Magnetic Field Antenna
1. A magnetic field antenna comprising:
- a) an earplug body having a distal end and a proximal end;
b) a magnetic core section within the earplug body;
c) an antenna coil having at least one turn wrapped at least partially around the magnetic core section;
d) at least one electrical component within the earplug body and electrically coupled to the antenna coil; and
e) an eartip adapter at least partially made of magnetic material and located on the proximal end of the earplug body, the eartip adapter being acoustically coupled to the at least one electrical component.
A magnetic field antenna that provides high efficiency and a compact form factor. Electromagnetic shielding of electrical components used in the antenna is provided, and one embodiment of the invention is a wireless battery-free communications earplug.
- 1. A magnetic field antenna comprising:
a) an earplug body having a distal end and a proximal end; b) a magnetic core section within the earplug body; c) an antenna coil having at least one turn wrapped at least partially around the magnetic core section; d) at least one electrical component within the earplug body and electrically coupled to the antenna coil; and e) an eartip adapter at least partially made of magnetic material and located on the proximal end of the earplug body, the eartip adapter being acoustically coupled to the at least one electrical component.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
- 12. A magnetic field antenna comprising:
a) a body having a distal end and a proximal end; b) a magnetic core section within the body adjacent to the distal end; c) an antenna coil having at least one turn wrapped at least partially around the magnetic core section; and d) at least one electrical component within the body, electrically coupled to the antenna coil, wherein the antenna coil is located such that at least one turn of the antenna coil, projected into a perpendicular field axis plane, circumscribes an area that overlaps at least an area of the at least one electrical component projected onto the perpendicular field axis plane.
- View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21)
- 22. A wireless earplug comprising:
a) an earplug body having a distal end and a proximal end and an outer surface comprising a mechanical barrier adjacent the distal end of the earplug body and a base adjacent the proximal end of the earplug body; b) a magnetic core section within the earplug body inside the mechanical barrier; d) a speaker having a speaker output, located within the earplug body, and electrically coupled to the antenna coil; e) a magnetic shunt magnetically coupled to the magnetic core section and at least partially enclosing the speaker to provide at least partial magnetic shielding of the speaker; and f) an eartip adapter located on the proximal end of the earplug body, the eartip adapter being acoustically coupled to the speaker output.
- View Dependent Claims (23, 24, 25)
This application is a continuation of co-pending U.S. application Ser. No. 14/191,783, entitled “Magnetic Field Antenna”, which was filed on Feb. 27, 2014, and published on Jun. 26, 2014, as published application number 2014/0177863, and which is a continuation-in-part of co-pending U.S. application Ser. No. 12/832,363, entitled “Wireless Earplug with Improved Sensitivity and Form Factor”, filed Jul. 8, 2010, which issued on Apr. 8, 2014 as U.S. Pat. No. 8,693,720, which claimed the benefit of Provisional Application No. 61/224,531, filed Jul. 10, 2009, entitled “Wireless Earplug with Improved Sensitivity and Form Factor”, and was a continuation-in-part of U.S. application Ser. No. 11/837,129, entitled “Wireless Communications Headset System Employing a Loop Transmitter That Fits Around the Pinna”, which was filed Aug. 10, 2007, and issued on Apr. 1, 2014, as U.S. Pat. No. 8,688,036, which claimed the benefit of Provisional Application No. 60/824,091, filed Aug. 31, 2006, entitled “Wireless Communications System Employing a Loop Transmitter That Fits Around The Pinna”. The aforementioned applications and patents are hereby incorporated herein by reference.
This invention relates to the field of wireless communications earplugs, magnetic field antennas and radio frequency identification devices.
Aircraft radios and intercoms typically provide electrical audio outputs for connecting aviation headsets. The audio signal from an aircraft radio, provided as an electrical signal at an audio output, can directly drive an aviation headset that incorporates headset speakers with enough sensitivity to provide clear acoustic audio communications.
