Cold Plasma Therapy Device with Enhanced Safety

This invention discloses a cold plasma therapy device with enhanced safety. The plasma therapy device comprises a dielectric barrier made of a material with high dielectric constant (i.e., relative permittivity). Hence the thickness of the dielectric barrier can be increased to produce similar plasma intensity in comparison to a dielectric barrier with a low dielectric constant. The increased thickness enhances the mechanical durability of the dielectric barrier. When the thickness of the dielectric barrier is larger than the maximum discharge gap of the ambient air (or the supplied gas medium) under the voltage applied, no arc discharge will be produced even when there is a crack across the thickness of the dielectric barrier. This minimizes the risk of subject tissue damage from possible electric shocks.

FIELD OF THE INVENTION

This invention generally relates to a plasma therapy device, and more specifically, to a cold plasma therapy device with enhanced safety.

BACKGROUND

Plasma, as the fourth fundamental state of matter, is a neutral ionized gas composed of positively charged ions, electrons, and neutral particles. In typical thermal plasma, all particles approach thermal equilibrium due to intensive collisions between electrons and heavy particles. The temperature in such plasma can reach several thousand degrees. On the other hand, there is another type of plasma in which electrons and heavy particles are in thermal non-equilibrium. In this case, the temperature of the heavy particles is much lower than that of the electrons. This type of plasma is called non-thermal plasma or cold plasma. The heavy particle temperature in cold plasma is typically between 25° C. and 45° C. The plasma discharge may take place in ambient air or in specially supplied gas flow. Many reactive species, including oxygen-based radicals, nitrogen-based radicals, and other components, are generated in the cold plasma. This complicated chemistry can lead to various interactions between cold plasma and biological tissues, allowing the cold plasma to be used for biomedicine.

Dielectric barrier discharge (DBD), which involves electrical discharge between two electrodes separated by an insulating dielectric barrier, is one effective method to produce cold plasma. For biomedical applications, the living tissue is often employed as one of the electrodes, and the plasma discharge is produced between the dielectric barrier and the subject tissue. In general, a high voltage in the range from several kV (kilovolt) to a few tens of kV is supplied to the electrode to produce the plasma discharge. Under continued usage, the dielectric barrier may be damaged by mechanical, thermal, or other reasons or even by the plasma discharge and develop cracks in it. Such cracks can lead to arc discharge directly from the electrode to the subject tissue, which may cause severe tissue damage.

SUMMARY OF THE INVENTION

It is the overall goal of the present invention to solve the above-mentioned problems and provide a cold plasma therapy device with enhanced safety. The plasma therapy device comprises a dielectric barrier made of a material with high dielectric constant (i.e., relative permittivity). Hence the thickness of the dielectric barrier can be increased to produce similar plasma intensity in comparison to a dielectric barrier with a low dielectric constant. The increased thickness enhances the mechanical durability of the dielectric barrier. When the thickness of the dielectric barrier is larger than the maximum discharge gap of the ambient air (or the supplied gas medium) under the voltage applied, no arc discharge will be produced even when there is a crack across the thickness of the dielectric barrier. This minimizes the risk of subject tissue damage from possible electric shocks.

DETAILED DESCRIPTION

In one exemplary embodiment of the present invention, the cold plasma therapy device comprises a dielectric barrier discharge (DBD) probe100as shown inFIG. 1, which connects to a high voltage power supply through a high voltage cable (both not shown). The power supply is preferably a pulsed power supply with an adjustable repetition rate and output voltage. The output voltage is preferably in the range from 1 kV (kilovolt) to several tens of kV or even higher. The DBD probe100comprises an electrode102enclosed in a close-ended tube104, which serves the dielectric barrier. The high voltage from the power supply produces a cold plasma discharge in the ambient air or in a supplied gas medium between the dielectric barrier104(i.e., the close-ended tube) and the subject tissue106. Electrode102is made of an electrically conductive material such as a metal (e.g., copper) connected to the high voltage cable. The close-ended tube104can be cylindrical shaped or in other shapes suitable to be applied to the subject tissue106. The end of tube104can be flat, spherical, or in different shapes depending on the application conditions. The close-ended tube104is made of a material with a high dielectric constant (i.e., relative permittivity). Preferably, the dielectric constant of the material is >5 and more preferably >10 or even >20. One example of such material is zirconium oxide (zirconia), which has a dielectric constant of >25. In comparison to the material with a relatively low dielectric constant (e.g., quartz, which has a dielectric constant of 3.8), the zirconia-based dielectric barrier can be made much thicker to produce similar plasma intensity under the same applied voltage since the capacitance of the dielectric barrier is proportional to εr/d, where εris the dielectric constant and d is the thickness of the dielectric barrier, respectively. The increased thickness enhances the mechanical durability of the dielectric barrier. In an exemplary embodiment, the thickness of the zirconia-based dielectric barrier is larger than the maximum discharge gap of the ambient air (or the supplied gas medium) under the voltage applied such that no arc discharge will be produced even when there is a crack across the thickness of the dielectric barrier. As one example, the ambient air has a breakdown voltage of 3 kV/mm at standard atmospheric pressure. When the thickness of the zirconia-based dielectric barrier is made greater than 6 mm, no arc discharge will be produced between the electrode and the subject tissue under a supplied high voltage of 18 kV even in case the dielectric barrier is cracked. This minimizes the risk of subject tissue damage from possible electric shocks. In a slight variation of the present embodiment, the dielectric barrier of the DBD probe is made of a composite material comprising two or more layers of materials with high dielectric constants to further reduce the risk of crack induced arc discharge.