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Infrasound Junior Research Group

Working Group 1.02

Profile

In a joint initiative with the TU Braunschweig, PTB launched a junior research group to study infrasound. The group investigates the generation, propagation, and perception of low-frequency airborne and structure-borne sound.

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Research/Development

Infrasound Drone by Ramesh Raja Subramanyam

My research focuses on measuring low-frequency noise emitted by large power stations and wind turbines. In my doctoral project, I plan to use drones that allow for noise measurements at varying distances and altitudes. This approach aims to achieve more accurate measurements of low-frequency noise. However, since drones themselves are a source of noise, it is essential to filter or shield their noise from the measurement sensors. Therefore, one of the objectives of the work is to develop quiet drones that emit little to no noise in the low-frequency range. Once the quiet drones are developed, the measurement sensors will be mounted on them, and the drones will be used to measure noise radiation. Outdoor measurements are subject to uncertainties, as atmospheric conditions such as wind velocity and temperature can affect the results. Hence, my research includes an uncertainty analysis of atmospheric parameters, along with countermeasures to improve measurement accuracy. For instance, portable wind screens or wind filter arrays that dampen atmospheric noise in the low-frequency range will be developed and studied for their effectiveness. In quantifying uncertainties, the sensor and drone assembly must be calibrated for its signal-to-noise ratio. A reference infrasound noise source for outdoor measurements will be developed for this purpose.

Publications and Presentations
Subramanyam, R.; Castro Mota, R.; Picker, K.; Wittstock, V.; Jacob, S. "Experimental Low-Frequency Noise Characterization of an Octocopter Drone," AIAA 2024-3343. 30th AIAA/CEAS Aeroacoustics Conference (2024)
Subramanyam, R.; Castro Mota, R.; Jacob, S. A quarter wave infrasonic noise generator. Internoise 2024, Nates, France  (2024)
Can Drones Serve as Carriers for Acoustic Measurement Equipment? QuietDrones 2024, Manchester, United Kingdom (2024)

 

Sound propagation in atmospheric ducts by Rafael Castro-Mota

My research focuses on the propagation of low-frequency sound through the atmosphere. Low-frequency sound signals are only lightly damped in the atmosphere and can, therefore, travel over long distances. Certain atmospheric conditions, such as temperature inversions and winds, can bend acoustic waves and channel them along large "atmospheric ducts." These ducts concentrate sound energy, allowing acoustic signals to travel even further.

I am working to model these atmospheric ducts in order to create efficient noise prediction models. I am developing a specialized numerical approach that simplifies the acoustic field by representing it as a set of propagating acoustic modes. While this research is currently focused on computer simulations, it contributes to a crucial understanding of the physics of atmospheric wave propagation. This understanding will ultimately help develop measurement procedures to accurately determine the strength of low-frequency outdoor noise sources.

Publications and Presentations
Castro Mota, R.; Kirby, R.; Williams, P.; Jacob, S. Efficient modeling of atmospheric infrasound propagation with the Semi-Analytical-Finite-Element (SAFE) method. Internoise 2024, Nante France
Castro Mota, R.; Kirby, R.; Williams, P.; Jacob, S. Modelling Low-Frequency Sound Propagation in a Ducted Atmosphere Using a Semi-Analytic Finite Element Method, Acoustics 2024, Brisbane, Australia

 

Perception of low-frequency sound by Mohammad Mkanna

In my project, I investigate the human perception of low-frequency sound on a fundamental level, aiming to understand how these sounds are processed by the auditory system and the brain. To do this, I present specially designed acoustic stimuli to participants through highly calibrated microphones in our controlled acoustic labs. These stimuli are crafted to trigger the auditory system, and the neural responses that follow are processed by the brain—a process that we can measure and analyze using an electroencephalogram (EEG). We are particularly focused on understanding the brain’s reaction to signals that are at or below the typical threshold of hearing. These are sounds that humans may not consciously perceive, yet may still cause some form of brain activity. We explore the possibility that even sounds outside of conscious awareness can influence neural processes.

 

One of the major challenges in this research is that the EEG signals associated with sounds near or below the threshold of hearing are extremely weak, especially when compared to the vast array of other neural activities occurring in the brain at any given moment. As a result, a significant portion of my project is dedicated to the development and application of advanced data processing techniques. We apply modern, data-driven approaches to filter out noise and isolate the specific brain responses we are interested in. Through this, we aim to identify clear markers or indicators that will allow us to objectively measure the brain’s unconscious perception of low-frequency noise.

Publications and Presentations
Stefan Jacob, Christian Koch; Unveiling weak auditory evoked potentials using data-driven filtering. J. Acoust. Soc. Am. 1 October 2023

 

Infrasound Measurement Device by Criostoir Gerasch

My project involves designing, programming, and building a portable device that can accurately measure the level of infrasound noise in the immediate environment. Measuring infrasound requires specialized microphones, which are typically not portable and, therefore, cannot be used to capture infrasound exposure over extended periods. We address this issue by using modern micro-electromechanical system (MEMS) components, which are lightweight and energy-efficient. This allows our portable device to study daily infrasound exposure, for example, in people who live or work near large infrastructure that generates this noise.

The device is about the size of a modern smartphone and is battery-operated. It will continuously measure environmental noise and upload the data for accurate analysis. We take privacy seriously; the device is designed so that no personal data, such as speech, can be reconstructed from the recordings. The infrasound readings are time-stamped precisely and can be cross-checked with information provided by the device carrier to assess the effect of infrasound on the individual. Additionally, we are developing calibrators and defining precise calibration protocols for our devices to ensure trustworthy measurement results that can be used for further studies and conclusions.

Publications and Presentations
Gerasch, C.; Castro Mota, R.; Subramanyam, R.; Werhahn, O.; Brocard, R.; Jacob, S.; A Portable Dosimeter for Measuring Low-Frequency Noise Exposure. International Metrology Congress 2025, Lyon, France

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Information

Undergraduate Students
If you are interested in a Master or Bachelor thesis work, 
please contact Opens local program for sending emailstefan.jacob(at)ptb.de.

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