Piezoelectric Devices for Vibration Energy Harvesting

Transcription

1 NiPS Summer School 010 nergy Harvesting at micro and nanoscale Piezoelectric Devices for Vibration nergy Harvesting Vittorio Ferrari Dip. Ingegneria dell Informazione Università di Brescia - ITALY Sensors and lectronic Instrumentation Laboratory Activity: Sensors and instrumentation systems Analog and digital electronic circuits and systems for: sensor interfacing sensor communication and networking measurement applications Sensors, MicroSystems and lectronic Interfaces: Piezoelectric transducers, acoustic-wave and resonant microsensors MMS sensors and systems Contactless sensors lectronic interfaces for sensor signals nergy harvesting for autonomous sensors 1

2 Contents Introduction Piezoelectric effect for energy harvesting xamples of piezoelectric energy harvesters From raw harvested energy to usable power supply Prototypes of battery-less autonomous sensor modules Conclusions Contents Introduction Piezoelectric effect for energy harvesting xamples of piezoelectric energy harvesters From raw harvested energy to usable power supply Prototypes of battery-less autonomous sensor modules Conclusions

3 Sensor Systems sensor element microsystem/mms electronic board communication capability network connectivity Sensor elements into microsystems/mms into packaged electronic modules with wireless communication capability and network connectivity Systems of Systems sensor element microsystem/mms electronic board communication capability network connectivity sensor element microsystem/mms electronic board communication capability network connectivity sensor element microsystem/mms electronic board communication capability network connectivity Pervasive sensing and computing Ambient intelligence The internet of things 3

4 General Architecture of a RF Sensor RF link environment/ system/ process sensor external readout unit information Information flow requires exchange of energy Assuming the external readout unit is energetically self-sufficient the sensor needs power supply Power Supply Options: #1 RF link environment/ system/ process sensor external readout unit information Power supply internal to the sensor (on-board): Batteries Fuel cells 4

5 Power Supply Options: # RF link environment/ system/ process sensor external readout unit information Power supplied by the external readout unit: Passive RFId devices (class 1 and ) Passive telemetric sensors Chipless RFId sensors Power Supply Options: #3 RF link environment/ system/ process sensor external readout unit information Power extracted (harvested) from the surrounding ambient 5

6 nergy from Ambient: the idea is not new Water- and windmills. 1770, A.L. Perrelet, self-winding watch. 1930, Jaeger-LeCoultre, Atmos clock powered by thermal fluctuations. Present, Motorola PVOT hand-crank phone. Present, olic generators. Present, FreePlay, wind-up radio. 1956, Zenith, battery-less ultrasound remote. nergy Harvesting (Scavenging) Principle: nergy is extracted from the surroundings Surroundings nergy CONVRSION lectrical domain CONDITIONING LOAD nvironment Human body Radiant Kinetic Thermal The load can be: - lectronic circuits and devices - Sensors with wireless communication Autonomous Sensors - 6

7 Radiant nergy Harvesting Principle: nergy is extracted from the surroundings nergy CONVRSION lectrical domain CONDITIONING LOAD Radiant nergy Solar Radio Frequency Thermal Harvesting Principle: nergy is extracted from the surroundings thermal gradients nergy CONVRSION lectrical domain CONDITIONING LOAD Thermal nergy Thermoelectric effect Pyroelectric effect 7

8 Mechanical nergy Harvesting Principle: nergy is extracted from the surroundings nergy CONVRSION lectrical domain CONDITIONING LOAD Mechanical nergy Mechanolectrical Conversion Magnetic induction conversion lectrostatic conversion Piezoelectric conversion 8

9 Mechanolectrical Conversion Magnetic induction conversion: Magnetic induction conversion lectrostatic conversion Piezoelectric conversion NightStar flashlamp Mechanolectrical Conversion Magnetic induction conversion: Magnetic induction conversion lectrostatic conversion Piezoelectric conversion 9

10 Mechanolectrical Conversion Magnetic induction conversion: Magnetic induction conversion lectrostatic conversion Piezoelectric conversion Mechanolectrical Conversion lectrostatic conversion: Magnetic induction conversion lectrostatic conversion UCB, Berkeley, USA UCB, Berkeley, USA Piezoelectric conversion V.Ferrari Summer School: MIT, Boston, nergy Harvesting USA at micro and nanoscale, Aug. 1-6,

