Transmitter with Improved Sensitivity and Shielding

• US 20170104262A1
• Filed: 12/23/2016
• Published: 04/13/2017
• Est. Priority Date: 08/29/2012
• Status: Active Grant

• Current Assignee: Red Tail Hawk Corporation
• Original Assignee: Red Tail Hawk Corporation
• Inventors: Parkins, John W.
• Granted Patent: US 10,522,903 B2
• Time in Patent Office: Days
• CPC Class Codes: A61F 11/08 internal, e.g. earplugs
• CPC Class Codes: H01Q 1/2291 used in bluetooth or WI-FI devices of Wireless Local Area Networks [WLAN] H01Q1/241 takes precedence; WLAN in general H04W
• CPC Class Codes: H01Q 1/273 Adaptation for carrying or wearing by persons or animals
• CPC Class Codes: H01Q 7/06 with core of ferromagnetic material H01Q7/02 takes precedence
• CPC Class Codes: H04B 5/00 Near-field transmission systems, e.g. inductive or capacitive transmission systems
• CPC Class Codes: H04B 5/24 Inductive coupling
• CPC Class Codes: H04R 1/1008 Earpieces of the supra-aural or circum-aural type
• CPC Class Codes: H04R 1/1075 Mountings of transducers in earphones or headphones
• CPC Class Codes: H04R 1/1091 Details not provided for in groups H04R1/1008 - H04R1/1083
• CPC Class Codes: H04R 2209/022 Aspects regarding the stray flux internal or external to the magnetic circuit, e.g. shielding, shape of magnetic circuit, flux compensation coils
• CPC Class Codes: H04R 2420/07 Applications of wireless loudspeakers or wireless microphones
• CPC Class Codes: H04R 25/554 using a wireless connection, e.g. between microphone and amplifier or using Tcoils

Abstract

A magnetic field transmitter, especially a transmitter used in conjunction with wireless communications earplugs. In one embodiment, a plate of magnetic material is used behind a coil of electrical conductor to improve the efficiency of the transmitter and to provide electrical and magnetic shielding. The specific dimensions and characteristics of the preferred embodiment of the transmitter described herein provide for efficient wireless communications.

Claims

1. A magnetic field transmitter configured to generate a time varying magnetic field in response to a time varying input signal, the magnetic field transmitter comprising:

a) a transmitter coil winding constructed of a bundle of continuous conductor loops, the bundle having an inner perimeter and an outer perimeter separated by a distance, the transmitter coil winding having a number of turns N, a coil winding resistance R, an effective coil radius Re and a coil winding inductance L, a conductor having a cross-sectional area A, a total length l and a resistivity ρ

, wherein the inner perimeter of the bundle, the coil winding resistance and the coil winding inductance are selected such that;

i) the coil winding resistance and the coil winding inductance produces a break frequency fb for the transmitter coil winding of between 20 Hz and 2000 Hz,

where the break frequency is defined by the formula f_b=R/(2π

L) wherein the coil winding resistance R is defined by the formula R=ρ

1/A and the coil winding inductance L is defined by the formula L=N² (u_oπ

Re)/2 where the constant u_o is the permeability of free space; and

ii) the bundle having an annulus width and an annulus depth which are each smaller than a distance from a center of the bundle to the inner perimeter of the bundle; and

b) a backing plate comprised of low reluctance magnetic material having an upper surface and a lower surface, the lower surface of the backing plate being attached in close proximity to a lower surface of the transmitter coil winding, the backing plate having an outer perimeter that is approximately coincident with the outer perimeter of the transmitter coil winding.

2. The magnetic field transmitter of claim 1, in which the backing plate is perforated with at least one perforation.

3. The magnetic field transmitter of claim 1, in which the backing plate is cup-shaped and comprising a rim with an inner surface and an outer surface, the inner surface formed in close proximity to the outer perimeter of the transmitter coil winding and extending from the upper surface of the backing plate to the upper surface of the transmitter coil winding.

4. The magnetic field transmitter of claim 1, in which the transmitter coil winding has a front surface and a back surface separated by an annular depth L1, the magnetic field transmitter further comprising a magnetic core substantially filling a volume defined by the inner perimeter of the transmitter coil winding and the annular depth L1.

5. The magnetic field transmitter of claim 4, where the magnetic core is perforated with at least one perforation.

6. The magnetic field transmitter of claim 4, in which the magnetic core is grounded.

7. The magnetic field transmitter of claim 1, further comprising an audio acoustic speaker integrated with the magnetic field transmitter to produce an acoustic output from the input signal.

8. The magnetic field transmitter of claim 1, further comprising a wireless ear plug communications device magnetically coupled with the magnetic field transmitter to produce an acoustic output from the input signal at the earplug.

9. The magnetic field transmitter of claim 1, in which the continuous conductor loops are circular.

10. A magnetic field transmitter configured to generate a time varying magnetic field in response to a time varying input signal, the magnetic field transmitter comprising:

a) a transmitter coil winding constructed of a bundle of continuous conductor loops, having an inner perimeter and an outer perimeter separated by a distance and an annulus width and an annulus depth, the annulus width and the annulus depth being smaller compared to a distance from a center of the bundle to the inner perimeter of the bundle;

b) a backing plate of low reluctance magnetic material having a front side and a back side, the transmitter coil winding being fixedly attached in close proximity to the backing plate, the backing plate having a central area perforated with at least one perforation passing through the upper surface and the lower surface; and

c) an audio acoustic speaker configured to produce an acoustic output from the input signal and mounted adjacent to the at least one perforation in the backing plate, such that sound generated by the speaker passes through the at least one perforation in the backing plate.

11. The magnetic field transmitter of claim 10, in which the inner perimeter of the transmitter coil winding circumscribes an effective coil area in a range between 0.79 in² and 4.9 in².

12. The magnetic field transmitter of claim 10, in which the transmitter coil winding has a coil winding resistance R and a coil winding inductance L, the coil winding resistance and the coil winding inductance being selected to produce a break frequency f_b for the transmitter coil winding of between 20 Hz and 2000 Hz, wherein the break frequency is defined by the formula f_b=R/(2π

L).

13. The magnetic field transmitter of claim 10, wherein the magnetic backing plate is cup- shaped and comprises a rim with an inner surface and an outer surface, the inner surface being formed in close proximity to the outer perimeter of the coil winding and extending from the front side of the backing plate to the upper surface of the transmitter coil winding.

14. The magnetic field transmitter of claim 10, in which the transmitter coil winding has a front surface and a back surface separated by an annular depth L1, the magnetic field transmitter further comprising a magnetic core substantially filling a volume defined by the inner perimeter of the coil winding and the annular depth L1, the magnetic core being perforated by at least one perforation aligned with the at least one perforation of the backing plate.

15. The magnetic field transmitter of claim 14, in which the magnetic core is grounded.

16. The magnetic field transmitter of claim 10, further comprising a wireless ear plug communications device magnetically coupled with the magnetic field transmitter to produce an acoustic output from the input signal at the earplug.

17. The magnetic field transmitter of claim 10, in which the continuous conductor loops are circular.

18. The magnetic field transmitter of claim 10, in which the speaker is in a speaker housing mounted to the back side of the backing plate, the housing providing a separation space for a speaker diaphragm to vibrate without contacting the backing plate.