Nonlinear Energy Harvesting from vibrations

Transcription

1 Nonlinear Energy Harvesting from vibrations DIEEI University of Catania Italy 1

2 Outline The Energy Harvesting issue Non linear EH vs linear EH The proposed solutions & the Real LabScale Prototypes The mechanical characterization The electrical performances 2

3 THE ENERGY HARVESTING ISSUE simple vision of a WSN nodes Development of solutions aimed at powering wireless nodes by exploiting the energy scavenged from their operating environment in order to reduce (or eliminate) the need of periodic replacements of batteries (environmentally friendly). A WSN consists of: Sensors and actuators Microcontroller (μc) Radio Power 3

4 WHAT IS ENERGY HARVESTING? Energy harvesting or scavenging is a process that captures small amounts of energy that would otherwise be lost as heat, light, sound, vibration or movement, to provide electrical power for small electronic and electrical devices making them self-sufficient (replace batteries). Benefits: Maintenance free no need to replace batteries Improve efficiency eg computing costs would be cut significantly if waste heat were harvested and used to help power the computer Enable new technology eg wireless sensor networks (WSN) Environmentally friendly disposal of batteries is tightly regulated because they contain chemicals and metals that are harmful to the environment and hazardous to human health Opens up new applications such as deploying EH sensors to monitor remote or underwater locations The technologies employed, variously convert Solar radiation (PV) Wind Human power Body fluids Heat differences Vibration or other movements RF Vegetation Ultraviolet Visible light or Infrared. more options coming along to electricity (DC current). Requires expertise from all aspects of physics, including: Energy capture (sporadic, irregular energy rather than sinusoidal) Energy storage Metrology Material science Systems engineering 4

5 NEEDS Source Southampton University Hospital UK Remove the expense, inconvenience and pollution that results from frequent replacement of batteries in small devices Environmental savings Needs of the Third World (education and lighting) Needs in developed countries Source: IDTechEx report Energy Harvesting and Storage for Electronic Devices Autonomous WSN Smart systems Recharging the batteries Autonomous sensors Embedded sensor nodes 5

6 POWER REQUIREMENTS OF ENERGY HARVESTING Source: IDTechEx report Energy Harvesting and Storage for Electronic Devices Sensors typically require 1 to 5 mw. It is impractical or extremely expensive to change batteries in sensors in most of the envisaged locations. The same is true of active RFID but with a wider range of required power. 6

7 POTENTIAL ENERGY HARVESTING MARKETS Source: IDTechEx report Energy Harvesting and Storage for Electronic Devices Global market value of energy harvesting for small electronic and electrical devices in 214 7

8 Source Waseda University Source University of Michigan RESEARCH DEVELOPMENTS Tame bats A surveillance bat that will employ solar, wind, vibration and other sources to recharge its battery ($22.5 million) COM-BAT surveillance bat Electricity for underwater electronics Source Ocean Power Technologies a flag-like structure that moved with the tides to generate electricity 15 centimeter, one watt robotic spy Invisible harvesting Many new printed electronic devices are transparent including metal oxide transistors. Transparent, flexible printed battery that charges in one minute Vortex Hydro Energy VIVACE converter: a hydrokinetic power generating device, which harnesses hydrokinetic energy of river and ocean currents. It uses the physical phenomenon of vortex induced vibration in which water current flows around cylinders inducing transverse motion. The energy contained in the movement of the cylinder is then converted to electricity. Patent of University of Michigan 8

9 RESEARCH DEVELOPMENTS New healthcare harvesting A wearable battery-free wireless 2-channel EEG system integrated into a device resembling headphones has been developed, powered by a hybrid power supply using body heat and ambient light. New polymer and metal alloy capabilities Other promising approaches involve organic piezoelectric or electroactive polymers, possibly exhibiting electret properties as well. People power Implanted defibrillators and pacemakers powered electrodynamically from the human heart that they administer Biobatteries harvest body fluids Solar cells that work in the dark photovoltaics that can convert infrared as well as light into electricity Nantennas Nantenna array harvesting infrared MEMS Microminiature versions of favourite EH technologies (electrodynamics, thermoelectrics, piezoelectrics and photovoltaics), often with exotic new materials. Source Idaho National Laboratory 9

10 courtesy of bcp-energia Energy Harvesting sources Energy scavenging from wasted ambient energy sources: light, heat, vibrations, RF radiation, etc.. Wireless Sensor and energy harvester courtesy of SolarBotanic courtesy of Zhejiang Solar Panel courtesy of Perpetua Power Source Technologies Princeton University Source: Georgia Tech 1