11 Mechanolectrical Conversion Piezoelectric conversion: F + + q q Magnetic induction conversion - F - 33 mode 31 mode lectrostatic conversion NC -Tokin, Japan Piezoelectric conversion V.Ferrari Summer School: nergy MIT, Harvesting Boston, at micro USA and nanoscale, Aug. 1-6, 010 Mechanical nergy Harvesting Direct deformation (strain).g. piezoelectric fiber composites Impact & transient loads.g. piezoelectric thin plates Vibrations Seismic-mass inertial system THUNDR, Face International Corp, USA. (approximated for piezoelectric converters) C.B. Williams, R.B. Yates,, Sens. Actuat. A 5, 8-11 (1996). Unfavorable scaling with reducing dimensions 11

12 Contents Introduction Piezoelectric effect for energy harvesting xamples of piezoelectric energy harvesters From raw harvested energy to usable power supply Prototypes of battery-less autonomous sensor modules Conclusions The Piezoelectric ffect Discovered in by the Curie brothers Property of certain materials in which: a mechanical stress induces an electric charge (direct effect) an electric field develops a mechanical strain (converse effect) Direct effect: detection The effect is linear, as opposed to electrostriction Converse effect: generation 1

13 Applications of Piezoelectricity Sonic and ultrasonic wave generation and detection: Sensors and transducers Filters and resonators lectromechanical & Mechanolectrical conversion: Actuators Transformers Gas igniters Motors and machining tools Nebulizers and humidifiers nergy harvesters Quartz Piezofilm (PVDF) Crystal Structure and Properties The degree of structural symmetry affects the piezo and pyro properties of the material 3 classes (point groups) 1 non centrosyimmetrical 11 centrosymmetrical... 13

14 Crystal Structure and Properties The degree of structural symmetry affects the piezo and pyro properties of the material 3 classes (point groups) 1 non centrosyimmetrical 0 piezoelectric (stress-induced polarization) 11 centrosymmetrical quartz turmaline... Piezoelectricity in Quartz Z Y X Si + O - - X axis: electrical axis Y axis: mechanical axis Z axis: optical axis X X

15 Crystal Structure and Properties The degree of structural symmetry affects the piezo and pyro properties of the material 3 classes (point groups) 1 non centrosyimmetrical 0 piezoelectric (stress-induced polarization) 10 pyroelectric (polar with spontaneous polarization) 11 centrosymmetrical quartz turmaline... AlN ZnO... Crystal Structure and Properties The degree of structural symmetry affects the piezo and pyro properties of the material 3 classes (point groups) 1 non centrosyimmetrical 0 piezoelectric (stress-induced polarization) 10 pyroelectric (polar with spontaneous polarization) ferroelectric (pyroelectric with electrically-reversible polarization) 11 centrosymmetrical quartz turmaline... AlN ZnO... BaTiO 3 PbZr/ TiO (PZT)

16 Ferroelectrics Materials in this class exhibit the strongest piezo e pyro effects Monocrystals (e.g. Rochelle salt) or Polycrystals (e.g. PZT ceramics) Dipoles are arranged in domains Above T Curie the domains are randomly oriented Poling: an electric field is applied to orient the domains and set up a permanent polarization Lead Zirconate Titanate (PZT) Ferroelectric polycrystalline ceramic made by a solid solution of two perovskite type oxides (ABO 3 ): PbZrO 3 PbTiO 3 Above Curie temperature : cubic, nonpolar Below Curie temperature : rhombohedral/tetragonal, polar Large piezoelectric and pyroelectric effects High coupling coefficient Various compositions (PZT-4, PZT-5, PZT-5H Navy, ) Other commercial name: PX 16

17 Basics of Piezoelectricity (1) Interaction between lectrical and Mechanical domains described by linear piezoelectric constitutive equations Several options depending on the chosen M variables In the monodimensional simplified hypothesis: S = s T + d T = c S e T S D = dt + ε D = es + ε D S = s T + gd D T = c S hd T = gt + D ε = hs + D ε T d = ε g = s e = [ C/N] = [ m/v] S e = ε h = c d = [ C/m] = [ N/mV] T D g = 1 ε d = s h = [ m/c] = [ Vm/N] S D h = 1 ε e = c g = [ N/C] = [ V/m] ε = ε + de ; c = c + he T S D S S = strain [m/m] T = stress [N/m ] D = dielectric displacement [C/m ] = electric field [V/m] s X = elastic compliance [m constant X c X =1/s X = elastic stiffness [N/m constant X ε X = dielectric permittivity constant X d, e, g, h = piezoelectric constants xamples of Piezoelectric Materials TP38, Matroc lectroceramics. 17

