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Feasibility of Radio Frequency Based Wireless Sensing of Lead Contamination in Soil

Yixuan Gao, Tanvir Ahmed, Mikhail Mohammed, Zhongqi Cheng, Rajalakshmi Nandakumar

TL;DR

<3-5 sentence high-level summary> This work investigates a low-cost, portable RF-based approach to screening lead contamination in urban soils using SoilScanner, a multiband radio system. By leveraging frequency-dependent interactions of salts with RF signals, the authors differentiate Pb(NO3)2 from NaCl in lab-prepared soils and transfer the learning to field samples through a binary Pb threshold (200 ppm) with a 72% accuracy and 80% recall. The study introduces two salts-specific spectral metrics (Diff800 and Diff2300) and demonstrates a robust soft voting classifier trained on a small, augmented dataset, plus an open RF soil dataset. The results indicate feasibility for affordable in-situ Pb screening, with clear pathways and limitations identified for real-world deployment and chip-scale hardware development.

Abstract

Widespread Pb (lead) contamination of urban soil significantly impacts food safety and public health and hinders city greening efforts. However, most existing technologies for measuring Pb are labor-intensive and costly. In this study, we propose SoilScanner, a radio frequency-based wireless system that can detect Pb in soils. This is based on our discovery that the propagation of different frequency band radio signals is affected differently by different salts such as NaCl and Pb(NO3)2 in the soil. In a controlled experiment, manually adding NaCl and Pb(NO3)2 in clean soil, we demonstrated that different salts reflected signals at different frequencies in distinct patterns. In addition, we confirmed the finding using uncontrolled field samples with a machine learning model. Our experiment results show that SoilScanner can classify soil samples into low-Pb and high-Pb categories (threshold at 200 ppm) with an accuracy of 72%, with no sample with > 500 ppm of Pb being misclassified. The results of this study show that it is feasible to build portable and affordable Pb detection and screening devices based on wireless technology.

Feasibility of Radio Frequency Based Wireless Sensing of Lead Contamination in Soil

TL;DR

<3-5 sentence high-level summary> This work investigates a low-cost, portable RF-based approach to screening lead contamination in urban soils using SoilScanner, a multiband radio system. By leveraging frequency-dependent interactions of salts with RF signals, the authors differentiate Pb(NO3)2 from NaCl in lab-prepared soils and transfer the learning to field samples through a binary Pb threshold (200 ppm) with a 72% accuracy and 80% recall. The study introduces two salts-specific spectral metrics (Diff800 and Diff2300) and demonstrates a robust soft voting classifier trained on a small, augmented dataset, plus an open RF soil dataset. The results indicate feasibility for affordable in-situ Pb screening, with clear pathways and limitations identified for real-world deployment and chip-scale hardware development.

Abstract

Widespread Pb (lead) contamination of urban soil significantly impacts food safety and public health and hinders city greening efforts. However, most existing technologies for measuring Pb are labor-intensive and costly. In this study, we propose SoilScanner, a radio frequency-based wireless system that can detect Pb in soils. This is based on our discovery that the propagation of different frequency band radio signals is affected differently by different salts such as NaCl and Pb(NO3)2 in the soil. In a controlled experiment, manually adding NaCl and Pb(NO3)2 in clean soil, we demonstrated that different salts reflected signals at different frequencies in distinct patterns. In addition, we confirmed the finding using uncontrolled field samples with a machine learning model. Our experiment results show that SoilScanner can classify soil samples into low-Pb and high-Pb categories (threshold at 200 ppm) with an accuracy of 72%, with no sample with > 500 ppm of Pb being misclassified. The results of this study show that it is feasible to build portable and affordable Pb detection and screening devices based on wireless technology.

Paper Structure

This paper contains 35 sections, 6 equations, 12 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Related Work
  3. Background
  4. RF signal propagation
  5. RF-Signal propagation in soil
  6. Design
  7. RF signal affected by different soil salts
  8. Learning algorithm for lab prepared controlled soil samples
  9. Learning algorithm for uncontrolled field samples
  10. Feature Engineering
  11. Train-test-split
  12. Data Augmentation for Training Data
  13. Model Training
  14. Implementation
  15. Hardware
  16. ...and 20 more sections

Figures (12)

  • Figure 1: Flow chart of SoilScanner.
  • Figure 2: USRP setup.
  • Figure 3: Location dependency test.
  • Figure 4: Remounting test.
  • Figure 5: Received signal power (in dBm) variation with testing frequency a) 700-1000MHz, b)2300-2500MHz. Different colors represent different samples with varying Pb(No3)2 contents. c) is a zoomed-in view of b).
  • ...and 7 more figures