11 TYPES OF ENERGY HARVESTING MATERIALS Piezoelectric materials Mechanical stress electrical signal Human motion, low-frequency vibrations, and acoustic noise are just some of the potential sources that could be harvested by piezoelectric materials. Examples of piezoelectric EH: Battery-less remote control the force used to press a button is sufficient to power a wireless radio or infrared signal Piezoelectric floor tiles there is much interest in harvesting the kinetic energy generated by the footsteps of crowds to power ticket gates and display systems Car tyre pressure sensors EH sensors attached inside the tyres continuously monitor the pressure and send the information to a display on the dashboard Thermoelectric materials Temperature differences across the material electric voltage A temperature across a thermoelectric crystal (i.e. one side is warmer/cooler than the other), it causes a voltage across the crystal. Example of thermoelectric EH: Road transport Cars and lorries equipped with a thermoelectric generators (TEG) would have significant fuel savings (especially with the increasing cost of petrol). In 29, VW demonstrated this proof of concept. The thermoelectric generator of their prototype car gained about 6W from running on a highway, reducing fuel consumption by 5% Pyroelectric materials Change in temperature electric charge As the temperature of a pyroelectric crystal changes, it generates an electrical charge. Example of pyroelectric EH: The pyroelectric effect is used in some sensors, but it is still some way from commercial energy harvesting applications 11

12 ENERGY HARVESTING SOURCES courtesy of bcp-energia Energy scavenging from wasted ambient energy sources: light, heat, vibrations, RF radiation, etc.. Wireless Sensor and energy harvester courtesy of Zhejiang Solar Panel courtesy of SolarBotanic vibrations courtesy of Perpetua Power Source Technologies Princeton University Source: Georgia Tech 12

13 AVAILABLE MECHANICAL SOURCES Ambient vibrations come in a vast variety of forms Sustainable Dance Club Courtesy of SUNY Courtesy of Christian Croft Courtesy Seiko Watch Corporation Courtesy of Perpetuum Courtesy of University of Pennsylvania POWERLeap system Courtesy of Pavegen Patent of University of Michigan 13

14 ORDERS OF POWER 14

15 CONVERSION MECHANISM Macro-scale centimeter-scale MEMS 2.4μW 1.4μW 14 kw fabricated at Imperial College London fabricated at TIMA - EPFL 18μW 6μW 2 W T. Krupenkin and J. A. Taylor, Nature Communications 211 hybrid transduction mechanism. Hybrid energy harvesters could power Embedded handheld sensor electronics, nodes 18 October 21, SPIE Newsroom fabricated at IMEC 15

16 CONVERSION MECHANISM Macro-scale centimeter-scale MEMS 2.4μW 1.4μW 14 kw fabricated at Imperial College London fabricated at TIMA - EPFL 18μW 6μW 2 W T. Krupenkin and J. A. Taylor, Nature Communications 211 hybrid transduction mechanism. Hybrid energy harvesters could power Embedded handheld sensor electronics, nodes 18 October 21, SPIE Newsroom fabricated at IMEC 16

17 TRADITIONAL APPROACH A classical transduction mechanism is based on vibrating mechanical bodies (linear systems). In the vast majority of cases the ambient vibrations come in a vast variety of forms. The energy distributed over a wide spectrum of frequencies, typically confined in a maximal bandwidth of few thousand of Hz. Linear System MEMS PZT P D Vib. Output 17

18 LINEAR APPROACH Typical energy harvester principle MEMS PZT P D Vib. Output 18

19 LINEAR APPROACH some issues with linear resonant harvesters < Linear systems exhibit a resonant behaviour (i.e. resonance frequency). Transfer function presents one or more peaks corresponding to the resonance frequencies and thus it is efficient mainly when the incoming energy is abundant in that regions. Narrow frequency bandwidth: the generator must be designed for specific vibration sources and applications. Require resonance frequency matching with vibrational sources. 19

20 LINEAR APPROACH Linear some issues with and linear resonant nonlinear harvesters Strategies Linear resonant structures Require frequency matching with sources. Poor performance out of resonance. Difficulties in scaling and tuning at micro/nano scale. Wideband vibrations below 5 Hz (about the 9 % of vibrational sources) require a different strategy to efficiently harvest energy Suitability only with narrow band vibrations (e.g. from rotating machines). Frequency band matching issues in MEMS and NEMS technologies. Whishlist for the perfect vibration harvester: 1) Harvesting energy over a wide frequency band 2) No need for frequency tuning 3) Harvesting energy at low frequency (below 5 Hz) How to increase efficiency of energy harvester? 2

21 SOTA - WIDE BAND HARVESTER 21

22 NONLINEAR MECHANISM EXAMPLE 1 Nonlinear Linear vibration and energy harvesters nonlinear Strategies MEMS PZT P D Vib. m and c are constant terms while k(z) is a nonlinear function of the displacement z. Output Nonlinearity can be induced by: the geometry of the springs in the device; material nonlinearities or induced stress; mechanical coupling with other fields (magnetic and so on). U(z) is the nonlinear Duffing Potential. a and b are coefficients depending on both the geometry of the device and the permanent magnets. 22

