Electronic mosquito repeller

Here is the circuit diagram of an
ultrasonic mosquito repeller.The
circuit is based on the theory that
insects like mosquito can be repelled
by using sound frequencies in the
ultrasonic (above 20KHz) range.The
circuit is nothing but a PLL IC CMOS
4047 wired as an oscillator working
at 22KHz.A complementary
symmetry amplifier consisting of
four transistor is used to amplify the
sound.The piezo buzzer converts the
output of amplifier to ultrasonic
sound that can be heard by insects.

Components required for this circuit

IC CD4047
R1 - 10k
C1 - 4.7nF
C2 -22μF
Q1 - sl100 (2)
Q2 - sk100 (2)
K1 - piezo buzzer
12V DC battery