3/24/2004 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

3/24/2004 Broadband Seismometer Workshop, Lake Tahoe 2 Basic Idea Introduction

3/24/2004 Broadband Seismometer Workshop, Lake Tahoe 3 Tiltmeter Principle −Sensing: Bob Displacement −Pendulum: Mechanical Amplifier Pendulum Length : Amplification Gain Key Technologies ⇒ Lower Resonant Freq. = Higher Gain

3/24/2004 Broadband Seismometer Workshop, Lake Tahoe 4 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 by Electropolishing : ~ 30 mm −Flexures under Tension Avoid Buckling Key Technologies 20 cm Normal Pendulum Inverted Pendulum PayloadFrame Flexures / Hinges 20 cm

3/24/2004 Broadband Seismometer Workshop, Lake Tahoe 5 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 in Electrolytic Liquid etc. Key Technologies

3/24/2004 Broadband Seismometer Workshop, Lake Tahoe 6 New Tiltmeter Mechanics Compactness Dimension: ~ few cm Cube Key: Improving Flexures −Reduces Residual Elasticity −Reduced (< 30   m) Thickness Target Res. Freq. : 500 mHz −Corresponds 1 m Pendulum Mechanical Gain: ~ Key Technologies Conceptual Design

3/24/2004 Broadband Seismometer Workshop, Lake Tahoe 7 Optical Transducer Optical Lever / Fiber Photointerrupter Target Sensitivity: m (cf. Laser IFO 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? Key Technologies

3/24/2004 Broadband Seismometer Workshop, Lake Tahoe 8 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? Key Technologies

3/24/2004 Broadband Seismometer Workshop, Lake Tahoe 9 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 Calibration on the Site: Photon Drive Summary Can be converted to Seismometer R&D.