This paper presents a low-profile and autonomous piezoelectric energy harvesting system consisting of an extraction rectifier and a maximum power point tracking (MPPT) circuit for powering portable electronics. Synchronized switch harvesting on capacitor-inductor (SSHCI) technique with its unique two-step voltage flipping process is utilized to downsize the ponderous external inductor and extend application areas of such harvesting systems. SSHCI implementation with small flipping inductor-capacitor combination enhances voltage flipping efficiency and accordingly attains power extraction improvements over conventional synchronized switch harvesting on inductor (SSHI) circuits utilizing bulky external components. A novel MPPT system provides robustness of operation against changing load and excitation conditions. Innovation in MPPT comes from the refresh unit, which continually monitors excitation conditions of piezoelectric harvester to detect any change in optimum storage voltage. Compared with conventional circuits, optimal flipping detection inspired from active diode structures eliminates the need for external adjustment, delivering autonomy to SSHCI. Inductor sharing between SSHCI and MPPT reduces the number of external components. The circuit is fabricated in 180 nm CMOS technology with 1.23 mm ² active area, and is tested with custom MEMS piezoelectric harvester at its resonance frequency of 415 Hz. It is capable of extracting 5.44x more power compared to ideal FBR, while using $100~\mu $ H inductor. Due to reduction of losses through low power design techniques, measured power conversion efficiency of 83% is achieved at 3.2 V piezoelectric open circuit voltage amplitude. Boosting of power generation capacity in a low profile is a significant contribution of the design.

This paper presents an efficient hybrid energy harvesting interface to synergistically scavenge power from electromagnetic (EM) and piezoelectric (PE) sources, and drive a single load. The EM harvester output is rectified through a self-powered active doubler structure, and stored on a storage capacitor. The stored energy is then transferred to the PE harvester to increase the damping force and charge extraction. The total synergistically extracted power from both harvesters is more than the power obtained from each independently. The hybrid operation is validated through a compact and wearable platform that includes custom designed EM and PE harvesters for scavenging energy from human motion. The system supplies 1-3.4 V output for powering up wireless sensor nodes with a wide range of vibration frequency, and generates between 1-100 μW at 90% maximum power conversion efficiency. The solution has superior power generation performance compared to previous stand-alone systems in the literature.

This paper presents a self-powered interface circuit to extract energy from ambient vibrations for powering up microelectronic devices. The circuit interfaces a piezoelectric energy harvesting MEMS device to scavenge acoustic energy. Synchronous electric charge extraction (SECE) technique is deployed through the implementation of a novel multi-stage energy extraction (MSEE) circuit in 180nm HV CMOS technology to harvest and store energy. The circuit is optimized to operate with minimum power losses when input power is limited, and adapts well to operating conditions with higher input power. The highly accurate peak detector was validated for a wide piezoelectric frequency range from 20 Hz to 4 kHz. A charging efficiency of about 84% has been achieved for 4.75 V open circuit piezoelectric voltage excited at 390 Hz input vibration under nominal input power range of 30-80 μW. Power optimizations enable the circuit to maintain a conversion efficiency of 47% at input power level as low as 3.12 μW. MSEE provides up to 15% efficiency improvement compared to traditional SECE, and maintains power efficiency as high as possible for a wide input power range.

This paper presents a self-adapting synchronized-switch harvesting (SA-SSH) interface circuit to extract energy from vibration-based piezoelectric energy harvesters (PEHs). The implemented circuit utilizes a novel switching technique to recycle optimum amount of harvested charge on piezoelectric capacitance to strengthen the damping-force, and simultaneously achieve load-independent energy extraction with a single inductor. Charge recycling is realized by adjusting extraction-time, and optimized through a maximum power point tracker (MPPT) based on charge flipping dissipation. The circuit has been implemented using 180nm HV CMOS technology with 0.9 $\times$ 0.6 mm2 active area. Self-adapting SSH circuit has been validated with both macro-scaled and MEMS PEHs with different inductor values. The interface circuit provides maximum energy extraction for the full storage voltage range of 1.8-3.7 V. The implementation harnesses 500% more power compared to an ideal full-bridge rectifier, and outputs 3.4 $\mu$ W for 2.24 V peak-to-peak open-circuit piezoelectric voltage from MEMS PEH excited at its resonant frequency.