Yesterday Patently Mobile posted a report titled "Facebook is determined to stay ahead of Apple on HMDs and Win the Race on being first with Smartglasses to replace Smartphones." Part one laid out the overview of Facebook racing to develop smartglasses ahead of Apple and the first patent covered in the report is titled "Structured Light Depth Sensing." We ended yesterday's report by noting that there would be a series of patents to follow covering both smartglasses and Oculus-styled headsets. The next installment in this series covers Facebook's granted patent titled "optical microphone for eyewear devices," an invention designed to produce superior audio for future glasses-styled headsets.
Head-mounted displays in an artificial reality system often include features such as speakers or personal audio devices to provide audio content to users of the head-mounted displays. The audio systems in head-mounted displays can include microphones positioned at or near the entrances of a user's ears to measure the sound produced by the speakers and calibrate the audio system.
Current microphones for use in head-mounted displays, such as binaural microphones or microphone arrays embedded in frames of head-mounted devices, have limited sensitivity.
For example, typical microphones used in head-mounted devices have difficulty detecting audio pressure waves produced by bone conduction transducers, which generate particle displacements outside the ear in the nanometer or picometer range. To generate pressure waves that can be detected by existing microphones, bone conduction transducers must produce a very loud volume, which is unpleasant for the user.
Facebook's granted patent covers an audio system that includes an optical microphone for detecting audio waves with a higher sensitivity than previous microphones.
The audio system may be a component of an eyewear device that is a component of an artificial reality head-mounted display (HMD). The audio system includes at least one transducer that produces acoustic pressure waves, and an optical microphone to detect the acoustic pressure waves.
The optical microphone can be positioned at the entrance to the user's ear canal or in the vicinity of the user's ear. The optical microphone includes a laser that emits light that is separated into a sensing beam and a reference beam, e.g., using a beam splitter.
The sensing beam travels through an optical sensing pathway, such as an optical fiber. The acoustic wave interacts with the sensing beam while it is in the optical sensing pathway by altering the optical path length of the sensing beam.
A detector assembly receives the sensing beam from the optical sensing pathway, and also receives the reference beam. The detector measures the detected acoustic pressure wave based on the change in optical path length of the sensing beam. The audio system may adjust the acoustic pressure waves produced by the transducer based on the measurement of the detected acoustic pressure wave.
Facebook's patent FIG. 1 below is a perspective view of an eyewear device including an audio system; FIG. 2A is a profile view a portion of an audio system including an optical fiber microphone as a component of an eyewear device.
The sensor device #115 found on the bottom of the glasses frame noted in FIG. 1 estimates a current position of the eyewear device #100 relative to an initial position of the eyewear device. The sensor device includes a position sensor and an inertial measurement unit.
The audio system of the eyewear device comprises a transducer assembly #120 configured to provide audio content to a user of the eyewear device and an optical microphone assembly #125 configured to detect acoustic pressure waves produced by the transducer assembly.
Facebook filed for this patent in November 2018 and was granted by the U.S. Patent Office on April 7, 2020. You could check out the finer details of granted patent 10,616,692 here.
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