The wireless power transfer (WPT) efficiency to implanted bioelectronic devices is constrained by several frequency-dependent physical mechanisms. Recent works have developed several mathematical formulations to understand these mechanisms and predict the optimal operating conditions. However, the existing approaches rely on simplified body models, which are unable to capture important aspects of WPT. Therefore, this article proposes the efficiency analysis approach in anatomical models that can provide insightful information on achieving the optimum operation conditions. First, this approach is validated with a theoretical spherical wave expansion (SWE) analysis, and the results for a simplified spherical model and a human pectoral model are compared. The results show that although a magnetic receiver outperforms an electric one for near-field operation and both the sources could be equally use in the far-field range, it is in the mid-field that the maximum efficiency is achieved with an optimum frequency between 1 and 5 GHz depending on the implantation depth. The receiver orientation is another factor that affects the efficiency, with a maximum difference between the best and worst case scenarios around five times for the electric source and over 13 times for the magnetic one. This approach is used to analyze the case of a deep-implanted pacemaker wirelessly powered by an on-body transmitter and subjected to stochastic misalignments. We evaluate the efficiency and exposure, and we demonstrate how a buffered transmitter can be tailored to achieve maximum powering efficiency. Finally, design guidelines that lead to optimal implantable WPT systems are established from the results obtained with the proposed approach.

Implantable bioelectronic devices predominantly use wireless links for communication and/or power transfer. When considering transmitting implanted antennas, electromagnetic radiation through biological media is highly attenuated, and previous work has shown that the in-body path loss can be separated into three parts: the losses incurred by the propagating fields, the reflections at media interfaces, and the coupling of the antenna reactive near field and the lossy body. The first two are unavoidable, but a careful antenna design should minimize the near-field losses. Thus, quantifying the near-field losses of implanted antennas is useful in selecting the antenna topology for preliminary design. The aim of this paper is to present a simplified model of an implanted antenna that provides closed-form approximate expressions to estimate EM radiation from the implant. In particular, we extend the expressions for the reactive nearfield losses to both deep and shallow implants, by taking into account the implantation depth. Additionally, the proposed approximate method is verified by comparing the results obtained with the full-wave simulations in the case of a miniature implanted antenna, and with both simulated and measured results from two practical examples found in the literature.

In this paper, the combined antenna array is developed to maximize the Effective Potential Gain (Gep) within finite aperture area for the high-power (HP) ultra-wideband (UWB) radiation. The idea is to make the antenna element as small as possible, so that more elements can be arranged within prescribed aperture area to maximize Gep of the UWB system. On the other hand, the antenna element should match the pulse excitation. This means that, in the frequency domain, the working band of the antenna element should cover the spectrum of the radiated pulse; in the time domain, critical parameters of the radiated field (rise time of the monopolar pulse, e.g.) should not be distorted. And those can be the principles for the UWB antenna to match the pulsed excitation, based on which, the minimum size of the antenna element can be determined. With this method, a 4-element combined antenna array is designed. Also an impedance transformer and power divider are designed to feed the antenna array. Also, a big combined antenna is developed with the same aperture dimensions (30 cm × 30 cm) as the antenna array. Then, the performances of the antenna array and the big antenna are measured and compared. Compared with the big antenna, Gep of the antenna array is 21% higher under the applied excitation, which indicates that the proposed method can significantly improve Gep of the UWB system within the prescribed aperture area. Finally, the antenna array is furthermore optimized by adjusting the distances between the elements, and Gep is improved by another 11%, and the total improvement is 33%, the corresponding Effective Potential Gain is 1.49.

The traveling-wave Marx generator was first proposed by Carl Baum to analyze the switch-closure propagation process in fast pulsed-power systems. To improve the performance of the transistorized sub-nanosecond pulse generator, the traveling-wave Marx circuit with inter-stage transmission lines is studied. Simulations indicate that the delay time and the impedance of inter-stage transmission lines [microstrip lines on printed circuit board (PCB)] are main factors affecting the pulse waveform. Based on it, the series connection of modularized Marx circuits is proposed, which has the advantages of adjustable amplitude and bendable circuit layout. A compact high-amplitude pulse generator is developed with the amplitude of 8.2 kV, the rise time of 150 ps, and the PCB length of 35 cm. For higher pulse repetition rate, the heat dissipation design of PCB is necessary; however, due to the variations in the microstrip line structure, the commonly used metallic heat sink may cause a significant decrease in pulse amplitude. Thus, a novel heat dissipation design is proposed by optimizing the layout of metallic sinks and introducing heat-conducting ceramic sinks. A high-repetition-rate pulse generator is developed with the maximum pulse repetition rate of 600 kHz, the amplitude of 1.1 kV, and the rise time of 160 ps.

Output power of a transistorized pulser is usually limited by the power capacity of avalanche transistors. To improve the total output power, the power synthesis method is widely used, in which a single pulser with high output power and high time base stability is required. However, the time base stability tends to deteriorate as the output power increases. To improve the output power under the premise of high time base stability, from the perspective of carrier movement, the mechanisms of pulse jitter and pulse drift are investigated. It is found that the pulse jitter is caused by time dispersion of the ionization process in the collector depletion region, while the pulse drift is due to the decrement of the diffusion coefficient D_n and the electron mobility μ_n, which are both temperature-dependent. Based on the microscopic theoretical study, some macroscopic improvements on the time base stability are made. Some parameters of the trigger pulse and the circuit (e.g., charging capacitance) are optimized experimentally. Consequently, we achieved a pulser with an amplitude of 1.8 kV, pulse jitter of 25 ps, pulse drift of 100 ps/min at a pulse repetition frequency (PRF) of 100 kHz. Additionally, a new parameter k, the product of the highest PRF f and the peak power E_p, is defined to evaluate the output power. With almost the same time base stability, the proposed pulser has a k of 6.48 GHz W, which is improved significantly. Finally, a synthesized pulser with an amplitude of 2.5 kV and highest PRF of 100 kHz is achieved.

Performance limitations for implanted antennas, taking radiation efficiency as the metric, are presented. The performance limitations use a convex optimization procedure with the current density inside the implant acting as its degree of freedom. The knowledge of the limitations provides useful information in design procedure and physical insight. Ohmic losses in the antenna and surrounding tissue are both considered and quantitatively compared. The interaction of all parts of the system is taken into account in a full-wave manner via the hybrid computation method. The optimization framework is thoroughly tested on a realistic implanted antenna design that is treated both experimentally and as a model in a commercial electromagnetic solver. Good agreement is reported. To demonstrate the feasibility of developed performance limitations, they are compared to the performance of a loop and a dipole antenna showing the importance of various loss mechanisms during the design process. The trade-off between tissue loss and antenna ohmic loss indicates critical points at which the optimal solution drastically changes and the chosen topology for a specific design should be changed.