Science - USA (2022-05-06)

than those of the other damping materials
(Fig. 3D). Thus, in the case of the hydrogel
damper, the damping bandwidths are narrow
(80.59 Hz at 27°C and 169.3 Hz at 45°C),
whereas other dampers show broad band-

widths (Fig. 3E). Among a broader range of

material types in an Ashby plot, the hydrogel

damper is located close to conventional hydro-

gels, near the kilopascal range (Fig. 3F). The

hydrogel damper surpasses the tandover the

elastomers and polymers with the ranges of

the kilopascal modulus ranges.

We applied the hydrogel damper into bio-

electronics for continuous biosignal detection

without signal processing. The amount of

628 6 MAY 2022¥VOL 376 ISSUE 6593 science.orgSCIENCE

Peak frequency (Hz)

Signal-to-noise ratio (dB)

EEG

Selective mechanical signals

Electrical biophysiology

Neck

vibration

ECG

Actuator

Frequency (Hz)

0.1 1 10 100

Male voice

Gulping

motion

Frequency (Hz)

Alpha - EEG

10 Hz Actuation

10

B

C D

E

F

G

H

I

Tapping

Frequency (Hz)

0.1 1 10 100

Breathing &

Walking

ECG

J

Voltage (a.u.)

Commercial

Bandpass 0.5-40 Hz

Relaxing 6-7 Hz Tapping Walking Stretching

Hydrogel damper

Bandpass 0.5-40 Hz & Bandstop 7, 8 Hz Bandstop 1, 2 Hz Bandstop 10, 15 Hz

Hydrogel

damper

@45 °C

Hydrogel

damper

@27 °C

Bandpass

Reference

Eyes closed (8-12 Hz Alpha wave) Eyes opened (No signal)

0 40 80 120 160 200

Time (s)

Min

Max

Frequency (Hz)

0

10

20

0

10

20

0

10

20

Hydrogel damper

3M Electrode

Bandstop 10 Hz

g

A Voice Gulp

0.0

Reference Bandpass 80-200 Hz

01234 5

Time (s)

Voice Gulp

01234 5

1.0

0.0

Frequency (kHz)0.5

1.0

0.5

Min

Max

Min

Hydrogel damper @ 27 °C Hydrogel damper @ 45 °C Max

Bandstop1, 2 Hz

90 100 110 120 130 140 150 160 170 180

0

20

40

60

80

100

120

0.0 1.0 2.0 3.0 0.0 1.0 2.0 3.0

(^012012) 0.0 0.5 1.0 1.5 2.0
0.0 0.5 1.0 1.5
0.0 0.5 1.0
0.0 0.5 1.0 1.5 2.0
Time (s) Time (s) Time (s) Time (s)
Fig. 4. Demonstration of dynamic noise-damping by using the hydrogel
damper for high SNR detection of biophysiological signals.(A) Demonstra-
tion of human speech recording based on neck vibration by using wireless
mechanical sensing with the hydrogel damper and PDMS as a reference.
(B) Frequency ranges of a male voice and a swallowing motion (~20 Hz).
(C) Comparisons of auditory spectrograms measured (top) without and
(bottom) with the hydrogel damper during the pronunciation of“Viva la vida”
and the swallowing motion. Black and gray spectra show reference and
bandpass-filtered signals. The acoustic neck vibrations were detected with a
reference crack-based sensor on a piece of PDMS and the hydrogel damper
at 27°C and 40°C. For comparison, the signals from the reference crack-based
sensor were treated with bandpass filtering from 80 to 200 Hz. (D) SNR
comparison for the detected voice at each peak frequency for the hydrogel
damper and reference (PDMS) (n= 18 samples). (E) Potential application in
ECG detection on the skin with the hydrogel damper and a commercial 3M
electrode. (F) Frequency ranges of ECG, tapping, breathing, and walking
signals. (G) ECG signals measured with a commercially available 3M electrode,
after bandpass filtering of 0.5 to 40 Hz and (top) additional bandstop filtering
and (bottom) using the hydrogel damper under mechanical noise application:
tapping, breathing, and walking. (H) Another potential application in EEG
detection under 10-Hz noise applied with an actuator. (I) Typical frequency
ranges of EEG and 10-Hz actuation signals. (J) Wavelet analysis of EEG
signals with (middle) a 3M electrode, (bottom) a commercial electrode with
a bandstop centered at 10 Hz, and (top) the hydrogel damper during eye
closing and opening. The alpha wave region (8 to ~12 Hz) is targeted under
external mechanical noise (10 Hz).
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