characteristic evaluation of a solid polymer electrolyte sensor

5
TECHNICAL PAPER Characteristic evaluation of a solid polymer electrolyte sensor Manabu Otsuki Takeshi Okuyama Mami Tanaka Received: 4 September 2010 / Accepted: 28 March 2011 / Published online: 19 April 2011 Ó Springer-Verlag 2011 Abstract This paper describes a development of a cur- vature sensor using a solid polymer electrolyte (SPE) film. The SPE film has good flexibility, and can be used in air. In previous research, we clarified output response to defor- mation of the SPE sensor and the relationship between sensor output and sensor curvature. In this paper, output characteristics of the SPE sensor are investigated in detail. Four sensors with different length and width are prepared. And the influence of the SPE sensor on the sensor element shape is investigated. As a result, it is confirmed that there are a several sensors which cause a slight reduction of the sensor output because it is difficult to place the whole sensor element on the sample curve exactly. Concerning with the large sensor, it was confirmed that the reduction of the sensor output is not occurred. 1 Introduction Recently, functional polymers including PVDF with pie- zoelectricity and ionic polymer metal composites (IPMC) have been attracting attention, and several actuators and sensors have been developed (Shahinpoor 1998). In gen- eral, the functional polymers have advantages such as lightweight, flexibility and good workability. And they have another advantage that an external power supply is unnecessary, because functional polymers can convert electrical energy into mechanical energy by itself and can convert reversely. Especially, IPMC attracts attention in broad fields as an actuator which makes large bending deformation by low voltage (Konyo et al. 2000). IPMC has been investigated as a sensor, too (Bonomo et al. 2008). However, IPMC has the water evaporation problem in air. Therefore, a solid polymer electrolyte (SPE) has been expected as a functional polymer which makes deformation by adding voltage like IPMC in air (Cho et al. 2007). Authors have been developing an SPE sensor which has a layer structure. Fundamental characteristic evaluation of the sensor was carried out. It was observed that the output voltage of the sensor is associated with bending deforma- tion (Okuyama et al. 2009). Moreover, it was found that output voltage of the proposed sensor is proportional to the average of the curvature over the whole sensor element (Otsuki et al. 2009). However, in previous study, the influence of the sensor shape on the sensor output is not considered. In this paper, output characteristics of the SPE curvature sensor are investigated in detail. Four sensors which have different area size were prepared. Two of the sensors are square-shaped and the other two are rectangle-shaped. The influence of the SPE sensor on the sensor element shape is investigated. 2 Structure of SPE sensor Figure 1 shows the photograph and the structure of the SPE sensor. The sensor element has a basic structure that an SPE film is sandwiched between thin carbon films coated with Ag paste. In addition, they are covered with polymer films. And polyvinyl chloride film as a gripper is set around the sensor. Output voltage of the SPE sensor was generated M. Otsuki (&) Á M. Tanaka Graduate School of Biomedical Engineering, Tohoku University, Sendai, Japan e-mail: [email protected] T. Okuyama Graduate School of Engineering, Tohoku University, Sendai, Japan 123 Microsyst Technol (2011) 17:1129–1133 DOI 10.1007/s00542-011-1285-z

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Page 1: Characteristic evaluation of a solid polymer electrolyte sensor

TECHNICAL PAPER

Characteristic evaluation of a solid polymer electrolyte sensor

Manabu Otsuki • Takeshi Okuyama •

Mami Tanaka

Received: 4 September 2010 / Accepted: 28 March 2011 / Published online: 19 April 2011

� Springer-Verlag 2011

Abstract This paper describes a development of a cur-

vature sensor using a solid polymer electrolyte (SPE) film.

The SPE film has good flexibility, and can be used in air. In

previous research, we clarified output response to defor-

mation of the SPE sensor and the relationship between

sensor output and sensor curvature. In this paper, output

characteristics of the SPE sensor are investigated in detail.

Four sensors with different length and width are prepared.

And the influence of the SPE sensor on the sensor element

shape is investigated. As a result, it is confirmed that there

are a several sensors which cause a slight reduction of the

sensor output because it is difficult to place the whole

sensor element on the sample curve exactly. Concerning

with the large sensor, it was confirmed that the reduction of

the sensor output is not occurred.

1 Introduction

Recently, functional polymers including PVDF with pie-

zoelectricity and ionic polymer metal composites (IPMC)

have been attracting attention, and several actuators and

sensors have been developed (Shahinpoor 1998). In gen-

eral, the functional polymers have advantages such as

lightweight, flexibility and good workability. And they

have another advantage that an external power supply is

unnecessary, because functional polymers can convert

electrical energy into mechanical energy by itself and can

convert reversely. Especially, IPMC attracts attention in

broad fields as an actuator which makes large bending

deformation by low voltage (Konyo et al. 2000). IPMC has

been investigated as a sensor, too (Bonomo et al. 2008).

However, IPMC has the water evaporation problem in air.

Therefore, a solid polymer electrolyte (SPE) has been

expected as a functional polymer which makes deformation

by adding voltage like IPMC in air (Cho et al. 2007).

