Implementation of Multichannel Sensors for Remote Biomedical Measurements in a Microsystems Format
Abstract
A novel microelectronic “pill” has been developed
for in situ studies of the gastro-intestinal tract, combining microsensors
and integrated circuits with system-level integration
technology. The measurement parameters include real-time
remote recording of temperature, pH, conductivity, and dissolved
oxygen. The unit comprises an outer biocompatible capsule
encasing four microsensors, a control chip, a discrete component
radio transmitter, and two silver oxide cells (the latter providing
an operating time of 40 h at the rated power consumption of 12.1
mW). The sensors were fabricated on two separate silicon chips
located at the front end of the capsule. The robust nature of the
pill makes it adaptable for use in a variety of environments related
to biomedical and industrial applications.
Index Terms—Microelectronic pill, microsensor integration,
mobile analytical microsystem, multilayer silicon fabrication,
radiotelemetry, remote in situ measurements.
I. INTRODUCTION
THE invention of the transistor enabled the first radiotelemetry
capsules, which utilized simple circuits for
in vivo telemetric studies of the gastro-intestinal (GI) tract [1].
These units could only transmit from a single sensor channel,
and were difficult to assemble due to the use of discrete
components [2]. The measurement parameters consisted of
either temperature, pH or pressure, and the first attempts
of conducting real-time noninvasive physiological measurements
suffered from poor reliability, low sensitivity, and short
lifetimes of the devices. The first successful pH gut profiles
were achieved in 1972 [3], with subsequent improvements in
Manuscript received January 30, 2003; revised June 8, 2003. This work was sensitivity and lifetime [4], [5]. Single-channel radiotelemetry
capsules have since been applied for the detection of disease
and abnormalities in the GI tract [6]–[8] where restricted access
prevents the use of traditional endoscopy [9].
Most radiotelemetry capsules utilize laboratory type sensors
such as glass pH electrodes, resistance thermometers [10], or
moving inductive coils as pressure transducers [11]. The relatively
large size of these sensors limits the functional complexity
of the pill for a given size of capsule. Adapting existing
semiconductor fabrication technologies to sensor development
[12]–[17] has enabled the production of highly functional units
for data collection, while the exploitation of integrated circuitry
for sensor control, signal conditioning, and wireless transmission
[18], [19] has extended the concept of single-channel radiotelemetry
to remote distributed sensing from microelectronic
pills.
Our current research on sensor integration and onboard data
processing has, therefore, focused on the development of microsystems
capable of performing simultaneous multiparameter
physiological analysis. The technology has a range of applications
in the detection of disease and abnormalities in medical
research. The overall aim has been to deliver enhanced functionality,
reduced size and power consumption, through systemlevel
integration on a common integrated circuit platform comprising
sensors, analog and digital signal processing, and signal
transmission.

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