Fig. 2

Fig. 2 Schematic diagram of 3D FBG sensor.

a Working principle of fiber Bragg grating. The sensing principle of fiber optic grating is based on the periodic modulation of the effective refractive index within the core of the optical fiber. b Schematic of the microinjection with microforce sensor. Four optical fibers are arranged in the external contour of the glass needle at 90°, which senses the wavelength shift with the needle deformation. Each optical fiber contains an FBG sensor with a length of 1 cm. The four optical fibers need to be glued close to the needle tip to be more sensitive to the deformation of the needle. The glass needle (outer diameter 1 mm) has a hollow channel for injecting exogenous substances