Page 324 - Mechatronics for Safety, Security and Dependability in a New Era

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First, the radiation pattern was measured in the XZ-plane (refer to Figure 1) and the antenna was fully
rotated counter-clockwise around the Y-axis. Next the radiation patterns were measured in XY- and
YZ-planes in a similar manner. The measurement results are shown in Figures 2b, 2c, and 2d,
respectively. The radiation pattern measurements show that the antenna is quite unidirectional in the
XY- and YZ-planes. In the XZ-plane the radiation pattern is smaller and its shape is more elliptical
than circular. This must be taken into account when determining the exact placement of the Bluetooth
PCB within the earcup. The radiation pattern should be large in horizontal directions, but it may be
smaller in vertical directions. For example, the cellular phone may be on charge on a desk, and the user
may walk around freely on the same floor. Figure 2d shows that the plastic earcup has no significant
effect on the radiation pattern, hi fact, the measured radiation pattern is slightly greater with the
Bluetooth antenna installed inside the earcup. Thus, the plastic earcup will probably cause no
problems.

The prototype was tested in operation using three GSM cellular phones from different manufacturers,
and employing both headset and hands-free profiles. The phones were Sony Ericsson T68i, Nokia
3650, and Siemens SX-1. The prototype worked well with every phone and with both profiles. The
sound quality was rated quite good, and speech intelligibility also improved because the hearing
protector attenuates noise disturbance. When a directional noise-cancelling microphone is used, no
background noise is transmitted. The operating range of the device was approximately 10 m, and the
sound quality was rated good. The current consumption of the device was measured. The supply
current was 4 mA in standby mode and 40 mA in transmitting mode.

CONCLUSIONS
For most people, nowadays, a cellular phone is indispensable. However, in noisy environments its use
can be severely restricted, especially if a hearing protector is being worn.
A prototype of a Bluetooth hearing protector was developed to overcome this problem. The developed
device provides hearing protection while also permitting communication via a cellular phone without
the need for inconvenient cables. A microstrip antenna was also developed for the device. The antenna
was measured and performed well. The prototype supports both headset- and hands free profiles, hi
tests it was shown to be functional with three different cellular phones.

REFERENCES
Bray J. and Sturman C.F. (2001). Bluetooth Connect Without Cables, Prentice Hall.

Bravo-Escos M. (2002). Networking gets personal. 1EE Review 48:1, 32 - 36.
Olmos M., Hristov H.D., and Feick R. (2002). Inverted-F antennas with wideband match
performance. Electronics Letters 38:16, 845 - 847.

Ali M. and Hayes G.J. (2000). Analysis of Integrated Inverted-F Antennas for Bluetooth
Applications. IEEE-APS Conference on Antennas and Propagation for Wireless Communications,
Waltham, MA USA, 21-24.