Dag R Hjelme

• PhD
• Professor at Norwegian University of Science and Technology

Inversion of the photoplethysmographic (PPG) signal is a rarely reported case. This signal anomaly can have implications for PPG-based cardiovascular assessments. The conditions for PPG signal inversion in the vicinity of the dorsalis pedis (DPA) artery of the foot were investigated. Wireless multi-wavelength PPG sensing with skin-probe contact pre...

We demonstrate a high-resolution, low-cost interrogation technique using a square-wave modulated DFB laser diode. The method does not require knowledge of the frequency chirp function, instead using only three parameters: the laser diode average power, intensity modulation amplitude, and the average frequency. The last of which, we show can be easi...

Objective: Blindness deprives a person of a significant part of sensory information resulting in limited perceptual abilities and decreased quality of life. Although some aspects of visual information, like the shape of an object, can be conveyed by other senses, there is no easy way to perceive color without using sight. To address this issue, we...

Revealing availability threats and security attacks using State of Polarisation monitoring shows impact characteristics from a cable trencher passing over, moving a subsea cable carrying live traffic while dBQ value dips 0.6 dB.

A short aerial cable spun on a high-voltage line is used to monitor wind-induced stress on the cable infrastructure. Span-by-span localized early warnings may be issued based on the state of polarization transients.

Photobiomodulation causes an immediate increase in local blood flow. This study aimed to investigate the effect of 890 nm NIR exposure on local skin blood flow in young and middle-aged healthy subjects. In this placebo-controlled clinical trial, 12 young and 12 middle-aged healthy subjects received either continuous or intermittent NIR exposure (89...

Light-responsive polymers and especially amorphous azopolymers with intrinsic anisotropic and polarization-dependent deformation photo-response hold great promises for remotely controlled, tunable devices. However, dynamic control requires reversibility characteristics far beyond what is currently obtainable via plastic deformation of such polymers...

We fabricated single mode Ge28Sb12Se60 waveguides and resonators using e-beam lithography and achieved a propagation loss of 3.88 dB/cm at 3.66 µm. We compared BCl3 and CHF3 etch chemistries and determined CHF3 produced 1.5 dB/cm higher propagation losses at 3.6 µm due to C-H bond absorption. We use fabricated waveguides to detect an aromatic aldeh...

We demonstrate local small-magnitude earthquake observation using State of Polarization sensing on an alien wavelength in a live single-span passive submarine cable communication system. Distributed Acoustic Sensing verifies seismic waves propagating along the cable.

We demonstrate a high-resolution, low-cost interrogation technique using a square wave modulated DFB laser diode. With only three parameters, and without characterization of the dynamic frequency chirp, we achieve a spectral resolution of 0 . 05pm.

p>Objective: Blindness deprives a person of a significant part of sensory information resulting in limited perceptual abilities and decreased quality of life. Although some aspects of visual information, like the shape of an object, can be conveyed by other senses, there is no easy way to perceive color without using sight. To address this issue, w...

p>Objective: Blindness deprives a person of a significant part of sensory information resulting in limited perceptual abilities and decreased quality of life. Although some aspects of visual information, like the shape of an object, can be conveyed by other senses, there is no easy way to perceive color without using sight. To address this issue, w...

Light-responsive polymers offer unique possibilities for anisotropic manipulation of objects on the micron scale. Here we demonstrate the reversible anisotropic stretching of a polymeric surface made out of an azopolymer-elastomer blend, in response to green laser irradiation with varying polarization. We quantify the stretching parameters and the...

We demonstrate a fiberoptic sensor for measuring the lithium-ion concentration inside a lithium-ion battery (LiB), live during charge and discharge. The goal is to monitor the health of the battery based on the dynamic and state-of-charge dependent concentration of lithium ions in the electrolyte. An important factor to improve the sustainability o...

Accurate, in-field-compatible, sensing based on near infrared spectroscopy (NIRS) requires development of instrumentation with low noise and long-term stability. Here, we present a fully fiber-optic spectroscopy setup using a supercontinuum source in the long-pulse regime (2 ns) and a balanced detector scheme to demonstrate high-accuracy NIRS-based...

Reuse, refurbishing, and recycling are the most sustainable options for handling waste materials. However, for municipal solid waste (MSW) that is highly heterogenic, crude, contaminated, and decrepit, thermal conversion in waste-to-energy (WtE) plants is an option. In such plants, the fuel quality of MSW is difficult to predict and the substantial...

We fabricated GeSbSe waveguides and resonators using e-beam lithography and achieved a propagation loss of 4.4 dB/cm in the mid-infrared region. Using these devices we demonstrated optical sensing of aromatic aldehydes with a limit of detection of 0.25 μ mol/mL.

