An imminent breakthrough could radically alter both low-cost condition monitoring of healthcare patients and the performance of engineering structures, as Tom Shelley discovers
Single chips, powered by printed batteries, are set to
revolutionise the way in which human health and engineering
structural performance are monitored – aided and abetted by
a strip of disposable sticking plaster.
The monitoring system, developed to improve dramatically the care
of patients with chronic conditions, the elderly and expectant
mothers in their own homes, is already arousing interest in
mainstream engineering. And with the device held in place by a
modest strip of sticking plaster, its findings can be reported
wirelessly to a base station and database.
The system is the brainchild of Toumaz Technology in Abingdon,
Oxfordshire, originally spun out of Imperial College by Professor
Chris Toumazou, Keith Errey and Dr Alison Burdett. The business
started as a ‘fabless’ semiconductor company designing
integrated circuits, with a speciality in very low power signal
processing and wireless communications. At the end of 2005, they
decided the time was ripe to apply their expertise to the
healthcare market.
“Our vision is in developing products for monitoring vital
signs and bio-markers,” says Burdett. “Our chip sensor
interface and wireless platform are general purpose, but we want
to focus on the healthcare market. Healthcare in the UK has to
become more efficient. There are many instances where, if
patients could be continuously monitored, they would recover
better at home than in hospital.”
This was the driving force that led to the company developing a
small module capable of monitoring the human heart, using two ECG
electrodes and a temperature sensor. The tiny device (measuring a
mere 30mm x 45mm x 4mm thick) was powered by a single zinc oxide
hearing aid battery. “Size is everything in this
market,” Burdett explains. “Our vision is the digital
plaster. This should be disposable, with a three- or four-day
lifetime. We wanted to stay away from lithium batteries. Zinc
oxide has a very high energy density and is kinder to the
environment, so you can throw it in the bin. But the output is
typically only about 1.4V, which affects chip design. The module
has allowed us to do trials with early stage customers, while we
worked on the integrated circuit, which measures only 6mm x
6mm.”
Eureka was shown a mock-up of the chip-based device, which
includes a printed battery and printed antenna, all on a small
flexible PCB that would also, in practice, support a few tiny
capacitors, plus a crystal and sensors. For the wireless
communications, states Burdett, “the printed zinc oxide
battery produces only about 2mA peak - not enough to drive a
Bluetooth or Zigbee radio. So, for further power savings, we have
developed our own wireless protocol, which is simple, but very
programmable. The radio has a range of typically 5m, but it is
possible to increase this to 10m in a clear space. We want to use
it to get data to a network through a standard wireless network
terminal, such as a PDA version or mobile phone, with a simple
plug-in card communicate with the body-worn module.” A
partner, she adds, is developing a pre-prototype demonstrator
that sits inside the mobile phone.
Each chip can accept input from up to three sensors -
accommodating low-level voltage signals, such as might be
produced by ECG measurements - and has a Wheatstone Bridge
interface. It can also receive three accelerometer inputs and has
interfaces for specific chemical sensors, as well as having an
on-chip temperature sensor. Chemical sensors can be amperometric,
biasing the sensor with a voltage and measuring current, or
biased with current, using the chip to detect voltage drop.
The way the device makes and manages ECG measurements is
particularly clever. First, the combination of sensor, chip and
local base station has to learn what the heartbeats from a
particular patient are like. The sensing device, therefore,
begins by streaming all data to the local base station. After a
few beats – the actual number is programmable – the
base station constructs a template of the complete waveform and
passes this back to the sensor chip. That becomes the first
normal beat. Subsequent beats are then compared locally in the
sensor chip to this template. If an unfamiliar beat is seen
– ie, one that cannot be matched in the sensor chip –
this is passed to the base station and another template
generated, which is sent back to the sensor chip. Up to 16
different beats may be classified, or programmed and stored.
Every 10 minutes or so – again, the interval is programmable
– the sensing system communicates with a remote database and
sends a summary file of the data.
