RFID Technology for Monitoring Drug Intake

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16 Νοε 2013 (πριν από 4 χρόνια και 7 μήνες)

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RFID Technology for Monitoring Drug Intake

J. Jian,
M. Stanacevic
, S. Einav


of Elect. and Comp. Eng.

Stony Brook University

Stony Brook, NY 11794


R. Fine

School of Medicine

Stony Brook University

Stony Brook, NY



We propose a design of electronic monitoring system
for precise quantification of non
adherence. System based on
RFID technology, consisting of encapsulated tag inserted in the
pill and small externa
l reader worn on the body, would provide
cost, easy to operate, convenient and reliable solution for
patient’s medication taking behavior
Current RFID
technology solutions are not suitable to the non
problem due to presence of the
body as medium between tag and
reader. We propose a use of near
field UHF as a solution for
wireless link between tag and reader and we derive a technique
for selection of optimal frequency for wireless transmission.

adherence, RFID, inductive

coupline, near



The full benefit of medication can be achieved only if the
patient follows the prescribed treatment regiment sufficiently
closely. Besides affect
ing the outcome of the treatment, non
adherence also induces a high burden on the health care
system. It is estimated that a resultant cost related to poor
adherence in the United States reaches amount of $100 billion
a year, as of all medication
related h
ospital admission 33 to 69
percent are results of poor adherence [
]. Non
adherence with
medication regiment is also a critical part of clinical drug
trials, and in that case can result in misleading conclusions
drawn. These conclusions could have signific
ant impact on
millions of patients that may be future users of the researched

Direct methods for measurement of adherence are either
cumbersome, like directly observed therapy, or invasive and
expensive, like frequent measurement of level of
medicine or
metabolite in blood [
]. Indirect measurements that are based
on patient’s self
reporting or pill counts are highly inaccurate
and could be easily manipulated by patient. This leads to the
need for design of electronic monitors that would track

record how well patient is following the prescribed treatment.
To understand the requirements for this system, we need to
look at the reasons for patient’s non
compliance to the
treatment. There are many factors that can cause patient’s non

with the certain course of medication [
]. First
common reason is patient’s forgetfulness, especially among
elderly, to take his/her medications. Similar reasons include
poor communication between doctor and patient leading to
patients misunderstanding of

the doctor’s directions,
especially in case of complex treatments. In these cases,
systems based on monitoring patient’s preparation for taking
the medication, that is methods that detect for example time of
opening of the bottle with the pills, would be
valuable. Several
systems implementing this functionality are available
commercially [
]. These systems detect if the bottle with
pills is opened in time frame specified by the treatment, and if
they don’t detect any action by the patient, a reminder is

either automatically or through caregiver. Although these
systems are safe and simple, they can be easily manipulated by
patient, since they don’t detect what patient did with the
medication if it was really taken out of the bottle. This leads us
another set of reasons for non
adherence, that are related to
patient’s deliberate non
compliance, that is caused by patients’
unresolved concerns, related to his beliefs about medication or
treatment. Patient may be worried about side
effects of

he/she could not believe in the diagnosis, or could
view the medicine as too costly

. These are the reasons that
a system that directly monitors detection of the ingestion of
the medicine would provide effective and accurate solution for

There have been proposed few solutions for systems for
electronic monitoring of non
adherence based on ingestion of
the medicine, with an idea of embedding tracking devices in a
pill. The non
adherence would then be measured by detection
of thi
s device in the body. The system proposed by Sequella
Inc. is based on addition of a light
emitting fluorophore
molecule to the pill [
]. The presence of the pill in the body
would be quantified by detecting fluorophore in blood stream
through the skin. Th
e long
term effects of fluorophore have to
be studied and its potential effects are not understood. Another
proposed system is MagneTrace [
], which is based on
addition of small permanent magnetic tracer to the pill. To
detect ingestion of the pill, an ar
ray of magnetic field sensor
has to be carried around patient’s neck during the treatment.
This is highly inconvenient solution for the patient and can be
hardly used for long
term monitoring, expect in the case of
clinical trials.