23 NONLINEAR MECHANISM EXAMPLE 1 Linear and nonlinear Strategies Nonlinear vibration energy harvesters m and c are constant terms while k(z) is a nonlinear function of the displacement z. 23

24 NONLINEAR MECHANISM EXAMPLE 1 Nonlinear Linear vibration and energy harvesters nonlinear Strategies m and c are constant terms while k(z) is a nonlinear function of the displacement z. 24

25 NONLINEAR MECHANISM EXAMPLE 1 Prototype 1 and experimental setup aluminum beam 53mm x 8.5mm Δ=2mm 25

26 NONLINEAR MECHANISM EXAMPLE 1 System displacement Input 26

27 MICRO-MACHINED DEVICES (SOI TECHNOLOGY) EXAMPLE 2 o Fabrication (SOI TECHNOLOGY): SOI wafer: 15 μm c-si layer, 45 μm carrier substrate, 2 μm buried oxide Front and back side DRIE etching technique Fabrication: CNM, Barcelona, Spain 27

28 MICRO-MACHINED DEVICES (SOI TECHNOLOGY) EXAMPLE 2 o Fabrication (SOI TECHNOLOGY): SOI wafer: 15 μm c-si layer, 45 μm carrier substrate, 2 μm buried oxide Front and back side DRIE etching technique Fabrication: CNM, Barcelona, Spain 28

29 MICRO-MACHINED DEVICES (PIEZOMUMPS TECHNOLOGY) EXAMPLE 3 o Fabrication (PIEZOMUMPs TECHNOLOGY): A Silicon On Insulator (SOI) wafer based on 1 μm upper silicon layer and 4 μm thick of substrate with 1 μm of buried oxide has been used Front and back side DRIE etching technique Fabrication: MEMSCAP 29

30 MICRO-MACHINED DEVICES (SOI/PIEZOMUMPS TECHNOLOGY) Micro-machined devices o Bistable SOI and PIEZOMUMPs cantilever beam: After gluing a magnet, bi-stable behavior is obtained Displacement is electrically-measured through strain gauges 3

31 MICRO-MACHINED DEVICES (SOI TECHNOLOGY) EXAMPLE 2 Experimental Setup 31

32 MICRO-MACHINED DEVICES (SOI TECHNOLOGY) EXAMPLE 2 Experimental Setup MEMS device 32 Permanent magnets stack Output strain gauge 32

33 MICRO-MACHINED DEVICES (SOI TECHNOLOGY) EXAMPLE 2 Results o Positioning the permanent g / σ=2 μn Measures on SOI device =1.5 mm =1.6 mm =1.7 mm =1.8 mm =2.4 mm =4.5 mm 33

34 MICRO-MACHINED DEVICES (SOI TECHNOLOGY) EXAMPLE 2 Results o optimal distance of permanent magnet Maximum voltage 1g RMS Measures on PIEZOMUMPs g / σ=2 μn 34

35 A Wireless Sensor Node Powered by NonLinear Energy Harvester 35

36 TYPICAL EH ARCHITECTURE SCHEMATIZATION The general architecture of a Vibration Energy Harvesting system Vibrational source Acceleration amplitude Frequency Spectrum 36

37 TYPICAL EH ARCHITECTURE SCHEMATIZATION The general architecture of a Vibration Energy Harvesting system Vibrational source Coupling mechanical structure Acceleration amplitude Frequency Spectrum Linear Nonlinear 37

38 LINEAR VS NON LINEAR Linear Beam Fixed-Fixed Beam Y X System has two stable equilibrium states (S 1 and S 2 ), separated by unstable equilibrium state (U). The vertical moviment of the mass caused by vibrations creates the strain in the beam. The piezoelectric material convert this strain in a voltage. Stable equilibrium position n 1 U Instable equilibrium position Stable equilibrium position n 2 Neutral equilibrium position S 1 S 2 The device switching between its stable states allows for improving the efficiency of the energy conversion, from mechanic to electric 38

39 TYPICAL EH ARCHITECTURE SCHEMATIZATION The general architecture of a Vibration Energy Harvesting system Vibrational source Coupling mechanical structure Mechanicalto-electrical conversion Acceleration amplitude Frequency Spectrum Linear Nonlinear Piezoelectric Electrostatic Electromagnetic 39

40 TYPICAL EH ARCHITECTURE SCHEMATIZATION The general architecture of a Vibration Energy Harvesting system Vibrational source Coupling mechanical structure Mechanicalto-electrical conversion Electrical energy output Acceleration amplitude Frequency Spectrum Linear Nonlinear Piezoelectric Electrostatic Electromagnetic Direct powering batteries recharging? 4

41 DOUBLE PIEZO SNAP THROUGH BUCKLING HARVESTER Top view The DP-STB-NLH 1 cm Piezoelectric transducers Mide's Volture V21bl PET (PolyEthylene Terephthalate) beam 6 cm x 1 cm x 1 µm RF transmitter TI ez43 RF25 Linear Technology LT input/output storage capacitors Schematization of the bistable nonlinear harvester 41

