With the rapid development of the Internet of Things (IoT), piezoelectric energy harvesting has emerged as a highly promising power solution for autonomous IoT devices. To increase the extracted energy from the harvesters, various rectifiers have been developed. Bias-flip rectifiers, one of the most widely used rectifiers, utilize extra components to periodically flip the voltage across the harvester to achieve higher output power. This work proposes a bias-flip rectifier with an energy investment technique to boost the total harvesting power. By optimizing the energy invested from the load to the harvester and the loading conditions, the circuit can achieve higher FoM compared to conventional SSHI rectifiers under the same configurations. The proposed circuit was designed in a 180-nm BCD process, the simulation results show a 5.97 X energy enhancement compared to a full bridge rectifier (FBR) and a 1.2 X enhancement compared to conventional synchronized switch harvesting on inductor (SSHI) rectifiers.

Triboelectric nanogenerator (TENG), advantageous in high energy density and flexibility, is promising as a sustainable energy source but can hardly be used to power edge devices directly due to its high-voltage AC output and varying capacitive impedance. To address it, this work proposes a power-conditioning interface with a fully integrated dual synchronous switch harvesting on capacitors (D-SSHC) rectifier for triboelectric energy extraction. Furthermore, a full digital duty-cycle-based (DCB) maximum power point tracking (MPPT) algorithm is developed to optimize the energy harvesting efficiency with simple implementation and continuous tracking. Designed and fabricated in a 0.18-μm BCD process, the proposed interface can extract energy at a maximum output voltage of 70 V. According to the measurement results, it achieves 99% MPPT efficiency and an energy extraction improvement of 598% compared to a full-bridge rectifier.

Various bias-flip rectifiers were proposed to improve the energy extraction performance for piezoelectric energy harvesting (PEH), which requires a power supply. However, no stable power supply is available when the system starts from a cold state. Typically, during the cold state, the system operates as a passive full bridge rectifier (FBR) to build up a stable power supply by charging a capacitor and then switching to the active rectifier after the cold state. Unfortunately, the system cannot start up if the open circuit voltage from a piezoelectric transducer (PT) is lower than the required supply voltage level. As a result, the system would end up with cold startup failure. This paper proposes a 2-mode bias-flip rectifier, which addresses the startup issue by lowering the required input open circuit voltage from the PT. The proposed design was fabricated in a 180-nm BCD process. Measurement results show that the necessary open-circuit voltage from the PT is lowered by 73% to achieve a successful cold startup, and the proposed system achieves 1182% energy extraction enhancement compared to a passive FBR.

A triboelectric nanogenerator (TENG) is a novel device that utilizes contact electrification and electrostatic induction to convert mechanical energy into electrical energy. Its characteristics include high energy density and flexibility, enabling self-powering of electronic devices by harvesting mechanical energy from the environment. Its applications include biomedical devices, wearable electronics, and Internet-of-Things (IoT) sensors. Despite these advantages, extracting electrical energy from TENG remains challenging due to its time-varying nature and low internal capacitance. Effective power-management techniques are essential for TENG energy-harvesting systems, yet research on dedicated integrated power-conversion methods is currently limited. Given the growing interest in TENG, a comprehensive exploration of energy-harvesting systems is critically necessary. This article synthesizes and compares current advancements in triboelectric energy-harvesting systems, emphasizing strategies to enhance output power through various power-conversion techniques. Additionally, it explores techniques employed in other energy-harvesting systems to inspire innovative approaches in TENG system design.

This article presents a reconfigurable piezoelectric harvester array (RPA) designed for multi-input systems, which dynamically configures its structure based on the intensity of ambient vibrations. The proposed architecture enhances system efficiency by eliminating dc–dc converters and achieving maximum power point tracking through a single power stage. It also widens the input range by serially connecting PEH units, enabling operation at lower excitation levels. Additionally, this series connection reduces equivalent parasitic capacitance, improving flip efficiency and maximum output power improving rate (MOPIR).The proposed RPA is employed with classical parallel-synchronous switch harvesting on inductor technology and implemented using a 180 nm CMOS process. Experimental results demonstrate a conversion efficiency of up to 78%, an MOPIR of 5.93, and a minimum input voltage of 0.36 V. This highly integrated, wide-input-range, and energy-efficient scheme offers a novel approach to miniaturizing PEH systems. We present detailed design principles, operational mechanisms, and performance metrics, highlighting the RPA’s potential as a scalable and environmentally friendly solution for powering next-generation Internet of Thing devices.

