This paper presents a compact push-pull current-fed parallel resonant converter suitable for implementing a Transcutaneous Energy Transmission (TET) system to power heart assist devices. The new circuit topology integrates all three magnetic components of a conventional current-fed push-pull resonant converter including the DC inductor, phase splitting transformer and primary coil inductor into a coreless dual primary coil configuration, which significantly reduces the size and weight of the system. A stroboscopic mapping model is developed and used to analyse the circuit performance. Experimental results have demonstrated that the proposed converter performs very well and can achieve a DC to AC power efficiency of 90.5% at an output power of 10 W.

This paper presents a method to regulate the power transferred over a wireless link by adjusting the resonant operating frequency of the primary converter. A significant advantage of this method is that effective power regulation is maintained under variations in load, coupling and circuit parameters. This is particularly important when the wireless supply is used to power implanted medical devices where substantial coupling variations between internal and external systems is expected. The operating frequency is changed dynamically by altering the effective tuning capacitance through soft switched phase control. A thorough analysis of the proposed system has been undertaken, and experimental results verify its functionality.

A variable inductor based power flow control method is proposed to regulate the output voltage of a wireless power pick-up. The open circuit voltage variation of the power pick-up is compensated by controlling a magnetic amplifier type inductor in an LCL tuning configuration. The proposed control algorithm directly detects the output voltage of the power pick-up and feedbacks the voltage signal to update the tuning direction truth table discretely. According to the output voltage, the controller determines the direction of the equivalent inductance change of the magnetic amplifier. Both simulation and practical results demonstrated that the proposed control algorithm can effectively maintain the output voltage at a desired value after a short period of transient response. It has been found that the step-size of the variable inductor and sampling time are two key factors governing the control quality. These two parameters were selected based on the tolerance of the output voltage variation and the desired control speed.

We report the development of a novel technology that enables the wireless transmission of sufficient amounts of power to implantable physiological devices. The system involves a primary unit generating the magnetic field and a secondary pickup unit deriving power from the magnetic field and a power conditioner. The inductively coupled system was able to supply a minimum of 20 mW at all locations and pickup orientations across a rat cage, although much higher power of up to 10 W could be achieved. We hypothesized that it would be possible to use this technology to record a high-fidelity ECG signal in a conscious rat. A device was constructed in which power was utilized to recharge a battery contained within a telemetry device recording ECG signal sampled at 2,000 Hz in conscious rats (200-350 g) living in their home cage. Attributes of the ECG signal (QT, QRS, and PR interval) could be obtained with a high degree of accuracy (<1 ms). ECG and heart rate changes in response to treatment with the beta blocker propranolol and the proarrhythmic alkaloid aconitine were measured. Transmitters were implanted for up to 4 mo, and the characteristic circadian variation in heart rate was recorded. Such technology allows potentially lifetime monitoring without the need for implant refurbishment. The ability to provide suitable power levels to implanted devices without concern to the orientation of the device and without causing heating provides the basis for the development of new devices to record or influence physiological signals in animals or humans over significantly longer time periods than can currently be accommodated.

This paper presents a wireless power supply system for implantable biomedical devices. Magnitude of the input voltage supplied to the primary power converter is dynamically regulated according to the power demand of the device. The major advantage of such a system is that its average power loss is minimized. Unlike methods implemented at implantable secondary (pick-up) side, the magnitude regulation is undertaken at the external primary side. Thus the heating effect and physical size of the implantable secondary can be reduced. The system utilizes parallel tuning circuit to boost the voltage induced in the secondary pick-up, and does not require a tight coupling between the primary and secondary coils. As a result, the system has great tolerance to the variation in the air gap distance between the coils. The characteristics of the magnitude regulated power flow have been thoroughly analyzed, and both simulations and laboratory experiments have verified the proposed system.

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.

Resonant converters have been applied in wireless power supplies for implantable sensors due to their inherent advantages of low cost, high frequency and high reliability. However, the operating frequency of the resonant converter varies with the load and circuit parameters changes, which can significantly reduce the maximum power that the system can transfer. As a result the implanted sensors may not work properly because of insufficient power delivery. Uncertainty in frequency associated with system instability can contribute to electromagnetic interference for the implanted sensors, wireless communication networks, and other peripheral electronic devices. This paper proposes a new method to stabilize the system operating frequency using a fixed capacitor whose equivalent capacitance is controlled by semiconductor switches. Two control strategies based on Zero Voltage Switching techniques are analysed in details and practically implemented. The simulation and experimental results have demonstrated that the proposed method performs well in stabilizing the operating frequency of a wireless power supply system while maintaining the complete soft switching operation of the resonant converter.

It is very common in ICPT (inductively coupled power transfer) systems to use a DC inductor in a power pickup to increase output power. This is because the DC inductor helps to maintain a continuous current flow in the pick-up circuit so that power can be continuously delivered from the AC side of a rectifier to the DC side. However, how to determine the inductance of this DC inductor remains an unsolved theoretical problem, so trial and error approach is normally used in practical design. This paper analyzes in detail the effect of the DC inductance on the maximum power capacity of a parallel tuned pick-up, and the maximum possible power that can be transferred. Although it is difficult to determine the accurate maximum power when the equivalent series resistance of the inductor is considered, a suitable inductance is recommended for achieving the practical maximum power. Simulations and experimental results have proved the usability of these analyses results and the recommended inductance