Table of contents

The silicon-sensor field is now more than 35 years old, and meanwhile a deluge of novel silicon-based sensors has been presented in the literature. This review paper concentrates on the principal advances in the field of silicon sensors in the last decade. The material is dealt with according to the commonly accepted classification: radiant, mechanical, thermal, magnetic and chemical sensors. There have also been many new developments in the field of silicon-sensor technology. The most important of these are described in the section on technology. Modern information-processing systems need sensors which do not require periodic calibration and which also have a bus-compatible output. The last section describes the latest developments on smart sensors that meet these demands. The paper concludes with some remarks about the expected growth of the silicon-sensor field in the near future.

The design and construction of a fast polyvinylidenedifluoride (PVDF) piezoelectric gauge which is capable of being used near large current sources is described. An example of its use in the measurement of stress induced in composite plates subject to a simulated lightning strike is given.

A model gyroscope consisting of three coupled, spatially orthogonal electromagnetic ring-resonators is analysed. It is shown that, through an appropriate choice of inter-ring coupling components, the gyroscope can support a three-dimensional circulating or `gyrating` wave which, when subjected to an arbitrarily changing inertial rotation rate, can be described by an evolving wave amplitude state vector or `gyror`. When the effective resonant mode order takes the value N= 1/2 , the state vector transforms as a spinor and the gyrating wave becomes an inertially stable spinning wave. Despite its low sensitivity, this spin-gyroscope device is of interest since the measurable components of its state spinor are directly related to the parameters (angle-axis variables, quaternion components or Cayley-Klein parameters) which specify the orientation of the gyroscope relative to a fixed inertial frame.

Consideration is given to frequency estimates for continuous data trains of a fixed length amounting to at least five oscillations of a sinusoidal signal of constant frequency accompanied by low-level noise. The minimum variance of the frequency estimation is derived in terms of the noise spectral density at frequencies close to that of the signal. The extent to which several practical methods of frequency measurement can reach this limit is analysed. The case in which the frequency of the signal source may vary slightly within each data train is also included.

In this paper we describe a highly sensitive spatially resolving bolometer for heat pulse detection. The bolometer is based on a continuous strip of superconducting aluminium deposited on a sample by vacuum evaporation. In operation, the sample is cooled to just below the transition temperature of the aluminium and then a small part of the strip is biased onto its superconducting transition by heating it with a focused laser beam. The resistance of the strip is then very sensitive to the small changes in temperature brought about by phonon pulses incident on the biased section. By scanning the laser along the strip the position of the sensitive region can be moved. We have tested this bolometer by using it to measure the spatial dependence of the anisotropic phonon flux emanating from a heater on the opposite surface of a GaAs crystal. We show that the results are in good agreement with Monte Carlo simulations of the phonon focusing patterns. We also demonstrate that the bolometer can be biased using thin-film heaters so that, in systems without optical access, multiple bolometers can be used in close proximity without the need for a separate co-axial line to each one.

An original technique of electron paramagnetic resonance (EPR) at E and Q bands, via transmission through the sample, as in optical spectroscopy, is presented. The experiments are carried out at liquid helium temperature. The detector is a cooled bolometer placed near the sample. Details on the cells and set-ups are given. Results obtained on the sulphur donor in GaP are compared with those found by thermally detected EPR and demonstrate the strength of this bolometric transmission method in that range of microwave energies.

