Table of contents

An overview is given on the field of the terahertz-frequency electromagnetic waves, their properties and emerging applications. Some widespread sources with their advantages and drawbacks are presented; an emphasis is placed on the parametric generation sources that we build and use in our research. Several applications are then described: imaging techniques based on transmission, reflection and scattering, results in chemical imaging and electric field imaging, as well as linear scanning and the measurement of optical properties of highly-absorbing liquids.

This paper describes a compact imaging Fourier transform spectrometer with high numerical aperture. In comparison with other optical arrangements in which extended interferometer paths are required for the inclusion of dispersion compensation optics, this technique utilizes a rudimentary cubic beam splitter based Michelson interferometer with minimal optical path so that the numerical aperture of the system is maximized. Mathematical modelling is presented showing that the fringe distortions caused by the dispersion in the cubic beam splitter can be entirely removed without any loss of the spectral information. An illustration of the power of the technique is given classifying between different plant foliage performed using a Fisher discriminant function based optimal linear filtering.

A novel passive wireless-interrogation strain sensor is presented in this paper. The sensor employs a planar inductor with a series connected interdigital capacitor to eliminate the wire connection for power supply and data transmission. The sensor is activated by electromagnetic waves and the resonant frequency of the sensor is interrogated remotely with a single loop antenna by applying an oscillating signal to the antenna and monitoring the frequency response of the voltage across it. The prototype sensor and reader were designed and fabricated. The results of calibration on a constant-strain cantilever beam show great linearity and sensitivity. The innovative wireless strain sensing technology described herein has demonstrated a great potential to extend its applications in structural health monitoring, damage detection, condition-based maintenance, failure prevention and non-destructive evaluation.

Existing methods of improving particle filters mainly focus on two aspects: designing a good proposal distribution before sampling and allocating particles to a high posterior area after sampling. An auxiliary particle filter (APF) is one such simple algorithm belonging to the former aspect, which generates particles from an importance distribution depending on a more recent observation. Its weakness is that it requires a large number of particles. On the other hand, a kernel-based particle filter (KPF), which belongs to the latter aspect, is able to greatly reduce the number of particles required and is still able to capture good characteristics of the posterior density. However, a KPF does not take the current observation into account. To utilize their respective strengths, a new algorithm is proposed in this paper with the combination of an APF and a KPF, the APF for designing good proposal density and the KPF for exploring the dominant mode of the posterior density. Experimental results in several real-tracking scenarios demonstrate that the integrated algorithm surpasses the standard particle filter (SPF) when encountering weak dynamic models. Moreover, the proposed algorithm is also able to achieve a comparable performance with KPF whilst reducing computational cost.

Active shielding is commonly used to measure remote grounded capacitive sensors because it reduces the effects of both external noise/interference and parasitic capacitances of the shielded cable. However, due to active shielding, the measurement circuit can become unstable and inaccurate. This paper analyses these limitations theoretically and experimentally, and then provides guidelines for improving the performance of active shielding. One of the key points is the selection of the bandwidth of the amplifier that drives the shield of the coaxial cable. A wide bandwidth improves accuracy, but a narrow bandwidth improves stability. Therefore, there is a trade-off between stability and accuracy with respect to the bandwidth of the amplifier.

Phasemaps obtained by phase shifting techniques in digital photoelasticity contain ambiguous zones. To obtain total fringe order by phase unwrapping, the phasemap should be free of ambiguous zones. A new method is developed, which uses a dark field image for ambiguous zone identification and its correction. This methodology is explained and validated by solving a benchmark problem. As ambiguous zones are of arbitrary shape, an advanced boundary extraction method developed in-house is used for effecting the correction in practical problems. The performance of the new methodology is demonstrated by using the problem of a ring under diametral compression and a slice cut from a stress frozen model.

This paper reports on a method for detecting three-dimensional particle positions and conducting three-dimensional microflow diagnostics in a microvolume via a three-pinhole defocusing concept. A simple setup and an easy detection method are described. The calibration-based defocusing method is suggested in place of formulae introduced through geometric analyses in previous studies. Depth calibration was performed in a microvolume, and X–Y compensation functions were obtained. By using the calibration functions, three-dimensional particle positions can be calculated at a sub-micron depth resolution. The effects of pinhole masks made with different pattern sizes are also described. The developed method was applied to a microflow in a micro backward-facing step. Time-resolved particle trajectories and three-dimensional volumetric velocity fields at a depth of 50 µm were obtained and are presented here.

