**5. Skin technology and experimental results**

The basic structure of skin prototypes based on PVDF arrays is reported in Figure 9. Piezoelectric sensors have to be integrated on a rigid substrate and an elastomer layer is integrated on top as protective layer. This section briefly describes the technological solutions adopted to assemble the different building blocks. Details will be contained in a forthcoming publication.

The triangular geometry, taxel size and positions have been chosen to reproduce existing conformable skin patches manufactured at IIT (Italian Institute of Technology, Genoa) and based on capacitive transducers (*Roboskin project*).

Among technology solutions, how to provide PVDF films with metal contacts is a crucial point. Although metalized PVDF is commercially available, the brittleness of some of the available coatings (Copper over nickel, aluminum on chrome), the high roughness of the screen-printed silver ink solution and the impossibility of obtaining - as a prototyping service - custom patterning of the conducting film from the suppliers, convinced us that operating a "home-made" metallization was a better choice. We thus purchased *bare* piezoelectric polymer foils and made ad-hoc electrodes employing inkjet deposition technologies.

A whole metal layer (common ground) is deposited on top of the PVDF film, while patterned contacts with the same geometry of metal contacts on PCB (Figure 9) are deposited on the PVDF bottom side. Conductive glue has been used to fix the PVDF film on the PCB. The cover lay avoids short-circuits between taxels due to the employed glue. The protective layer is finally integrated on top. A Two-part silicone Sylgard® 184 Silicone Elastomer (*Dow Corning*) that cures to a flexible elastomer (PDMS) has been employed and it is directly polymerized on the PCB. Adhesion between PDMS and PVDF has been increased by the use of an *adhesion promoter*. A 2,5mm thick layer has been finally chosen as optimally meeting the application requirements.

**Figure 9.** Structure of skin prototypes based on piezoelectric polymer arrays.

626 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

the *frequency band of interest*.

Figure 8 shows that op amps in Table 5 satisfy the 1 Hz ÷ 1 kHz bandwidth specification for

The experimental results validate the proposed circuit approach. The behaviour of the interface electronics is linear in the given frequency range. The input signal range of the interface electronics was able to measure up to 3 orders of input force magnitude range. In order to extend the input range of the detectable signal up to the 5 orders of magnitude expected for the application, a variable gain amplifier is currently under development.

**Figure 8.** Comparison between the ideal and CA frequency responses using an ideal op amp, the

the different building blocks. Details will be contained in a forthcoming publication.

The basic structure of skin prototypes based on PVDF arrays is reported in Figure 9. Piezoelectric sensors have to be integrated on a rigid substrate and an elastomer layer is integrated on top as protective layer. This section briefly describes the technological solutions adopted to assemble

The triangular geometry, taxel size and positions have been chosen to reproduce existing conformable skin patches manufactured at IIT (Italian Institute of Technology, Genoa) and

Among technology solutions, how to provide PVDF films with metal contacts is a crucial point. Although metalized PVDF is commercially available, the brittleness of some of the available coatings (Copper over nickel, aluminum on chrome), the high roughness of the screen-printed silver ink solution and the impossibility of obtaining - as a prototyping service - custom patterning of the conducting film from the suppliers, convinced us that operating a "home-made" metallization was a better choice. We thus purchased *bare* piezoelectric

polymer foils and made ad-hoc electrodes employing inkjet deposition technologies.

OPA703 and the OPA348/7 with their corresponding finite GBPs.

**5. Skin technology and experimental results** 

based on capacitive transducers (*Roboskin project*).

Figure 10 shows some results of experimental tests on triangular prototypes. A sinusoidal mechanical stimulus has been applied in correspondence of a certain taxel, by means of an indenter stiffly connected to an electromechanical shaker.

**Figure 10.** Comparison between experimental data at different frequencies and Boussinesq's model. Mean of peak values of sinusoidal waveforms at different frequencies are shown.

The tests have been conducted by varying the amplitude of the input force for different frequency values. Figure 10 shows the measured charge at 12 Hz, 162 Hz and 362 Hz compared with the value obtained using the Boussinesq's equation (see Section 3.2). As it can be seen a good correspondence can be found. A good linearity is achieved over the whole explored range, and the same voltage-to-force behavior for different frequencies is recorded (in accordance with *d33* results reported in Section 3.1).