We propose a design of w
ireless system based on RFID
technology for monitoring of ingestion of medicine and
absorption into the body to insure proper dosage control and
usage. A system foundation is idea of embedding RFID tag in
a pill. Monitoring of non
adherence that is pill in
gestion in the
body, would consist of detection of the presence of the pill in
the body by establishing wireless link between tag and
This work is supported by School of Medicine, Stony Brook University.

external reader worn on the body. System has to be low
intrusive, safe and user friendly. Its performance will b
quantified by how reliably it can detect if the patient has taken
a certain medication or not. The main challenge in the design
of the proposed system represents the design of wireless link
and constraints imposed on the design of RFID tag and
external r

The main constraints on the systems stem from the
physical size of tag and reader antennas. The size of the tag
antenna is limited by the size of the pill, while the external
reader has to be fashioned in a way that makes it easy for the
patient to

wear it on the body. Influence of the external reader
on patient’s everyday activities has to be minimal. Possible
ideas include a necklace/pendant or a device that can be
clipped to the belt or a waistband. Under such conditions, the
maximum achievable d
istance at which the reader can detect
the presence of tag has to extend beyond the distance between
RFID tag inside the body and external reader.

Additional constraint in the design of wireless link is
introduced by human body as the medium between tag a
reader. There are three possibilities in design of wireless link.
Radiation at high frequencies (UHF) is used for long range
communications in open air, but as the radiation is
significantly attenuated by the body, it prohibits this type of
wireless lin
k. Inductive coupling at HF (1MHz

used for power coupling of implantable devices, works only
for very short distances, up to 10
, depending on the size of
the coils and their orientation.

We propose a use of
UHF, that

provides inhere
ntly stronger inductive coupling, and
although the attenuation by the body at this frequency range is
higher, it provides longer range of detection, up to 1
, which
is on the order of the required distance.

The challenge in the design of wireless link pr
extension of distance that can be achieved through near
UHF, since due to weak coupling between antennas only small
part of emitted power by external transmitter antenna reaches
RFID tag antenna. We modify the design of external reader to
ide elongated read range. We propose design of spatially
selective external reader, similar to standard beamforming
concepts used in the antenna design, based on gradient flow
method [
]. The spatial selectivity is possible as the region
of the possible

location of RFID tag is known. The similar
idea has been proposed for RFID tag localization, where
measurements of the first
order spatial gradients of the
magnetic field have been demonstrated [
]. The differential
signal was produced by oppositely woun
d coils. Standard
beamforming phased arrays techniques are not suitable for use
in external reader. The reason is that the performance of
beamforming algorithms directly depends on the aperture of
the array and with the decreasing distance between array
ements performance degrades, leading to requirement of
large form factor of external reader for extended range.




Currently radio
frequency identification (RFID) technology is
being used for wide variety of applications ranging from

control to automatic tracking systems [1
]. The
factors driving the technology are miniaturization and low cost
which have made the tags ubiquitous. RFID system is
composed out of two parts of the wireless link: RFID tag and
RFID reader. Tag is associa
ted with the product being tracked
or indentified, while the reader has a role of interrogator.

The aim of our work is to demonstrate a system
containing RFID tag that is inserted in a pill and enables
monitoring of ingestion of medicine and absorption in
to the
body to

insure proper dosage control and usage. The designed
system will be able to reliable detect if the patient has taken a
certain medication and dosage. The envisioned system is
shown in Figure 1.

Figure 1.
Envisioned system for drug intake

For the detection of the presence of RFID tag in the body, a
wireless link between tag and reader has to become active
once the tag embedded in the pill is inside the body. The main
goal in the proposed research, besides defining the shapes and

size of the antennas, is demonstrating capability of the reader
to detect the presence of tag at the physical distance between
tag and reader defined by the real world scenario. While the
size of RFID tag antenna is limited by the size of the pill, the
ze of antenna in RFID reader and position of the reader on
the body will be under the investigation in the overall system


FID tag

Tag contains an antenna, a microchip and sometimes a battery.
In the passive tag, the power comes from radiating RF
from the reader and no battery is used with the tag. In the case
of active tag, that incorporates nanobattery, extended
maximum detection distance between tag and the reader can
be provided, as well as reduced size of the reader antenna for
the fixe
d detection distance. However, addition of battery
could be critical for disposal of the tag. Unique identifying
data is stored inside the microchip. Data stored on the tag
indicates the pill's identification and this information is
conveyed to the reader.

