Ping-Tong Ho

Professor
Department of Electrical Engineering
University of Maryland at College Park

Education

• Sc.D. Massachusetts Institute of Technology

Research Interests

Reconfigurable Antennas

Current microwave and millimeter wave antennas cannot change their physical structures easily to adapt to signals of different frequencies and orientations, and the constant presence of conducting materials of which antennas are made is a source of pr oblems in stealth applications. A semiconductor becomes conducting when illuminated with light of the appropriate wavelength. This property can be used to write adjustable antennas on a semiconductor wafer. Following a feasibility study of this concept, w e have carried out an experimental demonstration of this concept at 2-4 GHz using a camera flashlight and a 4"- diamter silicon wafer. A reocnfigurable "bow-tie" antenna was tested and found to have an efficiency of only a few dB less than that of the sam e antenna made of metal, with an incident optical intensity of only about 10 W/cm^2. The experiemnt proved the practicality of the reconfigurable antennas and, using a mask like a liquid-crystal display panel, a computer- controlled reconfigurable antenna is feasible.

A Simple, Accurate Laser Ranger

Laser rangers, which measures distances, have found many applications in industry. So far, there has been no accurate, inexpensive, and simple rangers available. Laser ranging methods include interferometry and time-of- flight. Interferometry is the m ost accurate but is a comparative, not absolute, method of measurement. Time- of-flight measurements, as in a radar, require ultra- fast electronics for high spatial resolutions. A variation of the time-of-flight method has been demonstrated, which measur es the round-trip frequency instead of the delay time of the echo. An accuracy of 10 ppm has been achieved to 20 meters. Work is underway for further improvements.

Spatial Light Modulator

An experiment has started to design and fabricate a spatial light modulator, which accepts spatial information at the infrared and reads out in visible. The device is a hybrid of semiconductor and liquid crystal technologies, with an array of infrared semiconductor detectors biasing liquid crystal display which modulates the visible light. The device is expected to find applications in spatial information transmission and processing.

Working with P-T Ho are:

Mr. Tom Liu, Mr. T. N. Ding, Dr. Y. C. Liu and Dr. M. G. Li.

Mailing Address:

Ping-Tong Ho
Dept. of Electrical Engineering
University of Maryland
College Park, MD 20742
Phone: (301) 405-3740