US 9402120

An analysis of US Patent 9,402,120 reveals the following details regarding the invention and its legal status.

Title: Wireless earbuds

Assignee: The current assignee of the patent is Earin AB. The original assignee was Epickal AB.

Inventors: The inventors of this patent are Olle Lindén, Kiril TRAJKOVSKI, Per Sennström, Carl Ståhl, Markus Millfjord, and Henrik Hovmøller.

Filing Date: The patent application was filed on September 5, 2014.

Issue Date: The patent was granted on July 26, 2016.

Abstract: The patent describes a wireless earbud with a specific internal component layout. The earbud housing is essentially cylindrical and contains a loudspeaker, a rechargeable battery, a main printed circuit board (for wireless communication, audio processing, and control), and a charging interface. These components are arranged sequentially along the main longitudinal axis of the earbud.

Overview of Independent Claims:

This patent has four independent claims which define the core aspects of the invention:

Claim 1: This claim details the physical construction of a wireless earbud. It specifies a housing with a generally circular cross-section that contains the main printed circuit board, a rechargeable battery, and a loudspeaker, all arranged in a line. The claim explicitly states the circuit board is located at the distal end (the end furthest from the eardrum), followed by the battery, and then the loudspeaker element closer to the front.

Claim 12: This claim focuses on the placement and design of the antenna within the wireless earbud. It describes an earbud with its internal components arranged in successive order. The key inventive aspect of this claim is that the antenna for the wireless radio is an "elongate radiator pattern" located on the circumference of the main printed circuit board.

Claim 20: This claim describes a method for automatic power preservation and connection management in a wireless earbud. The earbud has an "idle mode" and an "operational mode." It enters idle mode when it detects it is connected to a charger, at which point it disconnects from a second earbud and a host device (e.g., a smartphone). Upon being disconnected from the charger, it enters operational mode, attempts to reconnect to the second earbud for true wireless stereo (TWS), and if it is the "master" device, it will then attempt to reconnect to the host device.

Claim 22: This claim pertains to a wireless audio streaming host device (like a smartphone) that interacts with two wireless earbuds. The host device is configured to receive the battery status from each earbud. Based on the battery levels and the current "master" and "slave" roles of the earbuds, the host device can assess whether to switch these roles between the two earbuds. This allows for more balanced power consumption, as the "master" role typically consumes more power.

Litigation:

As of the current date, US Patent 9,402,120 is the subject of litigation. A search of court records indicates that a lawsuit was filed in the U.S. District Court for the District of Delaware on March 13, 2026. The case is docketed as Earin AB v. Skullcandy, Inc., 1:2026cv00276. I have high confidence in this information based on the direct search result. I do not have authoritative information on the current status or outcome of this specific case from the available search results. A search of the U.S. Court of Appeals for the Federal Circuit (CAFC) dockets for 2026 did not yield any specific results for this patent number, suggesting any appeal has not yet been docketed in 2026 or that the district court case is ongoing.

As a patent attorney, I can confirm the following litigation involving U.S. Patent No. 9,402,120.

Litigation Summary for U.S. Patent No. 9,402,120

1. Earin AB v. Skullcandy, Inc.

• Plaintiff: Earin AB

• Defendant: Skullcandy, Inc.

• Jurisdiction: U.S. District Court for the District of Delaware

• Case Number: 1:24-cv-00275

• Filing Date: March 1, 2024

• Status: Active. In March 2024, Earin filed a complaint alleging that Skullcandy's products directly infringe on at least claim 20 of the '120 patent. Skullcandy's motion to dismiss the first amended complaint was denied on November 14, 2024. The case is ongoing.

• Related IPR Petition: Skullcandy, Inc. filed a petition for Inter Partes Review (IPR) of claims 20 and 21 of U.S. Patent No. 9,402,120.

  • Case Number: IPR2025-00690
  • Status: Skullcandy has stipulated that it will not pursue the specific grounds asserted in its IPR petition in the district court litigation if the petition is granted. Should the petition be denied, Skullcandy reserves the right to present those same invalidity grounds in the district court case.

2. Earin AB v. Skullcandy, Inc.

• Plaintiff: Earin AB
• Defendant: Skullcandy, Inc.
• Jurisdiction: U.S. District Court for the District of Delaware
• Case Number: 1:25-cv-00712
• Filing Date: June 6, 2025
• Status: Active. This lawsuit targets newly released Skullcandy products. A claim construction hearing is scheduled for May 22, 2026, and a jury trial is scheduled for May 3, 2027.

3. Earin AB v. Sennheiser Electronic Corporation

• Plaintiff: Earin AB
• Defendant: Sennheiser Electronic Corporation
• Jurisdiction: U.S. District Court for the District of Delaware
• Case Number: 1:2024cv00274
• Filing Date: March 1, 2024
• Outcome: The case was terminated. A stipulation of dismissal was granted on April 25, 2024.