Pills with medicine inside usually come in similar shapes, with
different sizes, with diameter of 5

and length ranging from

to 22
. We envision using a small passive RFID tag
embedded into a capsule that is inserted into the pill, as
illustrated in Figure 2. To enable detection of the antenna in
the body, tag’s antenna has to be active only when it is in the
body, while outside the body it should be inactive. To achieve
this goal, conducting polymer will be included in electrical
it of antenna. The system has to be able to distinguish
human body from different environments it could be exposed
to by the patient in the

effort to alter result of the system by
pill dumping. The RFID tag will be encapsulated
biocompatible material
insoluble in gastrointestinal (GI) tract.

On the small part of the surface of capsule, a conductive
polymer will be deposited that will be in part of electrical
circuit of tag’s antenna. Conductive polymer will the only part
of the antenna electrical circu
it that will be exposed to the
body. The conductive polymer would be conductive only in
the body and that would be the only time when tag antenna
could transmit the signal to the reader. The polymer becomes
conductive only when a certain level of pH value,

characteristic for the body fluids, is detected. In the case that
multiple capsules with RFID tags are present in the body, the
system would still be able to distinguish them based on their
unique identification stored in tag.

Figure 2.
Illustrated d
ection principle.


Tag Disposal and Safety

Another design issue in the proposed RFID system is how to
dispose tag from the body after the detection of the pill. The
capsule that contains the tag needs to be small enough to
easily pass through GI tract. Smal
l tag can then be discharged
from the body, without any additional harmful effects, as well
as the case of accumulation in the body a few tags over a
course of couple of days. The potential accumulation of
capsules in the digestive tract over a period of s
everal days
should not pose a threat to the health of the patient.

Excess power of EM radiation is a major concern when
designing a system for insertion into the human body. One of
the most important considerations in designing an RF system
is the amount
of EM radiation that a patient would be exposed
to. The safety of a patient is always the primary concern when
considering the system design. The IEEE has published
standards for safety limits dealing with these fields [
]. We
consider the limits for cont
rolled environments only: it is
expected that those patients using this device would be
informed of their exposure to EM radiation. While standards
specify the limits of EM

radiation that the human body can
safely be exposed to, there are few long term
test studies on
this subject and the true lim
its are less well defined


RFID Reader

The reader has to be able to detect tag in the body and store
the identification information on the ingested pill, together
with time stamp, time at which the pill was tak
en. The stored
information in the reader will be readout after certain time,
and presented to the doctor at the time of patients visit. This
device must be fashioned in some way that makes it easy for
the patient to wear on the body. Possible ideas include

necklace/pendant or a device that can be clipped to the belt or
a waistband. In this way, the patient would only have to wear
this device when they are taking their medication, and could
leave it elsewhere for the rest of the day. This transmitter will
only be activated at time when it is used by the patient. Once
activated, this reader wi
ll “search” for the tag’s transmitter.
When the pill is detected, this device will store that
information. This device could also beep in order to notify
patient that it has successfully detected ingestion of the pill
and that the patient can now safely re
move the device. Once
the information has been stored, this device will turn off. If the
pill is not detected for a certain amount of time after reader has
been activated, the device will turn off to save power, as it will
be battery operated. Since a bott
le of pills can last patients
over a month, the reader will have to last the same amount of





It the case of far field, where we have EM propagation,
presence of dielectric and lossy materials such as water
Boundary of far
field and near
field radiation as
a function of transmission frequency.

between the reader and tag antennas produces a strong
detuning of the tag and attenuates significantly the electrical
field. This prevents the use of far
field EM propagation in the
design of wireless link between RF read
er and tag inside the
body. In the case of the near
field propagation, with magnetic
field, these dielectric materials do not disturb such field,
making inductive coupling ideal match for wireless link
between external reader and RF tag inside the pill. Th
boundary between near
field and far
field propagation then
leads to the absolute limit of the reading distance as a function
of a transmission frequency. The approximate boundary
depends on the electrical size of antenna that is physical size
compared to

wavelength. In our case, the link setup leads to
design of wireless link that contains electrically small
antennas. For electrically small antennas, the near field region
is commonly given as
= λ
/ 2
π and Figure

the boundary as a function

of transmission frequency.

. Schematic of two coils used in inductive coupling. Coupling can be

represented by the magnetic field that is shared between the two coils.

