Investigation on Wireless Link for Medical Telemetry Including Impedance Matching of Implanted Antennas

Abstract

The development of biomedical devices benefits patients by offering real-time healthcare. In particular, pacemakers have gained a great deal of attention because they offer opportunities for monitoring the patient’s vitals and biological statics in real time. One of the important factors in realizing real-time body-centric sensing is to establish a robust wireless communication link among the medical devices. In this paper, radio transmission and the optimal characteristics for impedance matching the medical telemetry of an implant are investigated. For radio transmission, an integral coupling formula based on 3D vector far-field patterns was firstly applied to compute the antenna coupling between two antennas placed inside and outside of the body. The formula provides the capability for computing the antenna coupling in the near-field and far-field region. In order to include the effects of human implantation, the far-field pattern was characterized taking into account a sphere enclosing an antenna made of human tissue. Furthermore, the characteristics of impedance matching inside the human body were studied by means of inherent wave impedances of electrical and magnetic dipoles. Here, we demonstrate that the implantation of a magnetic dipole is advantageous because it provides similar impedance characteristics to those of the human body.

Revisiting the Analysis of Radiative Mid-Range Wireless Link for Pacemakers

“…The near-field distribution of a patch antenna inside the human tissue is presented to examine the gain reduction effect of the biomedical devices. The radiation characteristics are investigated for the patch antenna immersed with different depths of the human tissue, whose specification was presented in [ 10 ]. The size of the implanted patch antenna is 20 cm × 20 cm, which is located between two 3.4 mm thick substrates with ε r = 10.2.…”

“…Considering low available power for the implanted devices, an accurate estimating method of the wireless link is required [ 6 , 7 , 8 ]. A variety of techniques based on inductive, capacitive, magnetic, mid-field, far-field, acoustic, and optical link have been investigated for WPT applications [ 9 , 10 , 11 , 12 ]. In particular, mid-range applications made in the radiative near-field or far-field region have gained significant attention.…”

“…The effectiveness of the formula has been demonstrated through various cases of the power transmission in a free-space and more complex circumstances containing dielectrics between two antennas [ 36 ]. Recently, the formula has been applied to the wireless link for implanted biomedical devices [ 10 ]. Even though there are several recent advancements for the mid-range biomedical implanted devices, relatively little attention has been paid for accurately and efficiently analyzing the mid-range wireless link.…”

Antennas and Propagation: A Sensor Approach

“…In Ref. [ 2 ], radio transmission and impedance matching in medical telemetry are investigated. Impedance matching inside a human body is studied both for electric and magnetic dipoles.…”

Input Impedance Analysis of Wearable Antenna and Experimental Study with Real Human Subjects: Differences between Individual Users

“…In radio-frequency circuits and antennas, input and output impedances are designed to maximize power transfer and to minimize signal reflections. This principle, which is called impedance matching, also applies to wearable [15][16][17], implantable [18,19], and HBC systems [20][21][22][23][24][25]. The impedance between the electrodes should match that of the driving or receiving circuits to improve transmission efficiency and to reduce signal reflection.…”