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Sensors and Actuators A 208 (2014) 159– 165

Contents lists available at ScienceDirect

Sensors and Actuators A: Physical

jo ur nal homepage: www.elsev ier .com/ locate /sna

iezoelectric P(VDF-TrFE) transducers assembled with micro injectionolded polymers�

obert Schulzea,∗, Michael Heinrichb, Patryk Nossolb, Roman Forkec, Martynas Sborikasd,lexander Tsapkolenkoa, Detlef Billepc, Michael Wegenerd, Lothar Krollb,homas Gessnera,c

Technische Universität Chemnitz, Center for Microtechnologies (ZfM), Reichenhainer Straße 70, 09126 Chemnitz, GermanyTechnische Universität Chemnitz, Department of Lightweight Structures and Polymer Technology (SLK), Reichenhainer Straße 70, 09126 Chemnitz,ermanyFraunhofer Institute for Electronic Nano Systems (ENAS), Technologie-Campus 3, 09126 Chemnitz, GermanyFraunhofer Institute for Applied Polymer Research (IAP), Geiselbergstraße 69, 14476 Potsdam-Golm, Germany

r t i c l e i n f o

rticle history:eceived 9 October 2013eceived in revised form 4 December 2013ccepted 20 December 2013vailable online 30 December 2013

a b s t r a c t

A polymer-based uniaxial accelerometer with piezoelectric polyvinylidene fluoride copolymer (P(VDF-TrFE)) transducers and micro injection molded polypropylene (PP) structures has been designed,manufactured and characterized. The mass-loaded cantilever structure shows a quasi-static charge sen-sitivity of 0.69 pC/g and a resonance frequency of 735 Hz. Because of its efficient processing and itssmall dimensions the polymer-based sensor (polySENS) can be integrated into polymer-based compound

eywords:(VDF-TrFE)icro injection molding technology

ombined Simulation

structures in order to measure low-frequency vibrations. The focus of this contribution is on the design,processing as well as on the characterization of the polySENS accelerometer to determine the sensor prop-erties of the accelerometer due to manufacturing particularities. Additionally, investigations regardingthe applied materials and the manufacturing, in particular the mold filling have been done to qualify the

ach.

olymer-based transduceriezoelectric accelerometer

novel technological appro

. Introduction

The exploration of technologies for the manufacturing ofolymer-based composite components is the subject of scientificfforts for many years. Furthermore, the development of technolo-ies for producing polymer-based sensors is a current objective ofntensive scientific investigations. Hence, these functional struc-ures show a high potential, e.g. for structural health monitoring,ibration and noise detection as well as energy harvesting [1–3].he main focus of recent investigations is on manufacturing andpplication studies [4,5].

The injection molding as a large-scale production technologys characterized as highly cost- and energy-efficient [6,7]. It offershe potential for the manufacturing of custom-shaped components

ith high complexity and high aspect ratios. The injection moldingrocess is applied in the mass production of microelectronic pack-ges of integrated electronic components [8]. Fulfilling the need for

� Selected Paper based on the paper presented at The 17th International Con-erence on Solid-State Sensors, Actuators and Microsystems, June 16-20, 2013,arcelona. Spain∗ Corresponding author. Tel.: +49 371 531 38675.

E-mail address: robert.schulze@zfm.tu-chemnitz.de (R. Schulze).

924-4247/$ – see front matter © 2014 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.sna.2013.12.032

© 2014 Elsevier B.V. All rights reserved.

the integration of signal conditioning circuits together with sensorsusing at most the same technology is the basis for the applicationof polymer-based sensors.

Furthermore, the miniaturization of injection molded compo-nents describes a significant development [9]. Hence, mergingpolymer and micro technologies offer the potential for novelsensor and actuator applications, for example fully embeddedand low-cost sensors. To pursue this objective the integra-tion of piezoelectric polymer materials with micro injectionmolded components has been realized [10]. To exhibit the poten-tial of this technology, a low-cost piezoelectric accelerometer,see Fig. 1, based on a mass-loaded cantilever has been devel-oped. This polymer-based sensor (polySENS) with dimensions of5.75 mm × 5.75 mm × 1 mm can be directly integrated into a struc-tural component or housing.

