Schematic operating principle of the MiLD sensor
The micro laser Doppler sensor (MiLD) aims to measure the velocity of light-scattering objects and can be used for in vivo assessment of the flow velocity of blood in the skin. Numerous disease symptoms and healing processes can be monitored. Currently available systems use optical fibres, but they are sensitive to movement and thus can hardly be used for mobile applications. In addition, the significance of using only one wavelength of light is limited to relative and sample-specific analysis results.
To remedy this, the MiLD sensor has several directly integrated laser sources (VCSEL). The sensor principle is based on the Doppler effect, which causes a frequency shift of the irradiated laser light at the moving scattering centres, effectively causing the backscattered light to undergo a frequency broadening. This broadening in the frequency spectrum of some 10 kHz can be described very well with an exponential decay. Here, the exponent shows a linear relationship with the flow velocity.
Application fields and innovations
- Non-contact velocity measurement of solids and liquids
- Medical application for the evaluation of the blood flow situation
- Increased information content by using multiple wavelengths (3 light sources per sensor)
- Mobile applications and monitoring by:
- Compact design
- Light sources adapted to the application (LEDs, VCSEL, laser)
- Avoidance of optical fibres
→ reduced motion artefacts
Technical parameters chip:
- Sensor size: 3.5 x 5.5 x 0.8 mm³
- Emitted laser power: < 5 mW
- Available wavelengths: 670, 780, 850 and 980 nm, others on request
- Power consumption: < 10 mW
- Output signals: µA to mA
An in-house developed control and analogue two-stage pre-amplification (low noise, 100 Hz to 50 kHz bandwidth) can be used. A 24 bit, 102.4 kHz A/D converter or better is recommended for data acquisition. Evaluation of the data is done on the computer, evaluation software on request.
Parts of the research and development work were funded by the Federal Ministry of Economics and Technology (FKZ: VF140011).