Means-plus-function language in patent claims is interpreted very differently in Australia compared to the US. This can lead to vastly different findings with regards to validity and/or infringement.
The US approach to interpreting a means-plus-function limitation is unique. Such a limitation has its scope whittled down to the specific structure disclosed in the specification that enables the function to be achieved. This is counterbalanced somewhat by the doctrine of equivalents, which extends the scope of the claim to include mechanical equivalents of that disclosed structure.
This treatment of means-plus-function language is a consequence of 35 USC 112, paragraph 6, which states: “…An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.”
In Australia, there is no statutory law for forcing a narrow interpretation of means-plus-function language. From case law, interpretation of a patent claim is primarily dictated by the plain meaning of the words in the claims. Although a purposive construction should to be taken, it is not permitted to broaden or narrow the wording of a claim by referring to details recited in the body of the specification but not in the claims.1 There is no doctrine of equivalents, but the doctrine is not necessary because the claim is not narrowed to any specific embodiment(s) disclosed in the specification.
Australian law presently enables relatively broad claims compared to the level of disclosure provided in the body of the specification. The requirement for disclosure is to ‘describe the invention fully’, which means providing sufficient description to enable the person skilled in the art ‘to produce something within each claim without new inventions or additions or prolonged study of matters presenting initial difficulty’.2 In other words, only one way of achieving the claimed invention needs to be disclosed. Furthermore, the Australian requirement for a claim to be ‘fairly based’ on the specification allows that in a case where a claim is to a means for achieving a particular result, and that result is new, all ways of achieving that result are covered by the claim.3
Compared to the US, the Australian position often results in a broader claim, which is soundly based on the specification. The resulting broader claim interpretation may make it easier to catch a potential infringer. However, on the flip side, the broader claim has a greater likelihood of reading on prior art and therefore being found invalid.
Australian law will soon require a higher standard of disclosure than is presently the case. It is unknown whether and how these changes to Australian law will impact on means-plus-function language. However, the changes will, in any case, have no effect on already granted patents or on patent applications for which examination is requested on or before 12 April 2013.
1. Decor Corporation Pty Ltd and Another v Dart Industries Inc (1988) 13 IPR 385
2. Kimberly-Clark Australia Pty Ltd v Arico Trading International Pty Ltd (2001) 207 CLR 1, 
3. Lockwood Security Products Pty Ltd v Doric Products Pty Ltd  HCA 58