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Measurements of the mechanical impedance and of the vibration pattern of the human skull are described. In the frequency range from 200 to 1600 cps the skull was excited to vibrations by means of an electrodynamically actuated piston with small contact area. Data were obtained from living subjects, a dry skull preparation, and a human cadaver. The modulus of elasticity of skull bone, calculated from the resonance frequency of the skull, was found consistent with the value obtained by static methods. The propagation velocity of flexural waves in the skull bones, as calculated from the natural frequencies, agrees satisfactorily with the experimentally determined velocity. It is shown, finally, that a vibrating spherical shell is a suitable model for the skull and describes its vibration patterns with good approximation.

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The primary calibration of pressure transducers is at present realized by static methods. This paper describes a new route to gaining traceability for dynamic calibration using the acousto-optic effect. The pressure range under consideration is up to 100 MPa. We set out a description of the general principle employed to gain traceability, the experimental set-ups that are used for the realization and the thermophysical background of the measurements, and some numerical estimates on the expected results for two different pressure-transmitting media are shown.

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The autocorrelation function of the ventricular electrocardiogram was calculated on an IBM-650 computer. The resulting function can lie fitted by an exponential-cosine function. This result is typical for a mixture of periodic and unperiodic events. For different patients, various degrees of periodicity were put in evidence by this method on a quantitative basis; the ventricular response was never completely irregular. In all cases investigated so far, the period that corresponds to the periodic component of the autocorrelation function was more rapid than the average rate of ventricular conduction.