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Chronic wound monitoring can provide personalized pathophysiological information for wound management and treatment. Continuously monitoring the wound milieu via the holographic pH sensor can reflect the wound healing processes. However, the integration with wearable devices is hindered by its inherently restricted interrogation angle dependency within 5°. Herein, a ball bearing‐based double photopolymerization method is developed to fabricate holographic pH sensors with a broader interrogation angle range of 15°–60° in wound exudates. The fabricated holographic pH sensor is then integrated with the flexible ultrathin polyurethane substrate, which replays a total Bragg peak shift of approximately 150 nm with physiological pH changes from 7.00 to 8.75. The conformable holographic pH sensing bandages demonstrate the ability to quantify the pH value under various bending manipulations, simulating the mounting on the body surface. The reversibility in artificial wound exudate demonstrates the durability and capability of real‐time pH monitoring in the wound milieu with minimal effect on the replay wavelength. The addition of electrolytes, albumin, urea, uric acid, lactate, and glucose does not interfere with the readout over the physiological pH range of wound exudates. The obtained conformable holographic sensing bandage benefits the wound healing process monitoring through colorimetric interrogation at point‐of‐care (POC) settings. [ABSTRACT FROM AUTHOR]

This paper presents a holographic sensor based on reflection holograms recorded in the commercial photopolymer Bayfol® HX 200. The recording geometry and index modulation of the hologram were optimised to improve accuracy for this specific application. The sensor was subjected to tests using various analytes, and it exhibited sensitivity to acetic acid and ethanol. The measurements revealed a correlation between the concentration of the analyte in contact with the sensor's surface and the resulting wavelength shift of the diffracted light. The minimum detectable concentrations were determined to be above 0.09 mol/dm3 for acetic acid and 5% (v/v) for ethanol. Notably, the sensors demonstrated a rapid response time. Given that ethanol serves as a base for alcoholic beverages, and acetic acid is commonly found in commercial vinegar, these sensors hold promise for applications in food quality control. [ABSTRACT FROM AUTHOR]

Photopolymers are widely utilized as holographic recording media due to their ease of preparation and lack of wet chemistry post-processing. Holographic sensors constructed from a pH-sensitive photopolymer film have several applications in biosensors and the medical diagnostic field. However, the stability of photopolymer films in an aqueous medium is one of the most important challenges in their application for biosensing. Furthermore, the pH of the solution is another important parameter for biochemical reactions. In this work, we compared the pH sensitivity and stability of our holographic grating against two widely utilized classes of buffers; Phosphate Buffered Saline (PBS) and Tris-Acetate-EDTA (TAE) at two different pH values of 7.36 and pH 8.3, respectively. It was observed that a physiological pH (pH 7.4) had a negligible effect on the diffraction efficiency of the holographic sensor while it significantly deteriorated at a higher value of ~pH 8.3. This high sensitivity towards the minute pH difference of our holographic sensor could potentially be exploited for pH-based biosensing applications such as urea detection. [ABSTRACT FROM AUTHOR]

This paper presents a holographic sensor based on reflection holograms recorded in the commercial photopolymer Bayfol® HX 200. The recording geometry and index modulation of the hologram were optimised to improve accuracy for this specific application. The sensor was subjected to tests using various analytes, and it exhibited sensitivity to acetic acid and ethanol. The measurements revealed a correlation between the concentration of the analyte in contact with the sensor’s surface and the resulting wavelength shift of the diffracted light. The minimum detectable concentrations were determined to be above 0.09 mol/dm3 for acetic acid and 5% (v/v) for ethanol. Notably, the sensors demonstrated a rapid response time. Given that ethanol serves as a base for alcoholic beverages, and acetic acid is commonly found in commercial vinegar, these sensors hold promise for applications in food quality control.

