1. Advanced Wireless Transmission for Skin Patches and Implants
Smart Antenna
Research Laboratory
Mary Ann Ingram and Aravind Kailas
School of Electrical and Computer Engineering
Preliminary Results
Implanted Sensors
Statement of the Problem
Wireless transceivers on or in the body have a variety of applications in telehealth and telemedicine, and provide the user improved mobility and quality of life:
Remote patient monitoring
Neuro-stimulation and sensing
Athletic training aides
Remote drug delivery
However, body tissues strongly attenuate radio waves, making wireless transmission inherently unreliable
Radio connectivity becomes a function of body position and proximity to the wireless access point or hub device
Tissue heating and other issues imply severe limits on radio transmitter power
Battery replacement is at best inconvenient and at worst (for implants) creates a risk to the patient
Skin Patch Sensors
To wireless hub (PDA or bedside)
Power gain of about 14 dBm per antenna (range of 4m)
As distances between transmitters increases (i.e. as correlation decreases), power gain improves
Reduction in fade margin is achieved
Range extension
Testbed for Cooperative Transmission
Packet Delivery Ratio
Software Defined Radio
GNURadio is open source toolkit for building and deploying SDR systems
20 USRP board and 2.4GHz d’boards are used for testbed
Our Solution: Cooperative Transmission
Telemetry Network (TeNt)
Control and monitor GNURadio network by utilizing Micaz motes
One or more radios help other radios by transmitting copies of the signal
The copies are combined in the physical layer of the receiver- leading to improved reception
The benefits of CT:
Range Extension in highly attenuating environments
Reduces tissue heating by sharing the transmission energy across multiple locations
Gain from multiple cooperating radios
Average Distance = 5m
N = Number of Relays
3 mm
Electronic device
(e.g. switch)
Long wires
“Pore”
A Concept: Long-Wire Implant Bus (LIMBUS)
2nd conductor not used
Electrode
The PM/ICD, and neurostimulators can all operate via long wires, 40 cm and longer, lying in a vein and/or under the skin. ICD wires implanted in 18 year olds are expected to last 50 years or more. The LIMBUS long wire would be a generic integrated platform, supporting multiple sensors, electrodes, energy harvesters, a microprocessor and a radio. The wire therefore has a network bus architecture, with the various devices connecting to it through electronic switches.
(a)
(b)
100
10-1
10-2
10-3
10-4
10-5
10-6
Digital Sensor
with no relays
Electrode
Digital Sensor
Energy Harvester
(c)
(d)
Advantages:
Distributed sensing, stimulation, and computing on a single-wire platform that can be implanted using relatively simple and conventional surgical techniques. Prior art has a long wire for every electrode, and implantation for distributed electrodes is much more complicated
Uses mature wire technology as a basis
More efficient energy harvesting, because of multiple and distributed devices
Potentially more efficient antenna because of its length
(a) single device, (b) electrode detail (c) digital sensor detail, (d) long wire with integrated devices
Disadvantages:
Higher mechanical load on the wire
More friction (because of small lumps) during surgical implantation
More insertion loss (because of the switches) on the electrodes
More electrical noise on the electrodes (from the digital electronics)
~19 dB power gain
Prob. outage
TX/RX
Arms of the dipole
The secondary conductor
with two relays
SNR (dB)
When it is not a bus, LIMBUS is an efficient dipole antenna
Source: J. N. Laneman, Cooperation in Wireless Networks: Principles and Applications. Springer, 2006, ch. Cooperative Diversity: Models, Algorithms, and Architectures, pp