Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
1996-08-09
2001-08-28
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S234000, C324S228000
Reexamination Certificate
active
06281680
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the screening of diamond gemstones so as to distinguish and detect synthetic diamonds from natural diamonds. More particularly, the invention relates to a method and apparatus for the rapid screening of diamond gemstones to determine the need for further investigation by identifying those likely to be synthetic. The invention produces a negative response for natural diamonds but reacts to the magnetic properties of synthetic diamonds to provide an indicator thereof.
BACKGROUND OF THE INVENTION
With the advent of gemstone quality synthetic diamonds the need has arisen for a rapid screening system available and affordable for the local jeweler to establish with reasonable probability whether a given diamond gemstone is natural or synthetic.
Existing systems for detection of synthetic diamond gemstones are summarized in the article Shigley et al., “Sumitomo Synthetic Diamonds”,
Gems and Gemology
, Winter 1986, pages 192-208. As there indicated the various properties of diamonds and particularly those that distinguish natural from synthetic stones are compared. Testing procedures were set forth which included color, (which may involve spectroscopy examination), fluorescence, electrical conductivity, thermal conductivity, specific gravity, microscope inspection, reaction to polarized light, and magnetism. As to the latter, magnetism, the test procedure involved gross attraction of the tested diamond to a magnet. However, it was found that only one of the tested synthetic diamonds was attracted so that the reliability of a test as there proposed was found inadequate.
A subsequently published article by Shigley et. al., “Gemological Properties of the De Beers Gem Quality Synthetic Diamonds”,
Gems and Gemology
, Winter 1987, pages 187-206, repeated the previous work and investigation as applied to the De Beers synthetic diamond product. In addition to the tests earlier performed, the last publication also indicates that a test was conducted with catholuminescence and specific gravity investigations as well as chemical analysis of inclusions. As to the magnetic behavior it was noted that natural diamonds are only weakly magnetic if at all and that synthetic diamonds were believed to vary from strongly magnetic to non-magnetic. Accordingly, these studies concluded that magnetic investigation of synthetic diamond gemstones was not useful for identification. They further state that they foresaw difficulties in separating natural from synthetic colorless diamonds using any other conventional gemological technique.
In addition, various techniques have been used to determine the content of magnetic compounds such as magnetite and pyrhotite in ore samples. For example, U.S. Pat. No. 3,808,524 (Tarassoff et al., “APPARATUS FOR DETERMINING THE AMOUNT OF MAGNETIC MATERIAL IN A SAMPLE”) discloses an apparatus that determines the amount of a magnetic compound in an ore sample by inserting the sample into a coil of an oscillator and detecting the change in the oscillating frequency of the oscillator.
Conventional teachings in the synthetic diamond art indicate that synthetic diamond screening tests based on magnetic qualities of the diamonds are inadequate. Thus, these teachings suggest that methods such as those disclosed in Tarassoff would probably be ineffective. Accordingly, a need exists for a relatively easy to use and inexpensive method and apparatus for distinguishing between synthetic diamonds and natural diamonds.
SUMMARY OF THE INVENTION AND OBJECTS
In general, it is an object of the present invention to provide a method and apparatus for distinguishing synthetic diamonds from natural diamonds which will overcome the above limitations and disadvantages.
It is a further object of the invention to provide a method and apparatus of the above character based on a test for magnetic susceptibility of the stone.
It is known that natural diamonds exhibit very little if any magnetic behavior which could form the basis of their evaluation. However, synthetic diamonds have been found to contain magnetic inclusions inherent from the process from which they are made. Even though these inclusions can be quite small they are nevertheless found to exist in all synthetic diamonds that have been investigated whether or not detectable by the gross magnetic attraction methods mentioned in the literature. Even the clearest of synthetic stones contain ferrous material presumably more evenly distributed at the molecular level.
The present invention is based upon the realization that, contrary to conventional teachings in the synthetic diamond art, synthetic diamonds can be distinguished from natural diamonds by testing the magnetic properties of the diamonds. Specifically, trace amounts of iron are detected in synthetic diamonds using sufficiently sensitive instruments capable of detecting the effect the trace amounts of iron have on a magnetic field.
In a first embodiment, the present invention is predicated upon the realization that, given a suitably sensitive and appropriate instrumentation, it is possible to screen synthetic diamond gemstone from natural diamond gemstones by placing the stone under test into the core of an inductance in a linear oscillator circuit in which the magnetic character of the synthetic diamond changes the inductance and affects the frequency of the oscillating circuit in a way that a difference count can be obtained over a precisely repeatable interval for the condition of no sample present, compared to that when the sample is present, by an extremely sensitive but stable counting circuit. It is found that a reliable screening method can be based on this concept.
Generally, the invention provides a counter for measuring or counting transitions of an oscillator having an inductor in a frequency determining circuit. The inductor is in at least in part air cored, being wound around a core form having an opening therein for admitting a sample into the inductor core for testing. The method calls for upcounting the oscillations of the oscillator over a precisely repeatable time interval with no sample present and thereafter selectively placing an unknown sample diamond stone into coupled proximity or within the core of the inductor to change the oscillator frequency by an amount related to the ferromagnetic material contained therein. At that point the system is signaled to down-count the oscillations, subtracting the same from the up-count over a second time interval precisely equal to the first interval. The difference in counts is determined and displayed on a digital readout as a measure of the degree of likelihood that the sample under test is synthetic.
In a second embodiment, the diamond sample is positioned near a coil of a tuned circuit. When the diamond sample is a synthetic diamond, the iron in the diamond sample alters the parameters of the coil (e.g., the “Q” of the coil) which, in turn, changes the amplitude of the output signal of the tuned circuit. The change in amplitude is detected and displayed to indicate the degree of likelihood that the sample under test is synthetic.
The second embodiment typically provides an even more sensitive screening device than the first embodiment. First, the second embodiment uses a fixed frequency oscillator. As a result, its sensitivity is not affected by frequency drift as much as the first embodiment. Second, using tuned circuits and a differential amplifier, this embodiment can detect very small changes in the Q of the coil. Consequently, this embodiment provides a very sensitive screening apparatus.
In a third embodiment, the diamond sample is moved within a magnetic field. When the diamond sample is a synthetic diamond, iron inclusions within the diamond disturb the magnetic field. This disturbance generates a signal that is detected by the screening apparatus. This signal is amplified and processed to generate a display indicating the degree of likelihood that the sample under test is synthetic.
Typically, this embodiment provides an even more sensitive screening device than the
Matthews Marion
Perry Charles R.
Chrisie, Parker & Hale, LLP
Matthews Marion
Patidar Jay
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