Dm Holburn

A combined heart rate and movement sensor: proof of concept and preliminary testing study.

Objective: Heart rate monitoring has previously been used as a technique for measuring energy expenditure (EE) in field studies. However, the combination of heart rate monitoring with movement sensoring could have theoretical advantages compared to either method used alone. Therefore, this study was undertaken to develop and validate a new combined heart rate monitor and movement sensor instrument (HR+M) for measuring EE.Methods: The HR+M instrument is a single-piece instrument worn around the chest which records minute-by-minute heart rate and movement. Eight subjects underwent an individual calibration in which EE and heart rate were measured at rest and during a sub-maximal bicycle ergometer test. They then wore the HR+M for 24 hours in a whole-body calorimeter and underwent a standard protocol including periods of physical activity and inactivity. Minute-by-minute heart rate was converted to EE using individual calibration curves with the motion data discriminating between periods of inactivity and activity at low heart rate levels. EE was also calculated using the HRFlex method which relies on heart rate alone. Both estimates of EE were compared to EE measured in the whole-body calorimeter.Results: The mean percentage error of the HR+M method calculating TEE compared with the gold standard of the calorimeter measurement was 0.00% (95% CI of the mean error −0.25, 1.25). The HRFlex method using the heart rate information alone resulted in a mean percentage error of 16.5% (95% CI of the mean error −0.57, 1.76).Conclusions: This preliminary test of HR+M demonstrates its ability to estimate EE and the pattern of EE and activity throughout the day. Further validation studies in free-living individuals are necessary.Sponsorship: NJW is an MRC Clinician Scientist Fellow. KLR holds an MRC PhD scholarship.European Journal of Clinical Nutrition (2000) 54, 409–414

Integrated transceivers for optical wireless communications

Line-of-sight free-space optical links can provide extremely high bandwidth communications, but this usually requires that transmitter and receiver are precisely aligned. In order to allow terminals to be mobile, links must be able to track users within their field of view so that the link is maintained. There are various means to do this, but all require complex subsystems with a number of different optical, optoelectronic, and electrical components. A solid-state tracking architecture is introduced and a seven-channel tracking system demonstration described. The system is designed to operate at 155 Mb/s and is, to the best of our knowledge, the first that uses an integrated approach. Arrays of novel resonant cavity LED (RCLED) emitters that operate at 980 nm are used as sources. These are flip-chip bonded to arrays of CMOS driver circuits and integrated with the necessary transmitter optics. The receiver uses a back-illuminated detector array flip-chip bonded to arrays of custom CMOS receivers. All these components are custom and have performance substantially better than nonoptimized commercially available components. In the paper, the design and fabrication of the optics, optoelectronics, and electronics required for this is described. Successful operation of all the subsystems is detailed, together with results from an initial link demonstration.

High-speed integrated transceivers for optical wireless

Optical wireless LANs have the potential to provide bandwidths far in excess of those available with current or planned RF networks. There are several approaches to implementing optical wireless systems, but these usually involve the integration of optical, optoelectronic, and electrical components in order to create transceivers. Such systems are necessarily complex, and the widespread use of optical wireless is likely to be dependent on the ability to fabricate the required transceiver components at low cost. A number of UK universities are currently involved in a project to demonstrate integrated optical wireless subsystems that can provide line-of-sight in-building communications at 155 Mb/s and above. The system uses two-dimensional arrays of novel microcavity LED emitters and arrays of detectors integrated with custom CMOS integrated circuits to implement tracking transceiver components. In this article we set out the basic approaches that can be used for in-building optical wireless communication and argue the need for an integrated and scalable approach to the fabrication of transceivers. Our work aimed at implementing these components, including experimental results and potential future directions, is then discussed.

Experimental demonstration of cascaded AWG access network featuring bi-directional transmission and polarization multiplexing

We present the first experimental demonstration of a bidirectional cascaded arrayed-waveguide grating (AWG) access network combining one NxN AWG in the central office with multiple 1xN AWGs at the distribution points, such as to individually address N(2) users with only N wavelengths. Downstream and upstream data share the same optical path. BER curves were measured using 2.5Gb/s data stream in each direction, and error free transmission achieved for downstream and upstream, with only 0.3dB power penalty for simultaneous transmission. The addition of two orthogonal polarization-multiplexed channels per wavelength doubled the number of possible end users. Error free transmission was achieved with simultaneous upstream and downstream transmission of a composite signal featuring eight 2.5Gb/s channels (2 polarizations x 4 wavelengths).

