Apparatus and process for detecting man-made gemstones

An apparatus and process for detecting man-made gemstones using an alternating current conducted through a sample gemstone is provided. The apparatus includes a hand-held housing in which is disposed electronic circuitry, a probe which extends from the housing, and a transmitting stimulus electrode in the form of a body-contact touchpad. The electronic circuitry includes a filter for eliminating non-transmitted signals sensed by the probe, and produces an alternating current signal, preferably in sine wave form, for delivery to the touchpad. The alternating current signal is transmitted through the operator of the apparatus into the sample gemstone. The operator probes the gemstone by touching the conductive probe to the gemstone in an attempt to sense signals conducted through the gemstone. An alarm is activated upon the detection of the conducted transmitted signal, indicating that the gemstone is man-made.

BACKGROUND OF THE INVENTION 
This present invention relates to the diamond and jewelry industry and is 
directed to the need for a means of easily and rapidly identifying 
man-made gemstone simulants. 
Many types of simulated diamonds have been created and are cut to resemble 
diamond for many reasons. The most common of these simulants have been 
cubic zirconia, synthetic colorless sapphire, yttrium aluminum garnet 
(YAG), gadolinium gallium garnet (GGG), synthetic spinel, synthetic rutile 
and strontium titanate. Although most are for legitimate use in low priced 
jewelry applications, unfortunately, some are used for fraudulent 
purposes. 
Although most of these simulants are readily detected by persons who have 
been trained to recognize physical properties such as the refractive 
index, dispersion of light, hardness and other qualities of the gemstone 
which differentiate these materials from genuine natural diamond, lay 
people are easily fooled by these simulants. Until recently, one of the 
most effective means of detecting simulants was to use a device which 
could measure the relative thermal conductivity of the simulant materials 
and compare this property to that of natural diamond. These devices depend 
upon the fact that diamond conducts heat more rapidly than any of the 
above materials being cut to resemble diamond. 
However, there are other simulants which conduct heat in a similar manner 
as natural diamond. One of these simulant materials is colorless or 
near-colorless synthetic diamond grown with the preferred nickel catalyst 
method. A more recently developed diamond simulant is synthetic moissanite 
(silicon carbide) which has very similar physical properties as natural 
diamond. A thermal testing of synthetic moissanite or colorless synthetic 
diamond will test positive as natural diamond. Additionally, although 
there are differences in hardness, specific gravity, refractive index and 
dispersion between natural diamond and moissanite, due to the oftentimes 
only slight differences in these physical properties even trained 
professionals have difficulty distinguishing between the two. 
Research into the properties of silicon carbide (moissanite) revealed that 
it was being used in semi-conductor applications which led to the 
conclusion that differences in resistivity and/or electrical conductance 
could be detected in the silicon carbide material which could be used as a 
distinguishing characteristic between natural diamond, with the exception 
of a very rare type IIB blue diamond, and synthetic moissanite. 
Accordingly, devices have been produced which attempt to measure the 
conductivity of synthetic moissanite samples. Testing of moissanite 
samples further revealed that although silicon carbide was conductive in 
many cases, there are also samples which are only semi-conductive. 
Furthermore, the various facets of the moissanite gemstone and the 
semi-conductive portions of the gemstone create a diodic junction which 
allows direct current only through certain connecting points of the 
gemstone. Prior detection devices have utilized high voltage direct 
current (DC) signals in an attempt to stimulate and detect conductivity by 
exceeding the reverse breakdown voltage of these junctions. Due to the 
power requirements, these devices are commonly plugged into an external 
power source such as a wall outlet. Even with the increased voltage 
levels, prior moissanite detecting devices must thoroughly probe the 
gemstone to find conductive connecting points. These points can be quite 
difficult to find in semi-conductive gemstones, and if not found the 
tester falsely determines the moissanite sample to be natural diamond. 
It has been observed through experimentation that certain man-made 
gemstones, such as moissanite, exhibit diode-like characteristics when 
tested with metal probes, and that those characteristics vary in both 
degree and polarity from sample to sample. It is therefore desirable to 
employ an alternating current through the gemstone sample to maximize the 
likelihood of detecting conductive points on such samples. 