Continuous history
In this way, a complete and continuous history can be built up of
the patient’s ECG, yet only a minute amount of data is
passed through the network. Additionally, and critically, if a
beat or series of beats is seen that cannot be matched with any
of the known templates, or if a beat is detected that fits the
shape of a previously programmed beat – say, for a known
arrhythmia suffered by the patient - the system is able to send
high-resolution digitised data through the network in real time.
This data represents a period leading up to the triggering event,
as well as subsequent to the event.
The other striking part of the whole process comes through a
collaboration with Oracle, which has developed healthcare
products based on enterprise solutions that are now in service in
the NHS and overseas. At present, nearly all patient data is
entered manually, but the healthcare providers would like this to
be automated. Toumaz and Oracle have put together a demonstration
system that uses a local Oracle Lite database on a PDA or other
small device that, by communicating with the main Oracle
database, is able to alert a doctor, medical service and/or
patient when an action needs to be taken.
In the medical field, apart from monitoring the elderly and
chronically sick, there are other areas of application. “We
are just now defining a trial around children and young people
with early stage type 2 diabetes to find what measures are
successful in getting people to modify their activities to
maintain and improve health,” says Burdett.
“Accelerometer data can, for example, be used to monitor
exercise activity.
“In another trial in May, we will start monitoring women in
the last month of pregnancy, as an alternative to ultrasonic
monitoring every day, which is invasive. In the last month of
pregnancy, you get a strong foetal ECG signal. We have been
talking to various parties about Parkinson’s disease,
monitoring the effects of anti-tremor drugs. It would be so much
easier to establish a personalised dose, if you can exactly
measure its effects. Blood flow, related to blood pressure, is
something we are looking at. There are some nice time-of-flight
techniques for monitoring flow - or just looking at rising or
falling blood pressure is enough for some conditions.”
Sports colleges and sports training organisations are also
showing great interest, particularly for elite athletes training
for national Olympic teams. And it goes way beyond the strictly
medical as well. For example, a wind turbine blades manufacturer
has approached the company, looking for a means to monitor tip
vibrations by using a mechanism that is small, light and
wireless. The range of potential applications for this technology
seems vast.
At present, the system is available as a small PCB-based unit,
forming part of a reasonably priced development kit. Once it goes
into large volume production, however, the disposable sensing
systems are likely to cost only a few pounds each to manufacture
– making them indispensable additions to both the
engineer’s toolbox and the doctor’s bag.
“Development kits are in the region of a few thousand
pounds, depending on customisation,” says the company.
“Modules are £300-500 and – when the chip goes into
production – the volume price for the chip is initially
expected to be less than $30 (£15).”
As for timing, Toumaz intends to start supplying development kits
to customers this month. “We can produce the modules and are
developing the chip,” says Burdett. “We are now pretty
much coming to the end of testing.” The chip device is built
around the Toumaz radio transceiver and baseboard controllers, a
set of intelligent sensors interfaces and drivers, an 8-bit 8051
RISC processor, 32K of program memory and 32K of data memory.
These amounts were apparently dictated by the need to be able to
run the ECG algorithm. “We have strategies for mitigating
against interference. If you go out of range, it will store its
data and transmit it when you get within range.” For the PCB
module, this has already been available for some while.
“There are so many applications we can supply for, if you
can make devices small enough and low enough in power
consumption,” Burdett concludes. “We are only limited
by our imagination.”
www.toumaz.com
Design Pointers
*l Devices can accept input from up to three sensors and report
wirelessly to a PDA or mobile phone base station
* The PCB module version is powered by a zinc oxide hearing aid
battery
* The 6mm square chip-based version sits on a small, flexible PCB
with a printed zinc oxide battery and printed antenna. It should
eventually be cheap enough to be disposable. The concept is to
have complete sensing systems on sticking plasters
For more technical
developments see www.eurekamagazine.co.uk