In the literature, a few PVDF-based accelerometers built up withconventional precision engineering approaches in the dimensionsof several centimeters are reported [11–13]. In [11] a design for highacceleration measurement is proposed. Furthermore, the moni-toring of low frequency vibrations is a significant measurement

scenario [12]. These sensors have in common that the dimensionsare in the range of several cm, which is inappropriate for the usein integrated systems. Benech et al. [13] note that PVDF accelero-meters are suitable for low-cost applications. The recent progress

160 R. Schulze et al. / Sensors and Actuators A 208 (2014) 159– 165

i[tie

tmq

2

sttTas

aaastiCctfips

lfsmbCssTmtp

i

F

Fig. 1. Manufactured polymer-based piezoelectric accelerometer.

n the field of piezoelectric MEMS lead to a cost reduction of thin14] and thick film [15] based piezoelectric accelerometers. Thus,he miniaturization of PVDF-based accelerometers as well as thentegration into polymer-based compound structures becomes rel-vant to maintain the advantages of PVDF-based sensors.

The novelty of the presented approach necessitates fundamen-al studies of the applied materials and manufacturing steps by

eans of a defined design. All these investigations contribute toualify the manufacturing of the novel polymer-based sensors.

. Design and theory

In order to utilize new technologies like micro injection molding,imulation methods have to be acquired or adapted. To understandhe particularities of the used technology and materials, a conven-ional piezoelectric uniaxial accelerometer design has been chosen.he polySENS has been laid out for low-frequency measurementsnd consists of a piezoelectric unimorph cantilever connected to aeismic mass.

In ref. [16] a model for a mass loaded piezoelectric bimorphccelerometer can be found. The theory is documented in ref. [17]nd contains also a description of a piezoelectric bimorph as anccelerometer with and without mass loading. In ref. [18] it washown that the model of the bimorph type is also valid to describehe functionality of a unimorph type. Consequently, a correspond-ng model of the unimorph type has to be derived. Therefore, theombined Simulation method [19] is used. It allows the simplifi-ation of the designed geometry and the study of effects such ashe real clamping that is different to the theoretically assumedxed support. Additional technology related effects such as war-ing due to residual stress is determined due to mold-filling processimulations.

The Combined Simulation gives the opportunity to deriveumped sensor parameters of the FE-model shown in Fig. 2. There-ore, the model is reduced to a cantilever structure and a lumpedeismic mass. The corresponding lumped element model of theass-loaded cantilever accelerometer is shown in Fig. 3. This model

uilds the basis for the design of Application Specific Integratedircuits (ASICs) which provide the signal conditioning of the sen-or signals. Amplification and impedance matching of the sensorignal is essential for transmission and further signal processing.his model can further be reduced because of the negligible beamass mB in contrast to the seismic mass m (m � mB). Additionally,

he acceleration source can be merged with the lever structure. Theiezoelectric transducer is described with the equations:

− jωCBu = 1v (1)

Y

+ 1jωnK

v = 1Y

u (2)

Fig. 2. FE-model of the polymer-based piezoelectric accelerometer.

In order to determine the parameters short-circuit mechanicalcompliance nK, blocking capacitance CB and gyrator-like transducercoefficient Y three virtual experiments were performed. For the firststatic FE-simulation using ANSYS simulation software, the sensoris electrically short-circuited resulting in a voltage of u = 0, nK isdetermined due to the displacement �F at a specific force load FU

nK = 1jω

vF

= − �F

FU(3)

In the second simulation experiment, the sensor is driven inactuator mode with a voltage U. Considering the fact that the dis-placements �U and �F have to eliminate each other because ofsuperposition, Y is calculated out of the displacements as a resultof both experiments [19]

Y = U

F ′U

∣∣∣∣�=0

= − �F

�U

U

FU(4)

Furthermore, the free capacitance C0 is determined out of thegenerated charge Q via

C0 = 1jω

i

u= Q

U(5)

Using Eqs. (1) and (2), the electrical blocking capacitance CB canbe calculated as

CB = C0 − nK

Y2(6)

Extending the validness of this model up to the first resonancefrequency the mechanical mass mB and friction impedance r of theaccelerometer is calculated with

mB = 1

(2�f0C )2nK

(7)

r = �

�f0nK(8)

Thereby, f0C is the first resonance frequency of the cantilever and� is the damping ratio. The presented model of the mass-loadedcantilever is valid up to the first resonance frequency f0 which islower than the resonance frequency of the cantilever f0C.

