Location dependency and antenna /body/sensor-lead interaction effects in a cell-phone based GSM 1800 telemedicine link

The error-free requirement of today´s cellphone based telemedicine systems demands investigations into the potential causes of service degradation. Measuring the Received Signal Strength Indication (RSSI) level at an 1800 MHz handset, it was found that building construction parameters and multiple- and single-body effects may all negate the monitoring objectives. Furthermore, FDTD simulations revealed the effect that sensor-leads passing close to the handset´s antenna can have on system performance. Changes in lead orientation in the near field of the radiating unit (cell-phone & antenna) result in profound differences in the far field patterns. This is attributed to the biphasic nature of the conduction current density (J) distribution typically found along the wire/s emanating from the handset. J distribution is dominated by the magnetic coupling component in the near field region; an increased separation between the antenna and the sensor lead results in a smaller coupled current, and a consequent rise in system efficiency.