Wearable Antennas for Smart Clothing

“Antennas are well-known and well-researched, but traditionally they have been situated on rooftops or towers,” explains MSc (Tech) Tiiti Kellomäki. Her doctoral dissertation explores the applicability of certain antenna structures for body-worn use.

“The human body absorbs most of the power, rendering the radio link inefficient. With clever designs the link can be improved. At best, the human body can even be used as a passive part of the antenna.”

At the frequency of the regular FM broadcast radio (100 MHz), the size and posture of the user's body play a major role in the antenna properties. On the other hand, a GPS antenna (1600 MHz) can be placed on the back or the wrist and will perform equally. Now the distance between the antenna and the body plays a major role in the connection. A metallic sheet between the antenna and the user prevents the body from affecting the antenna but makes the antenna large and clumsy. It is easier to manufacture simple, one-layer antennas without a metal sheet, but such an antenna must be worn at a sufficient distance from the skin. Kellomäki's dissertation discusses the effect of this distance.

“For example, the GPS antenna should be placed a couple of centimetres from the body. This may sound a lot, but outdoor clothing is usually thick and loose enough to satisfy this.”

Wearable computing is the next step in electronics. A smart shirt with embedded sensors can be used to measure the heart rate or other vital signals of a patient. With an integrated antenna, the data can be transmitted to the user's own terminal or directly to a hospital. Future patients can stay in the comfort of their own homes, while their status is being constantly monitored and emergency aid can be sent in without delay.

As part of her dissertation, Kellomäki designed an identification tag antenna that is worn on the shirt collar. It can be used in the access control of nursing homes. If a patient with a memory disorder walks out the front door, the tag triggers an alarm. The concept is similar to burglar alarms found in all supermarkets, only now the tag is comfortably integrated into clothing.

“When I get old, I will explain the nurse how I used to design such antennas. ‘Of course you did,’ says the nurse and helps me to the communal room for yet another round of Snakes and Ladders.”
 

Public defence of a doctoral dissertation on Friday, 23 March
 

The doctoral dissertation of MSc (Tech) Tiiti Kellomäki in the field of electronics “Effects of the human body on single-layer wearable antennas” will be publicly examined at the Faculty of Computing and Electrical Engineering of TUT in room TB109 in the Tietotalo building (address: Korkeakoulunkatu 3, Tampere, Finland) on Friday, 23 March, 2012 at 12:00.

The opponents will be Professor Peter S. Hall (University of Birmingham, UK) and Professor Sergei Tretyakov (Aalto University). Professor Lauri Kettunen from the Department of Electronics will act as Chairman.

Further information:
Tiiti Kellomäki, tel. +358 40 849 0095, tiiti.kellomaki@tut.fi