UV-C Demo Case

In the previous blog post published HERE, we introduced the concept of using solid-state UV lighting for disinfection. We discussed the mechanisms of action, considered several basic formulas for calculating the required UV exposure for specified disinfection ratio, underlined several advantages of using Solid-State Lighting (SSL) UV solutions over some traditional methods, and finally, promised that with the help of experts from EBV Electronics, such concept could be easily implemented. Therefore, in this blog post, we will focus on practical implementation.

Picture 1: UV-C Demo Cases and Smart UV Sphere are different realization approaches based on the same electronics hardware. The sphere realizes the theoretical optimal optical design while the cases are more convenient for day to day handling, demonstration and lab-experiments.

In collaboration with several major semiconductor manufacturers, including ams OSRAM, Luminus, Infineon + Cypress and STMicroelectronics, the EBV Elektronik expert team has designed UV-C Disinfection Demonstrators for disinfection of small to medium-sized objects up to 99.9% (or higher for medical-grade use-cases). Featuring state-of-the-art Luminus and ams OSRAM UV-C LEDs operating at around 275 nm, the UV Disinfection Demonstrators can successfully handle all types of pathogens. The demonstrators utilize some not-so-common techniques to enable a set of unique features, such as automatic exposure adjustment based on the detected object surface, UV LED performance monitoring and compensation, and the ability to study the detection of microbial contamination based on intrinsic UV-A fluorescence under UV-C excitation (UV-A detection). These features, combined with a range of built-in safety measures to prevent dangerous UV-C leakage, set this demonstrator apart from similar solutions on the market, showcasing the design advantages of using UV SSL solutions combined with the latest technologies in sensing, control, and power management.

The Hardware Implementation

There are two different mechanical designs of the UV-C Disinfection Demonstrator. They are both based on the same concept, using the same mainboard. However, each of them has some practical advantages in particular use-cases. One demonstrator is designed as an easily portable case with a box-shaped disinfection chamber. It features either Luminus XBT-1313-UV or OSRAM OSLON® UV3636 LEDs. Luminus LEDs are efficient UV-C LEDs with a peak wavelength from 270- 280 nm, an emission angle of 150°, and a radiant flux of around 4 -6 mW at standard 40 mA driving condition; they can also be overdriven up to 100 mA corresponding to 12 mW UV-C output or more. These ultra-compact LEDs have a tiny footprint of 1.3 x 1.3 mm. Their compact size, combined with high efficiency, robust package with ESD protection, and competitive pricing, made them a perfect choice for the smaller disinfection chamber of the case demonstrator version.

The second demonstrator is designed in a spherical shape, 300 mm in diameter. It features a larger disinfection volume and more powerful OSRAM OSLON® UV3636 Midpower high-performance UV-C LEDs with the peak wavelength at 275 nm, emission angle of 120°, and radiant flux of 12 mW at 100 mA (SU CULCN1.VC). These LEDs feature an AlGaN-based Flip Chip technology in a robust package with a ceramic substrate, gold coating, and quartz glass. The OSRAM OSLON® UV3636 family shares a compatible footprint and enable drop-in replacement with different power classes from shares a compatible footprint and enable drop-in replacement with different power classes from 4.7 to 42 mW. We realized two disinfection chamber designs: a spherical demonstrator version and the easily portable UV-C demo cases.

Both ams OSRAM and Luminus are reputable manufacturers of specialized SSL solutions with a long tradition on the market. They both offer a wide portfolio of UV devices, ranging from highly efficient and compact low-power solutions, ideal for smaller battery-powered UV disinfectors, up to much larger multi-chip high-power solutions, capable of delivering more than 100 mW of radiant flux, effectively reaching sufficient UV-C doses even in much larger chambers. Therefore, choosing state-of-the-art UV-C LED solutions from ams OSRAM and Luminus was a logical choice for our UV experts.

Picture 2: Microbiological studies show here a better than 99,9 % reduction of E.Coli (also called log 3 reduction) for the initial settings (1 minute at low intensity) without or with UV-C-blocking cover on the left or right respectively.

