1. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 1 Akiteru Takamori Earthquake Research Institute, University of Tokyo In Collaboration with: Alessandro Bertolini (Universita di’ Pisa) Riccardo DeSalvo (California Institute of Technology) Compact Tiltmeter with Folded Pendulum

2. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 2 Motivation Observation in ‘Frontier’ Region Deep Underground (Boreholes) −Stable Environment without Surface Perturbations Seafloor −Observation near Subduction Boundaries Array Observation −Higher Spatial Resolution Mobile Observation Introduction Provide Instruments Suitable for:

3. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 3 Basic Concept Problems in Conventional Tiltmeters Water Tube Tiltmeter −Requires Large Room −Immobile Electrolytic Tiltmeter −Unstable in Long Term Large Drift Related to Liquid Content Introduction ⇒ Overcome these problems by using Compact Solid State Instrment Water Tube Tiltmeter

4. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 4 Basic Concept Introduction

5. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 5 Tiltmeter Principle Very Traditional −Sensing: Bob Displacement −Pendulum: Mechanical Amplifier Pendulum Length : Amplification Gain Key Technologies ⇒ Lower Resonant Freq. = Higher Gain

6. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 6 Low Frequency Mechanics Folded Pendulum (FP) −Normal Pendulum + Inverted Pendulum Kinematics Ideally Dominated by Gravitational Forces −Low Resonant Frequency Tuned by Changing Load Distribution Limitation Set by Residual Elasticity in Pivots/Hinges −Position Control Required To Keep System in Linear Region Key Technologies

7. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 7 Low Frequency Mechanics Key Technologies Normal Pendulum Inverted Pendulum

8. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 8 Example of Folded Pendulum Accelerometer for Astrophysical GW Research Ultra-thin Flexures for Hinges −Reduce Residual Elastic Force Key to Realize Low Resonant Freq. −Achieved Res. Freq. < 500 mHz −Machined by Electropolishing : ~ 30  m −Flexures under Tension Avoid Buckling Key Technologies

9. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 9 Example of Folded Pendulum Key Technologies 20 cm Normal Pendulum Inverted Pendulum Payload Frame Flexures / Hinges

10. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 10 Precision Micro Machining Electropolishing Routinely Used for Surface Treatment −Reduce Surface Roughness to Submicron Level Machining Precision: ~ 1   m −Optimization of Current and Density, Temperature, Flow of Electrolytic Liquid etc. Key Technologies

11. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 11 New Tiltmeter Mechanics Compactness Dimension: ~ few cm Cube Key: Improving Flexures −Reduces Residual Elasticity −< 30   m Thickness −Modified Shape Target Res. Freq. : 500 mHz −Corresponds 1 m Pendulum Mechanical Gain: ~ few to several tens Key Technologies Inverted Pendulum 10   m Membranes Conceptual Design

12. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 12 Optical Transducer Optical Fiber Sensor Optical Lever / Reflective Displacement Sensor Target Sensitivity: 10 -10 m (cf. Laser IFO 10 -11 m ) Produces Linear Signal −Defines Unique Operating Point Requires some R&D Effort −Intensity Modulation −Drift of Fiber Position? Key Technologies

13. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 13 Optical Transducer Optical Lever Key Technologies

14. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 14 Optical Transducer Reflective Displacement Sensor Key Technologies

15. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 15 Optical Actuator Wireless Electro-Magnetic Actuator Utilizing Si Solar Cell −Modulation in Light Intensity NO Active Component near Mechanics Electro-Magnetic Interaction −~ few mA, mN Force Easily Achievable Sufficient to Control Small FP −Strong Dependency on Temperature Requires External Calibration on Site Key Technologies

16. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 16 Optical Actuator Wireless Electro-Magnetic Actuator Key Technologies

17. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 17 Optical Calibrator Photon Drive Recoil Effect in Photon Reflection −Momentum Conservation NO Active Component Radiation Pressure Force −Force Amplitude 7 nN @ 1 W Light i.e. 0.1  rad for 10 g, 200 mHz Pend. Likely Too Weak to Control Proof Mass on its own −Purely Intrinsic Process Induced Force: Intrinsically Known ⇒ Useful for Accurate Calibration on Site Key Technologies P: Intensity of Light [W] c: Speed of Light [m/s]

18. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 18 Optical Calibrator Photon Drive Key Technologies P: Intensity of Light [W] c: Speed of Light [m/s]

19. 03/24/2004 Broadband Seismometer Workshop, Lake Tahoe 19 Summary Key Technologies and Scientific Gain Compact & Precise Low Freq. Mechanics ⇒ Allow Instrum. to Fit Tight Space (ex. Boreholes) Achieve High Mobility Realize Nearly Identical Instrments Optical Link ⇒ Reliable Operation at Remote Sites / in Hazardous Environment Optical Transducer & Actuator ⇒ Passive and Reliable Provide Accurate Calibration on Site: Photon Drive Summary Can be converted to Seismometer R&D.