Final Project
EM in Bioengineering Analysis
Comparative Study of Cell Phone Radiation Effects on Human Body
Objective:
Start with the draft of a human head and cell phone antenna HFSS model and modify it. Run the simulation and analyze the amount of current and the I2R heat factors for the two components.
Procedure:
In this project you will start with a simplified model of a human head, which contains two concentric spheres – the outer sphere is designated as made of “corning glass” and the inner one is designated as made of “sea water.” The first approximates human skull (bone tissue) and the second approximates blood. Your first task will be to replace “corning glass” with “bone tissue” and “sea water” with “blood” – see the section Modifying the HFSS Model below for details.
Your second task then becomes to add another sphere to the human head model, which will have the material “brain matter (grey)” and will be placed inside the head model as shown in Figure 1(a) below (exact placement coordinates and the sphere radius are up to you):
Figure 1 (a) Simplified model of a human head after adding Brain matter (front view); (b) Simplified model of a human head after adding Eye Model (top view).
Your third task will be to place a model of an eye near the head (yes, the overall model will be quite far from being anatomically accurate, but our goal is not to overcomplicate it) and assign the appropriate material to it. An example of placement is shown in Figure 1(b). The exact coordinates and eye model radius are up to you.
Once the model is thus modified, you will run a simulation of it and perform the experiments as described in the sections below.
Modifying the HFSS Model:
• Go to Files/PROJECTS/FINAL_ANSYS and download either the .zip, or the two .aedt/.aedtresults items. Extract them into the same folder and open the .aedt model draft. You might need to “Save As” it to be able to edit this HFSS model.
• Perform a web search of common cell phone operating frequencies and select one frequency for your Project. Note that the helical cell phone antenna model is already included in the draft, with the ground plane and the Port completely set up with proper type of excitation. (If you wanted to design and draw your own antenna – and if you are registered for ECE 430 this Spring – don’t worry: We’ll have a project on antenna design & simulation in it!)
• Visit the webpage of the Italian National Research Council (INRC), which contains a large database of electromagnetic (EM) properties for various human tissues: http://niremf.ifac.cnr.it/tissprop/ . Scroll down to Applications and click on “All Tissues, Single frequency”. Type in the value of cell phone operating frequency determined in Step 2 above and click ‘Go.’ Record all EM properties for the following four materials:
• Bone tissue
• Blood
• Brain (grey matter)
• Eye
• Go back to the model and assign new materials to the Bone and Blood objects by clicking Material Add Material and filling in the values recorded from INRC’s website. Validate the new materials.
• Draw a sphere inside the head model as illustrated in Figure 1(a) and assign Brain (grey matter) material to it. Perform Boolean subtraction of this sphere from the Blood one (make sure to have Blood in “Blank” and Brain in “Tools” and also check ‘Clone tool objects before subtracting’ box – see Lab 2 for a refresher on subtraction). Note that you only need to subtract it from Blood and not from the Air, since the entire head model has been subtracted from the Air in my draft already.
• Draw a sphere outside the head model as illustrated in Figure 1(b) and assign Eye material to it. Perform the Boolean subtraction of this sphere from the Air (make sure to have Air in “Blank” and Eye in “Tools” and also check ‘Clone tool objects before subtracting’).
• Modify the Analysis. This is a single-frequency simulation at the cell phone frequency only. The draft model already has Analysis set up, but you may need to change its frequency, depending on which frequency you selected in Step 2 above. Check the max number of passes (should be 6) and the max Delta_S (should be 0.06). More info on these simulation parameters is in the section below. Verify that the HPC is set to utilize 4 cores (check Step 29 in Lab 2 for a refresher).
• Perform Validation on your modified HFSS model. The Excitation and all Boundary setups should already be there in the draft model, so Validation should pass with no errors.
Experiments:
Run the Analysis.
Note: The base draft model I made for you had taken about 1 hour to simulate. Expect yours to take even longer due to the additions. Simulation times between 1 and 2 hours are to be expected, so budget your time accordingly.