Published applications US 2009/0041285 and US 2010/0296667, of which this application is a continuation-in-part, describe components of a system that can be used for wireless earplug communications. In one embodiment described in US 2009/0041285, a magnetic field antenna (MFA) may be used as a battery-free wireless communications earplug in which only passive electrical components are employed. The sensitivity of the antenna achieves adequate sound pressure level (SPL) and perceived acoustic volume with typical aircraft radios, and the small earplug size provides a comfortable earplug.
A pair of magnetic loop transmitters, such as a loop transmitter that fits around the pinna of the user as seen in at least FIG. 12 of US 2009/0041285, can be installed in a headset instead of the speakers, or used in conjunction with the speakers. The audio electrical signal output from the aircraft radio can drive these loop transmitters in a headset and be received by the battery-free communications earplugs of US 2009/0041285 and US 2010/0296667 with enough system sensitivity to drive the speakers of the earplugs to achieve high enough SPL for clear speech communications and high speech intelligibility, while providing an earplug design that fits in a human ear.
Moreover, electromagnetic shielding of electrical components used in wireless earplugs is important to prevent pickup of spurious fields. However, the antenna must be small enough to fit comfortably in the human ear. Large communications earplugs tend to be uncomfortable because they put pressure on the ear. Moreover, a large earplug may interfere with a headset earcup when the earplug and headset are worn together to provide “double hearing protection”. A higher sensitivity MFA device can achieve the same sensitivity as a lower sensitivity MFA but in a smaller package size.
It is known in the art that an antenna coil can be constructed using a helical coil of wire with at least one turn. According to Faraday'"'"'s Law, also well-known in the art, a time-varying magnetic field passing through the inner region of a coil will produce a voltage on the ends of the coil proportional to the time derivative of the magnetic flux through the turns. The magnetic flux through a coil is proportional to the density of magnetic field lines passing through it. When an antenna coil is used to generate a voltage from a magnetic field, it is called a receiver coil. When an antenna coil is used to generate a magnetic field by applying a voltage or current to the coil, it is called a transmitter coil.
Electromagnetic waves impinging on electrical components can produce undesired voltages and currents that cause undesired effects. The source of the electromagnetic waves may be a remote communications transmitter, the transmitter antenna of an embodiment of the invention or they may be stray electromagnetic waves generated by other equipment. It is undesirable for the electrical components used within the antenna to generate voltages from external fields in an unpredictable way. Even connection wires benefit from electromagnetic shielding. In particular, electret microphones are sensitive to electromagnetic fields, and this is a known problem in the art.
An embodiment of the MFA described herein has an antenna coil for sensing a magnetic field and/or creating a magnetic field, a magnetic core within the coil, a magnetic core extension used to redirect magnetic field lines through the magnetic core and antenna coil, any electrical components coupled to the antenna coil, and any magnetic material used as a magnetic shunt to at least partially shield an electrical component coupled to the antenna coil. The MFA may be housed within a suitable structure for particular applications. For example, an embodiment of the invention can be enclosed at least partially within an earshell to create a wireless communications earplug, among other applications.
In embodiments of the invention, the coil core and core extension together can form an antenna body where the coil core and core extension comprise multiple parts or a single mechanical part.
In one embodiment of the invention, a microphone is used in an MFA earplug transmitter to sense SPLs in the user'"'"'s ear and transmit SPL levels to a remote receiver for noise dosimetry purposes. Any shielding that shunts the electromagnetic field away from the microphone in this embodiment is highly desirable.
In accordance with a preferred embodiment of the invention, at least a portion of the antenna body of the MFA is used as a continuation of the magnetic core for an antenna coil, thus directing a greater number of magnetic field lines through the antenna coil. In a preferred embodiment, the antenna body of the MFA also provides a magnetic shunt around at least one electrical component electrically coupled to the antenna coil to provide at least partial magnetic shielding of the electrical component.
It should be noted here that for explanatory purposes the figures herein include indications of unperturbed field lines, redirected magnetic field lines and optimal orientations of the MFA relative to the field. The field lines and orientations are provided for illustrative purposes and should not be taken to be exact representations of optimal orientations and magnetic field line paths.
