Applied physics: Gravity measurements on chips
Gravimeters have applications ranging from oil exploration to the detection of underground tunnels, but size and lack of portability have limited their field use. A device the size of a postage stamp promises fresh opportunities. See Letter p.614
 Gravimeters can measure tiny variations in the local gravitational acceleration, with sensitivity high enough to measure Earth's tides: the elastic deformation of the Earth's crust caused by the changing relative phases of the Sun, Earth and Moon. Existing gravimeters are bulky and costly, but now Giles Hammond and colleagues have developed a compact and inexpensive microelectromechanical gravimeter with a novel 'anti-spring' design. They use it to measure gravitational acceleration with sufficient sensitivity and stability to detect Earth's tides. The small size and low cost of the device mean it could be mounted on a drone for surveying and exploration roles, used to monitor volcanoes or built into multi-pixel density-contrast imaging arrays.
Structural Synthesis of Zhang Heng's Seismoscope with Cam-linkage Mechanisms
This work synthesizes the topological structures of the lost Zhang Heng's seismoscope, which was invented in ancient China in 132 AD, with cam-linkage mechanisms. Based on the study of the literature and seismology, the design specifications of Zhang Heng's seismoscope are defined and concluded. According to the concepts of generalization and specialization subject to the concluded design specifications, all feasible interior mechanisms with cams and links that meet science theories and techniques of the subject's time period are receated. Two examples, one with five members and six joints and the other with six members and eight joints, of the interior mechanism of Zhang Heng's seismoscope are derived with 2 and 11 feasible designs, respectively.
The Development of Ancient Earthquake Instruments
This paper studies sensing element designs in ancient seismometers and describes the developments of ancient earthquake instruments. A basic seismograph comprises a seismometer, a recording system, and a timing system. The major difficulty in the development of a seismograph was the design of the seismometer. And, the break through was the use of a pendulum system as a sensing element that responded to ground motion and did not move with the ground. Early seismoscopes were primarily intended to determine that an earthquake had happened. The first seismoscope invented by Zhang Heng was Hou Feng Di Dong Yi made in ancient China around the year 132 AD. The truly successful seismographs were first designed and built in the 1880s by a group of British scientists in Japan. In 1906, Boris Galitzin developed a working electromagnetic seismograph with a great sensitivity. Finally, a comparison with the recording systems of ancient seismographs is concluded.Copyright © 2006 by ASME