Principles and mechanisms of ultraviolet light emitting diode technology for food industry applications

peer-reviewedThe application of ultraviolet (UV) light to water, food contact surfaces and medical equipment for microbial inactivation is widely employed. To date, UV disinfection sources employed are primarily low-pressure and medium-pressure mercury lamps; emitting monochromatic and polychromatic light, respectively. Despite the widespread use of mercury lamps, there are multiple drawbacks associated with their use including; high energy consumption, large size which limits reactor design, high heat emission and the presence of mercury. Light emitting diodes (LEDs) have potential for use as a highly efficient UV decontamination technology. Recent advances in semiconductor development have resulted in UV-LEDs becoming more widely available. UV-LEDs emit monochromatic light, which enables customised UV-LED disinfection systems at specific wavelengths to be developed. The application of UV-LEDs for disinfection purposes has been studied in recent years, particularly with respect to water disinfections systems. In this review, studies relating to UV-LED food applications are discussed. Furthermore, the chemical changes induced in foods, as a result of UV treatment, together with advantages and limitations of the technology are outlined

InAlN-based LEDs emitting in the near-UV region

Fully functional InAlN-based ultraviolet LEDs emitting at 340–350 nm were demonstrated for the first time; detailed electrical and optical characterization is presented and discussed. Results from the measurements at pulsed conditions are in agreement with the attribution of the dominant electroluminescence peak to near-band-edge emission. The composition of the AlGaN barriers was chosen to give the same internal polarization field as that of the InAlN wells. A simulation study of this polarization-matched heterostructure shows a significant increase in the electron-hole overlap integral if compared with a standard AlGaN/AlGaN active region having the same level of carrier confinement. Limitations and problems of these preliminary devices are also presented, and possible future work aimed at increasing their efficiency is discussed

High power surface emitting InGaN superluminescent light-emitting diodes

A high power InGaN superluminescent light-emitting diode emitting normal to the substrate is demonstrated. The device uses a structure in which a monolithically integrated turning mirror reflects the light at both ends of the in-plane waveguide to direct amplified spontaneous emission downward through the transparent GaN substrate. Record optical peak powers of >2 W (both outputs) are reported under pulsed operation at 1% duty cycle. A broad, smooth emission spectrum with a FWHM of 6 nm centered at 416 nm is measured at peak output and ascribed to very low feedback associated with the turning mirror and antireflection coating

Size-dependent bandwidth of semipolar (1122) light-emitting-diodes

The limited modulation bandwidth of commercial light-emitting diodes (LEDs) is one of the critical bottlenecks for visible light communications. Possible approaches to increase the bandwidth include the use of micron sized LEDs, which can withstand higher current densities, as well as the use of LED structures that are grown on different crystal planes to the conventional polar c-plane. We compare c-plane InGaN/GaN LEDs with semipolar ( 112¯¯¯2 ) LEDs containing a 4- and 8-nm single quantum well. The modulation bandwidth of semipolar LEDs with active areas varying from 200×200 to 30×30μm2 is shown to be governed by both current density and size. A small signal bandwidth of over 800 MHz for a relatively low applied current density of 385 A/cm2 is reported for 30×30μm2 LEDs with 8-nm thick quantum well. An optical link using an easy non-return-to-zero ON–OFF keying modulation scheme with a data rate of 1.5 Gb/s is demonstrated

Causes of Death Among Women Aged 10-50 Years in Bangladesh, 1996-1997

Limited information is available at the national and district levels on causes of death among women of reproductive age in Bangladesh. During 1996-1997, health-service functionaries in facilities providing obs-tetric and maternal and child-heath services were interviewed on their knowledge of deaths of women aged 10-50 years in the past 12 months. In addition, case reports were abstracted from medical records in facilities with in-patient services. The study covered 4,751 health facilities in Bangladesh. Of 28,998 deaths reported, 13,502 (46.6%) occurred due to medical causes, 8,562 (29.5%) due to pregnancy-related causes, 6,168 (21.3%) due to injuries, and 425 (1.5%) and 259 (0.9%) due to injuries and medical causes during pregnancy respectively. Cardiac problems (11.7%), infectious diseases (11.3%), and system disorders (9.1%) were the major medical causes of deaths. Pregnancy-associated causes included direct maternal deaths (20.1%), abortion (5.1%), and indirect maternal deaths (4.3%). The highest proportion of deaths among women aged 10-19 years was due to injuries (39.3%) with suicides accounting for 21.7%. The largest pro\uadportion of direct obstetric deathsoccurred among women aged 20-29 years (30.5%). At least one quarter (24.3%) of women (n=28,998)did not receive any treatment prior to death, and 47.8% received treatment either from a registered physician or in a facility. More focus is needed on all causes of deaths among women of reproductive age in Bangladesh

