Wireless Power Transfer
Through the use of inductive coupling, a voltage can be induced without a direct contact. Several heart pumps on the market are using this coupling such as the Abiocore and Thoratec. Using the following design, we hope to attain a wireless power transfer able to transmit 20 watts of power from an external battery to the internal system.
Figure – Schematic of Inductive Coupling Power Transmission System
DC/AC Inverter
A transformer is used to convert a direct current to an alternating current using inductive coupling. A DC voltage is applied to the secondary coil (labeled SEC in diagram) and induces an AC voltage on the primary current. The DC to AC converter being used is a 60Hz monostable multi-vibrating circuit. The center lead of the primary coil has 15 volts applied to it, causing the BJT transistors to turn on and off. This oscillation will induce an AC voltage across the primary coil. The frequency of the oscillation is based on the resistor value R.
Figure – Example of a DC to AC Converter (by Harry Lythall)
Figure – Coil Diagram of Transformer (a) Example of Transformer (b)
Schematic of Inverter
AC/DC Rectifier
An AC to DC converter, also known as a rectifier is used to deliver a direct current to the heart pump. It takes the negative portion of an AC voltage and makes it positive. This is generally done using diodes. In order to eliminate ripples in the response, a capacitor can be added. In order to eliminate design and manufacturing time, an AC to DC converter will be purchased off the shelf. The GCS20 delivers 20W and 15V and comes in a small package, which is ideal for this application where there is limited space available.
Figure – Example of a Rectifier
Figure – Board Layout of AC/DC Rectifier
Charging Circuit
The internal package will include a Sonata 4400 rechargeable lithium ion battery that will require a charging circuit.
Figure – Example of Charging Circuit
Design of Coils
Litz wire will be used for its reduction of skin effect. As the frequency of a wire increases, the current is drawn to the edge of the conductor and away from the center. Therefore thicker gauge wire is a waste of area, since most of the current is at the surface. Litz wire contains several strands of high gauge wire that have a small cross sectional area. Although the initial design is for a low frequency system (60Hz), high frequency systems are more commonly applied (20kHz).
Turns of coil=16
Wire Material = 22 AWG Copper Litz wire (Approx 20 internal wires of gauge 30)
Diameter of coil = 7.1cm
Possible configuration of coils
Potential Packaging of Coils
Will take the form of the Thoratec TETS by creation of a mold and filling with polyurethane resin and coated with silicon.
Packaging of the electrical components not considered for detailed design since design is subject to change based on experimentation of coils.