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Fig. 4. Sensor calibration function for PMMA. Continuous lines show the constant mass, and dashed lines show the constant stress of PMMA film. From described simulation and experimental results constant mass and constant stress curves in resistance vs. resonance frequency changes coordinate system, shown in Fig 4, were built. The mass is per single cell and in this case it is linearly related to the volume of the PMMA film limited by the single CMUT cell area. Cubic spline interpolation was used to smooth the constant mass lines. Using this calibration function one can relate the changes of the sensor readings (resonance frequency and resistance change) with the mass of the film built on the sensor area if the stress of the film is known. For increased accuracy, the stress of the film can be measured, for instance, using the method described by Yara lioglu et al. [8]. It is important to note that increasing mass of the film on the sensor surface, if related with simultaneous development of significant elasticity and stress, can cause the increase of

Figure 4 Sensor calibration function for PMMA. Continuous lines show the constant mass, and dashed lines show the constant stress of PMMA film. From described simulation and experimental results constant mass and constant stress curves in resistance vs. resonance frequency changes coordinate system, shown in Fig 4, were built. The mass is per single cell and in this case it is linearly related to the volume of the PMMA film limited by the single CMUT cell area. Cubic spline interpolation was used to smooth the constant mass lines. Using this calibration function one can relate the changes of the sensor readings (resonance frequency and resistance change) with the mass of the film built on the sensor area if the stress of the film is known. For increased accuracy, the stress of the film can be measured, for instance, using the method described by Yara lioglu et al. [8]. It is important to note that increasing mass of the film on the sensor surface, if related with simultaneous development of significant elasticity and stress, can cause the increase of

Related Figures (4)

Fig. 1. a) CMUT capacitive cell structure used in finite element analysis; b) photograph of the multiple sensor elements wirebonded to the printed circuit board.
Fig. 1. a) CMUT capacitive cell structure used in finite element analysis; b) photograph of the multiple sensor elements wirebonded to the printed circuit board.
conditions, two kinds of the films, coated over the CMUT surface with different curing regimes, were prepared. Films with elevated stress and elasticity were prepared according to PMMA datasheet: after PMMA spin coating sensors were cured for 2 min at 180 °C on the hotplate, followed by natural cooling at room temperature. PMMA films processed this way were passing the PMMA glass transition temperature Fig. 2. Finite element model verification: a) measured frequency spectra of the real part of the CMUT impedance as a function of bias voltage; b) peak resistance values and resonance frequency of two sensor elements; markers show measured values, and lines show finite element model output: frequency — continuous line; resistance — dashed line.
conditions, two kinds of the films, coated over the CMUT surface with different curing regimes, were prepared. Films with elevated stress and elasticity were prepared according to PMMA datasheet: after PMMA spin coating sensors were cured for 2 min at 180 °C on the hotplate, followed by natural cooling at room temperature. PMMA films processed this way were passing the PMMA glass transition temperature Fig. 2. Finite element model verification: a) measured frequency spectra of the real part of the CMUT impedance as a function of bias voltage; b) peak resistance values and resonance frequency of two sensor elements; markers show measured values, and lines show finite element model output: frequency — continuous line; resistance — dashed line.
Fig. 3. Simulated and measured CMUT resonance frequency (a) and peak resistance (b) changes due the loading of the surface with PMMA. Markers show measurement results and lines show simulated results. Triangle markers show the results obtained from two experiments, when the PMMA film was coated on the sensor surface and cured at 180 °C, thus passing the glass transition temperature. Square markers show the values measured when PMMA film was dried at 50 °C, without glass transition.
Fig. 3. Simulated and measured CMUT resonance frequency (a) and peak resistance (b) changes due the loading of the surface with PMMA. Markers show measurement results and lines show simulated results. Triangle markers show the results obtained from two experiments, when the PMMA film was coated on the sensor surface and cured at 180 °C, thus passing the glass transition temperature. Square markers show the values measured when PMMA film was dried at 50 °C, without glass transition.
Fig. 5. Immunosensor readings in resonance frequency and resistance changes coordinate system after surface modification by BLV gp51 (diamonds) and after interaction with analyte anti-gp51 (squares).
Fig. 5. Immunosensor readings in resonance frequency and resistance changes coordinate system after surface modification by BLV gp51 (diamonds) and after interaction with analyte anti-gp51 (squares).
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