1. Medical Instrumentation Ⅱ 동서의료공학과 2005200431 이건우 -Sensor-

2. X Y M F = MG Fig1.1 A A = X·Y “On the surface, the (average) force per unit area is denoted as σ. F is sometimes called ‘load’.” : “Stress” (solid material), pressure – liquid, air … unit: [N/ ] ▶ (Axial) Stress

3. L F Wall Fig1.2 δ ▶ Strain : “Strain”, unitless ( [m/m] ) ε

4. ▶ σ & ε curve 1. Brittle material (glass) σuσu linear region (elastic region) rupture nonlinear region σ u : ultimate stress ε “Not linear over a wide range.” Fig1.3

5. ▶ σ & ε curve 2. Ductile material (Al) σuσu σ ys σ Pl elastic region plastic region rupture σ ys : Yield stress σ Pl < σ ys < σ u Fig1.4

6. ▶ σ & ε curve 2. Ductile material (steel) σ Pl elastic region for elastic region (linear region) ( σ ≤ σ Pl ) rupture σ = E · ε Fig1.5 E: Young’s modulus (modulus of elasticity)

7. L F Wall Fig1.6 δ Negligible ▶ Cantilever σ = E · ε £ε£ε “If you know ε, you can find force.” E: constant A&L are almost constant

8. L Wall Fig1.7 F L+δ F = α · ε “If force is applied, the subject on the cantilever is stretched.”

9. ▶ Strain gage “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.” Fig1.8

10. Substrate Electrical wire Fig1.9 Strain gage Soldering connections Fig1.10 change of resistance

11. L A ρ ρ : resistivity Fig1.11 ▶ Resistance “The Length is stretched, ρ,L,A are changed. But volume is constant.” Strain ε =

12. L D Fig1.11 ∆L D- ∆D ▶ Poisson’s ratio, μ D: diameter piezoresistive effect dimensional effect

13. ▶ Problem PiPi PoPo catheter liquid sensor diaphragm 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.

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

15. ▶ Answer (b) Draw bridge circuit. And declare each strain gage’s position. S1 S3 S2 S4 S1 S2 S3 S4 a b - + 1V Vo

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

17. Thank you for your attention! :D