Energy harvester and a wearable device

1. An energy harvester comprising:

an inner band;

an outer band arranged to surround the inner band, wherein the inner band is coupled to the outer band at a fixed end and the inner band is spaced from the outer band at a free end; and

an energy generator arranged to generate electric energy through relative movement between the inner band and the outer band at the free end.

2. An energy harvester in accordance with claim 1 , wherein the energy generator is positioned on the surface of the outer band.

3. An energy harvester in accordance with claim 2 , wherein the energy generator is positioned along the length of the outer band between the fixed end and the free end.

4. An energy harvester in accordance with claim 1 , wherein the outer band is elliptic whereby the inner band and the outer band intersecting with each other at the fixed end and separating from each other at the free end.

5. An energy harvester in accordance with claim 4 , wherein the energy generator is positioned at a vertex of the ellipse of the outer band.

6. An energy harvester in accordance with claim 1 , wherein the outer band is formed by a composite layer.

7. An energy harvester in accordance with claim 6 , wherein the composite layer includes an elastic substrate layer and a piezoelectric layer attached thereto, whereby the piezoelectric layer is arranged to generate electric energy in response to deformation of the substrate layer.

8. An energy harvester in accordance with claim 7 , wherein the elastic substrate layer is sandwiched between two said piezoelectric layers.

9. An energy harvester in accordance with claim 7 , wherein the piezoelectric layer is further covered by a protection layer.

10. An energy harvester in accordance with claim 1 , wherein the outer band is of uniform thickness or width across its length along which one or more energy generators are disposed thereon.

11. An energy harvester in accordance with claim 1 , wherein the outer band is of variable thickness or width across its length to form one or more spots at which the stress is concentrated and on which the energy generator is disposed, thereby facilitating the generation of electric energy by the energy generator.

12. An energy harvester in accordance with claim 1 , further including one or more linkage extending across the inner band and the outer band and the linkage includes said energy generator.

13. An energy harvester in accordance with claim 1 , further including an elastic membrane arranged to wrap the inner band and the outer band together to form a composite band.

14. An energy harvester in accordance with claim 13 , wherein the elastic membrane is at least one of waterproof and dustproof.

15. An energy harvester in accordance with claim 13 , wherein the wrapped inner band and outer band are invisible through the elastic membrane.

16. An energy harvester in accordance with claim 1 , wherein the inner band is formed by a first material and the outer band is formed by a second material with a higher stiffness than the first material.

17. An energy harvester in accordance with claim 1 , further including a mass at a position proximate to the free end to facilitate the movement of the outer band through its vertical movement, thereby increasing the magnitude of generated electric energy by the outer band.

18. An energy harvester in accordance with claim 17 , further including an electronic device arranged to receive electric energy from the energy generator.

19. An energy harvester in accordance with claim 18 , wherein the electronic device is received by the mass.

20. An energy harvester in accordance with claim 1 , wherein the energy harvester includes at least two said energy generators and the two energy generators are in at least one of serial connection and parallel connection.

21. An energy harvester in accordance with claim 1 , further including a rectifier arranged to receive generated electric energy from the energy generator and to convert received electric energy in alternating current to direct current.

22. An energy harvester in accordance with claim 1 , wherein the inner band includes a first arm and a second arm connectable together to form a closed loop and releasable from each other to form an open loop.

23. An energy harvester in accordance with claim 1 , wherein the inner band is arranged to secure to a human limb for generating electric energy in response to the movement of the outer band activated by the movement of human limb.

24. A wearable device comprising: a wearable strap formed by the inner band and the outer band of the energy harvester in accordance with claim 1 , and a mass arranged to receive at least a portion of the wearable device.