42 6 cm DOUBLE PIEZO SNAP THROUGH BUCKLING HARVESTER 2.5 cm 3.5 cm 3.56 cm 6 cm Flexible precompressed PET beam + suitable proof mass implementing the bistable mechanism Two piezoelectric vibration energy harvesters V21BL (Volture) connected in a parallel configuration Y ΔY/2 ΔX Cantilever Cantilever Max tip-to-tip displacement =.46 cm F Proof mass Piezoelectric Piezoelectric on both faces Specifications - v21bl Device size (cm): 9.4 x 1.7 x.8 Device weight (g): 3.26 Active elements: 1 stack of 2 piezos Piezo wafer size (cm): 3.56 x 1.45 x.2 X fixed-fixed PET beam t ΔY/2 Pre-compression ΔY= 2 mm Inertial mass ( 3g) 42

43 MECHANICAL BEHAVIOR OF THE STB-NON LINEAR HARVESTER Elastic Potential Energy U(x) [N*mm] The STB harvester can be modeled as a classical second order mass-damper-spring system, with an additive nonlinear term related to the bistable potential energy function U ( x) a x b x m x dx ax 3 bx F( t) Displacement x of the central mass along X-axis from initial position [mm] 43

44 STATIC CHARACTERIZATION OF THE BEAM BEHAVIOR Acceleration [m/s 2 ] Goal: measurement of the minimum acceleration required to implement the switching mechanism between the two stable states of the device. Methodology: Experiments consisting of loading the pre-compressed beam with reference masses (forces) until switching occurs m proof =6g m proof =12g m proof =18g Distance between stable equilibrium positions DX [mm] Pre-compression DY [mm] Acceleration required to make the beam switch between its stable states, with different proof masses loading the beam. The continuous lines denote interpolation models. acceleration values are compatible with standard sources 44

45 STATIC CHARACTERIZATION OF THE BEAM BEHAVIOR Reaction force along X-axis [mn] Elastic Potential Energy U(x) [N*mm] Reconstruction of the reaction force (x) The pre-compressed beam was stressed by a controlled force applied orthogonally to the beam center. A load cell (Transducer Techniques GSO-1) was used to independently measure the force Observed Predicted DU b 2 /4a Displacement along X-axis from stable states [mm] Displacement x of the central mass along X-axis from initial position [mm] To fit the observed behavior, a Nelder Mead optimization algorithm was implemented through a dedicated Matlab script exploiting the following minimization index: J F F real pred 2 Freal ( x) a x b x Parameters estimated (in case of pre-compression Y of 3 mm ): a = 1.39e-4 kg/m 2 s 2, b=.98 kg/s 2 U

46 THE DYNAMIC MECHANICAL CHARACTERIZATION RMS Acceleration [m/s 2 ] Goal: estimation of the minimum acceleration (vs stimulus frequency) able to make the device switch between its stable states. Methodology: the beam was subjected to several repeated cycles of a periodic sine mechanical stimulation in the range [4-15] Hz applied via a standard shaker. A reference laser system (Baumer OADM 12U643/S35A) was used to obtain an independent quantification of the beam switching while the analog accelerometer (Freescale Semiconductor MMA7361L) was used to independently measure the acceleration applied The envisaged broadband operation of the proposed bistable architecture emerges via the possibility of inducing switching events by slightly supra-threshold acceleration values for the entire frequency range of interest frequency [Hz] Dynamic mechanical characterization of the DP-NLH device in case of a beam pre-compression of 3 mm and a proof mass of 6g. 46

47 V piezo [V] ELECTRICAL CHARACTERIZATION OF THE NONLINEAR HARVESTER V piezo [V] V acc [V] V acc [V] V piezo [V] V piezo [V] V accel [V] V accel [V] Goal: Investigation of the electrical performances of the DP-STB device in terms of electrical power generated for different values of acceleration, pre-compression, proof mass and resistive load. Methodology: the device was subjected to several repeated cycles of a periodic sine mechanical stimulation in the range [4-1] Hz applied via a standard shaker. 8 6 Piezoelectrics Accelerometer Piezoelectrics Accelerometer a RMS = 9.81 m/s a RMS = m/s f= 4 Hz R load = 1MΩ time [s] time [s] 3 2 a RMS =16.81 m/s 2 Piezoelectrics Accelerometer a RMS = m/s 2 Piezoelectrics Accelerometer f= 1 Hz R load = 1MΩ time [s] time [s] 47

48 Power [ W] ELECTRICAL CHARACTERIZATION OF THE NONLINEAR HARVESTER Electrical power produced by the DP-NLH device as been evaluated as V 2 RMS where V RMS is the RMS voltage measured across the load R (.1 1 kω) / R a RMS = m/s 2 a RMS = m/s 2 a RMS = m/s 2 f=4hz f=5hz f=8hz f=1hz a RMS = m/s 2 R = 5 kω Frequency [Hz] Power [µw] a RMS = 9.81 m/s Load resistance [ ] frequency broad band operation 48

