An Efficient Power Management Unit With Continuous MPPT and Energy Recycling for Wireless Millimetric Biomedical Implants

TL;DR

This work tackles powering battery-free millimeter-scale biomedical implants with magnetoelectric wireless power transfer by designing a fully integrated PMU that co-optimizes the transducer impedance and power path. The key contribution is a parallel REG and STO architecture with capacitance redistribution, augmented by a skewed-duty-cycle MPPT (SD-MPPT), a real-time regulation-efficiency optimizer, and an adaptive high-voltage charging stage capable of delivering up to 12 V. Measurements show a peak MPPT efficiency of $98.5\%$, a peak overall efficiency of $73.33\%$, and HV charging efficiency up to $37.88\%$, validating robust performance under motion and variable input. The integrated mm-scale implant demonstrates practical viability for continuous neural stimulation and sensing with energy recycling to extend external power delivery lifetimes, highlighting the method’s potential to enable battery-free, wireless biomedical devices.

Abstract

Biomedical implants offer transformative tools to improve medical outcomes. To realize minimally invasive implants with miniaturized volume and weight, wireless power transfer has been extensively studied to replace bulky batteries that dominate the volume of traditional implants and require surgical replacements. Ultra-sonic and magnetoelectric WPT modalities, which leverage low frequency acoustic electrical coupling for energy transduction, become viable solutions for mm-scale receivers. This work presents a fully integrated power management unit for ME WPT in millimetric implants. The PMU achieves load independent maximum power extraction and usage by continuously matching the impedance of the transducer, dynamically optimizing the power stage across varying input divided by load conditions, and reusing the storage energy to sustain the system when input power drops. Its parallel-input regulation and storing stages architecture prevent the cascading power loss. With the skewed-duty-cycle MPPT technique and regulation efficiency optimizer, the PMU achieves a peak MPPT efficiency of 98.5 percent and a peak system overall efficiency of 73.33 percent. Additionally, the PMU includes an adaptive high-voltage charging stage that charges the stimulation capacitor up to 12 V with an improved efficiency of 37.88 percent.

Figures (27)

• Figure 1: Magnetoelectric power transfer for mm-scale bio-implants yu_magni_2020chen_wireless_2022.
• Figure 2: Demands of PMU design for ME/US WPT biomedical implants: (a) co-design of PMU and transducer; (b) miniature energy buffer for body motion tolerance; (c) efficient high voltage charging stage for neurostimulator.
• Figure 3: Prototyped mm-scale implant packaged with the $5\times 2\times 0.2~mm^3$ tri-layer ME transducer, supercapacitor, 0201 stimulation capacitor, and the three 01005 decoupling capacitors.
• Figure 4: (a) Generic Butterworth Van-Dyke (BVD) model of ME/US transducers. (b) Simplified uncoupled model used in most PEH studies.
• Figure 5: (a) Impedance measurement waveform of a tri-layer and a bi-layer ME transducer. (b) Model parameters obtained by fitting the impedance measurement.