18 A Piezoelectricity Modeling Making reference, for T = c S e instance, to the formulation: S D = es + ε passing to global variables force F, displacement X, voltage V, and current I, an equivalent-circuit representation can be drawn: l F, X I V c A ea ea F = X V F = k X V l l l S ea ε A ea S Q = X + V I = jωx + jωc V l l l F jωx 1 / k V ea l jωx ea l C S I V F jωx 1 / k α = ea l * C S α : 1 * DC-responding ideal transformer I V Piezoelectricity Modeling ea F = k X V l ea S I = jωx + jωc V l! Spring constant k (capacitance C) depends on electrical (mechanical) boundary conditions Spring constant: lectrically F shorted = X Capacitance: Mechanically I clamped = jωv k C S Mechanical spring F F lectrically opened Mechanically free jωx 1 / k jωx 1 / k lectrical capacitor α : 1 C S Piezoelectric element F X = k I = C jωv C S I I A + eh = k l S D V V A + ed = C l > k T > C S 18

19 lectro-mechanical Coupling The energy transfer between the M domains can be expressed by the electromechanical coupling factor κ: κ F jωx 1 / k (stored energy) = = (supplied energy) M α : 1 (stored energy) M (supplied energy) By reflecting the corresponding impedance through the transformer ports it results: κ = α α + k C S e = D c ε S d = s ε T C S I V Power Conversion from Vibrations A vibrating structure is assumed to move with dynamic displacement x(t) with respect to a fixed reference A seismic equipment is used to convert the displacement x into an inertia force acting on the proof mass m This in turn causes a relative displacement y(t) between the structure and the proof mass generating a stress in the piezo A lumped-element model can be used to describe the system around resonance z x x y x k vibrating structure piezoelectric element I vibrating structure m r vibrating structure piezo V m Z L 19

20 Piezoelectric Power Conversion m z y x k m r vibrating structure piezo 1 / k F Z y r L jωy 1 / k F y = - ω mx I C S Z L V α : 1 In general, a maximum exists to the power that can be extracted by an ideal converter This power limit occurs at resonance and for a converter with a purely resistive mechanical impedance adapted to r: P m X&& = 8r lim = m a 8r x z Piezoelectric Power Conversion y x k m r vibrating structure piezo F Z y r L jωy 1 / k m 1 / k F y = - ω mx at resonance r I C S Z L V α : 1 In general, a maximum exists to the power that can be extracted by an ideal converter This power limit occurs at resonance and for a converter with a purely resistive mechanical impedance adapted to r: P m X& = 8r lim = m a 8r x Same results as in: C.B. Williams, R.B. Yates,, Sens. Actuat. A 5, 8-11 (1996). 0

21 Piezoelectric Power Conversion m z y x k m r vibrating structure piezo Z L F y 1 / k r F y = - ω mx jωy 1 / k I C S Z L V α : 1 Assuming Z L = R, the transfer function between F y and Y is: S Y 1+ jωrc = S F jωrα + (1 + jωrc ) ω m + jωr + k + k y I F y = Y F y I Y = jωrα [ ] The transfer function between F y and I is then: S + (1 + jωrc ) jωα [ ω m + jωr + k + k ] Piezoelectric Power Conversion The electrical power P on a resistive load R is: P R I = R Fy jωα = S jωrα + (1 + jωrc ) P is a function of R that maximizes to P opt at the optimal resistive load R opt P opt is a function of frequency that maximizes at about the short-circuit natural frequency: k + k ωsc = m P opt tends to P lim with increasing the electromechanical coupling factor κ [ ω m + jωr + k + k ] R.D hulst, J.Driesen, I, (008). 1

22 z Piezoelectric Power Conversion y x k m r vibrating structure piezo Z L F y m 1 / k r F y = - ω mx The energy balance gives: 1 1 F ydt & my& y = + k + k y + ry& ( ) dt + Kinetic energy lastic energy The transferred energy is in turn: V 1 S α ydt & = C V + VIdt lectrostatic energy Dissipated energy Load energy jωy 1 / k α : 1 αv ydt & Transferred energy I C S Z L V Contents Introduction Piezoelectric effect for energy harvesting xamples of piezoelectric energy harvesters From raw harvested energy to usable power supply Prototypes of battery-less autonomous sensor modules Conclusions