We report on the optical characterization of very high-efficiency and high-resolution holographic volume phase transmission gratings. The gratings are recorded in a new photo-polymerizable mixture made by epoxy-resin and multi-acrylate. The epoxy-resin used is known to make tenacious acrylate-based films. The holographic mixture contains two photo-initiators, the synergic effect of which enables a reliable photo-polymerization process in the visible region of the electromagnetic spectrum. The recorded holograms are mechanically stable, show long-term temporal stability and very high values of diffraction efficiency, coupled with good angular selectivity due to a relatively narrow band of wavelengths. We measured the intensity of the transmitted beam and calculated the intensity of the diffracted beam at different wavelengths, deriving the refractive index modulation and the grating pitch by fitting the experimental data with a slightly modified theoretical approach. These kind of mixtures can be used in several fields of application, such as chemical or bio-sensors, high resolution optical sensors, high-density optical data storage, encryption and security. [ABSTRACT FROM AUTHOR]

Holographic sensors are optical devices capable of tuning reflection wavelength, dependent upon nanostructured variations in refractive index. Computational modelling is utilized to simulate the recording and swelling characteristics of developed doubly photopolymerized (DP) holographic sensors. The holographic devices simplify fabrication processes, reduce financial costs, and improve biocompatibility. A holographic grating is achieved through in situ photopolymerization of a highly crosslinked polymer to produce nanostructured refractive index modulation. The unique swelling characteristics DP holographic sensors possess necessitate the development of system‐specific computational modelling. Hydrogel parameters, including film thickness, refractive index change, layer number, and external medium refractive index are examined for their effect on reflection spectra. Optimized computational models are utilized to study the effect of differential swelling rates of individual layer spacings on sensor response, indicating an idealized reduction in a swelling of 50% for the highly crosslinked region. A 2D photonic crystal geometry with additional periodicity is developed, to inform further sensor design opportunities. Optimized parameters for both 1D and 2D photonic structures will assist the further development of DP holographic sensors. [ABSTRACT FROM AUTHOR]

Photopolymers are widely utilized as holographic recording media due to their ease of preparation and lack of wet chemistry post-processing. Holographic sensors constructed from a pH-sensitive photopolymer film have several applications in biosensors and the medical diagnostic field. However, the stability of photopolymer films in an aqueous medium is one of the most important challenges in their application for biosensing. Furthermore, the pH of the solution is another important parameter for biochemical reactions. In this work, we compared the pH sensitivity and stability of our holographic grating against two widely utilized classes of buffers; Phosphate Buffered Saline (PBS) and Tris-Acetate-EDTA (TAE) at two different pH values of 7.36 and pH 8.3, respectively. It was observed that a physiological pH (pH 7.4) had a negligible effect on the diffraction efficiency of the holographic sensor while it significantly deteriorated at a higher value of ~pH 8.3. This high sensitivity towards the minute pH difference of our holographic sensor could potentially be exploited for pH-based biosensing applications such as urea detection.

We report on the optical characterization of very high-efficiency and high-resolution holographic volume phase transmission gratings. The gratings are recorded in a new photo-polymerizable mixture made by epoxy-resin and multi-acrylate. The epoxy-resin used is known to make tenacious acrylate-based films. The holographic mixture contains two photo-initiators, the synergic effect of which enables a reliable photo-polymerization process in the visible region of the electromagnetic spectrum. The recorded holograms are mechanically stable, show long-term temporal stability and very high values of diffraction efficiency, coupled with good angular selectivity due to a relatively narrow band of wavelengths. We measured the intensity of the transmitted beam and calculated the intensity of the diffracted beam at different wavelengths, deriving the refractive index modulation and the grating pitch by fitting the experimental data with a slightly modified theoretical approach. These kind of mixtures can be used in several fields of application, such as chemical or bio-sensors, high resolution optical sensors, high-density optical data storage, encryption and security.

Phase-shifting digital holography is widely considered to be a groundbreaking method to quantitatively investigate the phase distribution of specimens, such as living cells. The main flaws of this method, however, are that the requirement for several sequential phase-shifted holograms eliminates the possibility of single-shot imaging and complex configurations would also increase the temporal noise. The present paper aims to validate a single-shot, common-path, phase-shifting digital holographic microscopy, employing a self-referencing geometry. A Ronchi ruling, located in the Fourier plane of a standard microscopic imaging system, produces multiple replicas of sample information in the image plane. The phase retrieval algorithm is performed by superposition of the sample-free portion of each replica with the object information, and requires at least three adjacent diffraction orders. To evaluate the performance of the proposed method, the phase distribution of silica microspheres as a test sample and the morphology of red blood cells as a biological specimen are determined. This configuration offers improved temporal stability in comparison with previously reported Mach–Zehnder interferometers, and may serve as an alternative for real-time surveying of nanometric and subnanometric fluctuations of living microscopic specimens. [ABSTRACT FROM AUTHOR]

