EnergyScavengingFromLowFrequencyVibra6onsTzenoGalchev,HanseupKim,andKhalilNajafiEngineeringResearchCenterforIntergradedWirelessMicrosystems

ElectricalEngineeringandComputerScienceDepartment,UniversityofMichigan,AnnArbor,MI48109‐2122USA

Power Availability From Vibration

Motivation Ambient Energy

Electrical Energy

Energy scavenging from ambient sources:

  Long life time   Clean generation process   Small size using MEMS

Sources: Heat, light, acoustic, vibration, etc.

Storage Element

Power Electronics

Energy Scavenger

Generic Energy Scavenging Device

The energy scavenging advantage: long life time

Two application types. 1)   Device is difficult to access – Biomedical, environmental monitoring, security applications, oil

exploration, etc 2)   Too many device deployed (100-1,000s) – Sensor networks for industrial & building

automation, military applications, etc

FAQ: Isn’t the amount of generated power too low and unpractical? Generic Wireless Sensor

Peak Power Consumption = 5mW Duty Cycle = 1%

Average Power Consumption = 100µW

Battery Capacity = 2,880J/cm3 Lithium

Power = 90µW Lifetime = 1 year

Energy Harvesting Power = 100µW

Lifetime = Device existence

1W

100mW

10mW

1mW

0.1mW

100 1k 10k 100k 1M

Sensors Speech, Audio, Hi-Fi

GSM UMTS Bluetooth

Zigbee

PicoRadio

Red: Short Range Blue: Long Range

Power

Date Rate, Bits/sec.

Standby Power

Long Term, Untethered Operation

z = relative displacement y = magnitude of input

Energy converted by performing work against a damping force.

  Max acceleration amax is ω2Yo

  Max damping force < mamax

  Assuming a motion range of 2Zmax and postulating that energy is extracted in both directions, the energy extracted per cycle is:

  Max achievable power is:

€

Energy = 4Zmaxmamax = 4Zmaxω2Υo

€

Powermax =2πΥoZmaxω

3m

Scavenging from Low-Frequency Vibrations   Applications

  Implantable and wearable devices   Environmental monitoring   Structural monitoring   Security applications   Agriculture

  Challenges 1.  Lower expected power density

  Larger displacements   Weaker damping forces

2.  Frequency is not constant

  More than 95% of vibration work so far uses resonant systems, which are ineffective in these conditions

0.00001 0.0001 0.001 0.01 0.1

1 10

100 1000

10000 100000

1000000 10000000

0.001 0.1 10 1000

Pow

er (

mW

)

Volume (cc)

0.5g, 1Hz 0.5g, 10Hz 0.5g, 60Hz 0.5g, 120Hz

Power Availability

  Increase in the required spatial displacement   Low-frequency vibrations have higher amplitudes

vs.

Generator 2 Input = 9.8m/s2 at 100Hz Q =10 Zppk = 0.5mm

Generator 1 Input = 9.8m/s2 at 10Hz Q =10 zppk = 50mm

  Damping force for velocity damped generators f = dż   ż ~ ω   piezoelectric and electromagnetic

  Bandwidth   Generator 1 has a 3dB bandwidth of 1Hz.   2 Approaches so far – neither of which is applicable

1.  Tuning 2.  Many resonant elements with different frequencies

Parametric Frequency Increased Generator

  Advantages   Large bandwidth to accommodate

unpredictable ambient environments   Higher energy density at low

frequencies   Better scalability in the micro scale   More universally applicable

  Disadvantages   Reduced maximum power output   Minimum input limit

Performance Illustration

Acknowledgements Publications 1. T. Galchev, H. Kim, and K. Najafi, ”A Piezoelectric Frequency Increased Power Generator for Scavenging Low-Frequency Ambient Vibration,” IEEE MEMS, Hong Kong, China, 2010. Accepted. 2. T. Galchev, H. Kim, and K. Najafi, ”A Parametric Frequency Increased Power Generator for Scavenging Low-Frequency Ambient Vibrations,” Eurosensors, Lausanne, CH, 2009. 3. T. Galchev, H. Kim, and K. Najafi, "Non-Resonant Bi-Stable Frequency Increased Power Generator for Low-Frequency Ambient Vibration," TRANSDUCERS'09 Denver, CO, 2009. 4. UM Technology Disclosure #4362 – “Non-Resonant Frequency Power Scavenger Architecture For Low-Frequency Ambient Vibration”

N

S

N

S

N

S

Inertial Mass

Frequency Increased Generator (FIG)

Actuation Magnet Magnetic

Actuation Site

Spring Suspension

Coil

Frequency Increased Generator (FIG)

Power Generation Magnet

Spacer

Time Displacement

Magnetic Force

Upper FIG Voltage

Top & Bottom: High Frequency Elements

Shaker Table

Aluminum Assembly

Micro Positioner

Generator Area

Middle: Low-Frequency Actuator

Top and Bottom FIGs

Micropositioners

Actuation Magnets

Inertial Mass & Suspension

Oscilloscope trace showing the parametric generator operation from an external acceleration of 1g at 10 Hz. The top and bottom voltage waveforms correspond to the top and bottom FIG devices as the inertial mass snaps back and forth between them. The bottom plots shows instantaneous power from FIG 2.

Measured vs. simulated performance of the PFIG generator as a function of the FIGs spring constants (all other parameters constant). Input acceleration is 1g at 10 Hz.

Measured frequency response of the PFIG generator. The cut-off frequency is determined by the inertial mass/spring suspension natural frequency. By altering the suspension stiffness the bandwidth can be increased to a suitable value. Input acceleration is 1g at 10 Hz.

Test Setup

Second Generation PFIG PerformanceComparison

InputAccelera=on

(g)

InputFrequency

(Hz)

Volume(cm3)

PeakPower(µW)

AveragePower(µW)

PowerDensity(µW/cm3)

Arakawa 0.4 10 0.4 6 ‐ ‐

Kulah ‐ 1 ‐ 0.004 ‐ ‐

Miao 1.8 10 0.6 ‐ 1.2 2

Saha 0.5 2 12.7 300 ‐ ‐

Saha 1 2.5 12.7 1860 ‐ ‐

PFIGGen1 1 10 3.68 558.3 39.45 10.7

PFIGGen2 1 10 2.12 288 5.8 2.74