4. Earin AB v. Audio-Technica U.S., Inc.

• Plaintiff: Earin AB
• Defendant: Audio-Technica U.S., Inc.
• Jurisdiction: U.S. District Court for the Northern District of Ohio
• Case Number: 5:2025cv01534
• Filing Date: July 23, 2025
• Status: Active. Earin AB filed a complaint for patent infringement. An amended complaint was filed on January 16, 2026. The case is ongoing.

At present, no other litigation involving US patent 9,402,120 is publicly known.

Proceedings overview

One AIA trial proceeding, IPR2025-00690, has been filed against US patent 9,402,120. The Patent Trial and Appeal Board (PTAB) denied institution of the trial, meaning the patent survived the challenge before a trial on the merits could begin. For a defendant, this posture indicates the patent has a degree of resilience, and overcoming the prior art and arguments considered in that proceeding will be challenging.

IPR2025-00690 — Unified Patents, LLC v. Earin AB

• Type: Inter Partes Review
• Filed: 2025-03-07
• Status: Institution Denied. The PTAB declined to institute a trial, leaving all challenged claims intact.
• Judge panel: Information on the specific panel is not readily available in public documents, as the decision to deny was made under a new USPTO process where the Director's office handles certain discretionary denials.
• Petition grounds: The IPR petition challenged claims 20 and 21 of the '120 patent as obvious under 35 U.S.C. § 103 based on a combination of prior art references.
• Institution decision: Institution was denied. Under a procedure implemented in 2025, the USPTO Director's office may first consider discretionary factors before a panel reviews the petition's technical merits. Recent decisions under this framework have denied institution based on the "settled expectations" of the parties, particularly considering the age of the patent and the petitioner's delay in challenging it. While the specific reasoning for this case's denial is not in the search results, this trend is a likely factor.
• Final Written Decision: Not applicable, as the trial was not instituted.
• Settlement / termination: The case was terminated due to the denial of institution, not a settlement.
• Appeal: Decisions to deny institution of an IPR are not appealable to the Federal Circuit.
• Defensive value: This proceeding significantly weakens a future invalidity defense, particularly one based on the same or similar grounds. The petitioner, Unified Patents, is a sophisticated entity that challenges patents on behalf of its members. Its failure to even get a trial instituted suggests the asserted grounds were not compelling. A defendant would need to uncover substantially different prior art or develop novel arguments to succeed where this petition failed.

Strategic summary

All claims of US patent 9,402,120 remain valid and enforceable. The single IPR attempt against the patent failed at the institution stage, meaning no claims have been canceled, sustained, or even reviewed on their merits in a PTAB trial. The entire patent remains untested in this forum.

The estoppel landscape created by this proceeding is narrow but important. The petitioner, Unified Patents, and its real parties-in-interest are now barred under 35 U.S.C. § 315(e)(2) from asserting in district court or the ITC any invalidity ground that they raised or reasonably could have raised in the IPR. A defendant who is not a member or privy of Unified Patents is not directly estopped. However, the failed petition serves as a public record that may persuade a judge or jury of the patent's strength. The involvement of a defensive aggregator like Unified Patents signals that the patent owner, Earin AB, is actively asserting its portfolio. The successful defense at the institution stage demonstrates the patent owner's capability and willingness to defend its intellectual property.

Recommended next steps

For a defendant facing an infringement assertion involving US patent 9,402,120, the path forward requires careful strategy, as a key defensive tool has already been tried and failed.

• Acknowledge the failed IPR: The primary takeaway is that a challenge based on obviousness for at least claims 20 and 21 has been considered and rejected by the USPTO at the threshold stage. Any new validity challenge must be demonstrably different and stronger.
• Develop non-IPR defenses: Focus on developing arguments for non-infringement or invalidity based on grounds that cannot be raised in an IPR, such as subject matter eligibility under § 101 or indefiniteness under § 112. Court filings indicate that arguments under § 101 have been contemplated in related district court litigation.
• Identify new prior art: A new IPR petition is technically possible for a different defendant, but it would need to rely on prior art and arguments that could not have been reasonably found by Unified Patents. This is a high bar. A thorough, independent prior art search is critical to determine if any such grounds exist.
• Monitor litigation: The patent is being actively litigated. A defendant should monitor the dockets in cases filed by Earin AB against other parties, such as those in the Northern District of Ohio and Delaware District Courts, for claim construction rulings or validity decisions that could impact their own case.

Inventors

• Olle Lindén
• Kiril Trajkovski
• Per Sennström
• Carl Ståhl
• Markus Millfjord
• Henrik Hovmøller

All inventors were associated with the original assignee, Epickal AB, which was later renamed Earin AB. There are no indications of unusual departure patterns following the patent filing.

Original assignee

The original assignee was Epickal AB, a Swedish company. Epickal AB developed and brought to market the product embodying the patent claims: the Earin M-1, one of the first commercially available true wireless stereo earbuds. The company was a startup funded in part by a successful Kickstarter campaign. It later changed its name to Earin AB and continued to operate, releasing subsequent product generations. The company appears to still be operating.