23 Mechanical nergy from Vibrations Nanoscale nergy Converters A single piezoelectric nanowire of BaTiO 3 excited by vibrations generates current M.F. Yu et al., ScienceDaily, 8 September

24 Nanoscale nergy Converters Piezoelectric nanowires of ZnO deflected by an AFM tip or excited by ultrasound waves generate current Z.L. Wang et al., SPI Newsroom, 5 March 008. Nanoscale nergy Converters 4

25 Nanoscale nergy Converters Microscale nergy Converters Piezoelectric MMS under typical excitations generate in the order of 1 µw Resonant frequency = 184 Hz. Resonant frequency = 13.9 khz. D. Shen et al., Sens. Actuat. A 154, (009). D. Jeon et al., Sens. Actuat. A 1, 16- (005). 5

26 Application to TPMS Next generation Tire-Pressure Monitor Systems (TPMS) will dismiss batteries and rely on energy harvesting MMS converters can find their way in the field Macroscale nergy Converters: commercial devices 6

27 Macroscale nergy Converter 1.0 u L F W T W = 15mm L = 40mm T = 500µm PZT: Piezokeramika 856 d 33 = 590pC/N d 31 = -60pC/N ε r = 4000 i V BAM PIZOLCTRIC LAYR V L [V] V L [V] C P =151pF R P =363MΩ (A = 13.6V) V.Ferrari C L [pf] C L [pf] M.Ferrari et al., I Trans. Instrum. Summer Meas. School: 55, nergy (006). Harvesting at micro and nanoscale, Aug. 1-6, 010 acceleration [g] R L [MΩ] Resistive load R L Computed xperimental f [Hz] Capacitive load C L Computed xperimental P L [µw] P L [µw] Computed xperimental R L (MΩ) Computed xperimental Film Properties Alumina substrate W = 18 mm L = 31 mm Film Thickness = 15 µm W L Harmonic steel substrate W = 5 mm L C = 35 mm L P = 30 mm W L C L P D [µc/cm ] [MV/m] time [ms] - room temperature [MV/m] parameter BULK CRAMIC THICK FILM rel. dielectric const. ε Τ /ε o ± 10 density ρ [g/cm 3 ] ± 0.1 7

28 Limitations with Resonant Converters Best harvesting effectiveness is when the converter operates at mechanical resonance This is problematic to guarantee with frequency-varying vibrations and is considerably sub-optimal for wideband noise f 0 f 0 frequency frequency Lowering the converter quality factor increases the bandwidth, but worsens the peak response f 0 frequency Frequency Up-Conversion Mechanical methods have been proposed to up-shift the vibration frequency where the converter is more responsive D.G. Lee et al., Proc. Transducers & urosensors 07, (007). 8

29 Frequency Tuning An adjustable axial tension changes the beam resonant frequency C. ichhorn, F. Goldschmidtboeing, P. Woias, Proc. PowerMMS 008+microMS008 (008). The method is not self adaptive lectrical automatic tuning can be used, but this requires extra energy MultiFrequency Converter Array Multiple converters combined to obtain a wider equivalent bandwidth: Vo/Vi [db] f [Hz] 3 MFCA on the vibration exciter (shaker). Silicon MMS with PZT films: Design: University of Brescia Fabrication: CNM, Barcelona, Spain In collaboration with: 500? µm m M. Ferrari et al., Sens. Actuat. A 14, (008). 9

30 Multi-Frequency Converter Array MMS Implementation PZT low-curing-temperature film IDT electrodes (d 33 mode) mbedded piezoresistors M.Guizzetti, PhD Thesis, University of Brescia (010). Multiple-Converter System Multiple converters are coupled into a single structure Z. Chew, L. Li, Sens. Actuat. A 16, 6-9 (010). 30

31 Nonlinear Approach: Theory Bistability is exploited to amplify displacement induced by random vibrations due to stochastic resonance For decreasing values of d: Quasi linearity Nonlinearity Bistability M. Ferrari et al., Sens. Actuat. A, in press. Nonlinear Approach: xperiment Bimorph cantilever beam fabricated with: Stainless steel Low-curing-temperature PZT films M. Ferrari et al., Sens. Actuat. A, in press. 31

