Satoki Ogiso

Analysis of sound propagation in human head for bone-conduction headphones using finite element method

In this paper, we evaluated the characteristics of the bone-conducted sound propagation in the human head through computer simulation using a reduced head model with finite element method. The model was made of three spheres, which represent the skin, skull and brain, and the brain was represented by the water for simplicity. The step response of the head was investigated to show that the sound propagation would be generated in the form of longitudinal and bending wave through the head. From the simulation results, the sound speed of the longitudinal and bending waves were approximately 1500 m/s and 260 m/s, and the latter was compatible with the previously measured sound speed of bone-conduction.

Measurement of the differential transfer function between bone-conduction and air-conduction for sound localization

In this paper, a measurement of the difference between air-conduction and bone-conduction transfer functions was performed. The transfer function was measured by canceling air-conduction and bone-conduction sound each other. The transfer function was measured for 30 kinds of frequencies ranging from 100 Hz to 15 kHz for 6 subjects. From the results, the frequency characteristics of amplitude difference measured using all subjects have the common dip at approximately 3 kHz and peaks at 3 to 7.5 kHz in this case, and the cepstrum insists that the BC sound arrives to the inner ear 0.2 ms prior to the AC sound. The frequency characteristics of phase differences have the linear part, and it would indicate that AC and BC sound would have different propagation time. With these differential transfer functions, the spatial audio can be realized by compensating BC sound as if it is AC sound.

Estimation of contact force and amount of hair between skin and bone-conducted sound transducer using electrical impedance

Noninvasive bone-conducted hearing aids require the consistent fitting of transducers for consistent hearing. In this paper, a method of estimating the contact force and amount of hair between a persons skin and a bone-conducted sound transducer using electrical impedance is proposed. Experiments are conducted with a human surface model consisting of hair, skin, and bone. The estimator is implemented with a three-layered neural network. Ten measurements for 70 conditions are conducted by changing the contact force from 0 to 5 N and the amount of hair from 0 to 169.6 mm3. With the trained estimator, it is possible to estimate contact force and the intermediate material thickness with mean errors of 0.025 N and 0.424 mm3. This result supports the feasibility of the proposed method and contributes to the reproducible placement of the bone-conducted sound transducer.

Effect of parameters of phase-modulated M-sequence signal on direction-of-arrival and localization error

In this paper, signals for acoustic beacons with M sequence are evaluated with various parameters for self-localization of mobile robot. The effect of (i) baud rate, (ii) carrier frequency and (iii) order of M sequence on DOA estimation error and localization error are evaluated by computer simulation. As a result, localization is possible with same class or more precision compared to the result from sound beacon with three chirp signals within 5 kHz-18 kHz by choosing the appropriate parameters, which are (i)baud rate is more than around 8 kHz and (ii)carrier frequency is 10 kHz. Particularly, (i) baud rate and (ii) carrier frequency have influence on the localization error. However, the localization error do not change into even a further baud rate in this condition if baud rate is higher than carrier frequency. In this simulation, no influence is confirmed from (iii)order of M sequence. The result indicates that M sequence can be used as signal of acoustic beacons instead of chirp, which occupies frequency band.

Effect of characteristics compensation between air-conduction and bone-conduction headphones on sound localization in an anechoic chamber

Bone-conduction (BC) headphones are used when users need to hear provided sounds as well as environmental sounds since they do not occlude the environmental sounds. Sound localization characteristics of the BC sounds are usually worse than that of the air-conduction (AC) sounds. If the frequency characteristics of AC sounds can be reproduced with BC headphones, better sound localization with BC headphones can be achieved. To compensate the frequency characteristics difference between these sounds, a method to measure the frequency characteristics difference is proposed. Also, compensated BC sound is examined by localizing sounds. At first, the difference between AC and BC sounds are measured by tuning their amplitudes and phases to cancel at perceiving sound. The measurements were conducted for 30 frequencies in the audible range. Second, localization characteristics are measured in an anechoic chamber. The sounds are presented from AC and BC headphones using the corresponding head related transfer functi...

Measurement of the distance difference of acoustic beacons using direct conversion receiver

The purpose of this paper was to develop a triangular surveying method based on the time of flight between the acoustic beacon and the single microphone with the aim of improving indoor localization services. In the proposed method, plural amplitude modulated signals were applied as the beacon signal to reduce the effect of disturbing noises, and direct conversion receivers were used to cancel the difference of synchronization between the transmitter and the receiver. The performance of the proposed method was evaluated by moving the microphone between a pair of acoustic beacons which were not synchronized to the receiver. From the results of the evaluation, the utility of the proposed method was confirmed in most of the ranges. This method could be a major step forward in improving indoor localization services.

Front edge location estimation for flexion axis using length meter with accelerometer and gyroscope

Front edge location estimation for flexion axis has been demanded in several fields such as civil engineering or construction. Recently, there are several methods to achieve front edge location estimation using gyroscope. However, these methods require such as fiber optic gyroscope to reduce the effect of the drift. Therefore, front edge location estimation using low-cost type of sensors is still demanded. In this paper, the front edge location estimation method for flexion axis using a triaxial gyroscope, accelerometer and a length meter was proposed, to achieve drift-free location estimation by low cost sensors. The performance of the proposed method was evaluated using reduced model. From the experiments, the major cause of the error (the drift of the gyroscope) was found to be reduced to 2/3 to 1/2 compared to the previous method, and the estimation error could be minimized within 4%.