Optics: measuring and testing – For light transmission or absorption
Reexamination Certificate
2000-01-19
2003-07-08
Smith, Zandra V. (Department: 2877)
Optics: measuring and testing
For light transmission or absorption
C356S437000
Reexamination Certificate
active
06590661
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
This invention relates to methods for sensing sound waves, and in particular, using optical means to detect sound waves through certain corresponding changes in the optical properties of air or other optically transparent or semitransparent medium through which the sound propagates.
Current methods for sensing sound waves typically involves the sound waves impinging on a diaphragm or other mechanical surface, and then using an electrical, or in some cases optical, means to detect the movement of said diaphragm or other mechanical surface. Such traditional microphones typically need to be located close to the source of the sound waves so that the diaphragm moves according to the sound waves to be sensed with adequate fidelity and signal strength, and so that the effects of noise and other undesired sounds is minimized. Locating the microphone close to the source of the sound can be problematic, for example, when the microphone is being used to monitor sound waves from a person who needs to be somewhat mobile (for example, a performer on a stage) or does not have a hand free to hold the microphone. Also, traditional microphones typically obstruct the view of a performer's face. And often microphones need to be hidden from view, for example for motion picture actors and people on television. Or surveillance and security applications may require that the microphone be located a distance from the sound source. Failings with traditional microphones themselves are that they: require cables or other transmission means to relay their sensed sounds to a receiving device, require careful mechanical design and assembly to provide good performance, due to their mechanical nature they have a limited range of frequencies to which they are sensitive, and are often fragile. Also, due to environmental factors, such as electromagnetic fields, pressure, and temperature, or the presence of corrosive or combustible gases, it may be difficult to get acceptable performance from such traditional microphones. And the connectors and cables of traditional microphones are also expensive, subject to wear and damage, and are a source of electromagnetic field induced and electromechanical contact noise. Finally, high quality microphones are large, and as is often seen at press conferences, mounting larger numbers of them on a podium can be a problem.
Prior art has attempted to solve these limitations in a variety of ways.
Wireless microphones are widely used by business meeting presenters, stage performers and other actors. Typically a small battery-operated radio-frequency, infrared light or ultrasonic sound transmitter unit (about the size of a pager) is clipped to the presenter's belt, and a cable leads from this transmitter to a small microphone, which is often then clipped to the presenter's clothing, as close to their mouth as is convenient. The transmitter transmits the presenter's audio to a receiving unit typically located within 2 to 30 meters, and this receiving unit is then connected to an audio amplifier, a recording device or other equipment. There are many shortcomings of this method. For example, the transmitter's battery can fail at an inopportune time. Radio frequency or other types of interference from other equipment or transmitters can disrupt or degrade the signal. The requirements of routing the microphone cable through one's clothing, finding a place to mount the transmitter, and mounting the microphone close to the presenter's mouth are often a problem requiring undesirable trade-offs of audio quality versus convenience. For higher audio quality, larger microphones must be used and positioned in front of the performer's mouth (as is often seen by singers at concerts), and these obstruct the audience's view of the performer's face. Also, each presenter must have a transmitter; and this can be costly, and requires coordination of the radio frequencies used. Alternatively, sharing a unit is difficult as it is awkward to quickly transfer it to another person. Finally, the whole system of microphone, battery, transmitter and receiver is time-consuming to set-up, trouble-shoot and transport.
High-quality microphones are often mounted on long poles. Such boom microphones are often used for television programs and motion pictures. These can be mounted on wheeled dollies; in which case they are they are large, and have heavy counterweights so that the booms can be up to 5 to 10 meters in length. Or the boom microphones can be hand-held, in which case the boom length is typically quite limited, for example to 2 or 3 meters. In any case, such boom microphones typically require a full-time operator to ensure that the microphone itself is as close to the (moving) performer as possible, while staying out of the field of view of the camera (which can often change to a wider view, requiring the microphone to first be moved). Also, the maximum distance from the actor to the microphone is limited by the audio quality required (background noise and reduced frequency response are a problem at more than a meter or two).
U.S. Pat. No. 3,633,705 to Teder describes a microphone with a tubular housing to aid in rejecting unwanted noise. Such microphones are large, and still need to be close to the sound source, are effective for only some frequencies and directions of noise and require careful mechanical assembly.
A microphone mounted near the focus of a paraboloid-shaped plastic reflector is often used to increase the directionality of a microphone, so that such microphones can be located a distance from the sound source, as in U.S. Pat. No 3,895,188 to Ingraham. Due to the nature of such reflected sound waves, such systems have a poor frequency response characteristic, are often too sensitive to wind, handling and other noise sources, pick-up undesired sounds behind the intended sound source, and require trial-and-error focussing adjustments according to the distance to the sound source.
Sensing sound waves and other vibrations (such as those from rotating machinery) through optical means is the subject of much prior art. A method of sensing vibrations and other very small movements of surfaces is described in U.S. Pat. No. 5,029,023 to Bearden et al. This involves coherent laser lit reflected from the measured surface to be fed back into the laser cavity and measuring the resulting varying light output of the laser. The distance over which such a system operates is limited by the coherence length of the laser light source, which is typically less than a meter. Also, to sense sound would require a reflective diaphragm to be located near the sound source, and for this diaphragm to be precisely aimed to return the laser light. Also, the physical characteristics of the diaphragm affect the fidelity of the sensing of the sound waves. Such complex and high-cost systems are typically more suited to experimental and laboratory use than industrial and commercial applications. U.S. Pat. Nos. 5,202,939 and 5,392,117 to Belleville et al. describe an interferometry-based method for detecting small displacements, such as due to the stress of a structural member which is located at the end of an optical fiber cable. Such systems are suited more to instrumentation applications, and require a fiber optic cable to be run all the way to the sound source.
U.S. Pat. Nos. 5,146,083 and 5,200,610 to Zuckerwar et al., and U.S. Pat. No. 5,262,884 to Buchholz describe systems which use a fiber optic cable to illuminate an optical element, with said optical element being mounted on a flexible membrane or diaphragm which vibrates according to the ambient sound waves. The motion of the optical element relative to the illuminating fiber optic cable affects the amount of light directed back to the same or a second fiber optic cable, and this is sensed at the far end of the fibe
Smith Zandra V.
Stock Gordon J
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