The penetrating power of X-rays can be increased by

The penetrating power of X-rays, often referred to as the 'quality' or 'hardness' of the beam, is directly determined by the energy of the X-ray photons. This energy is controlled by the accelerating potential difference (voltage) applied between the cathode and the anode. When the potential difference is increased, electrons are accelerated to higher kinetic energies before striking the target, resulting in the production of X-rays with shorter wavelengths and higher frequencies [1]. These high-energy photons have greater ability to penetrate dense materials [1]. In contrast, the filament current only controls the number of electrons emitted (thermionic emission), which affects the intensity or quantity of the X-rays produced rather than their individual energy or penetrating capability. Therefore, increasing the potential difference is the mechanism to increase penetration [1].

Sources

1. [1] https://www.ncbi.nlm.nih.gov/books/NBK564332/