Portable optical oxygen sensor based on time-resolved fluorescence

A new, simple signal processing, low-cost technique for the fabrication of a portable oxygen sensor based on time-resolved fluorescence is described. The sensing film uses the oxygen sensing dye platinum meso-tetra (pentfluorophenyl) porphyrin (PtTFPP) embedded in a polymer matrix.

The ratio measures sensitivity of the sensing film, where 0 and 100 represent the detected fluorescence lifetimes from the sensing film exposed to 100% nitrogen and 100% oxygen, respectively. The experimental results reveal that the PtTFPP-doped oxygen sensor has a sensitivity of 2.2 in the 0%–100% range.

A preparation procedure for coating the photodiodes with the oxygen sensor film that produces repetitive and reliable sensing devices is proposed. The developed time-resolved optical oxygen sensor is portable, low-cost, has simple signal processing, and lacks optical filter elements. It is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optical based sensors.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrialproducts

CO2 transmitter/sensor installs in ventilation channels

The CO2 Transmitter Series EE85 for HVAC from E+E Elektronik has been designed for accurate measurement of CO2 levels in heating, ventilation and air conditioning (HVAC) applications.

It is available for measuring ranges of 0 to 2000ppm and 0 to 5000ppm. Its compact design allows easy installation in ventilation channels. CO2 detection is based on the accurate, non-dispersive infrared technology (NDIR).

Aging effects are compensated by a patented auto-calibration procedure, which is the basis for the outstanding long-term stability of the series. Due to a small differential pressure created by a special construction of the sampling head, a small stream of air from the duct is led to the CO2 sensing cell and back into the duct.

The air diffuses into the CO2 sensing cell through a diaphragm. The closed loop air stream and the diaphragm protect the CO2 sensing cell from pollution and by this avoid pollution related errors. Demand controlled ventilation based on CO2 minimizes fresh air to re-circulated air ratio which has a relevant impact on energy saving.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Platinum–aluminum nitride–silicon carbide diodes as combustible gas sensors

In this article we report on the novel use of a Pt/AlN/SiC structure as a combustible gas sensor. This device structure was fabricated by depositing a 2000 Å thick layer of AlN on the SiC substrate at 900 °C by laser ablation.Catalytic Pt gates were deposited onto the AlN at room temperature either by laser ablation or by rf sputtering.

The electrical characteristic of the resultant devices from room temperature to 650 °C revealed current rectifying behavior. Most importantly, their electrical characteristic changed in response to propane, propylene, and CO introduced into their ambient at temperatures as low as 250 °C.

They responded to changing gas composition over a wide range of combustible and oxygen concentrations from lean to fuel rich conditions. The response was a function of the ratio of combustible/oxygen concentration rather than to the absolute combustible concentration. However, this relationship exhibited some degree of combustible specificity.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Ultra-sensitive, vibration-tolerant gas sensor makes field applications more practical

A research team from Adelphi University, Garden City, New York, USA, has now developed a new device-gas sensor that can detect ultra-low concentrations of gases like nitrogen dioxide accurately and nearly instantaneously. The device works even when experiencing small vibrations, which is important if the instrument, is deployed in the field, where it could be shaken by passing cars, near-by machinery or by thermal changes or air currents. The researchers describe the new detector in a paper in The Optical Society's journal Applied Optics.

"Our sensor is much faster and has the potential for much higher sensitivity -- if employing better matched optical mirrors -- than the previously reported results. It opens the door to interesting, real-time investigation of trace gas concentrations," said Gottipaty Rao, a physicist at Adelphi University, Garden City, New York, USA.

The detector uses a tried-and-true measurement technique called cavity ring-down spectroscopy (CRDS). With CRDS, a laser shoots a pulse of light into a precisely aligned cavity formed by mirrors. When the pulse ends, the light bounces around in the cavity and slowly leaks out. The time it takes for the light to escape is called the ring-down time. If the cavity contains a small amount of gas that absorbs the wavelength of the laser, the ring-down time will decrease since some light is lost to the absorption. Measuring the change in ring-down time indicates the concentration of the trace gas.

In order for the sensors to work, the laser must be resonant with the cavity, meaning that the wavelength of the light "matches" the cavity length in such a way that the light bounces around for a long time. Standard CRDS sensors are susceptible to vibration-induced errors, since small shifts in the length of the cavity can dramatically reduce the sensitivity. As a result, special vibration-isolation equipment must be employed to use CRDS in the field.

