In the Wheatstone bridge circuit shown in Figure 1(b), the variation in the output voltage (ΔV) of
the pressure sensor was caused by a change in the resistances (R1, R2, R3, and R4) of the four
piezoresistors on the silicon membrane. As shown in Figure 1(a), the four piezoresistors were oriented
in the direction of the current flow. Because the resistance change ratio, ΔR/R, for piezoresistor R1 is
equivalent to that of R3 when pressure is applied to the silicon membrane, the resistance change ratio
of R2 is equivalent to that of R4. Using ΔR1/R1 = ΔR3/R3 and ΔR2/R2 = ΔR4/R4, the variation of the
output voltage induced by the silicon membrane deflection is given by: