[WIP] Asymmetric CPW structures

nbs/palace_2d_cpw.py

@@ -5,7 +5,7 @@
 #       extension: .py
 #       format_name: percent
 #       format_version: '1.3'
-#       jupytext_version: 1.19.2
+#       jupytext_version: 1.19.3
 #   kernelspec:
 #     display_name: .venv
 #     language: python
@@ -25,6 +25,10 @@
 # %% [markdown] papermill={"duration": 0.003686, "end_time": "2026-06-12T07:04:20.157977", "exception": false, "start_time": "2026-06-12T07:04:20.154291", "status": "completed"}
 # ### Define GSG electrode
 
+# %%
+# %load_ext autoreload
+# %autoreload 2
+
 # %% papermill={"duration": 2.54829, "end_time": "2026-06-12T07:04:22.708430", "exception": false, "start_time": "2026-06-12T07:04:20.160140", "status": "completed"}
 from pathlib import Path
 
@@ -48,28 +52,41 @@ def gsg_electrode(
     length: float = 800,
     s_width: float = 20,
     g_width: float = 40,
-    gap_width: float = 15,
+    g_width_top: float | None = None,
+    g_width_bottom: float | None = None,
+    gap_width_top: float = 15,
+    gap_width_bottom: float = 15,
     layer=LAYER.TopMetal2drawing,
 ) -> gf.Component:
     """
     Create a GSG (Ground-Signal-Ground) electrode.
 
+    Supports different gap widths on the top and bottom sides
+    of the signal electrode for asymmetric CPW modelling.
+    Also supports different ground electrode widths.
+
     Args:
         length: horizontal length of the electrodes
         s_width: width of the signal (center) electrode
-        g_width: width of the ground electrodes
-        gap_width: gap between signal and ground electrodes
+        g_width: width of the ground electrodes (default, used if g_width_top/bottom are None)
+        g_width_top: width of the top ground electrode (overrides g_width)
+        g_width_bottom: width of the bottom ground electrode (overrides g_width)
+        gap_width_top: gap between signal and top ground electrode
+        gap_width_bottom: gap between signal and bottom ground electrode
         layer: layer for the metal
     """
+    g_width_top = g_width if g_width_top is None else g_width_top
+    g_width_bottom = g_width if g_width_bottom is None else g_width_bottom
+
     c = gf.Component()
 
-    r1 = c << gf.c.rectangle((length, g_width), centered=True, layer=layer)
-    r1.move((0, (g_width + s_width) / 2 + gap_width))
+    r1 = c << gf.c.rectangle((length, g_width_top), centered=True, layer=layer)
+    r1.move((0, (g_width_top + s_width) / 2 + gap_width_top))
 
     _r2 = c << gf.c.rectangle((length, s_width), centered=True, layer=layer)
 
-    r3 = c << gf.c.rectangle((length, g_width), centered=True, layer=layer)
-    r3.move((0, -(g_width + s_width) / 2 - gap_width))
+    r3 = c << gf.c.rectangle((length, g_width_bottom), centered=True, layer=layer)
+    r3.move((0, -(g_width_bottom + s_width) / 2 - gap_width_bottom))
 
     c.add_port(
         name="o1",
@@ -92,7 +109,15 @@ def gsg_electrode(
     return c
 
 
-c = gsg_electrode()
+c = gsg_electrode(
+    length=800,
+    s_width=20,
+    g_width=40,
+    g_width_top=40,
+    g_width_bottom=40,
+    gap_width_top=15,
+    gap_width_bottom=15,
+)
 cc = c.copy()
 cc.draw_ports()
 cc
@@ -121,8 +146,10 @@ def gsg_electrode(
 mode_sim.set_airbox(margin_x=50.0, margin_y=50, z_above=100.0, z_below=100.0)
 mode_sim.set_geometry(c)
 
+freq = 30e9
+
 mode_sim.set_cross_section("x=0")
-mode_sim.set_boundary_mode(freq=50e9, num_modes=2, save=2)
+mode_sim.set_boundary_mode(freq=freq, num_modes=2, save=2)
 
 # Inspect the geometric cross section before meshing.
 section = cross_section.extract_plane_section(c.copy(), stack, axis="x", value=0.0)
@@ -165,21 +192,82 @@ def gsg_electrode(
 importlib.reload(field_viz)
 importlib.reload(palace_results)
 
