Method and apparatus for manipulating the shape of hair

1. A hair styling apparatus comprising:

first and second arms, the first and second arms being movable towards and away from one another;

first and second electrodes provided on the first and second arms respectively, such that the electrodes oppose one another;

drive circuitry for supplying current to the first and second electrodes, to cause an alternating electric field to be produced in the vicinity of the electrodes in use, and thereby cause dielectric heating of hair placed between the electrodes in use;

current sensing circuitry that senses current applied to the first and second electrodes;

a microprocessor that receives an output signal from the current sensing circuitry, that determines, from changes in the output signal, a change in coupling of energy from the alternating electric field to the hair during heating of the hair and that controls the drive circuitry to vary the current supplied to the first and second electrodes in dependence upon the determined change in coupling of energy from the alternating electric field to the hair during heating of the hair

wherein

each of the electrodes comprises a first conductive region interdigitated with a second conductive region, the first conductive region being a negative electrode and the second conductive region being a positive electrode;

the first conductive region of the first electrode opposes the second conductive region of the second electrode;

the second conductive region of the first electrode opposes the first conductive region of the second electrode; and

the drive circuit is configured to drive the first and second conductive regions of each electrode with drive signals that are 180 degrees out of phase with one another.

2. The hair styling apparatus of claim 1 , wherein the microprocessor determines from the output signal from the current sensing circuitry a frequency of the electrical energy at which better coupling of the alternating electric field to the hair takes place than with other frequencies and controls the drive circuitry to adjust the frequency of the electrical energy so as to be at or around the determined frequency.

3. The hair styling apparatus of claim 2 , wherein the microprocessor determines the frequency of the electrical energy at which better coupling of the alternating electric field to the hair takes place by determining the frequency of the supplied electrical energy at which the magnitude of the sensed current is at a peak.

4. The hair styling apparatus of claim 3 , wherein the output signal from the current sensing circuitry is representative of the magnitude of the current drawn by the electrodes;

wherein the microprocessor is configured to:

cause the drive circuitry to vary the frequency of the electrical energy;

receive said output signal from the current sensing circuitry in respect of each of a plurality of frequencies and thereby determine the frequency of the electrical energy at which a peak in the sensed current is obtained; and

cause the drive circuitry to supply the electrical energy at or around the determined frequency for a period of time.

5. The hair styling apparatus of claim 4 , wherein the microprocessor is configured to cause the drive circuitry to generate the test signal or test signals comprising the different frequency components whilst simultaneously supplying electrical energy to the electrodes at the determined frequency to cause heating of the hair.

6. The hair styling apparatus of claim 5 , wherein the test signal or test signals are at a low amplitude relative to the electrical energy supplied at the determined frequency.

7. The hair styling apparatus of claim 1 , wherein the microprocessor is configured to control the drive circuitry to vary a frequency of the electrical energy supplied to the first and second electrodes.

8. The hair styling apparatus of claim 7 , wherein the microprocessor is configured to vary the frequency of the electrical energy using a frequency hopping technique across a range of frequencies or in a sweeping manner across a range of frequencies.

9. The hair styling apparatus of claim 7 , wherein the microprocessor is configured to apply a test signal to the electrodes comprising a plurality of frequencies simultaneously.

10. The hair styling apparatus of claim 1 , further comprising a switch for detecting whether the first and second arms are closed together and cutting off the supply of electrical energy to the electrodes if the first and second arms are not detected as being closed together.

11. The hair styling apparatus of claim 1 , wherein the first arm bears a first dielectric heating plate, and the second arm bears a second dielectric heating plate, the first dielectric heating plate incorporating the first electrode and the second dielectric heating plate incorporating the second electrode.

12. The hair styling apparatus of claim 11 , wherein at least the first dielectric heating plate has a plastic outer surface which forms a contact surface for hair sandwiched between the plates during use.