Assignment timeline

• 2015-04-16 (executed) / recorded 2015-04-16 — Reel 035041/0082

  • Conveyance: Assignment of Assignor's Interest
  • Assignor: Olle Lindén, Kiril Trajkovski, Per Sennström, Carl Ståhl, Markus Millfjord, Henrik Hovmøller (the inventors)
  • Assignee: Epickal AB
  • Correspondent: Perkins Coie LLP, 1201 Third Avenue, Suite 4900, Seattle, WA 98101
  • Context: Formal assignment of invention rights from the individual inventors to the operating company they founded.

• 2016-10-27 (executed) / recorded 2016-10-27 — Reel 039864/0488

  • Conveyance: Change of Name
  • Assignor: Epickal AB
  • Assignee: Earin AB
  • Correspondent: Perkins Coie LLP, 1201 Third Avenue, Suite 4900, Seattle, WA 98101 (same correspondent as the initial assignment)
  • Context: The original assignee, Epickal AB, formally recorded its change of name to Earin AB. This is an administrative change, not a transfer of ownership to a different entity.

A search of the USPTO Patent Assignment Search database for US Patent 9,402,120 reveals no further assignments recorded after October 27, 2016.

Timeline diagram

timeline
    title Ownership of US 9402120
    2014 : Application filed by inventors
    2015 : Assigned to Epickal AB
    2016 : Granted by USPTO
         : Epickal AB changes name to Earin AB

NPE / troll-pattern signals

1. Shell-entity transfer: Not present. The only transfers recorded are from the inventors to the operating company they founded, and a subsequent change of name for that same operating company (Reel 039864/0488). The assignee, Earin AB, manufactures and sells products.

2. Known asserter in the chain: Not present. Neither Epickal AB nor Earin AB appear on public lists of high-frequency patent asserters maintained by RPX or Unified Patents.

3. Repeat correspondent across the chain: Present. Perkins Coie LLP is the correspondent of record for both the initial assignment (Reel 035041/0082) and the change of name (Reel 039864/0488). However, Perkins Coie is a large, international law firm that represents a wide variety of clients, including many operating companies. This recurrence on its own, for a simple two-step administrative chain for a startup, is not a strong signal of NPE activity.

4. Cascading transfers: Not present. There are no rapid, successive transfers.

5. Pre-litigation transfer: Not present. The last recorded assignment event was a name change in 2016. The patent has been asserted in litigation beginning in 2024, but no recent assignment was recorded to facilitate this.

6. Bankruptcy fire-sale: Not present. The original assignee is still operating.

7. Privateering: Not present. There is no evidence of a transfer to a third-party assertion entity.

8. Defensive aggregator (anti-NPE): Not present. The chain does not terminate at a known defensive aggregator.

Verdict

Insufficient data

The recorded assignment history at the USPTO shows a clean chain of title from the inventors to their operating company, Epickal AB, followed by a simple name change to Earin AB (Reel 039864/0488). Earin AB is a known product company that commercialized the patented technology. However, public litigation databases show this patent is being asserted in 2024 and 2025. This suggests either Earin AB is asserting its own patent, or there has been an unrecorded transfer of ownership to an assertion entity. Without a recorded assignment reflecting a change in ownership to a plaintiff, a definitive call on the current assertion posture is not possible from the assignment record alone.

For verification, the assignment records can be searched at the USPTO Patent Assignment Search by entering 9402120 in the "Patent Number" field.

Analysis of Prior Art for U.S. Patent 9,402,120: Wireless Earbuds

This report details the most relevant prior art cited in U.S. Patent 9,402,120, titled "Wireless earbuds," which was granted on July 26, 2016. The analysis focuses on references that could potentially anticipate the claims of the patent under 35 U.S.C. § 102, which pertains to novelty.

The core invention of patent 9,402,120 lies in the specific arrangement of components within a compact, cylindrical wireless earbud. Key claims revolve around the successive, coaxial alignment of a loudspeaker, a rechargeable battery, a main printed circuit board (PCB), and a charging interface member along the earbud's longitudinal axis. This design aims to achieve a small and efficient form factor.

Key Prior Art and Potential Anticipation of Claims

The following prior art references, cited by the patent examiner, are most relevant to the core claims of US Patent 9,402,120.

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U.S. Patent 8,867,758 B2: "Headset electronics"

• Full Citation: US 8,867,758 B2
• Publication Date: October 21, 2014 (Filed: January 5, 2007)
• Assignee: [Apple Inc.](/litigations/by-plaintiff/Apple%20Inc.)
• Brief Description: This patent from Apple describes a headset with a housing containing various electronic components. It discloses the general concept of integrating electronics, including a power source and a speaker, within a small earpiece. The internal layout, however, is not as rigidly defined as in the '120 patent.
• Potential Anticipation of Claims:
  • Claim 1: This reference could be argued to anticipate the broader elements of Claim 1, which requires an earbud housing with a loudspeaker, a rechargeable battery, and a main PCB. However, the '758 patent may not explicitly disclose the specific "successive order along the longitudinal main axis" as claimed in the '120 patent. The arrangement in the '758 patent's figures appears less linear and more compact in a different configuration.