This embodiment is sized to fit in a human ear with an eartip 10 that at least partially acoustically seals the communications earplug 2 to the walls of ear canals (not shown) to provide acoustic noise attenuation. Eartips can be universal fitting—such as the triple-flanged elastomer eartip 10 shown in
The magnetic material of a core and core extension increases the voltage sensitivity of a receiver coil by redirecting magnetic field lines through the inner region of the coil. Magnetic material has a lower reluctance compared to air, and a given magnetic field line takes the closed path of lowest reluctance to complete its path from the transmitter out to the environment and back around the transmitter. (Note that electrical resistance in electrical circuits is analogous to magnetic reluctance in magnetic circuits.) Small gaps, approximately up to 0.03 inch, of non-magnetic material between a core and core extension may be tolerated in some applications, but non-magnetic gaps are undesirable because they reduce sensitivity of the antenna.
As an example, when a receiver coil of outer diameter 0.30 inch is wrapped around a magnetic core of length 0.32 inch, which is also used as a bobbin for wrapping the coil, an open circuit voltage is measured at the coil ends. If the coil geometry remains the same, but the magnetic core is doubled in length, the voltage may be increased by 50 percent. In this way, the voltage sensitivity of the receiver has increased significantly.
If one end of the same receiver coil with magnetic core is placed on top of a rectangular enclosure of 0.16 inch height, 0.28 inch width and 0.39 inch length made from 0.010 inch thick magnetic metal, the coil voltage may be increased by 40%. This is also a significant sensitivity increase. Magnetic enclosures of this approximate size can be used to house and shield electrical components such as speakers, microphones, accelerometers, passive electronic circuits, wires, circuit boards, battery-powered systems, batteries, digital circuits, memory chips, digital signal processors, analog-to-digital converters, digital-to-analog converters and many other electrical devices.
The speaker 16 has a speaker outlet 14 that allows sound generated by the moving speaker diaphragm 20 to travel through an eartip adapter 36 via a sound channel 40. In this embodiment of the invention, the interior parts are symmetric about the earplug axis 4 except for the coil ends 26 and 28, the helical geometry of the antenna coil 21, the speaker terminals 18 and 19 and perforations 34.
An eartip adapter is a mechanical part with two ends that provides at least a mechanical means for attaching an eartip and a sound channel within its interior for acoustically coupling sound from one end of the eartip adapter to the other end. The barb 38 shown in
The eartip has a sound channel 27 through its center to allow sound to travel from the speaker outlet 14 through the eartip adapter sound channel 40 and through the eartip sound channel 27 out the eartip outlet 12 into the ear canal to be heard by the user. Eartip adapters can be used with other acoustical components that require sound coupling such as microphones.
A magnetic field B is used to provide communications information to the user. The magnetic field B direction, at a given point in time, is indicated by field vector v. The magnetic field B may be of oscillatory, pulsed or other time-varying natures. Non-time-varying static fields are ineffective because the antenna coil 21 only responds to the time-derivative of the field.
In the field shown in
In this embodiment, the transmitter coil 49 is positioned in close proximity to the communications earplug 2. The transmitter coil 49 can be placed within a headset earcup or helmet or embedded in a wall or headrest or other apparatus. The transmitter coil 49 in this embodiment is enclosed in a plastic carrier 51.
The loop transmitter 52 that fits around the pinna has the significant benefit compared to other loop geometries in that it will not mechanically interfere with the communications earplug 2 or pinna 44, because the loop transmitter 52 has a large open center, in this embodiment. The loop transmitter 52 can be placed within a headset earcup or helmet or embedded in a wall or headrest or other apparatus. Because the loop transmitter 52 can be worn around the pinna 44 and has an open center, it can be placed close to the communications earplug 2 so that the communications earplug 2 overlaps a loop transmitter 52 geometry plane 7, indicated by perpendicular dashed lines. This improves the sensitivity of the system, compared to loop transmitters worn adjacent to the pinna 44 or on the ear, because the magnetic field B strength diminishes as the separation between the geometry plane 7 of the loop transmitter 52 and communications earplug 2 increases.
