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Patent Application Titled "Fiber Optic Hydrophone Sensors and Uses Thereof" Published Online

June 5, 2014

By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors Daryoush, Afshin S. (Bryn Mawr, PA); Lewin, Peter A. (Wyndmoor, PA); Minasamudram, Rupa Gopinath (Bangalore, IN); El-Sherif, Mahmoud (Bala Cynwyd, PA), filed on January 21, 2014, was made available online on May 22, 2014.

No assignee for this patent application has been made.

Reporters obtained the following quote from the background information supplied by the inventors: "Hydrophone devices are capable of detecting pressure amplitude in immersion media such as liquids or gases and in solids as well. Several different types of hydrophone devices are known in the art. New applications for sensing and use of pressure amplitude in liquids, solids and gases, including clinical, sonar, and communication applications require improved hydrophones for calibration, metrology, medical metrology, elasticity of medium, imaging, detection, therapy, diagnosis, and the like.

"One type of hydrophone device known in the art is a piezoelectric hydrophone device. Piezoelectric hydrophones may be used for measurement of large frequency bandwidths; however, problems arise from the generation of high temperatures and cavitation effects that are produced by High Intensity Focused Ultrasound (HIFU) fields, High Intensity Therapeutic Ultrasound (HITU) fields, lithotripter fields or the like. These problems generally could lead to device failure due to high pressure amplitudes. Currently, such devices tend to be costly and cumbersome, and tend to have large apertures which can spatially average certain acoustic fields. For example, existing hydrophone probes have aperture diameters on the order of about 500 .mu.m or more which introduces spatial averaging of acoustic fields beyond 3 MHz. This spatial averaging can lead to errors in detection and faithful reproduction of the pressure-time waveform of the measured acoustic wave and result in poor spatial resolution.

"Other acoustic pressure sensors have been proposed as well, including a limited range of fiber optic based pressure sensors that exploits amplitude variations. There are at least two other broad classifications based on the sensing mechanism for these sensors, namely phase modulated and wavelength modulated pressure sensors. Included in phase modulated sensors are Mach-Zehnder interferometers, Fabry-Perot resonant structures and multilayer resonant structures that act as microinterferometers. These interoferometric phase schemes however, are subject to phase fluctuation which may result in higher amplitude noise of the sensor signal. Phase fluctuations, temperature drift and other problems associated with phase modulated fiber optic hydrophones can cause errors in measurement.

"Wavelength modulated phase sensors employing external Bragg's cells, fiber Bragg gratings (FBGs) and distributed Bragg reflectors have also been proposed. These fiber optic hydrophone devices perform acoustic sensing based on an acoustically induced change in the wavelength of optical signals passing through the given sensor. These wavelength modulated sensors are usually distributed along the length of the fiber and have sensing dimensions on the order of a few millimeters. The typical range for sensing regions in wavelength modulated sensors is on the order of about 600 .mu.m to about 3 mm. This large sensing dimension causes the sensors to suffer from poor spatial resolution thus limiting the resolution bandwidth. For this reason, wavelength modulated fiber optic hydrophones cannot be used in many ultrasound applications.

"Thus, what is needed is a novel, high sensitivity sub-micron resolution rugged hydrophone probe that would be able to characterize acoustic fields in the frequency range up to 100 MHz while minimizing spatial averaging, phase fluctuations, or both."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "Accordingly, the present invention provides for systems for detecting changes in pressure in an immersion medium such as a liquid, a gas, or a solid, the system comprising: an optical fiber, wherein said optical fiber has a core diameter at an immersion surface contact of the fiber of less than 10 .mu.m; and a layer of material deposited on said end of the fiber, wherein said layer of material has a thickness of from about 2 nm to about 10 nm. In another embodiment, the fiber may have a diameter of less than about 20 um, and the diameter may be selected based on the frequency of the ultra sound.

"The present invention also provides for methods for detecting changes in pressure in an immersion medium, such as a liquid or gas, or in a solid (collectively media or medium), the method comprising: contacting the medium with a fiber optic, wherein said fiber optic integrated with a light source and a detector, and wherein said fiber optic has a diameter of less than 10 .mu.m at an immersion surface contact of the fiber; providing a thin layer of material on the immersion surface contact, wherein said thin layer of material is of a thickness in a range of from about 2 nm to about 10 nm; and detecting Fresnel back reflections from the immersion end of the fiber.

"Also provided are methods of making a device for detecting acoustic waves in an immersion medium such as a liquid, gas, or solid, comprising: providing an optical fiber having a core diameter at an immersion surface contact of less than about 10 .mu.m; and depositing on said immersion contact surface of the fiber a layer of material having a thickness of from about 2 nm to about 10 nm.

"The general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims. Other aspects of the present invention will be apparent to those skilled in the art in view of the detailed description of the invention as provided herein.


"The summary, as well as the following detailed description, is further understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings exemplary embodiments of the invention; however, the invention is not limited to the specific methods, compositions, and devices disclosed. In addition, the drawings are not necessarily drawn to scale. In the drawings:

"FIG. 1 depicts an example of a prior art fiber optic hydrophone.

"FIG. 2 depicts an example embodiment of an experimental setup of the present invention.

"FIG. 3 depicts examples of fiber optic hydrophone immersion surface contact geometries.

"FIGS. 4(a), (b), , (d), (e) and (f) depict a series of immersion surface contacts and different associated geometries. FIGS. 4(a)-(b) depict a fiber with a straight cleaved immersion end, FIGS. 4-(d) depict a fiber with a cylindrically etched immersion end, and FIGS. 4(e)-(f) depict a fiber with a tapered immersion end.

"FIG. 5 depicts a previous model suggesting that there was no improvement in hydrophone sensitivity for a coating thicknesses for gold of less than about 30 nm.

"FIG. 6 depicts surprisingly good experimental results for sensitivity of a fiber optic hydrophone with thin layers of gold on the immersion end of the fiber.

"FIGS. 7(a) and (b) depict the sensitivity effects of core diameter in an example embodiment of a cylindrically etched fiber and the sensitivity effects of taper angle in an example embodiment. The units on the left side of the graph would show a relative improvement in sensitivity in dB and exists as an example."

For more information, see this patent application: Daryoush, Afshin S.; Lewin, Peter A.; Minasamudram, Rupa Gopinath; El-Sherif, Mahmoud. Fiber Optic Hydrophone Sensors and Uses Thereof. Filed January 21, 2014 and posted May 22, 2014. Patent URL:

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Source: Politics & Government Week