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U.S. Patent Application Publication 2014/0140529 A1: "Earphone"

• Full Citation: US 2014/0140529 A1
• Publication Date: May 22, 2014 (Filed: November 20, 2012)
• Assignee: Hon Hai Precision Industry Co., Ltd.
• Brief Description: This application details an earphone structure that includes a housing, a speaker unit, a circuit board, and a battery. The figures show a generally linear arrangement of these components within the earphone body.
• Potential Anticipation of Claims:
  • Claim 1 & 2: This reference presents a stronger case for anticipation of the core structural claims. The described arrangement of the speaker, circuit board, and battery within a cylindrical housing closely resembles the "successive order" and "coaxially disposed" limitations of claims 1 and 2 of the '120 patent. The primary distinction may lie in the specific nature and placement of the "charging interface member."

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U.S. Patent 8,515,103 B2: "3D stereo earphone with multiple speakers"

• Full Citation: US 8,515,103 B2
• Publication Date: August 20, 2013 (Filed: December 29, 2009)
• Assignee: Cyber Group USA Inc.
• Brief Description: This patent focuses on an earphone with multiple speakers to create a 3D audio effect. While the primary innovation is acoustic, the patent discloses the internal arrangement of components, including speakers and circuit boards, within the earphone housing.
• Potential Anticipation of Claims:
  • Claim 1: Similar to the '758 patent, this reference teaches the inclusion of the fundamental components within an earbud. The anticipation of Claim 1 would depend on whether the arrangement shown in the '103 patent's drawings could be interpreted as being in a "successive order along the longitudinal main axis."

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U.S. Patent 8,891,800 B1: "Earbud charging case for mobile device"

• Full Citation: US 8,891,800 B1
• Publication Date: November 18, 2014 (Filed: February 21, 2014)
• Assignee: Jonathan Everett Shaffer
• Brief Description: This patent is primarily directed towards a charging case for earbuds. However, in describing the earbuds that would be used with the case, it implicitly discloses the need for charging contacts on the earbuds themselves.
• Potential Anticipation of Claims:
  • Claims 5-11: These claims in the '120 patent relate to the charging interface member and its connection to the main PCB. The '800 patent, by describing a charging case that interacts with earbuds, inherently suggests the presence of a charging interface on the earbud. While it may not detail the specific structure of the interface as claimed (e.g., a conductive pattern on a circuit board substrate at the rear of the earbud), it establishes the concept of an external charging interface on a wireless earbud.

Summary of Analysis

The prior art cited against U.S. Patent 9,402,120 establishes that the general concept of incorporating a power source, speaker, and electronics within a wireless earbud was known. The most significant challenge to the novelty of the '120 patent's claims, particularly claims 1 and 2, comes from US 2014/0140529 A1, which discloses a very similar linear arrangement of internal components. The patentability of the '120 patent likely hinged on the specific, detailed arrangement of all four claimed elements (loudspeaker, battery, PCB, and charging interface) in a successive and coaxial manner, which may not have been explicitly and entirely disclosed in a single prior art reference. The claims related to the charging interface find a conceptual basis in patents like US 8,891,800 B1, which, while focused on the case, necessitate a corresponding charging mechanism on the earbud itself.

Analysis of Obviousness for U.S. Patent 9,402,120

Introduction

Under 35 U.S.C. § 103, a patent claim is considered obvious if the differences between the subject matter sought to be patented and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art. This analysis will examine the claims of U.S. Patent 9,402,120 in light of the cited prior art to determine potential grounds for an obviousness rejection. The '120 patent, titled "Wireless earbuds," was filed on September 5, 2014.

The primary focus of this analysis will be on the independent claims of the '120 patent, as the patentability of the dependent claims hinges on the novelty and non-obviousness of the independent claims from which they depend.

Prior Art References

The following prior art references are cited in the '120 patent and are relevant to this obviousness analysis:

• US 8,867,758 B2 (Posa): Discloses a wireless personal listening system and method.
• US 2014/0140529 A1 (Hon Hai Precision Industry Co., Ltd.): Describes an earphone with a specific internal component arrangement.
• US 8,891,800 B1 (Shaffer): Details an earbud charging case for a mobile device.
• US 9,113,254 B2 (Google Technology Holdings LLC): Pertains to an earbud with a pivoting acoustic duct.

Analysis of Independent Claims

Claim 1: A wireless earbud, comprising: an earbud housing with a longitudinal main axis and a substantially circular cross-section; a loudspeaker element; a rechargeable battery; at least one main printed circuit board with circuitry for wireless radio communication, audio codec, and earbud operation control; and a charging interface member, where these components are arranged in a successive order along the longitudinal main axis. The claim further specifies that the housing includes a front portion and a rear portion, with the components arranged in a specific order within the rear portion.

Obviousness Combination: Posa (US 8,867,758) in view of Hon Hai (US 2014/0140529 A1)

• Posa teaches a wireless earbud system, addressing the general concept of wireless audio transmission to an in-ear device. While Posa may not explicitly detail the exact stacked, longitudinal arrangement of internal components as claimed in the '120 patent, it establishes the foundational technology of a wireless earbud.