-# If this kernel still holds an older PalaceTextResults object, rebuild it from disk.
-if not hasattr(mode_results, "modes"):
-    mode_results = palace_results.load_text_results("./palace-sim-cpw-waveport-2d")
+# If this kernel still holds an older PalaceTextResults object (e.g. from a
+# previous run_local that didn't set freq_hz), patch in the correct frequency.
+if not hasattr(mode_results, "freq_hz") or mode_results.freq_hz is None:
+    mode_results.freq_hz = freq
 
-# Pretty-print mode summaries (k_n, n_eff, eta_eff).
+# Pretty-print mode summaries with phase velocity (Im/Re k_n, v_p, n_eff).
 mode_results.print()
 
-# Dictionary-like access to parsed mode values.
-m1 = mode_results["mode_1"]
-print("mode_1 dict:", m1)
-print(f"mode_1 n_eff = {m1['n_eff']}, mode_1 k_n = {m1['k_n']}")
-
 # Centralized plotting utility from gsim source with tuned defaults.
-fig, ax, stream_inputs = plot_fields_2d("./palace-sim-cpw-waveport-2d")
-print(
-    f"streamplot grid={stream_inputs.u.shape}, "
-    f"seeds={stream_inputs.start_points.shape[0]}"
+# For boundary mode, cycles=[1, 2] selects the ParaView cycles corresponding.
+# Use chip_bounds to crop the airbox — here (y_min, y_max, z_min, z_max)
+# covers the electrode stack without the surrounding air region.
+# chip_ymax = 90  # g_width_top/2 + max_gap + s_width/2 + margin
+# chip_ymin = -60
+# chip_zmax = 30.0  # top of metal + small margin
+# chip_zmin = -10.0  # bottom of stack + small margin
+
+fig, axes, stream_inputs_list = plot_fields_2d(
+    "./palace-sim-cpw-waveport-2d",
+    field="E_real",
+    scalar="real",
+    cycles=[1, 2],
+    # chip_bounds=(chip_ymin, chip_ymax, chip_zmin, chip_zmax),
+    show=True,
 )
+
+# %% [markdown]
+# ### Phase analysis of the electric field in the two gaps
+#
+# For a quasi-TEM CPW mode, the electric field in the two gaps (signal-to-ground) should be $180^\circ$ out of phase. We probe the complex $\vec{E}$ field at points inside each gap and compare their phases.
+
+# %%
+import numpy as np
+import pyvista as pv
+
+from gsim.palace.results import load_fields
+
+# Geometry parameters matching the gsg_electrode() call above.
+_s_width = 20
+_gap_width_top = 15
+_gap_width_bottom = 15
+
+# Probe points: middle of each gap, at the metal layer height (z ~ 0).
+#   top gap center:    y = +s_width/2 + gap_width_top/2
+#   bottom gap center: y = -s_width/2 - gap_width_bottom/2
+gap_top_y = _s_width / 2 + _gap_width_top / 2
+gap_bot_y = -(_s_width / 2 + _gap_width_bottom / 2)
+probe_pts = np.array([[0.0, gap_top_y, 0.0], [0.0, gap_bot_y, 0.0]])
+
+print("Probe points:")
+print(f"  top gap center:    y = {gap_top_y:+.2f}")
+print(f"  bottom gap center: y = {gap_bot_y:+.2f}\n")
+
+for mode_idx in [1, 2]:
+    ds = load_fields("./palace-sim-cpw-waveport-2d", cycle=mode_idx)
+
+    # Build a pyvista PolyData probe set and sample the dataset.
+    probe = pv.PolyData(probe_pts)
+    sampled = probe.sample(ds, snap_to_closest_point=True)
+
+    # Complex E = E_real + 1j * E_imag (3-component vectors).
+    er = np.asarray(sampled.point_data["E_real"]).reshape(-1, 3)
+    ei = np.asarray(sampled.point_data["E_imag"]).reshape(-1, 3)
+    ec = er + 1j * ei
+
+    # Use the vector sum's phase as a robust scalar.
+    phase_top = np.angle(np.sum(ec[0]))
+    phase_bot = np.angle(np.sum(ec[1]))
+    delta = np.degrees(phase_top - phase_bot)
+    delta = (delta + 180.0) % 360.0 - 180.0  # wrap to (-180, 180]
+
+    print(f"Mode {mode_idx}:")
+    print(
+        f"  top gap    |E|={np.abs(ec[0]).mean():.4e},  phase={np.degrees(phase_top):+7.1f} deg"
+    )
+    print(
+        f"  bottom gap |E|={np.abs(ec[1]).mean():.4e},  phase={np.degrees(phase_bot):+7.1f} deg"
+    )
+    print(f"  phase difference = {delta:+7.1f} deg  (expect ~180 for quasi-TEM)\n")