Therefore, what is needed is a detector for man-made gemstones which can be 
used to detect synthetic gemstones which cannot be detected by heat 
conductivity devices. What is also needed is a detector which is 
unaffected by the diodic effect of man-made gemstones and is able to 
detect conductivity in conductive and semi-conductive gemstones. Further, 
a detector is needed which is small, uncomplicated and battery powered. 
The present invention fulfills these needs and provides other related 
advantages. 
SUMMARY OF THE INVENTION 
The present invention resides in an apparatus and process for 
differentiating natural diamond from man-made gemstones using an 
alternating current conducted through a sample gemstone. The apparatus 
comprises, generally, an electrode which delivers an alternating current 
stimulus generated by electronic circuitry, and a probe conductively 
coupled to sensing electronic circuitry. 
In its preferred form, the apparatus comprises a hand-held housing in which 
is disposed the electronic circuitry and from which extends the probe and 
the transmitting stimulus electrode in the form of a body-contact 
touchpad. A power source, preferably in the form of a battery disposed 
within the housing, provides power for the electronic circuitry. The 
electronic circuitry includes a filter comprised of a transimpedance 
amplifier and a synchronous detector comprised of an 
inverting/non-inverting amplifier and a low-pass filter for eliminating 
non-transmitted signals sensed by the probe. The electronic circuitry also 
includes means for producing an alternating current sine wave stimulus 
signal. Upon detection of the transmitted signal, an audible or 
light-emitting diode alarm indicates to the user the presence of a 
man-made gemstone. 
In order to test a sample gemstone, an operator of the apparatus powers on 
the apparatus and holds the housing with at least a portion of the 
operator's body contacting the touchpad while holding the gemstone in the 
other hand and probes the gemstone by touching the probe of the apparatus 
to the surface of the gemstone. The electronic circuitry produces an 
alternating current signal in sine wave form and delivers this signal to 
the touchpad. A detector switching signal in phase with the alternating 
current signal as well as a direct current bias voltage are also created 
by the circuitry. The alternating current signal is transmitted through 
the operator of the apparatus touching the touchpad and into the sample 
gemstone. 
The operator probes the gemstone by touching the conductive probe to the 
gemstone in an attempt to sense signals conducted through the gemstone. 
When a signal is sensed by the probe, the electronic circuitry utilizes a 
filter to determine whether the sensed signal is the transmitted signal or 
a non-transmitted signal, such as noise or capacitively coupled signals. 
Detecting and filtering the signal is accomplished by chopping a portion 
of any ninety degree shifted, capacitively coupled sensed signal, 
comparing the phase of the sensed signal with the detector switching 
signal, rectifying the signal into a direct current, and measuring an 
increase in voltage over the bias voltage which has been superimposed on 
the sensed signal. When the circuitry determines that the transmitted 
signal has been conducted through the gemstone, an alarm is activated to 
notify the user that the sample gemstone has conducted the transmitted 
signal and that the sample gemstone is not diamond. 
Other features and advantages of the present invention will become apparent 
from the following more detailed description, taken in conjunction with 
the accompanying drawings which illustrate, by way of example, the 
principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In accordance with the invention, a detecting apparatus, generally referred 
to by the reference number 10, is provided for distinguishing between 
natural diamonds and man-made simulents, including moissanite. The 
apparatus 10 comprises a hand-held housing 12 in which is disposed 
electronic circuitry, a signal transmitting stimulus electrode in the form 
of a body-contact touchpad 14 extending through or on the surface of the 
housing 12, a conductive probe 16, and an alarm 18 (FIGS. 1-3). 
The conductive probe 16 is typically formed of a rigid conductive metal and 
may be coated with gold or other highly conductive metals to enhance its 
signal sensing abilities. The apparatus may be constructed such that the 
probe 16 is attached to a spring (not shown) which allows the probe 16 to 
partially retract into the housing 12 upon contact with a rigid surface so 
as to protect the metal probe 16 from being bent or broken while in use. 
The apparatus may also include a cap 20, as illustrated in FIG. 1, which 
removably attaches to the housing 12 and covers the probe 16, acting to 
protect the probe 16 when the apparatus is not in use. 
The stimulus electrode touchpad 14 is formed of any suitable conductive 
material which is comfortable to the operator's touch, such as small 
copper wires or a metal plate resting on the surface of the housing 12. 
