Wireless telemetry systems

Figure 7.9 Block diagram of a conventional wireless telemetry system.

Wireless pH measurement systems have been used in clinical studies. Unlike a standalone pH electrode, a power source, control electronics, and a signal transmitter have to be incorporated into a wireless system. Watanabe et al. [138] have reported a wireless pH sensor to record salivary pH continuously. The sensor system transmits pH data via a telemetry system for about 19 hours with a 3V lithium battery (190mAh). The error of transmitted pH data was less than 0.15 pH in the range of pH 5.0 to 9.0. 

A simplex telemetry system is employed for the transmission using straightforward modulation schemes such as amplitude modulation, on-off keying, amplitude-shift keying, and phase-shift keying [101-103]. Because the physiological signals vary slowly, such modulation schemes are preferable for miniaturized and low-power wireless biosensors. 

Using CT scanners has some advantages like being widely available, having high spatial resolution and showing 3-D information about the prosthesis and the internal tissues of the stump, but the challenge is that they require the subjects to be positioned supine [13]. The use of photoelectric sensor reported to have some limitations because it is not wireless and a cable connects the sensor to data acquisition system. But it is said to be overcome by radiofrequency telemetry systems. [1]. 

These applications, by nature, impose serious limitations on power and area in the design of neural-recording systems. Researchers have developed several kinds of neural-recording systems [23-27], and those systems are generally composed of preamplifiers to amplify the small extracellular potentials, low-pass filters to reject the high frequency noise, multiplexers, and analog-to-digital converters (ADCs) followed by the wireless telemetry circuits to transmit data out of the body. 

To support these applications, a neural-recording system has to meet challenging requirements imposed by the environment. First, it should be able to record a large number of channels simultaneously and high-resolution recording can advance fundamental neuroscience studies and has the potential to improve the performance of neural prosthetic devices. Second, a wireless telemetry that transmits recorded neu-... 

Rao et al. [140] described a study using a commercial pH sensitive radio-telemetry capsule (RTC) to evaluate small bowel and colonic transit time in athletes with gastrointestinal symptoms. The RTC (type 7006 Remote Control Systems, London, UK) consists of a glass electrode with an integral reference cap and battery. RF transmissions from the capsule are detected by a solid-state receiver worn on the belt of the patient. The recorder samples the pH from the capsule at 6 second intervals for a period of 24 hours. They used pH changes as an indication of the pH capsule s movement. A sharp rise in pH from around pH 2 to pH 6 indicates that the capsule has moved into the duodenum from the stomach. Then the pH progressively rises to a plateau around pH 8, which indicates that the capsule has moved into the terminal ileum. Another commercially available wireless pH sensor (Bravo) from Medtronic Inc. has been used to measure esophageal pH for a period of 48 hours and it will be discussed later. 

Two of the primary applications for wireless data communications systems are to enable mobile or remote connections to a LAN, and to establish wireless communications links between SCADA remote telemetry units (RTUs) and sensors in the field. Wireless card connections are usually used for LAN access from mobile computers. Wireless cards can also be incorporated into RTUs to allow them to communicate with sensing devices that are located remotely. 

Witters, D., Portnoy, S., Casamento, Ruggera, R, Bassen, H., Medical Device EMI FDA Analysis of Incident Reports, and Recent Concerns for Security Systems and Wireless Medical Telemetry, Proceedings of the 28th IEEE EMBS Annual International Conference, 2006, pp. 1289-1291. 

Andre L. C. Araujo was bom in Fortaleza, Brazil, in 1973. He is currently an Associate Professor with the Department of Telecommunications Engineering, Federal Institute for Education, Science, and Technology of Ceara (IFCE), Fortaleza, Brazil. He works toward the Ph.D. degree in Robust Control Theory with the Federal University of Ceara (UFC), Fortaleza, Brazil. His research interests include telemetry, wireless sensor networks, embedded systems, and data communications. 

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