Ultrasonics 91 (2019) 52–61

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Ultrasonics
journal homepage: www.elsevier.com/locate/ultras

Enhancement in mechanical quality factors of poly phenylene sulﬁde underhigh-amplitude ultrasonic vibration through thermal annealing

T⁎

Jiang Wu , Yosuke Mizuno, Kentaro Nakamura
Laboratory for Future Interdisciplinary Research of Science and Technology, Tokyo Institute of Technology, Yokohama 226-8503, JapanA R T I C LE I N FO

A B S T R A C T

Keywords:
Q factor
Thermal annealing
Poly phenylene sulﬁdeOur previous study shows that poly phenylene sulﬁde (PPS) provides relatively high mechanical quality factors(Q factors) at ultrasonic frequency compared to other commonly-used functional polymers, and has potential as
the vibrating body of a functional ultrasonic transducer. Since PPS has semicrystalline frameworks, its Q factors
may be enhanced through thermal annealing. Prior to examining this feasibility, we developed a method for
estimating Q factors under high-amplitude longitudinal vibration. Q factor is originally deﬁned as the ratio of thereactive energy to the dissipated energy, both of which are calculated from the vibration velocities on the outersurface of a cylindrical specimen. Using this method, we experimentally investigated how annealing temperatures and times aﬀect Q factors of PPS. The results demonstrate that thermal annealing is an eﬀective way toenhance Q factors of PPS at the heating temperatures of 100 °C and 150 °C, relatively high compared to the glasstransition temperature of PPS (90–95 °C). The Q factors at several tens of kilohertz are almost doubled after
annealing owing to the enhancements in degrees of crystallinity. As the annealing time increases, the Q factors
initially become higher, and gradually approach their saturated values at a suﬃciently long time. Besides, annealing temperatures aﬀect the change rates in Q factors, but have no observable eﬀect on the saturated Q
factors.

1. Introduction
Ultrasonic transducers are core components for high-power ultrasonic applications, e.g. ultrasonic cleaning, homogenization, atomization of liquid, and enhancement of chemical reaction [1–4]. In general,they comprise piezoelectric ceramics and vibrating bodies. Metals arecommonly used as vibrating bodies in conventional ultrasonic transducers. To reduce weight of transducers, polymers are potentially applicable as vibrating bodies owing to their low densities. Moreover, it isfeasible to improve production eﬃciencies of ultrasonic transducers as
their polymer vibrating bodies can be directly fabricated by molding
methods instead of machining methods [5]. We have reported that poly
phenylene sulﬁde (PPS) exhibits low mechanical loss in high-amplitude
ﬂexural vibration [7,8], and tested several functional ultrasonic devices
with PPS [5,6,8]. In particular, the PPS-based airborne ultrasonictransducers provided better performance than the commercially-available ones [8]. To gain a deeper understanding on vibrational characteristics of PPS, it would be meaningful to evaluate the mechanicalloss in high-amplitude longitudinal and torsional vibrations.
Mechanical quality factors (Q factors), inversely proportional tomechanical loss, demonstrate the suitability of a material as the⁎vibrating body [1,9]. To overcome the shortcoming of the existing
methods, we proposed new methods on the basis of the original deﬁnition of Q factor, and measured the Q factors of several commonlyused polymers in ﬂexural vibration [6], and metals in torsional vibration [10]. Since longitudinal vibration are the most widely used in industrial applications [1,4], a method is required for estimating Q factors
in longitudinal vibration.
PPS belongs to semicrystalline polymers [11], of which the degreeof crystallinity is thought to be increased via thermal annealing[12,13]. In general, materials with regular atomic (or molecular) frameworks, e.g. ceramics and metals, tend to exhibit low mechanical loss
(high Q factors) [1]. It implies that, by carrying out thermal annealingon commercial PPS products in laboratory, their Q factors may be enhanced; however, the validity should be assessed. Besides, the relationship between Q factors and annealing conditions, e.g. temperatures and times, is required to be clariﬁed for practical applications.
In this study, ﬁrst, we introduce a new method capable of measuring
Q factors in high-amplitude longitudinal vibration. To validate thismethod, we measure the Q factors of stainless steel, and compare theresults with the previous reports. Subsequently, we estimate the strain
and frequency dependences of Q factor of PPS in both longitudinal andCorresponding author.
E-mail address: wujiang@sonic.pi.titech.ac.jp (J. Wu).