In this paper, we analyse the applicability of dynamic speckles for distance measurement to any rough surface. The technique is based on spatial filtering of a speckle pattern generated when the object surface is scanned by a laser beam deflected from an acousto-optic device. An extremely short response time was achieved because of the high scanning speed provided by the acousto-optic deflector. We have developed a prototype of the distance-measuring system and studied its performance. The measurement setup has a very simple configuration. The distance can be measured within as short a time as 50 ns, but with rather high inaccuracy caused by the stochastic nature of the speckle effect. The data averaging is easily implemented within a single scan and allows us to achieve an accuracy of 110 µm within the time window of 2.5 µs. An analysis of the factors affecting the performance of the proposed technique is carried out. It is shown that the response time can be diminished by an order of value using an acousto-optic crystal with higher acoustic speed. The proposed technique may be useful for monitoring the geometrical parameters of fast moving or rotating surfaces in various industrial applications.

A hybrid sensor for measuring longitudinal surface displacement including surface undulation and surface roughness over a wide range from nm to a few hundred µm has been developed. Two main sensors are incorporated in a single body, i.e., it is a hybrid system, with one sensor based on laser reflection for nm-scale measurement, while the other is based on imaging the irradiated portion for µm-scale measurement. A preliminary experiment using this hybrid sensor showed that the sensor for measuring surface undulation has a longitudinal resolution of 1 nm and a measurement frequency of 24 Hz, and that the sensor for measuring surface roughness has a longitudinal resolution of 2 µm, a measurement range of ±300 µm and a measurement frequency of a few hundred Hz. This hybrid sensor is relatively compact and its cost/performance ratio allows its practical use.

This contribution demonstrates that a one-end free capsular fibre Bragg grating, well documented as a strain-free temperature sensor head to discriminate temperature effect from a fibre Bragg grating strain sensor, successfully functions as an acousto-ultrasonic sensor. It implies that both built-in strain and temperature compensation sensors can be utilized for acousto-ultrasonic damage detection. The wave sensing principle of the capsular fibre Bragg grating is explained on the basis of the existence of a fibre-guided wave. Furthermore, it is reported that the capsular fibre Bragg grating is a resonant acousto-ultrasonic sensor through frequency analysis of the sensor responses. Finally, we present a method capable of controlling the resonance frequency of the capsular fibre Bragg grating.

Volume estimation is particularly important in clinical medicine. Accurate volume estimation can provide quantitative information from which the follow-up therapy can be derived. In this paper, an efficient approach to volume estimation in a sequence of freehand ultrasound images is proposed. By integral of vector areas along the path of centroids of serial cross-sections, 3D volume estimation can be represented as 2D area calculation, where a fast mapping algorithm generating 2D representation is presented so that the position of interpolation points can be calculated with high efficiency. Meanwhile, to improve the accuracy, the cubic spline with second-order continuity is proposed for interpolation of 2D representation. Volume estimation on simulating phantoms for parallel cutting, fan cutting and random cuttings is provided. The experimental results show that the 2D representation generated by the fast mapping algorithm is highly efficient with less than 0.001 ms for 100 cross-sections. Quantitative comparisons show that the proposed interpolation method can approximate the original volume more precisely as compared to the Catmull–Rom (CR) spline, especially in the case of small number of cross-sections. In all cases, our approach can obtain accurate results at an error of less than 2% for ten cross-sections. Additionally, volume estimation on a high intensity focused ultrasound (HIFU) lesion based on linear B-scan and rotational B-scan sequential images are also performed. The experiments show that the proposed approach is promising and may have potential in clinical applications.

Previously, we developed a simple semi-theoretical calibration procedure for a pulsed photoacoustic set-up. Also, we analysed the simplest, idealized case: top hat spatial profile of the laser beam and an exponential decay of excitation energy. The spatial profile of the laser beam is usually considered to be top hat or Gaussian in the photoacoustic measurements. In reality, there are always small discrepancies. Also, in these measurements the excitation energy decay is usually considered to be an exponential one. This assumption is commonly valid. Still, a non-exponential decay can exist as well. In this paper, we have examined the influence of these discrepancies on the measurement of the vibrational-to-translational relaxation time, as well as on the calibration of the photoacoustic set-up. We have theoretically examined gas mixtures in the case of pulsed excitation (multiphoton regime). Then, we have verified theoretical conclusions in one experimental example. It has been shown that the non-ideal profile and excitation energy decay can significantly influence the measurement of the vibrational-to-translational relaxation time. Also, it has been shown that they do not significantly influence the calibration of the photoacoustic set-up.