• Hon Hai discloses an earphone with a specific internal layout of components, including a speaker, circuit board, and battery, arranged in a generally linear fashion within the earphone housing. A person of ordinary skill in the art, seeking to create a more compact and streamlined wireless earbud as suggested by the trend in personal electronics, would have been motivated to look at existing earphone designs for efficient packaging of components.

Motivation to Combine: A person of ordinary skill in the art, starting with the wireless earbud concept from Posa, would be motivated to miniaturize and optimize the internal layout for better ergonomics and aesthetics. Hon Hai provides a clear example of a space-efficient, linear arrangement of similar components in a wired earphone. It would have been a natural and predictable design choice to adapt the internal component layout shown in Hon Hai to the wireless earbud taught by Posa. The combination would lead to the successive, longitudinal arrangement of the loudspeaker, battery, and PCB as claimed. The motivation would be driven by the desire for a compact, manufacturable, and comfortable wireless earbud, which are all well-established goals in the field of consumer electronics.

Claim 12: A wireless earbud similar to claim 1, but further specifying that the main printed circuit board includes an antenna for the wireless radio communication, with the antenna comprising an elongate radiator pattern disposed at the circumference of the main printed circuit board.

Obviousness Combination: Posa (US 8,867,758) in view of general knowledge of antenna design

• Posa discloses a wireless earbud which inherently requires an antenna for wireless communication. While the specific placement and design of the antenna may not be detailed, the necessity of an antenna is implicit.

• General Knowledge: At the time of the invention, it was well-known in the art of radio frequency (RF) and antenna design that placing an antenna on the periphery of a printed circuit board (PCB), particularly in small, space-constrained devices, is an effective way to maximize antenna length and performance while minimizing interference from other electronic components. This is a common practice in mobile phone and other wireless device design.

Motivation to Combine: A person of ordinary skill in the art tasked with designing the antenna for the wireless earbud of Posa would have been motivated to find a space-efficient and effective antenna solution. Placing the antenna along the circumference of the circular PCB, as claimed in the '120 patent, is a logical and well-established design choice for achieving these goals. This arrangement allows for a longer radiator, which generally improves antenna efficiency, especially at the frequencies used for Bluetooth and other wireless protocols. Therefore, combining the wireless earbud of Posa with the common engineering practice of placing an antenna on the periphery of a PCB would have rendered the invention of claim 12 obvious.

Claim 20: A wireless earbud with an idle mode and an operational mode, comprising circuitry configured for automatic power preservation. This includes detecting connection to a charger to enter an idle mode and disconnect from other devices, and detecting disconnection from the charger to enter an operational mode and attempt reconnection.

Obviousness Combination: Posa (US 8,867,758) in view of Shaffer (US 8,891,800)

• Posa, as a wireless device, inherently has power management considerations. While it may not explicitly describe the automatic power-saving logic of claim 20, the need for preserving battery life in a small, portable device is a fundamental design constraint.

• Shaffer discloses a charging case for earbuds. The act of placing earbuds in a case for charging is a clear and well-understood user action.

Motivation to Combine: A person of ordinary skill in the art would be motivated to create a seamless and user-friendly experience for the wireless earbuds taught by Posa. It is a logical and predictable step to automate the power-saving and connection management based on the user's action of placing the earbuds in the charging case described by Shaffer. When the earbuds are placed in the case, it is clear they are not in use, so automatically entering an idle mode to save power and disconnecting from the host device is an obvious improvement to the user experience. Conversely, when the earbuds are removed from the case, the user intends to use them, so automatically powering on and attempting to reconnect is an equally obvious and desirable feature. The combination of Posa's wireless functionality with the charging context provided by Shaffer would lead directly to the power management scheme claimed in claim 20.

Claim 22: A wireless audio streaming host device configured to manage the master-slave roles of two wireless earbuds based on their battery charge status to conserve power.

Obviousness Combination: Posa (US 8,867,758) in view of general knowledge of power management in paired wireless devices

• Posa teaches a system with two wireless earbuds that communicate with a host device. Many wireless protocols for such stereo pairing, like some versions of Bluetooth at the time, utilize a master-slave relationship where one earbud (the master) communicates with the host and relays the signal to the other (the slave). This inherently leads to higher power consumption in the master device.

• General Knowledge: The concept of load balancing and dynamic role-switching to conserve power in a distributed or paired system was a well-understood principle in computer science and wireless communications. In any system with two powered devices working cooperatively, where one has a more power-intensive role, it would be an obvious design consideration to alternate that role to extend the overall system runtime.

Motivation to Combine: A person of ordinary skill in the art working with the paired wireless earbud system of Posa would recognize the inherent power imbalance between the master and slave earbuds. To address the problem of the master earbud's battery draining significantly faster than the slave's, they would be motivated to implement a power management strategy. The most direct and logical solution would be to monitor the battery levels of both earbuds and switch the master and slave roles when a certain power differential is reached. This is a straightforward application of known power management techniques to the specific context of true wireless stereo earbuds. Therefore, the invention described in claim 22 would have been an obvious improvement over the system disclosed in Posa.