Concerning the lever structure nearby the acceleration sourcein Fig. 3 with the transmission ratio � = l2/l1 it has to be remarkedthat the presented design shows a complex excitation behavior dueto the distributed mass. Related to the standard mass-loaded can-

tilever accelerometer described in [20], a lumped mass with thecenter of mass at the cantilever tip is assumed. This assumption isnot valid for the polySENS structure because of a center of mass off-set in z-direction. This leads to a decrease of the cantilever bending

R. Schulze et al. / Sensors and Actuators A 208 (2014) 159– 165 161

Fig. 3. Lumped element model of a mass-loaded cantilever accelerometer.

Table 1Accuracy of the LEM derived by the Combined Simulation.

Property LEM (Combined Simulation) FEM full model Relative error

mbiaf

2

wwFtwmftcfwLh

pse

fst

2

iNaAcraefop

f0 334.2 Hz 332.1 Hz 0.64%SU 184.5 mV/g 183.7 mV/g 0.44%SQ 0.962 pC/g 0.960 pC/g 0.17%

oment and consequently sensor sensitivity in z-direction causedy tilt of the mass. But, simultaneously the sensitivity in x-direction

s increasing [21]. This effect can be considered by modeling a leverccording to [16] which transmits the center of mass force to a tiporce.

.1. Combined Simulation results

According to the presented theory, the virtual experimentsere carried out for the polySENS accelerometer cantileverith 3 mm2 PVDF-copolymer transducer without residual stress.

rom the first experiment the displacement at voltage excita-ion �U/U = 13.5 nm/V and the blocking capacitance CB = 5.22 pFere determined. The results of the second and third experi-ent for the short-circuit compliance and cantilever resonance

requency are nK = �U/F = −25.8 mm/N and f0C = 3261.75 Hz, respec-ively. Out of these values, the lumped parameters transduceroefficient Y = 1.9e−6 V/N, cantilever mass mB = 9.23e−8 kg andriction impedance r = 3.78e−4 Ns/m assuming a quality factor Q = 5ere calculated and used to perform a network simulation with

Tspice IV simulation software. The seismic mass m = 8.67e−6 kgas been calculated analytically.

To verify the model, the Combined Simulation results were com-ared with the results of a full FE simulation of the accelerometerhown in Fig. 2. The results are summarized in Table 1, the relativerror between the LE and the FE model is less than 1%.

Additionally, the simulation time can be reduced significantlyrom several minutes to a few seconds depending on the mesh den-ity and sampling points. A detailed discussion about simulationime by means of an optimization example can be found in [19].

.2. Process simulation of the micro injection molding

Changes of the dynamic behavior may arise due to process-nduced distortions and stress within thermoplastic parts.on-uniform cooling and inconsistent shrinkage causes warpagend can be considered in injection molding simulations usingutodesk Moldflow Insight. Out of these simulation results, con-lusions related to thermo-mechanical properties and occurringesidual stress were derived. The residual stress is translated ton initial stresses for structural analysis. In this way the influ-

nce of the manufacturing process on properties like the resonancerequency of the polySENS base body were examined. Besides rhe-logical, thermal and mechanical properties as well as shrinkage,rocess settings related to the injection molding machine like mold

Fig. 4. (a) Result of the warp analysis and (b) resulting density distribution (scalefactor: 10). (For interpretation of the references to color in the text, the reader isreferred to the web version of the article.)

surface temperature, melt temperature and flow rate were consid-ered in injection molding simulations.

Especially the temperature and flow rate input have been setequivalent to the experimental settings to investigate the resultingstiffness of the material. All other parameters for the fill and packphase were set to the recommended values for the chosen ther-moplastic material from the Autodesk Moldflow Insight materiallibrary. For the warp analysis 4-node linear tetrahedral elementswere converted to 10-node quadratic tetrahedrons to increase theaccuracy of the structural calculation. The result of the warp anal-ysis and the resulting density distribution is shown in Fig. 4. Amaximum deflection of 180 �m through the volumetric shrinkagecan be observed on the outer edge of the seismic mass. The densityacross the polySENS structure is shown as very homogeneous. As aresult it is concluded that the center of mass is in the middle of theseismic mass body and the lever model is applicable. Consequen-tial, the lumped mass m can be calculated by m = �V, where � is thedensity and V the volume of the seismic mass. To investigate theinfluence of the deformed geometry on the resonance frequencyf0B of the polySENS base body the model has been prepared withFE software ABAQUS.

