T 0048/86 12-01-1988

Reasons for the Decision

1. The appeal is admissible.

2. There is no objection to the present version of Claim 1, since its subject-matter is adequately based on the original disclosure.

3. Novelty.

3.1. None of the documents referred to in II above describes an ultrasonic transducer comprising a polymer piezoelectric film with a reflective layer, the thickness of which lies in the range claimed in the characterising part of Claim 1. The conventional transducer mentioned in the impugned patent, column 1, lines 46-53, comprises a L/4- reflector, whereas the thickness range claimed in Claim 1 extends from 3 l/16 to l/32.

3.2. In the ultrasonic transducers known from documents D1, D2 and D3 the polymer film is backed with a metallic layer, which is only stated to serve as an electrode and in D1 and D2 is of unspecified thickness. In D3, where the transducer is mounted on a brass rod, the thickness, 1000A, of the metallic layer is well below l /32 and the rod is said to be of arbitrary length.

3.3. Documents D4 and D11 are exclusively concerned with ultrasonic transducers with ceramic piezoelectric elements. In the transducer known from D4 the electrodes and potting material of the ceramic element are structured to provide for impedance matching and damping. In document D11, theoretical and experimental values are indicated for the sound emission from the oscillating ceramic element at various frequencies as a function of the influence of the damping effect of a backing layer.

3.4. Document D7 theoretically describes the reflectivity and transmissibility of a plate in dependence on its thickness and the ratio of its acoustic impedance to that of various neighbouring media.

3.5. The other documents cited by the Appellant or in the European Search Report do not come closer to the subject-matter of Claim 1 and need not be discussed for an assessment of novelty. Therefore, the subject-matter of Claim 1 is considered novel.

4. Inventive step.

4.1. The prior art which comes nearest to the subject-matter of Claim 1 is that indicated in the description of the impugned patent, column 1, lines 46-53 and covers the preamble of Claim 1. Starting thus from the Respondent's own prior art statement, which was expressly confirmed to be valid in the oral proceedings, the objective problem underlying the impugned patent is to provide an ultrasonic transducer which retains the flexibility of its polymer piezoelectric film and the reflective layer of which is easy to etch; see the impugned patent column 1, line 53 to column 2, line 4. A person skilled in the art, who used the conventional L/4-transducer in practice, would automatically become aware of the fact that the provision of the L/4-reflective layer, although improving the conversion efficiency and broadening the frequency-band characteristic, seriously reduces the flexibility of the piezoelectric polymer film. Difficulties in etching the conventional L/4-layer would also appear during processing in practice. Whenever a problem consists solely in eliminating deficiencies of an object, which come to light when it is in use, the posing of such problem is obvious and cannot be considered to contribute to the inventive merit of its solution; see also the decision T 109/82, OJ EPO 1984, 473, point 5.1.

4.2. It remains to investigate whether it is obvious to a skilled person to solve the above-mentioned problem by reducing the conventional reflective layer thickness from L/4 to the claimed values in between 3 l/16 (l/5.3) and l/32.

4.2.1. Competent for one part of the above-mentioned problem, is the person skilled in the mechanical flexibility of composite material layer systems. The Board considers that such a person would know that the stiffening of a flexible polymer film by a backing layer becomes less with decreasing rigidity of the backing. The fact that the rigidity of the layer decreases with its thickness by no means represents an inventive finding but belongs to the normal general knowledge of the skilled person. Thus, simply by applying his routine abilities the skilled person would arrive at the finding that much of the flexibility of a polymer film can be retained if a reflective layer of thickness less than the conventional value of L/4 layer is used.

Furthermore, it is considered to form part of the general knowledge of the processing engineer, who is competent for the remaining part of the above-mentioned problem, that thinner material layers can be etched more easily and precisely.

For the above reasons the Board is convinced that it is obvious for a skilled person to find out in which direction he has to work in order to overcome the disadvantages of the prior art. Therefore, the Respondent's argument of hindsight - cf. point VII-b above - does not appear relevant and no inventive step can be seen in the skilled man's solution to reduce the conventional L/4-thickness of the known reflective layers of polymer piezoelectric films.

