A DEVICE WITH A RECEIVING ANTENNA AND A RELATED POWER TRANSFER SYSTEM

Abstract

The present invention is about a device with a receiving antenna (110), wherein the receiving antenna (110) comprises a secondary coil (112), and being arranged for inductively connecting to a transmitting antenna (200) comprising a primary coil (202). The device of the invention is characterized in that the receiving antenna (110) further comprises a tertiary coil (114) arranged to have connection to a load in the device; and a capacitor (142) to which the secondary coil (112) is connected; and there is an encapsulation (120) comprising a low liquid permeability and non-conductive material encapsulating at least a part of the receiving antenna (110). Additionally, the present invention is about a power transfer system.

Claims

1. A device with a receiving antenna (110), wherein the receiving antenna (110) comprises a secondary coil (112), and being arranged for inductively connecting to a transmitting antenna (200) comprising a primary coil (202); characterized in that the receiving antenna (110) further comprises: a tertiary coil (114) arranged to have connection to a load in the device; and a capacitor (142) to which the secondary coil (112) is connected; and there is an encapsulation (120) comprising a low liquid permeability and non-conductive material encapsulating at least a part of the receiving antenna (110) such that the windings of the tertiary coil (114) are outside the encapsulation (120).

2. The device of any one of the preceding claims, wherein in the receiving antenna (110), there is an element (118) including ferromagnetic material, for focusing the magnetic field of the transmitting antenna (200) into the receiving antenna (110).

3. The device of the claim 2, wherein the secondary coil (112) is arranged to couple to the tertiary coil (114) through the element (118) for creating a transformer between the secondary coil (112) and the tertiary coil (114).

4. The device of any one of the preceding claims, wherein the secondary coil (112) and the capacitor (142) constitute a secondary circuit and the encapsulation (120) is arranged to encapsulate substantially the complete secondary circuit with the element (118) constituting one package.

5. The device of any one of the claims 1-3, wherein the encapsulation (120) is arranged to encapsulate substantially the complete receiving antenna and to have hermetic vias for the connection to the load.

6. The device of any one of the preceding claims, wherein the secondary coil (112) and the tertiary coil (114) are arranged concentric one upon the other such that they couple.

7. The device of any one of the claims 1-5, wherein the secondary coil (112) and the tertiary coil (114) are arranged next to each other such that they couple.

8. The device of any one of the preceding claims, wherein the said low liquid permeability and non-conductive material of the encapsulation (120) comprises one of ceramics and plastic.

9. The device of any one of the preceding claims, wherein the receiving antenna (110) is arranged to resonate substantially at the same frequency as the transmitting antenna (200).

10. The device of any one of the preceding claims, wherein there is a further casing enclosing the entire receiving antenna (110).

11. The device of any one of the preceding claims, wherein at least one of the encapsulation (120) and the casing includes an ultrasonic or laser welding for preventing any leakage.

12. A power transfer system including a transmitting antenna (200) and a device of the claim 1 located such that they are inductively connected.

Description

[0043] In the following, the invention is described in more detail with reference to the attached drawings, wherein:

[0044] FIG. 1 shows the assembly of three coils

[0045] FIG. 2 shows an equivalent circuit of the assembly in FIG. 1

[0046] FIG. 3 shows a cross-section view of the receiving antenna configuration with an encapsulation

[0047] FIG. 1 shows the assembly of the three coils 112, 114 and 202. The primary coil 202 is connected in series with a compensating capacitor 210 which together form a transmitting antenna 200. Secondary coil 112 and tertiary coil 114 are around an element including ferromagnetic material e.g. a ferrite rod 118 and a capacitor 142 and a resistance 144 are connected to the terminals.

[0048] The generation of mutual inductances is visible in equivalent circuit of FIG. 2.

[0049] The approach of the FIGS. 1 and 2 is especially advantageous for applications where the dimensions of the primary and secondary coils 202 and 112 are far different from each other, which leads to a weak magnetic coupling.

[0050] The geometric dimensions of the primary coil 202 are determined by the needs of the application. The number of turns N.sub.1 imposes the value of the coil windings self- inductance L.sub.202, and a trade-off has to be found between the required current through L.sub.202 and the dissipated power in the coil windings resistance R.sub.202.