This article presents a 6.78-MHz switching-mode wireless power transfer (WPT) receiver (RX) with single-stage dual-output regulation and improved adaptability to link variations for biomedical applications. Based on a modified voltage doubler topology, it optimally transitions between voltage mode (VM) and resonant current mode (RCM) to extend the WPT range without compromising efficiency or delivered power. Seamless mode transition is achieved with no dead zones or output undershoots, thanks to the proposed quasi-open-circuit mode detection leveraging existing operational states without power-carrier interferences. The essential advantages of switching mode are consolidated via transient modeling. To meet dual-voltage-domain supply requirement in bio-implants, the RX uses stacked dc nodes in the voltage doubler to generate two regulated outputs with only three power switches. Designed and fabricated in a 180-nm CMOS technology, the proposed RX regulates two dc outputs at 1.8 and 3.3 V, respectively, with unobservable load-transient over/undershoots and cross-regulations. Using a 3.3-V-supplied class-D transmitter (TX), a 13.5-mm-radius TX coil, and an 11.5-mm-radius RX coil, the RX achieves a maximum WPT range of 7.5 cm under both 50-kΩ load conditions, demonstrating a 42% extension compared with VM-only operation. Real-time mode transition is validated through coil separation distance transients between 3 and 5.5 cm. In addition, with adaptive delay compensation in both VM and RCM operations, the RX achieves a peak power conversion efficiency (PCE) of 92.3% at a maximum output power of 171 mW.

A single transmitter source can power multiple ultrasound piezoelectric transducers to enhance the harvested power; however, the received ultrasonic signals vary in phase and amplitude across each element. This paper introduces a fully integrated, high-frequency SSHC rectifier tailored for miniaturized multi-piezo implants to efficiently harvest power at variable phase offsets with a compact form factor. The design incorporates a novel phase-splicing flipping capacitor-sharing technique between all four ultrasound piezoelectric transducers to improve area efficiency. The proposed 4-stage SSHC rectifier can harvest 5.94x more power than a full bridge rectifier operating at a high ultrasonic excitation frequency of 780 kHz. The proposed system was designed using 180-nm BCD process technology for a 2x2 piezoelectric transducer array, with each element featuring an internal capacitor (C_P) of 63.7pF.

This article presents a self-powered, bipolar, rectifierless series synchronized switch harvesting on inductor (BiReL-SSHI) interface circuit for piezoelectric energy harvesting. At both the positive and negative peaks of the piezoelectric transducer (PZT) voltage, a synchronous switch is automatically activated, enabling energy transfer from the PZT to a storage capacitor, while the inductor simultaneously inverts the PZT voltage for the next half cycle. Compared to conventional full-bridge rectifiers (FBRs) and series synchronized switch harvesting on inductor circuits, the BiReL-SSHI topology employs fewer components by optimizing the positive and negative synchronous switches, thereby reducing power loss and improving energy extraction efficiency. Experimental results show that the BiReL-SSHI achieves a 5.4× improvement in power extraction compared to an FBR, when the open-circuit voltage (V _oc) of the PZT is 8 V. Furthermore, in scenarios where a high V _oc is converted to a low output voltage, the BiReL-SSHI achieves superior energy transfer efficiency compared to other interface circuits. Experimental results further demonstrate that at a 3.3 V output under identical vibration conditions, the BiReL-SSHI delivers 5.86× higher output power than the FBR.

This article presents a 13.56-MHz wireless power transfer (WPT) system with coupling variation robustness and high efficiency for powering biomedical implantable devices (IMDs). To sustain reliable power transfer against inductive-link fluctuation, a hybrid voltage-/current-mode (V/CM) receiver (RX) is proposed to provide CM recovery when the coupling becomes weak for VM operation. To optimize the end-to-end (E2E) efficiency, a digital pulsewidth modulation (PWM)-based global power regulation technique is proposed, which allows a fully on/off operation of the three-mode power amplifier (PA) at the transmitter (TX) side and fast load-transient responses. Moreover, the system adopts a fully integrated voltage-sensing load-shift-keying (LSK) demodulation technique, which replaces conventional current sensing methods with a streamlined implementation and reduced power consumption. Both prototype TX and RX chips were fabricated in a 180-nm CMOS process. The proposed system, powered by a 1.8-V supply at TX, realizes a regulated 1.8-V dc output at RX. With the help of the hybrid V/CM RX, the proposed system achieves an up-to-150% WPT range extension compared to VM-only operation and an up to 7.2-cm WPT range. Benefiting from the global digital-PWM regulation, it achieves up to 72.3% E2E efficiency over the loading range from 0.18 to 81 mW. A 10- μ s load-transient recovery is also attained at a 164 × load step with a 110-mV undershoot and unnoticeable overshoots.