We developed a novel miniature micro-lensed fibre probe for Raman spectroscopy. The fibre probe consists of a single negative-curvature fibre (NCF) and a spliced, cleaved, micro-lensed fibre cap. Using a single NCF, we minimized the Raman background generated from the silica and maintained the diameter of the probe at less than 0.5 mm. In addition,...

The successful development of a system realizing color sonification would enable auditory representation of the visual environment. The primary beneficiary of such a system would be people that cannot directly access visual information—the visually impaired community. Despite the plethora of sensory substitution devices, developing systems that pro...

Preparing students for real-life challenges is one of the crucial goals of engineering education. Nevertheless, gaining practical, industrial experience takes time and effort that usually lays beyond the classical curricular activities. This paper describes our approach, which promotes cooperation between academia and industrial partners to the ben...

Classification of municipal solid waste using deep convolutional neural network model applied to multispectral images

Near infrared spectroscopy (NIR) is a promising technique for continuous blood glucose monitoring for diabetic patients. Four interferents, at physiological concentrations, were introduced to study how the glucose predictions varied with a standard multivariate calibration model. Lactate and ethanol were found to interfere strongly with the glucose...

We present a Mach-Zehnder interferometer assisted ring resonator configuration (MARC) to realize resonator transmission spectra with unique spectral signatures and significantly large effective free spectral ranges. Transmission spectra with unique spectral signatures are generated by changing the angular separation between the through port and the...

We demonstrate monitoring of phase-transitions in binary liquid mixtures by combining a fiber Bragg grating and a thin-core fiber interferometer. Temperature and refractive index sensing enable direct measurements of concentration changes below the melting point.

A stable and low-noise system is required to measure small changes in bio- chemical constituents such as glucose. We discuss the requirements and limitations to achieve the necessary stability using a supercontinuum source.

To realise the goal of high efficiency, low-pollution, sustainable and abundant energy sector, hydrogen will play a significant role in energy storage [1]. Gas composition measurements for H2 energy storage applications mainly consist of detecting gas concentrations such as H2 to evaluate the electrochemical processes as well as their performance....

The fusion of sensors or data is today often used for increasing precision in navigation, position and location of mobile objects in the shipping industry, GPS systems, and smartphones. This is due in part that some information may not be reliable when using the sensor data sources individually. By fusing several independent sensors containing indi...

In recent years, post-process high-speed, modern signal conditioning methods, low-power and low-cost microelectronic hybrid circuits and advances in miniaturisation technologies have driven improvements in sensor manufacturing [1]. Additionally, the sensor must have a high degree of efficiency relative to its calibration circumstances and sensing m...

Light has the properties of both particles and waves, depending on the situation. In Young’s double-slit interferometer, light behaves like waves, creating a pattern similar to what one could make with water ripples in a pond.

Increased knowledge on fluid-solid phase transitions is needed, both when they are undesired and can impair processes operation, and when strict control is required in fields such as food technology, the pharmaceutical industry and cryogenic CO2 capture. We present experimental results and theoretical predictions for the solid-formation and melting...

Fast and accurate continuous glucose monitoring is needed in future systems for control of blood glucose levels in type 1 diabetes patients. Direct spectroscopic measurement of glucose in the peritoneal cavity is an attractive alternative to conventional electrochemical sensors placed subcutaneously. We demonstrate the feasibility of fast glucose m...

Fiber optic sensors offer a new and unique way to detect and analyze phase transitions, due to their small thermal mass and inert material. This paper presents and demonstrates a dual-sensor system to detect and analyze phase transitions in pure water and aqueous ethanol mixtures. With a multi-mode interferometer based on a thin-core fiber, and a f...

Convolutional neural networks (CNNs) are widely used for image recognition and text analysis, and have been suggested for application on one-dimensional data as a way to reduce the need for pre-processing steps. Pre-processing is an integral part of multivariate analysis, but determination of the optimal pre-processing methods can be time-consuming...

We present the fabrication and characterization of optical fiber reflection probes based on surface-enhanced Raman scattering (SERS) and micro-lensed multimode fibers. For the SERS substrate, a nano-sphere lithography method is used. Comparison of SERS measurements with three different fiber probe configurations is presented. The proposed optimized...

We present a silicon waveguide-based microring resonator sensor with high Q-factor and enhanced dynamic range. Q-factor of 57,000 and dynamic range of 3.7 nm is reported for a microring with a radius of 45 pm.

Visible and near-infrared spectroscopy are widely used for sensing applications but suffer from poor signal-to-noise ratios for the detection of compounds with low concentrations. Enhancement by surface plasmon resonance is a popular technique that can be utilized to increase the signal of absorption spectroscopy due to the increased near-field cre...