The MFA 22 comprises an antenna body 29, the antenna coil 21, and any coupled electrical components used in the embodiment, such as the speaker 16 in this embodiment. The antenna body 29 comprises the magnetic material that significantly contributes to redirecting an ambient magnetic field B through the antenna coil 21, such as the magnetic core 30 and magnetic speaker case 32, in this embodiment.
The antenna body 29 directs magnetic field lines through the antenna coil 21 by creating a low-reluctance path through the antenna coil 21. The reluctance of magnetic material is lower than that of air, and this provides an “easier” path for the magnetic field to travel through space. To the extent that more magnetic field lines are directed through the antenna coil 21 the voltage generated at the coil ends 26 and 28 is higher and the sound generated by speaker 16 is louder. The coil-sensed field lines 54 in
Without magnetic material redirecting the magnetic field and at large distances from the magnetic field transmitter in the far field, the field lines would be uniform and straight, as shown in
Only two coil-sensed field lines 58 are shown in this example, illustrating that fewer field lines would be sensed by the receiver coil 21 if magnetic material were not employed in the antenna body 29, thus showing the benefit of incorporating an antenna body 29 constructed of magnetic material.
The effective antenna length AL1 is the total length along the field vector v of the antenna body 29 incorporating magnetic material. The magnetic field is a far field; that is, the field lines are straight in the vicinity of the antenna body 29 when the antenna body 29 is not present, as shown in
This embodiment of the invention incorporates a magnetic shunt 56, as seen in
The length of such a path along the field axis v that overlaps with the coupled electrical component effective length is the magnetic shunt length. In this embodiment, the magnetic shunt length is indicated by SH1. The magnetic shunt 56 reduces the magnetic field that travels through the coupled electrical component, providing a shielding effect and increases the effective length of the MFA body, which improves sensitivity.
When the MFA 22 is oriented in a magnetic field for maximum sensitivity, as shown in
The projected first turn 24 defines a turn projected area 31 that is, in this embodiment, the same as the cross-sectional area of the magnetic core 30. The outline of the projected speaker 16 defines a projected component area 33, which comprises the area within the outline of the projected component. The intersection of the turn projected area 31 and the projected component area 33 result in another area, which in this embodiment is equal to the first turn projected area 31.
Thus, when the MFA 22 is placed in a far field with optimal orientation with regard to sensitivity at least one turn of the coil 21 is “coincident” with a coupled electrical component of the MFA 22. This geometry results in an antenna coil 21 and at least one coupled electrical component that are generally along the magnetic field path and enables an antenna body 29 geometry that can provide a low reluctance path through an antenna coil in a small package that can yield a relatively high sensitivity and shielding of electrical components.
The embodiment in
In this embodiment, the circuit board 74 and electronics circuit 72 are well shielded within the antenna body 70 and the speaker 16 is partially shielded by shunting effects of the antenna body 70. Even though this embodiment does not incorporate a solid magnetic core like the embodiment shown in
The embodiment shown in
This embodiment does not employ a generally cylindrical geometry for a speaker 92 or speaker case 84, as seen in
It can be seen in
An embodiment of the invention shown in
A view into the distal end of this MFA 93 is seen in
The effective MFA length is indicated by AL2. It can be seen that the speaker case 94 adds to this length when the MFA 93 is rotated in the field. The speaker case 94 provides a magnetic shunt 102 that redirects at least one field line around the speaker 96, the speaker 96 being a coupled electrical component. The effective magnetic shunt length is indicated by SH3 while the effective speaker length (effective part length) is indicated by PL2. The effective magnetic shunt length SH3 is shorter than the effective speaker length PL2, but still provides the benefit of increased effective MFA length AL2 and some shielding. An effective magnetic shunt length to effective part length ratio of a coupled electrical component, for example in this embodiment SH3/PL2, of at least 1/10 is desired to achieve redirection of the magnetic field around a coupled electrical component.
