Undergraduate Engineering Capstone

Engineering capstone is the final undergraduate engineering project students complete in their undergraduate degree. Teams of 6 to 7 students are assigned a project provided by local industry partners or university faculty and completed over the span of their final year (2 terms).

The project assigned to my team was titled "Development of miniaturized readout electronics for microwave ice sensing applications in harsh environments".

Project Overview (The Why)

Ice buildup is a serious issue in aerospace and wind energy systems, where accumulation can reduce aerodynamic performance and create safety hazards. Our capstone project focused on designing a portable Scalar Network Analyzer (SNA) capable of detecting ice using microwave resonant sensors. The device measures shifts in resonant frequency from Split Ring Resonators (SRRs), allowing ice formation to be detected in real time. The objective was to create a lightweight, field deployable alternative to traditional laboratory network analyzers for use in wireless microwave sensor networks.

The project was initially defined through its proposal and later expanded upon by our client Dr. Mohammad H. Zarifi.

Key takeaways of this proposal were the projects objective, device specifications, and constraints. More on this will be duscussed when going over the desing process.

Meet the team

With a project such as this a capable team was required. The students assigned to this project were,

• Michael Bell - Electrical Engineering

• Mathew Bishop - Electrical Engineering

• Aiden Macson - Electrical Engineering

• Radu David - Computer Engineering

• Supreet Dhatt - Electrical Engineering

• Duncan Rabenstein - Electrical Engineering

Each of the students have skillsets in electronics, hardware, and software, making for a strong team to tackle our assigned project.

Design Process (The How)

The team was tasked with designing a scalar network analyzer (SNA) for wireless sensing and ice-detection applications. The specifications we needed to conform to were as follows:

• Operational frequency range of 10-18 GHz (Ku band)
• Dynamic range of ≥ 50 dB
• Power output of -5 dBm
• Measurement resolution of 32 sample points over range
• Low power & portable optimization (battery operated)

The key challenges were achieving the desired operational frequency range while maintaining moderate dynamic range.

What is an SNA?

A scalar network analyzer is a device that will output a sinusoid wave that is swept over a defined frequency range, and measures the amplitude response of a device under test (DUT). This response allows users to see the magnitude frequency response of a device, which in our case allows us to measure microwave ice detection sensors.

Proposed Approaches

To design this SNA the team focused on the devices RF structure. I was personally tasked with developing the RF subsystems in such a way that there were options balancing performance, cost, and complexity.

Design 1

This design utilizes only a voltage controlled oscillator (VCO) and power detector.

• Simple
• Very few components
• Components are expensive for operating range

Design 2

This design utilizes a double conversion methodology incorporating frequency mixing and filtering.

• More affordable components
• Still relatively simple
• More components
• Longer design timeframe

Design 3

This design expands on the double conversion methodology by adding frequency multipliers and amplifiers for additional range and flexibility.

• Most flexible with affordable parts
• Most complex
• Large part count
• Longest design timeframe

Design 4

This design utilizes frequency multiplication at its output and a down-conversion stage at its input to make it flexible yet simple.

• Complex but simpler
• Manageable number of parts
• Moderate design timeframe

Initial Prototype

Given the timeline constraints of this project, we decided to proceed with the first design, utilizing a single VCO and power detector. We opted to use connectorized RF components to reduce any possible troubleshooting time in the future. The two major RF components we used were the HMC733 VCO by Analog Devices and the ZV47-K44RMS+ Power Detector from Mini-Circuits.

With these building blocks, the team began working on the device. We used an ESP32 microcontroller in addition to a number of components for power distribution and amplification. A printed circuit board (PCB) was developed to host all the power regulators and voltage conversion stages. The resulting unit was not glamorous, but it demonstrated the projects feasibility.

In addition to the VCO and power detector, we used two Mini-Circuits ZX60-R5183P+ amplifiers (approx. 8 dB gain). These amplifiers were used for wireless measurements using horn antennas.

Improvements to the software

With the first prototype built, a simple graphical user interface (GUI) was designed. There were a number of iterations that this software went through. The members working on the software were Supreet, Duncan, and Aiden.

First UI Revision

The first GUI designed was barebones and made to function-test the first prototype.

Second UI Revision

The second GUI was a polished version of the first, with more attention to the design and user experience.

Third UI Revision

The final GUI incorporated all the features the team set out to include.

Final Design

With the results we were achieving, we looked into areas of our design we could improve. Two distinct areas of improvement we discovered were power consumption and user experience.

New PCB

A new PCB was designed for the device to incorporate new power distribution networks. I was tasked with designing the second PCB iteration which meant designing a new power supply for the device.

We wanted to be able to intelligently control the devices power distribution to optimize for power consumption. To do so, I incorporated a switch-mode power supply to provide the ESP32 with 3.3V, and a switch-mode power supply to provide the 18V required for tuning the VCO. To power the RF components such as the power detector, amplifiers, and VCO, I utilized linear regulators with an Enable/Disable feature for a smooth DC output that I can turn on and off using the ESP32.

Enclosure

We achieved an improved user experience for the final design's software as shown in UI Iteration 3, but we also worked to improve the devices presentation as well. An enclosure was designed by Mathew, Aiden, and Radu, to incorporate all the components while keeping the dimensions within the desired volume.

Resulting Product (The Outcome)

Closing in on the projects completion date the team conducted a final assembly of the device. The result was a product of everyones commitment, hard work, and ingenuity.

Testing

Testing the device, results showed minimal error and useable accuracy, making this device suitable for microwave sensor technologies. Below is a figure of a test done using a SRR. The blue trace shows the SRR's characteristics on a Keysight N5222B vector network analyzer which will be used as our baseline. The red trace is our SNA's measurement. Overall, the relative error between the SNA's results and the baseline was -4.34% in amplitude and +0.35% in frequency.

Conclusion

We successfully built a portable device that allows for microwave ice detection and sensing technology to be implemented at a lower cost. Instead of using large and expensive lab equipment, this device can be deployed in real environments like wind turbines, drones, or aircraft surfaces for ice detection applications that will provide improve safety.

Final Video Presentation

The final video presentation of our device: