose a design of a heterogeneous sensor node where we exploit the low-power nanotube gas sensor and the more accurate MOX sensor. This work performs energy consumption simulations for three event-driven scenarios to evaluate the power consumption reduction, as well as the limitations of carbon nanotubes. Our results show the benefits of the proposed approach over the scenarios with adaptive duty-cycling with only MOX gas sensors, proved with 20%-35% node lifetime prolongation. The delay introduced due to the nanotube recovery time can be overcome by radio duty-cycled activity for detecting alarm messages from the neighbour nodes

Pulsed-temperature metal oxide gas sensors for microwatt power consumption

Metal Oxide (MOX) gas sensors rely on chemical reactions that occur efficiently at high temperatures, resulting in too-demanding power requirements for certain applications. Operating the sensor under a Pulsed-Temperature Operation (PTO), by which the sensor heater is switched ON and OFF periodically, is a common practice to reduce the power consumption. However, the sensor performance is degraded as the OFF periods become larger. Other research works studied, generally, PTO schemes applying waveforms to the heater with time periods of seconds and duty cycles above 20%. Here, instead, we explore the behaviour of PTO sensors working under aggressive schemes, reaching power savings of 99% and beyond with respect to continuous heater stimulation. Using sensor sensitivity and the limit of detection, we evaluated four Ultra Low Power (ULP) sensors under different PTO schemes exposed to ammonia, ethylene, and acetaldehyde. Results show that it is possible to operate the sensors with total power consumption in the range of microwatts. Despite the aggressive power reduction, sensor sensitivity suffers only a moderate decline and the limit of detection may degrade up to a factor five. This is, however, gas-dependent and should be explored on a case-by-case basis since, for example, the same degradation has not been observed for ammonia. Finally, the run-in time, i.e., the time required to get a stable response immediately after switching on the sensor, increases when reducing the power consumption, from 10 minutes to values in the range of 10-20 hours for power consumptions smaller than 200 microwatts