49 ENERGY STORAGE AND POWER MANAGEMENT LTC Piezoelectric Energy Harvesting Power Supply Up to 1mA of Output Current Selectable Output Voltages of 1.8V, 2.5V, 3.3V, 3.6V Batteries or capacitors 49

50 ENERGY STORAGE AND POWER MANAGEMENT LTC supercapacitor Load Energy source Energy Harvester Storage Load to supply The LTC has an internal full-wave bridge rectifier accessible via the differential PZ1 and PZ2 inputs that rectifies AC inputs such as those from a piezoelectric element. The rectified output is stored on a capacitor at the VIN pin and can be used as an energy reservoir for the buck converter. 5

51 ENERGY STORAGE AND POWER MANAGEMENT 51

52 NLH + LTC Investigation of the capability of the NLH to generate power to supply electronic. The device was subjected to several repeated cycles of a periodic sine mechanical stimulation at 1Hz. The time for first activation of the output, the time required for consecutive activations and the time assuring a high V o, have been evaluated. V c Supercapacitors V O P GOOD enable pin C STORAGE = 47 µf a RMS =9.81 m/s 2 R load = 1 kω C STORAGE = 94 µf a RMS =9.81 m/s 2 R load = 1 kω t t onvo t onpgood t Δt 52

53 NLH + LTC a RMS = 9.81 m/s 2 f s =1Hz a RMS = m/s 2 f s =1Hz LOAD [Ω] t [s] t [s] t onpgood [s] t onvo [s] LOAD [Ω] t [s] t [s] t onpgood [s] t onvo [s] k k supercapacitors 47µF 2.2k k supercapacitors 47µF 2.2k k k k k k k k supercapacitors 94µF 2.2k k supercapacitors 94µF 2.2k k k k k k

54 DP-STB + LTC t' [s] t' [s] Dt [s] Dt [s] t onpgood [s] t onpgood [s] a RMS =9.81 m/s C STORAGE = 47 µf a RMS =9.81 m/s 2 a RMS =11.43 m/s 2 a RMS =12.11 m/s 2 C STORAGE = 47 µf 1 a RMS =9.81 m/s 2 a RMS =11.43 m/s 2 a RMS =12.11 m/s a RMS =11.43 m/s 2 a RMS =12.11 m/s 2 C STORAGE = 47 µf Load resistance [ ] Load resistance [ ] Load resistance [ ] a RMS =9.81 m/s 2 a RMS =11.34 m/s 2 a RMS =12.11 m/s 2 a RMS =9.81 m/s a RMS =11.43 m/s C 2 STORAGE = 94 µf C 3 a RMS =12.11 m/s 2 2 STORAGE = 94 µf C STORAGE = 94 µf Load resistance [ ] Load resistance [ ] a RMS =9.81 m/s 2 a RMS =11.43 m/s 2 a RMS =12.11 m/s Load resistance [ ] 54

55 NLH + LTC RF-TX Goal: Investigation of the capability of the DP-STB device to power a RF - TX Producer Max Frequency Communication Power supply Board Power Consumption (max values) Texas Instruments 16MHz USB/2.4GHz V Only processor Active mode 39µA Stanby mode 1.4µA RF Transceiver RX mode 18.8mA TX mode 21.2mA a RMS [m/s 2 ] t [s] t [s] t onpgood [s] t on-pin6 [s] t PGOOD -PIN6 [s] Pushbutton two LEDs CC25 Chip Antenna MSP43F Accessible Pins supercapacitor 47µF supercapacitor 94µF PIN6 is a digital output pin on the RF receiver (RX) 55

56 NLH + LTC RF-TX Voltage [V] Voltage [V] acceleration [m/s 2 ] acceleration [m/s 2 ] Voltage [V] acceleration [m/s 2 ] acceleration V C Enable RX digital output t' Dt Dt time [s] acceleration V C Enable RX digital output.5 t' Dt Dt Dt Dt time [s] acceleration V C Enable RX digital output time [s] Signals have been acquired by a Lecroy 65A WaveRunner digital oscilloscope The Enable pin, is logic high when the output voltage is above 92% of the target value (set to 3.3 V). The node is able to scavenge energy from wideband vibrations to transmit data by the SimpliciTI network 2.4 GHz. 56

57 Conclusions A batteryless wireless node powered by a nonlinear bistable energy harvester has been discussed. The node is able to scavenge energy from wideband vibrations to transmit 2.4 GHz. Results obtained encourage the use of proposed nonlinear harvesters to power wireless sensor nodes. Future works Characterization of the behavior of the device with a noisy input stimulation Development of an analytical model including the mechanical to electrical conversion. ACKNOWLEDGMENT The authors gratefully acknowledge support from the US Office of Naval Research (Global), and the US Army International Technology Center (USAITC). 57

