By means of subsequent additive gold evaporations each electrode has shown a different thickness, resulting in distinct oscillation frequencies, always lower than that of the blank quartz. The geometry of each electrode has been tuned in order to keep most of the vibrational energy near to the region of the electrodes (energy trapping) and their area has been taken below the Bechmann’s number, so that the responses of the anharmonic overtones are negligible [14]. With this particular design and optimizing the distance between the electrodes [15], it is possible to maintain the channel-to-channel interference at a very low level.The implemented MQCM (Figure 1) is a four-ports network, characterized by a scattering matrix, representing the reflected and transmitted powers at each port, in the frequency domain.

In this way, the network is fully characterized by knowing the 10 independent coefficients, Sij.Figure 1.The prototype of a MQCM layed on a single quartz plate used for the electrical characterization.The outline of the scattering matrix measurements is depicted in Figure 2. The Sij parameters have been measured by a network analyzer (Agilent Technologies E5061A), exciting the jth port with a driving power in the frequency range of interest and reading the reflected power on the ith port. Contemporarily, the remaining two ports have been closed with the internal adapting impedance of the instrument, i.e. 50��.Figure 2.Outline of the scattering coefficients measurements for the MQCM device, represented as a four-ports network (on the left).

The scattering matrix (on the right) is characterized by 10 independent parameters, since the matrix is reciprocal (i.e. sij=s …The resulting scattering parameters are plotted in Figure 3 and and4.4. The absolute values of the reflection parameters point out the good separation of the four channels in the frequency range of interest, while the moduli of the transmission parameters, showing typical values of less than -60 dB, indicate the low existing channel-to-channel crosstalk, always less than -40 dB [16]. This result ensures that the channels oscillate almost independently on each others.Figure 3.Moduli of the reflection parameters of the four ports network corresponding to the MQCM.Figure 4.Moduli of the transmission parameters of the four ports network corresponding to the MQCM.

In order to test the characteristics of the MQCM transducer a chemical sensor has been implemented utilizing a new semiconducting co-polymer, namely poly [phenylacetylene-(co-2-hydroxyethyl methacrylate)] (P(PA/HEMA)), synthesized in the form of monodispersed nanospheres. Cilengitide The use of different reaction conditions during the synthesis of this co-polymer allows to modulate dimension, polydispersity and superficial charge of the beads [17].