About the GEM-3

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

 

 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

 

 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.

 

Sensor Specifications

 

The basic GEM-3 Package consists of a 40-cm diameter sensing head, handle boom, console and display unit, and battery charger. Standard software includes WinGEMv3, Windows-based operation software. The 96-cm head, due to its size, must be mounted on a cart.

 

Programmable Operation

Bandwidth                       30 Hz – 96 kHz

Frequency domain           10 frequencies typical

                                      Options -Single, or stepping frequencies

Sampling rate                  30 Hz

 

Hardware

Sensor head                   40cm diameter; Options, 30cm, 64cm, or 96cm in diameter

Console                          11cm x 17cm x 5cm anodized aluminum box (2.5 kg)

Rechargeable battery       12 VDC

 

Output

Inphase and quadrature in ppm at each frequency

Apparent conductivity at each frequency

Apparent magnetic susceptibility at lowest frequency used

Powerline amplitude

 

Software

WinGEMv3 – Windows-based upload and data download through a PC

PPM to conductivity or susceptibility conversion programs

Realtime detection audio output

 

Optional Software:           EMIS discrimination software

 

GEM-3 Data Examples

 

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