Capturing the Sound - The Electromagnetic Diaphragm (EmD)

 

Capturing heart and lung sounds is the most critical aspect of stethoscope design. Acquire the sound accurately, and anything is possible. The patented Electromagnetic Diaphragm (EmD) is unique to a Thinklabs stethoscope, and is the key to audio quality. The ds32 is the first stethoscope to use EmD technology.

 

Audio Transmission - 100% End-to-End Electronics

 

Having captured an accurate signal, electronic signal transmission right to the eartips ensures crisp clear sound on the ds32. A simple experiment with your conventional stethoscope shows you why you need End-to-End Electronics.

Form and Function - Design Matters

 

The stethoscope is the icon of medicine. The challenge is to upgrade the technology at every level without disturbing the iconic character of the stethoscope. The ds32 maintains the stethoscope form.

 

Result - The User Experience

 

The leap from no-technology to high-technology has to be achieved while making the device easier to use, and to make patient examination a more productive and more rewarding experience.

 

 
The culmination of Technology and Design is the User Experience.
The stethoscope must blend seamlessly into the workflow, becoming easier to use, a more productive diagnostic tool.

 

The starting point was to research the best way to capture heart, lung and other body sounds - clearly, faithfully, and without nosie or interfererence. This simple statement of purpose conceals years of investigation, testing, refining, perfecting. Following the sensor design, we had to develop the signal processing and electronics. Then comes the design - turning technology into a product that makes that technology easy to use, so that it becomes an integral part of the examination process. The learning then comes from you, the clinician, as we observe, listen, refine, and continue to advance stethoscope techonology. Ultimately, it is about physician and patient, nurse and patient, and better healthcare. We are but one part of something much bigger than ourselves, and that is the true meaning, and the true reward.


The authentic sound of a Thinklabs stethoscope starts with the patented Electromagnetic Diaphragm (EmD).

Thinklabs is the only company that uses a traditional diaphragm material as the means to convert sound to an electronic signal.

The result - the natural and familiar tone of a traditional stethoscope, with all the power of clean electronic amplification.

 
The Diaphragm as Transducer

 

In a conventional stethoscope, the diaphragm vibration causes air pressure behind the diaphragm to change, which passes up the tubes as a sound wave to impinge pressure changes on the listener's eardrums. Losses occur through the tubing and there is no amplification.

Thinklabs developed a technology that replaces air pressure changes with electric field changes. Having captured diaphragm movement as an electrical signal, it can be amplified and processed with the full power of current technology. The resulting electrical signal is a perfect analog of the air pressure changes at the diaphragm of a traditional stethoscope, ensuring that the electrical signal truly captures the authenticity of stethoscope sound enabling you to use a Thinklabs stethoscope with no "ear re-training".

 

The Electromagnetic Diaphragm (EmD)

 

Thinklabs diaphragm technology has been implemented as the Electromagnetic Diaphragm (EmD) used in Thinklabs stethoscopes. The EmD is coated internally with a conductive surface. Spaced behind the diaphragm is a metal plate which is charged to a high voltage, thereby setting up an electric field behind the diaphragm. As the diaphragm moves, the voltage on the plate changes due to changes in the electric field. The beauty of this solution is that the diaphragm moves exactly as it would in a conventional stethoscope, and therefore the vibratory response is identical. The result is a sound familiar to the clinician, but amplified and processed to extract the optimal frequency response.

 

Patents

 

Thinklabs has patents for Electromagnetic Diaphragm technology, as well as other technologires related to diaphragm transducers.

 

 

A conventional stethoscope transmits sound via pressure waves traveling in the hollow tubing. A tube or pipe is a natural acoustic filter – talk through a tube, and the sound at the other end is significantly modified.

It is therefore apparent that to achieve perfect transmission, electronics and wiring has to replace air. Replace pressure waves at the speed of sound with electrical signals at the speed of light.

 

During our research, we wondered if some air tubing transmission would be acceptable. Could we, for convenience, use the binaural heapdhones of a conventional stethoscope? The sound would be electronic for most if the distance, but the last 10-12 inches (25-30cm) would be acoustic tubing. It would certainly make for a simpler headphone design, and almost every other electronic stethoscope today uses air tubing for sound tranmission, even if there is some electronic portion in, say, the chestpiece.

