Terahertz Torching

Abstract

Close collaboration between the Bioelectronics department at Delft University of Technology and the Neuroscience department at the Erasmus Medical Centre has resulted in a successful tethered design for a real-time epileptic seizure detection and suppression method for mice. The goal of the Neuromate project is to develop this method into a wireless setup containing group-housed freely moving and interacting mice for use in behavioural studies. The system will include continuous monitoring and stimulation at set points in time. The Neuromate project comprises three links, two of which have previously been established.

The main goal of this study was to find and evaluate a technique to complement the current Neuromate project with a wireless downlink, channelling the communication from the researchers towards the mice.

This new downlink should fit in the ongoing project and meet particular specifications. The most critical requirements are that it should be lightweight and small-scale and should allow simultaneous multi-user communication. Also crucial are the prevention of interference with the two other links, reliability and low power consumption. The three most promising techniques, power source keying, optical wireless transmission and terahertz torching are elaborated.

Terahertz (THz) torching, covering the high thermal part of the THz band (10 to 100 THz), was chosen as the technique to be developed in this thesis. This decision was based on the fundamental limitations of power source keying and optical wireless transmission, which appear in the weighted criteria evaluation of the requirements. The challenges of THz torching are mainly practical, while fundamentally it provides the opportunity to form a reliable non-interfering wireless link. The feasibility of THz torching for our specific application was tested by creating a proof-of-principle and conducting five different experiments.

The prototype includes two components. The first is a thermal source, which in the final design will be placed above the cage, and the second is a pyroelectric detector, which will later be positioned on top of the head module of each of the mice. During the experiments, communication with the recently developed THz torch was proven to be feasible. Experiment 1 resulted in an optimum data rate of 35.71 bps, allowing for the simultaneous stimulation of the mice. And the divergence of the source was sufficient to cover the entire cage, as it was found in experiment 3 that an angle of 50° was the maximum misalignment still allowing reliable transfer of the data. However, the prototype did fail to reach the required distance. In experiment 2 only 8 cm could reliably be bridged. The source was not strong enough to overcome the attenuation in the air. A more powerful source will allow an increased reachable distance, making sure the entire cage is covered.

In this work, an innovative and promising proof-of-concept has been realized for the wireless downlink of the Neuromate project.