Featured | LEDs | IR-LEDs | Sensors | Health | Nov 01, 2019

Measuring the Oxygen Content of Blood with LEDs

Pulse oximetry is a non-invasive method for determining haemoglobin (Hb) saturation through oxygen in the blood and heart frequency. It uses the fact that oxygen-rich and oxygen-poor haemoglobin absorb red and infrared light differently. In order to measure the oxygen content reliably, LEDs with high performance, constant quality and low scattering are needed as light sources. With the WL-SMTW and WL-SITW series, Würth Elektronik has suitable red and infrared LEDs in its portfolio. In addition, there is a matching light sensor available: The phototransistor WL-STTW can reliably detect both red and infrared light.

Pulse oximeters can use two different measurement methods to detect the oxygen content in the blood: transmissive oximetry passes two wavelengths of light through a body part, for example a fingertip or earlobe. Reflective oximetry is used in fitness trackers or smart watches. Both methods measure the oxygen content in the blood on the basis of two basic principles: First, they distinguish between oxygen-rich oxyhaemoglobin (HbO2) and oxygen-poor deoxyhaemoglobin (Hb), and then they detect the oxygen saturation only in the arterial blood.

Different absorption spectra of the blood components

Pulse oximeters take advantage of the fact that red and infrared light is absorbed differently by oxygen-rich and oxygen-poor blood: HbO2 absorbs more infrared light and less red light than Hb. Due to the higher reflection of red light it appears bright red. By contrast, Hb absorbs more red light and thus appears darker.

Transmissive pulse oximetry usually uses a red LED in the range of about 650 nm and an IR LED in the range of about 900 nm. Both LEDs screen a fingertip and a phototransistor on the other side captures the relative amount of absorbed red and IR light. A micro-controller then determines the proportion of Hb and HbO2 and calculates the oxygen content from the measured parameters. In fact, only the arterial blood is of interest. With pulse oximetry it is possible to detect the oxygen content only of arterial blood. This is based on the fact that the amount of absorbed red and infrared light varies with every heartbeat due to the pulsating changes in blood volume. By contrast, veins, bones and tissue show relative constant absorption characteristics.

Reliable measurements need the right components

The right components are essential to reliably determine the oxygen content of blood. The LEDs and photodetectors that are used are particularly important. Würth Elektronik's red LED 150224SS73100 is characterized by an exact wavelength of 652 nm and high efficiency. With a current of IF=20mA a typical luminous intensity of 130 mcd is achieved. In combination with a good phototransistor this results in a high signal-to-noise ratio. In order to obtain a good signal-to-noise ratio with the IR LED as well, it should have about twice the luminous intensity of the red LED in this application. The LED 15414194BA210 from the WL-SITW-SMT series is particularly suitable here, as it has a very high efficiency and a high radiation intensity. The phototransistor WL-STTW SMT, 1541411NBA2010 is recommended as light sensor. Although the component has the highest light sensitivity at a wavelength of 940 nm, it also detects light signals with a wavelength of 660 nm. Therefore, only one single phototransistor is needed for the measurement. The perfect emitter-detector combination from Würth Elektronik for pulse oximetry and other IR applications is available from stock in any quantity.

Further information can be found at we-online.de/web/en/wuerth_elektronik/start.php, katalog.we-online.de/en/led/WL-SITW and katalog.we-online.de/en/led/WL-STTW

About Würth Elektronik eiSos Group:

Würth Elektronik eiSos Group is a manufacturer of electronic and electromechanical components for the electronics industry and a technology company that spearheads pioneering electronic solutions. Würth Elektronik eiSos is one of the largest European manufacturers of passive components and is active in 50 countries. Production sites in Europe, Asia and North America supply a growing number of customers worldwide. - we-online.de/web/en/wuerth_elektronik/start.php

FEATURED

Epoxy Features Very Low Coefficient of Thermal Expansion

Epoxy Features Very Low Coefficient of Thermal Expansion Master Bond EP30LTE-2 has been developed for joining dissimilar substrates exposed to thermally or mechanically induced stresses. It can be used for sealing, coating and encapsulating, especially for small to medium sized castings where a very low coefficient of thermal expansion (CTE) is required. Read more »

FEATURED

New BJB LED Connector for Linear LED Modules: Book 21 Compliant

New BJB LED Connector for Linear LED Modules: Book 21 Compliant Lampholders were standard in older, traditional lighting systems. Modern LED fixtures that utilize non-replaceable LEDs create several assembly and field-replacement disadvantages. Zhaga Book 21 addresses these shortcomings by standardizing linear 'socketable' LED modules. In accordance with Book ... Read more »

FEATURED

EzyLED™ Now Stocked at Digi-Key

EzyLED™ Now Stocked at Digi-Key American Bright, a global LED lighting solutions manufacturer, announced a series of EzyLED 3030. American Bright's EzyLED™ is a proprietary LED device with a built-in IC. This patented design drastically reduces the need for additional circuitry and other on-board components making it the ideal ... Read more »

FEATURED

Cree Expands Design Possibilities for Architectural Lighting with the Worldwide Proven CLQ6A LED

Cree Expands Design Possibilities for Architectural Lighting with the Worldwide Proven CLQ6A LED These SMD LEDs are packaged in an industry standard PLCC8 package. These high performance 4 color SMT LEDs are designed to work in a wide range of applications. A wide viewing angle and high brightness make these LEDs suitable for signage applications. Read more »

FEATURED

Measuring the Oxygen Content of Blood with LEDs

Measuring the Oxygen Content of Blood with LEDs Pulse oximetry is a non-invasive method for determining haemoglobin (Hb) saturation through oxygen in the blood and heart frequency. It uses the fact that oxygen-rich and oxygen-poor haemoglobin absorb red and infrared light differently. In order to measure the oxygen content reliably, LEDs with ... Read more »

EDITORIAL

LpS/TiL 2019 - Europe's Foremost Lighting Conference Discussed Latest Lighting Trends

LpS/TiL 2019 - Europe's Foremost Lighting Conference Discussed Latest Lighting Trends Last week saw the co-hosted LED professional Symposium +Expo (LpS), Trends in Lighting Forum &Show (TiL) and for the first time the Digital Addressable Lighting Interface (DALI) Summit return to Bregenz, Austria. The three international conference and exhibition events were carefully curated to ... Read more »

EDITORIAL

The 2019 LpS & TiL Award Winners: Celebrating the Complete Spectrum of Light

The 2019 LpS & TiL Award Winners: Celebrating the Complete Spectrum of Light It is a great pleasure for the LpS and TiL organization committee to announce the award winners for 2019. For the second time in a row, after the traditional cruise on the lake from Bregenz to Lindau, the gala dinner at the Eilgut Halle has proven to being a great place for the LpS & TiL award ... Read more »

page_peel