A scanning photo acoustic technique to determine the thermal transport parameters, thermal diffusivity, effusivity and conductivity, as well as heat capacity of paint coatings on different backings is described. These parameters are obtained by measuring the normalized photo acoustic phase values from paint coatings of varying thicknesses and then fitting the experimental data with the theoretical expression for phase. Results are reported on four different black paint coatings on a metallic backing. The values obtained for thermal diffusivity are comparable to those reported in the literature following other techniques. Measurements have also been carried out on paint coatings over backings that are good as well as poor thermal conductors. No significant changes in the values of the thermal parameters of paint coatings could be detected for different backing materials with widely differing thermal properties.

Infrared emissivity is a necessary parameter for computing models to predict road surface status and pavement temperature irrespective of the weather situation. In this work a new experimental device based on the indirect method was developed for the measurement of surface emissivities. The surface is exposed to modulated isotropic infrared radiation. The intensity reflected by the surface of the sample in a given direction is measured by a detector operating in the spectral range 1–40 µm. This large spectral range allows measurement of the total hemispheric emissivity defined in this case as emissivity. The effect of the temperature modulation frequency, surface composition and surface roughness on the emissivity measurements was investigated. The results show good ability of the device for the determination of emissivities at room temperature.

As more and more features are packed onto smaller silicon chips, there is a need to optimize wafer fabrication process conditions to the fullest. Closed-loop control is one approach for meeting the rising need for more stringent control over the absolute and spatial temperature of wafers undergoing the post-exposure bake (PEB) process. For an automatic control loop to be implemented successfully, the feedback signals must be accurate and reliable. However, in situ temperature measurement systems based on either contact or non-contact sensors cannot achieve the required accuracy. Another challenge is to measure the wafer temperature without disrupting the manufacturing process. In this paper, a non-intrusive method that uses the readings from two contact sensors and the recursive least-squares algorithm to estimate the sensor model is described. When the sensor model is identified, the inverse model method is applied to achieve fast and accurate temperature measurements. Experimental results demonstrate that the algorithm is able to provide accurate real-time temperature measurement, which may be used as the feedback signal to achieve closed-loop control.

This work demonstrated the feasibility of detecting severe acute respiratory syndrome associated coronavirus (SARS-CoV) using microcantilever technology by showing that the feline coronavirus (FIP) type I virus can be detected by a microcantilever modified by feline coronavirus (FIP) type I anti-viral antiserum. A microcantilever modified by FIP type I anti-viral antiserum was developed for the detection of FIP type I virus. When the FIP type I virus positive sample is injected into the fluid cell where the microcantilever is held, the microcantilever bends upon the recognition of the FIP type I virus by the antiserum on the surface of the microcantilever. A negative control sample that does not contain FIP type I virus did not cause any bending of the microcantilever. The detection limit of the sensor was 0.1 µg ml⁻¹ when the assay time was <1 h.

This paper describes the failure analysis of an uncooled infrared focal plane array (IRFPA) under a high-g inertial load system using finite element simulation and experimental validation methods. The uncooled IRFPA, responding to a source of infrared (IR) radiation with spectral range from 8 µm to 14 µm, is a cantilever array, which consists of two materials with mismatched thermal expansion coefficients. The radiance distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array using a visible optical readout method. Based on this principle, room-temperature infrared imaging was developed under a static gravity environment, as described in our previous paper (Li C et al 2006 Meas. Sci. Technol.17 1981–6). But under a dynamic inertial load, the rotation angle of every pixel includes not only the thermal–mechanical part but also a part induced by the inertial load. In the elastic deformation range, with a linearly increasing acceleration, the deformation angle induced by the inertial load increases linearly, which is validated by finite element simulation. This linear change in deformation, which can be subtracted from the total rotation angle in the optical readout using certain arithmetic, will not influence the imaging result. It is noteworthy that failure stress will occur when the deformation angle induced by the inertial load moves into the plastic deformation range, and the optical readout cannot image the IR object. Through finite element simulation the critical load resulting in IRFPA failure is 2715g, and this can be validated through impact using a Hopkinson bar after the IRFPA is placed in vacuum. By finite element simulation, the initial IRFPA surface profile without IR radiance after the 2715g load showed a conicoid characteristic. Simulation of the failure analysis of the uncooled IRFPA under 2715g acceleration predicts the military application of IRFPAs for an uncooled infrared imaging system in the high-g tactical range.