According to the experimental results for the tensile bar Young’modulus, depending on the injection speed of 750 mm/s, we usedthe mechanical parameters for the modal analysis: Young’ modulusY = 1.010 GPa, Poisson’s ratio �pp = 0.392 and density � = 889 kg/m3.The modal analysis models have exactly the same mesh for the

undeformed and warped model extracted by Autodesk MoldflowInsight.

The calculation of the first resonance frequency gives f0B = 83 Hzwhich is marginal different to the results of the simulation

162 R. Schulze et al. / Sensors and Actuators A 208 (2014) 159– 165

F the bot

ctiten

idttAd

3

occ

sii2ctppsdepm

tmasti

ocopv1ao

ig. 5. Residual stress in the polySENS accelerometer base body (a) on top and (b) ato the web version of the article.)

onsidering the residual stress f0Bpre = 84.6 Hz. It is expected thathe application of the piezoelectric layer lead to a more dramaticncrease of the resonance frequency up to f0 = 333 Hz and thereforeo stiffening of the mass loaded cantilever. Furthermore, the influ-nce of deformed geometry in combination with additional layer isot defined and has to be investigated.

The residual stress after the warp analysis was additionallynvestigated. Fig. 5 shows that there is a difference in the stressistribution at the frame and seismic mass (18 MPa) compared tohe cantilever structure (10 MPa). This stress difference might leado additional stiffening after piezoelectric transducer application.t this stage it is not possible to estimate this influence because itepends strongly on the processing.

. Micro injection molding technology

Multi component micro injection molding allows the fabricationf sensors with a single manufacturing step [22]. This includes theombination of different materials, the establishing of an electricalonnection and an encapsulation.

A challenge arises due to the choice of transducer materialsuch as PVDF-copolymers concerning the temperature regime dur-ng back injection molding of sensor sheets. The common usednjection temperature of the applied polypropylene (PP) with00–300 ◦C is much higher than the Curie temperature of PVDFopolymers, which is in the range of 100–135 ◦C depending on theype of copolymer. It is moreover higher than the melting tem-erature of approximately 155 ◦C. By using appropriate tools androcess parameters (temperature regime, holding time and pres-ure) the necessary temperature for injection molding is locallyrastically reduced. Thus, the temperature for combining the piezo-lectric material with the substrate is achieved without losing theiezoelectric functionality. The first experiments concerning theulti component micro injection molding shows promising results.Currently, the piezoelectric sensor sheets are applied to the

hermoplastic component subsequently to the micro injectionolding step for prototyping purpose. For the application process

specifically developed adhesive tape was used to avoid additionaltiffening of the sensor structure. Recent investigations focusing onechnological implementation and process optimization for a directntegration of the PVDF-copolymer transducer are in progress.

For a reproducible production of the base body, the mold fillingf the seismic mass which is attached to the frame via a 50 �m thinantilever is required. Thus, there is a high risk for solidificationf the polypropylene within the cantilever. It is shown that theolySENS micro injection molding tool has been manufactured

ery accurately. An experimental standard deviation of less than% has been determined for the dimensions of the seismic masss well as for the cantilever. This leads to a relative uncertaintyf less than 3% related to the seismic mass volume and causes a

ttom. (For interpretation of the references to color in the text, the reader is referred

similar sensitivity change. The same relation can be noted for thethickness and length of the cantilever. Consequently, a compliancedeviation of 1% results in a sensitivity change of 1% as well.Assuming shrinkage, a maximum sensitivity uncertainty of 4% isestimated. Thus, reproducibility within an injection-molded batchis given under invariable process conditions.

3.1. Base body material

For the manufacturing of the piezoelectric accelerometer basebody neat polypropylene (HJ325MO, Borealis AG, Vienna, Austria)was used. This polypropylene is a crystalline homopolymer whichis developed especially for high-speed injection molding and con-tains nucleating and antistatic additives for simple mold plate-out.Because of its high melt flow it is suitable for very thin componentswith a long flow length.