Highlights • Hydrogel based holographic sensor as an optical sensing platform is proposed to response the characterization of solution. • Methacrylic acid with carboxyl groups functionalizes the polymer for improving the sensing selectivity. • The reversibility experiment reveals the applicability of the novel holographic sensor. Abstract We proposed a novel photosensitive hydrogel based holographic sensor for the detection of hydrogel swelling and hence the chemical concentrations, which formed by thermally polymerizing 2-hydroxyethyl methacrylate. Holographic volume grating recorded in the hydrogel as an optical sensing platform was employed in response to the hydrogel deformation induced by target molecules. Co-monomer methacrylic acid with carboxyl groups functionalized the polymer matrix for improving the selectivity. Peak wavelength shift of the diffraction spectrum was a significant parameter in sensing the pH value of the buffer. The extracted time constant of the wavelength shift curve evaluated the sensitivity of the novel holographic sensor. There were good exponential relations between peak wavelength and pH value with various thicknesses. The novel sensor could be considered as an effective platform for sensing the analytes concentration of solution. The reversible measurement experimentally demonstrated the repeatability of the holographic sensor. The novel photosensitive hydrogel and its sensor provided a probability for sensing the performance of solution and accelerating the development of water resistant holographic sensor based on polymer hydrogel. [ABSTRACT FROM AUTHOR]

Holographic sensor based on photopolymer has been much attention due to simple process,low cost,excellent performance,and obvious optical phenomenon. The fringe space recorded in the materials is changed when the environmental condition changes,especially temperature and humidity. It provides wavelength shift of diffraction peak,and the corresponding sensing process can be achieved. Temperature as a significant parameter can directly affect the sensing measurement of holographic sensor. This paper developed a novel N-isopropylacrylamide photopolymer with thermal-sensitivity,and the corresponding novel sensor based on the polymer. The comparison of thermal-sensitive capacity tests indicates an obvious improvement of * wavelength shift in response to the environmental conditions in novel photopolymer system. Temperature and humidity are two significant parameters for the holographic sensing response. The experimental result shows the blue shift of peak wavelength in exponential form at corresponding environmental conditions. In view of the evident experimental phenomenon and low cost,the corresponding experimental setup would be able to make the student understand the development of holographic optical elements and application area. [ABSTRACT FROM AUTHOR]

The increasing consumption of illicit drugs has become a worldwide social and medical problem. Eradicating the supply and use of these drugs requires the development of devices that provide a fast, selective and simple response in seized powder samples. This paper describes a novel strategy for the design and development of a holographic sensor modified with a rationally designed receptor for the detection of cocaine. The receptor was designed by reviewing protein–cocaine interactions, particularly those of human carboxylesterase-1 and catalytic monoclonal antibody GNL7A1, and constructing a four-component Ugi library of putative cocaine-binding ligands. A hybrid hydrogel of poly (2-hydroxyethyl methacrylate–co-ethylene dimethacrylate-co-methacrolein) was used as the carbonyl source for the Ugi reaction. A Bragg diffraction grating comprising gold nanoparticles was fabricated in the polymer gel and the replay wavelength of the combinatorial library of Ugi-modified holographic sensors measured via a spectrophotometer in response to cocaine as a function of pH and ionic strength. A smartphone-based instrument and cloud-based algorithm was developed, optimised with training and test samples of cocaine and used to assess the presence of cocaine in seized field samples. These findings confirm the potential application of this analytical method in field testing for illicit drugs. [ABSTRACT FROM AUTHOR]

The transmission spectrum of a holographic sensor (silver nanograins embedded in a polymer matrix) is shown to be well described by expressions for the Rayleigh light scattering and absorption by silver nanograins. The optical characteristics of the medium are determined in the Maxwell Garnett approximation. In the presence of a holographic structure, a dip appears in the spectrum. A possibility of obtaining the approximating curves depends on the approximation range. The spectra are well approximated both in the presence and in the absence of an interference structure. For different approximation ranges, the dip parameters coincide despite the values of the background parameter associated with absorption can differ significantly. [ABSTRACT FROM AUTHOR]

