Abstract
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.
Highlights
Long Range Wide Area Network (LoRaWAN) is one of the best wireless technologies for the Internet of Things (IoT) [1,2]
(401–406 MHz) [20], it can be tuned to other bands such as the Industrial Scientific and Medical (ISM) 433 MHz band, which is frequently used for Implanted Medical Devices (IMD)
This paper shows the feasibility of communication based on receiving backscatter LoRa packets at a shifted channel for implanted devices
Summary
Long Range Wide Area Network (LoRaWAN) is one of the best wireless technologies for the Internet of Things (IoT) [1,2]. Its popularity is due to the robust modulation scheme based on chirp spread spectrum (CSS) modulation [3,4,5]. LoRa receivers exhibit an impressive sensitivity which, depending on the spread factor used, can be as low as −148 dBm (Semtech SX1276 [6]). As a result of this sensitivity, radio links of several kilometers long can be designed [7]. LoRa is based on a low power modulation designed to send small data packages over long distances, operating on a battery. It can demodulate signals which are 7.5 dB to 20 dB below the noise floor
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