ANTENNAS HAVE been used in a range of medical applications for biotelemetry, diagnosis, and treatment purposes. Now, a slotted waveguide antenna is at the heart of a proposed method for repairing bones and solving growth problems. Part of an implant, this wireless battery system is the work of Ian Griggs from Echidna Surgical Solution Pty. Ltd. (Victoria, Australia) together with Parisa Zakavi and Nemai Chandra Karmakar from Australia's Monash University.
This slotted waveguide antenna was devised for an intramedullary nail called the Echidna Pin. That pin is a treatment option for bone fracturesespecially in the clavicleas well as congenital disorders that require bone lengthening. The pin comprises five static parts and a dynamic portion, which is moved to change the pin's total length. By enabling the distance between the two surgically broken pieces of bone to be changed, the pin allows soft tissue and bone volume to expand.
In both the E- and H-planes, the proposed antenna offers a 3-dB bandwidth of 65 deg. It provides gain of 7.7 dBi at 21 GHz. If a small Perspex plate is placed after the waveguide launcher, satisfactory return loss is achieved at all resonant frequencies even as the length of the waveguide changes.
Because the antenna is conformal to the body, it will not place pressure on tissue. The antenna actually uses the hollow structure of the pin as a waveguide. To prevent fluid from entering the waveguide and damaging its internal electronics, it is protected by a thin, low-loss laminate.
In addition, the proposed antenna is circularly polarized. To transmit power to an implanted antenna in the femur, for example, the transmitting antenna can be placed in any orientation relative to the implant and still deliver adequate power to the receiver. See "Wireless Orthopedic Pin for Bone Healing and Growth: Antenna Development," IEEE Transactions On Antennas And Propagation, Dec. 2010, p. 4069.