We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner–Freedman window and derive a universal formula for the holographic speed of sound for any mixed boundary conditions of the scalar field. As an example, we numerically construct the most general class of planar black holes coupled to a single scalar field in the consistent truncation of type IIB supergravity that preserves the S O ( 3 ) × S O ( 3 ) R-symmetry group of the gauge theory. For this particular family of solutions, we find that the speed of sound exceeds the conformal value. From a phenomenological point of view, the fact that the conformal bound can be violated by choosing the right mixed boundary conditions is relevant for the existence of neutron stars with a certain mass-size relationship for which a large value of the speed of sound codifies a stiff equation of state. In the way, we also shed light on a puzzle regarding the appearance of the scalar charges in the first law. Finally, we generalize the formula of the speed of sound to arbitrary dimensional scalar-metric theories whose parameters lie within the Breitenlohner–Freedman window. [ABSTRACT FROM AUTHOR]

The synthetic holographic stereogram printing technique can achieve a three-dimensional (3D) display of a scene. The development and research status of the synthetic holographic stereogram printing technique is introduced in this paper. We propose a two-step method, an infinite viewpoint camera method, a single-step Lippmann method, a direct-write digital holography (DWDH) method and an effective perspective images’ segmentation and mosaicking (EPISM) method. The synthetic holographic stereogram printing technique is described, including the holographic display with large format, the large field of view with no distortion, the printing efficiency, the color reproduction characteristics, the imaging quality, the diffraction efficiency, the development of a holographic recording medium, the noise reduction, and the frequency response analysis of holographic stereograms. [ABSTRACT FROM AUTHOR]

Optical sensor based on pH-sensitive hydrogel has important practical applications in medical diagnosis and bio-sensor areas. This report details the experimental and theoretical results from a novel photosensitive polymer hydrogel holographic sensor, which formed by thermal polymerization of 2-hydroxyethyl methacrylate, for the detection of pH in buffer. Volume grating recorded in the polymer hydrogel was employed in response to the performance of solution. Methacrylic acid with carboxyl groups was selected as the primary co-monomer to functionalize the matrix. Peak diffraction spectrum of holographic grating determined as a primary sensing parameter was characterized to reflect the change in pH. The extracted linear relation between peak wavelength and pH value provided a probability for the practical application of holographic sensor. To explore the sensing mechanism deeply, a theoretical model was used to describe the relevant holographic processes, including grating formation, dark diffusional enhancement, and final fringe swelling. Numerical result further showed all of the dynamic processes and internal sensing physical mechanism. These experimental and numerical results provided a significant foundation for the development of novel holographic sensor based on polymer hydrogel and improvement of its practical applicability. [ABSTRACT FROM AUTHOR]

Background Oriented Schlieren method was used to obtain diffusion coefficient of glucose in hydrogel in the experiment with radial symmetry. [ABSTRACT FROM AUTHOR]

In this paper, the holographic superconductor model with two s-wave orders from 4 + 1 dimensional Einstein–Gauss–Bonnet gravity is explored in the probe limit. At different values of the Gauss–Bonnet coefficient α , we study the influence of tuning the mass and charge parameters of the bulk scalar field on the free energy curve of condensed solution with signal s-wave order, and compare the difference of tuning the two different parameters while the changes of the critical temperature are the same. Based on the above results, it is indicated that the two free energy curves of different s-wave orders can have one or two intersection points, where two typical phase transition behaviors of the s + s coexistent phase, including the reentrant phase transition near the Chern–Simons limit α = 0.25 , can be found. We also give an explanation to the nontrivial behavior of the T c – α curves near the Chern–Simons limit, which might be heuristic to understand the origin of the reentrant behavior near the Chern–Simons limit. [ABSTRACT FROM AUTHOR]

Point-of-care diagnostics will rely upon the development of low-cost, noncomplex, and easily integrated systems in order to examine biological samples such as blood and urine obtained from the patient. The development of metal ion sensors is a subject of significant relevance for physiological samples. The level of different blood electrolytes, mainly H+, Na+, K+ and Cl− is considerably used to monitor irregular physiologies. The particular challenge in biosensing, and in fact for any other sensor, is signal differentiation between non-specifically bound material and the specific detecting of the target molecule/ion. The biosensors described in this paper are fabricated by a holographic recording of surface relief structures in a photopolymer material. The surface structures are modified by coating with either dibenzo-18-crown-6 (DC) or tetraethyl 4-tert-butylcalix[4]arene (TBC), which are embedded in a polymer matrix. Interrogation of these structures by light allows indirect measurement of the concentration of the analyte. The influence of polymer matrices with different porosities, plasticised polyvinyl chloride (PVC) and a sol-gel matrix, on the performance of the sensors for detection of K+ and Na+ is examined. Here we demonstrate a proof of concept that by using a matrix with higher porosity one can increase the sensitivity of the sensor. The results showed that the DC sensing layer provides a selective response to K+ over Na+ and the TBC modified grating is more responsive to Na+ over K+. The sensor responds to K+ and Na+ within the physiological concentration ranges.

