Objectives 1. Introduction 2. Limitation of the present system 3. Suggestion that is offered 4. Transducers 5. Ambient energy 6. Electrical damping 7. Electrostastic transducers 8. Electromagnetic transducers 9. Piezoelectric transducers 10. Conclusions

Introduction  Focuses on the need for energy investment.  Boosting of output power by increasing damping energy.  Transducers included : electrostatic, electromagnetic, piezoelectric.

Limitations of the present system  Wireless micro sensors use small batteries to meet the power demands.  Miniaturized batteries unfortunately exhaust easily.  This limits the deployment of the micro sensor devices to few niche markets.  Increase in the budget.

Suggestion that is offered  Harnessing ambient energy.  Increasing the electrical damping force against which the transducers work.  Investing energy to increase the damping.

Transducers  Converts one form of energy to another.  Can be any conversion.  Used for measuring purposes.

Ambient energy  Also known as Energy Scavenging or Power Harvesting.  Process of obtaining energy from environment.  Classified as Energy reservoir, Power distribution or Power scavenging methods.  Enable battery independent wireless or portable systems.

Electrical damping

Inferences from the above circuit

Output power for low and high k values

CONTD…  Investing voltage in capacitor or current in inductor raises damping force.  Rise in voltage or current → rise in battery investment → square of voltage or current.  E F - E INV rises with V INV and I INV.

ELECTROMAGNETIC TRANSDUCERS

Coupling electromagnetic energy with parallel resonant tank

INFERENCES FROM CIRCUIT

Proposed system  Removed capacitors and replaced diodes.  Synchronous on chip MOSFETs.

WORKING  S EPD and S END close during positive half cycle.  Energizes L S through L p.  S EPD and S PD close and S END opens : negative half cycle.  Depletion of L s energy to V BAT.  Current reverses ; invests into L S.  S END closes and S PD opens.  Current increases below I INV by Δi L.  Invested into V BAT  Cycle concludes. Final energy = 0.5L S (I INV +Δi L ) 2 ΔiL ≈ 2V EMF.S(PK) /ω o L s

PERFORMANCE  At 0.06, Po increases iff I INV <400µA.  AT 0.03, Po peaks at 750µA.  K c << 1,conduction losses increases.  Investment below threshold holds no good.

ELECTROSTATIC TRANSDUCERS

BASIC PRINCIPLE  C VAR precharged by energy investment.  Used to establish electrostatic attraction and opposes physical movement.  Vibrations produces energy ; F DE is higher.  F DE increases as square of v c ;also E C.  Implies higher voltage induces more damping  More damping ⇒ more output power.  v c close to V MAX ⇒ more energy generated.

TYPES OF CONNECTIONS TYPES OF CONNECTIONS PERMANENT CONNECTION :  Constraining C VAR voltage with Li battery : no additional capacitor needed.  disadvantage : V BAT not the max voltage sustained.  C CLAMP used to overcome the above difficulty.  T x invest energy E INV from V BAT : precharging both capacitors.  Discharges after harvesting cycle.  C CLAMP >> C VAR, more conduction losses. ASYNCHRONOUS CONNECTION :  T X charges C VAR near V MAX before the other..  Higher than C CLAMP high voltage.  Interface circuit transfers energy from C CLAMP to V BAT.  Less energy transfer.  Diode dissipates power.

PROPOSED CONNECTION  T X charges C VAR to C CLAMP initial voltage.  S 3 closed ; energy extracted into C CLAMP.  T X discharges C VAR to V BAT  De energizing less often  S 3 dissipates less power.  Cvar remains near to V MAX.

PERFORMANCE

PIEZO ELECTRIC TRANSDUCERS  Charge generated in response to mechanical vibration.  OC current energizes and de energizes C P.  C P charged to V BAT + 2V D.  Excess flows through rectifier.  Unloaded : C P charged to 2V OC C P.  Loaded : excess charge to V BAT. BATTERY COUPLED DAMPING E H =2(Q OC – 2V BAT C P )V BAT

RECYCLING INDUCTOR:  L RE and S RE included.  C P ‘s energy recycled in the opposite direction.  Positive half cycle : C P charged to V BAT  Negative half cycle: S RE closes ; L RE de energizes C P.  Collects all of Q OC.  S RE dissipates energy. E H = 2Q OC V BAT =4C P V OC V BAT

BATTERY DECOUPLED DAMPING  Decouple V BAT : increased damping energy.  Vibrations charge C P to max value.  Discharges through L H and D N in positive cycle.  L H and D I negative cycle.  De energizes to V BAT.  C p energizes with 2V OC in half cycle.  Twice as E H ’ and 4 times E H ’’.

PROPOSED SYSTEM  Energy gained reinvested to other half.  Precharged C P to –2V OC.  Voltage increased to 4V OC.  Energy increases with square of voltage. E H ’’’ = 0.5C P (-4V OC ) 2

PERFORMANCE  Increasing investment diminishes P O.  More energy transfer through switches.  Conduction losses increases.  Enlarged FET’s balances losses ; raises P O.  72000µm raised 56% P O.

CONCLUSION  Shows that investing energy increases output power.  Coupling factor of transducers low ⇒ low power.  Invest energy to raise electrical damping.  Transducers draw more energy.  Limitation in increasing output power.

References  G. Chen et al., “Circuit design advances for wireless sensing applications,” Proc. IEEE, vol. 98, no. 11, pp. 1808–1827, Nov  S. D. Senturia, “Energy-conserving transducers,” in Microsystem DesignNew York: Springer-Verlag, 2001, pp. 125–145  L. Xun and S. Y. Hui, “Simulation study and experimental verification of a universal contactless battery charging platform with localized charging features,” IEEE Trans. Power Electron., vol. 22, no. 6, pp. 2202–2210, Nov. 2007

 R. J. M. Vullers et al., “Micropower energy harvesting,” Solid State Electron., vol. 53, no. 7, pp. 684–693, Jul  M. Kiani and M. Ghovanloo, “An RFID-based closed- loop wireless power transmission system for biomedical applications,” IEEE Trans. Circuits Syst. II, Exp. Briefs, vol. 57, no. 4, pp. 260–264, Apr  C. Chih-Jung et al., “A study of loosely coupled coils for wireless power transfer,” IEEE Trans. Circuits Syst. II, Exp. Briefs, vol. 57, no. 7, pp. 536–540, Jul

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