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This work describes a novel fully integrated rectenna circuit using tunnelling-based devices for implanted medical devices. An ASPAT (Asymmetric Spacer Layer Tunnel Diode) was used as the active rectifier due to its high non-linearity and temperature insensitivity features. A miniaturized geometry rectenna (1×5mm 2 ) with improved matching characteristics was demonstrated, by integrating a Cockcroft-Walton rectifier with an L-shaped planar folded antenna structure operating at ISM frequency bands. The circuit performance was experimentally explored at various separation distance between transmitter and receiver units. For a 5cm transmission set-up, the rectenna with a single-stage rectifier delivered 0.8V output at 20dBm transmit power. An extended doubler configuration exhibited enhanced performance when multiple stages are used, is predicted to reach 0.24mW output power at 23dBm transmit power and yielding ~1.6V output voltage with an efficiency of 0.12%. These findings can assist in compensating for the degraded antenna gain attributed to the extremely small effective-radiating area of 0.04λ. Furthermore, the ability of controlling the antenna input impedance helps in circumventing the requirement for a matching circuitry thereby offering further reduction in chip size.Index Terms-Planner folded antenna, wireless power transfer, biomedical implant devices, near-field RF powering, ASPAT-based circuits. I. INTRODUCTIONN recent years, a surge of interest in wireless sensor networks and implantable devices has occurred to meet the increased end-user demands in industrial and health care monitoring fields [1][2]. Smart implants are an effective monitoring technique for physiological signal sensing from human bodies and sending it to the patients and/or their medical doctors to be checked afterwards using a mobile application [3]. The possibility of communicating with implanted devices wirelessly has been reflected in a few available systems, such as brain-to-nerve interconnections for brain injury detections [4], monitoring of blood pressure in the brain cavity and retinal implants [5]. The issues to consider for in-body devices concern overall chip size, its power consumption and compatibility with medical treatment restrictions. Ultimate chip dimensions of <10mm 2 -scale can be implanted by minor surgical treatment and the use of a zerobias detector significantly minimizes power consumption of the system. The dimensions of the embedded electronic sensors in the system can be as small as <0.015mm 3 [3], and thus the challenge emerges from miniaturization of the antenna. This in turn greatly limits the amount of received/transmitted RF power when operating in the

This work reports on the design and analysis of a folded antenna operating at mm-wave frequencies. Prior to this, several folded antennas operating at 7, 9 and 10GHz frequencies were used to validate the simulation procedure performed. A mm-wave folded antenna with a resonant frequency of 39GHz was then simulated. A relatively small antenna geometry was achieved without sacrificing its gain and other crucial characteristics. A 3.5dB gain and 4.6dBi directivity were obtained with a frequency bandwidth reaching 780MHz. The main and secondary arm widths of the folded antenna are key in determining the real and imaginary parts of the antenna impedance, providing a degree of freedom for the designer to get the antenna well-matched with the subsequent integrated circuit. This provides useful features including the capability of reducing the overall antenna dimensions and avoiding matching circuits.

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