1

Design and Development of an NQR-based

explosive detection system for humanitarian demining

Y. Otagaki, P. Farantatos, W. Rafique

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Outline

• Introduction to ACRA project

• Technology overview

• Integrated system specifications

• Principle of NQR

• Portable system

• Interference cancellation

• Conclusion

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1. Develop an NQR-based anti-vehicle mine (AVM) detector suitable for use and production in the humanitarian context 2. Develop methodology for using dialogue and data to direct NQR demining activities for maximum positive impact in the minimum possible time

Project - A Clear Road Ahead

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ACRA Team

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ACRA team at the Symposium

Dr Sarah Njeri Working in the African Leadership centre at King’s College London. Currently looking into the peace-building aspect of humanitarian demining

Dr Jamie Barras Working in the department of Informatics at King’s College London. He is the technical lead in the KCL NQR group.

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Mine Detection Technologies Overview

P. Farantatos

Method Range Cost ($) Problems

Metal detector <20 cm <5000 False alarms

Ground Penetrating Radar (GPR) <1 m <10000 False alarms, not for clay soil

Odor ~ cm <10000 Not sensitive enough, wind influence

Nuclear Quadrupole Resonance (NQR) ~ cm >10000 Weak signals

Nuclear Quadrupole Resonance (NQR):

• 14N (found in explosive materials: TNT, RDX) is particularly sensitive to NQR

• Detection specific to the explosive material, not the casing

• Current R&D focus on ameliorating detection strength

Detects explosive content

Detects … metal

Detects large underground anomalies

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NQR Detection System - Requirements

P. Farantatos

• Functional Requirements: Humanitarian Demining Setting

• Low-cost • Portability • Rugged design • Easy to assemble • Low-resource setting adaptable

• Engineering Requirements

• Low power consumption • Off-the-shelf components • Reproducible open-source design • Simple manufacturing specifications • Low-weight

• General technical Specifications for NQR-based explosives detection

• RF power driving circuit • Probe sensor transceiver • DSP RF noise cancellation

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NQR Detection System – Hardware Specs

P. Farantatos

Power Supply

Power Amplifier Spectrometer Probe Circuit Coil

Component Spec Engineering Requirements’ Conformance

Power Supply 12V batteries Low-cost, off-the-shelf available

Spectrometer FPGA-based Low-cost, small size, low-weight

Power Amplifier Class-D In-house design, >90% efficiency, small size, low power consumption, low-weight, low-cost open-source design

Coil Magnetic Loop Antenna Negligible material costs, simplified construction, low-weight, easily reproducible, high efficiency

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Coil Sensor: Electrically-Small Loop Antenna

P. Farantatos

Features Benefits

Hollow copper tube Negligible costs, easy DIY construction, high efficiency

Near-field operation Behaves as magnetic field probe

Diameter dimension Proportional to Anti-Vehicle Landmine size

Plastic encapsulation Suitable for durable operation on-the-field, configurable as an on-the-ground “mat” sensor

(Y. Sotiriou, 2018)

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Resonance freq≠Resonance freq

Ex. sound

Tuning fork

Resonance

11 11

Resonance freq≠Resonance freq

Ex. sound

Tuning fork

Resonance

12

Resonance freq≠Resonance freq

Ex. sound

Tuning fork

Resonance freq=Resonance freq

Resonance

13

Resonance freq≠Resonance freq

Ex. sound

Tuning fork

Resonance freq=Resonance freq

Absorb

Resonance

14

Resonance freq≠Resonance freq

Ex. sound

Tuning fork

Resonance freq=Resonance freq

Absorb Emit

Resonance

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Proton Neutron

AC magnetic

field

Nuclear

AC magnetic

field

Particular frequency

QR (Quadrupole resonance)

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NQR control unit

Transmitter receiver

unit

10 cm

Antenna

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FPGA

Receiver I-V

amplifier

AD

converter Post

amplifier

Cs

Cs’

Cp

Class-D amplifier

NQR control unit Transmitter receiver

unit Antenna

TR switch

Q switch

Power

supply

18

FPGA

Receiver I-V

amplifier

AD

converter Post

amplifier

Cs

Cs’

Cp

Class-D amplifier

NQR control unit Transmitter receiver

unit Antenna

TR switch

Q switch

Power

supply

Transmission pulse

19

FPGA

Receiver I-V

amplifier

AD

converter Post

amplifier

Cs

Cs’

Cp

Class-D amplifier

NQR control unit Transmitter receiver

unit Antenna

TR switch

Q switch

Power

supply

Transmission pulse

20

FPGA

Receiver I-V

amplifier

AD

converter Post

amplifier

Cs

Cs’

Cp

Class-D amplifier

NQR control unit Transmitter receiver

unit Antenna

TR switch

Q switch

Power

supply

Transmission pulse

21

FPGA

Receiver I-V

amplifier

AD

converter Post

amplifier

Cs

Cs’

Cp

Class-D amplifier

NQR control unit Transmitter receiver

unit Antenna

TR switch

Q switch

Power

supply

Transmission pulse

Sample

22

FPGA

Receiver I-V

amplifier

AD

converter Post

amplifier

Cs

Cs’

Cp

Class-D amplifier

NQR control unit Transmitter receiver

unit Antenna

TR switch

Q switch

Power

supply

Transmission pulse

NQR

signal

Sample

23

FPGA

Receiver I-V

amplifier

AD

converter Post

amplifier

Cs

Cs’

Cp

Class-D amplifier

NQR control unit Transmitter receiver

unit Antenna

TR switch

Q switch

Power

supply

Transmission pulse

NQR

signal

Sample

24

FPGA

Receiver I-V

amplifier

AD

converter Post

amplifier

Cs

Cs’

Cp

Class-D amplifier

NQR control unit Transmitter receiver

unit Antenna

TR switch

Q switch

Power

supply

Transmission pulse

NQR

signal

Sample

25

Where we were

35 kg

Mains powered

£35,000

Where we are

1 kg

Portable battery

£1,000

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Previous control unit

New control unit with a power

amplifier

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Control board

DE0-Nano Development and Education Board

(Altera corp.)

$79

Size：49*75.2mm

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Class D amp

(Z~1 ) Commercial amp

(Z=50 )

Power amplifier

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Class D amp

(Z~1 ) Commercial amp

(Z=50 )

x 1/10

Power amplifier

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Field test at Columbia

System for Ammonium nitrite

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• In NQR signal detection, interference can be a major hurdle in detecting the NQR from the signal of interest.

• Interference can be caused by several factors such as impurities in the NQR sample, due to detection hardware or the background environment.

• Main cause of the interference are signals due to radio transmission in the outdoor environment and it is difficult to shield against at it.

Interference Problem in NQR

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• In order to cancel the interference, we first divide the data into small parts, with each part containing a single echo, and then we performs interference cancellation for each part separately.

• It is done by setting a fixed threshold value which equals to twice the value of the average threshold spectrum intensity.

• This cancels all the interference frequency components whose spectrum intensities are higher than the threshold.

Interference Cancellation in NQR Signal

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Results for Interference Cancellation

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THANK YOU FOR YOUR ATTENTION!