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Battery-Less IoT Device: Energy Harvesting Project

This project focuses on harvesting and converting ambient RF waves into usable energy to power IoT devices with minimal cost and efficient operation. The team is working on implementing antenna and power circuit platforms, along with embedded systems for data recording and transmission. They aim to create a prototype device under $100 that is portable, efficient, and reliable for demonstration.

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Battery-Less IoT Device: Energy Harvesting Project

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  1. Battery-less IoT Devices Battery-Less IoT Device SD-DEC19 Team 21 Advisor: Dr. Henry Duwe Clients: Dr. Nathan Neihart Dr. Daji Qaio http://sddec19-21.sd.ece.iastate.edu/

  2. Member Contributions • Antenna design and testing • Matt & Mohamed G • Power System & Rectifier design and testing • Derek & Adi • Microcontroller functionality, communications, and testing • Mohammed Al-Mukhaini & Brad • Website design/maintenance • Mohammed Al-Mukhaini & Derek • Documentation • All members • Outreach/ meeting coordination • Mohammed Al-Mukhaini

  3. PROJECT PLAN

  4. Problem Statement • General Problem statement: • Harvest RF energy and convert it into a form useable by a microcontroller • General Solution Approach: • Harvest and convert ambient RF waves into DC • Gradual charge and storage (capacitor) • Low Power Mode Microcontroller

  5. Conceptual Sketch

  6. Functional Requirements Energy Harvesting • Harvest RF signal from WiFi router Power • Long term low voltage storage • Regulated Voltage supply to microcontroller Rectifier • Rectified & Multiplied voltage ≥ 1.8 V Embedded Systems • MSP430 microcontroller • Record temperature via internal ADC • Store and transmit data at a later time

  7. Non-functional Requirements • Portability • Prototype reasonable size • Compatible • Efficiency • Reasonable operation and charging time • Testability • Reliable for demonstration • Reasonable cost • Under $100

  8. Market Survey • Not many other manufacturers • Powerspot kit • www.powercastco.com • Focused on harvesting • Not communicating • HUGE potential • Network of batteryless devices • Self-sustaining • Remotely located • Dependable

  9. Potential Risks Device Safety • ESD • Fall height Financial Safety • Unfeasible to implement • Parts are too expensive Public Safety • Device is above head height • Touching may induce a shock

  10. Resource Cost Estimate

  11. SYSTEM DESIGN

  12. Functional Modules

  13. Antenna Circuit Platforms • Patch Antenna radiating at 2.4GHz • Easy to manufacture, low-profile • Generating low power • Moderate antenna efficiency Figure 01: 2.4 GHz Patch Antenna

  14. Antenna Circuit- Simulation • Simulation, tuning, and validation done through HFSS • dB gain values, radiation pattern and S parameters

  15. Power Circuit Platforms • Cockcroft-Walton Voltage Multiplier (CW) • Rectify & Multiply • 2 Stage multiplier • Primary Component • Schottky diode (Skyworks Schottky Diode SC-79) • Low forward voltage drop • Negligible leakage current Figure 04: Schematic of CW voltage multiplier Figure 5: PCB design of CW voltage multiplier

  16. Power Circuit- Simulation • Using ADS (Advanced Design Systems) • Tests include: S-parameter, transient, and harmonic balance Figure 06: Rectifier circuit simulation Figure 07: Rectifier Schematic on ADS

  17. Embedded Systems Platforms (MSP430FR2100) • MSP430FR2100 MCU • Voltage Range: 1.8v - 3.6 v • Low Power Modes • Different current supply demand • System clock up to 16MHz • FRAM - 1KB • Unified memory program, constants, and storage • 10-bit ADC • Integrated UART functionality

  18. Embedded Systems- Testing and Simulation • MSP-EXP430FR5994 • Code Composer Studio • Energia Current Developments • Temperature data recorded and stored in FRAM • Previously recorded data is not overwritten • Display and measure energy profile

  19. Building Block Implementations Figure 8: Hardware flow Implementation Figure 9: Software flow control Implementation

  20. CONCLUSION

  21. Project Milestones & Schedule • MCU code working on development board - May 2019 • Rectifier circuit built - Mid September 2019 • Energy harvesting circuit built - October 2019 • Prototype board assembled - October 2019 - early December 2019 • Final product assembled - Mid December 2019

  22. Current Status

  23. Plan for next semester • Finalize software and flash code onto FR2100 MCU • Incremental tests, culminating in full test • Delivery of final product

  24. QUESTIONS?

  25. Energy Storage - Capacitor • Capacitor to store charge • Power demand • X = 1.8V = min voltage for MSP430 • W = ideal steady operation power (watts) • t = operating time • Vs = starting voltage (output of rectifier) • VC = Vs * e-t / (RC) • W = X2 / R => R = W / X2 • VC = Vs * e(-t*X^2) / (WC) • X≤ Vs * e(-t*X^2) / (WC) • With all other variables found, solve for C

  26. Justification - Rectifier V0 = 2nVMAX - ⃤ V0 Ideally, ⃤ V0 = 0. But due to not-fully-charged capacitors, we have: Larger C = smaller ⃤ V0 loss Proof: https://www.hindawi.com/journals/jece/2017/4805268/ (plan to test with several different types of capacitors empirically)

  27. Justification- Schottky Diodes • No depletion region → low forward voltage drop • Electrons present on both sides of the junction • Current conduction due to electron movement only → negligible leakage current • No reverse recovery time • Instantaneous switching action

  28. MSP430 Energy Consumption • Current draw drops rapidly when switching to lower power modes • Efficiency increases when operating at higher frequencies and lower voltages

  29. FR 4 Parasitics Calculation • Capacitance Parasitics • Trace Inductance Parasitics • Inductance Parasitics

  30. Potential Risks Headache Device Safety • ESD • Fall height Financial Safety • Unfeasible to implement • Parts are too expensive Public Safety • Device is above head height • Touching may induce a shock Electric Shock Electrostatic Discharge Short Circuit LOW RISK FACTOR

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