A simple and cost-effective spectrometer dedicated to line-intensity monitoring in the soft X-ray range has been realized, installed and tested in the RFX reversed field pinch experiment for the study of magnetically confined fusion plasmas. The technique of photon energy selection by means of multilayer material filters has been applied to the instrument described here, which, together with the associated electronics, has been designed in an original compact version for RFX. This present version allows on-line monitoring with good time resolution (10 kHz bandwidth) of line emission from carbon and oxygen in their H- and He-line states (which fall within the soft X-ray energy range), but, with modifications of the set of material filters, different wavelength ranges can be chosen and then other lines can be monitored. A detailed description of the instrument is given here and the data analysis technique is presented. Particular attention is dedicated to a critical analysis of the technique and to the discussion of the experimental errors which may be associated with this measurement; new results on the estimate of systematic errors and experimental improvements to eliminate the problem of continuum radiation are presented. As a demonstration of the proper operation of the instrument, data taken under a wide range of conditions in 0.5-0.6 MA RFX plasmas are shown and discussed. Good agreement of the measurements with other spectroscopic diagnostics already operating on the machine is found; by exploiting the high time resolution of the instrument, interesting results concerning the RFP configuration`s dynamics are obtained. Based on this prototype, a multichord diagnostic has been designed for imaging the impurity emission radial profiles.

This paper describes an investigation into the use of an optical fibre sensor to measure the flow of pneumatically conveyed solid particles. Typical results for the mass flow rate of dry sand versus transducer output voltage are presented for a 1 mm diameter sensor fibre. The frequency bandwidth of the sensor is determined for a range of fibre diameters and compared with the calculated response obtained using spatial filtering considerations.

Detailed flow characterization and turbulence investigation in large facilities using laser velocimetry present several difficulties essentially due to the size of the optics to be installed, the limited optical access and the required window quality. The mosaic laser velocimeter is a new instrument: its compact and robust optical head is a probe introduced into the flow, but with a 467 mm working distance, so that negligible disturbances are induced at the probe volume level. The basic principle is the following: the image of the trajectory of a particle, crossing a 400 mu m probe volume illuminated by a focused argon laser beam, is made by a receiving optics on a mosaic of optical fibres, each fibre being linked to a photomultiplier; these fibres are arranged along two concentric circles: the external one is used for measurements, the internal one for validation purposes. Two velocity components, in the plane perpendicular to the receiving optics axis, are deduced from the recognition of the addresses of the lighted fibres and from the measured time interval between the pulses delivered by the corresponding detectors. The possibilities of this new instrument have been compared with those of a classical 3D laser velocimeter by making detailed measurements in the wake and in the boundary layer of an aerofoil in a 1.4 m by 1.8 m subsonic wind tunnel: the good agreement obtained with respect to the results of mean velocities and turbulence have brought a high degree of confidence for the future employment of the mosaic laser velocimeter in larger subsonic or transonic facilities.

The instability of source and absorber temperatures and their influence on the Mossbauer spectrum is briefly discussed. A simple source thermostat was designed for the purposes of precision Mossbauer spectroscopy. The hyperfine alpha -Fe parameters were studied in detail as functions of the temperature. As a result temperature coefficients for the central shift and magnetic splitting of alpha -Fe were obtained at 298 K.

The first half of the paper shows how a least-squares analysis may be applied to a bilinear model relating the uncorrected reflection coefficients observed with an open-ended probe to the complex permittivities of dielectric materials at the probe aperture. A large number of reference materials should be chosen, with dielectric data available from independent sources of varying accuracy in the literature, and the best-fit parameters derived for the bilinear model. The absolute residuals in epsilon ` and epsilon ``between the model and the reference data may then be obtained: they encompass errors in the data, in the measurements and in the model. Laboratory measurements on 17 different materials are intercompared in this way in the second half of the paper. The frequency range is from 20 MHz to 2 GHz and the residuals are compared at +25 degrees C and -20 degrees C using probe diameters of 7 and 22 mm. For the smaller probe and with a range of relative permittivities from 1 to 80, residuals rarely exceed +or-1 in epsilon ` or epsilon `` for any material from 100 MHz upwards; for the larger probe residuals are satisfactory down to 20 MHz though not up to 2 GHz. They are significantly reduced if the range of permittivities is more restricted (which is clearly a limitation of the model) and they are significantly reduced at -20 degrees C if a new calibration is adopted, rather than using the model parameters determined from measurements at +25 degrees C.