Table 1 Comparison of optical and sonic properties of water, hydrogel and elastomers.

From: Hydraulic hydrogel actuators and robots optically and sonically camouflaged in water

 

Water

Hydrogel

Ecoflex

Elastosil

Sylgard 184

n

Refractive index

1.3330

1.3365

NA*

NA*

1.4225

I/I 0

Transmittance (relative to water)

100%

>90%

< 5%

<0.1%

>90%

c

Speed of sound (m s−1)

1447.5

1485.7

983.4

979.6

1022.4

z 0

Acoustic impedance (Pa s m−1)

1.448 × 106

1.487 × 106

1.052 × 106

1.058 × 106

1.053 × 106

R

Acoustical reflection coefficient

0

0.013

0.158

0.156

0.158

  1. *Ecoflex and Elastosil are optically translucent to opaque elastomers; therefore, their refractive indices are not available.
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