One Case a Day | China: Determination of Implicit Limitations for Missing Essential Technical Features - Supreme People's Court Intellectual Property Final No. 779 (2025)

Case Introduction
Today’s case is a fresh ruling from ten days ago—one of the few cases involving the issue of missing essential technical features and where the second-instance court reversed the judgment. In this case, the parties had no dispute over whether the claims lacked essential technical features (which the author found surprising). The only point of contention was whether Claim 1 implicitly recorded the corresponding content.

Readers may consider the following question while reviewing this case:

The two features—“two permanent magnets arranged side by side in parallel” and “the magnetic sensing unit positioned on the central axis of the two permanent magnets”—appear to optimize the technical solution. However, is it possible that a technical solution lacking these two features still outperforms existing magnetic pressure sensors using a single permanent magnet?

Readers are welcome to share their thoughts in the comments.

Case Information

• Application Number: 201510552636.1
• Invention Title: A Magnetic Pressure Sensor
• Invalidation Decision Information: No. 581032
• First-Instance Information: (2025) Jing 73 Xing Chu No. 2023
• Second-Instance Judgment Date: December 21, 2025
• Second-Instance Judgment: (2025) Supreme People's Court Intellectual Property Final No. 779

Basic Facts
The involved patent relates to a magnetic pressure sensor, which improves upon an existing magnetic pressure sensor using a single permanent magnet (refer to the figure below, annotated by the author based on the involved patent). The linear region of a single permanent magnet is very small, and its magnetic field is strong, making it prone to saturation and thus unsuitable for thinner and lighter sensor designs.

The examination basis for Claim 1 is as follows:

1. A magnetic pressure sensor, comprising a bracket (15), a magnetic sensing unit (11) fixed inside the bracket, and two permanent magnets (12A, 12B). The magnetic sensing unit (11) has a sensitive axis (1). It is characterized in that the two permanent magnets (12A, 12B) are respectively arranged along the direction of the sensitive axis (1) of the magnetic sensing unit and are located on the same side of the magnetic sensing unit (11). The two permanent magnets (12A, 12B) are of the same size and have the same magnetization direction (31). The direction of the sensitive axis (1) of the magnetic sensing unit (11) is parallel to the magnetization direction (31) of the permanent magnets.

All parties explicitly agreed on the following:

First, the following are essential technical features for solving the technical problem of this patent:
① “Two permanent magnets of the same size and with the same magnetization direction are arranged side by side as shown in Figure 1” and
② “The magnetic sensing unit is positioned on the central axis of the two permanent magnets as shown in Figure 1.”

Second, Claim 1 does not explicitly define the above technical features.

Controversial Focus
Whether Claim 1 of this patent lacks essential technical features. Further, the second-instance court held that the substantive focus of the parties’ dispute in the second instance was to determine whether Claim 1 of this patent implicitly defined the essential technical features of “two permanent magnets arranged side by side in parallel” and “the magnetic sensing unit positioned on the central axis of the two permanent magnets.”

The challenged invalidation decision held that when determining whether a claim lacks essential technical features for solving the technical problem, it is inappropriate to directly interpret the claim based on the technical problem claimed in the description and to treat technical features recorded only in the description but not in the claims as implicitly defined technical features in the claim for solving that problem.

The patentee argued that the purpose of this patent is to increase the linear width of the sensitive element in the pressure sensor, i.e., to expand the linear region where the magnetic field strength changes with position. Specifically, addressing the scenario in the prior art where only a single permanent magnet provides a linear detection region, Claim 1 defines the arrangement of the permanent magnets as “two permanent magnets of the same size, with the same magnetization direction and parallel orientation.” Based on this, a person skilled in the art would arrive at the only possible arrangement: two permanent magnets arranged side by side in parallel. Further, based on the fundamental principles of permanent magnet magnetic field distribution, a person skilled in the art would clearly know that the central axis position of these two permanent magnets is where a linear magnetic field strength variation region exists. Combined with the purpose of the invention described in the specification and the limitation in Claim 1 that “the two permanent magnets are respectively arranged along the direction of the sensitive axis of the magnetic sensing unit and are located on the same side of the magnetic sensing unit,” a person skilled in the art would inevitably choose to position the magnetic sensing unit on the central axis of the two permanent magnets. Therefore, considering the description and drawings, a person skilled in the art can make the only reasonable choice for the arrangement of the permanent magnets and the magnetic sensing unit based on the claims, and Claim 1 does not lack essential technical features.

