Petals have six rows of sensors, R0 to R5, on each face. R0, R1 and R2 have a single sensor; R3, R4 and R5 have two rows of sensors side-by-side. Each sensor has two or four rows of strips.
We have designed sensors which cover a petal with minimal gaps between them, and minimal but sufficient overlaps to neighbouring petals. Building in the stereo rotation of strips into the sensor design allows this. In the "Stereo Annulus Design" the strips are all full length; the guard structures and cut edge follow the stereo angle.
Why circular arcs at the inner and outer edges? Making the outer edge of R2 and inner edge of R3 into circular arcs simplifies dealing with the transition from rings with one sensor per row to rings with two sensors per row. Making the inner edge of R0 an arc of a circle, and the outer edge of R5 an arc of a circle makes these sensors cover the required radii without protruding beyond where they are needed. Then making all inner and outer edges, and all row boundaries, into arcs of circles gives one uniform family of sensors - the so-called "Stereo Annulus Design". All strips within a given row have the same length and therefore same noise and performance, while row lengths vary to maintain occupancy below 1 %.
The TDR/LTF design is available in EDMS. The input file jul16.geom gives the requirements and basic design dimensions. The resulting cut corners, active edges, and pitch are given in the .ods file.
The .svg images illustrate the sensors and how they are arranged on a petal. In the sensor pictures: The outer light grey circle is the original wafer. The smaller circle is the usable area. The wedge-shape with curved left and right edges are the sensors, with the cut-line around outside of the dark grey band, which represents the guard-ring area. The blue interior is the active area, with red strips. Each sensor has a coordinate system indicated at the centre; the axis are 10.000 mm long.
The algebra used and definitions of corners A, B, C, D and a, b, c, d is documented here.