58 DIEEI University of Catania, Italy InkJet Printed Snap Through Buckling Harvester Smart&Authonomous Sensing Development of Low Cost Printed Devices for Energy Harvesting from Environmental Vibrations (CSP6N1EJEPC3), DEPARTMENT OF THE ARMY ARMY MATERIAL COMMAND RESEARCH, DEVELOPMENT AND ENGINEERING COMMAND INTERNATIONAL TECHNOLOGY CENTER-ATLANTIC UNIT (ITC-AC) Substrate IJP electrodes PZT Clamping System The STB beam is implemented via a PET (PolyEthylene Terephthalate) substrate Mass IJP STB Harvester Clamping System

59 DIEEI University of Catania, Italy The proposed approach: Snap Through Buckling Harvester Smart&Authonomous Sensing Main challenges: The low cost mechanical structure implementing the non linear switching mechanism ; The technology to realize electrodes, sensors, readout systems and functional layers; The mechanic-electric conversion. F Stable state ΔY/2 t Proof mass ΔY/2 Z ΔX Y Stable state X Solution: a two-end clamped PET beam exploiting snap-through buckling approach, low cost COTS devices and direct printing methodologies.

60 DIEEI University of Catania, Italy Smart&Authonomous Sensing Elastic Potential Energy U(x) [N*mm] Mechanical Behavior of the STB-Non Linear Harvester The STB harvester can be modeled as a classical second order mass-damper-spring system, with an additive nonlinear term related to the bistable potential energy function U ( x) a x b x Displacement x of the central mass along X-axis from initial position [mm]

61 DIEEI University of Catania, Italy Smart&Authonomous Sensing Static characterization of the beam behavior Goal: measurement of the minimum acceleration required to implement the switching mechanism between the two stable states of the device. Methodology: Experiments consisting of loading the pre-compressed beam with reference masses (force) until switching occurs. Acceleration required to make the beam switch between its stable states, with different proof masses loading the beam. The continuous lines denote interpolation models. acceleration values are compatible with standard sources

62 DIEEI University of Catania, Italy FEM (Finite Element Method) Analysis in Ansys Input: External force, F est Output: Displacement ΔX S 1 and S 2 are the stable equilibrium states estimated when the force is null f 1-2 e f 2-1 are the static forces allowing the commutation between two stable states. 1 NODAL SOLUTION 1 NODAL SOLUTION STEP=1 STEP=1 SUB =32 SUB =15 TIME=1 TIME=1 UX (AVG) UX (AVG) RSYS= RSYS= Fest>f2-1 the beam switches from the state S 2 to the state S 1 SMN =-.149E-6 SMX =.7135 MN S 1 MX S 2 SMN =-.799 SMX =.434E-7 S 1 MN S 2 MX DMX =.7135 DMX =.799 Z X Y Z X Y -.149E E-3 Forza_ Forza_ E E-7 1 NODAL SOLUTION 1 NODAL SOLUTION STEP=1 STEP=5 SUB =32 SUB =11 TIME=1 TIME=5 Fest<f2-1 the beam doesn t switch UX (AVG) RSYS= DMX =.7135 SMN =-.149E-6 SMX =.7135 MN S 1 MX UX (AVG) RSYS= S DMX =.69 SMN =-.98E-8 SMX =.69 1 MX MN S 2 S 2 Z X Y Z X Y -.149E E-3 Forza_ Forza -.98E-8.657E Smart&Authonomous Sensing

63 DIEEI University of Catania, Italy Reaction Force [mn] FEM (Finite Element Method) Analysis in Ansys To improve performances of FEM predictions the following correction model has been estimated Fˆ a F F FEM where Fˆ denotes the force required to switch the beam estimated by model starting from the simulated values, and a F =.8 and b F =.8 N are fitting parameters obtained by applying a least mean squares minimization algorithm FEM Observed Estimated b F Pre-compression DY [mm] Static force required to make the beam switch between its stable states. Comparison between observations, FEM simulations, and estimations obtained by model for different precompression values, are shown. Smart&Authonomous Sensing

64 DIEEI University of Catania, Italy Smart&Authonomous Sensing FEM (Finite Element Method) Analysis in Ansys The model adopted to describe the relationship between the minimum acceleration a m enabling the beam switching, and X as a function of the proof mass m, is a m DX m DX DX m 2 2 m i i i i m where: m i (i=6 g, 12 g, 18 g) represents the proof mass = e-4 m 4 kg 6 /s 2 = m 4 kg3 /s 2 =.2683 m 4 /s 2 =.17 m kg 6 /s 2 = m kg 3 /s 2 = m/s 2 fitting parameters estimated by applying the Nelder Mead nonlinear simplex optimization algorithm with the following functional J J 3 i 1 N i a real m i N a pred m i 2 i : 1 6g 2 12g 3 18g

65 DIEEI University of Catania, Italy Acceleration [m/s 2 ] Investigations of dynamic performance of the IJP-STB harvester Goal: estimation of the minimum acceleration (vs stimulus frequency) able to make the device switch between its stable states. Methodology: the beam was subjected to several repeated cycles of a periodic sine mechanical stimulation in the range [4-2] Hz applied via a standard shaker. A reference laser system (Baumer OADM 12U643/S35A) was used to obtain an independent quantification of the beam switching while the analog accelerometer (Freescale Semiconductor MMA7361L) was used to independently measure the acceleration applied DY=1mm DY=3mm Smart&Authonomous Sensing Frequency [Hz] Minimum acceleration assuring the switching mechanism as a function of the stimulus frequency and the beam precompression. A proof mass of 6 g was used to load the beam.