https://doi.org/10.1016/j.ultras.2018.07.003
Received 17 March 2018; Received in revised form 3 June 2018; Accepted 11 July 2018
Available online 17 July 20180041-624X/ © 2018 Elsevier B.V. All rights reserved.

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Fig. 1. Conceptual schematics of Q-factor measurements from vibration velocity distributions in (a) longitudinal and (b) torsional vibrations.

torsional vibrations. Finally, we investigate how Q factors of PPSchange with varying annealing temperatures and times.

Ek-Lt =

2.1. Method for measuring Q factors in longitudinal vibration
As depicted in Fig. 1(a), longitudinal waves are excited on a cylindrical specimen. The vibration velocity distribution along the z axisvLt(z) is measured on the outer surface of the specimen. The directionsof the vibration velocities are parallel to the z axis. In practical measurements, the amplitudes and phases at discrete points on the surface
are recorded. Points A, B, and C are adjacent sampling points with smallintervals Δz. Their vibration velocities are vA = VA·exp(jθA),
vB = VB·exp(jθB), and vC = VC·exp(jθC), where Vi and θi respectively
represent the amplitude of the vibration velocity and the phase between
the vibration velocity and the reference signal at the i point. The crosssections LL and LR are located in the middle of points A and B, andpoints B and C, respectively. The local Q factor in a small region LL–LR
equals the ratio of the reactive energy Ek-Lt to the dissipated energy Ed-Lt
[9]:

Ek-Lt
Ed-Lt

Ed-Lt =

2π
(Pin-Lt−Pout-Lt ),ω(3)where ω denotes the angular frequency, Pin-Lt and Pout-Lt represent theactive vibration powers ﬂowing across LL and LR, respectively. In
longitudinal vibration, the active vibration power PLt(z) across a certain
cross-section is calculated from the force along the z axis FLt(z) and thelongitudinal vibration velocity vLt(z) [14]:PLt (z ) =1∗
Re[FLt (z )·v Lt(z )].
2(4)

Note that both FLt and vLt are deﬁned as complex numbers. Re means
the real part, and the asterisk indicates the complex conjugate. The
relationship between FLt(z) and vLt(z) in longitudinal vibration is expressed as [15]

.
(1)

LL-LR

(2)

where Δm denotes the mass of the region, S represents the cross-sectional area, and ρ is the density of the specimen. The mechanical constants of PPS and stainless steel, tested in this study, are listed inTable 1.
The dissipated energy Ed-Lt is derived from the reduction in theactive vibration power in a period is given as

2. Principles and methods

QLt = 2π·1
1
ΔmVB2 = ρS ΔzVB2,
2
2

The reactive energy Ek-Lt stored between LL and LR is expressed as

Table 1
Mechanical constants and wave speeds of PPS and stainless steel.
Materials

PPS
Stainless steel

Mechanical constants

Wave speeds

Elastic
modulus (GPa)

Density(×103 kg/m3)

Poisson’s ratio

Longitudinal
wave speed (m/s)

Torsional wave
speed (m/s)

3.45
197

1.35
7.85

0.36
0.31

1599
5010

969
3095

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Fig. 2. Vibration velocity (or strain) distributions on cross-sections of cylindrical specimens in (a) longitudinal and (b) torsional vibrations.

