Group 249
From ECE Department Wiki
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Project Description
Everyday we are surrounded by charge, magnetic fields, and electric fields throughout our daily routine. The target of our project is to create a toolset that gives timely, consistent, and repeatable measurement of the following: magnetic fields, static electric fields, changing electric fields, and charge. The frequency of the sources and sensors this design targets ranges from DC to the GHz. There are many types of sources and their measurements can be quite difficult due to many variables. These variables consist of internal noise, external noise, bandwidth, sensitivity, resolution, range, and other sources separate of those we wish to measure. Efforts will be taken to eliminate as many of these variables as possible to create accurate results.
Members
- Andy Kottsick
- Jeremy Lee
- Jeremy Purcell
- Mike Newell
Advisors
- Dr. Schroeder
- Dr. Nelson
The Emag Sensor Gang
From left to right: Andy Kottsick, Jeremy Purcell, Jeremy Lee, Mike Newell.
Requirements
- 1. The sensors will cover three frequency ranges. The ranges, along with static fields are: 1Hz-10KHz, 100kHz-10MHz, 100MHz-2.5GHz.
- 2. Each sensor must be able to accurately measure the source for which it is designed.
- 3. The sensors shall not significantly interfere with surrounding electronic devices, especially other sensors or field sources.
- 4. The sensors need to be isolated from outside and undesirable sources, including other sensors.
- 5. The sensors need to have test points for measurements that may be hooked up externally such as to an oscilloscope or one’s own external circuitry.
- 6. Finished product needs to be relatively inexpensive, modular, and adaptable to future designs.
- 7. It shall be possible for other students and faculty to build and use for educational purposes as long as they are supplied with proper instruction.
- 8. Each sensor should have the ability to output resulting measurements to a graphical interface that can be read and understood in an easy manner.
Early Prototypes
Static Charge / Electric Field Measurement
The following picture is an early prototype that was used for the testing of the Field Mill design. The Field Mill is commonly used to measure charge in clouds. We decided to use it on a smaller scale to measure surface charge on objects placed above it. We tested our initial 4 blade copper block plate, a two blade copper plate, and a cardboard block plate. The latter two helped us eliminate some of the theories we had behind the operation of the Field Mill. All three of these blocking plates worked. The two blade had about half the output as the 4 blade and the card board blade had fairly weak output, but still functionally worked. Our resulting theory is that the rotating plate changes the amount of charge attracted to the sensing plate below which causes a change in the flow of current through the charge amplifier creating an AC signal at the output.
Time Varying Electric / Magnetic Fields from 1MHz to 200MHz
Mike, enter some info.
Static Magnetic Field Measurement
Early prototypes of the Flux-gate.
Time Varying Electric / Magnetic Fields from 600MHz to 2.4GHz
The picture below is of our initial prototype for a Log Periodic Dipole Array. The reason we chose to use a log periodic dipole is becasue it offers a large bandwidth with a relatively low voltage to standing wave ratio (VSWR). The longest dipole element is designed to be half wave resonant at the lower limit of our frequency range (600MHz). There is a spacing factor then considered for how each of the dipole elements are spaced from each other. This spacing pattern continues until the dipole length at which the higher frequency limit is half wave resonant. This would be the shortest dipole length on the Dipole Array.
Final Sensors
Field Mill
The following is a picture of the final Field Mill that we created. For the final sensor, we integrated the Field Mill sensor apparatus into the PCB board that housed our support circuitry. The amount of charge can then be found from the LCD display along with the polarity of the charge exposed to the Field Mill. The polarity of charge is determined from the phase of the output and the current position of the rotating plate and is also displayed on the LCD. More detailed information can be found in the Final Document.
Flux-Gate
The image below shows the inside of the flux-gate enclosure. You can see the microprocessor and many of the internal components. The four blue pots are used for adjusting a cetain aspect of the drive signal. The two green connectors are for attaching the flux-gate to the circuitry. The PCB was designed to be very spacious which eliminates issues with manufactuing in house boards. This also helps eliminate crosstalk with other portions of the board.
Here is a photo of the finished flux-gate. The drive winding on this gate has roughly 250+ winds, while the sense windings are roughly 100+. The glass tube is used to protect the gate. The copper magnet wire used was 32 gauge and is easily damaged if not handled properly.
Loop Coils
Below is a picture of the two loop coils that were used to measure magnetic and electric fields. The smaller coil on the left provides readings in the frequency range of 40-200 MHz while the larger coil on the right is used for 1-30 MHz. As can be seen from the picture, the small coil has a tuning capacitor connected in series. For this coil, the particular frequency that is tuned in is around 94 MHz. Therefore, the coil works best near that frequency. A variable capacitor is used on the larger coil. The capacitor is set so the coil has a resonant frequency near 2.5 MHz. By connecting the coil to a spectrum analyzer and knowing the antenna factor at the frequency of interest, the corresponding magnetic and electric fields can be found.
Log Periodic Dipole
Andy, enter some info.
Files
| File: Files |
Code
| Code: Code Title |
Keywords
- Electromagnetic
- Electric Field
- Magnetic Field
- Sensors
- Charge
- Field Mill
- Flux-Gate
- Fields
- Log Periodic
- Antenna
- Loop Coil
- Dipole
- Calibration
Links
The following are some useful links that we had compiled. A really fun, yet simple charge detector is found in the first link under the Static Electric Field link. Check it out.
Contacts
Feel free to contact us about any questions about our design project.