The development of rapid and accurate biomedical laser spectroscopy systems in the mid-infrared has been enabled by the commercial availability of external-cavity quantum cascade lasers (EC-QCLs). EC-QCLs are a preferable alternative to benchtop instruments such as Fourier transform infrared spectrometers for sensor development as they are small an...

Biogas production is becoming significantly viable as an energy source for replacing fossil‐based fuels. The further development of the biogas production process could lead to significant improvements in its potential. Wastewater treatment currently accounts for 3% of the electrical energy load in developed countries, while it could be developed to...

During the process of converting the organic matter into methane, many volatile fatty acids (VFAs) are produced during acidogenesis and acetogenesis phases of the process. The main VFAs of interest are acetic acid, butyric acid and propionic acid. Although the production of these VFAs are essential for the production of methane, they also play an i...

Fabrication of multimode fiber optic interferometers requires accurate control of certain parameters to obtain reproducible results. This paper evaluates the consequences of practical challenges in fabricating reflection-based, fiber optic interferometers by the use of theory and experiments. A guided-mode propagation approach is used to investigat...

Biogas production is becoming significantly viable as an energy source for replacing fossil‐based fuels. The further development of the biogas production process could lead to significant improvements in its potential. Wastewater treatment currently accounts for 3% of the electrical energy load in developed countries, while it could be developed to...

Although biogas is not a new approach to producing renewable fuel, it could further be developed to improve its potential as an alternative energy source. To achieve this, vast improvements in the efficiency and cost of biogas production are essential. These enhancements require detailed systematic monitoring to attain a near-optimal biogas product...

The global demand for non-fossil energy sources is increasing rapidly. As a result, biogas presents a suitable alternative; however, first generation biofuels (e.g., sugar cane) potentially impact food crops globally. Second generation biofuels based on lignocellulose-based biomass are being used more frequently as they do not impact food crops. Fu...

The artificial pancreas requires fast and reliable glucose measurements. The peritoneal space has shown promising results, and in one of our studies we detected glucose changes in the peritoneal space already at the same time as in the femoral artery. The peritoneal lining is highly vascularised, covered by a single layer of mesothelial cells and t...

Designing of color sonification systems provides a possibility of contribution to various fields ranging from rehabilitation of visually impaired through color perception, multisensory art experience to consciousness studies. The design process itself requires understanding and integrating knowledge from many difficult and inherently different bran...

Many operating parameters, individually or together, may influence the performance of anaerobic digestion towards biogas or digestate yield and quality maximization. The most preferred method of optimizing an anaerobic digestion plant often relies on how carefully the crucial parameters, such as pH, temperature, organic loading rate, hydraulic rete...

The bulkiness of common transmission spectroscopy probes prevents applicability at remote locations such as within the body. We present the fabrication and characterization of lensed fibers for transmission spectroscopy in the near-infrared. Eigenmode simulations and measurements of the coupling efficiency are presented and applied to design the se...

The demand for fuel for utilisation of machinery and transport has culmi-nated in large amounts of fossil fuel usage in the last century. The environ-mental dangers attached with the usage of fossil fuels have created a large demand for alternative sources of fuels. There is an array of polysaccharides contained within macroalgae, such as mannitol,...

We present the fabrication and characterization of a novel sensing configuration based on surface-enhanced Raman scattering (SERS) and two micro-lensed optical fibers. The first micro-lensed fiber is used to excite surface plasmon resonance in a gold film deposited over a mono-layer of nano-sphere surface (AuFON), and the second lensed fiber is use...

The distribution of noble metal nanoparticles (NMNPs) in hydrogels influences their nanoplasmonic response and signals used for biosensor purposes. By controlling the particle distribution in NMNP-nanocomposite hydrogels, it is possible to obtain new nanoplasmonic features with new sensing modalities. Particle positions can be characterized by usin...

Frequent glucose monitoring is a fundamental part of diabetes management, and good glucose control is important for long-term health outcomes. New types of electrochemical sensors that allow for continuous glucose monitoring (CGM) have become an important tool for diabetes management, although they still have drawbacks such as short lifetime and a...

Background In diabetes research, the development of the artificial pancreas has been a major topic since continuous glucose monitoring became available in the early 2000’s. A prerequisite for an artificial pancreas is fast and reliable glucose sensing. However, subcutaneous continuous glucose monitoring carries the disadvantage of slow dynamics. As...

Output from statistical analysis in R for comparisons of IP sensors. (DOCX)

Output from statistical analysis in R for comparison of SC and IP sensors. (DOCX)

Biogas, as derived from the anaerobic digestion process, offers a versatile possibility of renewable and sustainable energy usage. When enriched, upgraded biogas can yield high levels of biomethane, allowing its use as an alternative to natural gas via existing natural gas grids or being directly consumed by transport vehicles as fuel. Currently, b...

