1. Evaluation of Large Signal Minor Loop Behavior in PMN-PT Ceramics Harold C.Robinson and Elizabeth A.McLaughlin NAVSEA Undersea Warfare Center Division Newport 1176 Howell Street, Newport RI 02841

2. abstract  The stress and polarization behavior (lanthanum doped PMN-PT) ▶ evaluate using unipolar, biased drive of up to 1.3MV/m under varying temperature and mechanical stresses  The strain vs. field 와 polarization vs. field loops (minor loops biase / full loops biase)  minor loops: rotate around the midline of the major loop ▶ smaller values for the large for the large signal piezoelectric and dielectric constants than major loop alon  Energy density, electromechanical coupling factor, dielectric loss factor  DC bias 와 AC drive field 의 함수로 계산 ▶ the strain energy density, electromechanical coupling factor (DC bias: increasing, AC drive: decreasing) ▶ dielectric loss factor (DC bias: decreasing, AC drive: increasing)

3. I. Introduction  The large signal electromechanical properties of electroactive materials  PZT,PMT-PT ceramics  transducer, actuator design  measuring under small signal condition(book value)  Not relevant to the conditions of their actual use.  Properties of linear materials(PZT) have exhibited considerable dependence upon AC drive field, prestress, temperature  Nonlinearities(the strain, polarization response<--hysteresis) can inaccurate determinations(result of a single large signal, all condition)  For accurately device performance(under actual condition) actual condition 에서 material properties 값을 측정 가능. 측정치가 적다면 material properties 를 결정할 타당성의 범위 확정.

4. I. Introduction  A series of biased minor loop measurements ▶ perform using NAVSEA Newport ’ s SDECS ▶ using combinations of two temperatures, four prestress levels, four DC bias levels, seven AC drive levels ▶ the stress, polarization : measured as a function of the applied field  The large signal electromechanical properties (piezoelectric constant, dielectric constant, dielectric loss factor)  The Young ’ s modulus as a function of applied DC bias (at each temperature from the stress-strain response) ▶ so, the large signal properties were used to compute the equivalent coupling factor, energy density of the material SDECS: Stress Dependent Electromechanical Characterization System

5. II.MEASUREMENTS >  be subjected to two cycles of full unipolar drive  the initial electrical conditions were the same(for each biased minor loop)  AC drive field was reduced to measure the minor loop response over six cycle  The sample had returned to its original state  The first and last cycles(minor loop segment) were discarded to remove the effects of any transients

6. II.MEASUREMENTS > 3kpsi at PMN-PT is 0.34MV/m(bias level)  이하 : see the character of the minor loops  이상 : hysteresis 감소, minor loops are indistinguishable  the initial two cycles followed the outermost loop  The AC drive level was reduced the polarization and strain loops  be different than that predicted from the slope of the major loop ∴ major loop 만의 data 로 제작한 transducer 는 예상치 못한 결과를 낳는다.

7. III. MATERIAL PROPERTIES  The large signal material properties The piezoelectric constant relative permittivity dielectric loss factor electromechanical coupling factor the strain energy density

8. III. MATERIAL PROPERTIES 3kpsi(21Mpa) 의 압축응력 DC bias(4): △, □ (at ) ▲, ■ (at ) 1. 3kpsi 에서 piezoelectric constant 와 relative permittivity 의 특성 곡선

9. III. MATERIAL PROPERTIES 2. 3kpsi 에서 Dielectric loss factor 와 coupling factor 의 특성 곡선

10. III. MATERIAL PROPERTIES 3. 3kpsi 에서 Strain energy density 의 특성 곡선

11. conclusion  The minor loops tend to rotate about the center line of the major loop  Major loop 만으로 측정된 material properties 는 device 의 성능을 정확히 예측하기 어렵다.(in hysteretic situation)  Dielectric loss factor 는 온도가 상승하면 감소되고 또 한, 일정한 온도에서 DC bias 와 AC drive 를 증가시키 면 감소된다  Coupling factor 와 strain energy density 적당한 drive 에서 최고치를 가지고, DC bias 와 ac drive 가 증가하면 감소.