One proposed fix for the vibration sensitivity involves shifting the alignment of the laser and the cavity so that the laser will be resonant with the cavity in many different ways. If one resonance is eliminated by a length change (due to vibration), other resonances act as back-up. However, this fix reduces the sensitivity of the detector.

Rao and his colleagues tried a different approach. They used a high-power broadband laser, which contains a wider range of wavelengths than typical for CRDS lasers. Any slight shift of the cavity length due to vibrations simply shifts the cavity resonances to other wavelengths that the laser is already emitting.

The researchers tested the device by measuring trace concentrations of nitrogen dioxide. "If the wavelength of the laser is changed, the technique could also readily be applied to monitor other gases such as methane (a powerful greenhouse gas), ammonia (an air pollutant) and sulfur dioxide (a pollutant from fossil fuel burning power plants)," Rao explained.

Currently, monitoring of nitrogen dioxide in the atmosphere is done using chemiluminenscence, a chemical reaction that generates light, Rao said. It is not capable of real-time measurements and requires an elaborate calibration procedure to get the absolute concentration of the gas. CRDS has unique advantages over chemiluminenscence and Rao believes the new detector will make it a more practical tool for the field.

In addition, measuring trace concentrations of specific gases in a person's exhaled breath may be used to diagnose certain diseases or conditions, thus the device may eventually aid doctors in non-invasive breath analysis. "More importantly, our approach may also prove useful in developing a highly sensitive explosive detector -- especially applicable to security and air travel -- that targets nitro group (NO2) based explosives such as TNT, GN, RDX, HMX, PETN and TATB," Rao said.

"Even though the CRDS technique is powerful for trace gas detection, it has found limited use for field based monitoring applications primarily because of its sensitivity to vibrations. We demonstrate a simplified approach that makes the CRDS technique insensitive to vibrations and can be employed for field-based applications by an appropriate choice of a high power multimode laser and the species of interest," Rao explained.

The team says the device's sensitivity and response time could be even further improved by using higher reflectivity mirrors and optimizing the design of the cavity. "This would open up new possibilities in atmospheric monitoring, chemical reaction studies and explosive detection," Rao said.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Microwave Sensor: A Painless Way to Manage Diabetes?

Patients with diabetes struggle daily with painful finger pricks to monitor their blood sugar levels. Now, a new device developed by researchers the UK's Cardiff University delivers the same function as traditional glucose sensors but without the pain. The new wearable glucose monitor attaches to the body via sticky adhesives and records the blood sugar levels using microwave technology. Researchers say this device could reach the market in five years time, and has the potential to dramatically change how patients manage diabetes.

Diabetes is characterized by the body’s inability to regulate blood glucose levels. In type 1 diabetes, insulin is not made in enough quantities because the insulin producing cells (islet cells) are attacked and destroyed by the body’s own immune system. As a result, the body is unable to regulate blood sugar levels normally, and diabetics must take great care in monitoring their activity, diet, and glucose levels. This involves as many as six daily finger pricks to check for blood glucose levels.

To remove the stress of this process for the patients, the UK researchers developed a wearable device that measures glucose without the need for blood samples. Led by Adrian Porch and Heungjae Choi, the team’s device is small and attaches simply to a patient’s arm or side of the body with ordinary adhesives. The monitor works by sending microwaves into the skin, and transmitting the readings to a computer or smart phone for analysis.

“Conventional methods of monitoring blood glucose require the extraction of blood,” said Adrian Porch. “Our device is non-invasive — it does not require the extraction of blood apart from the initial calibration.”

And they say the microwave-based device is completely safe to attach to a human body. "It uses microwaves, but the levels are very, very low. Nowhere near the levels used in domestic cooking,” said Porch. He further clarified that the glucose sensor emits about 1000 times less microwaves than a cell phone.

In research studies, the device performed as well as commercially available glucose microwave sensors that rely on blood samples. The team plans to test this device in larger clinical trials this summer at the Swansea University’s College of Medicine in collaboration with Stephen Luzio.

“Patients are very keen on this,” said Luzio. “One of the big problems with patients measuring their glucose is they don’t like pricking their finger, so there’s a lot of interest.”

The incidence of diabetes is increasing at an alarming rate worldwide. In 2014, the World Health Organization (WHO) estimated 422 million people were diagnosed with diabetes. Furthermore, WHO projects that this chronic condition will rise to become the 7th leading cause of death in 2030. Because of this, a needle-free device for diabetes management is hugely attractive to health providers and patients. The team hopes to bring their device to the market within five years. 

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products