Matteo Pizzotti

Growing demand for safer and energy efficient vehicles is driving the development of advanced sensors, such as smart tires capable of sensing multiple parameters and processing data locally. However, this leads to increased energy requirements, incompatible with batteries of conventional tire pressure monitoring systems (TPMS). Strain energy harvesting offers a viable approach to harness the forces acting on tires. This article presents a complete energy harvesting solution for sustainable battery-less operation of automotive Bluetooth smart tire sensors. High-voltage synchronous electric charge extraction (HV-SECE) from flexible PVDF transducers is proposed, modeled in overdamped regimes, and validated for the first time in a realistic automotive scenario. The proposed HV-SECE circuits can manage input voltages up to 300 V and provide a 3 V regulated voltage in a minimum footprint area down to 22 × 20 × 7.3 mm. At 40 km/h, in 205/55-R16 tires, the maximum harvested power from 10 × 5 cm bimorphs made with 45 µm-thick PVDF foils amounts to 925 µW. Even at low speeds, HV-SECE interfaces can cold-start the wireless tire sensor in less than 60 s, faster than regulatory TPMS requirements, and ensure energy surplus.

The design of new a generation of smart tyre sensors directly powered by tyre motion, requires accurate information about electrical quantities related to electromechanical energy harvesters in realistic operating conditions. Transducers and circuits are not accessible inside tyres, and it is difficult to predict theoretically or numerically their behaviour. This paper presents a characterization methodology for energy harvesters in tyres based on wireless telemetry and on a series of specific measurements performed in an industrial-grade tyre test machine. A Wi-Fi modular telemetry platform is designed for acquiring inside tyres, at up to 14 kSa/s, open-circuit voltages up to ±160 V, and short-circuit currents up to ±18 mA, from piezoelectric transducers. A power estimation technique is executed locally to extract static power transfer characteristics. Measurements were performed in real-world conditions on commercial tyres in an industrial drum test machine operated at controlled speeds up to 40 km/h and axial loads up to 3 kN. Among its contributions, the paper analyzes the in-tyre behaviour of piezoelectric harvesters in terms of voltage, current, and power, and reports reference data from a relevant test environment to support power converter circuit design. To characterize joint in-tyre and energy-autonomous operation of piezoelectric transducers, power management circuits, and tyre sensors, fully functional electronic systems are validated on-field by the proposed telemetry platform. Validated circuits include passive rectifiers and synchronous electric charge extractors.

An integrated buck-boost DC/DC converter for interfacing battery sources to capacitive loads such as supercapacitors is presented. The converter features a current regulation circuit on the source side, which applies a predefined constant DC current to the battery source, thus preventing the application of sharp current pulses generally associated with conventional DC/DC switching activity and resulting in long-term battery degradation. In fact, flat current shaping positively affects lifetime of battery sources. A specific digital control technique is proposed, which guarantees low energy losses during conversion by implementing a stepwise pseudo-adiabatic energy transfer that limits the maximum current inside the circuit and reduces the damping effect on current oscillation due to resistive paths.

An integrated DC/DC converter with online monitoring of the degradation induced by hot-carrier stress (HCD) in new generation power LDMOS transistors is proposed. In particular, when a relatively high drain voltage is applied during on-state regime (switching phase), degradation mechanisms lead to an increase of the transistor on-resistance (R ON ). To this purpose, the converter is able to dynamically estimate the R ON of the power LDMOS and to provide its value to the user during normal operation. The presented solution, developed in STMicroelectronics 90nm BCD technology, features a non-invasive current sensing and voltage sampling architecture, which is applied to a common DC/DC boost converter to evaluate the resistance of the power LDMOS. Without lack of generality, this specific sensing structure can be applied to any kind of converter, e.g. buck or buck-boost, as it does not require any change in the main conversion circuit.

This paper presents a battery-less CMOS integrated RF tag with sensing and localization capabilities. In order to allow tag addressing, communication, and localization by external readers, the IC performs a back-scattering modulation of a sequence of received UWB pulses according to specific spreading codes. For this purpose a UWB RF switch is designed and connected to the UWB antenna. The adoption of backscattering is integral to achieve ultra-low power wireless communication. The use of quasi-orthogonal spreading codes allows communication and localization with multiple tags at the same time. The IC includes a low-power sensing interface suitable for internal temperature sensing or external capacitive sensors. The power required for operation is scavenged from an UHF signal and converted by means of an internal RF rectifier and of a dynamically reconfigurable charge pump circuit. An on-chip micropower oscillator clocks a digital control circuit. The circuit is implemented in a 0.18 μm CMOS process. The architecture of the IC and preliminary test results are disclosed.

