(11255 Geonics Brochure rev)

1 EM61-MK2 EM61 SMETAL DETECTORSEM61-MK2 EM61 SGEONICS LIMITEDEM61-MK2 Metal DetectorThe EM61-MK2 Metal Detector provides multiple measure-ments of the decay of the secondary magnetic field associ-ated with any metallic object. Data available from as many asfour time gates geometrically spaced in time from 216 sto1,266 s provide recognizable improvements in both detectionand earlier time gates available with the EM61-MK2 improve thedetection of smaller targets most significantly. The decay rate of thesecondary field associated with smaller targets is relatively quick;measurements at early times, therefore, are required to ensure thedetection of secondary magnetic field response that may not beavailable at later an example, a 20 mm projectile (ordnance item), oriented hori-zontally, is not detectable with the original EM61; comparatively, theearliest gate of the EM61-MK2 can detect the same target at adepth of 8 cm (3 in.)

2 Below surface. A 20 mm cartridge, oriented hori-zontally, detectable at 3 cm (1 in.) with the EM61, can be detectedTowed ArraysFor a substantial increase in productivity, particularly overlarger areas, multiple EM61-MK2 (or EM61) systems can beconfigured as a single array, to be towed behind a collection is supported by the DAS70-ML DataAcquisition System that can receive data from as many as sixindividual inputs simultaneously. With a maximum data collec-tion rate of 30 records (total) per second, travel speeds up to10 kilometers/hr are EM61-MK2 Metal Detector is a high power, high sensi-tivity metal detector suitable for applications in the detec-tion of both ferrous and non-ferrous on the design principles of time domain electromagnetics,each system includes a single transmitter coil and two receivercoils.

3 A primary magnetic field, generated by current supplied to thetransmitter coil, induces eddy currents in nearby metallic induced eddy currents decay with time at a rate that is depen-dent on the characteristics of the object producing a secondarymagnetic field with the same rate of decay. The time-decay of thesecondary magnetic field generates a signal within each of the tworeceiver coils, thereby confirming the presence of Domain Metal DetectionCommon applications, in several fields of geophysical practice,include the detection of environmental hazards such as drumsand underground storage tanks; utilities and infrastructure;construction and industrial waste; and, unexploded ordnance(UXO).

4 Recent advances in design and application have enhancedsystem performance since the successful introduction of the orig-inal EM61 Metal Detector. Providing greater functionality andenhanced detection within a wider range of operating environ-ments, the EM61-MK2 represents a superior choice for applica-tions in the detection of buried a depth of 38 cm (15 in.) with the EM61-MK2. (The same 20 mmcartridge is detectable at 68 cm (27 in.) when oriented vertically.)Additionally, the early gates of the EM61-MK2 provide an increase inthe response amplitude from any target, regardless of size, of two tofive times the response from the original EM61.

5 As a result, the depthat which any target can be detected is increased (see Figure 1).A mid-range time gate is included to provide a response equivalentto the original EM61. Data from the mid-range gate allows for acomparison with, and/or the continuation of data sets generatedwith the original late time gate provides further description of the time-decay associated with any target information for the development of an apparent time-constant to be associated with each target. Theapparent time-constant data normalizes the complete time-decay toa single number.

6 With the assumption that a unique apparent time-constant is associated with any target type, a simple level of discrim-ination becomes data can be easily integrated with GPS data with support from theDAS70 Data Acquisition System (see facing page) and an optionalGPS antenna addition to many new features, the EM61-MK2 continues toprovide the valuable benefits of features introduced with the originalEM61, including a calculation of the differential data to reduce orremove the effects of noise associated with surface and near-surface metal and a calculation of the apparent depth to the Below Surface (cm)100150200250 Outside Diameter LengthSteel PipesEM61 EM61-MK21 in 5 m2 in 5 m4 in 5 m8 in 4 mFigure 1.

7 Depth of Detection for Steel PipesDAS70 Data Acquisition SystemData collection and management with theEM61-MK2 is supported by the DAS70 Data Acquisition System, including theAllegro field computer as the principlecomponent. A simple nulling algorithm andreal-time graphic display of the data offerimprovements in data review and qualitycontrol. A 486 AMD, 100 MHz processorprovides for rapid data collection rates, toa maximum of 16 records per capacity data storage (24 MB) allowsfor extended periods of data collectionwithout , and importantly, the Allegroincludes two RS-232 serial input connec-tions (and a user-accessible PC card slot)that facilitate the simultaneous collection ofboth EM and GPS data into a single datafile.

8 An optional Trimble Ag114 GPS,providing sub-metre accuracy, is available tosupport the requirement for position (AirBorne)With the recent development of the EM61-AB, a prototype configuration is now avail-able to address the requirements for large-scale reconnaissance of properties conta-minated with unexploded a single, large transmitterloop with any of several possible receivercoil configurations, system componentscan be designed to optimize 3 4 5 6 70 1 2 3 4 5 Depth Below Surface (m)

9 Relative Response1 101 101 101 101 10EM61-MK2EM61-MK2HP1In addition to the standard configuration of the EM61-MK2, several modifications and variations areavailable to accommodate a broader range of (Hand-Held)The EM61-HH is a hand-held complementto the EM61-MK2, available as either acomplete system or an attachment only. Witha smaller coil configuration, several benefitsare provided including, an increase in spatialresolution; decreased sensitivity to culturalnoise (creating the opportunity for applica-tions indoors); and, improved access to areasof difficult terrain and/or dense components available for theEM61-HH include a second receiver coil for the determination of both differential data and an apparent depth to target anda GPS antenna 2: Relative Response with DepthHigh Power (HP) ModificationTo increase the depth at which any target isdetectable, the high power (HP) modificationprovides an eight fold increase in the amountof signal received by a standard transmittercoil, resulting in significant improvements inthe signal-to-noise ratio.

10 Relative to the stan-dard EM61-MK2 (or EM61), the depth ofdetection for any target will increase between45% and 80%, depending on target charac-teristics (see Figure 2).EM61S(Submersible)For operation in marine environments, theEM61S is a completely submersible coiland cable system capable of submersionto depths of more than 60 m. Available asan attachment to the standard EM61-MK2 (or EM61), the EM61S includes asingle coincident transmitter / receivercoil, with cable, only; without the secondreceiver coil, calculations of differentialdata is not commonly, the EM61S is secured toa submersible platform that is positionedand operated at the bed , environmental or otherrestrictions will require that the platform isremoved some distance from the bedplane.