32 Nonlinear Approach: Results Behaviour in agreement with theory: M. Ferrari et al., Sens. Actuat. A, in press. Nonlinear Single-Magnet Converter A ferromagnetic substrate is coupled to a fixed magnet PZT film F el V P Input mechanical excitation F A F Ah x Ferromagnetic cantilever decreasing d d N S t Permanent magnet Tip displacement x [mm] 3 F Av = α x β x F el = kx Stable states Time [s] U ( k α) = β 4 4 ( x) x x Output voltage V P [V] M. Ferrari et al., urosensors 010 and Procedia ngineering, in press. 3

33 Contents Introduction Piezoelectric effect for energy harvesting xamples of piezoelectric energy harvesters From raw harvested energy to usable power supply Prototypes of battery-less autonomous sensor modules Conclusions Power Supplied to a Resistive Load Average power into a resistive load R L : P = Sinusoidal regime at f 0 jπf0cprl 1+ jπf C R 0 P L P V R L VP 1 Popt = RL = ω C 4R 0 P L C P V P I L R L V L Broadband between f 1 and f f f jπfcprl 1 P = SV ( f ) df = P 1+ jπfc R R f1 P L L The power spectral density S VP ( f ), commonly used as an indicator of signal power, is not sufficient to describe P The weighting function H ( f ) should be also considered f1 S VP ( f ) H( f ) 1 df R L 33

34 Usable Power in lectronics A large power into a resistive load does not necessarily mean a correspondingly high usable power This is because power into a resistive load is associated to AC voltage (current) lectronic circuits and microsystems usually need DC power supply AC/DC converters, i.e. rectifier circuits, are required They in turn introduce nonidealities and losses, and pose requirements on the voltage levels to operate properly AC/DC Circuits in Sinusoidal State AC and DC driving of a resistive load: AC-driven load DC-driven load Synchronized Switch Harvesting on Inductor (SSHI) technique: Voltage has the same sign of velocity V.Ferrari D.Guyomar et al., I Trans. on UFFC, 5, (005). Summer School: nergy Harvesting at micro and nanoscale, Aug. 1-6,

35 AC/DC Circuits in Sinusoidal State SSHI for AC load driving: SSHI for DC load driving: V.Ferrari D.Guyomar et al., I Trans. on UFFC, 5, (005). Summer School: nergy Harvesting at micro and nanoscale, Aug. 1-6, 010 AC/DC Circuits in Sinusoidal State Power comparison under weak M coupling Power comparison versus the M coupling V.Ferrari D.Guyomar et al., I Trans. on UFFC, 5, (005). Summer School: nergy Harvesting at micro and nanoscale, Aug. 1-6,

36 Intermittent Operation Differences with respect to load driven under sinusoidal steady state arise when energy must be accumulated Surroundings nergy CONVRSION lectrical domain CONDITIONING LOAD If available power is insufficient for continuous supply of the system Intermittent operation CONVRSION STORAG SWITCHING LOAD Contents Introduction Piezoelectric effect for energy harvesting xamples of piezoelectric energy harvesters From raw harvested energy to usable power supply Prototypes of battery-less autonomous sensor modules Conclusions 36

37 Autonomous Module with RF Link The converted energy is stored and intermittently used to trigger a radio-frequency (RF) transmitter vibrations Piezoelectric Converter V P C b Rectifier and storage capacitor V C Sensing and switching DC Voltage regulator V R+ V R- RF Transmitter! No battery, no internal power sources! How a sensor can be inserted into the system?...considering that: the power budget is quite restrictive voltage and current levels are poorly defined suitable resolution should be granted RF Receiver Autonomous Sensor Module The converted energy is stored and intermittently used to trigger a radio-frequency (RF) transmitter V P V C V R+ vibrations Piezoelectric Converter C b Rectifier and storage capacitor Sensing and switching DC Voltage regulator V R- RF Transmitter RF Receiver sensor Oscillator The sensor (R or C) is inserted into an oscillator The oscillator frequency modulates the envelope of the RF carrier The measurement information is carried in the time domain 37

38 Autonomous Temperature Sensor VP VC VR+ DC vibrations Piezoelectric Converter Cb Rectifier and storage capacitor Sensing and switching VR- Voltage regulator RF Transmitter RF Receiver sensor Oscillator Thermistor response curve NTC pcos K164/10k f OSC 1.44 = ( R R ) C 1 + S S Sensitivity: S T 1. 3kHz C Standard deviation (30 repetitions): 3σ 30Hz Resolution: σ 10Hz RT = = = C V.Ferrari S khz C Summer School: nergy Harvesting T 1.3 at micro and nanoscale, Aug. 1-6, 010 Autonomous Temperature Sensor Piezoelectric vibration-powered module for temperature sensing and transmission of the reading over a RF link nergy conditioning and storage vibrations Signal conditioning and RF transmission Piezo bimorph 38