First-Instance Court’s Opinion
In this case, one of the purposes of this patent is to solve the technical problem of the narrow linear width of the sensitive element in the pressure sensor and to increase the linear region where the magnetic field strength changes with position. Specifically, addressing the scenario in the prior art where only a single permanent magnet provides a linear detection region, Claim 1 defines the arrangement of the permanent magnets as “the two permanent magnets are respectively arranged along the direction of the sensitive axis of the magnetic sensing unit,” “located on the same side of the magnetic sensing unit,” and “the two permanent magnets are of the same size and have the same magnetization direction.” According to paragraph [0028] of the description, the working principle of this patent is to apply the pressure F to be detected to the pressure sensor, causing bracket deformation and movement of the permanent magnets, thereby measuring the magnetic field change at the magnetic sensing element. At this point, given the known relationship between pressure and deformation, it is necessary to create a linear relationship region between the displacement of the permanent magnets and the magnetic field change for easy detection. Based on this, a person skilled in the art knows that the arrangement of the permanent magnets and the magnetic sensing element is related to magnetic field distribution, which in turn is related to the linear detection region. Considering the purpose of expanding the linear detection region and the technical features of the permanent magnets and the magnetic sensing unit already defined in the claims, a person skilled in the art can reasonably exclude non-symmetrically parallel arrangements of the permanent magnets. In other words, the permanent magnets should adopt a “left-right symmetrical and parallel arrangement.” Further, based on common knowledge in the field, it can be determined that the position on the central axis of two symmetrically parallel permanent magnets is the magnetic field linear variation region usable for detection, and the magnetic sensing unit would inevitably be placed there. This arrangement is consistent with the description in paragraph [0031] of the specification: “For this purpose, two permanent magnets may be used instead of a single permanent magnet. The magnetic field distribution is shown in Figure 9. It can be seen from the figure that the magnetic field lines are straight at the central axis position of the two permanent magnets, and the magnetic field in this region changes linearly with deformation (displacement in the z-axis direction). Moreover, the magnetic field in this position is smaller, and the linear region is larger. Therefore, using two permanent magnets is the preferred design of this invention.” It is also consistent with the arrangement shown in Figure 1 for the permanent magnets and the magnetic sensing unit and the magnetic field distribution shown in Figure 9, achieving the purpose of providing a larger linear detection range. Therefore, considering the description and drawings, a person skilled in the art can make the only reasonable choice for the arrangement of the permanent magnets and the magnetic sensing unit based on the claims, and Claim 1 does not lack essential technical features.

Second-Instance Court’s Opinion
When determining whether a claim lacks essential technical features, the claim should be interpreted reasonably and in accordance with the purpose of the patent invention. However, technical features implicitly defined in the claim that align with the purpose of the invention should be content that a person skilled in the art can directly and unambiguously derive from the wording of the claim to achieve the purpose recorded in the description, rather than directly “reading into” the claim technical content recorded only in the description that is necessary to achieve the purpose of the invention. Such interpretation exceeds reasonable and necessary limits and lacks corresponding legal basis.

In this case, according to paragraphs [0008] and [0031] of the description and Figure 1 of the drawings, it is clear that “two permanent magnets of the same size and with the same magnetization direction arranged side by side” and “the magnetic sensing unit positioned on the central axis of the two permanent magnets” are essential technical features for solving the technical problem of this patent. The parties had no dispute over this.

However, the wording of Claim 1 of this patent does not explicitly define “two permanent magnets arranged side by side in parallel” and “the magnetic sensing unit positioned on the central axis of the two permanent magnets.” Moreover, a person skilled in the art, by reading the relevant wording recorded in Claim 1 of this patent, cannot directly and unambiguously derive technical features such as “two permanent magnets arranged side by side in parallel” and “the magnetic sensing unit positioned on the central axis of the two permanent magnets.” That is, Claim 1 of this patent does not implicitly define the technical features of “two permanent magnets of the same size and with the same magnetization direction arranged side by side” and “the magnetic sensing unit positioned on the central axis of the two permanent magnets” that align with the purpose of the invention.

In summary, the lack of limitations in Claim 1 of this patent regarding the “side-by-side arrangement” of the two permanent magnets and the “positioning of the magnetic sensing unit on the central axis of the two permanent magnets” results in it lacking essential technical features.

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