Corrado Felini

Dynamic impedance matching network for RF energy harvesting systems

In this paper, an RF energy harvesting system with an improved dynamic impedance matching network (DyIMN) is proposed. With this solution, the minimum RF input power required for circuit operation is -10 dBm, allowing a working distance of 1.5 m from an RF energy source of 30dBm. The system was fabricated on an FR4 substrate using off-the-shelf discrete components and it is able to convert RF energy to regulated DC voltage in order to power general-purpose electronic devices. The experimental results demonstrate the capability of the system to obtain an optimum impedance matching with a received RF power in the range -10 - +5dBm.

Battery-less smart RFID tag with sensor capabilities

The pervasiveness of RFID technology in novel application fields, such as agriculture and food chain integrated management, is related to the addition of sensor and computational capabilities to the systems, and as a consequence, their powering becomes a challenge. Passively powered devices, such as inductively coupled passive HF RFID systems, utilize an external electromagnetic field to operate without an internal power source. This paper presents a battery-less RFID sensor useful to establish a safer and more manageable food supply chain of perishable comestibles.

A Monolithic Multisensor Microchip with Complete On-Chip RF Front-End

In this paper, a new wireless sensor, designed for a 0.35 µm CMOS technology, is presented. The microchip was designed to be placed on an object for the continuous remote monitoring of its temperature and illumination state. The temperature sensor is based on the temperature dependence of the I-V characteristics of bipolar transistors available in CMOS technology, while the illumination sensor is an integrated p-n junction photodiode. An on-chip 2.5 GHz transmitter, coupled to a mm-sized dipole radiating element fabricated on the same microchip and made in the top metal layer of the same die, sends the collected data wirelessly to a radio receiver using an On-Off Keying (OOK) modulation pattern.

An autonomous and energy efficient Smart Sensor Platform

A novel Wireless Smart Sensor Platform compatible with EPCglobal Class-1 Gen2 readers was developed. The platform is comprised of a five stage Dickson voltage multiplier, a dynamic impedance matching network (DyIMN), an XLP microcontroller (MCU) and an RFID tag IC with an embedded temperature sensor. Device range operations have been assessed up to a distance of 1.5 m from the RF source, corresponding to a minimum RF input power of -10 dBm. Firmware optimization leads to a reduction of power dissipation below 500nW in sleep mode, allowing an optimal energy harvesting and storage from the RF source. The harvested power enable logical operations to be completed from MCU, thus enabling sensing and storing of temperature measurements directly into the user memory of an RFID tag. Also the efficiency of the energy harvester is calculated from the MCU, hence tuning the DyIMN dynamically to respond over a wide range of input power and load impedance. The experiments demonstrate the feasibility of the system to operate autonomously within the reading range of a standard RFID reader, that acts both as RF power source and receiver of the data stored in the tag user memory.

Performance assessment of an enhanced RFID sensor tag for long-run sensing applications

In this paper we present a battery-less RFID sensor tag, operating at 868 MHz, characterized by a novel impedance matching, guaranteeing improvements in terms of wireless energy transfer efficiency. A more efficient energy transfer is of high interest for several applications and, in particular, for a reduced recharging time of the embedded capacitor. This represents a fundamental step to enlarge the range of applications usually limited to classic wireless sensor networks, such as data logging or environmental sensing in large spaces. Challenges related to energy replenishment and data collection should be taken into account to enable an effective deployment of large networks. In particular, we investigate on the number of mobile readers moving around a sensing network to gather data and transfer energy, such that all nodes are kept alive and all data is collected. The improvements introduced by the new RFID sensor tag for this application will be evaluated with respect to state-of-the-art devices.

Design and implementation of high resolution, high linearity temperature sensor in CMOS process

An high-resolution CMOS temperature sensor with high linearity in the range from 20°C to 90°C is presented. The circuit uses substrate bipolars as temperature transducers. The temperature sensor consists of two building blocks: a Proportional To Absolute Temperature (PTAT) voltage generator and a differential amplifier. The second block is necessary to obtain reasonable voltage level that can be either read with a simple setup using it as analog input for an ADC. The simulation predictions are confirmed with experimental data resulting from the IC fabricated in a standard 0.35μm CMOS technology.

SPICE modelling and experiments on a complete photovoltaic system including cells, storage elements, inverter and load

The design of a complete photovoltaic (PV) system and the precise evaluation of its performances under different conditions requires the use of an accurate simulation model. In this work, a SPICE model of a complete PV system, including a detailed model of PV cells and a multilevel inverter with load and energy storage elements, is presented. The simulation of the system as a whole allows determining the role of components and parameters as solar irradiation and cell temperature on the system performance. The global conversion efficiency and the total harmonic distortion (THD) of the output waveform are analysed in detail. The role and sizing criteria of storage elements placed in parallel with the PV modules are also analysed for various operating conditions. A PV system, including a specifically designed multilevel inverter, was built to perform efficiency and THD measurements that were compared with the simulation results to evaluate the model effectiveness.

RF-Powered HF-RFID Analog Sensors Platform

An RF powered UHF-RFID passive sensors platform was realized using discrete components and printed antennas designed to resonate at 868 MHz, used both for energy harvesting and data transmission. The tests demonstrate the possibility for the system to operate autonomously within the reading range of a standard RFID reader, that acts both as the RF power source and the receiver of the data stored in the tag user memory. The microcontroller can be interfaced on the same substrate with a sensor made of polymeric materials, sensible to physical parameters or chemical agents.

RF-powered UHF-RFID analog sensors platform

An RF powered UHF-RFID passive sensors platform was realized using discrete components and printed antennas designed to resonate at 868 MHz, used both for energy harvesting and data transmission. The tests demonstrate the possibility for the system to operate autonomously within the reading range of a standard RFID reader, that acts both as the RF power source and the receiver of the data stored in the tag user memory. The microcontroller can be interfaced on the same substrate with a sensor made of polymeric materials, sensible to physical parameters or chemical agents.

Enabling communication among smart tags in an UHF RFID Local Area Network

Adding computational and sensing capabilities to the new generation of passive UHF RFID tags has contributed to overcome the idea of considering them as mere identification transponders. These new functionalities give smart RFID tags the chance to be included in the global network of interconnected objects envisioned by the Internet of Things (IoT) paradigm. However, to fully enable RFID tags to participate in machine-to-machine (M2M) communications, RFID systems still lack an important feature, namely the capability of exchanging unicast messages between tags. In this paper, we propose an effective approach to enable real-time bidirectional communications among tags belonging to an RFID Local Area Network (i.e., under the coverage area of the same reader). The presented solution is based on the main idea of utilizing the User Memory of the tag as a virtual channel for transferring messages, and the tag reader as a message forwarder. As a proof-of-concept for our proposal, a novel smart RFID tag able to exploit the RFID radio interface for bidirectional real-time communications with other tags is designed, and experimental measures on the deployed testbed are discussed.