Product Introductions

Mat Sensor Using Piezoelectric Sheet

when a voltage is applied. In this mat sensor

1. Introduction

application, the piezoelectric effect is used, and theVALQUA has been developing organic piezoelectric
1）sheets using fluorine materials and abnormal vibration

voltage generated by applying force to the piezoelectric
sheet is used as a signal.

2）

detection systems as its application .

The characteristics of the fluorine material and thePiezoelectric effectInverse Piezoelectric effectMechanical strain
produces a voltage

Applying voltage producesa mechanical strain

carefully designed sheet structure enable piezoelectric
properties. As a result, our fluorine-based organic
piezoelectric sheet can be used even at highpossible with conventional organic（polymer-based）
piezoelectric materials. Other characteristic of thesesheets is that they do not lose their piezoelectric
properties even in high temperature and high humidity

Figure1 Functional expression mechanism of piezoelectric sheet2-2）Detection mechanism of conventional
mat sensors

environments（85℃ and 85% RH）. In addition, it is easy

Many mat sensors use a method called contact-type

to make them large in area, which is a common feature

method, as shown in Figure2. In the contact-typeof organic piezoelectric materials. This report

method, the contact points inside the sensor makeintroduced the mat sensor we have developed as ancontact with each other due to the applied pressure,

item that makes the most of these features.

which leads to conduction and detection of thepressure. It is a very simple detection mechanism, and2. Detection Mechanism

the mechanism is easily understandable. On the other2-1）Function of piezoelectric sheet

to separate the contact points, and thus the system ishand, this method requires a structure（e.g., a spacer）

First, the functions of piezoelectric sheet will be

anticipated to become complicated for large-area

explained. Piezoelectric sheets are a f orm ofsensors. In addition, it is expected that the effect ofpiezoelectric material. There are many inorganic andthe deterioration of the structure over time must beorganic piezoelectric materials. Also, there are several

considered as well.

types of detection mechanisms, but for simplicity, thedetection mechanism of our organic piezoelectric sheet

Contact point

will be explained as an example.
As shown in Figure1, piezoelectric materials have twoeffects. The piezoelectric effect, in which a voltage isgenerated when force is applied, and the inverse
piezoelectric effect, in which the material deforms

SpacerFigure2 Detection mechanism of sensor using contact-type method
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temperatures of 100℃ or higher, which was notNo.41

Mat Sensor Using Piezoelectric Sheet2-3）Detection mechanism of piezoelectric sheetPiezoelectric material
responsiveness

Figure3 shows the detection mechanism of aconsisting of a piezoelectric sheet and electrodes placedon both sides of the sheet. It detects the voltage
generated when the sheet itself is distorted in theLoad（press）

Load（press）

thickness direction by the applied pressure. Thissystem does not require a spacer, and it is relatively
easy to fabricate a thin, large-area sensor.

UnloadUnloadVoltage output

piezoelectric sheet. The sensor has a simple structure

Mat sensor responsiveness

UnloadFigure4 Responsiveness of piezoelectric material and mat sensor

3. Development Details3-1）Setting target performanceElectrodeAs a performance indicator for our mat sensor, wePiezoelectric sheetreferred to JIS B 9717-1:2001（Safety of machinery-

Figure3

Pressure-sensitive protective devices - Part 1: General

Detection mechanism of piezoelectric sheet

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mats and pressure-sensitive floors）. This JIS

perpendicular to the sheet surface. On the other hand,summarizes the required properties for mat sensors toother piezoelectric materials can detect force in thebe installed in factories and other facilities. In thisdirection of the surface（tension, compression, andproject, we used this JIS as a reference to proceed withtorsion）. When used as a mat sensor, detecting only

our development of a mat sensor that would satisfy thevertical force like our type is assumed to be anproperties shown in Table1.

advantage in some applications.
Next, we are going to explain how piezoelectric sheets

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principles for design and testing of pressure-sensitive

Our piezoelectric sheet detects force in the direction

detect force. In general, piezoelectric materials, whether
inorganic or organic, generate a voltage at the moment
when force is applied and thus can detect the force. Incontrast, they do not generate voltage when force isTable1

Test items and conditions

Test item

Test conditions

Mechanical properties
Durability test

2 million cycles vertical / diagonal room temperature
1 million cycles diagonally 14.5 degrees -20℃ , 50℃

Vibration test

1 ⇔30Hz/ up / down / left / right/ front/ back /5 minutes each

Static load test

Φ11/750N/8h,φ80/2000N/8h

On the other hand, as a mat sensor, there is also a need

Impactresistance test

R:10mm/1kg/ Dropped from:1000mm

to continuously detect force, not only at the moment

Weather resistance properties

when force is applied but also in the state when force is

Waterproof test

IP6X

being applied（i.e., when a person or object is on it）.