A method is proposed to verify the efficiency of low-power harvesting systems based on Photovoltaic (PV) cells for indoor applications and a Fractional Open-Circuit Voltage (FOCV) technique to track the Maximum Power Point (MPP). It relies on an algorithm to reconstruct the PV cell Power versus Voltage (P-V) characteristic measuring the open circuit voltage and the voltage/current operating point but not the short-circuit current as required by state-of-the-art algorithms. This way the characteristic is reconstructed starting from the two values corresponding to standard operation modes of dc-dc converters implementing the FOCV Maximum Power Point Tracking (MPPT) technique. The method is applied to a prototype system: an external board is connected between the transducer and the dc-dc converter to measure the open circuit voltage and the voltage/current operating values. Experimental comparisons between the reconstructed and the measured P-V characteristics validate the reconstruction algorithm. Experimental results show the method is able to clearly identify the error between the transducer operating point and the one corresponding to the maximum power transfer, whilst also suggesting corrective action on the programmable factor of the FOCV technique. The proposed technique therefore provides a possible way of estimating MPPT efficiency without sampling the full P-V characteristic.

In the new scenarios foreseen by the Internet of Things (IoT), industrial and consumer systems will be required to detect and localize tagged items with high accuracy using cheap, energy autonomous, and disposable tags. This paper discusses system-level and circuit-level aspects to be adopted for future generation passive radio-frequency identification (RFID) tags with localization capabilities. It is argued that RFID-enabled localization strategies, combining ultra-wideband (UWB) backscattering for communication/localization purposes and UHF for “on demand” powering of battery-less tags can be successfully exploited to this purpose. The proposed architecture adopts a small number of reference nodes, acting both as UWB readers and as UHF power sources. Architectural and circuital considerations on different design choices for the UWB-RFID tag are discussed, focusing on available off-the-shelf components. Power budget constraints for UWB backscattering operation and UHF wireless powering are derived in worst-case conditions. Furthermore, the simulation results, verified with experiments, prove the feasibility of cm-level localization accuracy at distances of several meters even in indoor scenarios where multi-path fading might be present.

This paper describes the architecture and the micropower design criteria of a battery-less, energy autonomous, individually addressable RF tag for UWB localization applications, with a focus on baseband circuitry. The tag includes a UHF rectifier, power conversion and management circuits, an addressable wake-up radio module, a microcontroller-based control unit, and circuits for UWB localization. The proposed circuit is suitable for UWB localization either by using passive backscattering of received UWB pulses, or by using active UWB pulses generators. Power for operation is scavenged from a modulated UHF carrier also used for addressing purposes. The circuit is implemented on discrete components in a 3.12 cm ² PCB area. The circuit can wake-up from fully discharged states and operates at distances as high as 10.8 m from a 2W-ERP source in the UHF 865-868 MHz RFID band with a +1.8 dBi receiving antenna. The quiescent power consumption of the tag is 3.88 μW, and the average power consumption at an addressing and activation rate of one time per second is 4.7 μW. The effectiveness of UWB localization was tested in a localization system based on time-difference-of-arrival (TDOA) estimations, consisting of multiple UWB readers and UHF transmitters.

We present a self-sustained battery-less multi-sensor platform with RF harvesting capability down to −17 dBm and implementing a standard DASH7 wireless communication interface. The node operates at distances up to 17 m from a 2 W UHF carrier. RF power transfer allows operation when common energy scavenging sources (e.g., sun, heat, etc.) are not available, while the DASH7 communication protocol makes it fully compatible with a standard IoT infrastructure. An optimized energy-harvesting module has been designed, including a rectifying antenna (rectenna) and an integrated nano-power DC/DC converter performing maximum-power-point-tracking (MPPT). A nonlinear/electromagnetic co-design procedure is adopted to design the rectenna, which is optimized to operate at ultra-low power levels. An ultra-low power microcontroller controls on-board sensors and wireless protocol, to adapt the power consumption to the available detected power by changing wake-up policies. As a result, adaptive behavior can be observed in the designed platform, to the extent that the transmission data rate is dynamically determined by RF power. Among the novel features of the system, we highlight the use of nano-power energy harvesting, the implementation of specific hardware/software wake-up policies, optimized algorithms for best sampling rate implementation, and adaptive behavior by the node based on the power received.

Wide-bandwidth lossless current sensors are critical in numerous applications, from current monitoring in DC-DC converters to non-invasive load monitoring. CMOS Hall sensor is a low-cost solution for current sensing and can be easily integrated as part of mixed-signal system-on-chips (SoCs). State-of-the-art CMOS Hall sensors offer only limited acquisition bandwidths of a few hundred kHz. This paper presents a 1 MHz Hall current sensor SoC integrating a broadband CMOS Hall sensor, two 2 MS/s ADCs and a multi-mode digital compressive sensing encoder for data rate reduction. The complete SoC is implemented in a STM 0.16 μm BCD technology, and occupies 16 mm² while consuming less than 94 mW at 1.8 V.