The ability to safely monitor neuropotentials is essential in establishing methods to study the brain. Current research focuses on the wireless telemetry aspect of implantable sensors in order to make these devices ubiquitous and safe. Chronic implants necessitate superior reliability and durability of the integrated electronics. The power consumption of implanted electronics must also be limited to within several milliwatts to microwatts to minimize heat trauma in the human body. In order to address these severe requirements, we developed an entirely passive and wireless microsystem for recording neuropotentials. An external interrogator supplies a fundamental microwave carrier to the microsystem. The microsystem comprises varactors that perform nonlinear mixing of neuropotential and fundamental carrier signals. The varactors generate third-order mixing products that are wirelessly backscattered to the external interrogator where the original neuropotential signals are recovered. Performance of the neuro-recording microsystem was demonstrated by wireless recording of emulated and in vivo neuropotentials. The obtained results were wireless recovery of neuropotentials as low as approximately 500 microvolts peak-to-peak (μVpp) with a bandwidth of 10 Hz to 3 kHz (for emulated signals) and with 128 epoch signal averaging of repetitive signals (for in vivo signals).

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Small phased-array antennas can be combined with dielectric lenses or planar lens-arrays to form directive beam-steering system. The use of the lens increases the size of the radiating aperture and enhances the directivity of the phased array, but it also reduces its scan field of view. However, the effect can be controlled by properly designing the phase delay profile across the lens. This paper presents the formulation and methodology for designing modified lenses that can allow the desired scan angle. The utility and limitations of the proposed approach will be illustrated by considering several design examples. Simulations suggest that a directivity enhancement of > 2 dB and wide scan field of view (up to 45 • off boresight) can be obtained for compact radiation systems employing small lenses and short separations between the lens and phased array. Larger directivity improvements in the range of tens of dB's are possible in systems with limited scanning capability by employing large lenses and greater phased array-lens separation. Ease of implementation and the ability of the proposed topology to adapt to the system requirements make this topology an interesting candidate for various millimeter-wave radio applications.

This paper describes a fully passive telemetry technique based on microwave backscattering. In this technique, a subharmonically-pumped passive mixer is coupled to a bio-probe and one or two miniature antennas. When interrogated by an RF excitation, this device generates an amplitude modulated RF backscattering component centered at twice the frequency of excitation. An external sensitive receiver can be used to demodulate the backscattering component and recover the bio-potential. A simple prototype based on solid state diodes has been fabricated and tested for 2.4/4.8 GHz and has the dimensions of 11.5x4.6 mm2 and thickness of approximately 1 mm. Experiments with this very simple device show that low-frequency signals (fm<1 kHz) as low as 1 mV can results in double-sideband levels of greater than -126 dBm for an incident RF power of less than 1 mW/cm2. The proposed device is intended to be coated with an insulating bio-compatible coating and serve as a telemetry chip for chronic implantation inside the body.