2.3 UV light illumination and measurement systems
The systems for UV light illumination and measurement are set up on an optical anti-vibration table to detect ultraviolet light, as shown in Fig. 4. The ultraviolet light emission diodes (UV LEDs) are used as sources of UV light illumination and the intensities of UV light are directly proportional to the applied current, as shown in Fig. 5, which indicates that the emission wavelength of the UV LED is almost fixed at 385 nm. The various UV light intensities are adjusted by changing the arrangement of the neutral density (ND) filter to investigate the influence on the frequency shifts of TFBAW oscillators. The ultraviolet light is focused on the active area of TFBAW device using a series of lenses. Consequently, accurate experimental data on ultraviolet light detection can be obtained using these UV light illumination and measurement systems.