Modern electronic systems can be composed, in the most general scenario, by networked electronic embedded systems operating in real-time in harsh environments and extreme conditions.
These systems could comply with demanding regulation constraints to achieve reliable and safe operations. For instance, Self-diagnostics of sensors is expected to be a key feature in order to early detect (incipient) faults (at component level) and limit their effects to the whole process. Solutions at system level as well as at component level should be adopted to design a new generation of electronic systems in order to increase reliability, safety, low power consumption and low cost.
Industrial automation, process control applications as well as a growing number of application domains (including robotics, automotive industry, aerospace industry etc.) are increasingly demanding cost effective and reliable sensing devices for feedback control, monitoring, diagnostics. The objective of our research is to investigate, at system and component level, architectures for the design of embedded sensing devices featuring low cost, reliability (intended as the robustness of the device), safety (intended as the capacity of generating correct measurements or estimates of process variables or even detecting faults) and low power consumption. Although the research is mostly focused on sensors, it is envisaged that this kind of work can be generalized to implement local (and embedded) feedback control and actuation to improve sensor performance or even process performance. Distributed electronic systems must comply with demanding regulation constraints (depending on the application) in order to guarantee acceptable levels of reliability and safety. In particular, self-diagnostics of sensors at component level (i.e. without processing at higher level, e.g. PLC or DCS) is expected to be a key feature in order to early detect (incipient) faults (at component level) and limit their effects to the whole process. The major sources of disturbance arise in the analog domain which is by far the most critical from the point of view of reliability, strongly affected by the complexity of the electronic circuitry.
Reliability can be improved by careful design as well as redundant design of critical subsystems or components; safety can be enforced by processing series of measurements (possibly from different transducers), e.g. using Kalman filters, statistical techniques or neural-networks. Hybrid analog/digital integrated circuits, possibly mechanically tightly bound with the transducers, could to a large extent increase noise immunity, reducing circuitry complexity and possibly development and manufacturing costs.
An effective approach to address the issues above is to move the diagnostic and prognostic features from the central control decision unit to the decentralized devices using a network of “smart” electronic embedded systems, interconnected by a field bus or embedded real-time sensor network. Reliability of remote units is achieved by hardware redundancy; diagnostic and prognostic features are implemented by dedicated data processing algorithms like Kalman filters, neural networks and/or novelty detection algorithms. Eventually remote sensor units transmit to the central controllers only structured measurements, including information on the sensor status and diagnostic information for system actions.
E. Bottino., P. Massobrio., S. Martinoia, G. Pruzzo., M. Valle, Low-noise low-power CMOS preamplifier for multisite extracellular neuronal recordings, in Microelectronics Journal (ISSN 0026 – 2692), Vol. 40, no. 12, pp. 1779–1787, Dec. 2009, Elsevier Publisher, DOI:10.1016/j.mejo.2009.10.003
Integrated Sensor Interfaces
Interface Circuits for Resistive Gas Sensors
Hand held systems for gas sensing play important roles in relevant domains e.g. in airports to detect gases released by explosives or drugs, in biomedical systems to diagnose the diseases through exhaled gas, in environmental monitoring to reveal contaminated areas in order to reduce the effect of pollutants and the human exposure to dangerous gases. Not limited to the applications mentioned above, gas sensors contribute in variety of novel applications including military, smart space, robotics, automation, and industrial control.
Since, Metal Oxide (MOX) gas sensors respond in a similar way to different types of oxidizing or reducing species, these sensors are not selective. Integration of heterogeneous nanostructured microarray gas sensors having different sensing materials while minimizing the sensing platform helped to overcome this limitation. Heterogeneous microarrays of oxide thin films for gas sensing applications enable the sensor to detect very small amounts of chemical substances. Each single (MOX) sensor composing the microarray shows good sensing properties in terms of sensitivity, response and recovery time and response amplitude when dealing with environmental pollution, Volatile Organic Compounds (VCOs) and explosive combustible gases.
Metal Oxide (MOX) resistive gas sensors are also known as chemo resistive sensors. The resistance of the sensing element of the sensor varies in the presence of targeted analyte: alteration in the oxide sensitive thin films occurs and this causes modification in the electrical conductivity of the oxide surface. As a result, the transducer of the sensor transforms the collected data about the concentration of the gas into an electrical resistance variation. Thus, an electronic interface circuit is required to evaluate the electrical measure of the sensing results and convert it to a digital data.
Based on their physical principle of operation, resistive gas sensors require very wide range interface circuit since the baseline resistance depends on several chemical and physical parameters, fabrication process, technology and the sensor operating conditions. Considering all these effects together a dynamic range of more than 150 dB is needed. Unfortunately, the use of a single traditional linear analog-to-digital converter would be unpractical; for this reason alternative interface circuit structures must be developed.
Quasi-digital electronic interface circuits in which the information about the sensor is converted into duty cycle, frequency, or period represent an effective solution when wide range resistances are considered. This allows merging the inherent simplicity of analog devices with the accuracy and noise immunity typical of digital sensors.
Therefore, an electronic interface circuit able to condition wide resistance range extending from hundreds of Ohms to tens of Giga Ohms and convert its variation into a period such that the output period is proportional to the measured resistance or to its variations, is required.
In this perspective, the main goal of the research is to develop an integrated electronic interface circuit able to tackle the wide resistance variation and convert it to a digital data.
Wireless Sensor Networks
A Wireless Sensor Network (WSN) is a distributed system made of autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively dispatch (through an RF communication channel) sensed data through the network to a main location. Each sensor network element (node) is usually composed by several parts: a radio transceiver with an internal antenna or connection to an external antenna, a microcontroller, an electronic circuit for interfacing with the sensors and an energy source, usually a battery or an embedded energy harvester. The topology of the WSNs can vary from a simple star to an advanced multi-hop wireless mesh.
Inside the COSMIC Lab we aim at developing Real Time Localization Systems (RTLS) focused on determining the most promising technology for indoor localization where GPS is not available. An indoor environment is hostile to radio communications because multipath and scattering issues are very difficult to overcome. The activity is also focused on the development of RTLS algorithms based on statistical parameters to mitigate the problems of radio transmission due to Non Lone Of Sight (NLOS) conditions between transmitter and receiver nodes. The most promising localization technology is certainly the Ultra Wide Band (UWB), the only one to provide localization accuracy less than 0.30 m. High accuracy is achieved by using message Time Of Flight (ToF) data at nodes and timed precisely pulse train. The localization accuracy and precision is increased by using Micro Electronic Mechanical Systems (MEMS) such as magnetometer, gyroscope and accelerometer. Applications involve tracking and Real Time Localization (RTLS) of workers/things in indoor environments such as shipyards and construction sites to increase safety and security.
Inside COSMIC lab Wireless Sensor Networks are also applied to develop monitoring systems like urban waste management and waste diffusion in fresh-water streams and in marine costal areas. Such systems need self powered nodes able to measure environmental parameters and to transmit sensed data to a central supervising station. In the the urban waste management system, the nodes on the bins measure the state of the bin (full/empty) and alert the central station when the full threshold is reached. The central station organize the bins collection with the main scope to reduce the management cost. The goal of monitoring marine water is to study waste diffusion near coastal area. Nodes on the buoys transmit sensed data at a long distance in order to reach the central station located on the coast.
W. Prodanov, M. Valle, R. Buzas, A Controller Area Network Bus Transceiver Behavioral Model for Network Design and Simulation, in IEEE Trans. on Industrial Electronics, Volume 56, Issue 9, Sept. 2009, pp. 3762 – 3771, 2009. DOI: 10.1109/TIE.2009.2025298.