Wireless link with inductive coupling uses two inductor
ils placed relatively close to one another. A primary coil,
external to the body, is driven with a RF amplifier to create an
electromagnetic field. The properties of this field depend on
the amount of current and physical properties of the wire loop.
The s
econd coil, on the implanted transponder, captures a
portion of this field. The captured field induces a current
through this secondary coil. The current depends on the
physical parameters of the system. The proportion of energy
caught by the secondary coi
l can be represented by the
coupling factor,
. This value, dimensionless and always
between 0 and 1, is an important factor in understanding the
operation of any inductively coupled system. While the
coupling factor is influenced by the characteristics of

entire system, it is primarily dependent on the sizes of the
coils, their distances from one another, and their relative
orientations. Using basic electromagnetic principles it is
possible to obtain a desired coupling factor for a detection of
tag in
RFID system on required distance. When the coils are
close, the coupling (or influence that changes in one have on
the other) is high. The coupling is representative of percentage
of the magnetic field,
, which the two coils share. Figure
illustrates th
e basic setup. In an ideal transformer the coupling
between the two coils is perfect, a coupling of 100%. The
same magnetic field flows through both coils; any change in
the current or voltage in one coil is reflected in the other. Real
transformers have a

lower coupling, 50
90%. In the case of
increased distance between the coils or different orientation of
the coils, this coupling is much lower, often 5% or below. This
low coupling value presents a problem for design of wireless
link, since it is harder t
o detect data transmitted by the RFID
tag through the inductive link.

Maximum RMS magnetic field strength defined by IEEE C95.1
2005 as a function of transmission frequency.

Important constraint in choosing the optimal frequency
stems from potential health risks of EM radiation.
Standard for Safety Levels with

Respect to Human Exposure
to Radio

Frequency Electromagnetic Fields,

3 kHz to 300
, defines the maximum RMS value of magnetic field
strength as a function of transmission frequency.

From Figure
, we can extract the maximum magnetic
field at specific
frequency. Wireless link with inducti
coupling uses two inductor coils placed relatively close to one
, as shown in Figure
. A primary coil, external to the
body, is driven with a RF amplifier to create an
electromagnetic field. The properties of this field depend on
the amount of c
urrent and physical properties of the wire loop.
The second coil, on the implanted transponder, captures a
portion of this field. The captured field induces a current
through this secondary coil.

or determination of the reading
distance we have to induce
a minimum voltage in the
secondary coil, that is part of the tag.

In determining the optimal frequency, we will fix the size
of the reader coil and find the maximum reading range for
each frequency. The magnetic field has the maximum value at
the centre
of the coil


is the diameter of the reader coil,

is the number of
number of turns and

is the coils current. From maximum
magnetic field, for specifi
c form factor, we can find the
aximum current that we can have in the reader ci
rcuit. The
voltage induced in the tag of specific dimension is







are inductances of reader and tag coil

is the parasitic resistance of tag’s coil,


parallel capacitance of a tag,

is the equivalent resistance of
the load in tag’s circuit and

is the coupling coefficient
between the coils:




is the radius of the tag’s coil and

is the distance
between the coils. By s

equal to 5 cm and

equal to 5
mm, with
the minimum voltage

of 1 V at the tag
, we
calculated that the optimal frequency of the transmission is 40

Simplified model of the inductively coupled system



The envisioned syste
m would provide detailed and accurate
record of medication behavior of patient to his/her doctor. It
would assist doctor in assessing the success of medication in
treatment of patient’s condition, without worrying if patient
took the medications at the wro
ng time or the wrong dosage or
did he start/stop taking them too late or too early. Current
techniques that have been developed to improve adherence of
patients only have limited impact, since it is difficult to assess
their performance. With qualitative m
easure of patient’s
adherence provided by the designed system, these techniques
could be significantly improved, since the results of the
proposed techniques could be easily accessed and their
performance can be evaluated. They would lead to improved
quality of the doctor
patient relationship and better
understanding of patient health beliefs.

The envisioned system
would also be an integral part of clinic drug trials. It would
provide researchers with detailed data and enable them to
short the evaluati
on phase of drugs research, leading to shorter
time to market for these drugs and lower cost.

The optimal
frequency of the wireless transmission for identification of the
pill has been derived as the first step in the

design of

monitoring sy



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