The UV-C Disinfection Demonstrator boasts a portable design with much flexibility. Both versions can be powered either by two Li-Po battery cells or directly from the USB-C port. It is a proof-of-concept on its own, as it provides fast charging for two Li-Po/Li-Ion battery cells utilizing the power delivery option of the USB3 interface (USB PD), direct power supply for the demonstrator via the USB-C port even with no batteries included, or power for connected USB On-the-Go (USB OTG) accessories, acting as a power bank. The fuel gauge function for the battery is also implemented, providing a readout of battery and charge parameters like the remaining power and displaying it on the TFT screen.

Besides all the components required for battery management and power supply, another mayor electronics part are LED drivers, well suited for both types of UV-C LEDs: low power (driving current < 100 mA) and high power (> 300 mA). The Demonstrator design features a mid-power LED driver, with the ability to drive up to six LED strings, sinking up to 130 mA (150 mA abs. max) per string. This IC is ideal for driving Low power UV-C LEDs, as their nominal driving current is only around 40 mA. The second LED Driver is a synchronous Buck/Buck-Boost LED driver used to drive a single High Power UV- C LED of OSRAM SU CULDN1.VC or Luminus XBT-3535-UV LEDs. Forward current is set via a fixed resistor to about 250 mA, although the hardware support even higher current ratings up to 1000 mA. Both LED drivers also support a rich set of protection and safety features, such as short-circuit detection, thermal and overvoltage protection, dedicated fault- reporting pins, and more. Dimming is achieved by PWM.

Figure 3: Block diagram of the UV-C Disinfection Demonstrator

Another essential component worth mentioning is the AMS AS7331TC spectral UV sensor. The AS7331TC is a test chip of a brand new UV spectral sensor announced by ams OSRAM, with UV interference filters applied to its calibrated optical channels as part of the CMOS process, ensuring no filter aging and drift over time and temperature. The AS7331TC covers the UV range from 238 to 415 nm, providing accurate readings for three UV bands individually (UV-A, UV-B, and UV-C) at incidence angles below 10°. Thanks to its fast front-end with three 16-bit A/D converters and daylight blocking filters (VIS + NIR), the AS7331 provides fast and highly accurate readings, even in harsh conditions. These features made it a perfect candidate for the UV-C Disinfection Demonstrator, allowing implementation of all the advanced features mentioned previously.

The device is controlled by the STMicroelectronics STM32F401 microcontroller (MCU). This MCU is part of the STM32Dynamic EfficiencyTM device range, offering the best balance of dynamic power consumption and processing performance,essential for battery-powered applications. The MCU governs the closed-loop control system, regulating UV-C radiant exposure according to the UV sensor data. It also provides a clean and intuitive user interface over a 3.5″ TFT touch screen, allowing users to set up and monitor all the disinfection parameters.

The design incorporates various auxiliary components, such as LDOs, level shifters, DC-DC converters, etc. It also includes the TLE4913, Infineon’s micro-power Hall switch in the SC59 3-pin package, which acts as a safety switch, preventing dangerous UV-C light from leaking when the disinfector is abruptly opened while operated.

How does it work?

In the previous blog post titled LEDs Go Anti-Viral, we explained the relation between the UV LEDs’ peak wavelength and their lifetime. We also discussed that the best compromise is to use UV-LEDs with a peak wavelength between 270 and 280 nm, as they do not require significant dosage corrections compared to the well-documented case studies performed with 254-nm Hg (mercury) tubes. The below diagram illustrates the necessary dose modifications according to the case studies conducted using Hg tubes:

Figure 4: Dose correction for Wavelength variation. Most scientific UV-C disinfection literature is based on the 254 nm emission of Hg-tubes. A Wavelength dependent germicidal effectiveness is specified by CIE155-2003. 

Before the disinfection process is started, the chamber must first be tared (zeroed out). This procedure is performed with an empty chamber, in which the total UV-C radiant flux is sensed using the AS7331TC. After inserting the object to be disinfected, the diffuse UV-C flux changes since most materials absorb more than 50% of the UV-C light. The MCU determines the object’s surface area based on the detected changes and adjusts the disinfection parameters accordingly. The detected surface area is displayed on the TFT screen, along with the calculated disinfection dose in mJ/cm2 and the time required to disinfect the detected surface area. The disinfection process can now be started via the touch-sensitive TFT screen. By providing closed-loop control, the MCU ensures the correct UV-C dosage is applied at all times.

