Biomedical Engineering Reference
In-Depth Information
Keywords
Contactless motion sensing
·
Respiratory monitoring
·
Apnea
·
Adult
·
Infant
·
UWB
·
Radar
·
System-on-chip
·
CMOS
·
Pulse generator
·
Low noise
amplifier
·
Multiplier
·
Delay generator
·
Integrator
Introduction
In February 2002, the Federal Communications Commission (FCC) authorized the
marketing and operation of a new class of products incorporating ultra-wideband
(UWB) technology [
1
]. The FCC, by modifying the 47 Code of Federal Regula-
tions (CRF) Part 15 regulations [
2
] allocated for the UWB systems an unlicensed
band 7.5 GHz wide (for the first time, in a nonexclusive way), in the range of the
radio-frequency spectrum 3.1-10.6 GHz. The maximum equivalent isotropic radi-
ated power (EIRP) in-band spectral density allowed for UWB devices has been set to
−
41.3 dBm/MHz, whereas different out-band restrictions have been set according
to the nature of the applications.
Both in-band and out-band restrictions allow the reduction of the interferences
with the other wireless communication services already operating in the same region
of the frequency spectrum. In the recent years, Asia and Europe adopted similar
regulations for the UWB applications in the same frequency band [
3
,
4
].
UWB devices can be exploited for the implementation of several wireless data
communication and contactless systems for mass-market applications, such as
ground penetrating radars, wall and through wall imaging, surveillance, high data
rate communication, and medical imaging. Due to the extremely low level of radiated
power spectral density (PSD), significant interests have been focused on medical ap-
plications. In this framework, particularly relevant is the opportunity offered by the
sensors for contactless respiratory rate monitoring. Such devices are expected to be
the enabling technology for a wide range of continuous bio-monitoring applications,
ranging from sleep-wake classifications of drivers in vehicles [
5
] to respiratory dis-
orders monitoring of adults and infants [
6
], from the fatigue detection for fitness
users to monitoring of patients in hospital and domestic environments.
The base concept of UWB devices is to generate, send, and receive extremely short
radio-frequency pulses, with time duration in the range of hundreds of picoseconds to
few nanoseconds. Very short pulses allow us to achieve a very high spatial resolution.
Large pulses allow longer communication ranges; however, their repetition frequency
must be kept lower in order to assure the compliance of the EIRP spectral density with
the emission mask of the standard regulations. Since pulses and echoes are radiated
and captured by means of antennas, it is very important that the antennas transmit
and receive the UWB signals without introducing a significant level of distortions.
Therefore, the bandwidth of the antennas must be wide enough (a few gigahertz) to
transmit and receive the UWB pulses properly.
The market penetration for these emerging devices is related to the opportunity of
implementing ultra-miniaturized low-power low-cost transceivers on standard sili-
con technologies. Complementary metal-oxide semiconductor (CMOS) has emerged
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