Cycle test

−20℃（12h）⇔ 50℃（12h）×10Figure4 illustrates the difference between theHeat aging test

66℃ /90 days room temperature 8 years
equivalent to exposure

High temperatureand high humidity
test40℃ /90-95%RH/56 days

High temperaturetest

50℃ /72 hours

Low temperature
test−30℃ /72 hours

continuously applied and thus cannot detect staticforce.

responsiveness of piezoelectric materials and theresponsiveness required for use as a mat sensor. As
shown in the figure, to detect continuous force, theoutput voltage waveform from the piezoelectricmaterial needs to be converted to a form suitable for amat sensor. In this project, we dealt with it bydesigning a dedicated control circuit to perform thewaveform conversion.
19Electrical properties
Dielectric strengthtest

AC0.72kV/1mA、DC1kV/ >100MΩProduct Introductions3-2）Examining mat sensor structure
We examined the structure of a mat sensor that would

4. Characteristics of developed productsatisfy the required properties described above. The

Figure6 shows the appearance of the developed matpressure-sensing itself could be realized with a simple

sensor system. The system consists of a mat sensor

structure of a sensor consisting of a piezoelectric sheet（right）and a control circuit（left）. The latter is used forand electrodes as described above.

output waveform conversion.

However, this sensor is very thin（several hundred

In this system, the LED lamp of the control circuitmicrons）and does not have sufficient mechanicallights up when pressure is applied to the mat sensor.

strength. The optimal structure was determined by

The control circuit can be further downsized andexamining a variety of structures to satisfy theexpanded functionally.

mechanical properties, weather resistance（waterAs for the functional expansion of the control circuit,resistance）, and electrical properties.

for example, it will be possible to detect only the forceof arbitrary magnitude by adding a threshold setting3-3）Performance evaluation method and results

function. Also, patterning the electrodes on both sides

The performance test was conducted according to theof the piezoelectric sheet will make it possible to detect

JIS standard（JIS B 9717-1:2001）. We measured thethe force distribution. Furthermore, if a wirelessvoltage output when force was applied to the mat

communication function is built-in, it can be used as ansensor before and during each test, evaluating theIoT device and monitored remotely.

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pressure detection performance of the mat sensor.
For the durability test, we fabricated JIS-compliant test
equipment and conducted the test. Figure5 shows anexample of the equipment, a durability test machine forthe vertical load. Two million cycles of force wereapplied for the durability test.
The developed mat sensor satisfied the properties

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shown in Table1.

Figure6Developed mat sensor system

5. Conclusion
Our fluorine-based organic piezoelectric sheet wasintroduced. This time, we were able to develop a matsensor that complies with the required properties of JIS
Figure5

Durability test machine (example)

B 9717-1:2001. The piezoelectric sheet has no
mechanical mechanism and can be used for a long time.
It is thus expected to have a long time stableperformance as a mat sensor.
The size, shape, and detection sensitivity can bedesigned according to the application. Also, since the20

Mat Sensor Using Piezoelectric Sheetpiezoelectric sensor is extremely thin（several hundredfor his great cooperation in the design and developmentmicrons）and flexible, it can be applied as a thin matof the conversion circuit for the output voltage

sensor. Taking advantage of these features, the sensor

waveform. I sincerely appreciate his contribution to thecould be used in the security and health care, which areproject.

related to safety and security. We would also like torespond from our readers.

6. Acknowledgments

7. References
1）Y oshiro Tajitsu and Tetsuya Komeda: Valqua
Technology News, No.26, 12-17（2014）.

I would like to express our gratitude to Dr. Yoshiro

2）Makoto Haneda, Hisataka Sato, Tetsuya Komeda,Tajitsu of Kansai University（Professor of the Faculty

Yasushi Aburatani: Valqua Technology News, No.36,of Engineering Science Department of Electrical and3-6（2019）.

Electronic Engineering, Trustee of Kansai University）

Tetsuya Komeda
Summer 2021

New Application Exploration
Advanced Technology Development Department
Research and Development Division

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