GEM-3 with a 40cm diameter disk
About the GEM-3
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GEM-3 is a broadband digital electromagnetic sensor
suitable for detecting buried metallic objects such as utilities,
unexploded ordnance (UXO), and landmines. It is light, portable, and
versatile. The basic unit weighs about 10 pounds (5kg). Since it is
completely digital, the sensor has the potential to be programmed in many
other operational modes.
GEM-3 with a 40cm diameter disk |
Through many field trials and surveys since it debuted in 1996, the GEM-3 has demonstrated some unique capabilities as summarized below:
| Detection
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In demonstrations at controlled test sites prepared by the US government, the GEM-3 routinely surpassed all other sensors. Optional audio output can facilitate realtime detection in rough and heavily vegetated areas. |
| Discrimination, Characterization, or Identification | Broadband EM data has demonstrated a strong potential for discriminating UXO or landmines from clutter based on Electromagnetic Induction Spectroscopy (EMIS). |
| Metal Detection in Magnetic Geology
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The GEM-3 quadrature components are relatively immune to magnetic soils or rocks. A sum of all quadrature components (the optional audio is based on this sum), therefore, is an excellent detection indicator. |
The GEM-3 sensor head contains three concentric coils. Two outer coils are used as a transmitter and the innermost one is used as a receiver coil. The two transmit coils creates a central magnetic cavity that produces zero output to the inner receiver coil. For a frequency-domain operation, the GEM-3 prompts for a set of desired transmitter frequencies. Built-in software converts this into a digital “bit-stream,” which is used to construct the desired transmitter waveform. This bit-stream represents the instruction on how to generate a complex waveform that contains all frequencies specified by the operator.
The principle of the GEM-3 operation is very similar to that of GEM-2; if you have further interest in learning how it works, please go to our GEM-2 page on this website.
Sensor Specifications
The basic GEM-3 Package consists of: a 64-cm diameter sensing head, handle boom, console and display unit, and battery charger. Standard software includes WinGEMv3, Windows-based operation software. The optional 96-cm head, due to its size, must be mounted on a cart.
| Programmable Operation | ||
| Bandwidth | 30 Hz to 24 kHz | |
| Frequency domain | Single, multiple, or stepping frequencies | |
| Maximum sampling rate | Approx. 15 Hz at one frequency or 8 Hz at 10 frequencies | |
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Hardware |
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| Removable sensor head | Sealed fiberglass, 64cm in diameter -standard; Options, 40cm or 96cm in diameter | |
| Console (CPU, display, etc) | 11cm x 17cm x 5cm anodized aluminum box (2.5 kg) | |
| Internal rechargeable battery | 13.2 VDC | |
| Coils configuration | Concentric | |
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Output |
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| Inphase and quadrature in ppm stored in the console; capacity is approx. 50,000 data points | ||
| The data are also available in realtime thru an RS232 port (“remote mode”) | ||
| Realtime digital display | ||
| Detection audio, representing the sum of all quadrature components - optional | ||
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Software and Operation Manual |
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| WinGEMv3 – Windows-based upload and data download through a PC | ||
| PPM to conductivity or permeability conversion programs - optional | ||
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GEM-3 Hardware Options |
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| 40cm or 96cm diameter sensing heads | ||
| 96-cm diameter head mounted on a 2-wheel cart with GPS | ||
| Realtime detection audio output | ||
| GPS antenna mount assembly | ||
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GEM-3 Software Options |
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| Conversion of ppm data to conductivity and permeability | ||
| EMIS discrimination software | ||