Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-05-12
2001-07-24
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S693000, C324S722000, C324S071100
Reexamination Certificate
active
06265884
ABSTRACT:
BACKGROUND OF THE INVENTION
Diamonds have an allure unlike any other gemstone. Through the ages, they have been sought after for their characteristically brilliant qualities and have been the subject of great treasures. There is such high demand for the stones, even today, that considerable research is under way to produce synthetic gems.
Gemstones such as cubic zirconium and silicon carbide, also known as moissanite, have become increasingly popular because they are almost indistinguishable from real diamonds with the naked eye. As a result, the market is flooded with these synthetic look-alike gemstones. Unfortunately, some of these gemstones, significantly lower in value, are sold as natural diamonds to the dismay of many unknowing purchasers. To combat these fraudulent or mistaken sales, several techniques have been suggested to determine the authenticity of a diamond.
One technique involves a relatively complex x-ray test that takes several hours to perform. Unfortunately, the associated testing apparatus is costly and most jewelers are not equipped with the instrumentation required to perform the test. Another technique involves testing the hardness of the gemstone by scratching or otherwise marring the surface of the gem. Needless to say, this method of defacing a gem is highly undesirable because it negatively impacts the value of the gem and alternative nondestructive methods of testing are available today.
Alternative non-destructive test methods include testing the optical transmissivity and thermal characteristics of a gem to determine whether it is a real diamond. In particular, one optical method involves transmitting light waves through the gem under test and, thereafter, determining which wavelengths of the light source have been absorbed. Generally, diamonds reflect certain wavelengths of light while silicon carbide absorbs certain wavelengths of light. Unfortunately, determining the authenticity of a diamond based on this method is not failsafe because the transmissivity of some diamonds is effected by their cut and mass.
Another non-destructive method of determining the authenticity of a diamond involves testing the thermal conductivity of the gem. The test process includes heating a probe of known mass to a predetermined level and touching the probe to the gem under test. A thermistor in the probe is used to detect the dynamic change in probe temperature as the gem absorbs heat energy from the probe thereby reducing its temperature; i.e. the temperature of the probe gradually decreases depending on the rate at which heat is absorbed by the gem under test. Based on the rate of temperature change of the probe, the thermal conductivity of the diamond is determined and, thus, whether the gem under test is a real diamond. The thermal conductivity test is widely used to distinguish cubic zirconia and diamond, but silicon carbide has a thermal conductivity which is about equal to that of diamond, making the test impractical for those gemstones.
Electrical resistance measurements have been used to distinguish gems. In particular, some thermal testers have included a two electrode device for detecting when a thermal test probe is erroneously in contact with a metal, which has a thermal conductivity very similar to that of natural diamonds. This prevented an operator from falsely identifying a gemstone as diamond when, in fact, the measuring device was measuring the thermal conductivity of the metal instead of the gem. Occasionally, this low impedance detection circuit, when used correctly, could positively indicate that a gem under test was a member of a more conductive class of moissanite. The tester, however, was unsuccessful at identifying the balance of moissanite gems that were less conductive.
Since the value of a diamond is in part dependent upon its weight, it is not uncommon to increase its size and, therefore, apparent value, by depositing simulant diamond material on an uncut or partly cut natural diamond. This combination, namely real and imitation diamond, is particularly difficult to distinguish from a completely natural diamond because in some respects the imitation-natural stone has qualities of a natural diamond while in other respects the imitation-natural stone has the qualities of a synthetic stone.
SUMMARY OF THE INVENTION
Most electrical meters are unable to distinguish gem impedances because the impedances are typically well above 10 meg-ohms. Some classes of synthetic gems can be distinguished if they have a low enough impedance, but this is rare. Based on lower voltage measurement systems, moissanite and natural diamonds are practically indistinguishable because neither gem type conducts electricity at these lower measuring voltages.
The present invention provides an apparatus and method for determining a gem type based on its electrical conductivity. In particular, an electronic circuit including the gem under test as part of a circuit path is used to measure its electrical conductivity and, therefore, gem type.
Moissanite and synthetic diamonds are distinguishable from natural diamonds based on differing electrical conductivities. Natural diamond stones are virtually non-conductive whereas moissanite and synthetic diamonds are slightly conductive when a high voltage greater than a breakdown voltage, inducing a small current to flow, is applied across the surface of the gem under test. The resistivity of moissanite or a synthetic diamond exposed to a voltage above the breakdown voltage is typically between 1 and 2000 mega-ohms, which is very difficult to measure with state of the art measuring devices. The present invention addresses the onerous task of determining whether a gem is moissanite or synthetic by providing a high voltage across a gem surface, typically greater than 300 volts, and measuring a minuscule current that flows through the gem.
A high voltage, including a high impedance source, applied between a first and second electrode contacting the gem under test induces a current to flow through the gem to a return reference voltage such as ground. The amount of current flowing through the device is measured using, for example, a high impedance resistor referenced to ground. A voltage on the resistor, indicative of the current flowing through the gem, is measured and compared to a predetermined threshold voltage. Measurements above the threshold voltage indicate that the gem is conductive and that the gem, therefore, is a synthetic diamond or moissanite. Conversely, measurements below a threshold voltage indicate that practically no current flows through the gem and that the gem, therefore, may be a diamond if other tests such as a visual and thermal conductivity tests are positive.
In the preferred embodiment, the gem is part of a resistor divider circuit, where distinguishing audio and visual queues are used to alert an operator whether a gem positively tests to be moissanite or a synthetic diamond.
The present invention also addresses when the impedance between the electrodes is so low that a material disposed between the electrodes is not moissanite or a synthetic diamond stone. For instance, it is possible that the test electrodes are erroneously connected to each other directly through a gem mount or that the purported gem is made of conductive plastic.
In the preferred embodiment, the current through the electrodes is limited so that a person accidentally in contact with the electrodes neither feels a shock nor is harmed by the voltage at the electrodes. Typically, the maximum safe and undetectable current through a human disposed between the electrodes is 150 micro-amps. This current limiting feature also protects the gem from damage.
The gem under test is optionally tested in a number of ways. A first method involves contacting the two electrodes at two different points on the gem under test. A second method involves connecting one electrode, such as a clip, to a conductive setting of gem and contacting the second electrode to the surface of the gem under test to create a circuit path with the gem disposed between the fi
Barrett David
Bogdan Randolph M.
Duderwick Wayne
Menashi Solomon
Brown Glenn W.
Ceres Corporation
Hamilton Brook Smith & Reynolds P.C.
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