 

What we found was that the maximum distance beyond which clarity was compromised was just a few inches! If we weren’t going to compromise sound, the loudspeakers had to be right at the eartips. Hence the design of Thinklabs stethoscope headphones.

 

A One-Minute Experiment to Validate End-to-End Electronics 

 

Play music through iPod-style earbud headphones, place them in your ears normally, and listen to the detail in the music. Now take a conventional stethoscope, set it to Bell position, and hold an earbud heapdhone up against the hole in the Bell. Ideally, seal the earbud so it is airtight against the Bell opening, using a soft material such as foam or even playdough. Now listen to the music through your stethoscope. Notice the loss of high frequencies and the dispersion of bass notes? Sound becomes "smeared" and dulled by the trip through the tubes.

Now you also know what you're missing when you listen to your patients with a conventional stethoscope. An "elegant proof", as we say in mathematics.

Combining a European design team and American engineers, we endeavored to integrate the familiar form of the stethoscope with advanced technology, to produce a result that works eginomically, technically, and clinically. We take you inside some of the decision-making processes.

 

Probe

 

The Probe is critical to the feel of the stethoscope. Users have developed their favorite way to hold a stethoscope – fingers parted in a V, gripping between thumb and forefinger, or some personal variation on these. We didn’t want users to have to change their personal grip or handling of the stethoscope.

 

And so the Probe of a Thinklabs stethoscope is reminiscent of a conventional 2-sided stethoscope (Bell/Diaphragm). It is the same size, and feels naturally familiar in the hands of the user. Machined aluminum alloy with (environmentally friendly lead-free)  hard chrome plating maintained the solid metallic quality of a conventional chestpiece, while adding to the acoustic performance. The Probe housing would be the most expensive mechanical part of the stethoscope, but the sense of quality is unmistakeable.

Primary color LEDs and the intuitive design of an analog watch-face were selected to display operating modes. Glance at the display and you immediately know whether you’re in Bell, Diaphragm, Amplify or Acoustic Modes.

 

Digital Control System (DCS)

 

The DCS houses the 2 AAA batteries, the control and signal processing electronics, and the Control Keys and Volume Control. At first glance, it seems that controls should be on the Probe, facilitating one-handed operation. We tried this on early prototypes. The problem we encountered was two-fold. First, the controls then dictate that there is only one way to hold the Probe, and it’s not like any method currently used by any practitioner. Second, adjusting the controls cause the user to move the Probe around on the patient’s skin, press against the patient to activate a key, and so on. Both these problems were anathema to our design priorities on user comfort and audio unadulterated by motion artifact.

 

AAA batteries were selected for their convenience. Two are used to provide the wattage to drive the headphones with sufficient power to provide undistorted bass. The internal battery voltage is boosted and regulated to ensure the same power regardless of battery voltage (until replacement levels, of course).

 

Headphones

 

Like the metallic Probe, stethoscopes derive their sense of quality from the solid metallic feel of the binaural headphones. This, and the need for durability, dictated the use of stainless steel for the headphone tubing.

 

Eartips are critical to stethoscope comfort. We’d like to say that we used complex anatomical models to design the eartips. Truth be told, we drew the design on our 3-D computer-aided design system, and got them right the first time! Design doesn’t usually work that way. We got lucky. We’ve found that for 99% of users, the eartips are perfect. For some users, a slightly larger design is would be helpful. Stay tuned or write to us, if you’re one of the 1%. The eartips are soft silicone, which is latex-free. We then discovered that due to the combination of amplification level and eartip softness, it was no longer necessary to use severe force on the spring to push the eartips into the ears, as is done with conventional stethoscopes. All we needed was a light spring, and the eartips sealed correctly. This was a major advance in stethoscope comfort! One doesn’t think of electronics as providing physical comfort, but this is exactly what happened. As we discussed in the section on 100% End-to-End Electronics (EEE), our tests showed that the loudspeaker drivers have to be right at the eartips. The loudspeakers also needed to be designed as essentially sub-woofers to reproduce heart murmurs which have significant low frequency content. This required specific tuning of the loudspeaker cavity, and the use of Neodymium magnets, which are used on most audiophile loudspeakers.

 

Attention to Detail

 

We started out by explaining that we had to maintain Form while achieving much more Function. We discovered that perfection means attention to every last detail, literally from Probe to eartip. The goal is that when you hold a Thinklabs stethoscope, you intuitively enjoy the result, without having to think about why.