13. A hair styling apparatus comprising:

first and second arms, the first and second arms being movable towards and away from one another;

first and second electrodes provided on the first and second arms respectively, such that the electrodes oppose one another;

drive circuitry for supplying electrical energy to the first and second electrodes, to cause an alternating electric field to be produced in the vicinity of the electrodes in use, and thereby cause dielectric heating of hair placed between the electrodes in use; and

a microprocessor and memory for controlling the drive circuitry to vary the electrical energy supplied to the first and second electrodes during heating of the hair,

wherein

each of the electrodes comprises a first conductive region interdigitated with a second conductive region, the first conductive region being a negative electrode and the second conductive region being a positive electrode;

the first conductive region of the first electrode opposes the second conductive region of the second electrode;

the second conductive region of the first electrode opposes the first conductive region of the second electrode; and

the drive circuit is configured to drive the first and second conductive regions of each electrode with drive signals that are 180 degrees out of phase with one another.

14. The hair styling apparatus of claim 13 , further comprising sensing circuitry for sensing a change in coupling of energy from the alternating electric field to the hair during heating of the hair; and

wherein the microprocessor is arranged to control the drive circuitry to vary the electrical energy supplied to the first and second electrodes in dependence upon the sensed change in coupling.

15. The hair styling apparatus of claim 14 ,

wherein the sensing circuitry determines a frequency of the electrical energy at which better coupling of the alternating electric field to the hair takes place than with other frequencies; and

wherein the microprocessor is further configured to control the drive circuitry to adjust the frequency of the electrical energy so as to be at or around the determined frequency.

16. The hair styling apparatus of claim 15 , wherein the sensing circuitry comprises current sensing circuitry for sensing the current drawn by the electrodes in dependence on the frequency of the supplied electrical energy, and wherein the determined frequency is the frequency of the supplied electrical energy at which the magnitude of the sensed current is at a peak.

17. The hair styling apparatus of claim 16 , wherein the current sensing circuitry senses the current drawn by the electrodes is configured to generate a feedback signal representative of the magnitude of the current drawn by the electrodes;

wherein the microprocessor is configured to cause the drive circuitry to vary the frequency of the electrical energy to supply test signals to the electrodes at a plurality of different frequencies across a range of frequencies;

wherein the microprocessor is configured to receive said feedback signal in respect of each of the plurality of frequencies and thereby determine the frequency of the electrical energy at which a peak in the sensed current is obtained; and

wherein the microprocessor is configured to cause the drive circuitry to supply the electrical energy at or around the determined frequency for a period of time.

18. The hair styling apparatus of claim 17 , wherein the microprocessor is configured to cause the drive circuitry to generate the test signal or test signals comprising the different frequency components whilst simultaneously supplying electrical energy to the electrodes at the determined frequency to cause heating of the hair.

19. The hair styling apparatus of claim 18 , wherein the test signal or test signals are at a low amplitude relative to the electrical energy supplied at the determined frequency.

20. The hair styling apparatus of claim 13 , wherein the microprocessor is configured to control the drive circuitry to vary a frequency of the electrical energy supplied to the first and second electrodes.

21. The hair styling apparatus of claim 20 , wherein the microprocessor is configured to vary the frequency of the electrical energy using a frequency hopping technique across a range of frequencies or in a sweeping manner across a range of frequencies.

22. The hair styling apparatus of claim 20 , wherein the microprocessor is configured to apply a test signal to the electrodes comprising a plurality of frequencies simultaneously.

23. The hair styling apparatus of claim 13 , further comprising: a switch for detecting whether the first and second arms are closed together and cutting off the supply of electrical energy to the electrodes if the first and second arms are not detected as being closed together.

24. The hair styling apparatus of claim 13 , wherein the first arm bears a first dielectric heating plate, and the second arm bears a second dielectric heating plate, the first dielectric heating plate incorporating the first electrode and the second dielectric heating plate incorporating the second electrode.

25. The hair styling apparatus of claim 24 , wherein at least the first dielectric heating plate has a plastic outer surface which forms a contact surface for hair sandwiched between the plates during use.