Development of a single-chip elasticity sensor using MEMS-based piezoresistive cantilevers with different tactile properties

Accepted Manuscript Title: Development of a single-chip elasticity sensor using MEMS-based piezoresistive cantilevers with different tactile properties Authors: Thanh-Vinh Nguyen, Ryota Tanii, Tomoyuki Takahata, Isao Shimoyama PII: DOI: Reference:

S0924-4247(18)31026-4 https://doi.org/10.1016/j.sna.2018.11.020 SNA 11115

To appear in:

Sensors and Actuators A

Received date: Revised date: Accepted date:

20 June 2018 2 November 2018 10 November 2018

Please cite this article as: Nguyen T-Vinh, Tanii R, Takahata T, Shimoyama I, Development of a single-chip elasticity sensor using MEMS-based piezoresistive cantilevers with different tactile properties, Sensors and amp; Actuators: A. Physical (2018), https://doi.org/10.1016/j.sna.2018.11.020 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Development of a single-chip elasticity sensor using MEMS-based piezoresistive cantilevers with different tactile properties

Authors:

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Thanh-Vinh Nguyen1, Ryota Tanii2, Tomoyuki Takahata2, and Isao Shimoyama1, 2 Affiliations: 1

Information and Robot Technology Research Initiative, The University of Tokyo, 7-3-1 Hongo,

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Bunkyo-ku, Tokyo, Japan. 2

Department of Mechano-Informatics, Graduate School of Information Science and Technology,

The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.

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Corresponding author: Isao Shimoyama

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Rm. 81B, Engineering Bldg. 2, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-

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8656, Japan. Fax: +81-3-3818-0835

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E-mail: [email protected]

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Tel: +81-3-5841-6318

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Highlights

We report a MEMS-based elasticity sensor that can measure the elasticity of an object without the information of the pressing force and object deformation.

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The proposed sensor utilizes the different tactile properties regarding to object elasticity at different locations on a single sensor chip.

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Simulations using finite element method were carried out to confirm the sensing principle.

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Fabrication of the sensor and results of the experiment carried out using the fabricated sensor were reported.

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Abstract In this paper, we propose a micro-electronic-mechanical systems (MEMS)-based tactile sensor 1

that can measure the elasticity of an object without having to measure the contact force and the object’s deformation. In our sensor design, a sensor chip that has three piezoresistive cantilevers is covered by a polydimethylsiloxane (PDMS) pad. The elasticity of an object pressed against the sensor is measured from the ratio of the deformations at different locations of the PDMS pad. One cantilever (C1) is designed to measure the deformation of the center of the PDMS pad, while the other two cantilevers (C2 and C3) are designed to measure the deformations of the outer ends of

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the PDMS pad. When the sensor is pressed against an object, the ratio of the deformations of the outer ends over that of the center of the PDMS varies depending on the object’s elasticity but not

on the pressing force. Therefore, it is possible to measure the object’s elasticity from the ratio of

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the cantilevers’ outputs. Here, we report on the sensor design, numerical analysis, sensor

fabrication, and demonstration of the elasticity measurement using the fabricated sensor. The proposed sensor is expected to be useful in practical applications, including robotic hand manipulation and tissue stiffness discrimination in minimally invasive surgery.

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Keywords: elasticity sensor, piezoresistive cantilever, MEMS, force sensor

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1. Introduction

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The tactile sensitivity of the human finger allows us to discriminate a soft object from a rigid object by simply pressing a finger onto the object in question. The ability to rapidly perceive an

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object’s elasticity is an important requirement for tactile sensors, especially for those designed for robot control [1-4] and minimally invasive surgery [5-9]. For example, when manipulating robotic

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hands, estimating the softness of the target object is crucial for determining the optimized contact forces that do not cause damage to the object. In minimally invasive surgery, a measurement of tissue stiffness is useful in locating tumors [10-12] or performing tissue cutting [13]. For the

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elasticity sensors used in these applications, one important requirement is a miniaturized size because the sensor must be installed in robotic hands and surgical tools. Moreover, a simple

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measurement principle is desirable for reducing calculations, which is crucial for the feedback control of a robot hand. The elastic modulus (i.e., Young’s modulus E) of a material is defined as the ratio of the stress

applied to the object made from that material to the strain of the object caused by the stress. Therefore, to measure the elastic modulus, generally both the force and the deformation