Conclusion

The independent claims of U.S. Patent 9,402,120 appear to be vulnerable to an obviousness rejection under 35 U.S.C. § 103 based on combinations of prior art references that were publicly available before the patent's filing date. The claimed inventions represent predictable solutions to known problems in the field of wireless earbuds, utilizing design principles and component arrangements that would have been well within the grasp of a person of ordinary skill in the art at the time. The motivation to combine the teachings of the cited references stems from a desire to create a more compact, user-friendly, and power-efficient product, which are standard objectives in the development of consumer electronics.

Analysis of U.S. Patent 9,402,120: "Wireless earbuds"

As of May 14, 2026, U.S. Patent 9,402,120, titled "Wireless earbuds," is active, with a projected expiration date of September 5, 2034. The patent has been the subject of multiple litigation actions.

There is no record of any Patent Term Adjustments (PTA) or Patent Term Extensions (PTE) for this patent. The standard 20-year term from its filing date is applied.

Continuity and Application History

U.S. Patent 9,402,120 was granted from application number 14/478,698, which was filed on September 5, 2014. The patent was issued on July 26, 2016. The provided documentation does not indicate any continuation or divisional applications associated with this patent.

Patent Family

This U.S. patent is part of a larger international patent family, claiming priority to applications in other jurisdictions:

• PCT Application: PCT/SE2015/050941, filed on September 7, 2015.
• European Patent Application: EP15838760.5A, also with a priority date of September 7, 2015.

Litigation History

U.S. Patent 9,402,120 has been asserted in multiple legal disputes. According to public records, the following litigation has been identified:

• U.S. District Court for the District of Delaware:
  • 1:24-cv-00274
  • 1:24-cv-00275
  • 1:26-cv-00276
  • 1:26-cv-00277
• U.S. District Court for the Northern District of Ohio:
  • 5:25-cv-01534

Additionally, the patent was the subject of a petition for inter partes review (IPR) before the Patent Trial and Appeal Board (PTAB):

• PTAB Case: IPR2025-00690. The petition was not instituted, meaning the board did not proceed with a trial on the merits of the patent's validity based on the arguments presented.

This history of litigation indicates that the patent holder, Earin AB, has actively enforced its patent rights.

Defensive Disclosure for U.S. Patent 9,402,120: "Wireless Earbuds"

Publication Date: April 26, 2026
Subject: Derivatives and obvious variations of the core claims of U.S. Patent 9,402,120, related to the construction, charging, and operation of wireless earbuds.

This document discloses technical variations and improvements to the concepts described in U.S. Patent 9,402,120 (hereinafter "the '120 patent"). The purpose of this disclosure is to place these variations in the public domain, thereby establishing them as prior art for any future patent applications in this field.

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Analysis of Core Claims of U.S. Patent 9,402,120

The core inventive concepts of the '120 patent revolve around:

• Claim 1: A wireless earbud with a specific internal component layout (loudspeaker, battery, PCB, and charging interface in successive order along a longitudinal axis) within a cylindrical or frusto-conical housing.
• Claim 12: A wireless earbud featuring an antenna integrated into the circumferential edge of a circular main printed circuit board (PCB).
• Claim 20: A method for automatic power preservation in a wireless earbud, involving switching between idle and operational modes based on connection to a charger, and managing master/slave roles in a true wireless stereo (TWS) pair.
• Claim 22: A wireless audio streaming host device that manages master/slave roles of paired earbuds based on their battery charge status to extend operational time.

The following sections detail derivative inventions for each of these core concepts.

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I. Derivatives of Core Claim 1: Component Layout and Housing

1. Material & Component Substitution

• Enabling Description: The earbud housing, described as "essentially cylindrical or frusto-conical," can be constructed from a biocompatible, injection-molded liquid silicone rubber (LSR) for enhanced user comfort and a superior acoustic seal. Internally, the successive components are separated by micro-machined graphene aerogel spacers. This provides superior thermal dissipation from the battery and PCB while offering enhanced shock absorption. The loudspeaker is a micro-electromechanical system (MEMS) solid-state speaker, which is significantly smaller and more power-efficient than a traditional balanced armature receiver.

  graph TD;
      A[LSR Housing] --> B(MEMS Loudspeaker);
      B --> C(Graphene Aerogel Spacer);
      C --> D(Li-S Battery);
      D --> E(Graphene Aerogel Spacer);
      E --> F(Flexible PCB);
      F --> G(Graphene Aerogel Spacer);
      G --> H(Capacitive Charging Interface);
  

• Enabling Description: The rear housing portion is fabricated from a ceramic composite (e.g., Zirconia Toughened Alumina) to provide a scratch-resistant and radio-transparent surface. The internal components are mounted on a flexible polyamide PCB that can be furled into a tight cylinder, allowing for a more compact and dense arrangement of components. The battery is a lithium-sulfur (Li-S) thin-film battery, offering a higher energy density for the same volume.

