Patent Description:
It is the object of the present invention to provide a method of adapting charging for an accessory device and a corresponding system.

In some embodiments, an accessory device is positioned proximate a wireless charging device, such as a near-field communication transmission coil. The wireless charging device provides a transmission energy that is received by the accessory device and induces an electrical current in the accessory device. Modulation of the transmission energy amplitude varies the induced current to transmit data to the accessory device. In some embodiments, a wireless charging device sets a first transmission amplitude to establish communication with the accessory device and, if the wireless charging device does not receive a recognized response from the accessory device, changes the transmission energy to a second transmission amplitude.

In some embodiments, a method of adapting the charging of an accessory device includes transmitting a first transmission signal at a first transmission amplitude, measuring a receiving load of the first transmission signal, and if the charging device does not receive a response signal to the first transmission signal, transmitting a second transmission signal at a second transmission amplitude that is different from the first transmission amplitude.

In some embodiments, a system for communicating with an accessory device wirelessly includes a transmission coil, a processor in data communication with the transmission coil, and a hardware storage device in data communication with the processor. The hardware storage device has instructions stored thereon that, when executed by a processor, cause the processor to transmit a first transmission signal at a first transmission amplitude with the transmission coil, measure a receiving load of the first transmission signal, and if the transmission coil does not receive a response signal to the first transmission signal, transmit a second transmission signal at a second transmission amplitude that is different from the first transmission amplitude.

Features and advantages of the disclosure may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. Features of the present disclosure will become more fully apparent from the following description and appended claims or may be learned by the practice of the disclosure as set forth hereinafter.

In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, at least some of the drawings may be drawn to scale. Understanding that the drawings depict some example embodiments, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:.

The present disclosure relates generally to devices, systems, and methods for docking an accessory device on a wireless charger. In some embodiments, the wireless charger is part of a dock integrated into another electronic device, such as a peripheral dock on a laptop computer. In some embodiments, the wireless charger is a dedicated dock for the accessory device, such as a charging cradle for a remote control.

In some embodiments, a user docks an accessory device on another electronic device to charge the accessory device. In some embodiments, the dock includes a transmission coil that produces a magnetic field. The magnetic field of the dock can magnetically couple the transmission coil to a receiving coil of the accessory device to induce an electric current in the receiving coil of the accessory device.

In some embodiments, a computer mouse can be docked on a wireless charging pad to charge the mouse between use sessions. In some embodiments, the accessory device is a wearable device, such as a smartwatch. In some embodiments, the accessory device is a stylus. In some embodiments, the accessory device is a keyboard. In some embodiments, the accessory device is a touch-sensitive device, such as a track pad, touchscreen, other capacitive touch-sensitive surface, other resistive touch-sensitive surface, or other touch-sensitive input mechanism. In some embodiments, the accessory device is an audio device, such as a wireless speaker, headphones, earphones, or other audio device capable of generating audio signals to communicate with a user.

In some embodiments, the electronic device is a computing device, including but not limited to a laptop computer, hybrid computer, foldable computer, tablet computer, smartphone, wearable computing device, or other computing device. In some embodiments, the electronic device includes a dock that contains a transmission coil. The transmission coil can send a transmission energy from the dock to the accessory device. When a transmission current is applied to the transmission coil in the dock, the transmission coil generates a magnetic field that extends beyond an outer surface of the dock. A receiving coil positioned within the magnetic field proximate the dock experiences the magnetic field. A varying magnetic field induces a current in the receiving coil. In some embodiments, the transmission coil produces a radio frequency (RF) signal in the near-field communication (NFC) frequency range.

In some embodiments, the transmission coil transmits energy from the transmission coil to the receiving coil to wirelessly charge and/or communicate with the accessory device. In some embodiments, the power supply is a battery. In some embodiments, the power supply is a capacitor. In some embodiments, the transmission coil modulates the transmission energy from the transmission coil to the receiving coil to communicate data from the dock and/or electronic device to the accessory device.

<FIG> is a perspective view of an embodiment of an electronic device <NUM> with an accessory device <NUM> docked thereto. The electronic device <NUM> illustrated in <FIG> is a laptop computer having a first portion <NUM> and a second portion <NUM> that are movable relative to one another, and the accessory device <NUM> is a stylus that pairs with the electronic device to provide inputs and inking functionally.