3.2. Process related material characterization

Compared to the classical injection molding process, the microinjection molding allows lower injection speed with a simple tem-perature management. Thus, lower cooling rates are set due toa high ratio between the injection mass and component surface.Therefore, the influences of different injection rates and mass tem-peratures on the mechanical stiffness of PP were investigated. In acomprehensive manufacturing study micro tensile bars were pro-duced.

Tensile tests were carried out according to DIN EN ISO 527 fordetermining the material stiffness. The material analysis indicatesa clear dependency of injection speed and mass temperature on themechanical stiffness of the PP. With stepwise increase of injectionspeed from 50 m/s up to 750 m/s, the Young’s modulus decreases ata constant mass temperature of 240 ◦C about 6.5% from 1080 MPato 1010 MPa. A similar trend has been observed for the variationof the mass temperature from 240 ◦C to 300 ◦C at a constant injec-tion speed of 50 mm/s. In this case a clear decrease of the Young’smodulus by 15.2% from 1085 to 920 MPa was determined.

Thus, it can be assumed that these results have significant influ-ence on the mechanical properties of polySENS accelerometer basebody. Referring to the manufacturing study, with increasing theinjection speed from in particular 50 mm/s to 250 mm/s, the sheareffect on the molecular structure of the PP is rising strongly. There-after, �-crystal phases are increasingly formed which reduce thestrength and therewith the modulus of elasticity and the yieldpoint. For a further increase in the injection speed it can be assumedthat the shearing action shows no further influence on the macro-

molecules and a formation of additional �-crystal phases does nottake place. In general, the areas of crystalline phases decrease withrising of mass temperature [23]. At the same time the amount ofthe �-crystal phases is growing in these areas. With increasing of

Actuators A 208 (2014) 159– 165 163

trch

mtpttt1ht

4

owtota

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4

7PtTttotmswwcn

4

mmq(n(tPo7ores

0

0.5

1

1.5

2

2.5

Sens

itivi

ty in

pC

/g

-180

-90

0

90

180

100010010

Phas

e in

°

R. Schulze et al. / Sensors and

he mass temperature, the melt remains longer in the temperatureange between 105 ◦C and 140 ◦C, which favor the formation of �-rystal phases [24]. In conclusion, the varying material propertiesave to be considered in the accelerometer simulations.

For the base body manufacturing a micro injection moldingachine Battenfeld Microsystem 50 was used. The mold surface

emperature of 50 ◦C, a melt temperature of 240 ◦C and a holdingressure of 350 bar were set. The volumetric injection flow ratehrough a 5 mm diameter injection plunger with a machine injec-ion pressure of 2500 bar and a flow front velocity were adjustedo 14.7 cm3/s and 750 mm/s, respectively. The shot volume of100 mm3 leads to maximal machine injection stroke of 56 mmeld by a machine clamp force of 80 kN. These processing parame-ers were used for the process simulations as well.

. Piezoelectric materials

Different investigations have to be carried out to develop anptimal piezoelectric material with high temperature stabilityhich shows good adhesion in an assembly. Beside the piezoelec-

ric transducer additional layers such as the electrodes have to beptimized concerning electrical and mechanical properties. Finallyhe electrical connection of the piezoelectric transducers is crucialnd purpose of recent investigations.

Different piezoelectric transducer materials are suitable formbedding in light-weight structures such as ceramics, classi-al [25] or relatively new studied ferroelectric polymers [26,27],olymer-ceramic composites [28] or novel cellular polymers [29].ere, the exemplary implementation of a polySENS accelerometerased on P(VDF-TrFE) has been realized.

.1. Preparation of the piezoelectric material

A copolymer of PVDF with trifluoroethylene (P(VDF-TrFE)5/25) was used as piezoelectric material. In order to prepare(VDF-TrFE) films, the copolymer powder was solved in a 1:1 mix-ure of dimethyl formamide (DMF) and methyl ethyl ketone (MEK).hin films were prepared by solvent casting accompanied by heatreatments at 80 ◦C and 160 ◦C in order to evaporate the solvent ando adjust the crystallinity. This technique allows the preparationf films with thicknesses of some to about hundred microme-ers. Here, a film thickness of 40 �m was adjusted. The films were

etalized with aluminum electrodes of 100 nm thickness on bothurfaces. In order to structure the electrode area, shadow masksere used during the metallization. With this procedure, electrodesith an overlapping area of 3.0 or 4.5 mm2 were processed which

ontains addition small not both side metalized areas for the con-ection of the transducer with the electric equipment.