The touchpad 14 is preferably located on either side of the housing 12 and 
is of such size that the operator of the apparatus 10 can easily grip it 
while in body contact with the touchpad 14. 
The alarm 18 may be any suitable audible or visual alarming device, but is 
preferably a red light-emitting diode. The housing 12 may also include a 
pocket-clip 22 for holding the apparatus 10 in the operator's pocket for 
easy retrieval. Although the apparatus 10 may be powered by an external 
source such as a wall socket through a plug 24 in the housing 12, the 
apparatus 10 can also be powered by a battery 26 disposed within the 
housing, as illustrated in FIG. 3, to allow the operator to freely 
transport the apparatus 10 without the concern for external power. The 
battery 26 is disposed within a battery compartment within the housing 12, 
and is normally enclosed by a cover 27. 
The process illustrated in FIGS. 4-6 are followed when a sample gemstone is 
to be tested. Preferably a green light-emitting diode 28 is lit when the 
apparatus 10 is powered on (block 30) to indicate that the apparatus 10 
has sufficient power. An alternating current is produced within the 
apparatus (block 32), and is conducted through the apparatus 10 and into 
the sample gemstone (block 34). The probe 16 is brought into contact with 
the gemstone (block 36) in an attempt to sense a signal (block 38). If no 
signal is sensed after probing the gemstone, the alarm is not activated 
and the operator knows that the gemstone is diamond, thus ending the 
process at block 40. However, if a signal is sensed, the electronic 
circuitry determines whether the sensed signal is the signal transmitted 
from the apparatus (block 42). If the signal is not the transmitted 
signal, nothing happens and the operator knows that the sample gemstone is 
most likely diamond as it is not conductive, and the process is ended at 
block 44. If the signal is determined to be the transmitted signal, the 
alarm is activated at block 46. 
FIG. 5, elaborates on the step of producing an AC signal as shown in block 
32 of FIG. 4. After powering on the apparatus 10, a bias voltage is 
created (block 48), a low voltage is created (block 50), and a high 
voltage is created (block 52). A sine wave oscillator converts the low 
voltage into an alternating current sine wave signal (block 54) which is 
amplified by the high voltage amplifier (block 56). 
Referring to FIG. 6, once a signal is sensed the following steps occur to 
determine whether the signal is the transmitted signal (block 42). The 
bias voltage is constantly applied to a transimpedance amplifier of the 
electronic circuitry (block 58). The sensed signal is converted to voltage 
and superimposed on the bias voltage at the transimpedance amplifier 
(block 60). A detector switching signal having an alternating current, 
typically in square wave, in phase with the transmitted signal is produced 
by a half-cycle comparator (block 62). It is a characteristic of 
capacitance that in the presence of an alternating current stimulus, the 
current through the capacitance leads the voltage across it in phase by 
ninety degrees, resulting in the sensing circuitry sensing non-transmitted 
signals such as harmonic noise and other capacitively coupled signals. 
Therefore, some stimulus will be coupled capacitively to the sensing probe 
due to the close proximity of the stimulus electrode and the probe. Thus, 
the circuit must differentiate between capacitively coupled signals and 
the transmitted signal conducted through the sample. To achieve this, a 
synchronous detection method is employed which is responsive to in-phase 
signals, while rejecting signals exhibiting the leading phase 
characteristic of capacitive coupling. Therefore, a capacitively coupled 
portion of the sensed signal is chopped off and the signal is compared to 
the detector switching signal (block 64) to determine whether or not the 
sensed signal is in phase with the detector switching signal (block 66). 
If the sensed signal is not in phase with the detector switching signal, 
the signal is determined to be noise or other capacitively coupled, 
non-transmitted signals 68 and nothing happens resulting in the end of the 
process (block 44) and the determination that the gemstone is most likely 
diamond as it is not conductive. However, if the sensed signal is 
determined to be the transmitted signal as it is in phase with the 
detector switching signal, the result is an increase in voltage detected 
by a comparator (block 70) which activates the alarm (block 46) indicating 
to the operator of the apparatus 10 that the gemstone is a man-made 
simulant. 