FLt (z ) =ES d [v Lt (z )]
·
,
jω
dz

Pin-Lt = −

(5)

⎜

⎟

(7)

Similarly, the power ﬂowing out of the region LL–LR is

where j is the imaginary unit, and E denotes the elastic modulus. Substituting Eq. (5) into (4), the active vibration power PLt(z) ﬂowing
across a cross-section is given asESd [v Lt (z )] ∗ ⎫PLt (z ) = −Im ⎧·v Lt (z ) ,
⎬
⎨
2ω
dz
⎭
⎩

ES
v −v v∗ + v B∗ ⎞ES
Im ⎛ B A · A·VA VB sin(θA−θB).
=
2ω
2 ⎠
2ωΔz
⎝ Δz

Pout-Lt = −ESv −v v ∗ + v B∗ ⎞ES
Im ⎛ C B · C·VB VC sin(θB−θC).
=
2ω
2 ⎠
2ωΔz
⎝ Δz
⎜

⎟

(8)

The strain at point B εB is given as

(6)

εB =

where Im represents the imaginary part. Eq. (6) should be discretized toestimate the active power from the vibration velocities measured at two
adjacent positions [15]. For example, the active power ﬂowing into theregion LL–LR is expressed as

1 −1 ⎛ v B−vAv −v
(εB + εB+) =·+ C B ⎞,
22ωj ⎝ Δz
Δz ⎠
−

(9)

where εB and εB are the strains in the regions A–B and B–C, respectively. In theory, from the vibration velocities of three adjacent+Fig. 3. Schematic of experimental setup. Using the transducers with piezoelectric ceramic elements polarized along the horizontal and circumferential directions,longitudinal and torsional vibrations can be excited on the specimens, respectively.
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points, the local Q factor and strain in the small region LL–LR are obtained. If the vibration velocities are measured over a large length along
the z axis, it is capable of estimating the strain dependence of Q factor
as the wave amplitudes decay gradually along the propagating direction.

{G

Pin-Ts= −Im ω ∫0R

r 2 d [v Ts (z )] ∗v Ts (z )·2πrdr
R
dz

()

GπR2
= 2ωΔz ·VI VII sin(θ I−θ II),}z = LL

(11)

and

GπR2
·VII VIII sin(θ II−θ III),2ωΔz

2.2. Method for measuring Q factors in torsional vibration

Pout-Ts =Ref. [10] has reported the Q-factor measurement method in torsional vibration. Here, we brieﬂy introduce this method as it is heavily
used in the study. It has two diﬀerences compared to the aforementioned method in longitudinal vibration. First, in torsional vibration,
the vibration velocities are measured orthogonally to the z axis [(seeFig. 1(b)]. Second, as depicted in Fig. 2(a), the vibration velocities are
uniformly distributed on a cross-section in longitudinal vibration.
Whereas, Fig. 2(b) demonstrates that, in torsional vibration, the vibration velocity on a cross-section decreases linearly from the outersurface to the central axis [16,17]. As Fig. 1(b) shows, when the vibration velocities at three adjacent points I, II, and III are respectively
vI = VI·exp(jθI), vII = VII·exp(jθII), and vIII = VIII·exp(jθIII), the reactiveenergy Ek-Ts, the input active power Pin-Ts, and the output active power
Pout-Ts can be calculated using the equations

respectively, where G denotes the shear modulus, and R represents theradius of the specimen. The strain distributions on cross-sections arecompletely the same to the vibration velocity distributions. It is worth
pointing out that, in torsional vibration, the result derived from thevibration velocities measured on the outer surface with Eq. (9) are themaximal strain; half of this value reﬂects the average strain on a crosssection.

