dr.ir. G. de Graaf

Bioelectronics (BE), Department of Microelectronics

Expertise: Microsystems for gas sensing, optical spectrometry and precision circuits for readout. Micromachining and microfabrication technology in general. COMSOL. Tanner Tools (LEdit), TFCalc, MacLeod (thin film optics).


Ger de Graaf was born a long time ago in Delft. He has been a staff member at the Electronic Instrumentation Laboratory of the Faculty of Electrical Engineering at Delft University of Technology since 1976.

He received his BSEE degree in Electrical and Control Engineering with honours from the Technische Hogeschool in Rotterdam in 1983. His graduation project was on the damping of piezo-electric accelerometers by active feedback, supported by Bruel&Kjaer. From 1992 to 1996 he was a system manager and also owned a part-time consultancy company specializing in computer controlled measurement systems, working on an automated system for the energy measurement of heating systems in apartment buildings.

He has worked on the design of circuits for optical sensors in bipolar and CMOS technology. After this he started working on MEMS, mainly on infrared sensors and capacitive accelerometers and mixed-mode CMOS signal processing circuits for these devices. Around 2003 he started his PhD project on infrared optical systems and in 2008 he received his Ph.D. Degree from Delft University with the dissertation "Mid-Infrared Microspectrometer Systems". He is a (co-)author of around 130 scientific publications and main author of around 30 international scientific papers since 1988. He is a member of the IEEE and holds one patent.He was a project leader in an STW project on sensors for natural and combustible gas and participates in the national EDGaR gas research project.


Currently I am a tutor and mentor for two groups in the first year student lab projects. At present I work on IC compatible gas sensors for gas sensing, impedance spectroscopy and optical spectroscopy for biomedical applications.

Projects history

CMOS-Compatible Hot-Wire CO2 Sensors

In the project, we have developed CMOS-compatible CO2 sensors that detect the CO2-dependent heat loss of a suspended hot-wire transducer using dedicated precision readout electronics.

  1. Opto-chemical pH detection of Myocardial Ischaemia using Fluorescent Hydrogels
    Ger de Graaf; Maurits Frans Vriesendorp; Amin Hassan; Patrick James French;
    IEEE Sensors Journal,
    Volume 22, Issue 11, pp. 10901-10909, June 2022. DOI: doi: 10.1109/JSEN.2022.3166709
    Keywords: ... Fluorescence, ischaemia, hydrogel, optical pH probe, HPTS, pyranine, fluorescent dye, dual wavelength excitation, ratiometric detection.

    Abstract: ... In this research fluorescent optochemical pH probes for the detection of ischaemia have been investigated. Myocardial ischaemia is the most prominent risk during heart surgery. During open heart surgery the heart is temporarily arrested and, since there no blood flowing, oxygen supply and removal of waste products is stopped and heart cells can be damaged. In this paper we propose a novel method to monitor the condition of the heart by placing optochemical pH sensors on several strategic places around the heart during surgery. Low cost opto-chemical pH sensors, using a HPTS (8-hydroxy-1,3,6-pyrene trisulfonic acid trisodium salt) fluorescent dye encapsulated in a thin bio-compatible hydrogel layer, were investigated for this application. Our research started with an extensive optical characterization of several types of hydrogel layers at different pH levels. Secondly a reflection probe prototype using several of these layers was designed, built and tested. Dual wavelength excitation and ratiometric detection of the fluorescent signals was used to detect the pH level. Typical output signals of 35% to 53% per pH in the range from 6.5-8.0 pH have been measured and a response time of typically 400 seconds was obtained for the prototypes. Finally based on our measurements on the HPTS layers and the reflection probe we propose an improved type of pH probe for the detection of ischaemia during open heart surgery.

    G. de Graaf; D. Kuratomi Cruz; J. Haartsen; F. Hooijschuur; P. French;
    IEEE Transactions on Biomedical Circuits and Systems.,
    Volume 13, Issue 5, pp. 1052-1062, 10 2019. DOI: 10.1109/TBCAS.2019.2930312
    Keywords: ... IR Sensor, heart rate, ear piece.

    Abstract: ... The heart rate is a vital indicator of the health state of an individual. By continuously monitoring it, the fitness and health of the cardiovascular system of a user can be analyzed and impending problematic health episodes could be addressed better. Existing techniques to measure heart rate, such as electrocardiogram or photoplethysmography, are either uncomfortable for the user, or are not low-power or sensitive to motion artifacts. Infrared thermography is a non-contact technique with improved user comfort and low power consumption. In this paper, we have analyzed, built, and tested a novel system that uses infrared differential thermometry to detect the heart rate in the auricle. The sensor system was fitted into a commercial headphone since this paper is a first step into integration of the system in a Bluetooth headset. To the best of our knowledge, there has been no previous work on the detection of the heart rate signal in the ear using infrared thermometry. Positive results have been obtained after extraction of the frequency features of the bioheat transfer signal on test persons in rest.

  3. Heart rate monitoring using infrared thermometry in an earpiece
    D. Kuratomi Cruz; G. de Graaf; J.C. Haartsen; F. Hooijschuur; P.J. French;
    In Ravinder Dahiya, Srinivas Tadigadapa (Ed.), 2017 IEEE SENSORS,
    IEEE, IEEE, pp. 3, November 2017.
    Keywords: ... Heart rate; Infrared Thermometry; Wavelet Transform..

    Abstract: ... Heart rate is a key factor in cardiovascular system monitoring and sports science. Some recent commercial applications use sensors in the ear but are faced with motion artifacts which corrupts the signal. Infrared thermography is a non-contact technique and may minimize motion effects with better user comfort and lower power consumption. We propose a novel system that uses infrared differential thermometry to detect the heart rate in the auricle. The signal analysis is performed using a continuous wavelet transform which extract frequency features of the bioheat transfer waveforms. Preliminary results taken from the neck provide proof of concept and similar results from the ear are expected.

    ISBN: 978-1-5090-1012-7

  4. Silicon carbide thin film encapsulation of planar thermo- electric infrared detectors for an IR microspectrometer
    V. Rajaraman; G. de Graaf; P.J. French; K.A.A. Makinwa; R.F. Wolffenbuttel;
    {van Honschoten}, J; H Verputten; H Groenland (Ed.);
    MME, , pp. 20-23, 2010.

  5. Optical measurements on drain fluid for the detection of anastomotic leakage
    L. Pakula; D. Tanase; G. de Graaf; P.J. French; K. Kraal; J.F. Lange;
    In s.n. (Ed.), Proceedings of the 3rd annual International IEEE EMBS Special Topic Conference on Microtechnologies in Medicine and Biology,
    IEEE, pp. 72-75, 2005. Editor onbekend JH.

  6. A CMOS Semi-Custom Chip for Mixed Signal Designs
    Van Genderen, AJ; Cotofana, SD; De Graaf, G; Kaichouhi, A; Liedorp, J; Nouta, R; Pertijs, MAP; Verhoeven, CJM;
    In Book of abstracts, ProRISC 2004,
    ProRISC, 2004.

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Last updated: 8 Feb 2023