What’s a Piezo Optomechanical Circuit?

Ever hear of a piezo-optomechanical circuit? We hadn’t either. Let’s break it down. Piezo implies some transducer that converts motion to and from energy. Opto implies light. Mechanical implies…well, mechanics. The device, from National Institute of Standards and Technology (NIST),  converts signals among optical, acoustic and radio waves. They claim a system based on this design could move and store information in future computers.

At the heart of this circuit is an optomechanical cavity, in the form of a suspended nanoscale beam. Within the beam are a series of holes that act as mirrors for very specific photons. The photons bounce back and forth thousands of times before escaping the cavity. Simultaneously, the nanoscale beam confines phonons, that is, mechanical vibrations. The photons and phonons exchange energy. Vibrations of the beam influence the buildup of photons and the photons influence the mechanical vibrations. The strength of this mutual interaction, or coupling, is one of the largest reported for an optomechanical system.

In addition to the cavities, the device includes acoustic waveguides. By channeling phonons into the optomechanical device, the device can manipulate the motion of the nanoscale beam directly and, thus, change the properties of the light trapped in the device.  An “interdigitated transducer” (IDT), which is a type of piezoelectric transducer like the ones used in surface wave devices, allows linking radio frequency electromagnetic waves, light, and acoustic waves.

The work appeared in Nature Photonics and was also the subject of a presentation at the March 2016 meeting of the American Physical Society. We’ve covered piezo transducers before, and while we’ve seen some unusual uses, we’ve never covered anything this exotic.

Beyond Measure: Instrumentation Essentials

The physical world is analog and if we want to interface with it using a digital device there are conversions that need to be made. To do this we use an Analog to Digital Converter (ADC) for translating real world analog quantities into digital values. But we can’t just dump any analog signal into the input of an ADC, we need this analog signal to be a measurable voltage that’s clean and conditioned. Meaning we’ve removed all the noise and converted the measured value into a usable voltage.

Things That Just Work.

This is not new information, least of all to Hackaday readers. The important bit is that we rely on these systems daily and they need to work as advertised. A simple example are the headlights in my car that I turned on the first night I got in it 5 years ago and haven’t turned off since. This is not a daytime running lights system, the controller turns the lights on when it’s dark and leaves them off during the day. This application falls into the category of things that go largely unnoticed because simply put: They. Work. Every. Time. It’s not a jaw dropping example but it’s a well implemented use of an analog to digital conversion that’s practical and reliable.

flow
Figure 1

Continue reading “Beyond Measure: Instrumentation Essentials”

Turning an Ordinary Pen into a Covert Radio Receiver

[Ben Krasnow’s] latest project will be good for anyone who wants a complicated way to cheat on a test. He’s managed to squeeze a tiny FM radio receiver into a ballpoint pen. He also built his own bone conduction microphone to make covert listening possible. The FM radio receiver is nothing too special. It’s just an off the shelf receiver that is small enough to fit into a fatter pen. The real trick is to figure out a way to listen to the radio in a way that others won’t notice. That’s where the bone conduction microphone comes in.

A normal speaker will vibrate, changing the air pressure around us. When those changes reach our ear drums, we hear sound. A bone conduction mic takes another approach. This type of microphone must be pressed up against a bone in your skull, in this case the teeth. The speaker then vibrates against the jaw and radiates up to the cochlea in the ear. The result is a speaker that is extremely quiet unless it is pressed against your face.

Building the bone conduction mic was pretty simple. [Ben] started with a typical disk-shaped piezoelectric transducer. These devices expand and contract when an alternating current is passed through them at a high enough voltage. He cut the disk into a rectangular shape so that it would fit inside of the clicker on the ballpoint pen. He then encased it in a cylinder of epoxy.

The transducer requires a much higher voltage audio signal than the litter radio normally puts out. To remedy this problem, [Ben] wired up a small impedance matching transformer to increase the voltage. With everything in place, all [Ben] has to do to listen to the radio is chew on the end of his pen. While this technology might help a cheater pass an exam, [Ben] also notes that a less nefarious use of this technology might be to place the speaker inside of the mouthpiece of a CamelBak. This would allow a hiker to listen to music without blocking out the surrounding noise. Continue reading “Turning an Ordinary Pen into a Covert Radio Receiver”

Making a Speaker with Resin, Magnets, and Wire

A speaker is just about the simplest electronic component possible, just barely more complex than resistors and wire. They’re also highly variable in their properties, either in size, shape, frequency response, and impedance. Obviously, building custom speakers would be of interest to a lot of people, but there aren’t many people out there doing it. [Madaeon] is one of those people. He created a speaker from scratch, using nothing but magnets, wire, and a bit of UV curing resin.

The frame of the speaker contains a magnet, and the coil of wire is carefully attached to the 0.1mm thin speaker cone with a bit of UV curing resin. All the parts are available on Thingiverse, but you will need a UV resin printer with a low layer height to print this thing out.

The speaker was built by [madaeon] as a demonstration of what the printer he built can do. It’s a fairly standard resin-based 3D printer built around a DLP projector. It’s also cheap, and unlike some other cheap resin-based 3D printers, there’s a reasonable likelihood his will ship within the next few months.

Powering an Ultrasonic Transducer

[Lindsay] has a wonderful writeup about a new toy in the shop, an ultrasonic transducer. The 28kHz, 70W bolt-clamped Langevin transducer by itself is not much use, you need a power supply, a horn to focus the energy, and a way to tune it. [Lindsay] starts off by showing how to find out the resonant frequency of the transducer, designing and building a high voltage high frequency AC power supply, and how to design a horn.

Not missing the meaning of DIY [Lindsay] casts and machines a horn for the transducer with a high level of precision as this will also tune the horn to the correct frequency. Once some brackets are machined the whole setup is put through some fun experiments in water and lemonaide, but the real purpose is to drill fine holes in glass for his home made Panaplex displays.

Join us after the break for a short video.

Continue reading “Powering an Ultrasonic Transducer”

Transmitting power and data through thick metal enclosures

So let’s say you have a submarine, or a nuclear containment chamber which has walls made of thick metal. Now let’s say you want to transmit power or data through this wall. Obviously you’re not going to want to drill a hole since this wall is either keeping seawater out, or potential contamination in, but wireless signals aren’t going to travel well through dense metal. [Tristan Lawry’s] entry in the Lamelson-MIT Rensselaer Student Prize seeks to address this issue by using ultrasound waves to transmit data and power.

In the video after the break [Tristan] speaks briefly about his project, then demonstrates the transmission of power and digital audio simultaneously through a two-inch thick steel plate. This is accomplished with a set of piezo transducers attached to both the inside and outside of the plate. Communications originate by feeding electricity to one transducer, which sends ultrasonic vibrations through the material to be received by its counterpart on the other side. It’s easy for us to understand data transmission conducted in this manner, after all that’s how the knock block receives information. What we don’t understand is how it can “transfer large amounts of electrical power”. If you can explain it in layman’s terms please do so in the comments.

Continue reading “Transmitting power and data through thick metal enclosures”