Projects:2014S1-14 Wearable RFID Antennas

Project Information

Smart Clothing For Patient Care

Wearable RFID Antenna

When providing care for patients, it is vital that care givers know what state their patient is in at all times. As the demand for medical care increasingly strains the ability for care practitioners to maintain this awareness, technology begins to play a more important role in maximising carer awareness across a larger number of patients.

By incorporating sensing and communication technology into patient garments, smart clothing can be created. To maximise the service life of these garments, RFID communication frameworks present an attractive option by removing the need for a power source on the wearer and using rectified RF energy. In order to make such a system possible, RFID antennas must be developed that are compatible with both RF and wearability requirements. The goal is to allow the system to be both functional and comfortable. With this in mind, the project team has set about designing flexible antenna systems to meet such a systems requirements. The antennas designed are all planar in topology and target efficient operation in the UHF RFID band. This band varies significantly from country to country which required consideration in the selection of antenna topology and the targeting of design bandwidth.

The planar antennas are fabricated using entirely flexible materials. Conductive layers are created from nylon fabric that is plated with thin layers of conductive material. Substrates for the antenna are provided by varying thickness layers of foam that provides a constant dielectric body beneath the antenna and feed structures. This allows antenna and feed impedances to be managed, a vital consideration when achieving energy efficiency.

Placing antennas on the human body presents an interesting challenge to the design team. The high water content and tissue structure of the body results in what can be considered to be an absorbent and highly lossy dielectric substrate in close proximity to the antenna. If not managed correctly this can result in poor matching and antenna performance.

In designing antennas that manage this fact, antenna and the body must both be incorporated into the design. This ensures that the antennas region of highest performance ends up in the target RF band once it has undergone the inevitable distortion resulting from human body proximity.

The requirement for flexibility presents an additional complicating factor. Whilst the use of flexible materials ensures comfort to the wearer, flexing of an antenna is liable to alter its operation to varying degrees. This adds an additional consideration to the design problem.

With the above in mind, a number of slot antennas have been designed. In order to maximise the RF compatibility with global UHF RFID bands, many of the antennas designed are based around variations of Ultra Wideband topologies. One series of antennas has been based on the Bowtie antennas as its fundamental base. Using electromagnetic equivalence principles, new antennas have been produced in a slot style. Various modifications have then been made to control their performance in the challenging body centric environment.

The antennas were fabricated and tested under a variety of conditions. Fairfield radiation was measured as this fundamentally impacts the read range of any RFID system utilising the antenna. The antenna matching and bandwidth was evaluated with the antenna under a variety of environments designed to simulate the body worn target application.

Group member

1.Joshua Brittain

2.Hassan Amirparast

Supervisors

1. Dr Thomas Kaufmann

2.Prof Christophe Fumeaux

3.Dr Damith Ranasinghe