Emilio Sardini

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. >

Kinetic and thermal energy harvesters for implantable medical devices and biomedical autonomous sensors

Implantable medical devices usually require a battery to operate and this can represent a severe restriction. In most cases, the implantable medical devices must be surgically replaced because of the dead batteries; therefore, the longevity of the whole implantable medical device is determined by the battery lifespan. For this reason, researchers have been studying energy harvesting techniques from the human body in order to obtain batteryless implantable medical devices. The human body is a rich source of energy and this energy can be harvested from body heat, breathing, arm motion, leg motion or the motion of other body parts produced during walking or any other activity. In particular, the main human-body energy sources are kinetic energy and thermal energy. This paper reviews the state-of-art in kinetic and thermoelectric energy harvesters for powering implantable medical devices. Kinetic energy harvesters are based on electromagnetic, electrostatic and piezoelectric conversion. The different energy harvesters are analyzed highlighting their sizes, energy or power they produce and their relative applications. As they must be implanted, energy harvesting devices must be limited in size, typically about 1 cm 3 . The available energy depends on human-body positions; therefore, some positions are more advantageous than others. For example, favorable positions for piezoelectric harvesters are hip, knee and ankle where forces are significant. The energy harvesters here reported produce a power between 6 nW and 7.2 mW; these values are comparable with the supply requirements of the most common implantable medical devices; this demonstrates that energy harvesting techniques is a valid solution to design batteryless implantable medical devices.

Self-Powered Wireless Sensor for Air Temperature and Velocity Measurements With Energy Harvesting Capability

Air temperature and velocity measurements are important parameters in many applications. A self-powered sensor placed in a duct and powered by an electromechanical generator scavenging energy from the airflow has been designed and tested. It periodically transmits the measured air temperature and velocity to a receiving unit. The system basically consists of two macroblocks, respectively: the self-power wireless sensor and the receiving unit. The self-powered sensor has a section devoted to the energy harvesting, exploiting the movement of an airscrew shaft keyed to a dc motor. The self-powered sensor adopts integrated devices in low-power technology, including a microcontroller, an integrated temperature sensor, and a radio-frequency transmitter at 433 MHz. The data transmission is realized in Manchester encoding, with amplitude-shift-keying modulation at 433 MHz, allowing covering a distance between the sensor and the reader on the order of 4-5 m, depending on the power supplied in transmission. The air velocity is measured through the rotor frequency of the electromechanical generator, whereas, for the temperature, a commercial low-power sensor is used. An experimental system has been designed and fabricated, demonstrating that the airflow harvester can power the self-powered wireless sensor permitting air temperature and velocity measurements. The system can be used for real-time monitoring of temperature and velocity. The sensor module placed into the duct does not require any batteries.

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.

Sensorized Glove for Measuring Hand Finger Flexion for Rehabilitation Purposes

Over the last 30 years, scientific and technological progress has boosted the development of medical devices that can assist patients and support medical staff. With regard to the rehabilitation of patients who have suffered from traumas, robotic systems can be an aid for rapid patient recovery. This paper focuses on studying and implementing a system for measuring the finger position of one hand with the aim of giving feedback to the rehabilitation system. It consists of a glove where sensors are mounted suitably configured and connected to an electronic conditioning and acquisition unit. The information regarding the position is then sent to a remote system. The objective of this paper is to provide a sensorized glove for monitoring the rehabilitation activities of the hand. The glove can have several other applications such as: 1) the recognition of sign language; 2) the diagnostic measurement of the finger movement at a distance; and 3) the interaction with virtual reality.

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. >

Measurement of small capacitance variations

A technique for measuring low-frequency and low-level capacitance variations is proposed. It is based on a lock-in detection circuit with a feedback loop, containing an integrator and a modulator for zeroing the capacitance mean value. This approach provides a good signal-to-noise ratio and high sensitivity. Capacitance variations can be on the order of 100 p.p.m. of the mean value, and the frequency of the variations can be as low as 0.1 Hz. Stray capacitances and the drift due to the environmental conditions are automatically compensated. The measurement technique, experimental apparatus, and initial results are described. Small variations, about 10 fF, have been measured in the presence of 10-pF mean value. >

Autonomous Sensor System With Power Harvesting for Telemetric Temperature Measurements of Pipes

In this paper, an autonomous sensor system, with low-power electronics for radio-frequency (RF) communication, incorporating a thermoelectric energy-harvesting module for unattended operation is presented. A target application is proposed for temperature measurement of walled-in pipes. When the autonomous sensor is placed on the heat source, a thermoelectric module harvests energy, powering the autonomous sensor. In this condition, no external power source is necessary, the temperature measurement is performed, and the data are saved into a nonvolatile memory. When the external readout unit is active, the electromagnetic field is used to power the autonomous sensor system and to communicate the data. An experimental setup has been arranged and characterized by measuring the temperature along the pipe, the voltage that can be generated by thermoelectric generators, and the influence of different materials on RF communication. The temperature data of the heat source, which are collected by the autonomous sensor, are compared with that of a reference thermistor. The measurement results show good agreement between the two measured temperature data sets. The experimental data demonstrate that the autonomous system works correctly for a temperature gradient that is higher than 9degC, within a readout distance of a few centimeters. The presented autonomous sensor system can be effectively used for measurements into a close environment in which a temperature difference is present.

Passive and Self-Powered Autonomous Sensors for Remote Measurements

Autonomous sensors play a very important role in the environmental, structural, and medical fields. The use of this kind of systems can be expanded for several applications, for example in implantable devices inside the human body where it is impossible to use wires. Furthermore, they enable measurements in harsh or hermetic environments, such as under extreme heat, cold, humidity or corrosive conditions. The use of batteries as a power supply for these devices represents one solution, but the size, and sometimes the cost and unwanted maintenance burdens of replacement are important drawbacks. In this paper passive and self-powered autonomous sensors for harsh or hermetical environments without batteries are discussed. Their general architectures are presented. Sensing strategies, communication techniques and power management are analyzed. Then, general building blocks of an autonomous sensor are presented and the design guidelines that such a system must follow are given. Furthermore, this paper reports different proposed applications of autonomous sensors applied in harsh or hermetic environments: two examples of passive autonomous sensors that use telemetric communication are proposed, the first one for humidity measurements and the second for high temperatures. Other examples of self-powered autonomous sensors that use a power harvesting system from electromagnetic fields are proposed for temperature measurements and for airflow speeds.

A new measurement method for capacitance transducers in a distance compensated telemetric sensor system

A measurement method for an inductive telemetric system useful for capacitance transducers is described. It is based on a physical model that also considers the leakage and coupled magnetic fluxes and the possible presence of parasitic elements. The model behaviour explains well the measured impedance diagram. Moreover it compensates the change of distance between the read-out and sensing inductors. The method has been experimentally tested showing good agreement with the reference quantities (about 0.6% of the reading value) and compared with a different one. A comparison with a measurement method usually proposed in the literature highlights the distance compensation and the possibility of a more general application. Theoretical explanations, experimental results and discussion are reported.