Ek-Ts =1
ρ ·Δz·
2R

3. Experimental results
3.1. Experimental setup
To verify whether the mechanical loss can be correctly evaluated byour method, we measured the Q factors of a stainless steel cylindricalbar in longitudinal vibration, and compared the results with the previously-reported values [18]. The experimental setup is schematicallyshown in Fig. 3. Longitudinal transducers with diﬀerent frequencies

2∫0 ⎛⎝VII· Rr ⎞⎠ ·2πrdr = π4 ρR2VII2 Δz,

(12)

(10)

Fig. 4. Distributions of vibration velocity in the z ranges of (a) 10–110 mm and (b) 29–34 mm, (c) reactive energy and dissipated power, and (d) local Q factor andstrain in the z range of 10–110 mm.
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were employed to excite ultrasonic vibration on a 10-mm-diameter
500-mm-long stainless steel specimen, of which one end was connectedto the transducers with bolts. When voltages were applied, longitudinal
vibration was generated on the specimens. An in-plane laser Doppler
vibrometer (IPV100, Polytec, Waldbronn, Germany) mounted on a
guide rail was moved along the z axis. The vibration velocities in the z
range from 10 to 110 mm were measured with an interval of 0.5 mm.
The amplitudes of the vibration velocities and the phases between thevibration velocities and the reference signal were detected with a lockin voltmeter (5560, NF Electronic Instruments, Yokohama, Japan).
3.2. Q factors of stainless steel
When a sinusoidal voltage with an amplitude of 30 V and a frequency of 30.30 kHz were applied, as shown in Fig. 4(a), a standing
wave with a maximal vibration velocity of approximately 1.5 m/s was
excited on the stainless steel specimen. Note that the driving frequency
was set to the resonance frequency of the entire vibration systemcomposed of both the transducer and specimen. Half of the wavelengthand the driving frequency are 82 mm and 30.30 kHz, respectively.

Fig. 5. Q factor of stainless steel as a function of strain under diﬀerent frequencies.

Fig. 6. Q factors of PPS as functions of strain under diﬀerent frequencies in (a) longitudinal and (b) torsional vibrations.

Fig. 7. Experimental procedures for investigating the eﬀects of annealing temperatures and times on Q factors of PPS.
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losses were measured before and after the specimen was ﬁxed to thetransducer, and the Q factors were derived from their diﬀerence. By
adjusting the voltage applied to the transducer, how Q factors dependon strains was investigated. For comparison, the results are plotted inFig. 5. Observably, our Q factors measured by our method have thesame tendencies with the previous results. However, at the strainof < 0.005%, our Q factors are higher than the values given in Ref. [18]because the mechanical loss generated on the contacting surface between the sample and the excitor (stainless steel bar and piezoelectrictransducer, respectively, in this study) is excluded [6].

Therefore, the wave speed is estimated to be 4969 m/s, close to thetheoretical longitudinal speed in stainless steel (see Table 1). It infers
that the longitudinal vibration was successfully generated on the specimen. Fig. 4(b) illustrates that there exist small variations in phases.
Though they are not observable in the overall phase distribution, thevariations enable nonzero values of the calculated local active powers.
Fig. 4(c) illustrates that, as z ranges from 25 to 64 mm, the reactiveenergy monotonically increased from 0.03 to 0.32 mJ. In contrast, thedissipated power yielded a reduction from 80 to < 15 mW. It can beobserved from Fig. 4(d) that the Q factor becomes higher with reducing
strain, though there exist several ﬂuctuations, which are possibly
caused by measurement errors in vibration velocities. Fig. 5 shows themeasured strain dependences of Q factor of stainless steel at diﬀerent
frequencies. At 30.30 kHz, the Q factor reached approximately 3600 at
the strain of lower than 0.002%, and sharply decreased to 260 when thestrain was reduced to 0.03%. At 0.005% strain, the Q factor exceeded
3000 at 30.30 kHz, and decreased to 2000 when the driving frequency
increased to 102.15 kHz.
Ref. [18] has introduced a method for measuring strain dependenceof Q factors: A magnetostrictive transducer was employed to excite
longitudinal vibration on a stainless steel specimen. The mechanical3.3. Strain and frequency dependences of Q factor of PPS
The 10-mm-diameter 250-mm-long PPS specimens used in thisstudy are TORAY’s products. Fig. 6(a) and (b) demonstrate the strain
dependences of Q factor of the PPS specimen under longitudinal andtorsional vibrations, respectively. Note that the abscissa of Fig. 6(b)represents the average strain. In longitudinal vibration, the Q factor at
48.34 kHz exceeded 300 when the strain was lower than 0.003%, anddecreased to approximately 100 when the strain increased to 0.018%.
When the strain was 0.01%, the Q factor decreased from 300 to 20 as

