Commissioner: Great Lengths Haarvertriebs GmbH
Parkring 9
8083 St. Stefan i. R.

Date of commission: October 20, 2000
Commission no.: 140
Appointed commission: Prof. Univ. Dipl. Ing. Dr. N. Leitgeb

1. Assignment
An appraisal regarding eventual damage that may be caused to hair and scalp using the ultrasound system Ultrasonic 5000 – Great Lengths

2. Principle
Foreign hair strands with the keratin polymer compound at the top end are used to extend the natural hair. To bond these to the natural hair, the foreign hair strand and the natural hair strand are placed into an ultrasonic transducer and held together with a pincer-type counter-piece. Brief exposure to ultrasound of only approx. 2 to 3 seconds heats the polymer, enclosing the hair and forming the desired bond with the natural strand of hair.
Ultrasonic waves are inaudible, mechanical waves with frequencies higher than the range of audibility, i.e. above 20 kHz. They disperse by material particles oscillating back and forth around their idle state and passing the movement on to adjacent particles. This occurs through the period pressure changes (longitudinal waves) generated and/or through the elasticity of the material (transversal waves). In the process, part of the energy is lost due to friction and causes the material to heat up. This makes this heating process substantially different from other heating processes.

  • When using a preheated fusion tool the heat is conducted from the tool to the hair and the adhesive. This creates a temperature drop from the surface of the tool to inside the hair strand and naturally causes much higher thermal stress on the hair.

  • Microwave heating would be unsuitable for this purpose: Microwaves aren’t mechanical, but rather electromagnetic waves and due to physics primarily transfer their energy to water molecules. Since neither the hair nor the adhesive are high in water molecules, they would hardly be heated and the majority of the energy would work on the water-rich brain and the brain fluid.

Appraisal (© Great Lengths)

Ultrasonic appraisal (© Great Lengths)

Transferring ultrasonic waves to material is not an easy task: It requires contact without any air. Ultrasound imaging for example therefore uses gel to create an airtight connection between the transducer and the skin. This method could not be used on dry skin. This basic principle of physics is beneficial in the Ultrasonic 5000 hair extension system by Great Lengths: Areas where the adhesive is located, heats, shapes and forms an airtight connection with the transducer surface, it’s easy to accept ultrasound. However, if the bare (round!) hair comes into contact with the transducer surface, ultrasound is difficult to transfer to it. It’s therefore reasonable to expect the heating the adhesive will quickly accelerate and then quickly decline once the tuft of hair has been flattened from the pressure of the tool and the round hair itself comes into contact with the transducer surface. Even if the hair is completely enclosed by the liquefied adhesive, it is extremely difficult for the ultrasonic waves to penetrate it due to physical reasons. (This is because of their small diameter compared to the wavelength and the acoustic resistance of different adhesives varying greatly.) The hair itself is therefore primarily heated indirectly due to the thermal conduction from the adhesive. Since the heat conductivity of hair is power, it would take a quite an amount of time for it to heat considerably. On one hand this means considerably heating will only occur in areas where the adhesive is located and the remaining hair is protected from heating. The transducer itself hardly heats up at all. On the other hand, this also means protecting the head and the scalp. Since the transducer can only emit a small amount of the ultrasonic waves into the air and the body’s surface furthermore deflects virtually all airborne sound, no significant amount of waves will be able to penetrate the scalp or the body, not even if the transducer comes into direct contact with the scalp.

3. Measurements
As experimental evidence of this context, for one we measured the heating inside the treated hair strand and on the other hand used an electron microscope to render the hair structure in the treated area at 1190x magnification and compared it with the untreated area.

1. The temperatures measured in the tuft of hair showed the trend expected based on physical correlations: After only approx. 2 to 3 seconds the adhesive liquefies quickly. This can be identified by the hair strand flattening and the hair spreading in a fan shape. Then the plasticized adhesive was compressed. This treatment process was repeated several times. Image 1 shows the temperature measurements for 20 treated hair strands. It shows the expected rapid temperature rise followed by a rapid drop once the hair spreads. Due to the higher thermal inertia of hair, their temperature rise is not dictated by the instant temperature of the adhesive but the temporal average over several seconds. As evidenced by the multiple measurements, this is within a range of only approx. 100°C. Based on these circumstances the hair can be expected not to be damaged.

Ultrasonic Image 1 (© Great Lengths)

2. The electron microscope images are shown below: Image 2 is an overview image at the edge of the bond area, image 3 is a detail magnification. Both images show there is no chemical or thermal change to the surface of the hair. The adhesive merely encloses the hair like a cuff and bonds them mechanically. The comparison with a section of hair taken approx. 1cm from the treated area (image 4) shows there is no noticeable impact on the hair.

Based on the thermal and visual examinations we can ascertain there is no hair damage associated with the use of the Ultrasonic 5000 hair extension system by Great Lengths. The physical principle of the generation and dispersion of ultrasound not only protects the surrounding hair but the head of the person being treated against the effects of ultrasound, which are relevant to health, as well.

Ultrasonic Images 2 to 4 (© Great Lengths)