A new eddy currents non-destructive evaluation technique for the investigation of deep defects is presented. The method joins the favourable features of the pulsed eddy currents approach with the peculiar properties of the Galois sequences to extend the detection area down to large depths. The proposed method has been successfully tested on a benchmark; the experimental results have been compared with the standard pulsed method and with numerical simulations. The comparisons confirmed the accuracy of the method and its effectiveness in allowing a significant improvement in deep defect detection.

A wavelet-based bootstrap method is proposed to generate surrogate data from inertial sensor noise time series and to construct bootstrap-based confidence intervals of selected parameters which are used to characterize their noise performance. The Allan variance, its links with wavelets and the whitening action of wavelet decompositions applied to long-memory stochastic processes are considered in developing the theory behind the proposed method. The conditions for the wavelet-based bootstrap method to work are discussed in the face of idiosyncrasies of inertial sensors, especially microelectromechanical systems-based (MEMS) inertial sensors. Computer simulation experiments demonstrate the validity of the method and its power in doing the statistical inference from a moderately small-size dataset; additionally, the wavelet-based bootstrap method is applied to the task of stochastic error characterization, in the case of a MEMS orientation sensor, which integrates a tri-axis gyro and a tri-axis accelerometer.

In this paper, a novel electrical time domain reflectometry (ETDR) measurement technique capable of measuring moisture distribution profile in a porous medium is presented. A signal calibration algorithm to interpret the ETDR waveform based on an empirical relation between moisture content and differential impedance of the medium was developed. The transient distribution of the moisture content in a concrete block covered with fibre reinforced polymer laminate on one end surface was experimentally measured. The experimental results were then compared with the solution of a finite element analysis. Good agreement was shown for the trend of the transient moisture distribution profile. It was demonstrated that the ETDR distributed moisture sensor developed in the current study was capable of measuring the variation of the moisture content distribution in a porous medium.

A new approach to measure Curie temperature (T_C) of materials with phase transition in the range from −5 °C to +70 °C is presented. In this work, measurements on potassium lithium tantalate niobate (KLTN) crystals are used to demonstrate the method. In this new approach the measurement is done directly over KLTN plates after cutting, without any additional processing. Contacts of conductive rubber are used as measurement points on the plates. Compared to traditional methods of T_C measurement, the presented method is faster, less expensive, non-destructive and easily enables the T_C topography on KLTN plates. The measurement set-up presented in this paper is fully automated and can measure T_C of 64 points on plates with area up to 40 mm × 40 mm with a resolution of 0.1 °C.

The remote field eddy current technique is used to inspect conductive pipes and to estimate the dimensions of flaws liable to exist in the conductive material. A data set which contains observations for calibrated flaws is used to learn the processing. This learning problem is addressed in the context of a small size data set in which the overfitting problem is often present. To obtain a robust estimation of flaw size, this problem is minimized as follows: the estimation of flaw size uses parameters whose number is chosen the smallest possible. To obtain this set of parameters, three approaches are proposed. A reduction of the data space dimension by means of principal component analysis and parametric modelling is carried out. Then, for both cases a bilinear regression is performed to estimate the flaw size. The third approach uses a neural network to learn the processing and to directly calculate an estimate of flaw size. An MDL (minimum description length) criterion is used in the learning step to choose the smallest number of required parameters and thus to avoid the overfitting risk. The three approaches are compared in terms of accuracy and robustness. A cross-validation test is carried out on noisy data.

Turbulent flows are often encountered in common practice, usually at high Reynolds number. The development of Lagrangian stochastic models of these flows requires knowledge of Lagrangian statistics. To study the Lagrangian statistics of turbulent pipe flow, a dedicated 3D particle tracking velocimetry set-up has been designed. In this paper, design parameters, selection criteria and solutions are discussed. The measurement accuracies are studied in detail. Typical 3D particle tracking velocimetry results for turbulent pipe flow are compared and found to be in good agreement with direct numerical simulations.