Fig. 8. Strain dependences of Q factor of PPS with varying annealing time. The annealing temperature is 150 °C. (a) and (b) Show the Q factors in longitudinal
vibrations with frequencies of 17 and 48 kHz, respectively. (c) and (d) Are the Q factors in torsional vibrations with frequencies of 16 and 48 kHz, respectively.

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Fig. 9. Strain dependences of Q factor of PPS with varying annealing time. The annealing temperature is 100 °C. (a), (b); (c) and (d) are the Q factors measured at 17
and 48 kHz in torsional vibrations; and at 16 and 48 kHz in torsional vibrations, respectively.

4. Eﬀects of annealing temperature and time on Q factors of PPS

the frequency increased from 16.85 to 66.80 kHz. In Fig. 6(b), at
16.31 kHz and < 0.005% strain, the Q factors exceeded 300. Clearly, as
the strain and the frequency become higher, there are observable decreases in the Q factors of PPS in both longitudinal and torsional vibrations. In particular, when the strains were lower than 0.01%, the Q
factors in longitudinal vibration have sharp reductions, but they are still
higher than the values in torsional vibration. Similar tendencies canalso be found in the cases of stainless steel specimens [10,18]. It is
assumed to originate from the non-uniformity of the mechanical loss
along the radial direction in torsional vibration. As mentioned above,the strain near the outer surface is theoretically twice the average strain
on a cross-section. Since the strains greatly aﬀect the mechanical loss
particularly at low strains [1], the mechanical loss near the outer surface should be higher than the average mechanical loss on the crosssection (the Q factors near the outer surface is lower the average Q
factors). In contrast, as the mechanical loss in longitudinal vibration is
uniformly distributed on a cross-section, the Q factors at the surfaces
should have negligible diﬀerences with the average Q factors. Thus, at a
certain strain of < 0.01%, the Q factors are lower for torsional vibration
than for longitudinal vibration.

After clarifying how strain and frequency aﬀect Q factors of PPS, in
this section, we explore the how Q factors change with varying annealing conditions. Fig. 7 illustrates the experimental procedures:(1) Measure the Q factors of the PPS specimen without annealing.
(2) Anneal the specimen for 6 h in a thermostatic chamber, of which
the temperature was maintained at 150 °C.
(3) Quench at 24 °C in air for 1 h.
(4) Measure the vibration velocities in the same region, and calculate
the Q factors. Cut a 2-mm-thick part from the free end of the PPS
specimen for measuring the degree of crystallinity.
Following the procedures (2)–(4), the Q factors were measured
when the annealing time reaches 18, 42, and 78 h. Another two PPS
specimens were heated at 100 °C and 80 °C, and the same measurements
were performed. To obtain observable variations in Q factors, we gradually increase the annealing intervals between measurements (6h →12 h → 24 h → 36 h), though they are generally set to constants in

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Fig. 10. Strain dependences of Q factor of PPS with varying annealing time. The annealing temperature is 80 °C. (a), (b); (c), and (d) are the Q factors in longitudinal
vibrations with frequencies of 17 and 48 kHz; and in torsional vibrations with frequencies of 16 and 48 kHz, respectively.