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measurements are required. These measurements can be obtained by combining a force sensor and an actuator, which control or monitor the displacement. For example, an elasticity sensor using a piezoelectric force sensor and an ultrasonic transducer were proposed to measure the stiffness of oral tissues during dental surgery [14]. Another study utilized a self-excited centimeter-long cantilever with two layers of lead zirconate titanate (PZT) for the elastic modulus measurement [15]. The drawback of these methods is the difficulty in miniaturizing the device 2

because both sensing and actuating parts are required. To create a miniaturized elasticity sensor, a method based on multiple deformation sensing elements fabricated on a single chip with different stiffnesses was proposed [16]. In this method, capacitive-type force sensors, which consist of membranes with different sizes, were fabricated on one chip. The elastic modulus of an object pressed against the sensor was determined from the relative deflections of the membranes, which are read as capacitance changes. This method allows for the measurement of elasticity

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without information regarding the object’s deformation. However, the direct contact of the test

object and the bare sensor chip with the electrodes is a significant drawback of this method, making it unsuitable for a tactile sensor.

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In this paper, we propose an elasticity sensor using MEMS-based piezoresistive cantilevers covered by an elastic pad (Fig. 1(a)). The cantilevers are designed to measure the deformations

of the center and the outer ends of the elastic pad. The amount of bending of the elastic pad is dependent on the object’s stiffness, i.e., the elastic pad bends more when the object is softer. This

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variation in the bending of the elastic pad results in the difference in the ratio between the deformation of the pad’s center and that of the pad’s outer end. In the linear regime, this ratio of

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the deformation is independent of the pressing force, and thus, the sensor can measure the object’s

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elasticity without having to measure the pressing force. Because the cantilevers are covered by the elastic cap, the sensor can be used as a tactile sensor that can be installed onto robotic hands

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and surgical tools. In this paper, we present the sensor design and sensing principle supported by the simulation results. Then, the sensor fabrication and experiment preparation are introduced.

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Finally, we demonstrate the ability of the fabricated sensor to measure an object’s elasticity based

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on the experimental results.

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Fig. 1: (a) Conceptual sketch of the proposed sensor for measuring elasticity. (b) Sensing

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principle of the sensor. (c) Effect of the shear force. (d) Design parameters of the sensor chip. 2. Design and sensing principle A conceptual illustration of the sensor device is shown in Fig. 1(a). The device consists of a

sensor chip with three piezoresistive cantilevers and an elastic pad attached to the surface of the chip. Each cantilever has two piezoresistors formed at the root. The cantilever deformation can

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be determined from the resistance change of the cantilever using the piezoresistive effect, which is widely applied for MEMS-based force sensors [17-23]. One cantilever (C1) is positioned at the center of the chip, and the other two (C2 and C3) are located at the outer edges of the chip. This arrangement allows for the simultaneous measurement of the deformations at the center and the outer ends of the elastic pad. The principle of the elasticity measurement is illustrated in Fig. 1(b). The resistances of cantilevers C1, C2 and C3 are defined as R1, R2 and R3, respectively. When the 4

sensor device is pressed against an object, the elastic pad contacts with the object with its entire surface area, while only the center part of the pad is pushed by the sensor chip. This condition allows the outer ends of the elastic pad to bend following the deformation of the object. We take advantage of the dependence of the bending of the elastic pad’s outer ends on the elasticity of the object. The softer an object is, the more the elastic pad’s outer ends bend, resulting in a larger deformation of the elastic pad’s ends in comparison with that of its center. Therefore, the object’s

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elasticity can be measured from the ratio of the deformation of the pad’s center over that of the

pad’s ends. In the proposed device, this deformation ratio is directly obtained as the ratio of the

output of C1 to that of C2 or C3. In this sensing principle, using C1 and either C2 or C3 is sufficient

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for the elasticity measurement. However, because the outputs of C2 or C3 are also changed by any shear force applied to the elastic pad, as shown in Fig. 1(c), it is better to use the average value of the outputs of C2 or C3 to eliminate the effect of the shear force. Thus, we use the following ratio obtained from the cantilevers’ outputs to estimate elasticity: ∆𝑅1 𝑅1 ∆𝑅 + 3 𝑅2 𝑅3

(1)

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𝑟 = ∆𝑅2

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The ratio r in Eq. (1) increases with the increasing elasticity of the object. Providing that the

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deformations of the PDMS pad and the cantilevers are within the linear regime, the ratio r is constant, regardless of the pressing force. Therefore, the elasticity of the object can be measured

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from the ratio r.