[0051] In a practical implementation, it is convenient to drive the primary coil windings with a block-shaped voltage waveform as generated by half-bridge converters with constant dc bus voltage V.sub.dc, and constant frequency f.sub.in. The rms fundamental component of the block shaped voltage V.sub.in is given by the equation 1 as

[00001]$\begin{array}{cc}{V}_{\mathrm{in}}=\frac{2}{\pi .Math.\sqrt{2}}.Math.V_{\mathrm{dc}}& \left(1\right)\end{array}$

[0052] The primary winding is then connected in series with a capacitor C.sub.210, whose value should be chosen such that

[00002]$\begin{array}{cc}\frac{1}{\sqrt{L_{202}.Math.C_{210}}}=2.Math.\pi .Math..Math.f_{\mathrm{in}}& \left(2\right)\end{array}$

[0053] This means that the self-inductance of the primary winding is series-compensated, independent of the relative position of the other windings.

[0054] The secondary and tertiary windings are tightly wounded around a small ferrite rod, with number of turns equal to N.sub.2 and N.sub.3 respectively. It is assumed that both windings have much smaller radii than the primary winding. The secondary winding, with self-inductance L.sub.112, is connected at its terminals to a capacitor C.sub.142. Finally, the tertiary winding is connected to a resistance R.sub.144, in which power dissipation is expected to occur according to the needs of the application.

[0055] By considering fundamental harmonic components, the voltage/current phasor relationships for the three windings is found to be

V.sub.1=jωL.sub.202I.sub.1+jωM.sub.02I.sub.2+jωM.sub.04I.sub.3=Z.sub.11I.sub.1+Z.sub.12I.sub.2+Z.sub.13I.sub.3   (3)

V.sub.2=jωM.sub.02I.sub.1+jωL.sub.112I.sub.2+jωM.sub.24I.sub.3=Z.sub.12I.sub.1+Z.sub.22I.sub.2+Z.sub.23I.sub.3   (4)

V.sub.3=jωM.sub.04I.sub.1+jωM.sub.24I.sub.2+jωL.sub.114I.sub.3=Z.sub.13I.sub.1+Z.sub.23I.sub.2+Z.sub.33I.sub.3   (5)

where ω=2πf.sub.in, and M.sub.02 is the mutual inductance between the primary winding and secondary winding, M.sub.04 is the mutual inductance between the primary winding and tertiary winding and M.sub.24 is the mutual inductance between the secondary winding and tertiary winding.

[0056] By connecting a capacitor to the secondary winding terminals, it follows from the notation on FIG. 2 that

[00003]$\begin{array}{cc}{V}_2=V_{C_{142}}=\frac{-1}{j.Math..Math.\omega .Math..Math.C_{142}}.Math.I_2=-Z_{C_{142}}.Math.I_2& \left(6\right)\end{array}$

[0057] The value of C.sub.142 should be chosen as

C.sub.142=1/ω.sup.2L.sub.112(1−k.sub.24.sup.2)   (7)

where k.sub.24=M.sub.24/√L.sub.112L.sub.114 represents the coupling between secondary and tertiary windings. By this way the self-inductances L.sub.112 and L.sub.114 and the mutual inductance M.sub.24 are fully compensated by C.sub.142 when I.sub.1=0.

[0058] The values of N.sub.2 and N.sub.3 impose the windings self- and mutual inductances L.sub.112, L.sub.114, M.sub.24 and may be determined in such a way to avoid saturation of the ferrite rod and to limit the maximal voltage on C.sub.142 at full load.