Authors have been developing an SPE sensor which has

a layer structure. Fundamental characteristic evaluation of

the sensor was carried out. It was observed that the output

voltage of the sensor is associated with bending deforma-

tion (Okuyama et al. 2009). Moreover, it was found that

output voltage of the proposed sensor is proportional to the

average of the curvature over the whole sensor element

(Otsuki et al. 2009). However, in previous study, the

influence of the sensor shape on the sensor output is not

considered.

In this paper, output characteristics of the SPE curvature

sensor are investigated in detail. Four sensors which have

different area size were prepared. Two of the sensors are

square-shaped and the other two are rectangle-shaped. The

influence of the SPE sensor on the sensor element shape is

investigated.

2 Structure of SPE sensor

Figure 1 shows the photograph and the structure of the SPE

sensor. The sensor element has a basic structure that an

SPE film is sandwiched between thin carbon films coated

with Ag paste. In addition, they are covered with polymer

films. And polyvinyl chloride film as a gripper is set around

the sensor. Output voltage of the SPE sensor was generated

M. Otsuki (&) � M. Tanaka

Graduate School of Biomedical Engineering, Tohoku University,

Sendai, Japan

e-mail: [email protected]

T. Okuyama

Graduate School of Engineering, Tohoku University,

Sendai, Japan

123

Microsyst Technol (2011) 17:1129–1133

DOI 10.1007/s00542-011-1285-z

Page 2: Characteristic evaluation of a solid polymer electrolyte sensor

by applying bending deformation. Although the output

generation mechanism of SPE sensors has not yet been

elucidated, the difference in electric double layer capacity

between the anodic and cathodic interfaces may be gen-

erated by applying bending deformation (Saito et al. 2009).

Dimensions of four sensors are listed in Table 1. Based

on shape (rectangular: R or square: S) and the size of the

sensor element (100, 200, 400, 900 [mm2]), four sensors

were described by the abbreviation. For example, R100

indicates the sensor with rectangular shape and the size of

100 mm2. Moreover, l means the length of the long side

and w means the length of the short side.

3 Experiment

3.1 Measurement condition

The influence of the sensor shape on the sensor output was

investigated. Ten kinds of acrylic cylinders whose radii are

10 to 50 mm were prepared as measurement sample as

shown in Fig. 2.

To perform the all measurements at unified position on

the sample, three base lines on the sensor, which are line 1,

line 2 and line 3, and a reference line on the sample were

defined as shown in Fig. 3. The line 1 is defined as the

center line of the sensor element which is parallel to the

width direction. And the reference line which is parallel to

the cylinder axis was set on the curve of the sample as

shown in Fig. 4. And ‘sensor-rotation angle’, h, is defined

as the sharp angle between line 1 and the reference line.

For example, when line 2 was placed on the reference line

as shown in Fig. 4, h was p/4 rad. The measurements were

carried out for three kinds of h (e.g. h = 0: when line 1 was

placed on the reference line, p/4 and p/2: line 3 was placed

on the reference line).

In the experiment, the sensor was operated manually.

First, the sensor was placed on the flat, and the voltage

adjusted to zero. Next, the sensor was placed on the curve

of the sample at three kinds of h as shown in Fig. 4. Then

the sensor was carried back to the flat. The output voltage

Ag pasteSPE material

Carbon films Polymer film

a

b

Fig. 1 Photograph and structure of the SPE sensor. a Photograph of

four sensors. b Cross section of the sensor on side view

Table 1 Properties of four sensors

Sensor symbol l (mm) w (mm) Area size of sensor

element (mm2)

R100 20 5 100

R200 20 10 200

S400 20 20 400

S900 30 30 900

Fig. 2 Measurement samples

π/4 radθ

Line 1

Line 2

Line 3

Sensor element

Lead

Center of the sensor element

l

w

Fig. 3 Positional relation between three base lines and the sensor

element

1130 Microsyst Technol (2011) 17:1129–1133

123

Page 3: Characteristic evaluation of a solid polymer electrolyte sensor

was measured using a data logger (KEYENCE products

NR-500, ST04, input impedance of 1 MX) at sampling rate

of 100 Hz. The sensor was kept on the sample for about

10 s. Output was measured five times for each condition.

The measurement was carried out at room temperature.

3.2 Result

Figure 5 shows the output voltage waveforms from S900 at

0 rad for the sample with 10 mm radius in five times

measurements. As the sensor was placed on the sample, the

output voltage increased. While holding on the sample, the

output was relatively constant. When the sensor was car-

ried back to the flat, the output voltage was back to zero.

The transient responses of the output are different for each

measurement due to manual operation. However, by

comparing the sensor outputs from five times measure-

ment, it was confirmed that the sensor output converge a

constant value under constant deformation. The average of

the sensor output with 25–30 s after beginning of the

measurement was calculated. In evaluation of the sensor,

the average value was used as the sensor output.

Figure 6 shows the relationships between the sensor

output and curvature for four kinds of sensors at 0 rad. For

all sensors, the relationship between the sensor outputs and

curvature are approximately in agreement.

