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Biomedical subjects

N E Evans

Publications and source records attributed to N E Evans.

18 recordsLinked to original sources
PubMed2003

Effect of a hands-free wire on specific absorption rate for a waist-mounted 1.8 GHz cellular telephone handset.

A common feature of cellular telephony is the use of a 'hands-free' audio extension lead connected to a waist-worn handset. Interaction between the transmitting antenna, the wire and the user's body can occur, with detrimental effects including polar pattern degradation, reduced efficiency and localized increases in specific absorption rate (SAR). Using a realistic full-body model of an adult male, finite difference time domain analysis was employed to investigate the coupling between a hip-mounted 1.8 GHz handset fitted with a monopole antenna and a 1 m long wire representing a hands-free wire. Conduction current densities were computed for three identifiable coupling modes: magnetic-only, conductive-only and combined conductive-and-magnetic. Magnetic-only coupling was dominant. Without the lead, placing the handset at waist height led to a 42.8% increase in the total energy deposited in the body, compared to use at the head. Introducing the lead further increased the body loss, with a reduction in system radiation efficiency from 52% to 43.7%. Without the hands-free lead, the peak 1 g and 10 g SARs were 0.450 W kg(-1) and 0.265 W kg(-1), respectively, for 125 mW transmit power. With the hands-free lead connected, these values increased to 1.14 W kg(-1) and 0.430 W kg(-1), respectively.

Adult↗
PubMed2000

Radiowave propagation from a tissue-implanted source at 418 MHz and 916.5 MHz.

Tissue-implanted ultra-high frequency (UHF) radio devices are being employed in both humans and animals for telemetry and telecommand applications. This paper describes the experimental measurement and electromagnetic modeling of propagation from 418-MHz and 916.5-MHz sources placed in the human vagina. Whole-body homogeneous and semi-segmented software models were constructed using data from the Visible Human Project. Bodyworn radiation efficiencies for a vaginally placed 418-MHz source were calculated using finite-difference time-domain and ranged between 1.6% and 3.4% (corresponding to net body losses of between 14.7 and 18.0 dB). Greater losses were encountered at 916.5 MHz, with efficiencies between 0.36% and 0.46% (net body loss ranging between 23.4 and 24.4 dB). Practical measurements were in good agreement with simulations, to within 2 dB at 418 MHz and 3 dB at 916.5 MHz. The degree of tissue-segmentation for whole-body models was found to have a minimal effect on calculated azimuthal radiation patterns and bodyworn radiation efficiency, provided the region surrounding the implanted source was sufficiently detailed.

Algorithms↗
PubMed2000

Reduction of Walsh-transformed electrocardiograms by double logarithmic coding.

This work presents an electrocardiogram ECG data reduction method based on Walsh spectrum double logarithmic quantization. The technique is theoretically justified for a simulated ECG and its practical efficiency confirmed using MIT/BIH arrhythmia database signals. By classifying a "good" compression as one with MSE < or = 0.005 for 1:1 spectral reduction, a normal/abnormal ECG mix returned an 87% success rate for waveforms stored with 8- to 11-bit resolution.

Arrhythmias, Cardiac↗
PubMed2000

The design and performance of a 2.5-GHz telecommand link for wireless biomedical monitoring.

This paper details the implementation and operational performance of a minimum-power 2.45-GHz pulse receiver and a companion on-off keyed transmitter for use in a semi-active, duplex RF biomedical transponder. A 50-ohm microstrip stub-matched zero-bias diode detector forms the heart of a body-worn receiver that has a (CMOS baseband amplifier consuming 20 microA from +3 V and achieves a tangential sensitivity of -53 dBm. The base transmitter generates 0.5 W of peak RF output power into 50 ohms. Both linear and right-hand circularly polarized Tx-Rx antenna sets were employed in system reliability trials carried out in a hospital Coronary Care Unit. For transmitting antenna heights between 0.3 and 2.2 m above floor level, transponder interrogations were 95% reliable within the 67-m2 area of the ward, falling to an average of 46% in the surrounding rooms and corridors. Overall, the circular antenna set gave the higher reliability and lower propagation power decay index.

Coronary Care Units↗
PubMed1999

The incidence of radio-frequency impulsive noise within hospital buildings: initial measurements in the 450 MHz band.

This paper reports on the incidence and level of man-made electrical impulse noise capable of causing interference to low-power, ASK and FSK radio biotelemetry links. Measurements were made at two acute hospitals, one in a residential area of Belfast, Northern Ireland and the other in an industrial part of Berlin, Germany. Monitoring was effected in the 450 MHz band using a communications receiver with its AGC line disabled and AM-detector AM output fed to a PC-based logger. The RF bandwidth was 20 kHz and a rotatable folded-dipole receiving antenna was used. Seven-day impulse counts were recorded at each location, for separate RF input thresholds of -100, -110 and -120 dBm and a common trigger window of 10 micros-10 ms. Histograms depicting the average pulse count per minute are presented; values range from a maximum of 55x10(3)/min for -120 dBm sensitivity in Berlin, to a minimum of 1.2/min for -100 dBm sensitivity in Belfast, both with vertical polarisation.

Artifacts↗
PubMed1999

FDTD analysis of close-coupled 418 MHz radiating devices for human biotelemetry.

This paper describes the finite-difference time-domain (FDTD) analysis of antenna-body interaction effects occurring when chest-mounted 418 MHz radio transmitters are used for medical telemetry applications. Whole-body software models (homogeneous, layered and tissue-segmented) were developed for an adult male subject. Using an electrically small (300 mm2) planar loop antenna, calculated radiation efficiencies ranged between 33.5% and 39.2% for a whole-body model, and between 60.7% and 66.1% for a torso; radiation patterns were found to be largely independent of model composition. The computed radiation efficiency for a 21.5 kg phantom representing a six-year-old female was within 1.1 dB of measured results (actual body mass 28 kg) and well-correlated azimuthal radiation patterns were noted.