This work presents a switched capacitor power converter (SCPC) with instant transient response and minimized steady-state output ripple. The proposed SCPC employs a hybrid control strategy that amalgamates the strengths of hysteresis and continuous frequency modulation (CFM) controls, thus elevating transient performance while maintaining a small steady-state ripple. The system adopts a 10 -phase interleaved recursive switched capacitor (RSC) topology with adaptive capacitor sizing to achieve configurable voltage-conversion ratios (VCR) with heightened efficiency, power density, and load ability. Additionally, a novel adaptive switch-sizing technique is introduced to improve light-load efficiency. Fabricated in 180-nm BCD technology, the chip supports a wide-range load current of 0.7mA-120mA and converts a 0.8 -to-3.6V input to a 0.25 -to2.4 V output with a peak efficiency of 87.1%. The proposed converter simultaneously achieves a low voltage ripple of 12 mV and an over-/under-shoot voltage of less than 50 mV even under significant load transient steps (171X).

A single-stage dual-output regulating voltage doubler (DOVD) is proposed for biomedical wireless power transfer (WPT) systems. Derived from the full-wave voltage doubler (VD) topology, it achieves ac-to-dc rectification and dual-output voltage regulation in a single stage by using only two power transistors. The DOVD's inherent voltage conversion ratio (VCR) of 2 enhances the overall voltage gain of a WPT system, thus extending the transfer range against varying link conditions. To eliminate cross-regulation between the two outputs and provide fast load-transient responses, a parallel pulse-frequency modulation (PPFM) controller is proposed. In addition, a digital-tuning adaptive delay compensation technique with fast error-variation responses is proposed to achieve soft-switching in the power stage. Implemented in a 180-nm Bipolar-CMOS-DMOS (BCD) technology and operating at 6.78 MHz, the proposed DOVD achieves dual regulated outputs at 1.8 and 3.3 V, a VCR of up to 1.875, and a power conversion efficiency (PCE) of up to 92.95% over an output power range of 2.6-90.5 mW. It also achieves instant load-transient responses and unnoticeable cross-regulation during 25× load transients at both outputs.

A triboelectric nanogenerator (TENG) is a kinetic energy transducer with small and time-varying internal capacitance, which increases the difficulties of extracting harvested energy. In this paper, an efficient rectifier, hybridizing synchronized electric charge extraction (SECE) and bias-flipping techniques, is proposed. The two techniques alternatively operate at opposite voltage polarities of the TENG. By taking advantage of the varying capacitance, the proposed synchronized extraction and flipping (SEF) rectifier shows significantly improved energy extraction performance. The design is implemented in a 180-nm high-voltage BCD technology, and the results show a 7.4X energy extraction enhancement, 65-V voltage tolerance, and 35-nA quiescent current.

Bias-flip rectifiers are commonly employed for piezoelectric energy harvesting (PEH). This article proposes a synchronized switch harvesting on an inductor (SSHI) rectifier with a duty-cycle-based (DCB) maximum power point tracking (MPPT) algorithm. The proposed DCB MPPT algorithm is based on the mathematically derived relation between the MPPT efficiency and the duty cycle of the bridge rectifier. The resulting equation shows that the MPPT efficiency only depends on the rectifier duty cycle, and is independent of any other system variables, such as voltage bias-flipping efficiency, the open-circuit voltage from the harvester, vibration frequency, etc. As a result, MPPT can be achieved by regulating the duty cycle, simplifying circuit implementation, and achieving self-regulating and continuous MPPT. This design was fabricated in a 180-nm BCD process. The measured results show 98% peak MPPT efficiency and up to 738% output power enhancement.