In some embodiments, a processor <NUM> of the electronic device <NUM> is located in the second portion <NUM> and is in data communication with a transmission coil <NUM> located in the first portion <NUM>. When the accessory device <NUM> is positioned in proximity to the transmission coil <NUM>, a receiving coil <NUM> receives a transmission energy from the transmission coil <NUM>, and the accessory device <NUM> enters a docked mode. In the illustrated embodiment, the bezel of the first portion <NUM> that contains the transmission coil <NUM> acts as the dock for the accessory device <NUM>. In some embodiments, the dock includes a retention mechanism, such as a mechanical retention mechanism, a magnetic retention mechanism, or an adhesive retention mechanism, to hold the accessory device <NUM> in proximity to the dock. In some embodiments, the dock is oriented such that gravity holds the accessory device <NUM> in proximity to the dock.

<FIG> is a side view of another embodiment of an accessory device <NUM> resting on a dock <NUM>. In some embodiments, the accessory device <NUM> has a housing <NUM>, with the receiving coil <NUM> positioned at or near a surface of the housing <NUM>. The receiving coil <NUM> is positioned proximate a transmission coil <NUM> of the dock <NUM>, such that a transmission energy <NUM> is transmitted to the receiving coil <NUM>.

In some embodiments, the transmission energy <NUM> is transmitted through one or more parts of the accessory device <NUM> and/or dock <NUM> en route to the receiving coil <NUM>. In some embodiments, the housing <NUM> of the accessory device <NUM> and/or a cover <NUM> of the dock <NUM> are at least partly transparent to the transmission energy <NUM>. In the illustrated embodiment with a transmission coil <NUM> that generates a magnetic field, the cover <NUM> is a non-magnetic material to allow the transmission energy <NUM> to pass through the cover <NUM> to the receiving coil <NUM>.

Referring now to <FIG>, in some embodiments, a method (<NUM>) of communicating via a wireless charging device includes transmitting (<NUM>) a first transmission signal at a first transmission amplitude with a transmission coil and measuring (<NUM>) a receiving load of the transmission signal. In some embodiments, the transmission signal is a power signal to establish communications for powering or charging an accessory device. When a metallic or otherwise ferromagnetic object is proximate the transmission coil, the first transmission signal induces a current in the object and the transmission coil experiences a receiving load. Measuring the receiving load of the transmission signal allows the wireless charging device to detect the presence of the object in proximity to the transmission coil.

In some embodiments, induction of a current through a magnetic coupling causes bouncing. Bouncing is the generation of multiple signals as an electrical contact or electrical coupling opens or closes. Debouncing detects the multiple signals and ensures that only a single signal will be acted upon for a single opening or closing of a contact. In some embodiments, the method includes debouncing a response signal from the accessory device to ensure a receiving load is measured accurately.

In some embodiments, the first transmission signal includes a modulated signal to communicate with the receiving coil of the accessory device. The transmission coil provides the modulated signal by changing the amplitude of the first transmission signal during the first transmission signal. An accessory device can receive and interpret the amplitude modulations of a first transmission signal and subsequently respond to the first transmission signal. A response from the accessory device confirms to the wireless charging device that the object in the magnetic field of the transmission coil is a chargeable accessory device and the wireless charging device can begin charging the accessory device.

In some embodiments, the first transmission signal fails to communicate with the accessory device. In some embodiments, the communication fails because of foreign object interference. In some embodiments, the communication fails because of electromagnetic interference (EMI) or radio frequency interference (RFI). In some embodiments, the communication fails because the first transmission signal is underpower. In some embodiments, the communication fails because the first transmission signal is overpower.

In some embodiments, the method includes, if the transmission coil does not receive a response signal to the first transmission signal, transmitting (<NUM>) a second transmission signal at a second transmission amplitude that is different from the first transmission amplitude.

In embodiments where the communication fails because of overpower, the first transmission signal is saturating the receiving coil. A ferromagnetic object experiences a current in the presence of a varying magnetic field. However, the current cannot increase indefinitely as the amplitude of the magnetic field increases. The ferromagnetic object will experience a current up to a saturation point. Because the magnetic field can only induce a current up to the saturation point, variation of the amplitude of the magnetic field beyond the saturation point produces no changes in the electrical current. In some embodiments, a magnetic saturation of the receiving coil prevents communication by modulation of the magnetic field.

In embodiments where the receiving coil magnetically saturates and fails to send a response signal to the transmission coil of the wireless charging device, the wireless charging device sends a second transmission signal that has a second transmission amplitude that is less than the first transmission amplitude. In some embodiments, the second transmission amplitude is a percentage of the first transmission amplitude in a range having an upper value, a lower value, or upper and lower values including any of <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or any values therebetween. In some embodiments, the second transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the second transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the second transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the second transmission amplitude is between <NUM>% and <NUM>% of the first transmission amplitude. In some embodiments, the second transmission amplitude is between <NUM>% and <NUM>% of the first transmission amplitude.