The research reported herein integrates a generic holographic sensor platform and a smartphone-based colour quantification algorithm in order to standardise and improve the determination of the concentration of analytes of interest. The utility of this approach has been exemplified by analysing the replay colour of the captured image of a holographic pH sensor in near real-time. Personalised image encryption followed by a wavelet-based image compression method were applied to secure the image transfer across a bandwidth-limited network to the cloud. The decrypted and decompressed image was processed through four principal steps: Recognition of the hologram in the image with a complex background using a template-based approach, conversion of device-dependent RGB values to device-independent CIEXYZ values using a polynomial model of the camera and computation of the CIEL*a*b* values, use of the colour coordinates of the captured image to segment the image, select the appropriate colour descriptors and, ultimately, locate the region of interest (ROI), i.e. the hologram in this case, and finally, application of a machine learning-based algorithm to correlate the colour coordinates of the ROI to the analyte concentration. Integrating holographic sensors and the colour image processing algorithm potentially offers a cost-effective platform for the remote monitoring of analytes in real time in readily accessible body fluids by minimally trained individuals. [ABSTRACT FROM AUTHOR]

We further explore the connection between holographic O( n) tensor models and random matrices. First, we consider the simplest non-trivial uncolored tensor model and show that the results for the density of states, level spacing and spectral form factor are qualitatively identical to the colored case studied in arXiv:1612.06330. We also explain an overall 16-fold degeneracy by identifying various symmetries, some of which were unavailable in SYK and the colored models. Secondly, and perhaps more interestingly, we systematically identify the Spectral Mirror Symmetry and the Time-Reversal Symmetry of both the colored and uncolored models for all values of n, and use them to identify the Andreev ensembles that control their random matrix behavior. We find that the ensembles that arise exhibit a refined version of Bott periodicity in n. [ABSTRACT FROM AUTHOR]

In this paper, we will regularize the holographic entanglement entropy, holographic complexity and fidelity susceptibility for a configuration of D3-branes. We will also study the regularization of the holographic complexity from the action for a configuration of D3-branes. It will be demonstrated that for a spherical shell of D3-branes the regularized holographic complexity is always greater than or equal to the regularized fidelity susceptibility. Furthermore, we will also demonstrate that the regularized holographic complexity is related to the regularized holographic entanglement entropy for this system. Thus, we will obtain a holographic bound involving regularized holographic complexity, regularized holographic entanglement entropy and regularized fidelity susceptibility of a configuration of D3-brane. We will also discuss a bound for regularized holographic complexity from action, for a D3-brane configuration. [ABSTRACT FROM AUTHOR]

A theoretical model is developed to describe holographic sensing and swelling of grating fringe in photopolymer. In experiments, diffraction spectrum responses of grating are characterized to exhibit holographic sensing processes. Analytic expressions between swelling of grating fringe and environmental factors, such as relative humidity and organic vapor concentrations, are extracted based on experimental results. The primary factors are introduced into the model to simulate the sensing process, including swelling ratio, nanozeolites dispersion, and organic vapor absorption. Finally, numerical results are presented for improving the sensitivity of holographic sensor. This work can accelerate the development of holographic sensor and provide a theoretical base for exploring sensing mechanism of polymer. [ABSTRACT FROM AUTHOR]

Highlights: [•] Conventional and alternative methods for zeolite synthesis. [•] Parameters governing zeolite synthesis. [•] Crystallization of zeolites from organic- and inorganic-templated suspensions. [•] Zeolite with tunable size- and shape-dependent properties. [•] Zeolites for photovoltaics, sensors, and medical applications. [ABSTRACT FROM AUTHOR]

Abstract: The humidity and temperature responses of a reflection hologram recorded in a self-processing photopolymer layer have been characterised by measurement of the position of the maximum intensity in the spectral response of the hologram. It has been demonstrated that such a hologram can be used for indication of the relative humidity (RH) in a specific temperature range. The operational range and reversibility of the holograms have been characterised in a controlled humidity and temperature environment. The humidity studies were carried out in the range from 10 to 80% RH and the temperature range under study was 15–50°C. [Copyright &y& Elsevier]