The design parameters of the prototype sensor chip are shown in Fig. 1(d). Each cantilever is

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150 μm long, 100 μm wide, and 20 μm thick. The size of the cantilevers was based on that of the cantilevers in our previous tactile sensors [17, 18], which had a similar force range. Moreover, the cantilevers are designed to be thick enough to allow the direct attachment of the PDMS pad

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to the sensor chip without breaking the cantilevers. The sizes of the piezoresistors at the roots of the cantilevers are 20 μm × 20 μm. In the fabrication of the sensor chip, the through-holes underneath the cantilevers are created by etching the Si handle layer of a SOI wafer. The variation

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of the etching rate on the wafer can result in a variation of up to 10 μm in the sizes of the throughholes. Thus, the sizes of the piezoresistors were determined so that the piezoresistors will be located on the border of the through-holes for all the chips on the wafer. The distance between C2 (or C3) and C1 is 750 μm. The sizes of the sensor chip and the elastic pad are 3.5 mm × 4 mm ×

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0.3 mm and 4 mm × 2 mm × 0.5 mm, respectively. The elastic pad is attached to the sensor chip using polyimide double-sided tape (thickness: ~50 μm). 3. Numerical analysis We conducted a numerical analysis using simulation software (COMSOL Multiphysics, COMSOL) to confirm the sensing principle of the proposed sensor. Fig. 2(a) shows the model of 5

the simulation, in which a sensor device with a sensor chip and an elastic pad was pressed against an object. The base of the object was fixed when a uniformly distributed force of 1,000 N/m2 was applied to the upper surface of the sensor chip. The snapshots of the sensor chip and the cantilevers are shown in Fig. 2(b). The dimensions of the sensor chip and the elastic pad were the same as

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those described in Section 2.

Fig. 2: (a) Model used in the simulation. (b) Snapshots of the sensor chip and the cantilevers.

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The size of the object is 15 mm × 15 mm × 2 mm. For the sensor chip material, the mechanical properties of Si (i.e., density: 2239 kg/m3, Young’s modulus: 170 GPa, Poisson’s ratio: 0.28) were

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applied. For the elastic pad, we used the mechanical properties of PDMS with different Young’s moduli (i.e., density: 970 kg/m3; Young’s modulus Epad: 0.1 MPa, 1 MPa, and 10 MPa; Poisson’s ratio: 0.49). The Young’s modulus of the object Eobject was varied logarithmically in the range of

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10 kPa to 10 GPa. This range covers the elastic modulus of various objects, including some organs of the human body (e.g., muscle, skin, cardiac tissue, bone) [24], rubber, and acrylic resin. The

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density of the object was 1200 kg/m3. The Poisson’s ratio of the object νob, if not stated, was 0.3.

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Fig. 3: Simulation results. (a) Deformations and strains of the cantilevers in the cases of Eobject = 10 kPa and Eobject = 1 GPa. (b) Relationships between the strains ε1 and ε2 of the cantilevers and Eobject. (c) Relationship between the ratio ε1/ε2 and Eobject for different elasticities of the elastic pad.

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(d) Effect of the Poisson’s ratio of the object. (e) Effect of the object’s thickness. We define ε1 and ε2 as the average strains at the locations where the piezoresistors were designed for cantilever C1 and C2, respectively, as shown in Fig. 2(b).

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Fig. 3(a) shows the deformations and the strains of the cantilevers in the cases of Eobject = 10 kPa

and Eobject = 1 GPa. From this result, it is shown that as Eobject increased, the strain of the cantilever C1 increased, while that of C2 decreased. This tendency is clearly confirmed in Fig. 3(b), which shows the dependence of ε1 and ε2 to Eobject. The dependence of the ratio ε1/ε2 to Eobject is shown in Fig. 3(c) on a log-linear scale. This result shows that as Eobject increased, the ratio ε1/ε2 increased, which agrees well with the proposed sensing principle. For each value of Epad, there is a regime 7

of Eobject over which the ratio ε1/ε2 change was specifically large and the regime shifted to the direction of a higher Eobject as Epad increased. For example, the regime was found to be 104 Pa to 107 Pa for Epad = 0.1 MPa and 106 Pa to 109 Pa for Epad = 10 MPa. This result indicates that it is possible to adjust the elasticity range over which a high sensitivity can be obtained by changing the elasticity of the elastic pad attached to the sensor chip, i.e., a soft elastic pad is suitable for soft target objects and vice versa.

