A vibration energy scavenger, manufactured entirely by thick-film construction, has been developed to power autonomous subsystems in an embedded health and useage system. The device is constrained to a 2mm thickness and has been designed for a specific helicopter application. The resulting power output is capable of powering an ‘off-the-shelf’ microcontroller based system

Beeby, Steve

Harris, Nick

Tudor, John

Zhu, Dibin

English

Southampton (e-Prints Soton)

Thick-film Piezoelectric Vibration Harvesting –  A HUMS Application N.R.Harris*, S.P.Beeby, M.J.Tudor, D.Zhu School of Electronics and Computer Science, University of Southampton, Southampton, UK,  *Corresponding author: Email nrh@ecs.soton.ac.uk   Abstract: A vibration energy scavenger, manufactured  entirely  by  thick-film  con-struction,  has  been  developed  to  power autonomous subsystems in an embedded health and useage system. The device is constrained to a 2mm thickness and has been  designed  for  a  specific  helicopter application. The resulting power output is capable of powering an ‘off-the-shelf’ mi-crocontroller based system. 1  Introduction:  The  aim  of  the  EU Framework  7  project  TRIADE  [1]  is  to produce  a  credit  card  sized  module  for HUMS  (Health  and  Useage  Monitoring) for a selection of aerospace applications. The requirement is for the module to be self-contained  so  in  principle  it  can  be embedded in the structure that it is moni-toring.  The  system  uses  a  rechargeable battery,  which  is  recharged  primarily  by an inductive system, but included in the system is the capability for harvesting vi-bration energy, to augment the power in the  battery  and  also  give  the  option  of having  self  powered  distributed  sensors that interface to the main module. The vibration energy harvester is the sub-ject  of  this  paper,  and  uses  a  thick-film PZT  paste,  previously  developed  at  the University of Southampton [2], deposited onto a steel cantilever as the transduction method.  Displacement  of  the  cantilever distorts the PZT which generates electri-cal energy. We also report the integration of  a  seismic  mass  onto  the  cantilever, again  by  screen-printing,  leading  to  an entirely  screen-printed  piezoelectric  en-ergy harvester. The prototype energy harvester has been characterised  against  a  vibration  spec-trum taken from a PZL Helicopter and has been  demonstrated  powering  a  sensor based RF system (fig 1), thus validating its potential for practical applications. 2 Piezoelectric Energy Harvesting  The  generator  under  consideration  is  a bimorph construction, with the steel canti-lever  sandwiched  between  two  active piezoelectric generators (fig 2). The mass is  provided  by  screen-printing  tungsten onto  the  generator.  The  tungsten  paste developed has a density of 10,000kg/m3 (52% of the bulk material), and the PZT paste  has  a  d33  coefficient  of  about 130pC/N after poling [3]. Modelling of the generator  was  done  using  the  linear model  introduced  by  Roundy  [4]  which can be expressed as a b vtdz z zpztnn n m*231 2 2      (1) 0231 ztdmR v v C RpztnL p L   (2)  Fig. 2. Cross section of the bimorph  Fig. 1. The prototype self powered sys-tem where z is the displacement of the inertial mass, m; ζm is the damping factor, tpzt is the thickness of the PZT layer, b* is the ratio of strain to vertical displacement, a is the acceleration, RL is the load resis-tance, Cp is the capacitance of the PZT layer and v is the voltage across the elec-trodes. The target design for the generator was for  67Hz  with  an  input  acceleration  of 0.4g (3.9ms-2) peak, as this is one of the main resonances identified in the applica-tion.  A  further  constraint  was  the  peak displacement of the cantilever should be +/-2mm as defined by the package size.   3 Results  Although  some  generators  can  demon-strate  non-linear  characteristics,  the  ge-nerator described here appears linear as shown in fig 3.  For  the  two  generators  shown,  power outputs  of  197µW  and  240µW  were achieved at a frequency of 66.2Hz for the desired input amplitude. This frequency is 1.2% off the design value. These outputs correspond  to  power  densities  of  about 600µW/gpk compared with 118µW/gpk for the initially reported generator [5]. 4 Discussion   Although these levels are not high in ab-solute  magnitude,  they  are  sufficient  to charge  and  power  low  duty  cycle  sys-tems. The circuit shown in figure 1 has at its  core  a  Chipcon  CC2430  which  com-bines a 2.4GHz transceiver with an 8051 class  microcontroller  and  a  suit  of  sen-sors  (temperature,  pressure  and  accel-eration), with power stored in a superca-pacitor.  It  can  be  calculated  that  if  the system is duty cycled in that it is sent to sleep  for  the  majority  of  the  time  and wakes  up  to  perform  its  sensing  and transmission  (which  for  example  takes 10mS) then it requires 42 seconds to re-plenish  the  energy  used.  If  the  RF  sub section is not used every time, then this time reduces, as it is the radio system (in this case) that uses the most power.  3 Conclusions  This  work  has  demonstrated  a  vibration harvesting  piezoelectric  generator  that has been entirely fabricated by the thick-film  process,  giving  a  robust  design matched  to  an  aeronautical  application. Further, this generator has been charac-terised  and  incorporated  into  a  vibration  powered wireless sensing device with the dimensions  of  a  credit  card  suitable  for embedding in structures, that uses stan-dard electronic components. Future work is moving towards demonstrating this sys-tem on an aircraft, under the TRIADE pro-ject.  Acknowledgements  This work has been supported by the  European Union under grant number 212859 (TRIADE)  References [1]  TRIADE webpage http://triade.wscrp.com/ [2]  Torah,  R.,  Beeby,  S.  P.  and  White,  N.  M. (2005)  An  improved  thick-film  piezoelectric material  by  powder  blending  and  enhanced processing parameters. IEEE Transactions on Ultrasonics,  Ferroelectrics,  and  Frequency Control, 52 (1). pp. 10-16 [3]  Torah R N, Beeby S P, Tudor M J and White N  M  2007  Thick-film  piezoceramics  and devices Journal of Electroceramics 19(1) 97-112 [4]  Roundy S, Wright P H and Rabaey J M 2004 Energy  scavenging  for  wireless  sensor networks  with  special  focus  on  vibrations (Norwell, Massachusetts 02061 USA, Kluwer Academic Publishers) [5]  Stamos,  M.,  Nicoleau,  N.,  Torah,  R.,  Tudor, J., Harris, N., Niewiadomski, A. and Beeby, S. (2008) Screen Printed Piezoelectric Generator for  Helicopter  Health  and  Usage  Monitoring Systems.  PowerMEMS  2008,  9-12th November  2008,  Sendai,  Japan  Fig. 3. Measured and theoretical power outputs from two generators  

An improved thick-film piezoelectric material by powder blending and enhanced processing parameters.

Energy scavenging for wireless sensor networks with special focus on vibrations

Screen Printed Piezoelectric Generator for Helicopter Health and Usage Monitoring Systems. PowerMEMS

Thick-film piezoceramics and devices

Thick-film Piezoelectric Vibration Harvesting –A HUMS Application

Thick-film Piezoelectric Vibration Harvesting –A HUMS Application

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