A pattern recognition technique using sequences of marks for registration in electron beam lithography

A pattern recognition technique is described for precise registration in electron beam lithography. The usual simple mark on the substrate is replaced by a symbol of carefully chosen configuration, based on a pseudorandom binary sequence. The registration symbol obtained by rapidly scanning the electron beam in the region of the symbol is then cross correlated with a stored replica of the registration symbol, either by special purpose hardware or by programmed instructions. It is shown that with this method, registration symbols may be detected accurately even when heavily contaminated with noise, the signal‐to‐noise ratio being reduced to less than 0.25. The method also allows for the presence of unrelated artefacts in the vicinity of the symbol.

High speed integrated optical wireless transceivers for in-building optical LANs

12 Maintaining high bandwidth indoor optical wireless channels under a wide range of operating conditions usually requires relatively complex transceiver components. Integrating optical, optoelectronic and optical components using techniques that are suitable for mass manufacture is an important step in the development of these systems. This paper describes work to develop low cost integrated tracking transmitter and receiver components for use in a cellular indoor optical wireless network. A seven channel demonstrator operating at 155 Mb/s is under construction, using arrays of Resonant Cavity LEDs, PIN detectors, Silicon CMOS driver circuits and associated optics. Development of components, design methodology and initial results are detailed.

A CMOS Imaging Diversity Receiver Chip with a Flip-Chip Integrated Detector Array for Optical Wireless Links

An optical receiver circuit incorporating a novel current-mode, channel selection and combination circuit architecture is presented. Optical measurements at 310 Mb/s are demonstrated on the CMOS receiver chip flip-chip bonded to a custom detector array

Development of a CMOS 310-Mb/s receiver for free-space optical wireless links

12 This paper presents the design and implementation of a CMOS 310 Mb/s receiver for use in a multi-channel 155 Mb/s Manchester-coded optical wireless link. The receiver consists of a pre-amplifier followed by a post amplifier circuit. The pre-amplifier is a three stage transimpedance amplifier with an NMOS load at the output of each stage to control gain and stability. To allow the sensitivity of the performance to key parameters to be visualized a nomograph technique was developed. The contours of the nomograph show how DC bias, dominant pole frequency and the gain of each stage vary with transistor dimensions. This allows the designer to select transistor sizes for a given bit rate and for stable operation. The design has been optimized to achieve -30 dBm sensitivity at a BER of 10-9.

Design and analysis of a low-power highly linear mixer

This paper presents the analysis and design of a low power and highly linear mixer topology based on the differential derivative superposition method. The analysis focuses on both nonlinearity and noise performance. The linearisation mechanism is investigated in terms of Taylor series and Volterra series. A prototype mixer has been designed and is to be implemented in 0.18 µ m CMOS technology. Simulation shows this mixer achieves 19.7dBm IIP3 with 1.1dB power gain, 13.6dB noise figure at 2.4GHz and only 3.8mW power consumption. This performance is competitive with already reported mixers.

Topographical analysis in the SEM using an automatic focusing technique

A novel technique for automated topographical analysis in the SEM has been investigated. It utilizes a 16‐bit minicomputer arranged to act as an automatic focusing unit. The computer is coupled to the objective lens of the microscope, by means of a digital to analogue converter, and may regulate the excitation of the lens under program control. Further digital‐to‐analogue converters allow the computer to act as a programmable scan generator by applying ramp waveforms to the scan amplifiers, permitting the beam to be swept over a small sub‐region of the field of interest. The video signal is sampled and applied to an analogue‐to‐digital converter; the resultant binary numbers are stored in computer memory as an array of values representing relative image intensities within a subregion. A differencing algorithm applied to the collected data allows the level of objective lens excitation to be found at which the sharpness of the image is optimized, and the excitation may be related to the working distance for that subregion through a previous calibration experiment. The sensitivity of the method for detecting small height changes is theoretically of the order of 1 μm.