Diffuse optical tomography is an emerging biomedical imaging technique, due to its numerous advantages, such as low cost and non-ionizing radiation. In this work, we have developed a very simple setup, which included a single source – photodiode (SP) pair for scanning a sample of water with diluted Intralipid, simulating a biological tissue. LEDs emitting at 470, 525 and 624 nm, as well as a 650 nm Fabry Perot laser, were used as light sources. Scattered light from the sample was detected by the photodiode placed next to the LED. The SP distance could vary and the phantom could be scanned by moving the SP pair in precise, small and automated steps without any intervention during the measurements. Therefore, we obtained measurements from multiple locations on the sample, with just one SP pair. The presented experimental system verified the feasibility of deploying extremely low cost devices for detection and imaging absorbing objects of 1 cm height, placed inside a scattering medium. Maximum depth detection was 2.5 cm. As expected, the quality of the obtained images was degrading, as the object’s depth or the scanning step was increasing. Additionally, we developed Monte Carlo simulations of the setup, which achieved good agreement with the experimental results. We also conducted another set of simulations, studying the depth sensitivity of a single static SP pair considering a scattering medium similar to the experimental phantom with and without object. We observed that the depth sensitivity increases as the source wavelength increases from 450 nm to 650 nm.
It is known that the tempting features of free space Non-Line-Of-Sight (NLOS) communications systems operating in the Ultraviolet C-band between 200 and 280 nm are the significantly reduced solar irradiance on ground level, the intense scattering and its combination with strong absorption which ensures the covertness against distant eavesdroppers or jammers. In the majority of the experimental surveys that have been published so far, the performance of point-to-point links has been evaluated under clear atmosphere without taking into account the weather conditions. In this work, it is shown that harsh atmospheric conditions due to fog appearance can be advantageous to short distance NLOS transmissions at 265 nm. Initially, the impact of fog on the losses of the diffuse wireless channels was investigated theoretically. Afterwards, an experimental survey of both the losses and the performance of low rate amplitude signals’ transmissions for two atmosphere cases followed. Initially, the satisfactory relation between scattering and absorption at 265 nm was verified by deploying outdoor NLOS point-to-point links under clear atmosphere. The transmitter consisted of 4 Light Emitting Diodes and the optical part of the receiver included a filter and a Photo-Multiplier tube. Then, the beneficial impact of artificially generated fog on scattering was exploited not only to enhance the system performance but also to identify the modification of the conditions. The experimental results showed a clear decrease of both the losses and the Bit Error Rate under fog conditions making such a system a perfect candidate for low rate communications under dense atmosphere.