• Bluetooth
• Bluetooth security
• cybersecurity
• electromagnetic (EM) emissions
• electromagnetic shielding
• electromagnetic side-channel attacks (EM-SCAS)
• EM leakage mitigation
• information leakage protection
• metamaterials
• radio frequency (RF) shielding
• side-channel attacks
• wireless communication security

As wireless communication technologies continue to advance, so do the risks associated with Electromagnetic Side-Channel attacks (EM-SCAs), which exploit unintended electromagnetic (EM) emissions to extract sensitive information from electronic devices. Among the most vulnerable technologies are Bluetooth devices, which are widely used in both personal and industrial applications. This thesis focuses on characterizing the electromagnetic spectrum of a single Bluetooth device, more precisely a BT speaker, and developing a metamaterial-based shielding solution to mitigate EM leakage at specific frequencies, attempting to enhance device security against side-channel threats.
The first phase of this research involves the spectral characterization of Bluetooth emissions using a wideband measurement technique to analyze three different Bluetooth speakers' EM footprint in the frequency domain. These experiments are performed inside an anechoic chamber with the use of a simple loop antenna to capture EM emission. After this first assessment phase, a single device is used to carry on the rest of the research. Focusing on one specific speaker, reconstruction of the signal and identification of dominant frequency peaks is performed in order to pinpoint the critical frequencies where EM emissions are most pronounced, by measuring the signal and calculating the signal-to-noise ratio. The frequency-domain analysis allows to understand the spectral behavior of unintended EM emissions for this device and demonstrate that by using the wideband technique attackers can exploit them for side-channel attack, reconstructing the audio signal played by the speaker.
Based on these findings, the second phase of this thesis focuses on the design and implementation of a metamaterial-based shield to selectively attenuate EM radiation at the identified frequency peaks. Metamaterials are artificial structures engineered to exhibit electromagnetic properties not found in naturally occurring materials, allowing precise control over wave propagation, absorption, and reflection. In this study, Reconfigurable Intelligent Surfaces (RIS) are used, a class of metamaterials with adjustable properties, to enhance EM shielding effectiveness. The RIS-based shield is designed with programmable unit cells that can manipulate incident electromagnetic waves at the targeted frequencies. By carefully configuring the metasurface structure, we achieve selective absorption and reflection of Bluetooth emissions without significantly impacting overall device performance. This approach allows for precise frequency-selective attenuation, ensuring that only unintended EM emissions are suppressed while maintaining BT functionality efficiency.
Before proceeding with the experimental validation, a simulation phase is conducted to design and optimize the metamaterial shielding solution to mitigate unintended EM emissions. The simulations focus on modeling the interaction between EM emissions and the Reconfigurable Intelligent Surface (RIS)-based metamaterial to assess its effectiveness in attenuating specific frequency peaks identified during the spectral characterization phase. Using electromagnetic field simulation tools, different metamaterial unit cells configurations are tested to evaluate their ability to absorb, reflect, or redirect EM waves at the targeted frequencies without introducing excessive losses or distortions that could affect Bluetooth functionality. The simulation phase also allows for fine-tuning of the unit cell design, optimizing the resonance characteristics of the metamaterial to ensure selective suppression of emissions, and selecting the most effective design before fabrication. These simulation results provided critical insights into the expected shielding performance, guiding the development of the physical prototype and ensuring that the experimental measurements would align with theoretical predictions.
The final experimental phase is conducted under the same laboratory conditions as the spectral characterization measurements to ensure consistency and comparability of results. The prototype metamaterial shield is placed around the Bluetooth device to assess its effectiveness in attenuating EM emissions at the identified critical frequencies. Initial measurements show that while the shielding provides some attenuation, unexpected resonances and minor frequency shifts require adjustments to the metasurface design. After these refinements, further measurements confirm that the revised prototype successfully suppresses unintended emissions at the targeted frequencies, achieving the desired shielding effect. The results demonstrate that the RIS-based metamaterial solution effectively reduces EM leakage without significantly affecting Bluetooth functionality, validating the approach as a practical and adaptable countermeasure against electromagnetic side-channel attacks.
This research provides a novel and practical countermeasure for mitigating EM-SCAs, contributing to the broader field of wireless communication security. The findings highlight the importance of spectrum-aware security solutions and the potential of RIS-based metamaterials as a viable electromagnetic shielding technology. By bridging spectral analysis techniques with advanced material science, this study offers a new approach to safeguarding Bluetooth-enabled devices against emerging EM threats, ensuring both security and operational reliability.