Optics: measuring and testing – By dispersed light spectroscopy – With raman type light scattering
Reexamination Certificate
1999-12-22
2002-11-19
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With raman type light scattering
C356S328000
Reexamination Certificate
active
06483581
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to applied optics, spectra-chemical image processing, chemical identification, and chemical analysis. More specifically, the present invention relates to apparatus and methods for the non-destructive testing and identification of the composition of a sample of plastics or other materials using Raman spectroscopy and computerized signal processing.
A widespread need exists in industry and government for identifying materials. For example, automobile companies and plastics manufactures must identify and separate plastic resins in recycling operations. Pharmaceutical companies must monitor chemical constituents during drug production. Monitoring agencies and firms must assay waste stream flows into the environment. Law enforcement agencies must identify the presence of illicit drugs in the field in order to combat criminal drug trafficking.
In today's environmentally conscious society, simple economics provides a strong incentive for manufacturers to minimize their use of natural resources and public landfills. Substantial economic benefit can be gained by turning to recycling as a source for raw materials and as the ultimate repository for the manufactured goods. Using recycled raw materials in products can increase profits by saving materials costs and energy. Efficiently recycling packaging and production waste can save landfill charges and provide a cost recovery stream. Further, manufacturing goods with recycled content, and designing goods that themselves are recyclable, is a civic duty that also offers public relations benefits that are worthwhile from a marketing standpoint.
Many suppliers, however, face difficulties in using recycled feed streams. All companies face competition, and in the marketplace, price alone does not guarantee market share. Most manufacturers value quality and consistency of goods more than the abstract notions of civic duty and environmental policy. Further, many production lines operate with just-in-time inventories, in which a factory receives all the components necessary to assemble a product only hours before they are needed. The presence of only a few defective parts can shut down a production line until replacement parts arrive. Such a shut down can cost a manufacturer many thousands of dollars.
Thus, it is easy to understand why companies have been reluctant to include recycled materials in products. Recycled materials must have documented histories so that they are assured of compatibility with the manufacturing process. A misidentified piece of recycled material included with virgin material can destroy an entire production run. Maintaining the history of recycled goods, or even knowing their exact composition is difficult, if not impossible, with current technology.
Millions of tons of plastic and other materials are deposited in landfills or incinerated every year due almost solely to the lack of sufficient technology to avoid cross contamination between different types of plastic or other material during collection. The need therefore exists for an effective, economical means to identify a variety of materials, and-specifically plastics, on site in scrap yards, warehouses, factories and recycling centers. The successful commercialization of an instrument with such capabilities would greatly increase the recycling rates for plastics and perhaps many other materials. By offering a simple means to overcome the difficult problem of material identification, the present invention seeks to help make manufacturers more receptive to including recycled content in their products, and purchasers more confident of the quality of those products.
Many methods exist for identifying materials. One test for plastic materials, for example, involves the burning of a small sample of the plastic material. Upon smelling the smoke, a trained technician can identify several different classes of plastics with reasonable success. While this method can be employed in a laboratory, such methods are not appropriate or practical for commercial or production line applications. This type of chemical analysis would also not be acceptable to law enforcement personnel or the courts for the identification of Cocaine.
An assortment of analytical identification methods exist, such as Fourier Transform Infrared Spectroscopy (FTIR) and X-ray fluorescence (XRF), for the non-destructive testing of materials. An example of FTIR technology is disclosed in U.S. Pat. No. 5,510,619. While well known and used, the FTIR process is not practical in many commercial applications because the method is very sensitive to dirt, surface roughness, coatings, moisture, and sample motion during identification. The XRF process is also used but it is relatively expensive. Other analytical identification methods are disclosed, for example, in U.S. Pat. No. 5,256,880 and 5,512,752.
Raman spectroscopy, discovered by C. D. Raman in 1928, has many unique qualities that can be advantageously employed in the practical identification of materials. Raman signals, generated by the interaction of monochromatic light and a sample, are not affected by dirt, surface finish, coatings, or any motion of the sample being identified. Significantly, Raman signals are also not as sensitive to water, glass or quartz as other infrared signals. As a result, chemical samples can be contained within a glass vessel, or even suspended in an aqueous solution without affecting the Raman signal. The Raman process also has a significantly higher depth of field than other processes and can “look through” a container to the chemical sample contained inside.
Despite these advantages, Raman spectroscopy is not widely used because of a low signal to noise ratio inherent in Raman Spectroscopy. Traditionally, the excitation light source, typically a laser, is directed continuously against a chemical sample, and the Raman signal is collected over time. An example of such an apparatus is disclosed in U.S. Pat. No. 5,534,997. Increasing the power of the excitation laser in the Raman process can increase the strength of the Raman signal and reduce the required sampling time. However, the increase in power can cause thermal damage to the sample particularly if the sample has low thermal conductivity that is typical of plastics. The increase in power can also cause “black body” or thermal radiation that can overwhelm the Raman signal. It is commonly assumed, therefore, that Raman spectroscopy is not appropriate for the practical identification of highly energy absorbent materials such as black or highly pigmented plastics. In the extreme case, such highly absorbent materials can char or burn thus rendering the material unsuitable for further use.
What is needed is a system for analyzing and identifying the composition of a wide variety of materials that is fast enough for practical application in a commercial setting, insensitive to sample impurities or surface imperfections, tolerant of water and common sample containers, and which does not damage the sample being analyzed and identified.
SUMMARY OF THE INVENTION
A system satisfying these needs generally comprises a probe including a housing having an optical window through which visible and infrared light can pass. A monochromatic light source is provided with radiation optics optically coupling the light source to the optical window so that light emitted from the light source is directed through the window toward a sample causing the sample to produce a characteristic Raman signal. Sampling optics are coupled to the optical window to receive the characteristic Raman signal produced from the sample including at least one filter for removing unwanted spectral portions. A spectrograph is coupled to the sampling optics for dispersing the characteristic Raman signal into a spectrum to form a spectrographic output. An optical detector is coupled to the spectrograph to receive the spectrographic output and generate a digital map representing the Raman spectrum as a function of wavelength. A computer is coupled to the detec
Ben-Amotz Dor
Grant Edward R.
Haber Ken
Jiang Yanan
Laurence, Jr. George M.
Brinks Hofer Gilson & Lione
Font Frank G.
Punnoose Roy M.
Spectra Code, Inc.
LandOfFree
Raman system for rapid sample indentification does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Raman system for rapid sample indentification, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Raman system for rapid sample indentification will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2946199