Modeling and Measurement of Permittivity for Near Space Communications

Team NASAE, Not your Average Socially Awkward Engineers, is designing a circuit and package that can measure the permittivity of the air, as altitude changes, even near space, at 100 thousand feet.

Problem Statement
Our mission is to make new and exciting discoveries by designing, fabricating, and testing new devices to collect and analyze information about near space. The information to be measured is a quantity known as permittivity which describes a substance’s ability to resist an electric field. In order to measure permittivity in near space, aspects such as temperature, humidity, and signal frequency will need to be taken into consideration for accurate data collection. It is desirable to then plot this quantity with respect to time and position.

Mechanical Engineering Design Goals
Create a functional package (housing) for the electrical components to work and collect data properly. Model/Simulate forces, temperature, and other conditions on payload and package. Ensure that the payload will return to ground safely without affecting any of the packages inside. Find a material that will insulate our electric components to function at certain temperatures that will not interfere with data recording. Allows airflow to measurement devices. Allow component to work in different environments.

Electrical Engineering Design Goals
The goal of this project is to measure the permittivity of the air, from the ground to near space. We want to send a payload to near space, one hundred thousand kilometers, while measuring the permittivity as it goes up. At the very least, we will simulate this behavior using circuit design software. Permittivity: the ability of a substance to store electrical energy in an electric field. Basically, we want to measure the resistance of the air has to an electric field, or how long it takes for a charged particle to get from point A to point B. We will do this by measuring the capacitance of the air, as it goes higher into the atmosphere. Using equations that relate capacitance to permittivity, we will find what the permittivity of the air is, at certain points in the atmosphere.

Antenna Method
Using the Antenna method, we can calculate the permittivity by measuring the ratio of power transmitted to power relieved, and then using Friis Transmission Space Loss equation we would be able to calculate the phase velocity of the signal from which we can find permittivity.

The Package








Mechanical Analyses on the Package
Thermal Analysis Pictured to the right is a thermal analysis on the package that will be surrounding the circuit boards we create. This package will keep our electronics warm enough to operate during the flight. The circuit boards will be kept at about 20 °C, even at 100,000 feet.

Displacement Analysis Displacement Analysis of forces acting on top moving downward the box.

Strain Analysis Strain Analysis on Box as Forces Acting Downwards on top of the box.

Stress Analysis Stress Analysis on Box as Forces Acting Downwards on Top of the box.

Power Method
We will use a variant of the Friis equation, to find permittivity. We can do this by measuring the power transmitted, and the power received between two antennas.

Capacitor Method
The first method we designed to measure permittivity was to use a parallel plate capacitor. By using free space as a medium. By knowing the dimensions of the parallel plates and then measuring the capacitance we could directly relate it to the permittivity of free space using C=ϵ A/d. The problem with using this method is due to its inaccuracy at high frequencies. To measure the capacitance we would send a square wave with a period long enough for the capacitor in a series RC circuit to charge. Knowing the value of the resistor and the time it takes for the voltage to be 1/e (37%) of its maximum value we could then find the time constant of the circuit, from which we could get the capacitance. Unfortunately with this method the rise and fall times of the square wave source, when at the desired high frequencies, are no longer negligible. This leads to distortions in the discharge rate which leads to an inaccurate measurement of the capacitance. Because the goal of this project is to characterize permittivity at high frequencies we decided not to use this method.

Laser/Phase Velocity Method
The use of this system exploits the derivation of permittivity from the speed of light. With this system, a laser source would be used to generate laser pulses to be sent to a reflective object. The laser signal would be reflected back to the laser source where there is also a receiver. The time for this transmission would be clocked and with the distance between the laser and the reflective object constant, the speed of light can be calculated through the following development: vp = 𝑐/sqrt(μ𝑠*ε𝑠), where d is the distance between the laser and the reflective object, t is the time it takes for the laser to go to and reflect back from the object, ε is the permittivity, and μ is the permeability which can be assumed to be 1. One of the downfalls of this method is that accurate laser transmit and receive systems are costly. Also, in order for this to be a viable and accurate system, the distance between the laser source/receiver would have to be far enough apart such that the speed of the laser transmission can be clocked. In other words, this distance, would be dependent on how fast of a clocking rate the data acquisition scheme had. For instance, if a 100 MHz clocking rate was available, the period would be 10 ns. With the speed of light at about 3x10^8 m/s, the distance light would travel in 10 ns is 3 meters. So the distance of separation between the laser and the object should be at least 1.5 meters. Increasing this distance or increasing the clocking rate would increase accuracy. Considering we were confined to an area of about 30cm by 30cm, we would have to have a considerably high clocking rate to make this an accurate setup which further increases the design’s cost. If more space was provided however, this may be a fairly accurate scheme. Also, considering laser signals are usually in the infrared spectrum, the frequency range for such a system could vary from 300 GHz to 450 THz!