Neonatal Mortality in Rural Bangladesh: An Exploratory Study

Bangladesh has a neonatal death rate that is substantially high and demands urgent attention. To assess the causes of neonatal mortality, 1,019 pregnant women were followed up in eight randomly-selected rural areas of the country. Trained female interviewers visited the households of the subjects at four-week intervals to record neonatal deaths (within 28 days after birth). For each death, they administered a structured verbal autopsy questionnaire to the mother and/or a close family member. Based on these field data, three neonatologists arrived at a consensus to assign two causes of death - an originating cause and a direct cause. The neonatal mortality rate was 53.5 per 1,000 livebirths. The originating causes of death were pre-maturity/low birth-weight (30%), difficult labour (16%), unhygienic birth practices (16%), others (4%), and unknown (34%). The direct causes were sepsis (32%), asphyxia (26%), tetanus (15%), respiratory distress (6%), others (6%), and unknown (14%). According to the prevailing causes of neonatal deaths, implementation of intervention programmes, often in the community, that do not depend on highly-technical training or sophisticated equipment should be implemented

Comparison between different optical systems for optogenetics based head mounted device for retina pigmentosa

Optogenetics is a fast growing neuromodulation techniques as it can remotely stimulate neural activities of a genetically modified cells. The advantage of remotely controlling the neural activity triggered researchers to implement a headset to externally stimulate retina cells for people with retina pigmentosa. The wearable device requires an efficient optical system to focus the transmitted light pattern into the retina surface. In this work, three different lenses; contact lens, folded prism and linear lenses are used to evaluate the headset performance. A 90x90 μLED display is used as a light source and the optical efficiency for each lens is measured for different points over the lens area. Moreover, the impact of each lens on the headset performance in power and processing will be discussed in this work

Effectiveness of a novel UV light emitting diode based technology for the microbial inactivation of Bacillus subtilis in model food systems.

peer-reviewedThe objective of this study was to assess the effectiveness of a novel UV multiwavelength light emitting diode (LED) based technology for the inactivation of B. subtilis in two model food systems. The LED based system was used to treat B. subtilis bacterial cultures using various combinations of UV wavelengths (285, 365, 405, 285/365, 285/405, 365/405, 285/365/405 nm) for different treatment durations (5 & 10 min). Bacterial enumerations, post-treatment analysis and SEM imaging were carried out. UV treatment at 285 nm was found to be the most efficient individual wavelength for inactivation resulting in > 6 log10 reductions. Treatments at other wavelengths investigated also resulted in bacteriostatic effects. Synergistic effects were observed for treatment at a 285/405 nm combination in one model system. Growth kinetics were carried out using a modified Gompertz model and model fit was assessed by root mean squared error, accuracy factor and bias factor. Experimental data showed good fit with model employed with RMSE values ranging from 0.01 x 10-2 to 1.367 x 10-2 for 5 min treatment, and 0.01 x 10-2 to 0.210 x 10-2 for 10 min treatment. Multivariate analysis was also carried out using principal component analysis and explained 100% of the variation observed for 3 principal components. This study shows that UV-LED technology is effective as bactericidal and bacteriostatic technology, depending on wavelength used

Packaging technology for high power blue-green LEDs

High brightness LEDs (HBLEDs) have been fabricated on GaN semiconductor material grown on sapphire substrate. These devices provide an optical output power in excess of 50 mW at a driving current of 1 amp. For this hi-h current application, large size (1.8 mm X 0.6 mm) GaN LEDs are flip-chip mounted onto a heat sink to provide a low thermal resistance path from the junction to the ambient. For the flip-chip mounting, a Au/Sn/Au solder and a Au/Au thermal compression bonding process have been optimized. The bond strength of the Au/Sn solder joints and the Au-Au bonds is measured through shear testing. Good bond strength results of 224 g/f for the Au/Sn/Au solder and 288 g/f for the solid Au bonds have been achieved. The thermal modeling of the assembly is done with a finite element analysis and the optimum design has been adopted for this high current application. At present these assemblies are under lifetime test and so far nearly 6000 hours of continuous operation has been achieved

High bandwidth freestanding semipolar (11–22) InGaN/GaN light-emitting diodes

Freestanding semipolar (11–22) indium gallium nitride (InGaN) multiplequantum-well light-emitting diodes (LEDs) emitting at 445 nm have been realized by the use of laser lift-off (LLO) of the LEDs from a 50- m-thick GaN layer grown on a patterned (10–12) r -plane sapphire substrate (PSS). The GaN grooves originating from the growth on PSS were removed by chemical mechanical polishing. The 300 m × 300 m LEDs showed a turn-on voltage of 3.6 V and an output power through the smooth substrate of 0.87 mW at 20 mA. The electroluminescence spectrum of LEDs before and after LLO showed a stronger emission intensity along the [11–23]InGaN/GaN direction. The polarization anisotropy is independent of the GaN grooves, with a measured value of 0.14. The bandwidth of the LEDs is in excess of 150 MHz at 20 mA, and back-to-back transmission of 300 Mbps is demonstrated, making these devices suitable for visible light communication (VLC) applications