The paper highlights and provides solutions to the difficulties encountered with electrical probe measurements performed on a miniature, high capacitive impedance plasma device excited at 13.56 MHz. It is shown that a proper calibration of the phase angle between the circuit current and load voltage signals is required when commercial capacitive voltage probes (Tektronix P6139A and P5100 models) are used. A method to calculate the electrical characteristics of the plasma source and accounting for this calibration is described. The P6139A probe, which has the largest input capacitance and shortest cable length, introduced the smallest phase angle (−2 ± 1°), while the P5100 probe, which is used for higher input voltages and has a longer cable length, introduced a considerably larger phase angle (−34 ± 1°) for typical resistive loads. Simple circuit models are developed in an attempt to isolate the phase induced by the probe capacitance and cable length. The application of the proposed calibration to a miniature atmospheric pressure glow discharge source considerably reduced the error in the calculation of the power dissipated in the plasma device, though it remained relatively high (1 W ± 42%) due to the highly capacitive nature of the device.

Reliable and effective sensors for the accurate detection of hydrogen in air are essential for the safe operation of fuel cells, hydrogen fuelled systems and production, distribution and storage facilities. The paper presents a semi-automated facility designed and built for testing and validating the performance of such sensors under a range of conditions, representative of those to be encountered in service. Examples of characterization of some common sensor types are described as an example of the facility's functioning and of test methodologies.

This paper explores the limitation that is imposed on the spatial resolution of electrical impedance tomographic images by the relatively low numbers of independent projections. In the present work the levels of recoverable image content are improved by attaching electrodes to a rotating central impeller. Incorporating the rotational motion of the electrode array into an optimized measurement strategy provides more independent measurements without compromising the stability of a consistently regularized inverse solution. A new measurement strategy, together with a mesh mapping algorithm, delivers improved results, in terms of the image contrast, from experiments on a small laboratory vessel. Initial findings suggest that the use of non-stationary electrodes has the potential to produce images with four times the amount of independent information over a conventional EIT measurement technique. The challenges in implementing an impeller-mounted electrode array are briefly discussed.

Linear arrays of electrodes in conjunction with electrical impedance tomography have been used to spatially interrogate industrial processes that have only limited access for sensor placement. This paper explores the compromises that are to be expected when using a small number of vertically positioned linear arrays to facilitate 3D imaging using electrical tomography. A configuration with three arrays is found to give reasonable results when compared with a 'conventional' arrangement of circumferential electrodes. A single array yields highly localized sensitivity that struggles to image the whole space. Strategies have been tested on a small-scale version of a sludge settling application that is of relevance to the industrial sponsor. A new electrode excitation strategy, referred to here as 'planar cross drive', is found to give superior results to an extended version of the adjacent electrodes technique due to the improved uniformity of the sensitivity across the domain. Recommendations are suggested for parameters to inform the scale-up to industrial vessels.

Electronic nose (e-nose) architectures usually consist of several modules that process various tasks such as control, data acquisition, data filtering, feature selection and pattern analysis. Heterogeneous techniques derived from chemometrics, neural networks, and fuzzy rules used to implement such tasks may lead to issues concerning module interconnection and cooperation. Moreover, a new learning phase is mandatory once new measurements have been added to the dataset, thus causing changes in the previously derived model. Consequently, if a loss in the previous learning occurs (catastrophic interference), real-time applications of e-noses are limited. To overcome these problems this paper presents an architecture for dynamic and efficient management of multi-transducer data processing techniques and for saving an associative short-term memory of the previously learned model. The architecture implements an artificial model of a hippocampus-based working memory, enabling the system to be ready for real-time applications. Starting from the base models available in the architecture core, dedicated models for neurons, maps and connections were tailored to an artificial olfactory system devoted to analysing olive oil. In order to verify the ability of the processing architecture in associative and short-term memory, a paired-associate learning test was applied. The avoidance of catastrophic interference was observed.

