Project

Summary

The project aims to leverage the resources of the Fab Academy to advance doctoral research by developing an atmospheric pressure plasma reactor for disinfecting endoscopes. This involves designing the reactor using dielectric barrier discharge (DBD) technology and creating a high-voltage generator to power it. Atmospheric plasma, also known as cold plasma, operates at room temperature and can sterilize surfaces by disrupting bacterial defenses with reactive species like ions and UV photons. The project encompasses various components including the high-voltage generator, plasma reactor, measurement tools, and user interface, with a detailed plan for design, testing, and integration into the Fab Academy curriculum. The successful development and demonstration of the reactor highlight the practical applications of atmospheric plasma in medical sterilization, showcasing the potential for future enhancements and broader applications.

Below is the slide that summarizes the project, along with the one-minute video.

Introduction

General Idea

My project at the Fab Academy is all about harnessing its resources to advance my doctoral research. I’m diving into the world of atmospheric pressure plasma reactors, aiming to create a tool for disinfecting endoscopes. These reactors zap bacteria with atmospheric plasma, disrupting their defenses and making them harmless. I’ll be focusing on designing the reactor itself, using something called a dielectric barrier discharge (DBD), and crafting a high-voltage generator to power it up. By bringing this cutting-edge technology to the Fablab community, I hope to explore new applications and tackle practical challenges head-on.

The aim of the project is to design and develop an atmospheric plasma reactor and it’s high-voltage generator.

Atmospheric Plasma

Atmospheric plasma, often referred to as cold plasma, represents a captivating frontier in science and technology. Unlike traditional plasmas generated in high-temperature environments, atmospheric plasma operates at or near room temperature, making it suitable for a wide range of applications across various industries. At its core, atmospheric plasma consists of ionized gases containing a diverse array of reactive species, including ions, electrons, radicals, and UV photons. These reactive species endow atmospheric plasma with remarkable capabilities, ranging from surface cleaning and sterilization to material deposition and surface modification. By harnessing the unique properties of atmospheric plasma, researchers and engineers are unlocking innovative solutions to challenges in fields as diverse as healthcare, electronics, agriculture, and beyond.

Below is an illustration from Carles Corbella & al. showing, in the center, a diagram of the activity of such plasma and what it produces from a chemical point of view. On the left are various plasma reactor configurations, and on the right is a real picture of atmospheric plasma.

Some interesting reading

• A review of the literature on surface decontamination using atmospheric plasma.
• A review of plasma applications in medicine and biology
• More reading on plasma biomedical applications

Draft

The project begins with a draft. This is created using a block diagram shown below to help visualize the various elements.

Each block can be described in more detail in the next section. A brief description of the blocks is given here :

• HV Generator: this is the high-voltage generator. It is used to power the plasma reactor.
• Plasma Reactor: this is where the plasma is generated. It is powered by the previous block and is used to generate plasma. This plasma can be used for any application, such as surface disinfection.
• Software feedback control: This function regulates plasma generation according to measurements made on the plasma and on the electrical generator. In fact, it’s important to monitor and control what’s happening in the high-voltage generator.
• The user interface: This represents everything that comes into contact with the user, the means of influencing the system but also of obtaining information about it. *Measurement tools: these are simply the interface between the raw physical signal and the digital data transmitted to the controller.

Function Descriptions

1. HV Generator

This is the most complicated function. In fact, it requires a fairly advanced knowledge of power electronics, a field of electronics that focuses on energy transfer. Here, the idea is to start with a low-tension DC voltage generator (max 30V), which won’t need much power, so it’s a commercially available generator (my research lab has several, lucky me). An electronic circuit mainly composed of MOSFETs will transform this constant tension into an alternative one.Basically, the circuit will open one branch and then the other several thousand times per second. The result is an oscillating signal at the output. This is controlled by a microcontroller (an arduino, for example). Finally, there’s a transformer to switch from a low AC voltage to a (very) high AC voltage. In terms of current, we’re talking about milliamperes but yes, there’s a chance of electrocuting yourself to death, so you need to be extremely careful!

2. Plasma Reactor

This function groups together all the elements required for atmospheric plasma. The main element is the dielectric barrier in which discharges are created. These discharges are known as plasma. To have a dielectric barrier, you need two electrodes, one powered by high voltage, and the other connected to earth. A dielectric medium is also required, and this role is played by a noble gas. In fact, these gases can easily be ionized at high voltage, allowing plasma discharges to propagate through them. A fairly common example of plasma in a noble gas is neon or xenon light.