A photopolymerizable material for use in the visible normally consists of a dye sensitizer, a free radical generator, monomer/monomers and, optionally, a binder, and is prepared usually as a dry or liquid film. Upon illumination with light of appropriate wavelength, a photopolymerisation reaction is triggered, leading to a change in the film’s refractive index. Because the presence of the dye is essential, the film is usually made sensitive to light during its preparation. Here we separate the film preparation and the sensitisation processes. In this way the photopolymerisation process can be used to detect dye labelled analytes, providing an alternative to fluorescence detection methods that offers visual, easy to interpret information. Our approach also allows for a precise control of the spatial location of the photoinduced refractive index changes that can be utilised for holography, lithography and photonic device fabrication.

This study shows that a silicon–aluminum oxide–hafnium aluminum oxide-silicon oxide–silicon capacitor device with a high temperature pre-metal-anneal-treated and partially-nanocrystallized hafnium aluminum oxide, (hereafter PNC-SAHAOS) can successfully increase the performance of a nonvolatile ultraviolet radiation total dose (hereafter UV TD) sensor. The experimental results show that the UV-induced threshold voltage VT shift of PNC-SAHAOS was 10 V after UV TD 100 mW·s/cm2 irradiation. The UV-induced charge density of PNC-SAHAOS is almost eight times that of amorphous silicon–aluminum oxide–silicon nitride–silicon dioxide–silicon SANOS. Moreover, the charge fading rate of ten-years retention on PNC-SAHAOS, even at 85 °C, is below 10%. At 85 °C, the charge fading rate of ten-years retention on amorphous SANOS is almost twice that on PNC-SAHAOS. These results strongly suggest that PNC-SAHAOS could be the most promising candidate for next-generation nonvolatile UV TD sensor technology. [ABSTRACT FROM AUTHOR]

Point-of-care diagnostics will rely upon the development of low-cost, noncomplex, and easily integrated systems in order to examine biological samples such as blood and urine obtained from the patient. The development of metal ion sensors is a subject of significant relevance for physiological samples. The level of different blood electrolytes, mainly H+, Na+, K+ and Cl− is considerably used to monitor irregular physiologies. The particular challenge in biosensing, and in fact for any other sensor, is signal differentiation between non-specifically bound material and the specific detecting of the target molecule/ion. The biosensors described in this paper are fabricated by a holographic recording of surface relief structures in a photopolymer material. The surface structures are modified by coating with either dibenzo-18-crown-6 (DC) or tetraethyl 4-tert-butylcalix[4]arene (TBC), which are embedded in a polymer matrix. Interrogation of these structures by light allows indirect measurement of the concentration of the analyte. The influence of polymer matrices with different porosities, plasticised polyvinyl chloride (PVC) and a sol-gel matrix, on the performance of the sensors for detection of K+ and Na+ is examined. Here we demonstrate a proof of concept that by using a matrix with higher porosity one can increase the sensitivity of the sensor. The results showed that the DC sensing layer provides a selective response to K+ over Na+ and the TBC modified grating is more responsive to Na+ over K+. The sensor responds to K+ and Na+ within the physiological concentration ranges. [ABSTRACT FROM AUTHOR]

The authors recently developed a two-dimensional (2D) holographic electromagnetic induction imaging (HEI) for biomedical imaging applications. However, this method was unable to detect small inclusions accurately. For example, only one of two inclusions can be detected in the reconstructed image if the two inclusions were located at the same XY plane but in different Z-directions. This paper provides a theoretical framework of three-dimensional (3D) HEI to accurately and effectively detect inclusions embedded in a biological object. A numerical system, including a realistic head phantom, a 16-element excitation sensor array, a 16-element receiving sensor array, and image processing model has been developed to evaluate the effectiveness of the proposed method for detecting small stroke. The achieved 3D HEI images have been compared with 2D HEI images. Simulation results show that the 3D HEI method can accurately and effectively identify small inclusions even when two inclusions are located at the same XY plane but in different Z-directions. This preliminary study shows that the proposed method has the potential to develop a useful imaging tool for the diagnosis of neurological diseases and injuries in the future. [ABSTRACT FROM AUTHOR]