Figure 7 shows the relationship between the sensor

output and curvature for three kinds of h for each sensor. In

the case of S400 (Fig. 7c) and S900 (Fig. 7d), the rela-

tionship between the sensor output and curvature is not

affected by h. The results coincide with that in the previous

study (Otsuki et al. 2009). In the case of R100 (Fig. 7a) and

R200 (Fig. 7b), the output decreases slightly with rotating

the sensor to p/4 and p/2. Moreover, the amount of the

reduction increases with increasing the sensor curvature.

4 Discussion

In previous study (Otsuki et al. 2009), it is clarified that the

sensor output voltage corresponds with the average cur-

vature over sensor element. Therefore, when a part of

sensor element is not entirely fitted on the surface of

measuring object, the average curvature reduces. More-

over, according to increasing the ratio of small curvature

part on the sensor, the average curvature reduces, too. The

reduction of the average curvature results in the decrease of

the sensor output.

Focusing on sensor R100, R200 and S400, the sensor

output at h = 0 is the same, and the output at h = p/2 is

different. Moreover, the sensor element length parallel to

the circumferential direction of the sample is the same

relation. In fact, it is considered that the sensor output

decreases slightly with decreasing the sensor element

length parallel to the circumferential direction of the

sample.

Fig. 4 Aspect of measurement

0 10 20 30 40 50

0

0.2

0.4

0.6

Time (s)

Out

put v

olta

ge (

mV

)

Fig. 5 A typical response of the SPE sensor to measure the curve of

the sample

0 0.02 0.04 0.06 0.08 0. 10

0.1

0.2

0.3

0.4

0.5

0.6

Curvature (mm−1

Sens

or o

utpu

t (m

V)

R100R200S400S900

)

Fig. 6 The sensor output versus the sensor curvature for four kinds of

sensors

Microsyst Technol (2011) 17:1129–1133 1131

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Page 4: Characteristic evaluation of a solid polymer electrolyte sensor

Due to the manual operation, it is difficult to place the

whole sensor element on the sample curve exactly.

Therefore, it is considered that the gap between the sensor

element rim and the sample curve is occurred although the

gap is so small that it is seldom visible to the naked eye.

The influence of the gap on the sensor output increases

with decreasing the sensor length and width.

Furthermore, by comparison of S400 and S900, the

dimensions are different. However, the output character-

istic of the sensor was almost the same. The results suggest

that there is the critical width and length so that the

reduction of the average of the sensor curvature is occur-

red. The reason is as described above.

5 Conclusion

In this paper, characteristics of the SPE curvature sensor

were evaluated. As a result, it was confirmed that the

output voltage of the small sensor decreases slightly

because it is difficult to place the whole sensor element on

the sample curve exactly. Concerning with the large sensor,

it was confirmed that the reduction of the sensor output is

not occurred.

Acknowledgments The authors wish to thank Mr. Nozomu Sugoh,

Mr. Taketoshi Okuno and Mr. Ryota Komiya (KURARAY CO.,

LTD.) for providing us the sensor material.

References

Bonomo C, Brunetto P, Fortuna L, Giannone P, Graziani S (2008) A

tactile Sensor for biomedical applications based on IPMCs. IEEE

Sens J 8(8):1486–1493

Cho SM, Seo JH, Nam DJ (2007) An electroactive conducting

polymer actuator based on NBR/RTIL solid polymer electrolyte.

Smart Mater Struct 16:237–242

Konyo M, Tadokoro S, Takamori T (2000) Artificial tactile feel

display using soft gel actuators. Proceedings of 2000 IEEE

0 0.02 0.04 0.06 0.08 0.10

0.1

0.2

0.3

0.4

0.5

0.6

Curvature(mm ) -1 Curvature(mm ) -1

0 (rad)π/4 (rad)π/2 (rad)

0 0.02 0.04 0.06 0.08 0.1

0 0.02 0.04 0.06 0.08 0.1

Curvature(mm ) -1 Curvature(mm ) -1

0 0.02 0.04 0.06 0.08 0.1

0 (rad)π/4 (rad)π/2 (rad)

0

0.1

0.2

0.3

0.4

0.5

0.6

Sen

sor

outp

ut (

mV

)S

enso

r ou

tput

(m

V)

0

0.1

0.2

0.3

0.4

0.5

0.6

0

0.1

0.2

0.3

0.4

0.5

0.6

Sen

sor

outp

ut (

mV

)S

enso

r ou

tput

(m

V)

0 (rad)π/4 (rad)π/2 (rad)

(a) R100 (b) R200

(c) S400 (d) S900

0 (rad)π/4 (rad)π/2 (rad)

Fig. 7 Relationship between the sensor output and curvature at three kinds of h for each four kinds of sensors

1132 Microsyst Technol (2011) 17:1129–1133

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Okuyama T, Otsuki M, Komiya R, Sugoh N, Tanaka M (2009)

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Otsuki M, Okuyama T, Tanaka M (2009) Characterization of a

curvature sensor using a solid polymer electrolyte. Proceedings

of SPIE’s international conference on mechatronics and infor-

mation technology, vol 7500-0L

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