Magnetic compasses are widely used in vehicle navigation systems to measure the vehicle headings with respect to the Earth's magnetic north. Due to the local variation of the Earth's magnetic flux density and the induced magnetic field of the magnetized vehicle body, continuous calibrations of magnetic compasses are required to maintain accurate heading measurements. In this paper two different online compass calibration methods, one based on the parameter adaptation algorithm and the other based on the functional learning algorithm, are developed to achieve online self-calibration function for a flux-gate compass using GPS heading measurements as reference signals. Simulation and experiment results show that the algorithms are effective in removing the magnetic biases and providing a reliable method to improve the magnetic compass performance.

Numerous transient methods have been described and applied to measure the thermal conductivity, but none has reached the popularity of the line heat source (LHS) technique, also known as the transient hot wire method. One of the many advantages of the LHS is that it allows us to measure the thermal conductivity directly and almost independently of the otherwise influencing density and specific heat. In some cases, the LHS method cannot be applied because the probe cannot be made thin enough or long enough to regard the heat source as infinitely long. We study the transient behaviour of torus-shaped heaters numerically, and we propose a probe design that brings back the advantages of a LHS, at the expense of a moderate complexity added to the set-up; guard heaters above and below the heated torus minimize vertical heat flux and create a transient behaviour of the probe that is remarkably similar to that of a LHS. The remaining errors made in the determination of the thermal conductivity are ≈5 to 10% and are tolerable in many applications, and can be further reduced to less than 1% by modelling.

A new atomic beam source for use in laser-based experiments is described and characterized. The physically collimated source which has been tested using calcium, produces an atomic beam with low angular divergence and narrow transverse Doppler profile, as measured using fluorescence techniques with a near resonant laser beam. The low angular divergence of the source is essential for new experiments which study super-elastic scattering of electrons from laser prepared targets within a magnetic field, since the atomic beam must pass through a narrow gap between the coil windings. The beam density for calcium is calculated to be 2.8 × 10⁹ atoms cm⁻³ when the source is operated at a temperature of 1090 K. This is sufficient to produce good electron energy loss and super-elastic scattering signals, while ensuring negligible radiation trapping within the atomic beam.

Ink-jet microdispensing technology was used to develop an instrument for the quantitative determination of the olfactory threshold. An electrical pulse applied to the piezoelectric element produces a deformation that is transmitted to the fluid which results in a drop of fluid being ejected through the orifice mounted at one end of a piezoelectric tube. An electronic console actuates the piezoelectric dispensing elements and controls the number of drops that are dispensed and evaporated to create a fragrance cloud. The number of drops that are generated, evaporated and presented to the patient's nose for detection is adjusted according to a preset algorithm until the patient's threshold is discovered. Neurodegenerative disease patients tested with the developed olfactometer showed a significant elevation of their olfactory threshold as compared to normal controls. This result agrees with literature studies that indicate the sense of smell is one of the first affected by neurodegenerative disease. Through its precise control and detection capability, the digital olfactometer described in this paper can be used as an early screening tool for neurodegenerative disease through olfactory threshold determination.

A phase unwrapping method is developed to mathematically increase the depth-of-field for the 3D optical measurement of objects with laterally discontinuous surfaces, which contain disconnected high aspect ratio regions. This method is applied for laser holographic interferometry precision measurements. The phase wrap identification at boundary pixels, masking and recovery, dynamic segmentation and phase adjustment are developed to overcome the divergence problem in phase unwrapping of laterally discontinuous surfaces. An automotive automatic transmission valve body is applied as an example to demonstrate the developed method. Experimental results demonstrate that the proposed methods can efficiently unwrap the phase to increase the depth-of-field for laterally discontinuous surfaces. Effects of segment size and width of overlapped regions on the computational efficiency are investigated.

The design of a reference metal halide discharge lamp is presented. This lamp is meant as a common study object for researchers working on metal halide discharge lamps, who by using the same design will be able to compare results between research groups, diagnostic techniques and numerical models. The lamp exhibits all interesting plasma physical, chemical and material science problems, which are currently under investigation in various laboratories. The lamp filling is relatively simple and the design symmetric to allow realistic numerical modelling. Furthermore, it is adapted to enable the use of various diagnostics.

The principles of operation and design of a compact original optical polarization modulator are described. The proposed device can simultaneously and independently induce small changes in the ellipticity and polarization plane direction of a polarized light beam. The use of the modulator for simultaneous detection of low-level linear birefringence and dichroism is presented.