66 DIEEI University of Catania, Italy Acceleration [m/s 2 ] Displacement [mm] Smart&Authonomous Sensing Acceleration [m/s 2 ] Displacement [mm] Investigations of dynamic performance of the IJP-STB harvester Example of time series of signals output in case of sinusoidal solicitation at 6Hz with the strength close to the minimum value assuring the beam switching between its stable states ΔY= 1 mm ΔY= 3 mm laser laser 12.9 laser time [s] time [s] accelerometer accelerometer accelerometer ,5 1 1,5 2 2,5 3 3,5 4 time [s] time [s] PSD of the laser output signal

67 DIEEI University of Catania, Italy Smart&Authonomous Sensing Fitting observed behavior by the model The applied force was independently measured by the load cell (Transducer Techniques GSO-1) U ( x) a x b x where =b-c (*) Experimental set-up for the estimation of the potential form U(x). In order to fit the observed behaviors by model (*), a Nelder Mead optimization algorithm was implemented through a dedicated Matlab script exploiting the following minimization index: J 2 xreal x pred Freal Fpred 2 xreal Freal 2 x real and x pred refer to the measured and predicted displacement of the bistable device F real and F pred refer to the measured and predicted force 2

68 DIEEI University of Catania, Italy Reaction force along X-axis [mn] Reaction force along X-axis [mn] Smart&Authonomous Sensing Displacement x along X-axis [mm] Displacement x along X-axis [mm] Elastic Potential Energy U(x) [N*mm] Elastic Potential Energy U(x) [N*mm] ΔY= 1 mm Measured displacement Predicted displacement Displacement along X-axis from stable states [mm] time [s] Displacement x of the central mass along X-axis from initial position [mm] Estimated parameters: a = 2.567e-4 kg/m 2 s 2, b=.17, = kg/s 2 and d=1.e-4 kg/s ΔY= 3 mm Measured displacement Predicted displacement Displacement along X-axis from stable states [mm] time [s] Displacement x of the central mass along X-axis from initial position [mm] Estimated parameters: a=1.893e-4 kg/m 2 s 2, b=.31, = kg/s 2 and d=1.e-3 kg/s

69 DIEEI University of Catania, Italy Printed Electronics: Inkjet Printed Sensors Printed electronics is a set of printing methods used to create electrically functional devices. Paper has been often proposed to be used as substrate but due the rough surface and high humidity absorption other materials such as plastic, ceramics and silicon has been applied more widely. Several printing processes have been piloted and printing preferably utilizes common printing equipment in the graphics arts industry Printed Electronics Printed Sensors Low Costs/Low Performances Flexible substrates Inkjet Smart&Authonomous Sensing Wearable electronics (Active clothing) Smart Labels (RFID+sensors) Disposable devices (biomedical)

70 DIEEI University of Catania, Italy Review of Printing technologies in pills Smart&Authonomous Sensing Technology Advantages Drawbacks Screen printing several materials masks low resolution time consuming high cost production Desktop Inkjet printers good resolution low cost system low cost production restricted number of conductive materials Professional inkjet systems Mixed Screen & Inkjet printing high resolution several materials Low cost production good resolution several materials high cost system Mask time consuming high cost

71 DIEEI University of Catania, Italy Printed Electronics: Inkjet Printed Sensors Smart&Authonomous Sensing Chemistry Physics Before entering the market various technological improvements are still needed. MEMS & NEMS Technologies Electronics Engineering C H A L L E N G E S Inks Printing Systems Substrates

72 DIEEI University of Catania, Italy Printed Electronics: Inkjet Printed Sensors Smart&Authonomous Sensing Printing systems designed or optimized for the application Precision and accuracy Throughput / speed and productivity Maintenance and reliability Electronic fluids formulated to meet application standards Ink jet print engine engineered for the application Drop volume, velocity, and placement control Robust and resistant to electronic fluids High and precise drop throw rate Wide range of substrates and surface properties Everyday desktop printer (ie Epson) Microdrop inkjet system Dimatix DMP 28 Litrex M-Series inkjet system