[0059] For example, if P.sub.144 is the desired power that should be dissipated in R.sub.144, the resistance connected at the tertiary winding, it implies the rms tertiary current

[00004]$\begin{array}{cc}{I}_3=\sqrt{\frac{P_{144}}{R_{144}}}& \left(8\right)\end{array}$

[0060] From the conventions in FIG. 2 follows that V.sub.3=−R.sub.144I.sub.3 and V.sub.2=−Z.sub.C142I.sub.2. Therefore, after some manipulations with the voltage/current phasor relationships above, the rms primary and secondary currents are found to be

[00005]$\begin{array}{cc}{I}_1=\frac{-1}{\Delta }\left[\left(Z_{22}+Z_{C.Math..Math.142}\right).Math.\left(R_{144}+Z_{33}\right)-Z_{33}^2\right].Math.I_3& \left(9\right)\end{array}$
I.sub.2=1/4[Z.sub.12(R.sub.144+Z.sub.33)−Z.sub.13Z.sub.23]I.sub.3   (10)

where

Δ=Z.sub.13(Z.sub.22+Z.sub.C142)−Z.sub.23Z.sub.12   (11)

[0061] When all the rms currents are known, the rms value of the fundamental component of the input voltages is easily determined with

[00006]$\begin{array}{cc}{V}_{C.Math..Math.210}=Z_{C.Math..Math.210}.Math.I_1=\frac{1}{j.Math..Math.\omega .Math..Math.C_{210}}.Math.I_1& \left(12\right)\end{array}$
V.sub.in=V.sub.C210=R.sub.202I.sub.1=V.sub.1   (13)

which yields the dc bus voltage level

[00007]$\begin{array}{cc}{V}_{\mathrm{dc}}=\frac{\pi .Math..Math.\sqrt{2}}{2}.Math.V_{\mathrm{in}}& \left(14\right)\end{array}$

necessary to create a block-shaped voltage waveform by means of a half-bridge converter. Further the peak flux density on the ferrite rod is given by

[00008]$\begin{array}{cc}{\Psi }_2=\frac{\sqrt{2}}{N_2}.Math.\left(.Math.M_{02}.Math.I_1+L_{112}.Math.I_2+M_{24}.Math.I_3.Math.\right)& \left(15\right)\\ B_{\max .Math..Math.2}=\frac{{\Psi }_2}{A_2}& \left(16\right)\end{array}$

where A.sub.2 is the cross-sectional area of the ferrite core. All together, the power transfer efficiency is found to become

[00009]$\begin{array}{cc}\vartheta =\frac{R_{144}.Math.{.Math.I_3.Math.}^2}{R_{202}.Math.{.Math.I_1.Math.}^2+R_{144}.Math.{.Math.I_3.Math.}^2}& \left(17\right)\end{array}$

[0062] The FIG. 3 shows one embodiment of the encapsulation 120 of the invention. In this context, the material of the encapsulation is chosen to be hermetic and non-conductive, which usually means ceramics. The material used to encapsulate electronics should possess a high resistivity and high dielectric strength.

[0063] The proper encapsulation materials may comprise metals, such as titanium and its alloys, biograde stainless steel, cobalt based alloys, tantalum, niobium, titanium-niobium alloys, nitinol, MP35N, and some noble metals. They may also comprise glass, ceramics. Additionally, polymeric materials, such as epoxies, silicones, polyurethanes, polyimides, silicon-polyimides, parylenes, polycyclic-olefins, silicon-carbons, bentzocyclobutenes and liquid crystal polymeres, are applicable.

[0064] Ceramic encapsulation 120 of the ferrite 118 is straight forward. However, the encapsulation the capacitor 142 turns to be problematic. The capacitor would require hermetic vias to it in order to connect it to the secondary coil 112. These are not economically feasible with high currents.

[0065] The space limitations in implantable applications, especially in an intramedullary device, are evident. Therefore, it would be beneficial to limit the amount of different encapsulation layers. This can be realized by encapsulating the complete secondary coil 112 and ferrite into same package.

[0066] Typically in the electrical configuration, the secondary coil 112 is on the top of the tertiary coil 114. This makes the encapsulation 120 into a single package difficult.

[0067] The coil wires should be routed from the tertiary coil 114 to the driven load. However, by flipping the configuration such, that the secondary coil will be the centermost coil in the assembly, the problems of the wire routing can be solved. The windings of the tertiary coil 114 can now be set on the top of the encapsulation 120.

