Deeply implanted biomedical devices (DIBDs) are a challenging application of wireless power transfer because of the requirement for miniaturisation whilst minimising patient exposure to tissue heating. This work proposes a capacitively-coupled conductive power transfer method for DIBDs, which allows for the safe transfer of power into the body whilst using minimum implant volume. The method uses parallel insulated capacitive electrodes to couple uniform current flow into the tissue and implants. Analytical analyses are presented, which results in a two-port network that describes circuit operation. The two-port network is further simplified for typical DIBD applications where coupling to the external electrodes is low. This results in a simple circuit model of power transfer of which the parameters are easily obtained by experimental measurements. The proposed circuit model has been validated using circuit coupled finite element analysis (COMSOL) and benchtop experiments using a tissue phantom. In addition, the safety aspect of the method has been evaluated via COMSOL simulation of the specific absorption rate (SAR) for various implanted receiver dimensions and implantation depth. Finally, a completed power supply, unaffected by the implantation depth, running at 6.78MHz, delivering 10 mW deep into the body whilst meeting the IEEE C95.1 basic restriction is presented.

Transcutaneous energy transfer (TET) enables the transfer of power across the skin without direct electrical connection. It is a mechanism for powering implantable devices for the lifetime of a patient. For maximum power transfer, it is essential that TET systems be resonant on both the primary and secondary sides, which requires considerable design effort. Consequently, a strong need exists for an efficient method to aid the design process. This paper presents an analytical technique appropriate to analyze complex TET systems. The system's steady-state solution in closed form with sufficient accuracy is obtained by employing the proposed equivalent small parameter method. It is shown that power-transfer capability can be correctly predicted without tedious iterative simulations or practical measurements. Furthermore, for TET systems utilizing a current-fed push-pull soft switching resonant converter, it is found that the maximum energy transfer does not occur when the primary and secondary resonant tanks are “tuned” to the nominal resonant frequency. An optimal turning point exists, corresponding to the system's maximum power-transfer capability when optimal tuning capacitors are applied.

This paper presents a novel method of inductively powering an implantable telemetry device over a large area. The system is based around an array of individually tuned series resonant circuits distributed across a charging pad. By varying the frequency of the driving voltage, the location of the charging field is changed. Presented are a method of controlling the resonant frequency and techniques for determining the geometry of the charging pad. Results from a nine coil system operating between 97 kHz and 209 kHz are given which can deliver 100 mW to an implanted telemeter at a height of 5 cm above the charging pad.

Dynamic detuning methods have been used in inductive contactless power transfer (ICPT) systems for power flow control. However, the highly variable switching frequency involved in the detuning operation will contribute to electromagnetic interference (EMI) and power losses. It is difficult to determine the detuning frequency precisely due to nonlinear features of power pick-ups. Uncertainty in the operating frequency can result in difficulties in designing filters with suitable bandwidths and choosing suitable switching devices. Based on detailed analytical analysis in four segments of the detuning process, a numerical method is developed in this paper to determine the boundaries of the switching frequencies. An iterative algorithm is presented using a flow chart to illustrate the process taken in the numerical analysis. Simulation and practical experiments are conducted to verify the algorithm so as to ensure the calculated results are sufficiently accurate for designing EMI filters and choosing suitable switching devices.

This paper presents a capacitive pressure sensor interface circuit design in 180 nm XH018 CMOS technology for an implantable capacitive pressure sensor, which has a wireless power supply and wireless data transfer function. It integrates full-bridge rectifiers, shorting control switches, low-dropout regulators, bandgap references, analog front end, single slope analog to digital converter (ADC), I2C, and an RC oscillator. The low-dropout regulators regulate the wireless power supply coming from the rectifier and provide a stable and accurate 1.8 V DC voltage to other blocks. The capacitance of the pressure sensor is sampled to a discrete voltage by the analog front end. The single slope ADC converts the discrete voltage into 11 bits of digital data, which is then converted into 1 kbps serial data out by the I2C block. The “1” of serial data is modulated to a 500 kHz digital signal that is used to control the shorting switch for wireless data transfer via inductive back scatter. This capacitive pressure sensor interface IC has a resolution of 0.98 mmHg (1.4 fF), average total power consumption of 7.8 mW, and ±3.2% accuracy at the worst case under a −20 to 80 °C temperature range, which improves to ±0.86% when operated between 20 and 60 °C.