Archive for May, 2012
Micro-electromechanical systems (MEMS) use microminiature sensors and actuators. MEMS technology provides the benefits of small size, low weight, high performance, easy mass-production and low cost. This article is the first part of a three-part series on MEMS sensors. In the present article, we provide a general introduction to MEMS sensing and the primary sensing techniques. Next, MEMS-based bio-medical sensors are explained. We consider MEMS devices that are: designed to detect triglycerides, c-reactive protein, and glucose, respectively; bio-inspired robotic fingers with tissue softness characterization sensors for pressure measurement during surgical procedures; for counting blood cells; acoustic sensors for 2-D sound source localization; pressure measurement sensors on the wings of an insect-like flying robot; and ultra-miniature sensors for intramuscular pressure measurement.
This is the second of a three-part series on micro-electromechanical systems (MEMS) sensor technology. In the first part, a general introduction to MEMS sensing was given, including its underlying principles . Biomedical MEMS sensors were also described by reviewing the principles of bio-sensing and describing a typical set of biologically inspired sensors. In this part, mechanical sensors for displacement, acceleration, impact, vibration, force and torque, and stress and strain are discussed. Various applications of these sensors include high-g measurement, study of golf swing dynamics, vibration control of space inflatable structures, force and torque measurement in micro-robots, bone stress monitoring, metrology, and characterization of nano-scale structures. Some related technologies of MEMS sensors are discussed including compensation for environmental effects, the Casimir effect, and harvesting of energy for self-powered sensors. Also, the subject of sensor selection is addressed. Part 3 of the series will present MEMS sensing in the thermo-fluid and electromagnetic domains. (more…)
Spread spectrum communication techniques including in-time and frequency domains for direct sequence, frequency hopping, and time hopping are currently used in a large number of wireless applications. This article provides an overview of these techniques. Results of laboratory tests of a ZigBee network are presented, and experimental results are compared with theoretical expectations. Part 2 of this paper will present an application we developed for a wireless distributed measurement sensing and actuating system for water quality assessment.
Early Wireless Applications
Many innovative people have faced the challenge of developing long distance communications with various levels of success. One of the earliest techniques was using fire and smoke as visual signals. The first technical contribution to the field of telecommunication was made by Guglielmo Marconi (1874) who developed a practical wireless system to transmit telegraph messages. Although unsuccessful, Marconi’s system introduced telegraphy for marine signaling. A ships’ crew could be warned of potential dangers like rocky coastlines if wireless telegraphs were installed. This breakthrough led to substantial improvements in safety warning systems with performance that was independent of weather conditions such as rain, wind and smog.
Subsequently, the American Telephone & Telegraph (AT&T) company pioneered in moving the communication field forward after Alexander Graham Bell invented the telephone [1-2]. AT&T’s satellite communications enabled the first live television transmission across the Atlantic. In the early 1980s, mobile telephones were introduced, and since then the number of wireless spread spectrum applications has never stopped growing. Development in mobile telephone systems, in particular, has been driven by concurrent technological progress in high integration level component devices and interoperability of equipment from different manufacturers. (more…)