.2. Electric poling

Electric poling is used in order to render the PVDF copoly-er films piezoelectric. Therefore, sinusoidal electric fields with aaximum field strength of 75 MV/m and a bipolar electric field fre-

uency of 10 mHz are applied by means of an high voltage deviceTREK model 610C) controlled by a function generator. For thin-er films, the poling current was measured with an electrometerAgilent 3458a) operated in the current mode. Measurements onhinner films leads to the result that the coercive field of the usedVDF copolymer is about 45 MV/m and that a significant saturationf the hysteresis loop is obtained by a poling field strength of about5 MV/m. Similar dependencies were assumed for electric poling

f the here prepared thicker films, while the electrometer wasemoved from the measurement setup in order to prevent it fromlectrical breakdowns. The piezoelectric coefficients were mea-ured on reference samples which exhibit an electrode area of 1 cm2

Frequency in Hz

Fig. 6. Measured frequency response of the polySENS aceelerometer.

and which were processed and polarized similar to the smallerstructured polySENS transducers. The piezoelectric coefficientswere determined by means of a so-called quasi-static technique[26]. Therefore, dynamic excitations at a frequency of 2 Hz (Vibra-tion Exciter B&K 4810 by Brüel & Kjaer) with a bias force of 1.5 N andamplitude of 1.5 N were applied to the samples. The electric polingdiscussed above leads to piezoelectric activity with d33 coefficientsof about 20 pC/N which represents typical activities for PVDF orP(VDF-TrFE) films.

4.3. Processing of the piezoelectric transducer

After film and electrode processing as well as electric poling ofthe films, the transducer were cut either by hand or automated bylaser cutting. Therefore, the sample was cut at about 1 mm besidethe one-side or both-side metalized areas. These structured trans-ducer films were glued to the polySENS structures by means of adouble-sided tape (thickness 25 �m, research grade – not commer-cial). Finally, connecting wires were glued with conductive paint tothe one-side metalized electrode areas.

Consequently, the polySENS accelerometer prototype was pre-pared for the sensor characterization by inserting into printedcircuit board (PCB) for electrical and mechanical connection to themeasurement setup.

5. Sensor characterization

The polySENS have been characterized electromechanicallywith a setup containing a SR 830 lock-in-amplifier in a LabViewenvironment for stepping a sinusodial excitation of a vibrationexciter B&K 4809 amplified by using a B&K 2718 power amplifier.The polySENS was glued into a PCB and mounted with an adapter tothe vibration exciter. The acceleration was measured with a refer-ence sensor B&K 4382 screwed to the adapter. The reference signalswere conditioned by a B&K 2692 charge amplifer. The polySENSsignal was measured using a MMF M68-D1 charge amplifier.

Fig. 6 shows the sensitivity measurement results exemplarilyfor the 3 mm2 polySENS accelerometer. However, in the SR-830measurement, a big influence of the used low-pass with a timeconstant of 100 ms is observed in the phase signal which leads to aphase shift of 90◦ below 100 Hz.

In addition, the curve shows an influence of the measurementsetup around 300 Hz and 750 Hz, respectively. Analyzing the fre-quency response of the adapter together with the reference sensorwe could see a specific behavior to be the green curve in Fig. 7. The

164 R. Schulze et al. / Sensors and Actuators A 208 (2014) 159– 165

0

1

2

3

Rel

ativ

e Tr

ansf

erfu

nctio

n

Sens

itivi

ty in

pC

/g

polySENS polySENS+Adapter

Adapter

-180 -90

0 90

180

50 300 550 800

Phas

e in

°

Frequency in Hz

Fig. 7. Frequency response of the polySENS with respect to the measurement setup. (For iversion of the article.)

0

5

10

0 2 4 6 8 10 Cha

rge

in p

C

Acceleration in g

Type 1 (3 mm ) Type 2 (4.5 mm )

Fig. 8. Linear amplitude response for the two polySENS samples measured between0.01 g and 10 g.