[0068] Biocompatibility is defined as the ability of a material to perform with an appropriate host response in a specific application. When using a biocompatible material, such as gold, platinum, silver or gold-platted silver, for the windings of the tertiary coil 114, a long-term biocompatible solution is reached. Further, in the case of encapsulated active implants it is generally desirable, that the implant is nontoxic, noncarcinogenic and nonthrombogenic. Furthermore, the encapsulation should not cause any mechanical irritation in the surrounding tissues.

[0069] Further, the liquid leak inside the implant has to be prevented. Due to the need of connecting the windings of the tertiary coil 114 into the load some cables need to be routed. The introduction of body fluids has to be prevented. The fluids may reach the implant through capillary effect as the cables of the receiving antenna allow the direct path there. The physiological fluids contain several organic and inorganic materials and cellular components such as salts, enzymes, hormones, proteins and entire cells, which make the human body one of the most corrosive environments.

[0070] The prevention of the body fluids leakage may be achieved in several ways. In one embodiment of the invention, a hermetic via connector may be used to connect to the receiving antenna 110. Alternatively, the receiving antenna 110 may be over-molded with a polymer to stop liquid from penetrating into the cables. Further, the receiving antenna 110 may be encapsulated into a second hermetic packaging. Alternatively, the receiving antenna 110 may be encapsulated into a thermoplastic.

[0071] In a preferred embodiment of the invention an ultrasonically sealed encapsulation for the receiving antenna and a lipseal would be used. This ultrasonic welding of thermoplastic prevents the leakage from the interface of the antenna.

[0072] The encapsulation 120 may include an ultrasonic or laser welding for preventing any leakage. There may also be a further casing enclosing the entire receiving antenna 110. The further casing is preferably plastic encapsulation and it may also include an ultrasonic welding for preventing any leakage.

LIST OF REFERENCE MARKINGS

[0073] 110 receiving antenna [0074] 112 secondary coil [0075] 114 tertiary coil [0076] 118 element including ferromagnetic material [0077] 120 encapsulation [0078] 142 capacitor [0079] 144 resistance [0080] 200 transmitting antenna [0081] 202 primary coil [0082] 210 compensating capacitor [0083] L.sub.202 self-inductance of primary coil windings [0084] L.sub.112 self-inductance of secondary coil windings [0085] L.sub.114 self-inductance of the tertiary coil windings [0086] R.sub.202 resistance of the primary coil windings [0087] R.sub.144 resistance of the resistor in connection to the tertiary windings [0088] C.sub.210 capacitance of the capacitor in connection to the primary coil windings [0089] C.sub.142 capacitance of the capacitor in connection to the secondary coil windings [0090] M.sub.02 mutual inductance between the primary winding and secondary winding [0091] M.sub.04 mutual inductance between the primary winding and tertiary winding [0092] M.sub.24 mutual inductance between the secondary winding and tertiary winding [0093] V.sub.dc dc bus voltage [0094] f.sub.in constant frequency [0095] V.sub.in block shaped voltage [0096] V.sub.1 voltage of primary winding [0097] V.sub.2 voltage of secondary winding [0098] V.sub.3 voltage of tertiary winding [0099] V.sub.C.sub.142 voltage of capacitor in connection to the secondary coil windings [0100] V.sub.C202 voltage of capacitor in connection to the primary coil windings [0101] P.sub.144 power dissipated in a resistor [0102] N.sub.1 number of turns in primary windings [0103] N.sub.2 number of turns in secondary windings [0104] N.sub.3 number of turns in tertiary windings [0105] k.sub.24 coupling between secondary and tertiary windings [0106] I.sub.1 current primary winding [0107] I.sub.2 current secondary winding [0108] I.sub.3 current tertiary winding [0109] θ power transfer efficiency [0110] ψ2 peak flux [0111] B.sub.max2 peak flux density [0112] A.sub.2 cross-sectional area of an element including ferromagnetic material [0113] Z.sub.11 impedance factor [0114] Z.sub.12 impedance factor [0115] Z.sub.13 impedance factor [0116] Z.sub.22 impedance factor [0117] Z.sub.23 impedance factor [0118] Z.sub.33 impedance factor [0119] Z.sub.C.sub.142 impedance factor [0120] Z.sub.C202 impedance factor