A large test transmitter coil with multiple turns that has a radius ten times the maximum dimension of the MFA under test can be used to generate a field at its center that approximates a far field for easily determining the optimal antenna orientation relative to the field vector of a far field. The optimal magnetic antenna orientation may be determined by placing the MFA in the center of the test transmitter coil and rotating the MFA until the maximum antenna coil voltage is achieved. The orientation of the MFA relative to the center axis of the test transmitter coil is the orientation with maximum sensitivity.
The MFA 78 from the embodiment shown in
The magnetic cap 106 has a vent channel 110 for venting static pressure within the communications earplug 118 and distal end of speaker 16 and is magnetically coupled to the core/extension 109. The magnetic cap 106 also has a filter 108 that may be made from screen, foam, a gas-permeable membrane or other materials that allow for air pressure equalization but prevent dirt and small objects from passing into the interior of the communications earplug 118.
Within the magnetic eartip adapter 114 is an acoustic damper 112 used to control acoustic standing waves and electro-mechanical resonances of the speaker 16. Also within the magnetic eartip adapter 114 is a wax guard 116 used to prevent human ear wax from damaging the speaker 16 and clogging the eartip adapter sound channel 40.
A mechanical barrier 104 protects the MFA 78 from damage and can be made from molded plastic, overmolded plastic, overmolded elastomer and many other materials.
In this embodiment, the antenna body 107 forms at least part of the exterior surface of the communications earplug, which can yield a communications earplug 118 of smaller size. When incorporating a core/extension 109 that employs a hollow interior, it is possible to position the speaker 16 at the distal end and the antenna coil 21 at the proximal end by rotating the core/extension 109 180 degrees, and modifying the magnetic eartip adapter 114 and magnetic cap 106. This places the speaker 16 in the core/extension 109 so that the sound travels through the interior of the core/extension 109.
It can be seen in this figure that constructing the eartip adapter 114 from magnetic material substantially increases the effective length of the antenna body 107. A magnetic eartip adapter can increase voltage sensitivity of a magnetic antenna by over 10%. This novel eartip adapter serves mechanical functions, acoustical functions and antenna functions simultaneously.
This embodiment of the invention yields a very effective magnetic shield and long effective length AL3 while remaining a compact size that can easily fit within an ear. This embodiment will redirect more magnetic field lines into the antenna coil 21 compared to the previously described embodiments, as indicated by field lines 115. To further improve sensitivity, a comfortable eartip 10 could be manufactured using impregnated magnetic materials.
When a user talks, speech can be detected as sound pressure changes in the users ear canals, especially when the canal is sealed with an earplug.
This custom-molded eartip 120 has a custom-molded canal section 124 and a custom-molded concha section 122. The custom-molded concha section 122 can be eliminated in some applications where only the custom-molded canal section 124 is required. A sound channel 126 through the custom-molded eartip 120 delivers sound from the ear canal to the microphone 119 of the MFA 118.
The speaker case 130 in this embodiment is also the antenna body 130 and has effective antenna length of AL4. In this embodiment there are two magnetic shunt sections shunting the armature leads 13 and armature 132. The armature 132 shunt has length SH4. As seen in
The embodiment of
This signal is rectified by rectifier diode 164 which is then filtered by filter capacitor 166 to remove higher frequencies that are outside of the audio frequency communication signal bandwidth in order to recover the original audio frequency communications signal, to the extent possible, as is common in the art. The filtered signal is input to the speaker 16. The embodiment of this circuit could be used in a wireless battery-free communications earplug employing the AM technique. The circuit 173 is considered passive here because it does not require an additional DC current or DC voltage source to provide power for its intended function.
Using these components, and other circuits known in the art, the microphone 119 can cause variations in the electrical impedance “seen” by the coil 169, and this signal is re-radiated back through the transceiver coil 169 for pickup by a remote wireless receiver. The signal generated by the remote transmitter may be a pulsed signal, as in this embodiment, where the re-radiated signal generated by the MFA is picked up by a remote receiver during the periods when the remote transmitter is not transmitting signal, as is done in the art. Other circuits in additional embodiments could be employed to make use of a microphone 119 incorporated into the invention.