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We also investigated the effect of the Poisson’s ratio νob of the object. In the simulation, νob was

changed in the range of 0.25 to 0.45, while the elasticity of the elastic pad was held constant: Epad = 1 MPa. Fig. 3(d) shows the relationship between ε1/ε2 and Eobject for different values of νob. This

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result suggests that there is no significant effect of the Poisson’s ratio of the object on the relationship between ε1/ε2 and Eobject. In other words, it is possible to ignore the Poisson’s ratio of the object when estimating the object’s elasticity from ε1/ε2.

Finally, we investigated the effect of the object’s thickness tob. In the simulation, tob was varied

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from 1 mm to 8 mm, while the other dimensions of the object were held constant: length 15 mm and width 15 mm. Fig. 3(e) shows the simulation result, which indicates that the ratio ε1/ε2 tended

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the effect of the object’s thickness can be ignored.

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to increase when the object became thinner. However, as long as the object is thicker than 2 mm,

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4. Sensor fabrication

The fabrication process of the sensor chip is shown in Fig. 4. First, we created a piezoresistive

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layer on the Si layer of a silicon-on-insulator wafer (thickness: 20 μm/2 μm/300 μm) using rapid thermal diffusion [25]. Next, metal layers (Cr: 5 nm and Au: 50 nm) were deposited on the Si layer of the wafer. The cantilevers were formed by patterning the metal layers and etching the Si

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layer. Then, the piezoresistors at the root of the cantilevers were created by patterning the metal layers. Finally, the cantilevers were released by etching the SiO2 layer after the etching of the Si

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handle layer to create through-holes underneath the cantilevers. More details of the fabrication process can be found elsewhere [18, 19, 26]. The fabricated sensor chip is shown in Fig. 5(a). Fig 5(b) shows a zoomed-in view of the area where the cantilevers were designed. The initial values of the cantilevers’ resistances were approximately 1 kΩ. To assemble the sensor device, first the sensor chip was attached to a printed circuit board (PCB)

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with a Cu pattern that was aligned with the electrode pads of the sensor chip. The sensor chip was electrically connected to the PCB by bonding thin Au wires. Finally, a PDMS pad (size: 4 mm × 2 mm × 0.5 mm) was attached to the sensor chip using Kapton double-sided tape, which was initially attached to the bottom of the PDMS pad. As shown in Fig. 3(c), the range of the Young’s modulus suitable for the sensor varies when the elasticity of the elastic pad attached to the sensor chip is changed. In the fabricated device, the elasticity of the PDMS pad is ~1 MPa, and the sensor 8

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Fig. 4: Fabrication process of the sensor chip. (i) Forming the piezoresistive layer and depositing metal layers. (ii) Patterning and etching the device Si layer to form the cantilevers. (iii) Patterning

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the metal layers to create piezoresistors. (iv) Etching the Si handle layer and the SiO2 layer.

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Fig. 5: Fabrication results. (a) Photograph of the fabricated sensor chip. (b) Zoomed-in view

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showing the cantilevers of the sensor chip. (c) Photograph of the sensor device.

is suitable for the measurement of Young’s modulus values in the range of 10 kPa to 100 MPa.

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A photograph of the completed device is shown in Fig. 5(c). 5. Experiment and results

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5.1 Sample preparation

Samples with different elastic modulus values ranging from ~50 kPa to ~500 kPa were prepared

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as the testing materials for the fabricated sensor. These samples included blocks created from urethane resin or PDMS with different mixture ratios. The sizes of the blocks were 15 mm × 15 mm × 10 mm (Fig. 6(a)). We used the setup illustrated in Fig. 6(b) to measure the elastic moduli

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of the prepared samples. In the setup, a force gauge (DS2-50N, IMADA CO., LTD., Aichi, Japan) was attached to the linear stage (Standard Type Vertical Motorized Test Stand MX2, IMADA CO.,

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LTD., Aichi, Japan). The force gauge was pushed against the samples by moving the linear stage at a speed of 0.05 mm/s. The output of the force gauge was measured using a scope-coder (DL850, Yokogawa Test & Measurement Co., Tokyo, Japan). The elastic moduli of the samples were calculated from the pushing force measured by the force gauge and the deformations of the samples obtained from the displacement of the linear stage. The measurement results are shown

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in Fig. 6(c). As the control sample, a sufficiently stiff acrylic block (elastic modulus: 3.2 GPa) was also prepared. The measured data of the prepared samples were compared to the data of the acrylic block. 5.2 Experimental setup Fig. 7 shows the experimental setup used to test the fabricated sensor device with the prepared samples. The samples were placed beneath the sensor device, and the sensor was 10

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Fig. 6: Sample preparation. (a) Photographs of the prepared samples. (b) Setup to measure the elasticity of the samples prior to the experiment. (c) Measured Young’s modulus values of the

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samples.