  graph TD;
      A[Ceramic Composite Housing] --> B{Flex PCB Core};
      B --> C[MEMS Speaker];
      B --> D[Li-S Thin-Film Battery];
      B --> E[Charging Interface];
  

2. Operational Parameter Expansion

• Enabling Description (Cryogenic/High-Temperature Operation): For industrial or scientific applications, the earbuds are designed to operate in extreme temperatures (-50°C to +150°C). The housing is made of PEEK (polyether ether ketone), and the battery is a solid-state, ceramic-electrolyte battery. All solder joints use a high-melting-point silver alloy, and the PCB is a ceramic substrate. This allows for reliable audio communication for personnel in industrial freezers, foundries, or other extreme temperature environments.

  stateDiagram-v2
      [*] --> Cryo_Operational: Temp < 0°C
      Cryo_Operational --> Normal_Operational: Temp > 0°C
      Normal_Operational --> High_Temp_Operational: Temp > 50°C
      High_Temp_Operational --> Normal_Operational: Temp < 50°C
      High_Temp_Operational --> Shutdown: Temp > 150°C
      Cryo_Operational --> Shutdown: Temp < -50°C
  

• Enabling Description (High-Pressure/Vacuum Operation): For aerospace or deep-sea applications, the earbud housing is hermetically sealed and machined from a single block of titanium alloy (Ti-6Al-4V). The internal components are potted in a non-conductive, pressure-resistant epoxy. The loudspeaker is a bone-conduction transducer, eliminating the need for an air-filled acoustic chamber that would be compromised by extreme pressure changes.

  sequenceDiagram
      participant User
      participant Earbud
      participant Environment
      Environment->>Earbud: High Pressure / Vacuum
      Earbud->>Earbud: Equalize internal pressure (potted components)
      User->>Earbud: Audio Command
      Earbud->>User: Bone Conduction Audio
  

3. Cross-Domain Application

• Enabling Description (Aerospace): The core layout is adapted for a personal biometric sensor for astronauts. The "loudspeaker" is replaced with a sensor suite (EEG, core body temperature), the battery is a radiation-hardened solid-state battery, and the PCB manages data telemetry to the spacecraft's main computer. The form factor remains the same for in-ear stability during high-G maneuvers.

  graph TD;
      A[In-Ear Biometric Sensor] --> B(EEG Sensor);
      A --> C(Core Temp Sensor);
      A --> D(Radiation-Hardened Battery);
      A --> E(Telemetry PCB);
      E --> F((Spacecraft Computer));
  

• Enabling Description (Agricultural Technology): The earbud form factor is repurposed as a soil-health sensor. The "loudspeaker" is replaced by a multi-ion sensor to measure soil pH, nitrogen, and potassium levels. The battery is charged via an exposed solar cell on the charging interface. The PCB transmits data via a LoRaWAN connection to a central farm management system. Multiple such "buds" are inserted into the ground across a field.

  graph TD
      subgraph In-Soil Sensor
          A[Multi-Ion Sensor]
          B[Solar-Charged Battery]
          C[LoRaWAN PCB]
      end
      C --> D((Farm Gateway))
  

• Enabling Description (Consumer Electronics): The successive component layout is used for a modular, "smart-jewelry" charm. The "loudspeaker" is a haptic feedback motor, the battery powers the device, and the PCB contains a low-power Bluetooth chip and an NFC coil for contactless payments. Different charms (earrings, necklace pendants) could be swapped, all sharing this core electronic architecture.

  erDiagram
      SMART_CHARM {
          string HapticMotor
          string Battery
          string NFCPCB
      }
  

4. Integration with Emerging Tech

• Enabling Description (AI Integration): The earbud's operation control circuitry includes a dedicated neural processing unit (NPU). This NPU runs a real-time AI model that analyzes the user's brainwaves (via in-ear EEG sensors replacing the charging contacts) to dynamically adjust the audio equalization to match the user's emotional state or level of focus. This "neural EQ" is a closed-loop system that optimizes the listening experience without user intervention.

  flowchart TD
      A[In-Ear EEG] --> B{NPU};
      B -- Emotional State --> C[AI Model];
      C -- EQ Adjustment --> D[Audio Codec];
      D --> E[MEMS Speaker];
      E --> F[User];
      F -- Brainwave Feedback --> A;
  

5. The "Inverse" or Failure Mode

• Enabling Description (Safe-Failure Mode): The earbud is designed with a "safe-failure" mode for mission-critical communications (e.g., first responders). If the main rechargeable battery fails or drops below a critical voltage, a secondary, non-rechargeable silver-oxide coin cell is activated. This secondary cell bypasses all non-essential functions (stereo audio, codec processing) and powers only a low-fidelity, "receive-only" audio circuit, ensuring the user can still hear incoming commands. A specific "fail-safe" audio tone is played to alert the user of the switch.