A “Receiver” is a receiver coil along with any magnetic material used as a core within the internal region of the receiver coil. Magnetic material outside the region of an antenna coil and in close proximity to the core, preferably in mechanical contact with the core, may be called a “core extension”.
An “electrical component” is a component that relies on the flow of electrical current and/or voltage in order to serve its function.
A “coupled electrical component” is an electrical component which, if removed, would affect the electrical current through the antenna coil and/or voltage at the ends of the antenna coil. The ends of an antenna coil may be electrically coupled to electrical components in applications for various purposes including generating sound, sensing sound, sensing acceleration, and sending/receiving digital information, among many other purposes. Thus, coupled electrical components are considered herein to be part of an MFA. Coupled electrical components may be “directly coupled” to the antenna coil, where at least one end of the coil has a very low impedance path to the electrical component, for example using a wire, or “indirectly coupled” to the antenna coil, where the ends of the coil are not connected through a low impedance path to the electrical component.
“Electronic components” are a subset of electrical components and include “passive” electronic components (for example, resistors, capacitors, inductors and some diodes among other components) and “active” electronic components (for example, discrete solid-state components such as most transistors and some diodes, or integrated circuits such as operational amplifiers, memory chips, digital signal processors and microcontrollers, among others). As a more general definition as used herein, “passive electronic components” are those that require no battery or other direct current (DC) voltage source or DC current source to provide power for the component to provide its intended function, while “active electronic components” require a battery or other direct current (DC) voltage or current source to provide power for the component to provide its intended function.
When an antenna coil is used to generate a voltage from an ambient magnetic field it is called a “receiver coil”. When a coil is used to generate a magnetic field for reception by a remote device it is called a “transmitter coil”. A “transceiver coil” is a coil that is used for both transmitting and receiving magnetic fields.
“AF” or “Audio Frequency” refers to the range of frequencies which are audible to the human ear, generally accepted as between roughly 20 Hz and 20,000 Hz (20 kHz), although it will be understood that this varies among individuals and changes as an individual ages. The speech band is a subset of this range and is often defined as being between 300 Hz and 3,400 Hz (3.4 kHz) in telephony (communications) purposes, which is generally considered adequate for intelligibility of signals, although higher frequency sound between 3 kHz and 20 kHz can be included to improve intelligibility if desired. As used herein, “AF signals” or “audio frequency signals” refers to signals in the frequency range of human hearing (either the full 20 Hz to 20 kHz range, or a subset of this range), which can be used to directly drive a transducer or speaker to produce sound without need for demodulation or detection of a carrier.
“RF” or “Radio Frequency” refers to AC frequencies above generally 50 kHz or higher. As used herein, “radio frequency signals” refers to signals which carry audible information by having the audio frequency information modulating an RF carrier signal, and from which the audio frequency information must be demodulated or detected by a demodulator to drive a transducer or speaker. This definition used herein may include magnetic signals with frequencies which are ultrasonic frequencies (for example 20 kHz-40 kHz), but which are modulated by the desired AF information and require demodulation in the receiver.
The “sensitivity” of an MFA refers to the ability of the antenna to convert a magnetic field into a useful purpose, such as generating sound.
As used herein, “magnetic material” means a material having a substantially lower reluctance compared to air, which provides an “easier” path for the magnetic field to travel through space. Magnetic material may be magnetized, as in the case of a permanent magnet, where the magnetic material generates a magnetic field on its own and is attracted to non-magnetized magnetic material. Magnetic material may also not be magnetized, where the magnetic material does not generate a magnetic field on its own and is not attracted to non-magnetized material. In one embodiment of the invention, an antenna body incorporating magnetized material can be beneficial if it is desired to attach the antenna to non-magnetized magnetic material or for other reasons. However, in many circumstances the use of magnetized material in the antenna body is detrimental because it can interfere with devices, such as compasses, and in another embodiment the antenna body does not incorporate magnetized magnetic material.
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.