Akiteru Takamori Earthquake Research Institute, University of Tokyo In Collaboration with: Alessandro Bertolini ( Univ

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

2. Introduction Basic Idea Broadband Seismometer Workshop, Lake Tahoe

3. Key Technologies Tiltmeter • Principle • Sensing: Bob Displacement • Pendulum: Mechanical Amplifier Pendulum Length : Amplification Gain ⇒Lower Resonant Freq. = Higher Gain Broadband Seismometer Workshop, Lake Tahoe

4. Frame Inverted Pendulum Normal Pendulum Payload Flexures / Hinges 20 cm 20 cm Key Technologies Example of Folded Pendulum • Accelerometer for GW Detector • Precise Monolithic Construction • Minimizes Cross-Coupling • Ultra-thin Flexures for Hinges • Reduce Residual Elastic Force Key to Realize Low Resonant Freq. • Achieved Res. Freq. < 500 mHz • Machined byElectropolishing : ~ 30 mm • Flexures under Tension Avoid Buckling Broadband Seismometer Workshop, Lake Tahoe

5. Key Technologies Precision Micro Machining • Electropolishing • Routinely Used for Surface Treatment • Reduce Surface Roughness to Submicron Level • Machining Precision: ~ 1 mm • Optimization of Current and Density, Temperature, Flow in Electrolytic Liquid etc. Broadband Seismometer Workshop, Lake Tahoe

6. Key Technologies New Tiltmeter Mechanics • Compactness • Dimension: ~ few cm Cube • Key: Improving Flexures • Reduces Residual Elasticity • Reduced (< 30 mm) Thickness • Target Res. Freq. : 500 mHz • Corresponds 1 m Pendulum Mechanical Gain: ~ 20 - 50 Conceptual Design Broadband Seismometer Workshop, Lake Tahoe

7. Key Technologies Optical Transducer • Optical Lever / Fiber Photointerrupter • Target Sensitivity: 10-10 m (cf. Laser IFO 10-11 m ) • Light Source: Laser or LED? • Power Loss in Fiber vs. Available Power • Coherent Length affects sensitivity? • Produces Linear Signal • Defines Unique Operating Point • Requires some R&D Effort • Intensity Modulation • Drift of Fiber Position? Broadband Seismometer Workshop, Lake Tahoe

8. Key Technologies Optical Actuator • Wireless Electro-Magnetic Actuator • Utilizing Si Solar Cell • Directly Connected to Voice Coil • Fully Passive Components near Instrument • Electro-Magnetic Interaction • ~ few mA, mN Force Easily Achievable Sufficient to Control Small FP • Strong Dependency on Temperature • Requires External Calibration on Site • Photon Drive? Broadband Seismometer Workshop, Lake Tahoe

9. Summary 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 • OpticalTransducer & Actuator • ⇒Passive and Reliable • Calibration on the Site: Photon Drive Can be converted to Seismometer R&D. Broadband Seismometer Workshop, Lake Tahoe