# Development of Far-UVC-Based Surface Disinfection Prototype for Public Buses
## 2 Materials and Methods  
### Design of Far-UVC-based Disinfection System Prototype for Public Transport  
The main objective of the far-UVC disinfection system is to reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) surface contamination in public buses. A prototype of the disinfection system was developed based on previous studies [6; 7] demonstrating the disinfection effect of far-UVC irradiation. However, high doses of UV radiation also have a negative effect on the mechanical and aesthetic properties of the surfaces being disinfected [27]. Based on these assumptions, the disinfection system must operate in an optimal mode to inactivate viruses with the least negative impact on surfaces. This can be achieved by monitoring the occupancy of each area in a bus during a journey and selecting the optimum dose of far-UVC radiation in each area. Figure 1 shows the main components of a prototype of a disinfection system comprising a computer vision system and far-UVC radiation control system. The computer vision system uses a video camera to capture the image of the bus interior, which is processed using filters and noise reduction algorithms. An object detection algorithm is then used to detect passengers and calculate the occupancy of the bus interior. Disinfection of the bus interior is performed by a far-UVC radiation control system, which controls the exposure time and positions the lamps according to the occupancy of the bus interior zones. The computer vision system starts the process by capturing an image of the bus interior. It then defines a region of interest that includes the bus seats. The image is then processed by resizing, noise removal, sharpening, histogram equalization, and normalization. In the next step, the image is fed to a trained YOLO v7 model [28], which is capable of distinguishing only people in a video frame. Based on the detected persons, a list of all passenger coordinates in the video frame is generated, and the occupancy of the bus interior zones is calculated by outputting a heat map related to the bus interior zone coordinates. Figure 2 shows a detailed flowchart of the computer vision system. The far-UVC light sources of the prototype developed consisted of two Quantadose B-Series DF28B-B3 (Guangdong Excimer Optoelectronics Technology, Jiangmen, China) 20-watt filtered 222 nm far-UVC excimer lamp modules fitted with 222 nm bandpass filters and enclosed in protective housings to ensure lamp integrity and cooling. These lamp modules were powered by a dedicated 40W high-voltage excimer lamp electronic power supply. To increase the precision and accuracy of the far-UVC exposure, bandpass filters were used within the lamp modules to ensure that only the desired wavelength of UV light was emitted. In addition, the prototype incorporated a mech  
Figure 1: Block diagram of a prototypical far-UVC disinfection system. microcontroller and driven by stepper motors to manipulate the distance, position, and movement of each lamp module. By adjusting the distance between the irradiated surface and the far-UVC light source, the intensity of the far-UVC light exposure could be varied. The spectral characteristics of the far-UVC lamps were evaluated using an Avantes AvaSpec ULS2048 CL spectroscope (manufacturer AVANTES B.V., Apeldoorn, the Netherlands). The spectrogram of the direct light emitted by the lamps, which clearly shows a dominant wavelength of 222 nm, is shown in Figure 3.  
A X1-5 optometer (manufacturer Gigahertz Optik GmbH, Tuerkenfeld in Munich, Germany) equipped with a calibrated 222 nm sensor was used to measure radiant exposure. The far-UVC lamps were mounted on a robotic structure that allowed the lamps to be positioned in the appropriate row of bus seats and lowered to the seat surface to achieve  
Figure 3: Spectrogram of far-UVC lamp modules used in developed prototype of disinfection system. Figure 2: Flowchart of computer vision system for bus interior occupancy detection. the required amount of irradiation on the surface to be disinfected (Figure 4).