39 Autonomous Multi-Sensor Module The piezo harvester powers a module comprising sensors nergy is sequentially switched between the sensors Signals are transmitted in time multiplexing SNSOR Impedance Controlled Oscillator RF Transmitter RF Receiver SNSOR 1 Impedance Controlled Oscillator 1 SPDT switch Monostable Mechanical Vibrations Piezoelectric converter C b Rectifier and storage capacitor V C Sensing and switching DC Voltage regulator Autonomous Multi-Sensor Module The piezo harvester powers a module comprising sensors nergy is sequentially switched between the sensors Signals are transmitted in time multiplexing SNSOR Impedance Controlled Oscillator RF Transmitter RF Receiver SNSOR 1 Impedance Controlled Oscillator 1 SPDT switch Monostable V C DC 7 Cb 0.5 Piezoelectric Rectifier and Sensing and Voltage converter storage capacitor switching regulator A digital ID-code can also be transmitted for -1 module tagging and tracking Time [ms] V.Ferrari M. Ferrari et al., Smart Mater. Struct., 18, (009). Summer School: nergy Harvesting at micro and nanoscale, Aug. 1-6, 010 Mechanical Vibrations Vc,V RX [V] A.U. 39

40 Multi-Frequency Converter Array Multiple differently-tuned converters combined to obtain a wider equivalent bandwidth: Vo/Vi [db] V 1 V V 3 C D1 Cp1 m Vp1 1 D V1 Rp1 C DD Conductive base Cp Vp 0 V D Cb Rp C D3 Cp Vp3 V3 D -60 Rp f [Hz] m 3 m Measured frequency response. M. Ferrari et al., Sens. Actuat. A 14, (008). Multi-Frequency Converter Array: experimental results Wideband excitation: V [V] t [ms] Measured open circuit voltages of the three converters. 1 V Cb [V] fb fa 1 3 Cantilever t [s] 3 ALL Measured voltage across the storage capacitor. 1 M. Ferrari et al., Sens. Actuat. A 14, (008). 40

41 Multi-Frequency Converter Array: experimental results Wideband excitation: SNSOR Impedance-Controlled Oscillator MultiFrequency Converter Array Mechanical Vibrations VOSC RF Transmitter Switched-Supply Unit V Cb [V] 9 8 t switching 7 6 t switching ALL t [s] Measured voltage across the storage capacitor. Output Combinations in a MFCA Parallel-like combination: Rectified currents are fed to a single capacitor C I 1 P1 D I Cb C V 1 m 1 V V P1 R P1 V 1 D V 3 C P Conductive base V P R P m 3 m V C D D I C b V Cb C P3 C D I 3 V P3 R P3 V 3 D M. Ferrari et al., Proc. SNSORDVICS-010, (010). 41

42 Output Combinations in a MFCA Series-like combination: Rectified voltages on different capacitors are summed V 1 V V 3 m 3 m m 1 V P1 C P1 R P1 V 1 C D D C b1 V Cb1 Conductive base C P C D V P R P V D C b V Cb V Cb C P3 C D V P3 R P3 V 3 D C b3 V Cb3 M. Ferrari et al., Proc. SNSORDVICS-010, (010). Output Combinations in a MFCA xperimental results: Converter 1 Converter Converter 3 VP (V) Series-like configuration Parallel-like configuration The series-like configuration reaches the threshold to trigger the RF transmission It is especially suitable for arrays of low-voltage MMS converters M. Ferrari et al., Proc. SNSORDVICS-010, (010). 4

43 Contents Introduction Piezoelectric effect for energy harvesting xamples of piezoelectric energy harvesters From raw harvested energy to usable power supply Prototypes of battery-less autonomous sensor modules Conclusions Final Comments nergy harvesting for sensors is a fast-growing area evolving from gadgets to enabling technology in such fields as: Industrial control and automation Transport, automotive, avionics Power plants & distribution Structural monitoring Medical and healthcare Security and military University of Brescia is active in the field with: Applied research programs Projects in cooperation with industrial Partners Università di Brescia: Acknowledgments Marco Baù Michele Guizzetti Simone Dalola Daniele Marioli Marco Demori manuele Tonoli Marco Ferrari Stefano Zaiba 43