48 kHz, the saturated Q factor in torsional vibration was approximately
310, relatively low compared to the value in longitudinal vibration.
Fig. 9 plots the Q factors of PPS annealed at 100 °C. Before annealing, the strain dependences of Q factor of this PPS specimen (theblack dots in Fig. 9) have unobservable diﬀerences with those of theformer specimen (the black dots in Fig. 8). In Fig. 9(a), at 17 kHz and
0.01% strain, the Q factors increased by 60 after annealing for 18 h.
When the annealing temperature was maintained at 150 °C, the Q factors increased by 213 after the PPS specimen was annealed for 18 h. The
saturated Q factor, obtained after annealing for 78 h, reached 602, close
to 621, the value obtained at 150 °C. Clearly, annealing temperaturesaﬀect the change rates in Q factors (ΔQ/Δt), but have little inﬂuence on
the saturated Q factors. The results in Fig. 9(b)–(d) also support thisconclusion.
Fig. 10 shows the Q factors of PPS at the heating temperature of
80 °C. The Q factors exhibit unobservable variations though the PPS
specimen was annealed for 78 h; this time is suﬃciently long forachieving considerable Q-factor changes at 100 °C and 150 °C. To

previous studies [11,19]. Besides, it has been reported that the elastic
moduli and densities of semicrystalline polymers become higher after
annealing owing to the increase in degrees of crystallinity [1,14].
However, after PPS was annealed at 155 °C for 48 h, its elastic modulus
and density increased by < 0.16 GPa and < 0.10 × 103 kg/m3, respectively [20,21]; such small variations should cause negligible measurement errors. Thus, we did not change the mechanical constants
when calculating the Q factors under diﬀerent annealing conditions.
Fig. 8(a) and (b) show the Q factors in longitudinal vibration when
the driving frequencies are approximately 17 and 48 kHz, respectively.
When the frequency was 17 kHz and the strain was 0.01%, the Q factor
was 300 before annealing, and became higher with increasing time, andleveled oﬀ when the PPS specimen was annealed for 42 h. At 48 kHz
and 0.01% strain, the Q factor reached 436 after annealing for 78 h.
Fig. 8(c) and (d) demonstrate that, in torsional vibration, the Q factors
also exhibit observable enhancements via annealing. At 16 kHz, thesaturated Q factor exceeded 600, close to the value in longitudinal vibration with approximately the same frequency (17 kHz). However, at

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Acknowledgement
The authors thank the staﬀ members of the Precision and
Manufacturing Center, Technical Department, Tokyo Institute ofTechnology for machining the polymer specimens tested in this study.
This work was supported by JSPS KAKENHI Grant Number 17J05057.
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Fig. 11. Q factors of PPS in longitudinal vibration at 17 kHz and 0.01% strain
and degrees of crystallinity as functions of annealing time under diﬀerent
temperatures.

explain the reason for the Q-factor variations, the degrees of crystallinity of PPS samples with diﬀerent annealing temperatures and times
were analyzed by the X-ray diﬀraction method [22,23] [this analysis
was carried out by our agent company with a diﬀractometer (D2
PHASER, Bruker, Billerica, USA)]. The results as well as the Q factors inlongitudinal vibration at 17 kHz and 0.01% strain are illustrated inFig. 11. Clearly, the Q factors have identical tendencies with the degrees
of crystallinity. It indicates that the Q-factor enhancements of PPS annealed at 100 °C and 150 °C are caused by the increases in the degrees ofcrystallinity. However, there are almost no changes in the degrees ofcrystallinity, and consequently in the Q factors at the heating temperature of 80 °C probably because it is below the glass-transition
temperature of PPS (90–95 °C) [24].

5. Conclusions
Using our developed Q-factor measurement method, ﬁrst, we clariﬁed the strain and frequency dependences of Q factors of PPS, andsubsequently investigated how annealing temperature and time aﬀect
the Q factors. Through our experiments, we have drawn the following
conclusions:(1) A method for measuring strain and frequency dependences of Q
factor in high-amplitude longitudinal vibration is developed.
(2) The Q factors of PPS become lower with increasing strain and frequency in both longitudinal and torsional vibrations.
(3) It is capable of increasing Q factors of PPS via thermal annealing at
100 °C and 150 °C; these heating temperatures are higher than theglass-transition temperature of PPS.
(4) The enhancements in Q factors of PPS originate from the increases
in degrees of crystallinity after thermal annealing.
(5) The change rates in the Q factors is aﬀected by annealing temperatures. However, the saturated Q factors are independent of
annealing temperatures.

