An Ultraviolet C-Band LED device for disinfection of air, articles and indoor environment

Background: Commonly used items like wallets, keys, and phones are both tricky and impractical to disinfect from the dangers of harmful microbes. This study demonstrates the eﬃcacy of UVC-LED technology in creating an eﬃcient, useful, and practical solution. Methods: As a demonstration of the eﬃcacy of the UVC-LED light (275 nm), a panel of UVC LEDs was fabricated and was driven with a constant current electronic driver. Staphylococcus aureus and Escherichia coli were placed on Petri dishes, and placed 38 cm away from the UVC-LED panel. UVC ﬂux measured at the petri dishes was 0.093 mW/cm2 . The method involved exposing both the bacteria to UVC treatment for 4 and 8 minutes. For each petri dish, the number of colony forming units were compared before and after the treatment and compared to the control. Results: A signiﬁcant reduction in colony forming unit (cfu) counts was found in all samples for both sets of bacteria: 97.9% in the 4 minutes treat-ment(22.3 mJ/cm 2 ), and 99.9% in the 8 minutes treatment(44.6 mJ/cm 2 ). Conclusion: UVC-LED technology oﬀers an eﬀective, simple and inexpen-sive approach for disinfection.


Background
Given the relentless waves of viral and bacterial outbreaks with high fatality rates and contagiousness, it seems imperative that there be ways for all people to safely, effectively and conveniently disinfect surfaces and Outbreaks are mainly spread by contact or close proximity with other people, in often benign interactions -those that are not thought about or are paid little heed to, such as giving a grocer your credit card or shaking hands with a neighbor. Disinfection, even when using the right disinfectants is both tricky and impractical in many situations.
UVC LED technology, however, appears to be a useful solution in recent years, as research shows the antimicrobial properties of UVC technology, and its application in the disinfection of stethoscopes from nosocomial infections [1]. UV light has already been used for such therapeutic purposes as stimulating vitamin D production and treating psoriasis, as well as for sanitizing air, water, and the environment [2]. At its typical wavelength of 200 -280 nm, UVC radiation induces pyrimidine dimers in thymine and cytosine, breaking DNA molecules, inactivating germs and preventing them from growing or reproducing [3].

LED & Driver
The commercial packaged UVC LED was obtained from Shenzhen Sxstrong Technology Co. [4], with part number SXS-S3535UVC-20. It packages the bare chip PCD-10-V1 produced by Photon Wave Co. [5]. Optical spectrum of the LED emission was measured with a UV-VIS spectrophotometer FLAME-S-UV-VIS from Ocean Insight [6] calibrated with a DH-3 Plus UV-VIS-NIR light source producred from the same vendor. The emission spectrum is shown in Figure 1.

Controller
The LED matrix was driven with a Constant-Current Constant-Voltage (CC-CV) driven. Circuit design of the LED driver is shown in Figure 3.
The main control loop is provided by an LED Boost Driver chip RT8485 [7], which takes a 12V wall power supply as input and provides a constant current boosted output on the terminal VLED, which in turn is connected to the LED matrix. In the given configuration, the circuit provides 500 mA of In a practical circuit, the LEDCTL PWM singal is typically provided from a micro-controller.

Battery Backup for Portability
It was determined that making the device function untethered to a wall supply would make it highly portable, and with appropriate personal protection, the device could be carried around to disinfect areas and objects at places other than the main device. A battery pack was therefore built and integrated with the electronics to provide such a backup power supply.
Six cylindrical 18650-F5P Lithium NCM rechargeable cells from Cham [8] were connected in a three-in-series and two-in-parallel (3S-2P) configuration. In the control circuit of the device, provisions are made to linearly charge the battery pack from the wall supply, monitor the voltages, and balance the cells. Algorithms are also implemented in the microcontroller to estimate the State of Health of the battery pack, and report to the user in the event of a change of battery is warranted. These circuit diagrams and algorithmns are out of scope of the theme of this paper, but could be provided upon request to the author.

Results
Killing rates for the two different germs for two different UVC exposure times are summarized in Table 1.
It may be observed that while a 4 min exposure (dose of 22.3 mJ/cm 2 ) gets a decent killing rate of about 98%, an 8 min exposure (dose of 44.6 mJ/cm 2 ) offers an almost perfect disinfection at 99.9% log reduction.

Discussion
The MF-SAN device operating on the principle of UVC-LED technology can be used in many different ways.
The device as it is can be used to sanitize the room air. The fan draws the air in through the top, and blows it through the bottom vent holes, while the UVC-LEDs sanitize the air in the volume of the device. It is estimated that a room of size 15' x 10' x 10' can be sanitized at > 98% within 15 minutes.
The device can be be used to sanitize a number of different objects, such as utensils, phones, personal items, fruits & vegetables, as shown in Figure   5.
The device can also be used as a portable UVC gun to disinfect highcontact surfaces, such as in clinics and offices, as shown in Figure 6.
It has been estimated that the MF-SAN device may be produced rather inexpensively. At a production quantity of 10,000 units, the cost is estimated to be about USD 150 per unit.