Feasibility of Backscatter Communication Using LoRAWAN Signals for Deep Implanted Devices and Wearable Applications

This paper presents a method for low data rate transmission for devices implanted in the body using backscattered Long Range (LoRa) signals. The method uses an antenna loaded with a switch that changes between two load impedances at the rate of a modulating oscillator. Consequently, the LoRa signal transmitted by a LoRa node is reflected in the adjacent channels and can be detected with a LoRa gateway tuned to the shifted channels. A prototype developed to operate at Medical Implant Communication Service (MICS) and the Industrial Scientific and Medical (ISM) 433 MHz band is presented. The prototype uses a commercial ceramic antenna with a matched network tuned to the frequency band with high radiation efficiency. The effect of the coating material covering the antenna was studied. Simulated and experimental results using a phantom show that it is feasible to read data from deep implanted devices placed a few meters from the body because of the high sensitivity of commercial LoRa receivers.

Analysis and Optimization of Voltage-Driven Double-Balanced Passive Mixer for MICS Band Receiver

This paper presents analysis of a 25% duty-cycle fully-differential double-balanced passive mixer dedicated to medical implantable devices. The proposed passive mixer is part of a medical implant communication service (MICS) receiver front-end operating at 402–405[Formula: see text]MHz. By performing time-domain analysis, two LTI models have been developed to study the fully-differential double-balanced passive mixer: A simplified model and a complete model taking into account harmonic components. Both models account for the AC coupling capacitors at the mixer input and account for baseband voltage variation over one LO period. In this study it has been shown the ability of mixer input impedance matching by varying baseband resistor at the mixer output. The frequency of match can be controlled by varying the AC coupling capacitors and baseband capacitors. The performance of the proposed models was compared with that of the mixer and the results were very close. In particular, the results of simulations of the input impedance as a function of the baseband resistance and as a function of the IF frequency show the validity of the proposed models. The main parameters of the passive mixer such as input impedance, gain and noise figure (NF) were optimized taking into account the constraints of our application. The proposed mixer is designed to operate at LO frequency of 403.2[Formula: see text]MHz. Transistors size is optimized to meet the receiver specifications. The mixer realizes a conversion gain of 0[Formula: see text]dB and an NF of 4.8[Formula: see text]dB. Linearity simulations show 25.2[Formula: see text]dBm for IIP3 and 9.66[Formula: see text]dBm for [Formula: see text]dB. The mixer consumes 1.44[Formula: see text]pW without LO circuit.