In developing the transducer structure, Iwakura would or-ganize his thoughts by writ-ing down issues and ideas in his notebook almost every day. These small steps even-tually led to the development of an innovative structure.Takashi IwakuraAdvisor of the Technical Development Cent-er. Ever since joining Rion, he’s dedicated himself to the development of BA-type re-ceivers that use magnets and other prod-ucts. His success in the development of the core technology, the BA-S-type transducer, played a key role in the successful commer-cialization of cartilage conduction hearing aids.conduction via cartilage “cartilage conduction.”e Road to Developing a Hearing Aid Based on Cartilage ConductionProfessor Hosoi believes that the sound conducted by cartilage must have been heard by researchers throughout all ages and countries, but that they had simply overlooked it, chalking it up to bone con-duction sound. Aer studying cartilage vibration in detail, Professor Hosoi found mounting proof that his intuition had been correct.“Bone conduction is the pathway of sound transmission via vibration of the bone. So, bone vibration is a prerequisite for this pathway. Unlike bone conduction, the mechanism of cartilage conduction doesn’t necessarily require bone vibration. e outer half of the external auditory canal consists of a tube made of cartilage; the inner half consists of a tube made of bone. When you hold a transducer against the cartilage to induce vibrations, the tube of cartilage vibrates, generating sound inside the cartilage portion of the external auditory canal—in other words, inside the ear. is is similar to how, in a speaker, the cone vibrates and creates a compressional wave of air to generate sound. e cylin-drical cartilage portion of the external auditory canal serves as the cone. We did various experiments on auditory percep-tion and conrmed cartilage conduction sound had properties distinct from air conduction and bone conduction sound.”Ever since his discovery of the auditory pathway called cartilage conduction, which had been completely overlooked to date, Professor Hosoi published a string of papers on the subject together with the other scientists on his research team. He was convinced cartilage conduction would lead to the development of a new type of hearing aid.“e phenomenon of sound being trans-mitted via cartilage is equivalent to creating a sound source inside the ear. is means we can make a hearing aid or an acoustic instrument that allows the person wearing the instrument to hear a sound, but not the person standing next to him. In terms of hearing aids, we can generate sound just by placing the transducer in contact with the cartilage, without physical discomfort for the wearer. Bone conduction hearing aids have to be pressed rmly against the bone at the point of the bone conduction transducer. Lots of patients experience pain when they wear them. A cartilage conduction hearing aid can even be used by those suering from an occluded exter-nal auditory canal from any cause, simply by placing the transducer in contact with the cartilage. As an otolaryngologist, I’d wanted to provide a comfortable hearing experience to as many patients as possible. But for several years aer my discovery, I couldn’t get my papers published in any of the prestigious international journals—mostly, I think, because my peer reviewers were unfamiliar with the newly discovered phenomenon of cartilage conduction and because the literature had no previous research on the phenomenon. So my refer-ence sections were nearly empty. en one day, a chief editor of a medical journal was visiting Japan and I had the opportunity to demonstrate the cartilage conduction instrument to him in person. His reaction to experiencing cartilage conduction of sound was a very surprised ‘Oh!’ I got his attention. A paper I submitted soon aer was accepted and published. rough these eorts and by enlightening others, I managed to win increasing recognition for the phenomenon of cartilage conduction.”In 2010, the joint research with Rion began to develop a hearing aid based on cartilage conduction. At Rion, the search was on to nd ways to eectively apply this new auditory pathway to hearing aids.One Roadblock aer AnotherTakashi Iwakura serves as an advisor at Rion’s Technical Development Center. He’s one of the engineers who took on the chal-lenge of developing a cartilage conduction hearing aid. Quite early, he came across a seemingly insurmountable obstacle and concluded a commercial product wasn’t feasible. Iwakura explains his conclusion.“We were told piezoelectric transducers provided good hearing performance, so we started making prototypes. But they needed a power supply of at least 3 V for Cartilage Conduction Hearing AidAn ordinary hearing aid is worn by inserting a receiver into the ear. In contrast, with a cartilage conduction hearing aid, a part called a transducer is attached to the cartilage at the entrance of the external auditory canal. Amplied sound is transmitted to the cartilage. As with ordinary hearing aids, cartilage conduction hearing aids run on a single button cell battery. Currently, they can be purchased following consul-tations at any of 102 designated medical facilities around Japan.Scan this for product inquiries.3
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