Adult↗
PubMed1998

On the design and assessment of a 2.45 GHz radio telecommand system for remote patient monitoring.

This paper discusses the design and operational assessment of a minimum-power, 2.45 GHz portable pulse receiver and associated base transmitter comprising the interrogation link in a duplex, cross-band RF transponder designed for short-range, remote patient monitoring. A tangential receiver sensitivity of - 53 dBm was achieved using a 50 ohms microstrip stub-matched zero-bias diode detector and a CMOS baseband amplifier consuming 20 microA from + 3 V. The base transmitter generated an on-off keyed peak output of 0.5 W into 50 ohms. Both linear and right-hand circularly-polarised antennas were employed in system evaluations carried out within an operational Coronary Care Unit ward. For transmitting antenna heights of between 0.3 and 2.2 m above floor level. transponder interrogations were 95% reliable within the 82 m2 area of the ward, falling to an average of 46% in the surrounding rooms and corridors. Separating the polarisation modes, using the circular antenna set gave the higher overall reliability.

Equipment Design↗
PubMed1997

RF performance of a 418-MHz radio telemeter packaged for human vaginal placement.

The electrical and communication performance of a 0.8-microW UHF temperature telemeter designed for human vaginal placement is discussed; a solenoidal loop antenna was used, occupying a volume of 0.1 cm3. In situ, measured power absorption was between 19-25 dB, resulting in an effective operating range of 10 m. Capacitive loading lowered the antenna's resonant frequency by 1.4% and there was a significant polarization change in the radiated output.

Electric Conductivity↗
PubMed1996

Vaginal temperature sensing using UHF radio telemetry.

User-induced errors are common when women repetitively employ conventional probe type thermometers to chart their basal body temperatures in an effort to indicate ovulation. An alternative technique employing a two-part telemetric thermometer is proposed, with low-power, SAWR-controlled UHF radio as the transmission medium. Worn overnight in the vagina, the 1 microW erp telemetry transmitter sends pulse modulated data continuously to a microcontroller in a nearby receiver; a real time clock enables programmable sampling and storage of the subject's temperature to 0.1 degrees C resolution. Initial clinical results indicate an enhanced performance compared to oral and axillary temperature trends taken by a mercury-in-glass thermometer. Polar plots of both the isolated and body-worn telemetry transmitter are presented; body induced attenuations of up to 30 dB were measured.

Biomedical Engineering↗
PubMed1996

Digital transmission of 12-lead electrocardiograms and duplex speech in the telephone bandwidth.

A system was developed which allowed the simultaneous communication of digitized, full duplex speech and electrocardiography (ECG) signals in realtime. A single band-limited channel was used over a standard telephone line providing 3 kHz bandwidth. The full duplex speech was compressed to 2400 bit/s using linear predictive coding, while multiple ECG signals were processed by a novel ECG compression technique. Extensive use of digital signal processing reduced the combined bit rate to less than 9600 bit/s, allowing the use of low-cost commercial modems. The ECG communications system was tested in clinical trials. It enabled a hospital-based clinician to provide diagnostic and treatment advice to a remote location over the standard telephone network.

Analog-Digital Conversion↗
PubMed1996

Low-power radio telemetry: the potential for remote patient monitoring.

Radio-based signalling devices will play an important role in future generations of remote patient monitoring equipment, both at home and in hospital. Ultimately, it will be possible to sample vital signs from patients, whatever their location and without them necessarily being aware that a measurement is being taken. This paper reviews current methods for the transmission by radio of physiological parameters over ranges of 0.3, 3 and 30 m, and describes the radiofrequency hardware required and the carrier frequencies commonly used. Future developments, including full duplex systems and the use of more advanced modulation schemes, are described. The paper concludes with a case study of a human temperature telemeter built to indicate ovulation. Clinical results clearly show the advantage to be had in adopting radio biotelemetry in this instance.

Body Temperature↗
PubMed1995

Fading characteristics of a 2.3 GHz radio telemetry channel in a hospital building.

This paper reports on radio path attenuation measurements made in a hospital complex at a spot frequency of 2.340 GHz. Power loss figures for fixed path propagation in a variety of building types have been determined for proposed telemetry use in operational ward situations. Throughout the hospital, the radio paths assessed all exhibited a loss in excess of that calculated for free-space communications. Modern buildings had external wall losses of 10-25 dB, with dividing walls in wards contributing an additional 5 dB. Received signal strength levels indicated a Rayleigh distribution for obstructed paths. Temporal testing was used to find the rate and depth of signal fades caused by the movement of personnel and equipment during normal ward usage; signal level reductions of greater than 35 dB were common during busy periods.

Biomedical Engineering↗
PubMed1991

Clinical temperature acquisition using proximity telemetry.

This paper describes an electronic clinical thermometer which does not require a cable connection between the sensor and the temperature indicator. Several patients using individual battery-powered sensors can have their temperatures logged by a hand-held interrogating device held in close proximity. Temperature readout is virtually instantaneous and there is no interference between adjacent users. The device relies on radiofrequency-tuned circuit coupling for its operation.

Body Temperature↗
PubMed1990

Multichannel physiological monitor plus simultaneous full-duplex speech channel using a dial-up telephone line.

Because of bandwidth limitations, the Public Switched Telephone Network (PSTN) cannot normally accommodate simultaneous multichannel physiological signaling with speech. This communication describes work carried out to build a physiological monitoring system which can transmit up to six low-frequency data channels in the presence of a full-duplex speech channel using one telephone line.

Electrocardiography↗