Damiano Crescini

Low-cost accelerometers: Two examples in thick-film technology

Abstract In this paper, two different piezoresistive thick-film accelerometers are presented: a new high-sensitivity cantilever-type printed on a ferritic metal substrate and a ceramic twin-mass structure with an elevated figure of merit. Design and development are presented together with theoretical predictions and FEM analysis. Optimization procedures and limits are discussed in comparison with experimental results. The overall performance of the devices suggests that with proper control of screen-printing and firing processes, many applications in advanced industrial requirements will be possible in the near future.

A thick-film capacitive pressure sensor with improved linearity due to electrode-shaping and frequency conversion

Various methodologies are applied to the measurement of pressure. Among them, the capacitive pressure sensor is one of the most useful devices due to its high performance-to-price ratio, reliability and low power consumption. However, the early versions of capacitive pressure transducers had a general reputation of being highly nonlinear. This paper discusses a design approach to overcome this problem by choosing a new electrode shaping and coupling the sensor with an electronic circuit based on a relaxation oscillator. Moreover, the output signal in the form of a frequency makes the distance transmission and the interfacing with digital systems easier. The theory of operation is presented with a description of the sensors implementation in thick-film technology on ceramic substrates and with experimental results on its characterization.

MEMS Tilt Sensor with Improved Resolution and Low Thermal Drift

The purpose of this paper is to investigate the design methodology, test results, and potential applications of a high resolution and low thermal drift calibrated digital inclinometer based on a MEMS capacitive sensor. The inclinometer provides ±10° of measurement range in a rotational plane that is perpendicular to the earth’s gravity and it uses a primary sensing element based on high aspect ratio microstructures, processed by air gap insulated micro structure (AIM) technology. A signal conditioning electronics, processing the MEMS signals, enables flexibility in terms of linearization, thermal compensation and signal calibration. Resolution of ±0.002° has been found around 0° together with a thermal zero drift lower than ±0.002°/°C from 0°C to +50°C. The overall system consumes 15 mA dc current from a 5V supply. Examples of application fields include: platform stabilization, drill orientation, event detection and telematics/GPS.

Excess noise in thick film piezoresistors on a metallic substrate

The excess-noise behaviours of thick-film piezoresistors printed on metallic substrates and on alumina substrates are compared. The results obtained show that the excess noise is similar in both cases depending on the volume and on the refiring cycles, as reported in the literature for resistors on alumina substrates. The paper gives a detailed description of the method of measurement and instrumentation, in particular, of the low noise pre-amplifiers.

Renewable energy-harvested sensor systems for air quality monitoring

Wireless sensor networks (WSNs) devoted to environmental monitoring has preponderantly assumed the adoption of a portable and limited energy source, (e.g. lithium, alkaline, NiMH batteries), to support the sensor functionalities. The usage of environmental resources as energy booster is now rising up as a workable energy source dedicated to embedded and wireless computing systems where manual replacement of hundreds or even thousands of batteries on a regular basis is not practical. Consequently, substantial research efforts have been spent on designing energy-efficient smart sensor nodes and networks to maximize the lifetime of WSNs. However, in air quality monitoring systems sensors are required to operate for much longer durations (like years or even decades) after they are deployed. Following the above approach this paper presents SENNO (SENsor NOde), a renewable energy-harvested sensor node that intelligently manages energy transfer for continuous operation without human intervention during air quality monitoring. This paper discusses the challenges of designing an autonomous system powered by ambient energy harvesting. Preliminary results show that, the presented approach could effectively report and trace air quality levels.

Load cell for dynamic force measurements: An example in Thick-Film Technology

The application of load cells in industry generally requires good basic materials and accurate performance in a wide range of environments. Differences exist in manufacturing technologies, intended application, performance and cost; however, hysteresis, frequency response and creep can be a common source of errors in standard strain gauge cells. In this paper, we present a small structure based on piezoresistive effect, implemented in Thick-Film Technology (TFT) on 96% alumina substrate, working as load cell with high resonance frequency and low creep effects. The analytic model has been verified by using simulation based on finite element methods (FEM), resulting in satisfactory agreement. Based on a figure of merit (the product of the sensitivity and the square of the resonant frequency), optimized design rules are obtained for the sensors of various measure-ranges from 1 N to 10 N.

Opportunistic Routing and Data Dissemination Protocol for Energy Harvesting Wireless Sensor Networks

Recent advances in environmental sources harvesting technologies is a promising solution to provide sustainable energy sources for wireless sensor networks (WSN). Renewable energy sources such as solar, thermal and electromagnetic waves constitute viable alternatives to maximize the network lifetime. Therefore, networking software awareness and adaptability to energy availability conditions should translate into innovative supporting features for data gathering, aggregation, routing and dissemination. Thus, it is paramount to develop robust energy harvesting-aware networking platforms that support the above services and guarantee low energy consumption and data integrity in a noisy, constrained environment. In this paper, we present an opportunistic routing and data dissemination protocol for energy harvesting wireless sensor network (EH-WSN) based on cross-layer constructs that allows across the layers synchronization and coordination between the routing protocol and the application layer services. The OMNET++ based extensive simulation of this protocol showed promising results in terms of meeting application requirements of handling urgent traffic and delay tolerant traffic seamlessly and ensuring energy usage efficiency.

Feasibility of air quality monitoring systems based on environmental energy harvesting

Capillary wireless sensor networks dedicated to air quality monitoring have provided essential information on hazardous air condition, generating early warnings to prevent danger situation for human health. The arising problem connected to capillary networks is the adoption of environmental energy as primary and/or unique energy source instead of the replacement of hundreds or even thousands of batteries on a regular basis that leads to high costs and practical problems of devices management. Aim of this paper is to presents a multiparametric sensor node for air quality monitoring, able to work without battery and human intervention, harvesting energy from the surrounding environment for perpetual operation. A complete autonomy system has been designed, experimental results of the harvest energy section and the budget allocation of the power consumption of the system are presented. Moreover the paper shows the experimental results of the studies conducted on the sensors section. A tailored calibration process for the sensors and the energy recovery section could effectively lead the system to trace the air quality levels in indoor and outdoor application, in a sort of “set and forget” scenario. approach could effectively report and trace air quality levels.

High precision Thick-Film load cell for dynamic force measurement

The application of load cells in industry generally requires good basic materials and accurate performance in a wide range of environments. Differences exist in manufacturing technologies, intended application, performance and cost; however, hysteresis, frequency response and creep can be a common source of errors in standard strain gauge cells. In this paper, we present a small structure based on piezoresistive effect, implemented in Thick-Film Technology (TFT) on 96% alumina substrate, working as load cell with high resonance frequency and low creep effects. The analytic model has been verified by using simulation based on finite element methods (FEM), resulting in satisfactory agreement. Based on a figure of merit (the product of the sensitivity and the square of the resonant frequency), optimized design rules are obtained for the sensors of various measure-ranges from 1 N to 10 N.

Thick-film tilt sensors: Feasibility study example using free convective motion of an heating air mass

In this application a thick-film tilt sensor has been developed based on heat transfer by natural convection. The device measures internal changes in heat transfer due to the inclination caused by the force of gravity as an input. The device is functionally equivalent to traditional proof-mass accelerometer. The proof mass in the new thick-film sensor is a gas. The gaseous proof-mass provides great advantages over the use of the traditional solid proof mass. A conditioning electronics amplifies the signal variation induced by the inclination compensating the deviation due to the initial asymmetrical values of the bridge arms and their slow variations Preliminary tests on the first prototypes show an accuracy of about 2% full scale output, repeatability of about 0.2° and resolution better than 0.1 ° over a ± 20° range.