Linear vibrator

1. A linear vibrator comprising:

a substrate supplying electric power;

a case including a base supporting the substrate and a cover wrapping the base;

a stator fixed to either the base or the cover;

a vibrator including magnets each arranged to face both sides of the stator and a weight to which the magnets are fixed;

an inner spring coupled to both sides of the weight to wrap the weight; and

an external spring, both end portions of which are coupled to an inner lateral surface of the case to wrap the inner spring, and a part of which is coupled to the inner spring.

2. The linear vibrator of claim 1 , wherein the stator is arranged at the substrate and include a coil so wound as to generate a magnetic field in response to electric power.

3. The linear vibrator of claim 2 , wherein the weight includes a groove formed by a lateral surface not wrapped by the inner spring for accommodating the stator, where inner lateral surfaces facing the weight formed by the groove is formed with the magnets facing the stator.

4. The linear vibrator of claim 1 , wherein both end portions of the inner lateral surface are fixed at first and second lateral surfaces of the weight facing the magnets, and the inner spring wraps the first and second lateral surfaces and a third lateral surface connected to the first and second lateral surfaces.

5. The linear vibrator of claim 4 , wherein the inner surface includes a first inner spring unit fixed at the first lateral surface, a second inner spring unit fixed at the second lateral surface and a third inner spring unit connected to the first and second inner spring units.

6. The linear vibrator of claim 5 , wherein a gap formed by the first inner spring unit and the first lateral surface, and the second inner spring unit and the second lateral surface increase while turning from the distal ends of the first and second inner spring units to the third lateral surface.

7. The linear vibrator of claim 1 , wherein both end portions of the external spring are respectively coupled to the inner lateral surface of the cover facing the stator.

8. The linear vibrator of claim 7 , wherein the external spring includes first and second external spring units opposite to the lateral surfaces facing the weights, and a third external spring units connecting the first and second external spring units and coupled to a part of the inner spring unit.

9. The linear vibrator of claim 8 , wherein a gap formed between the third external spring units and the lateral surfaces narrows down while turning from the third external spring units to end portions of the first and second external spring units.

10. The linear vibrator of claim 1 , wherein the inner spring and the external spring have respectively different modulus of elasticity.

11. The linear vibrator of claim 1 , wherein each lateral surface of the inner lateral spring and the weight is coupled by welding.

12. The linear vibrator of claim 1 , wherein each of the inner and external springs takes the shape of a ‘U’, and each of the inner and external springs is coupled by welding.

13. A linear vibrator comprising:

a substrate supplying electric power;

a case including a base supporting the substrate and a cover wrapping the base;

a coil fixed at the case and applied with a first power for generating a first frequency corresponding to a first natural frequency, and with a second power for generating a second frequency corresponding to a second natural frequency;

a vibrator including a magnet facing the coil and a weight fixed by the magnet; and

an elastic member including an external spring elastically supporting the vibrator and having mutually different modulus of elasticity and an inner spring coupled to the external spring and the vibrator,

wherein the vibrator is resonated at the first natural frequency if the coil is applied with a power of the first frequency, and the vibrator is resonated at the second natural frequency if the coil is applied with a power of the second frequency.

14. The linear vibrator of claim 13 , wherein the external spring is fixed at the case, a part of the inner spring is fixed at the external spring and the magnet and the weight is fixed at the inner spring.

15. The linear vibrator of claim 13 , wherein both end portions of the inner lateral surface are fixed at first and second lateral surfaces of the weight facing the magnets, and the inner spring wraps the first and second lateral surfaces and a third lateral surface connected to the first and second lateral surfaces.

16. The linear vibrator of claim 15 , wherein the inner surface includes a first inner spring unit fixed at the first lateral surface, a second inner spring unit fixed at the second lateral surface and a third inner spring unit connected to the first and second inner spring units.

17. The linear vibrator of claim 15 , wherein a gap formed by the first inner spring unit and the first lateral surface, and the second inner spring unit and the second lateral surface increase while turning from the end portions of the first and second inner spring units to the third lateral surface.

18. The linear vibrator of claim 13 , wherein both end portions of the external spring may be respectively coupled to the inner lateral surface of the cover facing the stator.

19. The linear vibrator of claim 18 , wherein the external spring includes first and second external spring units opposite to the lateral surfaces facing the weights, and a third external spring units connecting the first and second external spring units and coupled to a part of the inner spring unit.

20. The linear vibrator of claim 18 , wherein a gap formed between the third external spring units and the lateral surfaces narrows down while turning from the third external spring units to distal ends of the first and second external spring units.