The chamber has to provide a high level of reflectivity for the UV light so that the estimations can be as accurate as possible. While aluminum offers high UV reflectivity of up to 90%, some specialized materials such as a porous PTFE coating are favorable, as they yield much higher reflectivity (up to 97 %). High reflectivity also reduces energy losses and helps achieve homogeneous lighting inside the chamber, providing greater disinfection efficiency. Additionally, the disinfected object should not be covered in dirt or dust, as it could prevent UV light from reaching the object’s surface.

The shape of the disinfection chamber is also vital for achieving homogenous illumination. In this regard, the spherical shape of the chamber is superior to the box shape, although rounding the corners significantly improves the illumination homogeneity. Disinfection chambers must be sealed tightly to avoid UV-C leakage, which can cause lower disinfection yields and inaccurate measurements. Finally, UV-C light represents a hazard to the human body since it breaks the bonds of DNA molecules in exposed tissue (similar to what it does to common pathogens), causing accelerated skin aging, eye damage, and skin cancer. As a precaution against accidental UV-C leakage, UV-C Demo Case uses a Hall IC switch that interrupts the power supply to the LEDs and stops the disinfection process if the case is opened during the disinfection process.

After the disinfection process has been started, the display shows the remaining time, dose counter, disinfection progress (in percents), and UV light intensity in each of the three UV bands: UV-A, UV-B, and UV-C. As mentioned before, the detection of the remaining microbial contamination can be performed by sensing the intrinsic UV-A fluorescence under UV-C excitation. Monitoring thoroughly the changes in the UV-A band (e.g. with the AS7331TC sensor), it is possible to estimate residual contamination by various pathogens. The diagram below illustrates one such case study conducted for several microbial species while irradiated by UV-C light peaking at 280 nm (Source: http://journals.sagepub.com/doi/10.1366/000370209789806993).

Figure 5: UV-A Fluorescence diagram: bacteria cultures irradiated with UV-C at 280 nm Picture adapted from Paper: Source: https://doi.org/10.1366/000370209789806993

Summary

If the current situation with the pandemic has taught us anything, it is that hygiene should not be taken lightly. Fortunately, collective awareness has risen high enough to realize that it is necessary to fight pathogens more aggressively and intelligently than ever before. The UV-C Disinfection Demonstrators clearly illustrate the advantages of using one such innovative and intelligent solution, offering greater flexibility and reliability than other, more common methods: instead of a “spray and pray” approach, the UV-C Disinfection Demonstrators rely on the science and expertise to provide a predictably high level of disinfection, as well as the residual pathogen monitoring principle based on the UV-A fluorescence, as mentioned before.

The UV-C Disinfection Demonstrators represent not only a stand-alone device that can perform surface disinfection of objects with great accuracy and reliability, but it is also a proof of concept and a reference design that can be scaled and enriched with features according to customer’s application-specific requirements. EBV Elektronik’s team of lighting experts (also known as the LightSpeed team) is ready to help you with your design by offering extensive support: whether you want to experiment with the described UV-C Demo Case yourself, conduct your own disinfection tests using an advanced UV sensor, or you just want to expand your arsenal of weapons in the fight against pathogens with knowledge on related topics such as UV-C, UV-A, and TiO2 disinfection, all you need to do is to register HERE (or email us at uv@ebv.com) and schedule an appointment. Our LightSpeed experts are happy to help you realize your project successfully. Let us win together!

Coauthors:

Zeljko Gajic – Technical Support Center Engineer Analog and Power

Business Development Manager IoT, UV, Home & Building at EBV. As a graduated physicist I am passionate about optoelectronics and spectroscopy on one side and deep technical and new commercial concepts beyond today’s status quo on the other side. My updates cover the latest trends and technologies in UV-LEDs, IoT, AI and smart consumer and building applications.