Adding discrete_transmit_power to math_functions, and it's use in exc…

…itation_function in base_classes. This allows the definition of an aperture with a specific total transmit power.

.gitignore

@@ -144,3 +144,4 @@ cython_debug/
 # End of https://www.toptal.com/developers/gitignore/api/python
 /examples/
 /lyceanem/_version.py
+/lyceanem/tests/rotation_tests.py

lyceanem/base_classes.py

@@ -381,11 +381,11 @@ def export_all_points(self, point_index=None):
     def excitation_function(
         self,
         desired_e_vector,
-        transmit_amplitude=1,
         point_index=None,
         phase_shift="none",
         wavelength=1.0,
         steering_vector=np.zeros((1, 3)),
+        transmit_power=1.0
     ):
         # generate the local excitation function and then convert into the global coordinate frame.
         if point_index == None:
@@ -404,7 +404,15 @@ def excitation_function(
             )
             aperture_weights = aperture_weights * phase_weights.reshape(-1, 1)
 
-        return aperture_weights * transmit_amplitude
+        from .utility.math_functions import discrete_transmit_power
+        if 'Area' in aperture_points.point_data.keys():
+            areas=aperture_points.point_data['Area']
+        else:
+            areas=np.zeros((aperture_points.points.shape[0]))
+            areas[:]=wavelength**2
+
+        calibrated_amplitude_density=discrete_transmit_power(aperture_weights,areas,transmit_power)
+        return calibrated_amplitude_density
 
 
     def export_all_structures(self):

lyceanem/utility/math_functions.py

@@ -74,6 +74,29 @@ def calc_normals(T):
 
     return T
 
+def discrete_transmit_power(weights,element_area,transmit_power=100.0,impedance=np.pi*120.0):
+    """
+    Calculate the transmitting aperture amplitude density required for a given transmit power in watts.
+    Parameters
+    ----------
+    weights
+    element_area
+    transmit_power
+    impedance
+
+    Returns
+    -------
+
+    """
+    #to start with assume area per element is consistent
+    power_at_point=np.abs(weights.reshape(-1,1))*element_area.reshape(-1,1) # calculate power
+    #integrate power over aperture and normalise to desired power for whole aperture
+    power_normalisation=transmit_power/np.sum(power_at_point)
+    transmit_power_density=(power_at_point*power_normalisation)/element_area.reshape(-1,1)
+    #calculate amplitude density
+    transmit_amplitude_density=(transmit_power_density*impedance)**0.5
+    transmit_excitation=transmit_amplitude_density.reshape(-1,1)*element_area.reshape(-1,1)*np.exp(1j*np.angle(weights.reshape(-1,1)))
+    return transmit_excitation
 
 @guvectorize(
     [(float32[:], float32[:], float32[:], float32)],