Biomedical Applications

Antenna Body Area Networks

Power Absorption (SAR): specific allowances of radiation Signal integrity Body is a lossy, complex medium for signal propagation Distortion of radiation pattern close to human?

Circular patch antenna Disadvantage: low efficiency due to the high dielectric constant:

– Low range in confined spaces – OK Silicone coating helps further miniaturization Broadside gain 0.55dB

Wireless PANs in Medical ApplicationsThe aim is the creation of a patient-centered RF hub that can receive vital signs from patients, concentrate them and send them to a base station in a relatively short range via a wireless personal area network (WPAN). WPANs can be used for connecting to a higher level network and the Internet (uplink) and even for wireless communication among the ECG sensors themselves (intrapersonal communication).

The criteria that are mostly considered for the selection of the most appropriate and efficient protocol in this area are:

Data rate Range Low battery power requirement Safety and reliability Security

Data Latency Safety and reliability Security Data Latency

ETSI ERM Task Group 30 – Medical Devices Its task is to propose and elaborate product specific standards and address frequency allocation matters in relation with radiocommunications applications for medical devices.

First implementation of 3 lead ECG and temperature sensor node Xbow's MICA wireless sensor node Sensing board on top:

Custom 3-lead ECG sensor Medical grade YSI400 temperature probe

Protocol choices for Transciever

Bluetooth ULP (Ultra Low Power) Wireless USB Zigbee Non-proprietory protocols – ANT Multi-hopping

body area network patient to patient

RF Power scavengingOperation modes:

Semi-passive tag: IC uses electromagnetic power distribution

Sensor uses battery Increased node's lifetime

Active tag: IC and sensor utilize battery Increased data range (>100 ft compared to 30 ft in semi-passive) Improved Signal to Noise ratio → noise immunity in harsh environments

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Energy Sources for Power Scavenging

Non-Invasive Method Investigation for Blood Pressure MeasurementsCuff

Accurate Non-continuous monitoring Discomfort from pressure

Arterial tonometer

Applies constant pressure on artery at the wrist Constant pressure creates discomfort

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Challenges of coughless methods Pulse Transit Time method (PTT)

The time taken for one arterial pulse pressure wave to travel from aortic valve to peripheral site.

Two different blood pressures have to be induced in order to make the method work

Detect PTT Pulse Oximeter

Diodes emits light and detect absorption of light. Light absorption differ due to SpO2 level and vessel expansion.

Impedance sensor Sends current between 2 points to detect impedance change from arterial

pulse. Current LifeSync system already contains impedance sensor for detecting

respiration. Issues with impedance detection

Impedance change can result from stretching skin as in respiratory. How to isolate the change from breathing and blood pulse?

Sakamoto’s Thorax Model A more accurate non-homogenous physical model contrary to Kubicek’s two cylinder

model.

Lungs, heart, aorta and veins are represented by geometric shaped contained in an elliptical cylinder defined as the body.

The model injects current with a band electrode at the neck. Simulates the different respiratory and cardiac phases through altering the resistivity

of the model.

Proposed Tool: Cylindrical Model Cylinder model with a 100mV point source in the middle bottom developed as a

starting point. Multiple point sources defined on outer lower surface of the electrode to simulate band

electrode. Objective: develop two electrically parallel, one inside another, to verify the model as

well as Kubiceks’ two cylinder formula. Find Zb and Zt separately with the tool, plug in formula. Model Zb and Zt together