<FIG> illustrates another flowchart illustrating a method of communicating using a wireless charging device. In some embodiments, the method (<NUM>) of communicating using a wireless charging device includes transmitting (<NUM>) a first transmission signal at a first transmission amplitude with a transmission coil and measuring (<NUM>) a receiving load of the transmission signal. If the transmission coil does not receive a response signal to the first transmission signal, the method further includes transmitting (<NUM>) a second transmission signal at a second transmission amplitude that is different from the first transmission amplitude. If the transmission coil does not receive a response signal to the second transmission signal, the method further includes transmitting (<NUM>) a third transmission signal at a third transmission amplitude that is different from the first transmission amplitude and the second transmission amplitude.

In embodiments where the receiving coil magnetically saturates and fails to send a response signal to the transmission coil of the wireless charging device, the wireless charging device sends a third transmission signal that has a third transmission amplitude that is less than the second transmission amplitude. In some embodiments, the third transmission amplitude is a percentage of the second transmission amplitude in a range having an upper value, a lower value, or upper and lower values including any of <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or any values therebetween. In some embodiments, the third transmission amplitude is less than <NUM>% of the second transmission amplitude. In some embodiments, the third transmission amplitude is less than <NUM>% of the second transmission amplitude. In some embodiments, the third transmission amplitude is less than <NUM>% of the second transmission amplitude. In some embodiments, the third transmission amplitude is between <NUM>% and <NUM>% of the second transmission amplitude. In some embodiments, the third transmission amplitude is between <NUM>% and <NUM>% of the second transmission amplitude.

In some embodiments, the third transmission amplitude is a percentage of the first transmission amplitude in a range having an upper value, a lower value, or upper and lower values including any of <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or any values therebetween. In some embodiments, the third transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the third transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the third transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the third transmission amplitude is between <NUM>% and <NUM>% of the first transmission amplitude. In some embodiments, the third transmission amplitude is between <NUM>% and <NUM>% of the first transmission amplitude.

In some embodiments, the modulation of the transmission signal is relative to a peak transmission amplitude. <FIG> illustrates an example transmission signal <NUM>. A first transmission signal <NUM>-<NUM> begins when the RF (e.g., magnetic) field is turned on at <NUM> and has a peak amplitude <NUM>. In some embodiments, the amplitude has an amplitude modulation <NUM> down to <NUM>%, <NUM>%, <NUM>%, <NUM>% of the peak amplitude <NUM>, or any values therebetween. The modulation depth is the amount of current variation that is induced in the receiving coil of the accessory device. If the amplitude modulation occurs above the saturation level <NUM> of the receiving coil, there is no modulation depth and the amplitude modulation <NUM> produces little or no change in the induced current.

In some embodiments, the modulation depth to communication data to through the wireless charging device is less than <NUM>% (e.g., the low points of the transmission signal are <NUM>% of the peak amplitude). In some embodiments, the modulation depth to communication data to through the wireless charging device is less than <NUM>%. In some embodiments, the modulation depth to communication data to through the wireless charging device is less than <NUM>%.

In some embodiments, the peak amplitude <NUM> and/or modulation <NUM> is above a saturation level <NUM> of the receiving coil. In some embodiments, the wireless charging device reduces the transmission amplitude to below the saturation level <NUM> of the receiving coil, such that the amplitude modulation of a second transmission signal <NUM>-<NUM> generates a modulation depth <NUM> less than a modulation threshold set in the system. In some embodiments, the modulation depth is detected by measuring the receiving load. Because the receiving load is related to the receiving coil response to the magnetic field, a stronger magnetic field produces an associated increase in the receiving load. In some embodiments, an increase in the transmission amplitude without an increase in receiving load indicates saturation of the receiving coil.

<FIG> is a flowchart illustrating another embodiment of a method according to the present disclosure. In some embodiments, another method (<NUM>) of communicating using a wireless charging device includes transmitting (<NUM>) a first transmission signal at a first transmission amplitude with a transmission coil and measuring (<NUM>) a receiving load of the transmission signal. The method further includes determining (<NUM>) a modulation depth based on the receiving load. If the modulation depth is greater than a modulation threshold, the method includes transmitting (<NUM>) a second transmission signal at a second transmission amplitude that is different from the first transmission amplitude. For example, if the modulation threshold is set at <NUM>%, and the modulation depth is determined to be <NUM>%, the method includes transmitting a second transmission signal at a second amplitude.