Table 2Properties for two polySENS sample types.

Property Sample 1 (3 mm2) Sample 2 (4.5 mm2)

Resonance frequency f0 in Hz 535 735Linear range (10%) in Hz 125 2753 dB-bandwidth in Hz 177 145

mmo

ttA

rfTt

6

uT

[5] I.M. De Rosa, F. Sarasini, Use of PVDF as acoustic emission sensor for in situ

Linear sensitivity S in pC/g 0.42 0.69Damping ratio � 0.17 0.1

easured transfer function (red curve) with respect to this realechanical input force (green curve) gives us the transfer function

f the polySENS (blue curve).Furthermore the amplitude response has been determined for

wo samples with different transducer lengths. The resulting elec-rical voltage is linearly proportional to the acceleration, see Fig. 8.ll measured properties of the sensor are summarized in Table 2.

A comparison of the simulation of Section 2 and measurementesults show that the processing leads to a significant change in theunctionality and the mass-loaded cantilever structure is stiffened.his leads to a reduction of the sensitivity as well as an increase ofhe resonance frequency.

. Conclusions

A polymer-based piezoelectric accelerometer fabricated bysing microinjection molding technologies has been presented.his polySENS shows a charge sensitivity of 0.69 pC/g and a

nterpretation of the references to color in the text, the reader is referred to the web

resonance frequency of 735 Hz, respectively. The sensor outputsignal as a function of the acceleration is linear between 0.01 gand 10 g. Studies concerning the relationship of the manufacturingprocess and the used materials have been carried out. The mea-sured sensitivity is slightly smaller than expected from simulations.Additionally, an increase of the polySENS resonance frequencyleads to the fact that the sensor is stiffened due to the manufactur-ing process. As a main factor the process induced stress is identified.The accelerometer shows the potential of polymer-based sensorsfor the integration in lightweight compound structures, e.g. forstructural health monitoring.

The further work will focus on the evaluation and quantificationof the residual stress, the manufacturing of the sensor in large-scale,the signal conditioning as well as the reliability of the sensor.

Acknowledgements

The work has been done in the framework of the nano systemintegration network of excellence nanett (03IS2011) funded by theGerman Federal Ministry of Education and Research. Financial sup-port from the German Research Foundation (DFG) as part of thecluster of excellence “MERGE” (EXC 1075) and the CRC/Transregio39 “PT-PISA” is also gratefully acknowledged.

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iographies

obert Schulze received his Dipl.-Ing. degree in electrical engineering from theechnische Universität Dresden in 2009. From 2009 to 2010 he worked at theraunhofer Institute for Electronic Nano Systems (ENAS) as research assistant inhe field of electromechanical systems simulation. Since 2010 he is with the Centeror Microtechnologies (ZfM) of the Technische Universität Chemnitz. The focus ofis work as research associate is on the design, simulation and characterization ofiezoelectric sensor systems. His research interests are mainly the integration ofolymer-based piezoelectric sensors as well electro acoustics.

ichael Heinrich received his Dipl.-Ing. degree in mechanical engineering espe-ially lightweight structure and polymer technology in 2004 from the Technischeniversität Chemnitz. Since 2004 he is research associate at the Institute ofightweight Structures in the group of Prof. Kroll. He aims for his Ph.D. degree focus-ng on effects of micro injection molded composites based on carbon nano tubes for

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electrical contacting of piezo ceramics. Since 2008 he is the leader of CompetenceCenter for Lightweight Structures e.V. and since 2004 he published more than 50articles and patents in the field of sensor and actuator integration.

Patryk Nossol received the Dipl.-Ing. degree in mechanical engineering especiallylightweight structure and polymer technology in 2009 at the Technische Univer-sität Dresden focusing on computer-aided and experimental sensitivity analysis ofmodal parameters for technical diagnostic of composites structures. Since then hejoined the Kroll group at Institute of Lightweight Structures at the Technische Uni-versität Chemnitz. Currently he works as a scientific assistant in the research groupComputation, Simulation and Design aiming for his Ph.D. in the field of structuralhealth monitoring of composite structures. Additionally he is research assistantin the Cluster of Excellence Merge Technologies for Multifunctional LightweightStructures.

