Medical Instrumentation II

Resistive Sensor  Strain gage : changes in L & ρ  Force sensing resistor : changes in A  Thermistor : changes in L  Potentiometer : changes in L Medical Instrumentation II

FSR(Force sensing resistor) Medical Instrumentation II F A & F is proportion. R & 1/F is inverse proportion. R Thermistor R F R T R∞R∞ NTC (Negative Temperature Coefficient)

Design. Medical Instrumentation II (A) (B) V 0 vs F or T : Non - linear

E[v] S3 R1 S2 S4 reference in = 0 ip = 0 IA VaVb Medical Instrumentation II (C) Bridge circuit (D) Linearigation RsRs RpRp Linear Range R

Capacitive Sensor Medical Instrumentation II A x Most capacitor sensor are based on changes in x

Inductive Sensor  Self Inductance  Mutual Inductance  Differential Inductance Medical Instrumentation II (1) Self Inductance x F (2) Mutual Inductance - b VsVs VoVo + a

- D Medical Instrumentation II (3) LVDT (Linear Variable Differential Transformer) D X = 0 b a c d e δ - δ VsVs V o (b) When core is at X = + δ (a) When core is at X = 0 (c) When core is at X = + δ V cd is Blue, V ef is Red and V o is Black V o = 0 f

Problem 13.  Using LVDT, A object that is a reciprocasting motion verticality direction measure location. This is y(t), changing by next page figure. 1 st coil’s voltage is V(t) = sin(2π x 1000t) [v].  (a) Design the LVDT output signal in 0 ~ 10ms. 2 nd coil’s phase isn’t delay, Suppose LVDT is linear in ± 20mm.  (b) Write verticality direction y(t) by LVDT output signal.  (c) Write calibration method for output voltage represent [mm] unit Medical Instrumentation II

Problem 13. LVDT Medical Instrumentation II 40mm F X=20mm X=0 X=-20mm 20mm -20mm 5ms10ms 180 ̊ Phase change t y(t)

Method 1. Rectifier + LPF No Phase change! FWR LPF V(t) V o (t) V(t) t Medical Instrumentation II

Method 2. Phase-sensitive demodulation Medical Instrumentation II X LPF V o (t) sin(2 πx10³t) V (t) IV o (t)I t g X g

Matlab 3.  5~10ms 사이에 0.01ms 씩 샘플링하여 그래 프 표현 filter 함수 배열 사용. Medical Instrumentation II

Piezoelectric sensor x V o (t) x(t) (1) Medical Instrumentation II

(2) I H I Tf c = 1 / 2πRC Medical Instrumentation II

 If you plan to use the piezoelectric sensor for measuring pulse the lowest frequency of pulse. Signal is assumed to be 0.1Hz. Medical Instrumentation II