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Biometrics & Authentication Smartphone security – It’s all in the eyes By Dr Stefan Margott Biometric methods for unlocking mobile devices are the new trend: the technology offers a high degree of security and is extremely user-friendly. Currently, a great number of manufacturers are developing solutions for iris recognition. Compact designs with reliable recognition features succeed with light sources specially designed for their application. A look on the smartphone or the tablet is enough to get the device touch screen ready for operation. Visitors of the Mobile World Congress in March 2015 were given an impression of this convenient type of access security, where Fujitsu presented an iris scanner for smartphones. The iris of the eyes is unique for each person and is therefore used for biometric identification. These systems gather typical bodily characteristics – in addition to the iris pattern, these are, for example, the fingerprint, the voice, the face or the vein pattern in the hand – and compare them with the stored data of certain persons. This type of access control has been established for a long time in many security areas in the industry, but also at some entry checks. Its use in laptops, smartphones or tablets is relatively new. Users become increasingly aware that their devices need better protection, as they contain critical personal data or professional information. Here, the unlocking with the aid of the inherent body characteristics offers a convenient and secure alternative to the management of complex passwords. Since mobile devices already offer facial or voice recognition and occasionally also fingerprint scanners, iris scanners are now the focus of many manufacturers. The method is very reliable compared to fingerprint sensors - see table 1. For example, the iris pattern does not change with age and is also not subject to any external influences such as injuries. The risk that the wrong person gains access (false acceptance) is as low as about one to one million. The rate of the false rejections, that is, an authorised user is rejected, is also very low at below one percent. The iris recognition additionally is considered to be extremely forgery-proof, while fingerprint scanners could be outsmarted in the past with the help of fingerprints that the users themselves leave on the touch screen. Iris scanners in a mobile device Iris scanners consist of a special infrared LED (IRED), which illuminates the eye in a targeted manner, and a camera sensor which records an image of the eyes. The software identifies the pattern of the iris in the camera images and compares it with the stored data of the authorised person. The sensor and the IRED are mounted behind the device cover and are optically separated by a light-impermeable web – see figure 2. A bandpass filter above the camera now lets the relevant wavelength range relevant for the IRED pass through. Thereby, a good signal-to-noise ratio at the sensor is guaranteed even with powerful ambient light, for example on a sunny day. High-contrast camera images are an important requirement for iris scanners, so that the iris pattern can be read out with the highest reliability. It has to be considered thereby that the image Fig. 1: Access by eye contact: many manufacturers of mobile devices view iris scanners as a secure and reliable solution for biometric access control. contrast also depends on the eye colour and on the wavelength of the used light source. For brown, the most predominant eye colour worldwide, very good results are only achieved with infrared light. Blue and green eyes are, however, best reproduced with visible light, however good results can also be achieved using infrared illumination. Iris scanners therefore typically operate with wavelengths between 700 and 900 nm. 810 nm is currently rated as a good compromise, in order to obtain high-contrast images for all eye colours. Additionally, the typical reflections of the cornea, which can have an interfering effect on the iris recording, are minimal in this spectral range. The amount of light falling onto the eye is particularly significant for the achievable image contrast. This is a challenge with mobile devices, where there is little space and the current usage has to be as low as possible. While stationary units can use several IREDs, designs for smartphones or tablets have to make do with only one transmitter if possible. What is important here is high optical performance. Osram Opto Semiconductors has therefore developed a powerful IRED with a wavelength of 810 nm (figure 3) especially for iris scanners. The SFH 4780S contains a highly efficient thin film chip, in which two emission centres are realised with the help of nanostack technology. Compared to conventional chips with only one light-generating layer, the transmitter will thus be brighter by approx. 70 %, The SFH 4780S thereby generates a typical optical performance of 680mW at 1A. The second aspect is the efficient use of the available light. This succeeds if the radiation angle of the IRED is narrow enough in order to direct all optical performance, if possible, to the eye area to be illuminated. Due to the restrictions applying in mobile devices regarding the component height, this can only be implemented with difficulty with conventional lenses. Osram uses the Oslux housing for the SFH 4780S, which was previously used with visible spectrum LEDs – for example for flashlight applications in a mobile phone. With the help of an internal reflector and a specially adapted lens, a flat transmitter resulted, with a height of only Dr Stefan Margott is LED Marketing Manager at Osram Opto Semiconductors – www.osram-os.com 28 Electronic Engineering Times Europe December 2015 www.electronics-eetimes.com


EETE DEC 2015
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