- Jan 23
- 3 min read

The FindMine Metal Detector goes from Research into Development

January 2024 | Metal Detector

In 2019 the Urs Endress Foundation started research activities with the aim of having its own UAV-compatible metal detector.

The research partner University of Applied Sciences Ulm has done a very good job, and realized and evaluated a system demonstrator in 2023.

The realized system is a continuous-wave (CW) differential metal detector with two operating frequencies, to be able to distinguish good or less conductive metals. The CW approach was chosen for better compatibility with the sensor-pod electronics, which are already in use in the FM ground penetrating synthetic aperture radar system (GPSAR). Another advantage of the CW approach is less EMC problems with the UAV and the sensor-pod electronics compared to a pulsed system. This is important concerning the UAV-payload which does not allows much room for heavy and big shielding measures.

A highlight of the FM metal detector is its multilayer PCB-based sensor head (Fig. 1a). It consists of stacked planar coils allowing different measurement modes. The planar coils are less sensitive to UAV-vibrations than wired coils and they are easier to adjust. In the present realization the adjustment can be done by pluggable jumper rows. The electronics of the metal detector is a stack of boards (Fig. 1b). The transmitter power amplifier and the microcontroller module are commercial of the shelf PCBs, the analog receiver and the embedded software are FindMine proprietary designs.

Fig. 1a: Photograph of the metal detector multilayer PCB-sensor. On top is the interface to the electronics. Mechanical fixtures must be done with plastic screws. In the middle of the coil-PCB there are six jumper rows for coil adjustments.

Fig. 1b: Photograph of the metal detector electronics. On top is the FindMine 3-channel analog receiver board. Bottom of the stack is the power amplifier. In between are microcontroller and power supply boards.

The system was tested in a rover platform on our test-field in Portugal in summer 2023 and was successful in a blind test with various APM and AVM dummies. As for the APM dummies, even low metal VS50 simulants could be detected.

The PCB sensor was operated 10cm above ground and the dummies had been buried in typical depths of 5cm for APMs and 12cm for AVMs.

In Figure 2 the metal detectors output signals in dB are overlayed to an orthophoto of an area in our test field. We got a 100% detection rate with a few false alarms which we did not examine further. As the test field is close to a construction site, some additional metal scrap is likely to be in the ground.

Fig. 2: metal detectors output signals

Motivated from these tests the FindMine gGMbH has started insourcing the research results for further development and reproduction. Next important development step will be the integration of the metal detection system in the FM sensor-pod and then operating it from a special UAV.

Some typical technical data of the first demonstrator of the FM metal detector system are in the following table:

CW frequencies low/high:	1.7kHz / 17kHz
Electronic weight:	700g
Sensor weight, including cables.:	600g
Power consumption:	15W
Power supply:	18V – 24V from UAV
Data output (3 channels):	40Mbyte/h
Sensor size (width / length):	37cm / 27cm
Resolution direction width:	20cm
Resolution direction length:	15cm
Maximum speed:	0.5m/s
CW frequencies low/high:	1.7kHz / 17kHz
Maximum detection distance of a Vallon Minehound Flush (minimum metal APM simulant).	16cm
Maximum detection distance of a metal Ceia AVM simulant:	> 30cm

Due to physics, a metal detector must be very close to the objects to be detected. So, UAV operation needs a UAV with special low altitude flight capabilities. Uneven terrain, natural obstacles (stones, plants) extending from the ground and aerodynamic ground effects, restrict the speed of low-altitude UAV flights drastically. As a result, the area throughput of an UAV-carried metal detector is very low.

This is the main reason for the FM approach, using the UAV-carried metal detector system only punctually for sorting detections form search flights with the FM GPSAR system into false alarms and true positives.