3. Measurement

This function consists, quite simply, of taking measurements of the various data needed to control the plasma reactor. Ideally, you’ll need :

• Measure the voltage and current at the high-voltage generator terminal.
• Measure signal distortion. (feasibility to be checked)
• Quantitatively measure what is produced by the plasma (quantity of ionized elements).

4. User Interface

The user interface will :

• Display control information to the user.
• Indicate if a problem is occurring/has occurred, and specify which one.
• Allow the user to interact with the device control (ignition, safety, plasma power selection, etc.).
• Select the operating mode.

Involvment into the FabAc’s Program

Here, I’ll summarize the direct links found between the project and the Fab Academy program.

Tasks Definition & Schedule

After analyzing where the various themes of the FabAC program fit in with my project, I decided to draw up a list of tasks and sub-tasks and distribute them in a schedule starting from the Midterm.

Tasks Definition

Tasks are divided by devices (HV Generator & Plasma Reactor).

HV Generator

The tasks concerning the high-voltage generator are defined below.

• Design of the PCB
  • Inverter
  • Output Devices (OLED screen)
  • Intput Devices (temp sensor, CO2 sensor ?)
• Manufacture the PCB & Components soldering
• Testing the PCB
  • Testing inverter - low voltage generation
  • Testing output device
  • Testing input devices
• Testing HV Generator
  • Testing connections
  • Testing high-voltage generation
• Design of the HV Generator
  • Design casing & PCB support
  • Design connections
  • Design HV transfomer
• Manufacture of the HV Generator
  • Manufacture of the casing
  • Assembly of the casing & connectors & Electronic components (PCB, HV Transfo, etc.)

Plasma Reactor

The tasks concerning the plasma reactor are defined below.

• Design of the Plasma Reactor
  • Include gas input
  • Include gas ouput
  • Include DBD
    • Include HV connection
    • Include Dielectric Barrier
  • Include Ground electrode
  • Include support system
• Manufacture of the Plasma Reactor
  • Gas system
    • Tubes
    • Tubes connectors
    • Gas adapter (parts used to connect tubes connector to plasma chamber)
  • Reactor system
    • HV Connector - HV DBD electrode
    • Mesh Tube
    • Mesh Connector - Ground electrode
    • Tube
• Testing the Plasma Reactor
  • Testing the gas system
  • Testing DBD

Schedule

The schedule includes tasks and their distribution over time.

Development

Project development was documented during week 18. The development followed the PDP methodology for Product Design Process.

Results

HV Generator

The final result of the generator is shown below. It can be controlled via the user interface accessible here.

High Voltage Generator - Inside

High Voltage Generator - Outside

Plasma Reactor

The final result of the plasma reactor is shown below.

Plasma Reactor - Outside

Final Setup

The final setup consists of a plasma reactor connected to a high-voltage generator and a gas supply. A computer with an interface is needed to control the high-voltage generator. A view of the setup is shown below.

Final Setup - From left to right : Low DC Power Supply, Plasma Reactor, HV Generator, Computer

Workflow

To switch on the plasma, you must :

• Make all connections (gas and voltage).
• Turn on the gas flow.
• On the UI, establish the connection, and switch on the signal after choosing its frequency.
• Activate the switch on the HV generator.
• Increase the DC voltage as you go in.

To switch off the plasma, you can either :

• Stop signal generation on the UI.
• Switch off DC power supply.
• Turn off the switch on the HV generator.

Here are a few images of the setup in operation.

Conclusion

In conclusion, the project successfully demonstrates the integration of multiple advanced technologies to develop an atmospheric plasma reactor for medical use. By combining 2D and 3D design, various fabrication processes, and electronics, the project not only highlights the practical applications of atmospheric plasma but also showcases the ability to create functional, innovative solutions within the Fab Lab environment. The results affirm the potential of atmospheric plasma technology in enhancing sterilization processes, contributing to advancements in medical safety and efficiency. Future work could expand on the feedback control systems and further optimize the reactor design for broader applications.

Appendix

Bill Of Materials

The BOM is available here.

License

To maintain control over the use of my work, I have selected the “Creative Commons Attribution - Non Commercial - CC-BY-NC” license. This license permits others to use, share, and adapt my work for non-commercial purposes while requiring attribution to me.

Files

• HV Generator - 3D Files
• Plasma Reactor - 3D Files
• KiCAD Files
• Source Code Files