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Fig. 7: Experimental setup.

pushed against the surface of each sample at a speed of 0.05 mm/s using the linear stage. We used goniometric stages to adjust the samples so that their surfaces were parallel with the surface of the sensor device. The fractional resistance changes of the cantilevers of the sensor chip were measured using Wheatstone bridge circuits connected to amplifier ICs (INA217, Texas

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Instruments Inc., Texas, USA). The Wheatstone bridge circuits allow us to measure the fractional resistance changes of the cantilevers as changes in the output voltages of the circuits. The voltage applied to the Wheatstone bridge was 1 V, and the gain of the amplifiers was 60 dB (1,000 times). The outputs of the amplifier ICs were recorded using the scope-coder at a sampling rate of 1,000 Hz. The measurement was repeated 10 times for each sample. The

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Fig. 8: Fractional resistance changes of the cantilevers when the sensor was pushed against (a)

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the acrylic pad (Young’s modulus: 3.2 GPa) and (b) the block of sample A (urethane, Young’s

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modulus: 57 kPa).

change in the fractional resistance of each cantilever was calculated from the measured voltage

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using the following relation: ΔR/R = 4ΔV/1000, where ΔV is the output of each amplifier IC. The noise level of the measurement circuit was approximately 5 mV, which corresponds to a

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fractional resistance change ΔR/R of 20×10-6 (-). 5.2 Experimental results

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The fractional resistance changes of the cantilevers when the sensor was pressed against the acrylic block and sample A (Young’s modulus: ~57 kPa) are shown in Fig. 8(a) and Fig. 8(b), respectively. In the case of the acrylic block, the fractional resistance changes of all the cantilevers were on the same order, while in the case of sample A, the fractional resistance changes of C2 and C3 were significantly larger than that of C1. Next, the mean value of the

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fractional resistance changes of C2 and C3: (ΔR2/R2 + ΔR3/R3)/2 was compared to ΔR1/R1 for all of the samples, as shown in Fig. 9(a). It is clear that ΔR1/R1 was proportional to (ΔR2/R2 + ΔR3/R3)/2 and that the proportional coefficient increased with the increasing elasticity of the object. From the slopes of the data shown in Fig. 9(a), we calculated the ratio r = (2ΔR1/R1)/(ΔR2/R2 + ΔR3/R3) for each sample and compared r with the ratio rstrain = ε1/ε2 obtained from the simulation. Ideally, these two values would be equal if the fabricated sensor device was 12

exactly the same as the model in the simulation. However, due to errors during the fabrication process, the ratio r could differ slightly from rstrain. Therefore, we used the data obtained for the acrylic block as control data to calibrate the sensor. More specifically, the measured ratio r for each sample was divided by the ratio obtained in the case of the acrylic block. Similarly, for the simulation results, the ratio ε1/ε2 was divided from the ratio obtained for acrylic. As shown in Fig. 9(b), the measured ratio r/rAcrylic has the same tendency with the proposed sensing principle, that

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is, when the elastic modulus of the sample increased, the ratio increased. Moreover, a good

agreement between the measurement results and the simulation results was also confirmed. These results indicate the ability of the proposed sensor to measure the elasticity from the ratio of the

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cantilevers.

Fig. 9: (a) Relationship between (ΔR2/R2 + ΔR3/R3)/2 and ΔR1/R1 for all of the samples. (b) Relationship between the elasticity of the samples and the ratio r = (2ΔR1/R1)/(ΔR2/R2 + ΔR3/R3) in comparison with the strain ratio obtained from the simulation results. The ratio r and the strain ratio were divided by the values corresponding to the case of the acrylic block. 13

In the proposed device, the sensing principle of the cantilevers is based on the piezoresistive effect. The resistances of the cantilevers also change with the temperature. One effective method to eliminate the effect of the temperature is to design a piezoresistor close to the cantilever. This temperature-compensating piezoresistor should have the same dimensions as that of the cantilever but does not have a through-hole underneath so it will not respond to the applied force. Therefore, the effect of temperature can be cancelled by subtracting the output of the cantilever