Jiang Wu was born in Liaoning, China, on January 29,
1988. He received the B.E. degree in mechanical engineering from Dalian University of Technology, China, in2010. From 2010 to 2012, he studied in the State Key
Laboratory of Robotics and System, Harbin Institute ofTechnology (HIT), China, and received the M.E. degree inmechatronic engineering from HIT in 2012. From 2012 to2017, he studied in the Future Interdisciplinary Research of
Science and Technology, Tokyo Institute of Technology(TITECH), Japan, and received Dr. Eng. degree in electricaland electronic engineering from TITECH in 2017. His research interest includes piezoresistive and piezoelectricmaterials, permanent-magnet-based sensing technology,
and polymer-based ultrasonic transducers and actuators.

This study demonstrates the eﬀectiveness of Q-factor enhancementof PPS through thermal annealing. The explorations of optimal annealing conditions, such as temperatures, times, and atmospheres ofannealing as well as quenching, would provide a meaningful knowledge
towards the practical applications of PPS to functional ultrasonic devices. It is also worth investigating whether thermal annealing is capable of improving the Q factors of other low-mechanical-loss polymers,e.g. poly ether ether ketone (PEEK) [5,6], in further studies.

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Yosuke Mizuno (M’14–SM’17) was born in Hyogo, Japan,
on October 13, 1982. He received the B.E., M.E., and Dr.
Eng. degrees in electronic engineering from the Universityof Tokyo, Japan, in 2005, 2007, and 2010, respectively.
From 2007 to 2010, he was involved in Brillouin opticalcorrelation-domain reﬂectometry for his Dr. Eng. degree atthe University of Tokyo. From 2007 to 2010, he was a
Research Fellow (DC1) of the Japan Society for the
Promotion of Science (JSPS). From 2010 to 2012, as a
Research Fellow (PD) of JSPS, he worked on polymer optics
at Tokyo Institute of Technology, Japan. Since 2012, he has
been an Assistant Professor at the Precision and Intelligence
Laboratory (presently, Institute of Innovative Research),
Tokyo Institute of Technology, where he is active in ﬁber-optic sensing, polymer optics,
and ultrasonics.
Dr. Mizuno is the winner of the Ando Incentive Prize for the Study of Electronics in2011, the Tokyo Tech Challenging Research Award in 2013, the Konica Minolta Imaging
Science Award in 2014, and the Japanese Society of Applied Physics (JSAP) Young
Scientist Presentation Award in 2015. He is a member of the IEEE Photonics Society(Senior Member), the JSAP, and the Institute of Electronics, Information, andCommunication Engineers of Japan.

Kentaro Nakamura (M’00) was born in Tokyo, Japan, on
July 3, 1963. He received the B.E., M.E., and Dr. Eng. degrees from Tokyo Institute of Technology, Japan, in 1987,
1989, and 1992, respectively.
Since 2010, he has been a Professor at the Precision andIntelligence Laboratory (presently, Institute of Innovative
Research), Tokyo Institute of Technology. His research ﬁeld
is the applications of ultrasonic waves, measurement ofvibration and sound using optical methods, and ﬁber-optic
sensing.
Prof. Nakamura is the winner of the Awaya Kiyoshi
Award for Encouragement of Research from the AcousticalSociety of Japan (ASJ) in 1996, and the Best Paper Awards
from the Institute of Electronics, Information and Communication Engineers (IEICE) of
Japan in 1998 and from the Symposium on Ultrasonic Electronics in 2007 and 2011. Healso received the Japanese Journal of Applied Physics Editorial Contribution Award fromthe Japan Society of Applied Physics (JSAP) in 2007. He is a member of the IEEE, the ASJ,
the JSAP, the IEICE, and the Institute of Electrical Engineers of Japan.

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