Daniele Marioli

Digital time-of-flight measurement for ultrasonic sensors

Ultrasonic sensor measurements are mostly based on the determination of the time of flight (TOF). The authors present the development of a digital algorithm for pulse-echo measurement applications, based on the use of a cross-correlation function to determine the TOF. Some experimental results are presented, and the possibility of realizing a low-cost real-time measurement system is considered. >

Characterization of Thermoelectric Modules for Powering Autonomous Sensors

The characterization of three commercial thermoelectric modules, designed for cooling/heating applications, is presented in order to employ the devices for power conversion, i.e as thermoelectric generators (TEG). The thermoelectric theory is briefly described at first, also taking into account the relationship between effective temperature difference across the TEG junctions and temperature difference applied externally, when insulating ceramic plates have a finite thermal conductance. Performances of thermoelectric modules are evaluated in terms of open-circuit output voltage and output power density for different temperature gradients and load conditions. Measurement techniques and experimental data are reported, showing the possibility of use thermoelectric devices for waste heat recover. A TEG was then used to supply an autonomous system that interfaces with a temperature sensor and periodically transmits the measurement information via a radiofrequency (RF) link. Experimental data show that the system works correctly and sends the RF signal when temperature difference applied across TEG is high enough.

Modeling, fabrication and performance measurements of a piezoelectric energy converter for power harvesting in autonomous microsystems

The present work deals with the energy conversion via the piezoelectric effect. A mechano-electrical energy converter based on piezoelectric thick films of lead zirconate titanate (PZT) deposited on a steel cantilever by a low-temperature process is presented. Modeling and measurement results on the performances of the piezoelectric converter are reported and their potential use in self-powered autonomous sensor devices is proposed

IEEE 1588-based Synchronization System for a Displacement Sensor Network

This paper deals with a displacement sensor network that is built over Ethernet and synchronized according to IEEE1588. Actually, distribution of precise time reference in an Ethernet network allows implementations of distributed measurement systems, overcoming limitations of complex architecture. The application of the well known IEEE1588 lets sensors to share the same time reference and, in the case of displacement measures, enables accurate calculation of cross-derived quantities (multidimensional speed and acceleration). In this work a description of the sensor architecture is given and the attention is focused on the IEEE1588 implementation. In particular the proposed low-cost system does not use any dedicated synchronization hardware but it can reduce the deviation from time reference down to 20 mus

Design and Implementation of a Wireless Fieldbus for Plastic Machineries

Fieldbus systems are well known in the industrial automation world. Due to the increasing demand for scalability and capability of working in harsh environment, the use of wireless communication is gaining in importance. In the past, some efforts were pursued to encapsulate wired standards over wireless link, but their diffusion is limited by reliability and predictability requirements. In addition, event-driven protocols borrowed from the consumer world (as IEEE802.11 or IEEE802.15.4) are not well suited for some industrial applications. In this paper, authors present the design and the experimental evaluation of a wireless real-time communication protocol that tries to overcome these limits. It exploits standard hardware to lower cost and implements a hybrid medium access strategy. Time Division Multiple Access scheduling is used to ensure time deadlines respect, while Carrier Sense Multiple Access with Collision Avoidance is used for acyclic communications, as those involved in network management. It has been successfully adopted for temperature monitoring in plastic machineries. The prototype network adopts star topology and can manage up to 16 nodes with a refresh time of 128 ms.

IEEE802.11 sensor networking

This paper deals with a smart-transducer wireless network for industrial applications. Thanks to its high popularity, a solution based on IEEE802.11 (also known as wireless fidelity or Wi-Fi) is experimentally investigated. A master-slave network organization is proposed to allow several sensors to be connected with generic Wi-Fi devices like PCs; a proprietary protocol over Internet Protocol (IP)/User Datagram Protocol (UDP) has also been developed. Last, some low-cost prototypes have been built to test the network behavior performances in terms of timing characteristics and power dissipation. Experimental results prove the applicability in a soft real-time (nontime-critical) industrial context.

High-accuracy measurement techniques for capacitance transducers

Capacitance transducers are used in different applications such as measurement of vibrations, displacement, pressure, fluid density and so on. Depending on the application, transducers can have both floating electrodes, or in some cases, one earthed. Shielding techniques introduce parasitic capacitances, the compensation of which requires methods ranging from measuring configurations for floating capacitances up to more complicated techniques when one of the two transducer electrodes is earthed. The authors present an instrument employing an auto-balancing technique via a negative feedback that zeroes the static value and the very slow fluctuations of both the transducer and the stray capacitances, allowing high signal amplification and thus high sensitivity. The measuring circuit is composed essentially of a phase-sensitive detector and an integrating feedback path. A sensitivity of 1 mV fF-1 and a measurement range up to 10 pF is obtained, while an equivalent capacitance noise of 0.5 fF has been measured in the presence of a three-decade bandwidth.

Improving the accuracy and operating range of quartz microbalance sensors by a purposely designed oscillator circuit

A method is presented to measure accurately the resonant frequency and to increase the functioning range of quartz microbalance sensors subject to heavy acoustic loading, such as encountered in in-liquid operation and with viscoelastic coating films. The method is based on an electronic circuit for the active cancellation of the crystal electrical capacitance, inserted in a phaselocked loop oscillator, which enables the tracking of the quartz series resonance with virtually zero error irrespective of the load. The principle is discussed, and experimental results confirming its successful application are presented.

A CMOS Integrable Oscillator-Based Front End for High-Dynamic-Range Resistive Sensors

A new oscillating circuit is proposed to estimate the resistance and parallel parasitic capacitance of resistive chemical sensors. The circuit is able to reveal the resistance in a wide range (from tens of kiloohms to more than 100 GOmega) due to the adopted resistance-to-time technique. In addition, the parallel capacitance (up to 50 pF) can be estimated. The circuit, which does not need any initial calibration, is very simple and compact and is suitable to be integrated with a standard CMOS technology to obtain a low-cost and low-power device for a sensor array interface. Different kinds of post layout simulations concerning the CMOS integrated implementation have been conducted. Experimental results obtained using a discrete prototype board, both on passive components and on real sensors (metal-oxide sensors), have shown good linearity and reduced percentage error with respect to the theoretical expectations.

Ultrasonic distance measurement for linear and angular position control

A robot-arm positioning control is described. It makes use of a microprocessor-based ultrasonic system and of a novel time-of-flight measurement technique. The experimental system consists of a three aligned ultrasonic transducers mounted on a rod. Two transducers work as receivers, while the third works both as a transmitter and a receiver. The system achieves a positioning accuracy of +or-0.1 degrees in the field of +or-10 degrees of misalignment for a distance ranging from a few centimeters up to 200 mm. For a higher distance range up to 300 mm, the position accuracy is +or-0.4 degrees . The system also performs distance measurement, using the same group of transducers. The system can be used in robotic applications in industrial environments, such as for orientation control or object grasping. >