While the simulation is running:
• Go to HFSS in the upper menu, then Solution Data, then click on Convergence tab. This will give you a glimpse into HFSS’s “inner workings.” Essentially, HFSS breaks the model down into 3-D segments (“tetrahedra”) and sets up, then solves a system of differential equations (kind of like Telegrapher Equations) for each such segment, also utilizing the boundary conditions for all adjacent segments. Once the solution is achieved, it is compared to an error factor, or the “Delta_S” (if you watched the Matrix trilogy, it is similar to what the Architect is charged with ). If the error factor exceeds the max value specified in the Analysis Setup, the program redefines the number and arrangement of the tetrahedra and attempts to refine the solution until this error is below specified value. For my simulation of this draft model, it took the program 4 passes, and the final Delta_S was about 0.02 (below the specified 0.06 max error).
• As the simulation runs, record values of the achieved Delta_S for each pass. Make a graph of Delta_S vs Pass_Number for your report.
When the analysis is complete, plot magnitude of the E-field inside the Brain, as well as inside the Eye, as per Lab 2 (see Step 36, but do not select “Sweep” – you will only have a single-frequency solution). Once you have the field plots inside those regions of interest, perform the following rough estimations:
• Estimate average values of the E-field inside the two regions of interest by using the colorbar values (it will be in V/m).
• Using the expression for current density, (where J is current density and s is material’s conductivity in Sm/m, given in the INRC’s database), estimate average current density in A/m2 for these two regions of interest.
• Find the average currents I1,2 flowing in the two regions of interest: Select a cross-sectional area inside each region and multiply J found above by the area.
• Estimate the resistance values of Brain and Eye by calculating: , where l is cylinder’s length, S is its cross-sectional area and s is conductivity of the cylinder’s material in Sm/s. (Imagine there being cylinders inside each of the objects, through which such currents will flow).
• Finally, calculate the products I2R (current-squared, multiplied by the resistance), which are representative of expected heat generated by a current flowing through a resistive object. It is believed that local heating of various organs by EM radiation can cause detrimental health effects, including cancers. Compare the two values and record your observations and analysis.
• BONUS: For additional points counted towards your final grade, you may perform an independent study into the health effects of the cell phone EM radiation based on the literature (e.g. IEEE Xplore), as well as try to convert the I2R factors into actual temperature increase in these regions over time (e.g. a one-hour call).
Individual Report:
The report should contain the following sections:
• Abstract: A brief summary of what the Project is about, what was done and what the results are.
• Group Work Acknowledgment (if applicable; see Group Work Rules below).
• Problem Overview: Your assessment of the problem and brief discussion of the solution to follow.
• Solution Outline:
• Screenshot of the completed modified HFSS model, with brief explanation of how you did it;
• Cell phone frequency selection – brief discussion (include any references);
• A table of all relevant EM values for your model’s materials, found from the INRC website;
• A screenshot of the simulation results: E-field magnitude in the Brain and Eye;
• Results and discussion for all 7 (or 8) Experiments listed above.
• Summary: A clear description of what was achieved and your interpretation of the results. Include the description of any challenges that you encountered during the project and how you could’ve done better.
• Conclusions: A brief statement on what you achieved, what you learned, what value the Project added to your education and what recommendations to fellow students and/or the instructor you would make.
Project Report Due Date & Format: December 7 (Monday) anytime – by email. Penalty for late submissions will be calculated based on time delay.
Group Work Rules:
You may (but don’t have to) work remotely in groups of up to 3 students on this Project’s HFSS part. This includes discussions of the design, work division, and using the same result output by all group members. Steps 3-7 (or 8) in the Experiment section of this assignment, however, must be 100% individual work. You may discuss approaches, but not re-use another student’s calculations and analysis. If you choose to work on the HFSS portion as a group, then make sure that each group member’s report contains acknowledgment of group work and estimates of each group member’s contribution expressed in percentage points and “signed” (type in the name) by each group member.