Professor Lewis Elfed

Project Supervisor: Professor Elfed Lewis Project No: EL 1
Project Title: An LED Based Optical Fibre Sensor Dynamic Response Simulator for a Clinical Linear Accelerator (Linac)
Course Suitability: BE ALL

Project Description:

The Optical Fibre Research Centre at UL (www.ofsrc.ul.ie) has recently been measuring the X-Ray output of machines for delivering radiotherapy treatment beams in oncology clinics. Clearly it is not possible to bring such X-Ray sources into the laboratory on health and safety grounds. However it may be possible to test the time response of our optical fibre sensors using LEDs which mimic the X-Ray beam pulse signal generated by the Linac.

A possible strategy for this is to use UV LEDs which are controlled from a digital pulse generator and use Optical fibre Sensors coated with UV sensitive phosphors (as opposed to X-Ray Sensitive). The setting up of such a system will prove very useful in characterising the response of the Optical Fibre Sensors and the optical connectors connected to them. A possible scheme for the system is shown in Fig 1 below. The sensor construction is shown in Figure 2. All fibres including the sensor are based on standard 1mm diameter Plastic Optical Fibre (POF).

It is required to build hardware and develop software to generate a rectangular pulse based generator for the LED driver which generates pulses over a range of frequencies from 60 Hz to 360 Hz in steps of 60 Hz. It is also required to design and build a stable pulsed LED Driver and Photodetector and Amplifier. The hardware is to be controlled and all date captured on a PC hosting LabVIEW software. All tests to be conducted in the ECE Project Labs.

 

Note: No prior experience of handling optical fibres is required for this project.

EL Image1

 

 
Fig1. Proposed Test Set up

 

EL Image2Fig 2. The Optical Fibre Sensor

 

Project Supervisor: Professor Elfed Lewis Project No: EL 2

Project Title: An LED Source Simulator for a Clinical Linear Accelerator (Linac)

Course Suitability: BE (Electronics or Robotics)

Project Description:

 

The Optical Fibre Research Centre at UL (www.ofsrc.ul.ie ) has recently been measuring the X-Ray output of machines for delivering radiotherapy treatment beams in oncology clinics. Clearly it is not possible to bring such X-Ray sources into the laboratory on health and safety grounds. However it may be possible to test the response of our optical fibre sensors using LEDs which mimic the X-Ray beam pulse signal generated by the Linac.

There is a requirement to build and thoroughly test an LED source which is capable of faithfully reproducing the pulsed X-Ray emission from a clinical linac. These pulses take the form of the waveform shown below in Fig 1.

 EL Image3

 

Fig 1. Time Resolved Signal from Linac Output

The waveform of Fig 1 is only one example of a real-time linac output pulse trace. The Linac machine can generate other lower pulse counts by removing the occasional pulse e.g. 1 in 4 or one in 3 from this. Further specific information on this can be provided if the project is selected.

It is required to build hardware and develop software to generate pulses of the above shape and frequency. A more detailed specification of the required individual pulse characteristics is given in Fig 2.

 

EL Image4

 

Fig 2. LED Pulse Shape Specifications
Project Supervisor: Professor Elfed Lewis Project No: EL 3
Course Suitability:    BE (All)

Project Title: An Optical Fibre Based and Temperature Stabilised Near Infra Red (850 nm) LED Source

Project Description:

LEDs are rapidly becoming deployed in a wide range of day to day applications e.g. illumination of signs. A wide range of these devices is now available for an equally wide range of applications. Some devices are intended for specialist uses and specifically coupling to optical fibres. LEDs are prone to changes in their intensity due to current variations, temperature fluctuations (chip and/or ambient) and ageing. Whilst the latter cannot generally be avoided it can be compensated for. The current can be accurately controlled by provision of a steady current via a current source. The temperature can be accurately controlled by maintaining the device in a temperature controlled environment. A method for achieving this which is rapidly gaining popularity is thermoelectric cooling using a device known as a Peltier Heat Pump.

A temperature controller based on a Peltier heat pump cooling and heating a copper block coupled to a heat sink is to be developed to enable the accurate temperature control (better than 0.1 oC) of the copper block. The block is to house a single LED source and a monitoring Photodetector (photodiode).   In this way the housing can be made small and the cooler can be used with relatively low power. It will be necessary to have the LED detachable from the block in the case of failure and for a fibre to be mounted on the optical output of the LED on the opposite side of the block. It will be necessary to mount the Photodetector in close proximity with the output of the LED so that it can be monitored and this signal used to correct for ageing by affecting small changes in the drive current of the LED.

A circuit has been developed to achieve this using proportional and Integral (P&I) control and initial work has been undertaken to implement this in LabView. Further work is necessary to implement PI control in hardware and improve the existing LabView based implementation.