Question

What is the G-factor in the strain gage, and why do we need to use materials with a high G-factors
in strain gages used for medical purposes.

Answer 1

A strain gage is an instrument used to measure "strain" or deforming force on an object. The G-factor or "Gage Factor" is a measure of the sensitivity of a strain gage. Gauge factor (GF) of a strain gage is measured as:

GF =

where, = change in resistance, R = original resistance, = change in length due to strain, L = actual length of the object. Materials with high GF are used for making sensitive strain gages that can detect very minute changes in strain. A high GF indicates that the gage is sensitive to very small strains.

In medical applications, strain gages are used for measuring flow of liquid in devices such as kidney dialysis machines and syringe pumps. Strain gages are also used for mammography machines for measuring the amount of force being applied on the patient for taking the image. Another use of starin gage is in CT-scan machines for maintaining uniform pateint-weight distribution during scanning. Since all these applications require highly accurate strain data for proper control of the respective devices, strain gages with high GF are used.