The purpose of this paper is to introduce and initially evaluate an experimental sensory substitution device (SSD), which converts color to audible sound. Our system, called Colorophone provides continuous information about the color, light intensity and distance. The color sonification method is inspired by the human visual system. While designing...

The distribution of noble metal nanoparticles in hydrogels are influencing their nanoplasmonic response and signal used for biosensor purposes. By controlling the particle distribution, it is possible to obtain new nanoplasmonic features with new sensing modalities. Particle distributions can be characterized by using volume-imaging methods such as...

We report on characterization of an optical fiber-based multi-parameter sensor concept combining localized surface plasmon resonance (LSPR) signal and interferometric sensing using a double-clad optical fiber. The sensor consists of a micro-Fabry-Perot in the form of a hemispherical stimuli-responsive hydrogel with immobilized gold nanorods on the...

We demonstrate a new single point, multi-parameter, fiber optic sensor concept based on a combination of interferometric and plasmonic sensor modalities on an optical fiber end face. The sensor consists of an extrinsic Fabry-Perot interferometer in the form of a hemispherical stimuli-responsive hydrogel with immobilized gold nanoparticles (GNPs). T...

Mid-infrared spectroscopy using multivariate analysis for quantification has high potential in biosensing. This case study on aqueous glucose solutions yields improved prediction errors by optimising preprocessing and wavelength selection procedures.

We demonstrate a multimode optical fiber sensor for spectroscopic Raman measurements of glucose concentration for the application in intraperitoneal glucose detection in diabetic patients. A regression model with a RMSEC of 2.2 mM was obtained.

We report on a new localized surface plasmon resonance (LSPR)-based optical fiber (OF) architecture with a potential in sensor applications. The LSPR-OF system is fabricated by immobilizing gold nanoparticles (GNPs) in a hydrogel droplet polymerized on the fiber end face. This design has several advantages over earlier designs. It dramatically incr...

ePoster presented at ATTD 2017.

ePoster presented at ATTD 2017.

Using estimation theory, we derive a lower resolution limit of resonant refractive index sensors in terms of resonance linewidth, spectral sampling resolution and signal-to-noise ratio. The result is confirmed using Monte Carlo simulation.

Rapid, accurate and robust glucose measurements are needed to make a safe artificial pancreas for the treatment of diabetes mellitus type 1 and 2. The present gold standard of continuous glucose sensing, subcutaneous (SC) glucose sensing, has been claimed to have slow response and poor robustness towards local tissue changes such as mechanical pres...

We present results from an evaluation of phase and frequency estimation algorithms for read-out instrumentation of interferometric sensors. Tests on interrogating a micro Fabry-Perot sensor made of semi-spherical stimuli-responsive hydrogel immobilized on a single mode fiber end face, shows that an iterative quadrature demodulation technique (IQDT)...

Over the last decade various optical fiber sensing schemes have been proposed based on local surface plasmon resonance (LSPR). LSPR are interacting with the evanescent field from light propagating in the fiber core or by interacting with the light at the fiber end face. Sensor designs utilizing the fiber end face is strongly preferred from a manufa...

We have developed an instrument for real time continuous interferometric measurement of dimensional change in stimuli-responsive hydrogel sensors. The instrument consists of a superfluorecent LED and a low-cost grating spectrometer. All signal conditioning and processing is performed using a microprocessor. We have tested the instrument with a gluc...

We present a novel fiber-optic biosensor utilizing hydrogel functionalized with enzyme sensitive cross-links. A proof-of-concept PSA sensor demonstrated linear response up to 4 μM and sensitivity better than 40 nM, with time response of 2 minutes.

We have carried out at laboratory test to study the feasibility of using thermal radiation detectors for online thermal monitoring of electrical systems in wind turbines. A 25 kW frequency converter is instrumented with a thermal camera, operating in the 8–14 μm wavelength range, and a single-pixel thermopile sensor, operating in the 4–8 μm wavelen...

Delay and packet delay variation are key parameters for real-time applications and packet-layer synchronisation. Demonstrated is an Ethernet integrated hybrid network enabling adding packet-traffic to a 10 Gbit/s Ethernet circuit without impacting packet-traffic delay, delay variation or packet loss. A scheduling algorithm increasing the throughput...

The aim of this study was to construct a glucose regulatory algorithm by employing the natural pulsatile pattern of insulin secretion and the oscillatory pattern of resting blood glucose levels and further to regulate the blood glucose level in diabetic pigs by this method. We developed a control algorithm based on repetitive intravenous bolus inje...