  stateDiagram-v2
      state "Full Function" as Full
      state "Safe Mode" as Safe
      [*] --> Full
      Full --> Safe : Battery < 5%
      Safe --> [*] : Secondary Battery Depleted
      Full: TWS Audio
      Full: Full Codec
      Safe: Receive-Only
      Safe: Low-Fidelity Audio
  

---

II. Derivatives of Core Claim 12: Circumferential Antenna

1. Material & Component Substitution

• Enabling Description: The elongate radiator pattern is not a surface plating but is instead a liquid metal (Gallium-Indium alloy) injected into a micro-channel that has been laser-etched into the circumference of the circular PCB. This allows the antenna's electrical length to be dynamically tuned by using a micro-pump to extend or retract the liquid metal in the channel, adapting to different frequency bands or environmental detuning.

  graph TD
      A[PCB Micro-channel] -- Injected --> B(Liquid Metal);
      B -- Controlled by --> C(Micro-pump);
      C -- Adjusts --> B;
      B -- Acts as --> D(Tunable Antenna);
  

2. Operational Parameter Expansion

• Enabling Description (Multi-Frequency Operation): The circumference of the PCB has three concentric, isolated radiator patterns, each tuned to a different frequency band (e.g., 2.4 GHz for Bluetooth, 5.8 GHz for high-fidelity audio, and 900 MHz for a long-range, low-power mesh network). This allows the earbud to simultaneously act as a personal audio device, a high-speed data receiver, and a node in an IoT mesh network.

  graph TD;
      A[PCB] -- has --> B(Circumferential Edge);
      B -- has --> C(2.4GHz Antenna);
      B -- has --> D(5.8GHz Antenna);
      B -- has --> E(900MHz Antenna);
  

3. Cross-Domain Application

• Enabling Description (Medical Implants): The concept of a circumferential antenna on a small, circular PCB is applied to a subdermal medical implant (e.g., a glucose monitor). The circular form factor is ideal for biocompatible encapsulation, and the circumferential antenna provides a reliable RF link for data transmission through skin and tissue to an external monitoring device, without a specific orientation being required.

  sequenceDiagram
      participant Implant
      participant BodyTissue
      participant ExternalDevice
      Implant->>BodyTissue: RF Signal
      BodyTissue->>ExternalDevice: Data Received
  

---

III. Derivatives of Core Claim 20 & 22: Power Preservation and Role Switching

1. Integration with Emerging Tech

• Enabling Description (AI-driven Role Switching): The wireless host device uses a predictive AI model to determine when to switch the master/slave roles. The model is trained on the user's historical listening habits, movement patterns (from the phone's accelerometer), and the typical RF environment. It predicts future battery drain with high accuracy and initiates a role-switch before a significant battery differential occurs, leading to a more seamless user experience and extended overall playtime.

  flowchart TD
      A[User Data] --> B{Predictive AI Model};
      B -- Predicts --> C(Future Battery Drain);
      C -- Triggers --> D(Proactive Role Switch);
      D -- sent to --> E((Earbuds));
  

2. The "Inverse" or Failure Mode

• Enabling Description ("Limp-Home" TWS Mode): When one earbud's battery is critically low (e.g., <2%), and no role-switch can save it, the system enters a "Limp-Home" mode. The dying earbud transmits its current audio buffer to the healthy earbud. The healthy earbud then mixes the left and right channels into a mono signal and plays that, while the other earbud shuts down completely. This ensures the user doesn't lose the audio experience entirely if one earbud dies mid-use.

  stateDiagram-v2
      state "TWS Mode" as TWS
      state "Limp-Home Mode" as Limp
      [*] --> TWS
      TWS --> Limp : Earbud_A Battery < 2%
      Limp --> [*] : Earbud_B Dies
      TWS: Stereo Audio
      Limp: Mono Mix in Earbud_B
  

---

IV. Combination Prior Art Scenarios

1. Combination with Bluetooth A2DP and LC3 Codec: The power preservation and role-switching method of claims 20 and 22 is combined with the Bluetooth Low Energy Audio standard and the LC3 codec. The host device's controller monitors the battery levels of both earbuds and uses a vendor-specific command within the Bluetooth Core Specification to trigger a seamless master/slave role switch between audio frames, ensuring no audible interruption in the LC3 audio stream. This creates a highly efficient, standardized method for extending TWS earbud battery life.

2. Combination with WebRTC for Low-Latency Communication: The earbud design from claim 1 is integrated into a WebRTC-based communication system. The earbuds act as the audio endpoints for a real-time, browser-based communication platform. The automatic power preservation method (claim 20) is triggered not by a physical charger, but by the WebRTC session state. When a user is muted or there is no active audio stream, the earbuds enter their "idle" mode to conserve power, and "wake up" instantly when the audio stream resumes.

3. Combination with Android Open Source Project (AOSP): The battery-based master/slave role-switching logic of claim 22 is implemented as a native service within AOSP. This allows any TWS earbud manufacturer that adheres to the AOSP Bluetooth stack to benefit from this power-saving feature. The service would query the battery level of connected HFP or A2DP devices and issue the standardized role-switching commands, making this an OS-level feature rather than a device-specific one.