Table 1 Comparison of state-of-the-art tactile super-resolution methods and force decoupling methods.

NA, not applicable; CCD, charge-coupled device; LED, light-emitting diode; PD, photodetector.

Tactile sensor typeSuper-resolution (tactile hyperacuity)Force outputSensor structure/
feature
Improvement of
localization
accuracy*
Ability to
measure force
magnitude
Decoupling methodNormal forceShear force
Sensor arrays
(super-resolved)
Planar capacitor arrays (8)~35-fold (from 4 to
0.12 mm)
Not reportedNAYesNot reportedComplex,
multi-electrodes,
and wires
Barometric (28)~15-fold (from 15 to
1 mm)
New structures and
advanced materials
Planar piezoresistive
sensors (13, 14)
~1–10 mmNANAYesNot reportedSoft, highly
sensitive, and not
robust
Giant magnetoresistance
(26, 27)
Piezoresistive sensors with
3D structure (1517)
NANot reported, but an
approximated model could
be obtained by data fitting
theoretically
YesYes
Capacitor arrays with 3D
structure (9, 10)
Decoupled designOptical (CCD camera
based) (20, 22)
~12- to 40-fold (from
4 to 0.1 mm)
Not reportedApproximated model by
data fitting; time-
consuming to calibrate
YesYesBulky and high
resolution
1D magnetized magnetic
bar based (2325)
4.7 mmNACompact and not
robust
Strain gauges (18)~2–4 mmNAMechanically decoupled by
complex mechanical
design and simple
calibration
YesYesComplex, robust,
mostly rigid, and
bulky
Differential piezoresistive
(19) and capacitive (11, 12)
sensor arrays
Optical (LED/PD arrays
based) (21)
Soft magnetic film (2D magnetization) (this work)~ 60-fold (from 6 to
0.1 mm)
YesSelf-decoupled by simple
calibration
YesYesCompact, robust,
and soft
Human skin (57)One order of
magnitude
YesSelf-decoupledYesYesCompact, robust,
and soft

*The improvement from physical resolution to super-resolution.

†The ability to measure the magnitude of the normal force applied on the tactile sensor only when the sensor is in super-resolution mode (partial contact rather than full contact).

‡This is the physical resolution (rather than super-resolution) calculated by the center-to-center distance of two neighboring sensing units, which is only applicable to sensor arrays. However, most of the sensor arrays can use appropriate super-resolution algorithms theoretically, although it was not reported in their original works.