4.2.2. In the Board's view the skilled person considering such a reduction in thickness would be aware that this might significantly alter the operating parameters of the transducer and would proceed with caution by trial and error, measuring these parameters at the different reflective layer thicknesses to assure himself that they suffered no radical deterioration.

If the graphs of Figure 7 of the impugned patent apply for all transducers having the features of Claim 1, as is tacitly assumed by the respondent in his argument that these properties are surprising and thus form the basis for a finding that the subject-matter of Claim 1 is inventive, the skilled person would, as a matter of course, find that these properties, far from deteriorating, showed a modest improvement with decreasing thickness. All the properties plotted in Figure 7 show only a slow progressive change with thickness rather than an improvement restricted to a narrow range of thicknesses.

No inventive merit can be attributed to selection of the end values of the range quoted in Claim 1. The upper limiting value is clearly quite an arbitrary value at which no sudden change in operating parameters or flexibility has been shown to occur.

Figure 7 of the impugned patent furthermore shows that a skilled person, continuing to work in the obvious direction and testing transducers with still thinner reflective layers, will realise both the continuing decrease of the peak transfer loss down to about l/32 and its increase beyond this value. Thus, a skilled person continuing the obvious reduction of the reflective layer thickness for optimum transducer flexibility will find the disadvantageous transducer properties for thicknesses smaller than l/32 by routine trial and error. For this reason also the definition of the lower limiting value l/32 of the claimed thickness region does not imply an inventive step.

Any skilled person performing the investigation discussed above would recognise that values between these limits would provide satisfactory results and that the best choice for a given application would depend on whether flexibility, precise etching or excellent electro-acoustic performance was the most important property.

4.2.3. A party, who wishes to rely on a prejudice, which might have diverted the skilled man away from the alleged invention has the onus of demonstrating the existence of such prejudice; see also the decision T 119/82, OJ EPO 1984, 217, point 14. The Respondent, however, has submitted no evidence, that in the prior art a real prejudice existed against any deviation from the conventional L/4-reflective layer thickness. For this reason, the Respondent's statement in point VII-b, that the skilled person hitherto believed that only reflective layers with L/4 thickness would result in a workable transducer, has to be assessed as a mere allegation.

A prejudice against the reduction of the conventional L/4 thickness of a reflective layer can also not be derived from any cited prior art document, in particular not from document D7, Figure 6. The Board agrees with the Respondent's view in point VII-c above with regard to the fact that Figure 6 of document D7 represents in particular the sound transmissibility of an aluminium plate in water at various plate thicknesses. However, the Board takes the view that a skilled person knows that there is an inverse relationship between transmissibility and reflectivity as shown in Bild 5 of D7 and that he will thus derive from the extremely flat minimum of the aluminium curve in Figure 6 of D7 the information that, in particular for a plate material with relatively high sound impedance, i.e. for small m-values, the plate is highly reflective not only at a thickness of L/4 but also at thicknesses well within the thickness region claimed in Claim 1. Equation 33 of document D7, which allow transmissibility values for a reflective layer in between two different media to be determined, leads to essentially the same results for a material combination used in a conventional ultrasonic transducer, for instance the polymer-reflective-layer- holder substrate materials of the preferred embodiment of the alleged invention. If an aluminium plate were only reflective at L/4, the transmissibility curve in Figure 7 would have the form of an extremely narrow minimum or even show a singularity.

4.3. The question as to whether a skilled person is able to derive from the transmitter behaviour of the transducer in Figures 4 and 5 of document D11 - i.e. from the conversion efficiency of electric energy into mechanical sound energy for a damped ceramic oscillator - any information about the sensor behaviour of such structure - i.e. about the conversion efficiency of mechanical sound energy into electric energy or about the amount of unconverted and thus transmitted sound energy - can be left open in view of points 4.1 to 4.2.3 above; cf. also point VI-c above.

4.4. For the reasons set out in points 4.1 to 4.2.3 above, the subject-matter of Claim 1 does not involve an inventive step within the meaning of Article 56 EPC and consequently the maintenance of the impugned patent with Claim 1 is prejudiced by Article 100(a) EPC. Claims 2-11 cannot be maintained because of their dependence on Claim 1.