| Diaphragm SG (Kulite sensor) |
[50,57] |
-
(i)
A circle-shaped sensing element with a diameter and thickness of 3.2 and 0.8 mm, respectively, and a four conductor ribbon cable of 0.5 mm thickness is attached to its bottom surface.
-
(ii)
It is a monolithic integrated circuit Wheatstone bridge formed directly on a silicone diaphragm.
-
(iii)
It could be inserted inside the socket.
-
(iv)
No longer used.
|
-
(i)
Strains
-
(ii)
Forces
-
(iii)
Direct pressures
|
-
(i)
Simplicity,
-
(ii)
High sensitivity, and
-
(iii)
Lightweight
|
-
(i)
Its stiff backing mismatches with the residual limb tissues, causing stress concentrations at the sensor edges,
-
(ii)
Loads are measured at isolated sites,
-
(iii)
When put in an array of sensing elements. It would be subjected to crosstalk due to its rigidity and the cables restrict the subject movement which alters the amputee’s normal gait.
|
| Piston-type SG |
[42,45,58,59] |
-
(i)
Small patches of silicone or metal,
-
(ii)
An assembly of SG sensing elements and cylindrical piston are configured in a cylinder-like housing, and
-
(iii)
Mounted onto the socket wall in locations of significance through drilled holes
|
-
(i)
Forces, and
-
(ii)
Normal & shear stresses
|
|
-
(i)
Holes in the socket wall alter the pressure distribution,
-
(ii)
Bulky size,
-
(iii)
The data cables increased the prosthesis weight, distorting the stress measurement.
-
(iv)
Require a relatively more power to operate.
|
| Single-point FSRs |
[60,61] |
-
(i)
A sensitive element in form of an elastomer, conductive ink, conductive rubber, or carbon fiber that is sandwiched between two layers of flexible polyester films glued by an adhesive to form a piezoresistive pressure sensor.
-
(ii)
Positioned in-situ inside the prosthetic socket
|
-
(i)
Forces,
-
(ii)
Direct contact pressures
|
|
|
| Array of Piezoresistive |
[60,62,63,64,65,66,67] |
|
-
(i)
Direct contact pressures
|
-
(i)
Requires no modifications in sockets, making them superior over piston-type SGs
-
(ii)
Most commonly used piezoresistive sensing sheets for interface pressure measurement inside prosthetic sockets.
-
(iii)
Provides higher spatial resolution.
-
(iv)
Satisfactory reproducibility and sensitivity,
-
(v)
Flexibility, and
-
(vi)
Thin structure.
-
(vii)
Simple electronics
|
|
| Capacitive (Single sensing element) |
[68,69,70,71,72,73] |
|
-
(i)
Forces
-
(ii)
Pressures
-
(iii)
Displacement
|
|
-
(i)
Their use in prosthetic sockets was limited due to their rigid substrates that do not comply with the residual limb geometry.
-
(ii)
Their sophisticated manufacturing techniques hindered low cost fabrication of multiple sensor arrays.
|
| “Novel” Capacitive (Array) |
[67,74] |
|
|
-
(i)
Showed no noticeable sensor drift occurred between pre- and post-test calibration.
-
(ii)
Acceptable reliability and accuracy, and
-
(iii)
Superior to piezoresistive sensors
|
|
| 3-D printed Capacitive |
[1] |
|
|
-
(i)
Low-cost and versatile solution with capability of adopting irregular shapes.
-
(ii)
Small in size
-
(iii)
Higher sensitivity and flexibility, lower temperature dependency, more robust structure, lower power consumption, better frequency response and a larger dynamic range than piezoresistive devices.
|
|
| Fibre-optics |
[3,75] |
-
(i)
The optical fiber based sensors (FBG) has a longitudinal periodic variation of the refractive index neff written in the core of optical fiber for generating the required spatial pattern. When an optical fiber with an FBG is coupled to a light source and subjected to any external mechanical forces, the light passing through it will be back-reflected by the FBG itself at a Bragg wavelength, λB, depending on the spacing between the periodic variations and the strain-optic effect.
-
(ii)
Could be inserted inside sockets, embedded in the socket wall, or embedded in the prosthetic silicone liners
|
-
(i)
Strains,
-
(ii)
Forces,
-
(iii)
Normal & shear stresses,
-
(iv)
Vibration,
-
(v)
Temperature, etc.
|
|
|
| Optoelectronic |
[76,77] |
-
(i)
Made of an external silicone bulk structure and a printed circuit board which accommodates an array of sensitive elements (LEDs & Photodiodes).
-
(ii)
Could be inserted inside sockets or embedded in the prosthetic silicone liners
|
|
-
(i)
Accuracy
-
(ii)
Sensitivity
|
-
(i)
Susceptible to EMIs
-
(ii)
Bulky
|
