Microwave Calorimeter

Sponsor: Chris LeachMerlyn Bluhm

Chris De La CruzBen Schaefer

High Power Microwaves (HPM)

~2-5GHz, ~1GW◦ Compare to 783GW

Used in◦ High resolution radar◦ Military “soft kill” of

electronics◦ IED’s

Used to measure microwave power

Traditionally used to measure endo- and exo-thermic chemical reactions

Container of alcohol◦ Absorbs microwave power◦ Expands into capillary tube◦ Gives energy change

Calorimeter Overview

Subcomponents

Physical housing◦ Microwave-

transparent case◦ Capillary tube

Microcontroller◦ Sensors◦ Heating/calibration

coils◦ Feedback◦ Signal/LCD output

Physical Housing - Case

Physical Housing–Capillary Tube

Coaxial capillary Height measured

via resistance◦ Wheatstone bridge

Microwave Source

~1GW ~14J

Goals of System

Accurately measure power

Provide method of calibration

Output scaled signals to oscilloscope and computer

• Chris Leach (Sponsor)– Calorimeter Body Design and Assembly– Physics Guru

• Merlyn– Software Development / Signal Processing

• Chris– Cap Tube Instrumentation, Temp Measurement

• Ben– Amplifiers, DAC, Sample and Hold, Heater Coil

Roles of Team Members and Sponsor

Microcontroller Block Diagram

Arduino vs PIC

• $30• C++ Programming• 14 Digital I/O ports (6 PWM)• 6 Analog input ports• Stackable thermocouple

module• Free multiplatform

software, tons of sample code

• No direct access to digital I/O ports

• Multiplexed analog ports

• Complications with installed software

– Calorimeter Body– Control Unit

• Capillary Tube• Heater / Calibration Coils• ? Temp Sensor / Feedback• Power System• MCU

– Software» Signal Scaling / Displaying» Calibration Controller» Data Archiving

– Calibration Phase– Experimental Data

Project Deliverables

Physical Dimensions◦ 4cm deep X 40cm diameter. Driven by:

source aperture diameter attenuation profile of source

Material◦ Aperture: HDPE/PiezoGlass◦ Body: HDPE/PiezoGlass or different material◦ Absorbing Material: Ethyl alcohol. (5,027 cm3 )◦ Machining capabilities will play a major role

Calorimeter Specifications

Removable Sensor Interface◦ Different tube sizes or additional thermocouples◦ Our Idea

Source and calorimeter specs will yield:◦ ΔT = 6.25 x 10-3 °C◦ ΔV = 0.0325 cm3

Calorimeter Specifications Cont…

Physical Dimensions ◦ Tube: 0.0314” (0.08 cm) dia X 4.0” (10.2 cm) length◦ Wire: 0.010” (4e-3 cm) dia◦ Predicted fill level during experiment: 3.5” (8.9 cm)◦ Must hold off main alcohol volume

Resistance◦ Conductivity of alcohol: 5.63e-8 S/m? => 17.8 MΩ/m◦ For coaxial geometry: R’ = 3.11 MΩ/m

Experiment◦ For 1cm initial fill level: R0 = 31 kΩ

◦ For 8.9 cm displacement at 14 J: delta R = 278 kΩ◦ Wheatstone bridge should not be required◦ Must know voltage breakdown specs of alcohol to optimize

detection circuit

Capillary Tube

• Expected Temperature Change: 6.25 x 10-3 °C– Very, very low and atypical

 • Thermocouple

– Sensitivity: 40 μV/°C , Accuracy: 1°C– Expected output: 0.24 μV w/o amplification– Not feasible

• RTD – Resistance Temperature Detector– Sensitivity: 1.8 mΩ/°C , Accuracy: 30 x 10-3 °C– Current constraint: 1mA– Expected output w/ Wheatstone bridge: 1 μV w/o amplification– Viable option but is accuracy adequate?

• May forgo temperature measurement – Physics say the capillary tube should be adequate

Temperature Measurement

300W DC Power Supply

PID algorithm to control temp

NiChrome Wire◦ Ohms/ft

Use IGBT for switching◦ Fast response time◦ Large power rating (1KW)

Heater Circuit

Amps, DAC, S&H

• Amplify small voltages from capillary tube and temp sensor

-mV => 0-5V Scaled

• DAC: Generate analog data from MC

- TBD

• S&H: Closed loop system between MC and S&H

- Collect data when we want it

• Implement sample code for analog voltage mapping– Read-in capillary tube resistance via voltage change

• Extrapolate total energy deposition from calorimeter dynamic equations

• Implement PWM signal to calibration power system

• Display / record experimental data

Software Development

• Current Issues– ΔT, 6.25 x 10-3 °C

• Resolved Issues– MCU choice– Alcohol Volume

Challenges and Concerns

Cap Tube Bench Test

Prototype Software for Functional I/O

Heater System Spec’ed◦ Power◦ NiCr◦ Other components

Calorimeter Fab Complete

Milestones for End of Fall Semester

Calorimeter Fab – Dec 2011

Controller Development – Dec 2011

Calibration – Feb 2012

Experiment/Testing – Apr 2012

Major Schedule Milestones

◦ Entrenched in all phases from initial design to final testing.

◦ Combination of digital, analog, software, power.

◦ Project emulates real world job scenario.

◦ Team effort

Why This is a Good Senior Design Project

Questions?