FIGS. 7 and 8 illustrate exemplary circuitry schematics which can be used 
to carry out the process described above. A power converter is illustrated 
in FIG. 7 and comprises a power source P1 having electrical contact points 
E1 and E2 and a ground. When the switch S1 turns the apparatus 10 on, 
power in the form of a direct voltage is sent through resistor R1, 
transistor Q1 and ground, and transformer T1. The battery voltage is 
stepped up to a higher voltage, typically up to 300 volts, by transformer 
T1, diode D1 and capacitor C1 and ground. The other portion of the initial 
voltage is regulated as it passes through diode D2, capacitor C2 and 
ground, voltage regulator U1 and turns on the green indicator light by 
passing through capacitor C3 and ground, light-emitting diode DS1 and 
resistor R2 and ground. The operating voltage +V is then supplied to 
oscillator U2, a transimpedance amplifier U3 and a comparator U4 coupled 
with capacitor C4 and ground for further processing. 
Referring specifically now to FIG. 8, the operating voltage +V is supplied 
to the oscillator U2A and U2B and corresponding resistors R3-7 and 
capacitors C5-7 which produces a low-voltage sine wave output at 
approximately 28 Hz. The low-voltage sine wave output is coupled to a 
high-voltage amplifier Q2 and corresponding resistors R9-14 and capacitor 
C8, which amplifies the alternating current sine wave and couples this 
resulting signal to the electrode touchpad. This operator contacts the 
touchpad with his or her body, which becomes a source of electrical 
stimulus to the sample gemstone under test. A comparator U4B and 
associated resistor R8 senses the oscillators instantaneous voltage and 
generates a high or low output corresponding to the positive or negative 
half-cycle, respectively, at the touchpad to create a signal in phase with 
the transmitted sine wave signal. This output signal from the comparator 
U4B controls the inverting/non-inverting amplifier U3B and associated 
transistor Q3, and resistors R20-22. 
A bias voltage is established using the supply voltage by a resistive 
divider comprised of resistors R15 and R17 and ground, variable resistor 
R18, capacitor C9 and ground, and buffer amplifier U2D. The bias voltage 
is typically one-half that of the supply voltage, but can be altered to 
raise or lower the sensitivity of the apparatus 10. The bias voltage is 
applied the transimpedance amplifier U3A and associated resistors R18 and 
R19, capacitor C10, and diode D3. Sensed signals are passed through the 
probe 16 and subsequently pass through the transimpedance amplifier U3A 
and associated components where the probe current is converted to a 
voltage which drives the inverting/non-inverting stage U3B, followed by 
the active low-pass filter U2C and associated resistors R23 and R24 and 
capacitors C11 and C12 and ground. 
The inverting/non-inverting stage U3B and the low-pass filter U2C form a 
synchronous detector, the output of which remains equal to the bias 
voltage under no-signal conditions. The leading-phase sine wave that 
appears at the transimpedance amplifier U3A output due to capacitive 
coupling is chopped to produce a signal at the output of the 
inverting/non-inverting stage U3B which has equal excursions above and 
below the direct current bias level, the average value as seen by the 
low-pass filter U2C being equal to the bias voltage level. Hum and other 
periodic noise are filtered out by the synchronous detector as they are 
not coherent with the detector switching signal and have no elevated 
direct current component after being rectified. 
On the other hand, when the probe signal is in-phase with the detector 
switching signal, the synchronous detector becomes essentially a full-wave 
rectifier, and the output of the low-pass filter U2C is a direct current 
voltage which is proportional to the amplitude of the in-phase signal, 
which is greater than the bias voltage. A threshold comparator U4A detects 
this increase in voltage and lights the light-emitting diode DS2 
associated with resistor R25 and capacitor C13 and ground, to indicate 
that the sample has conducted the transmitted signal and consequently the 
sample gemstone is a man-made simulant. 
The process and associate apparatus 10 of the present invention rejects 
signals with the leading phase characteristic common to noise and other 
non-transmitted signals, while accepting those signals with an in-phase, 
or the conducted transmitted signal, characteristic. This results 
improving the sensitivity of the apparatus 10. Due to the increase in 
sensitivity, not only are false positive results eliminated, but external 
power is not required and the apparatus 10 can be relatively small and 
battery powered enabling the operator to freely transport the apparatus 10 
within his or her pocket. 
Although a particular embodiment has been described in detail for purposes 
of illustration, various modifications may be made to each without 
departing from the scope and spirit of the invention. Accordingly, the 
invention is not to be limited, except as by the appended claims.