Boundary Condition Method
This method takes advantage of the reflections that occur at dielectric-dielectric boundary. By placing a thin sheet of material with a known dielectric between two antennas communicating across free space we could measure the incident, reflected, and transmitted power. From these we would be able to relate the permittivity of the free space to that of the medium. The issue with this method is that in order to eliminate incident angles the thin sheet would have to be perfectly orthogonal to the propagating wave, in practice this is difficult to achieve.

Benjamin VanSant
Mechanical Engineering Student

Hometown: Stanwood, WA

Hobbies and Interests: I love being outdoors and being active. Soccer, rock climbing, mountain biking, and snowboarding are a few of my favorite activities. I am interested in motorsports and racing. Someday I would love to find a job in that field, designing (or driving) high end cars or motorcycles.

Future Plans: Next year I will be entering the workforce. I am planning to move to either the Puget Sound area or southern California to find a design or manufacturing job which will give me the opportunity to grow as an engineer.

Email: vans6909@vandals.uidaho.edu



Brett Morris
Mechanical Engineering Student

Hometown: Oakley, CA

Hobbies/Interests: I am interested in how things work in mechanical systems and how they are designed. I always thought it was fascinating how people created 2D objects and transformed them into 3D models using CAD and other programs. Some of my hobbies are; snowboarding, video games, hanging out with family/friends, and sports.

Plan for Future: Pass the Fundamental Engineering exam as soon as possible and then start working towards passing the Professional Engineering exam. I would like to live and work in the Pacific Northwest.

Email: morr7547@vandals.uidaho.edu



Cameron Murdock
Electrical Engineering Student

Hometown: Laclede, ID

Hobbies/Interests: In general, my interests involve understanding how various systems work and how to improve those systems. In the field of Electrical Engineering, my interests include signal analysis and control theory. In my free time, I enjoy learning about new technologies and exploring the outdoors.

Plan for Future: As of now, I am not set on a particular path. I may go on to graduate school at Montana State University in order to study photonics so that I can eventually work at Bridger Photonics which is a company where I was an intern over the Summer of 2016.

Email: murd7115@vandals.uidaho.edu



Jeffrey Craig
Electrical Engineering Student

Hometown: Enumclaw, WA

Hobbies and interests: I am interested in technology in general. I like to build models, draw, and play videogames. It is fascinating how fast technology is growing, take the Nintendo Switch for example, it is so innovative. I have been involved with many engineering related clubs on campus, including IEEE, IMAPS, and ECE Ambassadors. Working on electrical projects on the side is also pastime of mine, I recently build a board that lights up with LEDs.

Plan for the future: After graduation I would like to work in the Seattle area. I have worked for the same company the past two summers, and would like to work for them again, in the avionics industry. It would be fun to eventually end up working for Nintendo though.

Email: crai5936@vandals.uidaho.edu



Ryan May
Electrical Engineering Student

Hometown: Boise, ID

Hobbies and interests: I am interested in communication systems as far as electrical engineering goes, I am also interested in science in general. Since my freshman year I have been involved in a research lab in the biology department investigating how transmissible vaccines could improve how we combat viruses in both epidemic and endemic situations through mathematical models. My hobbies include video games, mountain biking, and skiing.

Plan for the future: After graduating I plan to pursue a career involving communication, ideally working either with satellite communication or radar with ships and submarines.

Email: may6552@vandals.uidaho.edu