In some embodiments, the second transmission amplitude is a percentage of the first transmission amplitude in a range having an upper value, a lower value, or upper and lower values including any of <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or any values therebetween. In some embodiments, the second transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the second transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the second transmission amplitude is less than <NUM>% of the first transmission amplitude. In some embodiments, the second transmission amplitude is between <NUM>% and <NUM>% of the first transmission amplitude. In some embodiments, the second transmission amplitude is between <NUM>% and <NUM>% of the first transmission amplitude.

In some embodiments, the second transmission amplitude is less than the first transmission amplitude by the same amount at the modulation threshold. For example, if the modulation threshold is <NUM>%, the second transmission amplitude is <NUM>% of the first transmission amplitude.

In some embodiments, such as illustrated in <FIG>, the wireless charging device <NUM> includes a processor <NUM> (such as the processor <NUM> in the electronic device <NUM> of <FIG>) in data communication with a power supply <NUM> and a transmission coil <NUM> (such as the transmission coil <NUM> of <FIG> or other charging component that provides a charging energy to the accessory device). In some embodiments, the electronic device <NUM> is, or includes, the wireless charging device <NUM>. The charging device <NUM> further includes a hardware storage device <NUM> in data communication with the processor <NUM>. In some embodiments, the hardware storage device includes instructions stored thereon that, when executed by the processor, cause the processor to perform any of the methods described herein. In some embodiments, the hardware storage device is a solid-state hardware storage device. In some embodiments, the hardware storage device is a platen-based storage device. In some embodiments, the hardware storage device is an optical disk drive.

The present disclosure relates generally to systems and methods for docking an accessory device on a wireless charger. In some embodiments, the wireless charger is part of a dock integrated into another electronic device, such as a peripheral dock on a laptop computer. In some embodiments, the wireless charger is a dedicated dock for the accessory device, such as a charging cradle for a remote control.

In some embodiments, the electronic device is a computing device, including but not limited to a laptop computer, hybrid computer, foldable computer, tablet computer, smartphone, wearable computing device, or other computing device. In some embodiments, the electronic device includes a dock that contains a transmission coil. The transmission coil can send a transmission energy from the dock to the accessory device. When a transmission current is applied to the transmission coil in the dock, the transmission coil generates a magnetic field that extends beyond an outer surface of the dock. A receiving coil positioned within the magnetic field proximate the dock experiences the magnetic field. A varying magnetic field induces a current in the receiving coil. In some embodiments, the transmission coil produces a RF signal in the near-field communication (NFC) frequency range.

In some embodiments, a method of communicating via a wireless charging device includes transmitting a first transmission signal at a first transmission amplitude with a transmission coil and measuring a receiving load of the transmission signal. When a metallic or otherwise ferromagnetic object is proximate the transmission coil, the first transmission signal induces a current in the object and the transmission coil experiences a receiving load. Measuring the receiving load of the transmission signal allows the wireless charging device to detect the presence of the object in proximity to the transmission coil.

In some embodiments, the method includes, if the transmission coil does not receive a response signal to the first transmission signal, transmitting a second transmission signal at a second transmission amplitude that is different from the first transmission amplitude.

In some embodiments, another method of communicating using a wireless charging device includes transmitting a first transmission signal at a first transmission amplitude with a transmission coil and measuring a receiving load of the transmission signal. If the transmission coil does not receive a response signal to the first transmission signal, the method further includes transmitting a second transmission signal at a second transmission amplitude that is different from the first transmission amplitude. If the transmission coil does not receive a response signal to the second transmission signal, the method further includes transmitting a third transmission signal at a third transmission amplitude that is different from the first transmission amplitude and the second transmission amplitude.

In some embodiments, the modulation of the transmission signal is relative to a peak transmission amplitude. In some embodiments, the amplitude is modulated by <NUM>%, <NUM>%, <NUM>%, <NUM>%, or any values therebetween. The modulation depth is the amount of variation that is induced in the receiving coil of the accessory device. In some embodiments, the modulation depth to communication data to through the wireless charging device is less than <NUM>% (e.g., the low points of the transmission signal are <NUM>% of the peak amplitude). In some embodiments, the modulation depth to communication data to through the wireless charging device is less than <NUM>%. In some embodiments, the modulation depth to communication data to through the wireless charging device is less than <NUM>%.

In some embodiments, the wireless charging device reduces the transmission amplitude to below a saturation level of the receiving coil, such that the amplitude modulation of the transmission signal generates a modulation depth less than a modulation threshold set in the system. In some embodiments, the modulation depth is detected by measuring the receiving load. Because the receiving load is related to the receiving coil response to the magnetic field, a stronger magnetic field produces an associated increase in the receiving load. In some embodiments, an increase in the transmission amplitude without an increase in receiving load indicates saturation of the receiving coil.

In some embodiments, another method of communicating using a wireless charging device includes transmitting a first transmission signal at a first transmission amplitude with a transmission coil and measuring a receiving load of the transmission signal. The method further includes determining a modulation depth based on the receiving load. If the modulation depth is greater than a modulation threshold, transmitting a second transmission signal at a second transmission amplitude that is different from the first transmission amplitude. For example, if the modulation threshold is set at <NUM>%, and the modulation depth is determined to be <NUM>%, the method includes transmitting a second transmission signal at a second amplitude.

In some embodiments, the wireless charging device includes a processor in data communication with a power supply and a transmission coil. The charging device further includes a hardware storage device in data communication with the processor. In some embodiments, the hardware storage device includes instructions stored thereon that, when executed by the processor, cause the processor to perform any of the methods described herein. In some embodiments, the hardware storage device is a solid-state hardware storage device. In some embodiments, the hardware storage device is a platen-based storage device. In some embodiments, the hardware storage device is an optical disk drive.

The present disclosure relates to systems and methods for adapting the charging of an accessory device via a wireless charging device according to at least the examples provided in the sections below.

In an embodiment, the charged accessory device may be accessory device <NUM>. The following steps are performed at the charging device, which may be the electronic device <NUM>.

A first transmission signal is transmitted at a first transmission amplitude. The first transmission signal may be transmitted by the NFC transmission coil <NUM>. The first transmission signal may be transmission signal <NUM>-<NUM>. The first transmission amplitude may be peak amplitude <NUM>.

A receiving load of the first power signal measuring is measured. The measurement may be performed via the power supply <NUM>.

It is determined based on the measured receiving load whether a response signal is received from the accessory device. If the charging device does not receive the response signal, a second transmission signal is transmitted at a second transmission amplitude that is different from the first transmission amplitude and that is lower than the first transmission amplitude so as to reduce potential magnetic saturation. The second transmission signal, which may be transmission signal <NUM>-<NUM>, may be transmitted via NFC transmission coil <NUM>.

In another embodiment, the charged accessory device may be accessory device <NUM>. The following steps are performed at the charging device, which may be the electronic device <NUM>.

A first power signal is transmitted at a first transmission amplitude. The first power signal may be transmitted by the NFC transmission coil <NUM>. The first power signal may be transmission signal <NUM>-<NUM>. The first transmission amplitude may be peak amplitude <NUM>.

A modulation depth is determined based on the receiving load. The modulation depth may be modulation <NUM>. If the modulation depth is greater than a modulation threshold, a second power signal is transmitted at a second transmission amplitude that is different from the first transmission amplitude. The second power signal may be transmission signal <NUM>-<NUM>.

In another embodiment, a system is provided for communicating wirelessly with an accessory device. The accessory device may be accessory device <NUM>. The system comprises a transmission coil, which may be NFC Transmission coil <NUM>, a processor (which may be processor <NUM>) in data communication with the transmission coil, and a hardware storage device, which may be storage <NUM>, in data communication with the processor. The hardware storage device stores instructions that, when executed by a processor, cause the system to perform the following steps.

A first power signal is transmitted with a first transmission amplitude with the transmission coil. A receiving load of the first transmission signal is measured.

It is determined based on the measured receiving load whether a response signal is received from the accessory device. If the transmission coil does not receive the response signal, a second power signal is transmitted at a second transmission amplitude that is different from the first transmission amplitude.

The articles "a," "an," and "the" are intended to mean that there are one or more of the elements in the preceding descriptions. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are "about" or "approximately" the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within <NUM>%, within <NUM>%, within <NUM>%, or within <NUM>% of a stated value.

A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the scope of the present disclosure. Equivalent constructions, including functional "means-plus-function" clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words 'means for' appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims.

Claim 1:
A method of adapting charging for an accessory device (<NUM>, <NUM>), the method comprising:
at a wireless charging device (<NUM>, <NUM>):
transmitting (<NUM>) a first power signal (<NUM>-<NUM>) with a first transmission amplitude;
measuring (<NUM>) a receiving load of the first power signal; and characterised by determining based on the measured receiving load whether a response signal is received from the accessory device and whether a receiving coil of the accessory device magnetically saturates, wherein it is determined that the receiving coil of the accessory device magnetically saturates if an increase of the first transmission amplitude does not lead to an increase of the measured receiving load; and
if the wireless charging device does not receive the response signal and the receiving coil of the accessory device magnetically saturates, transmitting (<NUM>) a second power signal (<NUM>-<NUM>) at a second transmission amplitude that is lower than the first transmission amplitude so as to reduce potential magnetic saturation.