Marvin H. M. Cheng

Capacitive Pressure Sensor With Very Large Dynamic Range

A new capacitive pressure sensor with very large dynamic range is introduced. The sensor is based on a new technique for substantially changing the surface area of the electrodes, rather than the inter-electrode spacing as commonly done at the present. The prototype device has demonstrated a change in capacitance of approximately 2500 pF over a pressure range of 10 kPa.

High-Sensitivity Inductive Pressure Sensor

A new type of pressure sensors with extremely high sensitivity is introduced. Unlike piezoresistive, capacitive, and linear-variable-differential-transformer-based pressure sensors, the new sensor is based on a technique for substantially changing the inductance of a coil. The prototype device has demonstrated a change in inductance of approximately 34.5 mH over a pressure range of 10 kPa. The sensor offers a number of desirable features, including linearity, low temperature, and pressure hysteresis, in addition to small size.

Controller Synthesis of Tracking and Synchronization for Multiaxis Motion System

Accurate motion control for multiaxis motion systems is an important issue for manufacturing industry. In this brief, an adaptive robust control scheme is implemented to synthesize the compensator for tracking and synchronization with the consideration of cross-coupling dynamics among different axes. By using the adaptive strategies, the asymptotic convergence of both tracking and synchronization errors are achieved. The robust control scheme also guarantees the transient performance, tracking errors, and synchronization errors. Experimental results of a three-axis motion system that include system uncertainties and nonlinearity are also illustrated to verify the effectiveness of the proposed approach for different scenarios. The results indicate excellent transient performance as well as both tracking and synchronization accuracies.

Novel Capacitive Pressure Sensor

A new microelectromechanical-systems capacitive pressure sensor with extremely high sensitivity (2.24 ¿F/kPa) is introduced. The sensor essentially consists of a small drop of mercury and a flat aluminum electrode that are separated by a 1 ¿m-thick layer of Barium Strontium Titanate (a high dielectric-constant ceramic). The assembly constitutes a parallel-plate capacitor where the surface area of the electrodes is variable to a high degree. The mercury drop is pressured by a small corrugated metal diaphragm. As the electrode area of the parallel-plate capacitor varies, a total change in capacitance of more than 6 ¿F is obtained.

Synchronization Controller Synthesis of Multi-Axis Motion System

This paper investigates on motion synchronization of a multiple axes system. Two different control strategies, a cross-coupling controller in feedback loop and a linear quadratic optimal controller, were used to synthesize the synchronization compensator with the cross-coupling dynamics among the axes. These two methods are corresponding to SISO and MIMO approaches. With the strategies, the asymptotic convergence of both tracking and synchronization errors can be achieved. Simulation and experimental results of a three-axis motion system illustrate the effectiveness of the proposed approach.

Ultrahigh-Sensitivity Pressure and Vibration Sensor

A novel new ultrahigh-sensitivity pressure and vibration sensor is introduced. The sensor is based on the concept of using a variable ultracapacitor rather than a variable capacitor as a transduction mechanism. The variable ultracapacitor assembly consists of two electrodes on which carbon nano-tubes of a length of 20 μm are grown. One electrode is fixed and is fully immersed in the electrolyte, while the other electrode is movable and is positioned outside of the electrolyte. In response to pressure or vibration, an extremely small displacement of 20 μm (less than the width of a human hair) submerges the movable electrode into the electrolyte and results in a substantially large variation in capacitance (from zero to 54 μF in the present prototype).

Miniature Moisture Sensor Based on Ultracapacitor Technology

This paper introduces a new ultraminiature, ultrahigh sensitivity moisture sensor that is based on ultracapacitor technology. An ultracapacitor is assembled from ordinary activated carbon electrodes, however, unlike ordinary ultracapacitors, no liquid electrolyte exists inside the device. The ultracapacitor electrodes are placed on both sides of a layer of porous silicon in which potassium hydroxide in powder form is embedded. As moisture penetrates the porous silicon layer, a liquid electrolyte starts to form. The conductivity of the electrolyte, and hence the capacitance of the ultracapacitor assembly, increase as the amount of moisture increases. In the present prototype, an increase in the relative humidity from 5% to 80% results in a capacitance variation from 0 to 17 μF. The sensor can be very useful for monitoring moisture penetration inside small electronic devices and packages that are sensitive to moisture.

Adaptive robust control of tracking and synchronization for multi-axis motion system

This paper investigates on motion synchronization of a multiple axes system. An adaptive robust control scheme was used to synthesize the synchronization compensator with cross-coupling dynamics among axes. By using the adaptive robust strategies, the asymptotic convergence of both tracking and synchronization errors are achieved. The robust control scheme also guarantees the satisfaction of transient performance, tracking errors, and synchronization errors. Experimental results of a three-axis motion system that include system uncertainties are also illustrated to verify the effectiveness of the proposed approach. The results indicate the excellent transient and both tracking and synchronization accuracies.

Electrophoretic coating of carbon nanotubes for high energy-density capacitor applications

This paper reports the successful coating of carbon nanotubes (CNTs) grown on a metallic surface with particles of a ceramic dielectric material by using the electrophoretic deposition technique. Electrophoretic deposition, which is performed at room temperature, has achieved results that are far superior to chemical vapor deposition in this particular application. In an anticipated new breed of capacitors known as the “three-dimensional capacitors,” conventional metallic electrodes will be replaced by CNTs for substantially larger electrode areas. The development of such capacitors is awaiting a technique for successfully coating CNTs with high dielectric-constant ceramics. Such a development is reported here.

Frequency-Selective Seismic Sensor

Recent trends in earthquake monitoring and prediction have focused on the monitoring of seismic frequencies that are very close to the natural frequencies of buildings and other structures, such as bridges. This paper introduces a new type of seismic sensor that is highly sensitive to vibrations at one specific frequency. The sensor inherently rejects vibrations at all other frequencies. The sensors characteristic frequency must be tuned to match the natural frequency of the building or structure that is being monitored. The sensor is based on the fundamental principle of coupling an oscillating mass-spring system with an electromagnetic transducer consisting of a space charge and a toroidal coil. Analysis and experimental results show that the frequency selectivity of such a vibration sensing mechanism is substantially high.