Design News for Mechanical and Design Engineers

Tiny Spirals: Spiral antenna elements, wrapped around a high-dielectric ceramic core (not shown), form "twisted loops" that create magnetic reversals at the center of the antenna, which tightly confines the magnetic field and cuts induced noise.

The antenna's spirals surround a ceramic cylinder under an inch long. The arrangement produces an extremely tight antenna "near field." This field is the energy produced by the device that cannot be stored within the antenna itself. For Sarantel's patented design, this field is only slightly larger (on the order of 3-5 mm from the antenna surface) than the antenna itself. Thus, unlike previous antennas, the proximity of the user's body neither absorbs emitted energy nor distorts the field (antenna pattern). Such energy absorption also changes the effective length of the antenna, de-tuning it away from its natural frequency, further cutting efficiency.

Similarly, ensuring that antennas "play well" with the rest of a device—from the active electronics to the materials making up the case—is vital to communications range, clarity, and battery life. "Now designers don't have to 'design in' the antenna; it can be an afterthought," says Brad Hurte, president of Sarantel USA.

Other Fit and Forget™ antenna features include a balun (see figure). This carries an equal and opposite current to the antenna guide current so that no current need flow to a ground plane with its potential for channeling noise into the antenna.

CONTACT: Brad Hurte, Sarantel USA 19243 NE 149th St., Woodinville, WA 98072 Tel: (425) 861-0463; Fax (425) 881-8192 E-mail: bhurte@sarantel.com www.sarantel.com; or enter 509 at www.designnews.com/info.