Magnetically biased electromagnet for audio applications

• US 8,942,410 B2
• Filed: 12/31/2012
• Issued: 01/27/2015
• Est. Priority Date: 12/31/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Wilk, Christopher R., Johnson, Martin E., Kessler, Patrick, Johanningsmeier, Nathan A.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Joshi, Sunita
• Application Number:
  US13/731,973
• Publication Number:
  US 20140185859A1
• Time in Patent Office: 757 Days
• Field of Search: 381/412, 381/396, 381/388, 381/398, 381/333, 381/306, 381/400, 381/413, 381/421
• US Class Current: 381/412
• CPC Class Codes: H04R 2499/11 Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• CPC Class Codes: H04R 9/025 Magnetic circuit

Abstract

An electronic device having an enclosure having a top panel and a bottom panel. An electromagnet is mounted within the enclosure, the electromagnet having a core portion attached to the top panel and a coil connected to the core portion. An attractor plate is attached to the bottom panel, the attractor plate forming part of a magnetic circuit of the electromagnet such that when an electrical audio signal is applied to the electromagnet, the bottom panel vibrates and produces a sound. A permanent magnet is further attached to the core portion, the permanent magnet is configured to create a bias in the magnetic circuit so as to modify a distortion in the sound.

Claims

1. An electronic device comprising:

an enclosure having a top panel and a bottom panel;

an electromagnet mounted within the enclosure, the electromagnet having a core portion attached to the top panel and a coil connected to the core portion;

an attractor plate attached to the bottom panel, the attractor plate forming part of a magnetic circuit of the electromagnet such that input of an electrical audio signal to the electromagnet causes the bottom panel to move and produce an audible sound; and

a permanent magnet attached to the core portion, the permanent magnet made of a different material than the core portion and having a magnetic pole that faces the attractor plate such that the permanent magnet creates a bias in the magnetic circuit that modifies a distortion in the audible sound.

2. The electronic device of claim 1 wherein the distortion is caused by a rectification of the electrical audio signal and biasing of the magnetic circuit allows the electrical audio signal to be recreated as a dynamic force without the rectification.

3. The electronic device of claim 1 wherein the core portion comprises a coil support arm around which the coil is positioned, a first side arm and a second side arm, and wherein the permanent magnet comprises a first magnet and a second magnet, each of the first magnet and the second magnet positioned at ends of the first side arm and the second side arm, respectively, and having the same magnetic poles facing the attractor plate.

4. The electronic device of claim 1 wherein the core portion comprises a base portion having a coil support arm around which the coil is positioned, a first side arm and a second side arm extending therefrom.

5. The electronic device of claim 4 wherein the permanent magnet comprises a first magnet and a second magnet, each of the first magnet and the second magnet positioned at ends of the first side arm and the second side arm, respectively, and facing the attractor plate.

6. The electronic device of claim 4 wherein the permanent magnet comprises a first magnet and a second magnet, each of the first magnet and the second magnet positioned at sides of the first side arm and the second side arm, respectively.

7. The electronic device of claim 1 further comprising:

a resilient spacer positioned within the magnetic circuit, between the attractor plate and core portion.

8. The electronic device of claim 7 wherein the resilient spacer comprises a ferromagnetic material to improve an efficiency of the magnetic circuit.

9. The electronic device of claim 1 wherein the attractor plate is fixedly attached to a side of the bottom panel facing the electromagnet.

10. The electronic device of claim 1 wherein the attractor plate comprises a ferromagnetic material.

11. An electronic audio system comprising:

an enclosure having a first panel operably connected to a second panel;

a transducer mounted within the enclosure, the transducer comprising;

an electromagnet having a core portion mounted to the first panel and a coil positioned around the core portion;

an attractor plate mounted to a side of the second panel facing the first panel, the attractor plate forming part of a magnetic circuit produced by the electromagnet upon input of an electrical audio signal; and

a permanent magnet mounted to the core portion, the permanent magnet made of a different material than the core portion and configured to bias the magnetic circuit produced by the electromagnet such that a dynamic force between the first panel and the second panel is proportional to the electrical audio signal and results in an audible sound output; and

a processor in electrical communication with the transducer and coupled to a memory to execute an operating system program.

12. The electronic audio system of claim 11 further comprising:

a resilient spacer positioned within a gap between the electromagnet and the attractor plate.

13. The electronic audio system of claim 11 wherein the transducer, the memory and the processor are contained within the enclosure.

14. The electronic audio system of claim 11 wherein the dynamic force between the first panel and the second panel causes the second panel to move while the first panel having the electromagnet attached thereto remains substantially stationary.

15. The electronic audio system of claim 11 wherein the dynamic force causes one of the first panel and the second panel to produce the audible sound output, and the audible sound output is at a frequency below 1 kilohertz such that it enhances a bass response of a speaker within the audio system.

16. A method of outputting sound from an electronic device comprising:

generating an audible sound output by producing a dynamic force between a first panel and a second panel of an enclosure of an electronic device, wherein producing the dynamic force comprises applying an electrical audio signal to an electromagnet having a core portion and a coil attached to the first panel so as to create a magnetic circuit which attracts the second panel to the first panel; and

magnetically biasing the magnetic circuit so that

     1) the dynamic force is proportional to the electrical audio signal and

     2) the audible sound output enhances a bass response of the electronic device.

17. The method of claim 16 wherein the magnetic circuit is biased by a permanent magnet positioned within the magnetic circuit so as to increase a magnetic force between the electromagnet and the second panel.

18. The method of claim 16 wherein the magnetic circuit is biased using a direct current.

19. The method of claim 16 wherein biasing the magnetic circuit modifies a rectification of the electrical audio signal so that the sound can be recreated from the electrical audio signal without distortion.

20. The method of claim 16 further comprising:

an attractor plate attached to a side of the second panel facing the electromagnet such that the attractor plate is within the magnetic circuit and an attractive force between the attractor plate and the electromagnet pulls the second panel toward the first panel.