This article proposes a novel collaborative-flip synchronized switch harvesting on capacitors (CF-SSHCs) rectifier and multioutput synchronous dc-dc converters with shared capacitors. Compared to the traditional SSHC, our CF-SSHC rectifier can increase the number of flipping phases, potentially enhancing the flipping efficiency and output power under specific conditions where C FLY is close to C_P. The synchronous dc-dc converters reuse the flying capacitors to achieve a high maximum output power improving rate (MOPIR) over a limited input power range and provide multiple outputs. This work achieves an advanced number of flipping phases in capacitor-based rectifier interface technology and explores multiple-input multiple-output configurations, evaluating the system's performance under periodic and shock conditions for the first time. The system's adaptability to various piezoelectric transducer (PT) array configurations is validated, highlighting its potential for Internet of Things (IoT) networks. The design is fabricated in standard 0.18- μ m CMOS. Measurement results demonstrate that the voltage flipping efficiency of up to 83% is achieved. Compared with full-bridge rectifier (FBR), the MOPIR can be increased to 5.06 × and 4.78 × under off-resonance and on-resonance excitation, respectively. It can also achieve a 2.14 × power enhancement under shock excitation. Additionally, when the input power P INFBR is in the range of 1.42-28.4 μ W, the MOPIR of the proposed system is always greater than 4.

Piezoelectric energy harvesting (PEH) is a promising approach to collecting ambient kinetic energy as the power supply for electronic devices. In many PEH designs, the maximum power point tracking (MPPT) technique is exploited to enhance the output power of the system. However, a typical PEH system requires a separate power stage for MPPT, which requires a large external rectified capacitor for MPPT operation and suffers from cascaded power efficiency loss. This paper presents an MPPT-integrated bias-flip rectifier where the MPPT and AC-DC rectifier are merged into one stage, resulting in fewer off-chip capacitors, faster MPPT, and less cascaded energy loss. The proposed circuit was fabricated in a 0.18μm CMOS process, and the measurement results show a 7.7 × energy extraction enhancement.

In this paper, we present an equivalent circuit model that integrates a living myocardial slice (LMS) cultured on a microelectrode array (MEA) to effectively simulates a heart-on-a-chip (HoC) within Electronic Design Automation (EDA) software. The cardiac fiber model consists of cardiomyocytes interconnected by gap junctions to simulate the action potential (AP) conduction in the longitudinal direction. We systematically explored several parameters, including gap junction resistors, seal resistors, and electrode diameters, to assess their effects on local field potential (LFP). The model accuracy was validated through in vitro experiments using mouse LMS, confirming its potential for guiding HoC design in cardiac research.

Synchronized rectifiers offer promising solutions for piezoelectric energy harvesting; however, achieving the promised energy extraction performance necessitates using either a bulky inductor or multiple large capacitors, which cannot be on-chip integrated and increase the system form factor. This article introduces a fully integrated sequenced synchronized switch harvesting on capacitors (3SHC) rectifier. The input piezoelectric transducer (PT) uses microelectromechanical system technology. The cantilever is equally split into multiple strongly coupled subcantilevers, with each cantilever treated as an individual PT connected to the proposed rectifier. The 3SHC rectifier cyclically operates multiple times to synchronously flip the voltage of each cantilever sequentially. With the proposed design, all the flying capacitors only need to match the capacitance of each subcantilever; hence, they can be fully integrated on-chip. The design is fabricated using standard 0.18 μ m CMOS technology. Measurement results show that the proposed 3SHC rectifier attains an 80% voltage flip efficiency and achieves a 730% power enhancement compared to a full-bridge rectifier.

The various application scenarios of triboelectric nanogenerator (TENG) have attracted increasing research interest, while one of the biggest challenges is the energy extraction efficiency. Due to the small and time-varying inherent capacitor in a TENG, the previous energy extraction techniques e.g., full-bridge rectifier (FBR) and bias-flip (BF) rectifier, performed not well. To extract more energy from TENG, this article proposed a fully integrated switched-capacitor (SC) rectifier with an electrostatic charge boosting (ECB) technique, achieving simultaneous extraction from the synchronized triboelectric energy and self-excited electrostatic energy. The proposed rectifier was fabricated in a 180-nm BCD process. With the proposed ECB technique, the theoretical analysis and measurements show a quadratically increasing output power with respect to the rectification voltage, attaining a constant maximum power point (MPP) at the breakdown voltage of the circuit. A maximum output power of 127.6 μ W is measured with a TENG fabricated in-house. Compared to a passive FBR, the proposed rectifier enhances the output power by 14 times.