Ferran Reverter

Triboelectric nanogenerators (TENGs) have emerged as a promising solution for powering Internet of Things (IoT) sensor nodes and wearable electronics, owing to their use of low-cost, lightweight, and environmentally friendly materials. However, the distinctive characteristics of their electrical output, such as high voltage and time-varying internal capacitance, pose significant challenges for the design of efficient power management circuits (PMCs). The high output voltage of TENGs, which often exceeds the safe operating limits of integrated-circuit (IC) technologies, renders conventional IC-based PMCs unsuitable for optimal energy extraction. As a result, board-level PMCs, free from these voltage constraints, are essential for effectively managing the output power of TENGs. This article presents a comprehensive classification and critical review of recent board-level PMC designs tailored for TENG applications. Using a generic block diagram as a framework, various implementation strategies for each functional block are analyzed, highlighting their respective benefits and limitations. Particular focus is given to switching-stage configurations around the rectifier, which enable advanced techniques such as synchronous electric charge extraction (SECE) and synchronous switched harvesting on inductor (SSHI). A comparative analysis of representative PMCs is conducted based on key mechanical and electrical performance metrics. Finally, unresolved challenges and promising research directions are discussed, providing insights into future development of high-efficiency TENG-based energy harvesting systems.

In the field of power management circuits (PMC) for low-power thermoelectric generators (TEG) intended for autonomous sensors, this article experimentally evaluates the alternatives commercially available. Considering their limitations in terms of minimum input voltage and power efficiency, this article also proposes and experimentally characterizes a circuit topology that combines and interconnects two different PMC alternatives so as to achieve the benefits of both. Thanks to this interconnection, the resulting circuit can operate from a low input voltage (to be precise, an open-circuit voltage of the TEG equal to 40 mV), which is really attractive for TEGs under low thermal gradients, with a satisfactory power efficiency (i.e., up to 78%).

In the field of power management circuits (PMC) for low-power thermoelectric generators (TEG) intended for autonomous sensors, this article experimentally evaluates the alternatives commercially available. Considering their limitations in terms of minimum input voltage and power efficiency, this article also proposes and experimentally characterizes a circuit topology that combines and interconnects two different PMC alternatives so as to achieve the benefits of both. Thanks to this interconnection, the resulting circuit is able to start operating from a low input voltage (i.e., 40 mV of TEG open-circuit voltage), which is really attractive for TEGs under low thermal gradients, with a satisfactory power efficiency (i.e., up to 78 %).

This paper presents a low-cost interface circuit for accurate measurement of four-wire resistive sensors, with emphasis on RTD-based temperature sensing over a wide operating span. The circuit employs a switched Op-amp configuration controlled by a unipolar square-wave signal with 50% duty cycle, thereby eliminating the effect of lead-wire resistance without requiring matched components or bipolar excitation. The average output voltage represents the sensor resistance and reduces errors due to wire resistance, switch-ON resistance, and their mismatches. Theoretical analysis shows that dominant nonidealities, mainly Op-amp offset voltage and input bias current, limit the maximum relative error to 0.007%. Experimental results using OP07 and CD4053 ICs demonstrate linear operation for sensor resistances from 60 Ω to 390 Ω, with a maximum nonlinearity of 0.06% and a relative error of 0.09%. A low-cost LMC555-based control signal generator is also implemented, yielding comparable performance with the prior art. The proposed circuit provides a robust and cost-effective solution for four-wire resistive sensor and RTD interfacing.

This article presents a self-powered adaptive piling-up rectifier-less synchronized-switch-harvesting-on-inductor (APReL-SSHI) interface for piezoelectric energy harvesting (PEH). The proposed interface introduces two distinct operational modes, energy transfer mode (ETM) and voltage piling-up mode (VPM), that adaptively select the optimal mode based on varying vibration excitation levels to maximize energy extraction. This adaptive mechanism addresses the narrow optimal rectified voltage range (ORVR) limitation inherent in conventional S-SSHI rectifiers by enabling capacitor charging beyond standard thresholds. Experimental results demonstrate that the proposed APReL-SSHI circuit achieves up to 5.27 times the maximum output power compared to a full-bridge rectifier (FBR) and expands the ORVR by 4.16 times compared to a conventional S-SSHI circuit. Consequently, the APReL-SSHI delivers superior balance between these two key performance metrics compared to existing state-of-the-art rectifiers. Moreover, the circuit uniquely exhibits a secondary output power peak, reaching approximately 94% of maximum power when operated above the standard maximum power point (MPP) voltage. Under constant input conditions, the voltage associated with this secondary power peak is easily adjustable, thereby facilitating direct voltage matching for diverse load requirements and achieving near-MPP tracking efficiency of 94% without the need for an additional MPPT controller.

Triboelectric nanogenerators (TENGs) have emerged as a promising power solution for autonomous sensors, as they can be constructed using low-cost, lightweight, and environmentally friendly materials. However, the design of the ensuing power management circuit (PMC), intended to maximize energy extraction from the TENG, remains a challenge for circuit designers at both board and integrated circuit (IC) levels, especially due to the unique properties of the TENG output signal. Among the different circuit topologies proposed in the literature, this article focuses on the full-wave rectifier (FWR) with a dual output (DO). It is proposed to incorporate a switch at the input of the FWR-DO to increase the energy extracted from the TENG. The switch is instantaneously closed in synchronization with the maximum and minimum separation between electrodes, thereby generating a short circuit across the TENG. As a result of this short-circuit, the voltage at the two outputs of the FWR-DO can be adjusted independently to optimize energy extraction in both half cycles, which is not possible in conventional FWR-DOs. The proposed circuit, including the synchronized input switch, is evaluated theoretically, by simulations, and experimentally using an in-house fabricated TENG with a contact-separation topology. Additionally, its performance is compared with that obtained using conventional FWR and FWR-DO topologies. According to the results reported herein, the incorporation of the synchronized input switch generates an improvement in the energy extraction that depends on the symmetry of the voltage-charge plot related to the TENG. For the TENG under test, the energy improvement factor (with respect to FWR-DO) is 18% when the switch is incorporated.