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by that of the temperature-compensating piezoresistor, as reported in our previous study [27]. 6. Conclusion

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In this paper, we have designed and fabricated a MEMS-based sensor that can measure the elasticity of an object from the ratio of the outputs of the sensor chip’s cantilevers. This sensor design allows for an elasticity measurement to be performed without information regarding the pushing force and the deformation of the object. We reported the design and sensing principle

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of the sensor. A numeric analysis was conducted to confirm the sensing principle. The simulation results demonstrated that it is possible to tune the range of the sensor by changing

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the elasticity of the elastic pad attached to the sensor. Moreover, the effects of the thickness and

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Poisson’s ratio of the object were also investigated. A prototype sensor device was fabricated using the MEMS fabrication technique, and experiments using samples with elastic moduli in

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the range of ~57 kPa to ~600 kPa were conducted using the fabricated sensor. The experimental results revealed that the relationship between the ratio of the cantilevers’ outputs agreed well

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with the simulation results, which indicates that the proposed sensor is able to measure an object’s elasticity without knowing the pushing force or the object’s deformation. The proposed device is suitable for installation in robotic hands and surgical tools due to its compact size and

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simple sensing scheme.

ACKNOWLEDGEMENTS

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The photolithography masks were made using the University of Tokyo’s VLSI Design and Education Center (VDEC)’s 8 inch EB writer F5112 + VD01 donated by the ADVANTEST Corporation. This work was partially supported by JSPS Grant-in-Aid for Young Scientists (A) (Grant number: 17H04903), The Tateisi Science and Technology Foundation, and The Advanced

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[22] T. Mouterde, T.-V. Nguyen, H. Takahashi, C. Clanet, I. Shimoyama, D. Quéré, How merging

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droplets jump off a superhydrophobic surface: Measurements and model, Physical Review Fluids,

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2(2017) 112001.

[23] H. Takahashi, A. Nakai, N. Thanh-Vinh, K. Matsumoto, I. Shimoyama, A triaxial tactile

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sensor without crosstalk using pairs of piezoresistive beams with sidewall doping, Sensors and Actuators A: Physical, 199(2013) 43-8.

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[24] N. Sachot, E. Engel, O. Castano, Hybrid Organic-Inorganic Scaffolding Biomaterials for Regenerative Therapies, Current Organic Chemistry, 18(2014) 2299-314. [25] M. Gel, I. Shimoyama, Force sensing submicrometer thick cantilevers with ultra-thin

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piezoresistors by rapid thermal diffusion, Journal of Micromechanics and Microengineering, 14(2004) 423-8.

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[26] T.-V. Nguyen, T. Tsukagoshi, H. Takahashi, K. Matsumoto, I. Shimoyama, DepinningInduced Capillary Wave during the Sliding of a Droplet on a Textured Surface, Langmuir, 32(2016) 9523-9.

[27] N. Thanh-Vinh, T. Omiya, T. Tsukagoshi, K. Hirayama, K. Noda, K. Matsumoto, et al., High-sensitivity microelectromechanical systems-based tri-axis force sensor for monitoring

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cellular traction force, IET Micro & Nano Letters, 11(2016) 563-7.

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Author biography

Thanh-Vinh Nguyen received Bachelor degree in 2010, Master degree in 2012, and PhD in 2015 from the University of Tokyo. Since 2015, he has been a postdoctoral researcher at the University of Tokyo.

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His research interests include microelectromechanical systems and fluid dynamics.

Ryota Tanii received Bachelor degree in 2016 from the University of Tokyo. Since 2017, he has been

a master student at the University of Tokyo. His research interests include microelectromechanical

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systems and tactile sensor.

Tomoyuki Takahata received Bachelor degree in 2001, Master degree in 2003, and PhD in 2006 from the University of Tokyo. He joined the University of Tokyo in 2006 and is presently a Lecturer in

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the Department of Mechano-Informatics in the School of Information Science and Technology.

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His research interests include microelectromechanical systems, robotics and photonics.

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Isao Shimoyama received his B.E., M.E., and Ph.D. degrees in Mechanical Engineering from the University of Tokyo, in 1977, 1979, and 1982, respectively. He joined the University of Tokyo in

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1982 and is presently a Professor in the Department of Mechano-Informatics in the School of Information Science and Technology. He has been a MEMS Conference Committee member since

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1996, and his current research interests lie mainly in microsystems, including MEMS structures

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and insect-based functions.

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