Medical Instrumentation Sensor 2005200431 Axial Stress X Y

Medical Instrumentation Ⅱ -Sensor- 동서의료공학과 2005200431 이건우

▶ (Axial) Stress X Y A A = X·Y M F = MG Fig 1. 1 “On the surface, the (average) force per unit area is denoted as F is sometimes called ‘load’. ” : “Stress” (solid material), pressure – liquid, air … unit: [N/ ] σ.

▶ Strain L δ F Wall Fig 1. 2 ε : “Strain” , unitless ( [m/m] )

▶ σ & ε curve 1. Brittle material (glass) σu rupture “Not linear over a wide range. ” linear region (elastic region) nonlinear region Fig 1. 3 ε σu : ultimate stress

▶ σ & ε curve 2. Ductile material (Al) σu σys σPl rupture elastic region plastic region Fig 1. 4 σys : Yield stress σPl < σys < σu

▶ σ & ε curve 2. Ductile material (steel) rupture σPl elastic region for elastic region (linear region) (σ ≤σPl) Fig 1. 5 σ = E ·ε E: Young’s modulus (modulus of elasticity)

▶ Cantilever σ = E ·ε L δ F Wall Negligible Fig 1. 6 £ε E: constant A&L are almost constant “If you know ε, you can find force. ”

L F Wall “If force is applied, the subject on the cantilever is stretched. ” F = α ·ε L+δ Fig 1. 7

▶ Strain gage Fig 1. 8 “A strain gage is a device used to measure the strain of an object. The gage is attached to the object by a suitable adhesive. As the object is deformed, the foil is deformed, causing its electrical resistance to change. ”

Substrate Electrical wire Soldering connections Fig 1. 9 Strain gage Fig 1. 10 change of resistance

▶ Resistance L A ρ ρ : resistivity Fig 1. 11 “The Length is stretched, ρ , L, A are changed. But volume is constant. ” = Strain ε

▶ Poisson’s ratio, μ D L D- ∆D ∆L D: diameter Fig 1. 11 piezoresistive effect dimensional effect

▶ Problem liquid sensor catheter diaphragm Pi Po There are two p-type Si strain gage and two n-type Si strain gage. Strain gage’s sensitivity is. When pressure is not applied, it’s resistance is 50Ω.

▶ Answer (a) If pressure vary from 0 to 500 mm. Hg, what is each strain gage’s resistance? When pressure is not applied, it’s resistance is 50Ω. And sensitivity is. therefore, ☞ p-type strain gage’s resistance : 50+ Ω ☞ n-type strain gage’s resistance : 50 - Ω

▶ Answer (b) Draw bridge circuit. And declare each strain gage’s position. S 2 1 V a S 3 S 1 S 4 b - S 2 Vo + S 1 S 3

▶ Answer (c) Design flowing circuit. Vdc = 1 V, Vo = 0~1 V, Av = ? When Pressure(∆R) is zero, Vo=0 V. When P=500 mm. Hg,

Thank you for your attention! : D