### ASA 125th Meeting Ottawa 1993 May

## 3aPP8. The quadratic property of the human auditory sensation induced by
focused amplitude-modulated ultrasound.

**Shengke Zeng
**

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Richard B. Beard
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*Biomed. Eng. and Sci. Inst., Drexel Univ., Philadelphia, PA 19104
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Three modes of low-intensity ((less than or equal to)100 mW/cm[sup 2])
monotone amplitude-modulated (AM) ultrasound are focused on the region of the
human cochlear and the human auditory response patterns are observed. The AM
ultrasonic signal is defined as f(t) cos (omega)t, where f(t) is the monotone
modulation signal and (omega) is the angular frequency of the ultrasonic
carrier. The three modes of f(t) cos (omega)t are: (1) carrier-suppressed AM
mode, cos (Omega)t cos (omega)t; (2) square-rooted AM mode, (1+cos
(Omega)t)[sup 1/2] cos (omega)t; (3) standard AM mode, (1+cos (Omega)t) cos
(omega)t, where (Omega) is the angular frequency of the monotone. They are
applied in sequence to stimulate the subject. The pattern of auditory sensation
of the subject to the ultrasonic stimulations follows the square of the
modulation signal, f[sup 2](t), which are: (1) cos[sup 2] (Omega)t; (2) [(1+cos
(Omega)t)[sup 1/2]][sup 2]; (3) (1+cos (Omega)t)[sup 2]. The subject senses the
pure tone of 2(Omega) for the first mode of the ultrasonic stimulation, the
pure tone of (Omega) for the second mode of the ultrasonic stimulation, and the
mixed tones of (Omega) with relatively weaker intensity of 2(Omega) for the
third mode of the ultrasonic stimulation. The response patterns reveal that the
AM ultrasound induced human auditory sensation has the property of f[sup 2](t).
This quadratic property is similar to the parametric demodulation of the
focused AM ultrasound in water which has the form of d/dt[f[sup 2](t)], (B>>1)
[Novikov, Nonlinear Underwater Acoustics (Acoustical Society of America,
Woodbury, NY, 1987), pp. 86--95]. [Work partially supported by Electro-Stim
Corp.]