Smart Pill: GI Transit, RF Telemetry & pH-Triggered Release

Transit & Telemetry

Peristalsis rate 1.0×

RF carrier frequency 433 MHz

Enteric release pH threshold 5.5

Live Readouts

Esophagus · local pH 7.0

RSSI (received power)

−32.0 dBm

Transit time

0.0 h

Tissue depth to skin

4.0 cm

Drug released

How it works

The capsule advances along the GI tract at a speed set by peristaltic wave activity, passing through zones with very different local pH — a real ingestible sensor's design constraint (e.g. capsule endoscopy, enteric-coated telemetric capsules):

Esophagus  pH ≈ 7.0   (seconds)
Stomach    pH ≈ 1.5–3.5 (acidic, 1–4 h, gastric mixing)
Duodenum   pH ≈ 5.5–6.5 (bile/bicarbonate neutralizes acid)
Jejunum/Ileum pH ≈ 6.5–7.5
Colon      pH ≈ 6.5–7.5 (slower transit, bacterial fermentation)

Enteric-coated release: the coating is engineered to resist gastric acid and dissolve only once local pH exceeds a threshold pH_c — this protects the payload in the stomach and releases it in the small intestine:

release triggers when pH(t) ≥ pH_c
once triggered:  M(t) = M0 · e^(−k(t − t_release))   (first-order dissolution)

RF telemetry: the capsule's onboard transmitter reports position/sensor data through several centimetres of tissue. Received signal strength follows a log-distance path-loss model plus a tissue-absorption term that grows with both depth and carrier frequency (higher-frequency EM fields are absorbed faster by lossy biological tissue):

RSSI(dBm) = P_tx − 20·log10(d / d0) − α(f) · depth
α(f) ≈ α0 · (f / f0)          [attenuation coefficient rises with frequency]

Peristalsis rate — scales how fast the capsule moves through each GI segment, changing total transit time.
RF carrier frequency — higher frequencies (near 2.4 GHz, used by BLE-class telemetry) attenuate faster in tissue than lower ones (near 400 MHz, the MICS medical-implant band), visibly weakening the RSSI bar.
pH threshold — sets how alkaline the environment must become before the enteric coating dissolves and the payload releases; a low threshold releases in the stomach, a higher one delays release until deeper into the intestine.

Real-world relevance: this is the same trio of constraints (transit, pH targeting, wireless link budget) that governs real ingestible devices — capsule endoscopes, telemetric physiological-monitoring pills, and site-specific oral drug-delivery capsules.

Smart pill RF link to skin Released payload

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