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Recently, interest in the effects of radio frequency (RF) on biological systems has increased and is partially due to the advancements and increased implementations of RF into technology. As research in this area has progressed, the reliability and reproducibility of the experiments has not crossed multidisciplinary boundaries. Therefore, as researchers, it is imperative to understand the various exposure systems available as well as the aspects, both electromagnetic and biological, needed to produce a sound exposure experiment. This systematic review examines common RF exposure methods for both in vitro and in vivo studies. For in vitro studies, possible biological limitations are emphasized. The validity of the examined methods, for both in vitro and in vivo , are analyzed by considering the advantages and disadvantages of each. This review offers guidance for researchers to assist in the development of an RF exposure experiment that crosses current multidisciplinary boundaries.

The management of heart failure patients via the implantation of cardiac pacemakers has become a well-known therapy. However, the complications associated with traditional cardiac pacemakers are usually related to finite-battery life, transvenous pacing leads, and subcutaneous device pocket. In this paper, we propose a wearable RF-powered leadless pacing system, which can be implanted directly inside the heart and powered via RF energy, without any batteries or pacing leads. More specifically, we have realized a prototype rectenna-based leadless pacemaker (LP), the implant, which consists of an implantable rectenna, charging and pacing circuits, as well as the pacing electrodes. In addition, a wearable transmit-antenna array was designed, developed, and fabricated for RF energy transmission into the body. In an acute animal study, using ovine models, the proposed LP was implanted at the left ventricular apex by thoracotomy. Using the prototype wearable transmit-antenna array, the prototype LP was powered wirelessly and as a result, leadless pacing was successfully demonstrated in the in vivo ECG results. Besides measuring the efficiency of the rectenna, the computations of specific absorption rate (SAR) are presented and found to be under the IEEE recommended limits. We conclude that a wearable RF-powered leadless pacing system is realizable with the SAR under the safe levels. Thus, the proposed leadless pacing method has the potential to be significantly safer as it completely eliminates the battery, leads, and device pocket and all the associated complications.

A radio frequency (RF)-based medical device implanted deep inside a human body can be wirelessly powered using RF energy. However, this method experiences loss in the form of attenuation and absorption, which is caused by the lossy human body. The need for a path loss (PL) model is, therefore, necessary to characterise these losses. This study presents a novel PL method, which is based on the |S 21 | measurements, obtained from a series of experiments on two different Dorset breed ovine models. Also, the uncertainty analysis of the equipment has been performed and the available RF power inside the body at a proposed implant location has been computed. The results are then used to develop and propose an equivalent model for PL in an anechoic chamber. Overall, an approximate PL of 3.5 dB/cm in the ovine body was measured at 1.2 GHz. Moreover, it was concluded that with the inevitable errors in the equipment, the total PL for 6 cm deep implant location was ~21 dB with an uncertainty of 2.034 dB. The PL model presented is novel and has a great potential for applications in the design and development of RF-based implantable devices, especially leadless pacemakers.

In this paper, we designed a procedure for in vivo RF propagation measurements and presented initial results performed on human subjects. More specifically, two wooden frames with holes are manufactured to fix two broadband horn antennas. Then, a human subject is positioned between the prepared fixture and a vector network analyzer is used to measure the RF propagation at multiple distances. The experiments were performed in an anechoic chamber under an approved protocol. Initial experimental results showed that for a 3 ft distance between horn to horn with human subjects standing in between, 70% of power is lost in the human body and 30% is received by the second horn antenna at 900 MHz. However, the RF power loss increased up to 100% over a frequency range from 900 MHz−18 GHz when the horn antennas are in direct contact with the human subject.

Goal : The aim of this study is to develop a novel fully wireless and batteryless technology for cardiac pacing. Methods : This technology uses radio frequency (RF) energy to power the implanted electrode in the heart. An implantable electrode antenna was designed for 1.2 GHz; then, it was tested in vitro and, subsequently, integrated with the rectifier and pacing circuit to make a complete electrode. The prototype implanted electrode was tested in vivo in an ovine subject, implanting it on the epicardial surface of the left ventricle. The RF energy, however, was transmitted to the implanted electrode using a horn antenna positioned 25 cm above the thorax of the sheep. Results : It was demonstrated that a small implanted electrode can capture and harvest enough safe recommended RF energy to achieve pacing. Electrocardiogram signals were recorded during the experiments, which demonstrated asynchronous pacing achieved at three different rates. Conclusion : These results show that the proposed method has a great potential to be used for stimulating the heart and provides pacing, without requiring any leads or batteries. It hence has the advantage of potentially lasting indefinitely and may never require replacement during the life of the patient. Significance : The proposed method brings forward transformational possibilities in wireless cardiac pacing, and also in powering up the implantable devices.

A key component in the design of a printed Van Array is the requirement of the transmission line (TL) interconnects between the elements to be a factor of the operating wavelength. This results in interconnects that introduce a 2π phase shift. Traditionally, meander-lines have been used to design these interconnects; however, one drawback is the large space required for the layout. In this paper, a more compact Van Atta array that uses zero-phase composite right/left-handed TLs instead of meander-lines is presented. The result is a Van Array array that is 34.0% smaller at the operating frequency of 2.43 GHz. For validation, simulations are compared to measurements of several prototypes.

Many studies have been performed on exploring the effects of radio-frequency (RF) energy on biological function in vivo. In particular, gene expression results have been inconclusive due, in part, to a lack of a standardized experimental procedure. This research describes a new far field RF exposure system for unrestrained murine models that reduces experimental error. The experimental procedure includes the materials used, the creation of a patch antenna, the uncertainty analysis of the equipment, characterization of the test room, experimental equipment used and setup, power density and specific absorption rate experiment, and discussion. The result of this research is an experimental exposure system to be applied to future biological studies.