73 DIEEI University of Catania, Italy Printed Electronics: Inkjet Printed Sensors Smart&Authonomous Sensing Precision and accuracy Throughput / speed and productivity Maintenance and reliability Metalon JS-15 (black) product by Novacentrix PET Substrates EPSON inkjet printer

74 DIEEI University of Catania, Italy Smart&Authonomous Sensing InkJet Printed Snap Through Buckling Harvester A set of parallel and InterDigiTed (IDT) electrodes with different dimensions has been designed and realized to test the proposed technology Printed Bistable Harvester PBH1-1 PBH1-2

75 DIEEI University of Catania, Italy 1 cm InkJet Printed Snap Through Buckling Harvester Smart&Authonomous Sensing Active Material PZT Substrate IDT electrodes A PZT layer has been screen printed to convert strains due to the beam switches (induced by external vibrations) between its two stable states into an output voltage. 1 cm

76 DIEEI University of Catania, Italy InkJet Printed Snap Through Buckling Harvester Smart&Authonomous Sensing PZT Deposition and poling (Department of Information Engineering (DII) University of Breascia) Material Depositated Deposition technology Thickness Sintering temperature Poling IDT electrodes Piezokeramica APC 856 Screen Printing 5µm 1 C for 1 minutes 1V 13 C (1 min) Parallel electrodes Piezokeramica APC 856 Screen Printing 5µm 1 C for 1 minutes 1V 13 C (1 min)

77 DIEEI University of Catania, Italy InkJet Printed Snap Through Buckling Harvester Smart&Authonomous Sensing Layout IDT electrodes realized by inkjet printing PZT layer

78 DIEEI University of Catania, Italy Smart&Authonomous Sensing Electrical Behavior of the IJP - STB Harvester Goal: characterization of the electrical performances of the inkjet printed snap through buckling harvester. Methodology: the beam was subjected to several repeated cycles of a periodic sine mechanical stimulation in the range [4-2] Hz applied via a standard shaker. A reference proof mass is placed in the middle of the beam in order to reduce the required acceleration to make the device switching between its stable states. A reference laser system (Baumer OADM 12U643/S35A) was used to obtain an independent quantification of the beam switching while the analog accelerometer (Freescale Semiconductor MMA7361L) was used to independently measure the acceleration applied. proof mass IJP-STB harvester

79 DIEEI University of Catania, Italy Acceleration (m/s 2 ) Acceleration (m/s 2 ) Smart&Authonomous Sensing Voltage (V) Voltage (V) Power/frequency (db/hz) Power/frequency (db/hz) Power/frequency (db/hz) Power/frequency (db/hz) Electrical Behavior of the IJP - STB Harvester Examples of the experimental behavior of the device ΔY=1 mm and Acc max =28.9 m/s 2.5 Accelerometer STB Harvester Accelerometer Frequency (Hz) -5-6 STB Harvester time (s) ΔY=1 mm and Acc max =49.7 m/s Frequency (Hz) Accelerometer 47.8 STB Harvester time (s) -2 Accelerometer Frequency (Hz) -4 STB Harvester Frequency (Hz)

80 DIEEI University of Catania, Italy Acceleration (m/s 2 ) Acceleration (m/s 2 ) Smart&Authonomous Sensing Voltage (V) Voltage (V) Power/frequency (db/hz) Power/frequency (db/hz) Power/frequency (db/hz) Power/frequency (db/hz) Electrical Behavior of the IJP - STB Harvester Examples of the experimental behavior of the device ΔY=3 mm and Acc max =34.4 m/s Accelerometer STB Harvester Accelerometer Frequency (Hz) STB Harvester time (s) Frequency (Hz) ΔY=3 mm and Acc max =38.2 m/s Accelerometer 4.9 STB Harvester Accelerometer Frequency (Hz) STB Harvester time (s) Frequency (Hz)

81 DIEEI University of Catania, Italy V Av Peak [V] V AV Peak [V] Electrical Behavior of the IJP - STB Harvester norm V RMS V AvPeak and values as a function of the accelerations applied to the device for the two values of the pre-compression Acc max [m/s 2 ] Acc max [m/s 2 ] ΔY= 1 mm norm V RMS [V] Hz 12 Hz 8 Hz 1 Hz Acc RMS [m/s 2 ] Acc RMS [m/s 2 ] Acc max [m/s 2 ] Acc max [m/s 2 ] ΔY= 3 mm norm V RMS [V] Hz 12 Hz 8 Hz 14 Hz 1 Hz Acc RMS [m/s 2 ] Smart&Authonomous Sensing Acc RMS [m/s 2 ]

82 DIEEI University of Catania, Italy Electrical Behavior of the IJP - STB Harvester Smart&Authonomous Sensing An evaluation of the electrical power produced by the STB device has been performed by where R=1MΩ V AV Peak 2 V R AV Peak / is the average of the of the piezoelectric output voltage peaks measured across the load Powers in the order of 1 2 nw have been experimentally estimated

83 DIEEI University of Catania, Italy Smart&Authonomous Sensing