Testing XeThru capabilities: Signal Attenuation from building panels
At our Oslo office, we have lately been testing the XeThru capabilities and particularly its "see-through" feature; the XeThru technology founding principle. The purpose of this specific test was to investigate the signal attenuation of the XeThru module through different building materials.
The setup of the test consisted of placing an attenuation box which housed an occupancy sensor, on one side of a building material and an EmblaBot on the other side, exactly 1.5m away from each other. Three recordings were performed for each building material to eliminate any outliers and setup errors, following by three Line of Sight recordings. For accuracy sake, a camera was used to take a picture at each recording to confirm that both the XeThru sensor and the EmblaBot were stable in between recordings.
Figure 1: Sketch of measurement setup
A total of ten materials, all with different thickness levels were put to the test, ranging from the thinnest fiberboard (6mm) to the thickest brick wall (110mm). From the results in figure 2, we see that the 11mm drywall panel only attenuates the signal with 0.52dB which is a surprising result. Another interesting find is the attenuation through the masonry blocks compared to the brick wall. One possible reason why the masonry blocks attenuates about 5.3dB more than the brick wall, despite that the brick wall is 30mm thicker, might be that the signal has to propagate through several transitions of air and concrete compared to the brick wall. Hence, the signal experiences more spreading in the masonry blocks than through the brick wall. The percentage on top of each bar states the theoretical relative range reduction and needs to be checked with practical measurements in the future.
Figure 2: Signal attenuation comparison chart
Figure 3 shows that the line-of-sight recording in Group 2 is some dB is higher than in Group 1. This was due to the table that was used to place the masonry blocks and brick wall on. The height difference between the direct propagation path between the XeThru module and the reflected path from the table was so small that the energy was focused and was perceived as gain. To reduce this reflection, attenuation sheets were placed on the table as seen in the figure 4. However, the result will not be affected as the attenuation is based solely on the signal strength in the LOS and N-LOS measurements.
Figure 3: Table showing measurement data
Figure 4: Brick wall and masonry blocks measurement setup
To check the leakage from the attenuation, a metal reflector was placed at the opening and the same measurement procedure as for the building panels was performed. The two following pictures show two pulse-Doppler plots where the XeThru module was mounted with line-of-sight (left picture) to the reflector and the other with a metal reflector in front of the box. It clearly shows that the box does not leak as no RPM (frequency) components are present.
Figure 5: No leakage through attenuation box confirmed with range-Doppler plots.
This measurement session was our first take in trying to quantify the signal attenuation different building panels have on the XeThru sensor and the results proved to be surprisingly interesting. With its proven see through capability, we can definitely see the sensor in any type of building establishment and used in numerous security and safety applications. Moving forward, it is a matter of testing other types of materials, capturing additional data and extending the database.