Roman Forke received his Dipl.-Ing. degree in microsystem and precision engi-neering from the Technische Universität Chemnitz in 2005. From 2006 to 2009he got a Siemens scholarship to work toward his doctoral degree on the topic ofmicromechanical sensors for vibration and acoustic emission detection. He receivedhis Dr.-Ing. degree in electrical engineering from the same university in 2012. Since2009 he works as a scientific research engineer at the Fraunhofer Institute forElectronic Nano Systems (ENAS). His research interests are MEMS inertial sensors,especially the layout, system design and characterization of MEMS gyroscopes andaccelerometers for high-precision applications.

Martynas Sborikas completed bachelor in applied physics at the Vilnius University,Lithuania, and master degree in polymer science at Humboldt University in Berlin,Germany. During master degree studies he completed an internship at Bayer Mate-rial Science AG, Leverkusen, Germany, on novel ferroelectret material and industrialmanufacturing technique. Currently, he is a Ph.D. student at University of Potsdamand Fraunhofer Institute for Applied Polymer Research (IAP), Potsdam. His researchtopics are electroactive materials, especially the relationship between polymer andcomposite structure and the resulting electromechanical properties as well as thepreparation of optimized transducer for air-borne ultrasonic and non-destructivetesting applications.

Alexander Tsapkolenko received his diploma in micro- and solid state electron-ics from the South Russia State Technical University (Novocherkassk PolytechnicalInstitute) in 2009. Before, he received a diploma in linguistics for professional com-munications (German). Since then he studied micro- and nanotechnologies at theTechnische Universität Ilmenau and received his master degree in 2012. Currentlyhe is with the Center for Microtechnologies of the Technische Universität Chemnitzand his main research interests are on the integration of electronics and inertialsensor system into lightweight structures.

Detlef Billep received his Dipl.-Ing. degree in microsystem and precision engineer-ing from the Technische Universität Chemnitz in 1993. Afterwards he worked asresearch associate and received his Dr.-Ing. degree in electrical engineering fromthe same university in 2000. From 2005 to 2007 he worked as research engineerat SICK Engineering GmbH, Ottendorf-Okrilla. Since 2008 he is group leader of theMEMS/NEMS design group at the Fraunhofer Institute for Electronic Nano Systems(ENAS) and deputy head of the department Multi Device Integration. His researchinterests are MEMS inertial sensors for high-precision applications and he publishedover 50 articles and 5 patents.

Michael Wegener studied physics and mathematics at the University of Potsdamfrom 1990 to 1995. In 1998 he completed an industry internship at Huber & SuhnerAG in Switzerland. He received the Ph.D. degree in physics from the same univer-sity in 2000 and worked there as project manager until 2006. In 2007 he receivedhis Dr. rer. nat. habil. degree with research and developments of ferroelectrets asnew class of piezoelectric materials. Since 2007 he is with the Fraunhofer Insti-tute for Applied Polymer Research (IAP), Potsdam. His current research fields areferroelectric polymers, ferroelectrets as well as dielectric elastomer actuators.

Lothar Kroll received his Ph.D. degree in 1992 at Institute for Technical Mechanicsat the Technische Universität Clausthal and habilitated in 2005 at the TechnischeUniversität Dresden in the field of lightweight construction and material mechan-ics. Since 2006 he is Full Professor at Department of Lightweight Structures andPolymer Technology at Technische Universität Chemnitz and dean of the Faculty ofMechanical Engineering since 2013. Furthermore, Prof. Kroll is CEO of the FederalCluster of Excellence Merge and leader of the Fraunhofer Plastic Technology CenterOberlausitz since 2013. From 1987 he published more than 350 publications andpatents.

Thomas Gessner studied physics and received the degree in physics in 1979, thePh.D. degree in 1983 from the Dresden University of Technology and the Dr.-Ing.habil. degree from the Chemnitz University of Technology in 1989. Since 1991 he is

Director of the Center for Microtechnologies and since 1993 Professor for Microtech-nology, both at the Technische Universität Chemnitz. Moreover, Prof. Gessner is thefounder and director of the Fraunhofer Institute for Electronic Nano Systems (ENAS)since 2008. He is author or co-author of more than 750 publications and 77 patentsin 38 patent families in microelectronics and micro system technologies.