Apparatus and method for measuring dynamic torque for determining frequency-dependent shear in viscoelastic materials

A method of measuring dynamic torque to determine frequency-dependent shear, the method comprising:

• providing an apparatus, the apparatus comprising:
• at least one magnet,
• a viscoelastic specimen comprising a first end and a second end, wherein the first end is fixed to a structure,
• a motor secured to the second end of the specimen,
• a first coil and a second coil fixed to the motor,
• a mirror secured to the motor,
• a laser source, and
• a photodetector, wherein the mirror is positioned at a distance from the photodetector;
• providing a magnetic field via the magnet;
• positioning the motor proximate to the at least one magnet such that the motor is in the magnetic field;
• providing a current in the first coil via an amplifier, such that the first coil interacts with the magnetic field and the current to apply a force to the specimen;
• focusing the laser source on the mirror;
• providing a laser via the laser source, such that the mirror reflects the laser;
• detecting the laser reflect from the mirror via the photodetector, wherein a position of the laser detected by the photodetector changes as force is applied to the specimen;
• and
• calculating angular position using the formula
• θ
• =
• asin
• ⁡
• (
• δ
• L
• 0
• )
• ,
• where θ is the angular position of the viscoelastic specimen, δ is the change in position of the laser detected by the photodetector and L0 is the distance between the mirror and the photodetector.