numpy.where with a 2d array of tuples

Question

I have a 2D numpy array of tuples like below:

a = np.array([[(2, 3), (np.inf, 10)],
              [(2, 2), (7, 8)]], dtype=object) 

I used b = np.min(a) and got b = (2, 2).

However, when I try to get the index of the minimal element with np.where(a==b) I get an empty index array.

So how to use numpy.where with an array of object?

Thanks in advance for your help!